DECISION ANALYSIS SERIES 

The Decision Analysis Series has been established by NOAA's 

Coastal Ocean Program (COP) to present documents for coastal 

resource decision makers which contain analytical treatments of 

major issues or topics. The issues, topics, and principal investigators have been selected through an extensive peer review process. 

To learn more about the COP or the Decision Analysis Series, 

please write: 

NOAA 

Coastal Ocean Program 

Room 9700 

1315 East West Highway 

Silver Spring, MD 20910 

phone: 301-713-3338 

fax: 301-713-4044 

web: http://www.cop.noaa.gov 
Science for Solutions 

NOAA COASTAL OCEAN PROGRAM 

Decision Analysis Series No. 13 

Bering Sea FOCI Final Report 

S. Allen Macklin (Editor) 

National Oceanic and Atmospheric Administration 

Pacific Marine Environmental Laboratory 

7600 Sand Point Way NE 

Seattle, WA 98115 

December 1998 

Contribution 1964 from NOAA/Pacific Marine Environmental Laboratory 

Contribution B356 from Fisheries-Oceanography Coordinated Investigations 

U.S. DEPARTMENT OF COMMERCE 

William M. Daley, Secretary 

National Oceanic and Atmospheric Administration 

D. James Baker, Under Secretary for Oceans and Atmosphere 

National Ocean Service 

Nancy Foster, Assistant Administrator 

Center for Sponsored Coastal Ocean Research/Coastal Ocean Program 

David Johnson, Acting Director 
This publication should be cited as: 

Macklin, S.A. (Editor), 1998. Bering Sea FOCI Final Report. NOAA Coastal Ocean Program 

Decision Analysis Series No. 13, Silver Spring, MD 20910, 167 pp. 

NOTICE 

Mention of a commercial company or product does not constitute an endorsement by 

NOAAIERL. Use of information from this publication concerning proprietary products or the 

tests of such products for publicity or advertising purposes is not authorized. 

Contribution No. 1964 from NOAA/Pacific Marine Environmental Laboratory 

Contribution B356 from Fisheries-Oceanography Coordinated Investigations 

For sale by the National Technical Information Service, 5285 Port Royal Road 

Springfield, VA 22161 
CONTENTS iii 

Contents 

Part 1-Introduction .......................... 1 

Part 2-Population ecology and structural dynamics of walleye 

pollock. Theragra chalcogramma (Kevin M . Bailey) ...... 3 

Executive Summary ....................... 3 

Introduction ........................... 3 

Theoretical Framework: Structural Dynamics ......... 7 

2.2.1 Distribution and Macroecology ............ 7 

2.2.2 Metapopulations and Geographical Structure .... 8 

2.2.3 Genetic Structure ................... 10 

Characterization of Pollock ................... 12 

2.3.1 Distribution and Population Ecology ........ 12 

2.3.2 Year Class Dynamics ................. 17 

Population Structuring Mechanisms in Pollock ........ 17 

2.4.1 Regional Oceanography and Transport ....... 20 

2.4.2 Larval Transport, Eddy Retention, and Mortality . 21 

2.4.3 Migration Patterns and Philopatry .......... 28 

2.4.4 Genetic gnd Metapopulation Structure ....... 35 

2.4.5 Discussion of Gene Flow and Larval Transport ... 42 

2.4.6 Metapopulation Summary .............. 43 

Management Implications .................... 45 

Acknowledgments ........................ 48 

References ............................. 48 

Part 2A-The use of molecular techniques to dissect the genetic 

architecture of pollock populations (Dennis A . Powers) . . 55 

Part 2B-Trends in north Pacific pollock and 1998 harvest prognosis (Vidar G . Wespestad) ................... 65 

Pollock .............................. 65 

North American Pollock ................ 65 

Asian Pollock ...................... 68 

Prognosis Summary fir 1998 ............. 70 

Part 3-Biophysical processes relevant to recruitment dynamics of walleye pollock (Theragra chalcogramma) in the Eastern 

Bering Sea (J.M. Napp, A.W. Kendall. Jr., and J.D. Schumacher) ............................... 71 

Abstract .............................. 

Introduction ........................... 

3.1.1 Description of the Area ................ 

3.1.2 Description of the Problem .............. 

Physical Oceanographic Setting ................. 3.2.1 Marine Climatology and Sea Ice ........... 3.2.2 Oceanic Circulation .................. 

3.2.3 Eddies ......................... 3.2.4 Exchange Between the Oceanic and Shelf 

Regimes ......................... 

Production of Prey for Larval Pollock-Variability in the Timing and Magnitude of the Spring Phytoplankton Bloom ... 

3.3.1 Oceanic Regime .................... 3.3.2 Shelf Regime ...................... Larval Pollock Feeding ...................... 
3.4.1 Oceanic Regime .................... 89 

3.4.2 Shelf Regime ...................... 91 

3.5 Implications: Shelf and Oceanic Regimes as Feeding Environments for Pollock Larvae .................... 94 

3.5.1 Timing of Prey Production .............. 94 

3.5.2 Amount of Prey Produced. .............. 95 

3.5.3 Taxonomic Composition of Prey ........... 95 

3.5.4 Larval Condition .................... 96 

3.6 Conclusions ............................ 96 

3.7 Acknowledgments ........................ 98 

3.8 References ............................. 98 

Part 3A-Juvenile pollock studies (R.D. Brodeur) ........ 103 

Summary ............................. 103 

Summer Distribution of Age-0 Pollock on the Eastern Bering 

SeaShelf ............................. 103 

Distribution and Species Associations of Juvenile Pollock and 

ForageFishes ........................... 105 

Habitat Characteristics of Juvenile Pollock in the Eastern 

Bering Sea ............................ 105 

Distribution of Juvenile Pollock and Other Biota in Relation 

to Fronts ............................. 108 

Commensal Associations of Juvenile Pollock with Schyphomedusae ............................... 108 

Variability in Feeding and Condition of Age-0 Pollock in Relation to Fronts .......................... 112 

Age and Growth of Juvenile Pollock in Relation to the Fronts 112 

Covariation of Plankton, Juvenile Fish, and Seabirds at Tidal 

Fronts ............................... 115 

Predation on Juvenile Pollock by Major Teleost Predators . . 115 

Seabird Distributions Relative to Frontal Regions ....... 118 

Fur Seal Distributions Relative to Frontal Regions ...... 120 

Part 3B-Modeling the upper ocean production dynamics of 

plankton and larval pollock in the Bering Sea (Stephen M . Bollens and Bruce W . Frost) .................. 123 

Introduction ........................... 123 

Background ............................ 123 

Results .............................. 124 

Model Construction and Elaboration ........ 124 

Model Results-Generic Seasonal Cycles ....... 127 

Multi-Species Model and Assimilation of 1992-1994 

Physical Oceanographic Data ............. 128 

Future Activities and Anticipated Milestones .... 133 

Management Implications .................... 133 

References ............................. 133 

Part 3C-Seasonal sea ice in the Eastern Bering Sea (James D . Schumacher and Tina Wyllie-Echeverria) ........... 135 

Part 4-Administration and management of the Bering Sea FOCI 

Program (S . Allen Macklin) ................... 139 

4.1 Beginning of the Project ..................... 139 

4.2 Project Management ....................... 141 

4.3 Budget .............................. 142 

4.4 Competitive Process and Research Cycles ........... 142 

4.5 Meetings and Workshops .................... 143 

4.6 Field Experiments ........................ 143 
4.7 Data Dissemination ....................... 146 

4.8 Project Reviews ......................... 146 

4.9 References ............................. 146 

Part 5-Selected monitoring, modeling. and technical achievements (compiled by S . Allen Macklin) ............ 149 

5.1 Monitoring ............................ 149 

5.2 Modeling ............................. 150 

5.3 Technology ............................ 151 

5.4 References ............................. 160 

Part 6-Bering Sea FOCI Publication List ............. 163 
Bering Sea FOCI Final Report 

S. Allen Macklin (editor) 

Part 1 

Introduction 

To develop an understanding of stock structure and recruitment variation 

in Bering Sea pollock, the Coastal Ocean Program of the National Oceanic 

and Atmospheric Administration (NOAA) funded an 7-year (1991-1997), 

interdisciplinary project named Bering Sea Fisheries-Oceanography Coordinated Investigations (BS FOCI; Schumacher and Kendall, 1995) for which 

NOAA and academic researchers were selected through a competitive process (Macklin, this report). The project goals, based on recommendations 

from an international symposium on pollock (Aron and Balsiger, 1989) were 

to (1) determine stock structure in the Bering Sea and its potential relationship to physical oceanography, and (2) examine recruitment processes in the 

eastern Bering Sea. Both of these have direct implication to management. 

An integrated set of field, laboratory, and modeling studies were established 

to accomplish these goals. To address the first goal, project objectives were 

to establish details of oceanic circulation relevant to larval dispersal and 

separation of stocks, and determine if unique chemical or genetic indicators existed for different stocks. The recruitment component of BS FOCI, 

addressing the second goal, focused on understanding causes of variable mortality of pollock larvae in the different habitats of the eastern Bering Sea. 

The emphasis of recruitment studies was to determine the dominant physical oceanographic features (turbulence, temperature, and transport) that 

could influence survival of pollock larvae, and investigate factors controlling 

food production for the larvae. A later component contrasted juvenile habitat in three hydrographic regimes around the Pribilof Islands (Brodeur, this 

report). 

BS FOCI field studies included 20 cruises to the area, deployment of 

four long-term biophysical moorings (some of which supported meteorological sensors), use of over 40 satellite-tracked drifters, and a series of aircraft 

overflights (NOAA P3) using meteorological and ocean surface color and 

temperature sensors (Macklin, this report). Laboratory studies examined genetic relationships, chemical composition of otoliths, assays of pollock larval 

condition, and pollock larval feeding mechanisms and patterns. Modeling activities included basin circulation, one-dimensional nutrient-phytoplanktonzooplankton-fish relationships, and ecosystem aggregations. 

This report comprises six parts. Part 1 is this Introduction. Part 2 discusses BS FOCI's first goal, stock structure, and part 3 addresses BS FOCI's 

second goal, recruitment studies. Parts 4 and 5 present administration and 

management of the project, and technical achievements, respectively. A list 
2 S.A. Macklin (ed.) 

of BS FOCI publications, numbering about 70 at the time this report was 

written, is part 6 of this report. 
BERING SEA FOCI FINAL REPORT 3 

Part 2 

Population ecology and structural dynamics of 

walleye pollock, Theragra chalcograrnma (Kevin M. 

Bailey1) 

Executive Summary 

New paradigms for managing fisheries in a sustainable manner are under development; these renovated concepts will include better definitions of stock 

distributions, interrelationships, and conservation. Management of many 

marine fisheries has been based on the assumption of shallow (little) population structure with considerable gene flow. However, recent studies of 

several species (previously assumed to be panmictic) using high resolution 

techniques indicate more genetic structure than was found previously. These 

results have implications for effective management, as overfishing of local 

stocks can deplete the productivity of the larger (meta) population. A 

summary view of genetic structure in walleye pollock suggests a pattern 

of considerable geographic stock structure. Phenotypic differences between 

stocks, elemental composition of otolit hs, and parasite studies indicate restricted mixing of juveniles and adults. Genetic differences appear between 

broad regions, but resolution between adjacent stocks, especially within the 

eastern Bering Sea, is currently lacking. Genetic studies to date indicate 

a varying degree of genetic differentiation between pollock in the Gulf of 

Alaska and Bering Sea. The potential for gene flow during larval drift is 

high between adjacent stocks, but since there appears to be an unresolved 

degree of structuring within the Bering Sea, reduced gene flow due to larval retention mechanisms or strong natal homing and philopatry is possible. 

Significant progress has been made in understanding the genetic structure 

of pollock. 

2.1 Introduction 

Walleye pollock is among the world's largest commercial fisheries with annual harvests ranging from 4 to 7 million tons in the North Pacific Ocean 

over the past decade. In U.S. waters catches are on the order of 1.5 million 

metric tons with a dollar value exceeding hundreds of millions. A large portion of the resource is bound for the export market, contributing to reduction 

of the U.S. trade deficit. Without question, this natural resource is of critical importance to the health of domestic fisheries. Pollock is the dominant 

groundfish species in many of the regional ecosystems across the North Pacific Ocean, including the eastern Bering Sea, and has been implicated in the 

dynamics of higher trophic levels (see National Research Council, 1996). As 

a key element in the North Pacific ecosystem, pollock is the target species for 

numerous research programs, past and present, in the eastern Bering Sea as 

well as in other seas. The stock structure of pollock is important knowledge 

'Alaska Fisheries Science Center, NOAA, Seattle, WA 98115, U.S.A. 
4 S. A. Macklin (ed. ) 

for management of this resource because of the potential for overfishing of 

local stocks when it is assumed that large basin populations are panmictic. 

The stock structure of pollock across the North Pacific Ocean, and especially in the Bering Sea, has been a topic of investigation for many years. 

Many early studies were based on pollock's phenotypic characteristics, such 

as meristics and morphometrics, and other studies have been based on genotypic characters, such as DNA analyses. In general, biochemical genetic 

studies have weakly distinguished eastern Pacific populations from western 

Pacific populations, but phenotypic characters suggest a more detailed stock 

structure. Only recently, using high resolution molecular techniques (Powers, 

unpublished data: reported here) has there been good resolution between 

populations on either side of the Bering Sea and between Gulf of Alaska 

populations and eastern Bering Sea populations. 

Fisheries resource management is based on the concept of renewable 

stocks. For walleye pollock the regional stocks are managed separately; for 

example, the Gulf of Alaska population is managed separately from the 

Bering Sea, and the eastern and western Bering Sea and Aleutian Basin 

populations are managed separately. However, there may be isolated populations on even finer scales; within the Gulf of Alaska there may be separate 

spawning populations in Shelikof Strait, Prince William Sound, and the Shumagin Islands region. Furthermore, the degree of intermingling of stocks, 

recolonization of depleted areas from healthy stocks, and other ecological 

questions about resource mixing within the greater population framework 

are aimost compie~eiy unknown. 

Although the overall catch of pollock on the U.S. side of the North Pacific 

Ocean is relatively stable, some populations have experienced declines and 

fisheries closures in recent years, including stocks in Puget Sound, Shelikof 

Strait, Donut Hole, and Bogoslof Island. More recently, there are reports 

that the western Pacific stocks are in a state of decline. Although eastern 

Bering Sea shelf populations have been at healthy levels in the past, there 

is concern about the sustainability of present harvest levels. 

Pollock harvests were especially high from the mid-1980's through about 

1992 resulting from relatively strong recruitment, high abundance levels, and 

unrestricted high seas fisheries. Wespestad (1996) lists 12 geographically 

distinct stock (although not necessarily genetically distinct) groupings and 

their catch trends (Table 2.1). Biomass and catch trends for the major 

stock groupings indicate generally declining levels since the late-1980s in the 

major fishing grounds (Figs. 2.la, b). The greatest declines in biomass and 

catches for pollock have been away from the center of pollock's biomass. 

For example, in the Gulf of Alaska, catches peaked at 307,000 tons in 1984 

and have declined to 55,000 tons in 1996. At the extreme southern end 

of its range in the eastern North Pacific, pollock in southern Puget Sound 

may almost be extinct (Palsson et al., 1996). Likewise for the southern end 

of its range in the western North Pacific around northern Japan, catches 

are reduced by 3 to 4 times from their maximal values in the 1970's (H. 

Yoshida, Hokkaido Central Fisheries Experimental Station, Hamanaka 238, 

Yoichi-cho, Hokkaido 046, Japan, personal communication, February 1994). 

There are many complex and unresolved issues involving the structure of 
BERING SEA FOCI FINAL REPORT 5 

16 

+West Bering -A- W. Kamchatka -D- East Bering +Okhotsk 

0' 

1964 1967 1970 1973 1976 1979 1982 1985 1988 1991 1994 

Year 

Figure 2.1: Trends in major stock grouping of walleye pollock: (a) Abundance trends for major stocks, (b) 

catch trends for Asian and North American stocks (from Wespestad, 1996). 
6 S.A. Macklin (ed.) 

Table 2.1: Geographical distribution of walleye pollock stocks according to Wespestad (1996). 

Stock Stock characteristics 

North American 

Southeast Alaska-Canada Small stock-minor fisheries 

Western-Central Gulf of Alaska Variable stock, 50,000-200,000 t catch 

Eastern Bering Sea Large stock, 1-2 million t catch 

Asian 

Northwest Bering Sea 

Western Bering Sea 

East Kamchatka 

West Kamchatka 

North Sea of Okhotsk 

Sakhalin 

Kuril Islands 

Japan Sea 

Japan Pacific 

Mix of U.S. and Russian fish, 0.5:1 million t catch 

Moderate stock, 0.5-1 million t catch 

Small-medium stock, 100,000-300,000 t catch 

Large stock, near 1 million t catch 

Moderate stock, 0.5-1 million t catch 

Small stock, 65,000 t average catch 

Small-moderate stock 

Heavily fished 

Moderate catch to 0.5 million t 

the pollock population, including recent stock declines, discoveries of heretofore unknown stocks, potential consequences of fishing on certain elements 

of the population, possible relationships between subunits, and potential 

fishing pressure on the same subpopulation at different times from different geographic and quota regions. What is needed, but currently lacking, 

is an understanding of the macroscale population ecology of pollock that 

incorporates the relationship among different subpopulations of the greater 

metapopulation, the rate of gene flow between these subpopulations, the 

relationship between juvenile and adult distributions as linked together by 

ontogenetic migrations, and the magnitude of colonization processes. A theoretical framework about the geographical structure and population ecology 

of pollock needs to include recently developed ecological concepts that can 

help us better understand the dynamics of this species and consider new 

approaches to management. One such concept is macroecology, the study 

of patterns of distribution of organisms in relation to their environment 

(Brown, 1995). Many of the macroecological questions regarding pollock 

are unanswered, such as the relationship between range size and population 

abundance, and the effect of environmental factors on distribution of pollock. Another recent concept is that of metapopulation dynamics, the study 

of conditions by which the processes of population turnover and establishment of new populations are maintained in balance (Hanski and Gilpin, 

1991). Viewing pollock in the context of a metapopulation is a framework 

to study the linkage of stock structure, dispersal, and colonization events. 

In this report, the concepts of macroecology, metapopulations, and stock 

structure are reviewed and areas where they intersect are indicated. Historical and current information on pollock, including mechanisms that may 

isolate and maintain stock structure, are summarized and a "strawman" 
BERING SEA FOCI FINAL REPORT 7 

conceptual model of the population macroecology of walleye pollock is proposed. 

2.2 Theoretical Framework: Structural Dynamics 

The size of fish populations is determined by three major elements: (1) 

available habitat determines the potential size, (2) dynamics within local 

populations as influenced by the environment, competition, and predation 

determine the specific size of a subpopulation, and (3) movement and colonization determine the spread of a population and modify local dynamics. 

In this model, distribution, dispersal, and population structure are closely 

linked, interwoven characteristics of metapopulations. 

A population is a group of individuals of the same species living within a 

sufficiently restricted area such that any member can mate with any other; 

in large widespread populations it is recognized that individuals in the same 

locality are more likely to mate and share common ancestry. Thus local 

subpopulations can be made of largely intrabreeding units of geographically 

structured populations. Geographical structure in populations is the nonrandom pattern of spatial distribution that may be related to historical or 

current barriers between local populations, environmental patchiness, and/or 

environmental gradients. The term structural dynamics integrates change 

in population structure, and aspects thereof, such as range, genetics, and 

dispersal patterns. 

2.2.1 Distribution and Macroecology 

Geographic range considerations are an important characteristic of populations. Species with broad niches become both widespread and locally abundant (Brown, 1984), and large ranges, abundance, and invasion ability are 

linked characteristics within a species (Lawton et al., 1994). Species with extraordinary invasion abilities are generally those best adapted for marginal 

habitats (MacArthur and Wilson, 1967). As described below, these concepts are especially relevant to pollock population biology. On the other 

hand, specialized feeders, such as benthic feeding flatfishes, would appear to 

be tied to specific habitat requirements; thus they cannot move and colonize new habitats freely as adults or settled juveniles compared with species 

that have more generalized requirements. Furthermore, where the range of a 

species with specialized requirements is made of a mosaic of habitat patches, 

colonization by demersal stages may be impeded by regions of unfavorable 

habitat. 

Some populations may expand their range as they become more abundant, although others do not show this trend but show increases in local 

density. As noted above, species with highly specialized niches may not 

expand readily, and indeed no rangelabundance relationships have been 

found for some specialized flatfish species such as rock sole, Alaska plaice 

(McConnaughey, 1995), and American plaice (Swain and Morin, 1996). 

Thus for these species, the range size/population size relationship due to 

density-dependent dispersal may not occur. More generalized species such 
8 S. A. Macklin (ed .) 

as Atlantic cod (Swain and Wade, 1993) and arrowtooth flounder (McConnaughey, 1995) expand their range as abundance increases. 

Range expansions may be limited by physical impediments, such as temperature, salinity, and substrate availability, and by biological factors, including the presence of competitors and predators. There is also historical 

structure in the environment, such as changes in the occupation of niches 

due to disease and environmental events. Often when competition or predation pressure is removed there is an "ecological release" (MacArthur and 

Wilson, 1967), resulting in an invasion event. 

2.2.2 Metapopulations and Geographical Structure 

Within the distributional range of animals, there may be considerable structure. The realization that animal populations are composed of local populations has a rich history going back to Andrewartha and Birch (1954). 

In fisheries, knowledge of local populations goes back to the developments 

and ideas of Schmidt, Heincke, and Hjort in the early 1900s (Sinclair, 1988). 

The concept of population structure was formalized as that of metapopulations by Levins (1970). In the metapopulation view, a local population is 

the spatial unit within which most interaction such as breeding occurs, and 

a metapopulation is an ensemble of local populations (Taylor, 1991a) with 

some potential of interaction. 

Harrison (1991) showed five potential types of metapopulations with examples of their degree of dependency and interaction (Fig. 2.2). These include: (a) the Levins metapopulation, where population sizes are nearly 

equal and all populations interact and habitats are patchy within the range 

area; (b) the core-satellite (Boorman and Levitt, 1973) metapopulation 

where habitats are patchy within the range, but one major population is 

the source of fringe populations; (c) the patchy population, where habitats 

are continuous throughout the species range, but local populations are aggregated; (d) non-equilibrium population, which is like the Levins model 

except that there is no movement between local populations; and (e) an intermediate model between (b) and (c). According to Harrison (1991) the 

dominant metapopulation structure is that of a large local population in a 

large favorable habitat patch, surrounded by relatively unstable populations 

in smaller habitat patches. This is similar to the mainland/island population 

structure of MacArthur and Wilson's (1967) theory of island biogeography. 

In the metapopulation view, local subpopulations are connected by dispersal, which include larval dispersal and colonizing movements of adults. 

Migrations, which are movements of individuals coordinated in space and 

time (Quinn and Brodeur, 1991), can be ontogenetic, seasonal, or daily. 

These migrations are distinguished from dispersal or nomadic behavior, 

which is undirected and out of the natal or home range. Dispersal can 

occur due to environmental factors, such as El Niiio events, and also due to 

density-dependent effects. As demonstrated for some fishes, fidelity to home 

range depends on habitat quality (Matthews, 1990), which can depend on 

density. The advantages of dispersal are colonization of new habitats and 

avoidance of unfavorable local conditions (Quinn, 1993). The effectiveness 
BERING SEA FOCI FINAL REPORT 9 

Figure 2.2: Different kinds of metapopulations. Closed circles represent habitat patches; filled = occupied, 

unfilled = vacant. Dashed lines indicate the boundaries of populations. Arrows indicate dispersion or migration (colonization). (a) Levins metapopulation. (b) Core-satellite metapopulation. (c) Patchy population. 

(d) Non-equilibrium metapopulation. (e) An intermediate case that combines (b) and (c) (from Harrison, 

1991). 
10 S. A. Macklin (ed. ) 

of movement between populations depends on the extent of the movement 

and the mortality of the dispersing individuals. 

One of the major issues of the subpopulation concept is the fidelity to a 

home range or natal site (natal philopatry). Through natal homing, animals 

that stray away from their natal site may return for reproduction. In many 

fishes where juveniles and adults make seasonal and ontogenetic migrations 

related to feeding or reproduction, they may utilize either of three mechanisms, or a combination thereof, to return to their natal site and maintain 

philopatry including: (1) imprinting on environmental cues, (2) learning 

from other fishes (social tradition), or (3) genetically based homing. The 

nature of the homing mechanism, when it occurs, has some interesting implications for management issues, as discussed below. 

2.2.3 Genetic Structure 

How populations are organized as metapopulations and their genetic structure are closely linked; genetic structure being determined by the amount 

of gene flow between local populations. There are widely differing opinions 

on the degree of structure in marine fish populations, ranging from a lot 

of subpopulation structure to almost none. At one end is Sinclair's (1988) 

memberlvagrant hypothesis, whereby there are many discrete populations, 

genetically distinct through larval retention and mortality of vagrants. This 

concept was founded on observations of specific spawning locations that seem 

to favor retention of larvae. At the other end of the spectrum is Smith et 

al. (1990) whose dynzmic population concept has stocks with no discrete 

genetic status as homogeneous isolates, but as dynamic heterogeneous components of the species; some genetic differences may occur from isolation by 

geographical distance and gene selection. This concept arises from observations of high genetic variability within an area and low genetic differentiation 

between areas. 

Genetic divergence among subpopulations is promoted by mutation, genetic drift, and natural selection favoring adaptation to local environments 

and hindered by the homogenizing process of gene flow from movements of 

gametes, individuals, or populations (Slatkin, 1987). Phenotypic and genotypic characteristics have been used to distinguish fish subpopulations. The 

use of phenotypic characters is still widely practiced, but when used alone is 

generally received with some skepticism because phenotypes are influenced 

by environmental conditions as well as genetic makeup. Biochemical and 

molecular genetic techniques are powerful tools for fisheries; there have been 

many studies of protein polymorphisms and more recently molecular genetics, looking for differences between nearby geographical populations, with 

the goal of finding genetically isolated management units. Many studies of 

marine fishes fail to distinguish populations (Pawson and Jennings, 1996), 

either due to the state of technology as applied to population genetics, high 

levels of gene flow, either historical or ongoing, or poor resolution power due 

to small sample sizes (Taylor, 1991b). However, there have also been some 

great successes, e.g., distinguishing smelt populations on opposite sides of 

the St. Lawrence River (Bernatchez and Martin, 1996), mosquito fish pop- 
BERING SEA FOCI FINAL REPORT 11 

ulations within several hundred meters of shoreline (Kennedy et al., 1986), 

and Fundulus populations along coastal transects (Gonzalez-Villasenor and 

Powers, 1990). 

In marine fishes, the importance of larval dispersal on gene flow and 

population structure has been shown by several studies (Waples, 1987; also 

see Avise, 1994). For example, Doherty et al. (1995) used isozymes to show 

that a reef species Acanthochromis polycanthus, whose offspring are reared 

in the parental territory and lacks larval dispersal, demonstrates negligible 

gene flow over ca. 1000 km. Doherty showed that other species with larval 

dispersal had genetically homogeneous subpopulations resulting from gene 

flow. However, high dispersal potential may not always translate into high 

gene flow and genetic homogeneity. There may be physical impediments to 

dispersal, such as retention mechanisms, early life stages may not be passive 

drifters, and later stages may have natal homing mechanisms. 

There are several points of controversy about genetic differentiation, the 

most critical and pervasive being the selective neutrality of genes, about 

which there is still a lot of controversy (Gauldie, 1991; Avise, 1994; Rand, 

1996). Hedgecock (1994) has noted a high degree of heterogeneity on a microgeographic scale for some marine fish and invertebrate species and has 

proposed that a linkage between oceanographic conditions and variance in 

reproductive success of marine animals is related to genetic heterogeneity. 

Thus microgeographic heterogeneity results from temporal variation in the 

genetic composition of recruits due to selection on larval populations matching survival windows of favorable oceanographic conditions, or to geographic 

heterogeneity in the environment. 

The level of genetic diversity in the population is also important for 

successful population differentiation. For some species, both allozymes or 

mtDNA may have a low degree of allelic variation (Bentzen et al., 1997). 

For example, in western Atlantic cod Carr et al. (1995) found that 80% of 

samples for cyt-b gene in mtDNA were of one haplotype, with the remaining 

20% split between 16 other haplotypes. Differences between populations are 

determined by the statistical differentiation of the frequency distribution of 

a few rare haplotypes. Low levels of diversity in marine fish populations have 

been attributed to historical bottlenecks or recent founding of the population 

relative to the rate of mutation and genetic drift detectable in the particular 

genetic structure (mtDNA, microsatellite, etc.) analyzed. 

New techniques look promising for distinguishing subpopulations. 

Bentzen et al. (1997) have applied nuclear DNA microsatellite analysis to 

examine stock structure of western Atlantic cod. Previous studies using allozymes and mtDNA had limited success in differentiating cod stocks, but 

Bentzen et al. (1997) found multiple stocks using their technique. Microsatellite DNA sequences appear to have high resolution for stock structure analysis due to the high rate of change in these regions of the DNA molecules, the 

degree of allelic variation, and the likelihood that selection may be a minor 

factor in determining microsatellite allele frequencies (Wright and Bentzen, 

1994). Selection may promote or discourage population differentiation, and 

since microsatellites are noncoding regions of the genome, polymorphisms 

may be bound by structural contraints since there isn't a protein product. 
12 S.A. Macklin (ed.) 

2.3 Characterization of Pollock 

2.3.1 Distribution and Population Ecology 

The walleye pollock is a species with a very broad niche. Although commonly associated with the outer shelf and slope regions of oceanic waters, 

as a species it is capable of utilizing a wide variety of habitats including 

nearshore eelgrass beds (J. Norris, School of Fisheries, University of Washington, Seattle, WA 98195, personal communication), large estuaries like 

Puget Sound, coastal embayments, and open ocean basins such as the Aleutian Basin of the Bering Sea. Although adults of the species are often described as semidemersal, in some areas they are strictly pelagic (Bakkala, 

1993). Pollock commonly feed on a wide assortment of prey from pelagic 

copepods to epibenthic organisms, and pelagic and demersal fishes. 

Pollock has an extremely broad range from Puget Sound to the northern 

Bering Sea and on across the North Pacific Ocean (Fig. 2.3); it is most 

abundant in the eastern Bering Sea and the Sea of Okhotsk. In addition 

to an extensive range, the local abundance of pollock is usually high, often 

dominating regional groundfish communities. Given its ecological plasticity, 

broad range, and high levels of abundance, pollock appear to be a classical 

generalist species capable of invading and adapting to marginal habitats. 

The distribution of pollock is closely linked to temperature. The vertical distribution of juvenile pollock, and schools of adults and juveniles are 

influenced by fronts, temperature, and depth (Bailey, 1989; Swartzman et 

al. 1994). Interaction of temperature with behavior of pollock has been 

well-studied (Olla et al. 1996; Sograd and Olla, 1996). The horizontal distribution of pollock is limited by cold temperatures, from O0 to 2O, as shown 

by distribution of commercial catches, and catches of juveniles and adults 

in research surveys (Francis and Bailey, 1983). Detailed studies have not 

been conducted at high temperatures, but the range of pollock appears to 

be limited by temperatures of 10" to 12OC. 

We tracked the distribution pattern of several year classes in the eastern 

Bering Sea to examine ontogenetic dynamics in distribution of different year 

classes. The 1982 year class was found predominantly in the outer shelf 

region of the southeast Bering Sea as larvae (Fig. 2.4a); as age-0 juveniles 

they had moved northward and inshore (Fig. 2.4b). As age-1 fish, they 

had distributed themselves farther northward, and also a large portion of 

the population was found shoreward (Fig. 2.4~). As age-3 fish in summer, a 

portion of the 1982 year class returned to the southern outer shelf region, but 

a large number of fish remained in the northeast outer shelf (Fig. 2.4d). The 

1989 year class was not sampled as larvae, but as age-0 juveniles in summer 

it was broadly distributed across the middle shelf in the south and along the 

outer shelf region in the northwest (Fig. 2.5a). This pattern persisted for age1, age-2, and age-3 fish (Figs. 2.5b-d). Portions of the year class distributed 

inshore tended to persist there through age-3. The 1993 year class was 

sampled as larvae along the outer shelf region of the south (Fig. 2.6a). It 

was not sampled as age-0 juveniles, but as age-1's was found far northward 

in a band extending along the northern outer shelf (Fig. 2.6b, c). The 
BERING SEA FOCI FINAL REPORT 13 
14 S. A. Macklin (ed.) 

Figure 2.4: Relative distribution patterns of the 1982 year class of walleye pollock in the eastern Bering 

Sea: (a) larvae in June from ichthyoplankton surveys, (b) age-0 juveniles in autumn from midwater trawl 

surveys, (c) age-1 in summer from bottom trawl surveys, (d) age-3 in summer from bottom trawl surveys. 

Contour shows area of highest abundance. Dashed line shows approximate region surveyed. 
BERING SEA FOCI FINAL REPORT 15 

Figure 2.5: Relative distribution patterns of the 1989 year class of walleye pollock in the eastern Bering 

Sea: (a) age-0 juveniles in summer from midwater trawl surveys, (b) age-1 in summer from bottom trawl 

surveys, (c) age-2 in summer from bottom trawl surveys, (d) age-2 in summer from midwater trawl surveys, 

(e) age-3 in summer from bottom trawl surveys. Contour shows area of highest abundance. Dashed line 

shows approximate region surveyed. 

distribution of age-3 fish appears similar to that of age-2, perhaps with a 

slight shift southward (Fig. 2.6d). Overall, these patterns indicate generally 

northward movements of age-0 and age-1 fish. However, there appears to be 

considerable interannual variability in distribution patterns; sometimes these 

age groups move shoreward also. By age-3 it appears that pre-spawning fish 

shift their distribution southward again. 

Characterization of pollock as a colonizing species lends some support to 

historical suggestions that the rapid increase in pollock populations occurring in the late 1960s was due to an "ecological release" caused by harvesting 

off the competitive pressure of Pacific Ocean perch (Somerton, 1978) and decreases in abundance of Pacific herring. Under this scenario, pollock are a 

classic r-selected species with opportunistic rapid growth, early maturity, 

and high fecundity that were capable of rapidly taking over a niche opening; most likely, juvenile pollock were the stage capable of exploiting prey 

resources made available. The expanding population of juveniles could have 

made them the most available prey for pollock adults resulting in cannibal- 
16 S.A. Macklin (ed.) 

Figure 2.6: Relative distribution patterns of the 1993 year class of walleye pollock in the eastern Bering Sea: 

(a) larvae in May from ichthyoplankton surveys, (b) age-1 in summer from bottom trawl surveys, (c) age-1 in 

summer from midwater trawl surveys, (d) age-3 in summer from bottom trawl surveys (age estimated from 

length class). Contour shows area of highest abundance. Dashed line shows approximate region surveyed. 
BERING SEA FOCI FINAL REPORT 17 

ism in the eastern Bering Sea. In the Gulf of Alaska, an increase of pollock in 

the mid-1980s coincided roughly with a regime shift occurring in 1977-1978 

by Tsuji's (1989) assertion that during times of increasing commercial catch 

levels (and therefore abundance) pollock expand into adjacent waters. Likewise, Stepanenko (1997) reports range expansions of pollock in the Bering 

Sea related to increasing abundance and warming temperatures. 

Comparing the mean and variance of subpopulation abundances over 

time can characterize how populations are controlled in different areas of 

the species range. In the case of pollock, a plot of mean subpopulation 

abundance versus variability shows a slope less than unity, indicating that 

peripheral, less abundant pollock stocks vary more than central, more abundant stocks (Fig. 2.7). These results could either indicate more density dependence in the central stocks, including density-dependent colonization of 

peripheral populations, or that environmental conditions are more variable 

and have a greater effect on peripheral populations. 

2.3.2 Year Class Dynamics 

For all of the major pollock groupings stock fluctuations are strongly influenced by intermittent recruitment of strong year classes. For example, 

Fig. 2.8 shows the impact of a series of strong year classes on stock abundance in the Gulf of Alaska, as well as the drop in abundance related to 

subsequent recruitment of relatively poor year classes. In the eastern Bering 

Sea the 1978 year class comprised 67% of the pollock population in 1981 

and 53% of the population in 1982. Many regions share the same strong 

year classes; for example, 1978 was a strong year class in the Gulf of Alaska, 

Aleutian Basin, eastern Bering Sea, western Bering Sea, and Sea of Okhotsk. 

Likewise 1982, 1984, and 1989 were strong across the Bering Sea, although 

not in the Gulf of Alaska. Strong year classes in the Gulf of Alaska including 

1976, 1977, 1979, and 1988 did not appear strong in the Bering Sea. Therefore, although some strong year classes are shared, there is not a consistent 

association of strong year classes among the Bering Sea and Gulf of Alaska 

populations that would clearly indicate density dependent dispersal between 

these geographic regions. However, within the Bering Sea there appears to 

be an association of strong year classes among the different regions. The occurrence of similar strong year classes in different regions of the Bering Sea 

has been cited as evidence of panmixia within the Bering Basin (Dawson, 

1994). At the extreme ends of the range of pollock, e.g., Puget Sound, the 

strong year classes (1972-1975) were quite different from those in the major 

centers of abundance. 

2.4 Population Structuring Mechanisms in Pollock 

In fish populations, gene flow can occur as a result of movements of adult, 

juvenile, or larval stages. Species with a high degree of adult vagility living in 

fine-grained habitats often have little genetic structure in their populations 

(Avise, 1994). As well, species like salmon, whose larvae have little opportunity to mix, attain whatever gene flow between major drainages by straying 
LOG (AVERAGE ABUNDANCE) 

Figure 2.7: The standard deviation of pollock abundance against average abundance for seven stocks 

pollock, 1979-1991, showing that peripheral, less abundant stocks vary more than central, more abund

Upper line has a slope of unity, bottom line is regression line of stock data fslo~e = 0.864). 
BERING SEA FOCI FINAL REPORT 19 
20 S. A. Macklin (ed. ) 

and mixing of adult gene pools. In species whose adults and juveniles migrate widely, genetic structure may be maintained by natal homing, as is 

well recognized in Pacific salmon. For other species as well, such as rainbow 

smelt, natal homing ability seems quite remarkable (Bernatchez and Martin, 

1996). 

Walleye pollock provide an excellent opportunity to study different pop 

ulation structuring mechanims. Pollock appear to have immigrated to the 

North Pacific within a period between the submergence of the Bering Sea 

land bridge and the coming of the ice age, about 3-5 million years ago (Svetovidov, 1948). In faclj, the earliest records of gadids in the North Pacific are 

found in Pliocene sediments off the California coast. Pollock spawning populations are now found across the rim of the North Pacific Ocean from central 

Japan to Puget Sound. Larger populations are contained in the major basins 

of the Bering Sea and Sea of Okhotsk, but smaller populations are found in 

many bays, fjords, and sea valleys along the continental shelf. During the 

last period of major glaciation about 10,000-18,000 years ago, when sea levels could have been as much as 150 m lower than present day levels, the 

major basins were substantially more isolated with strong geographical barriers between populations. Many of the fjords presently inhabited by pollock 

would have been in the process of being scoured by glaciers. Consequently, 

pollock stock differentiation could have occurred by several mechanisms, including founder effects and genetic drift of small re-colonizing populations 

in the fjords, loss of genetic diversity by population bottlenecks, isolation by 

barriers and by distance combined with selection, and genetic drift. 

Pollock have been the subject of studies of larval transport in relation to 

oceanographic conditions in the Gulf of Alaska since 1981 (Kim and Kendall, 

1989). Pollock eggs and larvae are found in large aggregations that can be 

tracked and monitored (Bailey et al., 199613) and their distribution can be 

predicted reasonably well from ocean currents. Pollock larvae are also associated with oceanographic features such as eddies (Vastano et al., 1992; 

Schumacher et al., 1993). Larval abundance levels are correlated with environmental conditions related to transport (Bailey and Macklin, 1994) and 

recruitment levels of the population have been linked to events during early 

life history (Bailey et al., 1996a). In the following section, I discuss the role 

of variability in larval transport and retention by features, such as eddies, 

in mortality and genetic structuring of the walleye pollock population, and 

explore the possible linkages between them. These linkages are made using 

both published and original sources of data. Other mechanisms of population 

structuring in pollock are discussed, with the main emphasis on populations 

in the Bering Sea and Gulf of Alaska. 

2.4.1 Regional Oceanography and nansport 

In the Gulf of Alaska, the major spawning of pollock is in Shelikof Strait, 

a deep sea valley (>250 m) penetrating the continental shelf between the 

Alaska Peninsula and Kodiak Island. Flow in this region is dominated by the 

Alaska Coastal Current, which is one of the most vigorous coastal currents 

in the world with speeds of 25-100 cm s-I (Stabeno et al., 1995). The 
BERING SEA FOCI FINAL REPORT 21 

Alaska Coastal Current bifurcates east of Sutwik Island, with one branch 

continuing along the shallow continental shelf (-100 m) along the Alaska 

Peninsula. This branch has relatively weak flow, with speeds of about 10 

cm s-l. The other branch flows seaward through the sea valley with a 

portion that joins the Alaska Stream (with speeds of 50-100 cm s-l) and 

the remainder recirculating onto the shallow shelf. 

Frontal features, meanders, and eddies are prominent in the Shelikof sea 

valley (Vastano et al., 1992; Napp et al., 1996). Horizontal density gradients 

and vertical shear in the flow result in baroclinic instabilities, which generate 

eddies in the region. The location of eddy formation coincides with the area 

of pollock spawning (Schumacher and Kendall, 1995), and in the springtime 

spawning period three to four eddies form per month (Bograd et al., 1994), 

some of which may remain stationary for weeks (Schumacher et al., 1993). 

In the Bering Sea a cyclonic gyre dominates circulation, with the Kamchatka Current flowing southward along the western side and the Bering 

Slope Current northward along the eastern side of the central Aleutian Basin. 

Alaska Stream water can enter the Aleutian Basin through any of the deep 

Aleutian passes, but predominately through Amchitka, Amutka, and Buldiur 

Passes, and Near Strait. The transport through the passes varies on time 

scales of months. Over the main area of our interest, the southeast basin 

and the shelves, the flows of interest are the Bering Slope Current (BSC) 

and Aleutian North Slope Flow (ANSF). The ANSF flows eastward along 

the north slope of the Aleutian Islands and connects flow through the passes 

with the BSC. Instabilities in the BSC can result in onshelf flow from the 

basin onto the shelf. 

The shelf is divided into three regions, the inner shelf (depth <50 m), 

the middle shelf (50-90 m), and the outer shelf (100-170 m). Flow on the 

middle shelf is very weak (mean flow <1 cm s-l). Stronger flows occur at 

the transition zones between the inner middle shelf and the middle outer 

shelf. Flow along the 100-m isobath is generally northwestward at -5- 

10 cm s-l, while the northeastward flow along the 50-m isobath is weaker 

at -2-3 cm s-' (Schumacher and Stabeno, 1997). Flow along the 100-m 

isobath originates from onshelf flow from the basin and from flow through 

Unimak Pass. The flow along the 50-m isobath originates from the flow 

through Unimak Pass. 

Eddies in the eastern Bering Sea are relatively common (Schumacher 

and Stabeno, 1994), and are formed in regions of high current shear, or by 

the interaction of inflowing Alaskan Stream water with topography. Eddies 

that may transgress the continental shelf break up in shallow water over a 

period of days. Eddies may circulate vigorously (25 cm s-l), but their net 

movement is generally slow (1-5 cm s-l). Diameters of eddies may vary 

from 5-80 km. 

2.4.2 Larval Tkmsport, Eddy Retention, and Mortality 

Pollock spawn at predictable times and locations, generally in sea valleys, 

canyons, or indentations in the outer margin of the continental shelf; but 

they are also known to spawn in very deep water over the Aleutian Basin 
22 S. A. Macklin (ed. ) 

and in fjords (Fig. 2.3). These locations are known to be repeat spawning 

areas, year after year. In Shelikof Strait, Alaska spawning occurs during the 

last week of March and the first week of April. In the Bogoslof Island region 

in the Aleutian Basin, pollock spawn in late February to early March, and 

over the southeastern Bering Sea shelf most fish spawn from mid-April to 

May. Depending on the region, eggs are spawned deep in the water column 

(100-400 m) and after hatching the larvae are located in the upper portion 

of the water column (generally from 20-60 m depth). 

In Shelikof Strait, pollock show a mean downstream progression of their 

center of abundance over time (Fig. 2.9). However, there is a great deal of interannual variability within these mean patterns. Larval transport patterns 

show good correspondence with satellite-tracked drifter patterns. In years 

when larvae are transported onto the shallow shelf west of the sea valley, 

larvae drift downstream at speeds of 4 to 6 cm s-I (Hinckley et al., 1991). 

About 70 satellite-tracked drifters drogued at 40 m to simulate larval 

drift have been released in the Shelikof sea valley. The drifters show the 

pattern of bifurcation of the ACC and the variability in fate of larvae during 

the 50 d or so when they are planktonic (Fig. 2.10). Residence time of the 

drifters on the shelf ranges from 35-122 dl with a mean of 55 d. Drifters can 

exit the sea valley in about 15 d and enter the Alaska Stream where they 

are quickly transported westward. 

Eddies in the Shelikof Sea Valley can retain larvae for several weeks in the 

region. In 1990 an eddy was found with an aggregation of larvae (Fig. 2.11). 

Satellite-tracked drifters remained in the eddy for -22 dl until the eddy 

moved westward, and interacted with shallow topography of the shelf and 

disintegrated. 

The role of eddies in larval mortality is not completely understood. Eddies early in the spawning season before peak larval abundance have been associated with enhanced phytoplankton and zooplankton concentrations, and 

enhanced larval feeding and nutritional condition (Canino et al., 1991; Napp 

et al., 1996). However, the eddy in 1990 had similar microzooplankton concentrations, larval feeding, and condition compared to regions sampled outside the eddy, and mortality rates in the eddy were not significantly different 

from mortality rates calculated for the whole sea valley region (0.05-0.07 d-I 

in eddy based on birthdate cohorts: Bailey, unpublished data; 0.04-0.11 d-I 

for whole region: Bailey et al., 1995). How larvae are entrained in eddies is 

not well understood. Birthdate distributions of larvae within the 1990 eddy 

sampled about 20 d apart indicate that larvae continue to be recruited into 

the eddy well after it is formed, which complicates mortality calculations 

based on the conservation of properties within the eddy (Fig. 2.12). 

In some years with strong and frequent storm activity, wind-driven transport increases and flushes most larvae from the sea valley into the Alaskan 

Stream. An excellent example of this is 1991; winds were extremely high, 

with three storm events during the late April early May period, and drifter 

trajectories indicated that most water vigorously flowed out the sea valley 

(Fig. 2.13). Under these conditions, primary production and microzooplankton levels were depressed, larval feeding and nutritional conditions were poor, 
BERING SEA FOCI FINAL REPORT 23 
24 S. A. Macklin (ed.) 
BERING SEA FOCI FINAL REPORT 25 

Figure 2.11: Distribution of walleye pollock larvae during late May 1990. Lines are satellite-tracked drifter 

trajectories from releases on the larval patch in early May. Units in catch 10 m-2. 
26 S.A. Macklin (ed.) 

2MF90 Eddy Mean 

180 T 

Hatchdate 

4MF90 Eddy Mean 

"T 

Hatchdate 

Figure 2.12: Hatchdate distributions determined from otolith increment counts and day of capture for (a) 

larvae sampled at stations within the eddy in early May 1990, and (b) larvae sampled at stations within the 

eddy in late Mav 1990. 
BERING SEA FOCI FINAL REPORT 27 

Figure 2.13: Distribution of walleye pollock larvae during late May 1991. Lines are satellite-tracked drifter 

trajectories from releases on the larval patch in early May. Units in catch 10 mm2. 
28 S. A. Macklin led. ) 

and larval mortality was high (Bailey et al., 1995). In general, larvae experiencing conditions associated with high transport will have low survival. 

There are limited data to compare larval condition in the Alaskan Stream 

water compared to other areas. However, microzooplankton levels are relatively low compared to nearshore stations (Bailey et al., 1995) and larval 

growth rates are significantly lower than for larvae found over the shelf region. In 1991, the few surviving larvae that were caught at offshore stations 

had significantly lower growth rates than larvae caught in the sea valley (0.14 

mm d-l compared to 0.20 mm d-l; P < 0.05). 

In the eastern Bering Sea, larval pollock concentrations have not been 

tracked as effectively as in the Shelikof region. There are several areas where 

repeated spawning is known to occur (Fig. 2.14) and where larvae are frequently concentrated. F'rom drifter studies it appears that larvae from different areas can readily mix during the larval drift period. About 80 satellite 

tracked drifters have been released in the Bering Sea to study potential larval 

drift patterns (typical patterns are shown in Fig. 2.15). On the middle shelf 

area (50-100 m depth) the flow is weak and all drifters remained resident 

there for more than 60 d. Drifters released in the Unimak Pass spawning 

region are either transported along the 100-m isobath until reaching the Pribilof Islands, at which time they may circle the islands, flow eastward across 

the shelf along the 50-m isobath, or continue northward to St. Matthew Island. Residence time in the slope region is 30-90 d, with a mean northward 

velocity of 5 cm s-l. Drifters released near Bogoslof Island usually follow 

the ANSF into the BSC. Although about 15% of drifters go onto the shelf, 

drifters in this area may re-circulate in a small sub-gyre in the southeast 

corner of the Aleutian Basin. 

There are eddies in the Bering Sea similar to those in Shelikof Strait 

that may act as larval retention mechanisms (Fig. 2.16). An eddy found 

in 1993 over the southeastern corner of the Aleutian Basin was associated 

with very high numbers of larvae; however, it later entered the outer shelf 

and disintegrated, providing a vehicle for mixing of larvae between spawning 

regions. 

The Aleutian Basin region may act as a geographical barrier to gene flow 

across the Bering Sea. Microzooplankton concentrations are low and larval 

feeding levels are also low compared with other regions (Hillgruber et al., 

1995; Theilacker et al., 1996). Furthermore, studies of larval mortality done 

in the basin region indicate relatively low larval growth rates and potential 

for high levels of mortality (Dell'Arciprete, 1992). 

2.4.3 Migration Patterns and Philopatry 

Other mechanisms of maintaining population structure include philopatry 

and natal homing. Pollock show repeated and predictable spawning at specific sites and times, which is one piece of evidence for natal philopatry. 

Some of these persistent spawning sites are shown in Fig. 2.3. Among the 

best studied spawning aggregations is that in Shelikof Strait which has been 

monitored since 1981; the Shelikof Strait spawning aggregation is the largest 

spawning biomass in the Gulf of Alaska, and mostly spawns within a lim- 
BERING SEA FOCI FINAL REPORT 

175E 180 175W 170W 165W 160W 155W 

Figure 2.14: Major areas of spawning and larval concentrations in the eastern Bering Sea (shaded area). 
30 S. A. Macklin (ed .) 
BERING SEA FOCI FINAL REPORT 3 1 
32 S.A. Macklin (ed.) 

.:. .- 

Sea 

of 2.90 f$ 

Japan 

5r69. 

Figure 2.17: Recapture distribution for experiment in which 666 pollock were tagged and released (triangle) 

in the northern Sea of Japan on April 17,1968. Locations and dates of recaptures are shown by closed cirlces. 

H: Hokkaido Island, S: Sakhalin Island (from Tsuji, 1989). 

ited area (40 km x 80 km) during the first week in April (Kendall et al., 

1996). The geographic and temporal consistency of spawning for this and 

other spawning aggregations argues against the notion that the timing and 

position of spawning is random, depending on suitable conditions. 

Mark-recapture studies around Japan where pollock were tagged during 

the spawning season (April) showed dispersed feeding migrations but return 

homing to specific previous spawning locations (Tsuji, 1989; Fig. 2.17). In 

other studies, pollock tagged during the summer feeding periods were later 

recaptured across a wide geographical expanse (Fig. 2.18). Those recaptured 

around the time of the spawning season were located near well-established 

spawning grounds. Pollock appear to widely disperse after spawning, and 

the location of summer feeding grounds may vary. The fact that fish tagged 

in summer in the western Bering Sea were recaptured in the eastern Bering 

Sea, along with the significant population differentiation between eastern 

and western Bering Sea spawning pollock discussed below, indicates isolation 

of spawning groups even though they may mix during the summer feeding 

period. While not unequivocally proving natal spawning, the persistence of 

spawning locations over time (Fig. 2.3) and repeat spawning are two elements 

of natal philopatry. 
M S91 MOLL M EiLL 00 L 3 9Ll 3 01. L 3 59

I 1 I I I I I / I 
34 S.A. Macklin (ed.) 

Table 2.2: Summary studies of pollock stock structure using phenotypic characteristics. 

Author Method Area Results 

Ogata (1959) meristic-vertebrae 

counts 

Sea of Japan and Pacific 

Ocean side of Japan 

Sea of Japan has 3 different 

stocks. Sea of Japan differs 

from the Pacific Ocean side. 

meristic-vertebrae 

counts 

Sea of Japan, Okhotsk Sea, 

and Pacific Ocean near 

Hokkaido 

8 "local formsv2 groups in the Sea of Japan 

3 groups in the Okhotsk Sea 

3 groups in the Pacific Ocean 

Iwata and Hamai 

(1972) 

Hashimoto and Koyachi (1969) 

Janusz (1994) 

Temnykh (1991) 

Temnykh (1994) 

Ishida (1954) 

morphometrics-body 

length and other 

morphological features 

meristics and morphometric 

morphometrics 

northern Japan 3 groups discriminated 

Sea of Okhotsk 3 stocks distinguished 

Sea of Okhotsk S. Kurils population distinguished from N. Sea of Okhotsk 

morphometrics W. Bering Sea and E. 

Kamchatka 

W. Bering and E. Kamchatka 

stocks distinguished 

northern Sea of Japan, 

Okhotsk Sea, and northern Pacific Ocean coast of 

Japan 

Otolith size is larger in Sea 

of Japan pollock than Okhotsk 

Sea. Otoliths are similar between Sea of Japan and Pacific 

Ocean pollock. 

morphometricsotoliths 

British Columbia-Dixon 

Entrance, Strait of Georgia 

Shaw and McFarlane 

(1986) 

morphometricslength-at-age 2 stocks discriminated-Strait 

of Georgia pollock are smaller. 

Little interaction between pollock north and south of Queen 

Charlotte Sound. 

Thompson (1981) morphometricslength-at-age 

British Columbia-Dixon 

Entrance, Strait of Georgia, Queen Charlotte 

Sound 

3 separate stocks-ach area 

contains its own distinct stock. 

Little mixing occurred between 

them. 

Saunders et al. (1989) morphometrics, life history 

British Columbia Separate stocks in Strait of 

Georgia, Hecate Strait/Dixon 

Entrance, Queen Charlotte 

Sound and W. Vancouver I. 

Lynde et al. (1986) morphometricslength-at-age 

eastern Bering Sea and 

Bering Sea basin 

northeastern shelf and slope 

and Aleutian Basin represent 

one stock distinct from other regions of the eastern Bering Sea 

spawning time and location; morphometrics 

-length-at-age; fecundity 

Aleutian Basin and eastern 

Bering Sea shelf and slope 

3 spawning stocks in the eastern Bering Sea-basin, northeastern slope and eastern shelf 

and slope 

Hinckley (1987) 
BERING SEA FOCI FINAL REPORT 35 

Table 2.2: (continued). 

Author Method Area Results 

Mulligan et al. (1989) spawning time and lo- eastern Bering Sea and three spawning areas separated 

cation Aleutian Basin in space and time: EBS SE 

Shelf, EBS NW shelf, Aleutian 

Basin 

Serobaba (1977) morphometrics and northern, western, eastern different stocks occupy each remeristics and southern Bering Sea gion 

Dawson (1994) morphometrics Bering Sea Three stocks--eastern Bering 

Sea shelf, Aleutian Basin, and 

Aleutian Islands 

Janusz et al. (1989) meristics and morpho- Donut hole and eastern 2 stocks distinguished in Donut 

metrics Bering sea shelf Hole and eastern Bering Sea 

Nitta and Sasaki (1990) morphometrics Donut hole, eastern Bering Characteristics distinguish 3 

Sea, near Japan stocks, with about 90% classification accuracy 

Gong et al. (1990) meristics Asian and Bering Sea Asian and Bering Sea stocks 

distinguished but stocks within 

these regions not distinguished 

Wilimovsky et al. meristic (fin ray and entire Pacific Ocean morphometric-no strong evi- 

(1967) vertebral counts) and dence for discrete stocks. 

morphometric meristic-no differences between Bering Sea and Puget 

Sound pollock. No differences 

between Gulf of Alaska and 

Northern B.C. pollock. 

Koyachi and Hasimoto meristic-fin ray, gill entire Pacific Ocean 12 subpopulations, including 

(1977) raker, and vertebrae the Bering Sea and Gulf of 

counts Alaska 

2.4.4 Genetic and Metapopulation Structure 

We have summarized studies on stock structure of pollock according to their 

phenotypic, acquired, or genetically based nature. Briefly, phenotypic characteristics of pollock, such as meristic or morphometric measurements, both 

within small geographic regions and across much broader areas, have indicated considerable population structure (Table 2.2). For example, Koyachi and Hashimoto (1977) used differences in vertebral, gill raker, and fin 

ray counts to distinguish 12 groups of pollock across its range. Within 

much smaller geographic regions there are also distinct groups. For example, around the islands of Japan and Sea of Okhotsk, Iwata and Hamai 

(1972) identified eight groups, and in the Sea of Okhotsk three stocks were 

distinguished (Janusz, 1994). Within the eastern Bering Sea, including the 

eastern Aleutian basin, three to five stocks have been distinguished using 

morphometrics and life history characters (Lynde et al., 1986; Hinckley, 
36 S. A. Macklin (ed. ) 

1987; Dawson, 1994). Gulf of Alaska and Bering Sea populations appear to 

be phenotypically differentiated (Koyachi and Hashimoto, 1977). For example, Koyachi and Hashimoto (1977) and Hashimoto and Koyachi (1977) used 

differences in vertebral counts and in growth rates to distinguish 11 groups 

of pollock across its range. Within a small area, for example around the 

islands of Japan, there are also distinct groups (Iwata and Hamai, 1972). 

Naturally acquired tags, such as elemental composition of otoliths and 

parasite characteristics, indicate restricted mixing among pollock juveniles 

and adults of different subpopulations (Table 2.3). For example, the chemical 

"fingerprint" of otoliths near the nucleus (deposited during early larval life) 

could be utilized to assign fish to their capture location as juveniles with 

70-85% accuracy over broad regions of the eastern Bering Sea (Mulligan 

et al., 1989), indicating limited movement and mixing of fish from different geographic regions. Using parasite frequencies, adult pollock caught on 

the south side of Vancouver Island can be distinguished from those on the 

west side with about 75% accuracy (Arthur, 1983). In the Sea of Okhotsk, 

several different populations of pollock were distinguished based on parasite frequencies (Avdeev and Avdeev, 1989). By contrast, mark-recapture 

studies where pollock were tagged in summer indicate broad movement of 

individuals across areas of the Bering Sea (Fig. 2.18). However, critical studies of marking spawning pollock have not been conducted. Tagging results 

thus far indicate potential for dispersal during the summer feeding period. 

Historical tagging studies do not provide information indicating whether individuals are moving with large schools as migrating populations, whether 

individuals are vagrants and mixing with local populations, or if dispersal 

patterns in the Bering Sea are part of ordered seasonal migrations. Tagging 

studies around Japan do support dispersed feeding migrations and homing 

migrations to specific spawning areas (Tsuji, 1989). 

Studies using biochemical and molecular methods on pollock show mixed 

results for distinguishing stock structure of pollock, varying somewhat by 

technique (Table 2.4). Using allozymes, Grant and Utter (1980) detected 

minor differences between the Gulf of Alaska and Bering Sea, but no differences within either region. Using mtDNA sequence data from a 276 bp 

spacer sequence near the cytochrome b gene, and the left side of the control 

region, Shields and Gust (1995) reported slight genetic differences between 

eastern and western Bering Sea pollock. However, the season samples were 

acquired was not reported; if samples were collected in the summer feeding 

season when stocks may be mixed, genetical resolution can be blurred. The 

relatively small size of the control region of pollock mtDNA, lack of length 

mutations within the control regions sequenced to date, and the very low 

transition to transversion ratios of the control and spacer regions (1.2:l.O and 

1.29:1.0, respectively) suggest that these regions may not be variable enough 

to provide greater genetic discrimination among populations. Mulligan et al. 

(1992) employed mtDNA RFLP on fish collected during the spawning season 

and distinguished among stocks in the Gulf of Alaska, Donut Hole/Bogoslof 

Island, and Aleutian Island. Profiles from nine restriction enzyme digests 

yielded 65 composite genotypes. Pairwise comparisons of Gulf of Alaska ver- 
BERING SEA FOCI FINAL REPORT 37 

Table 2.3: Summary studies of pollock stock structure using acquired characteristics. 

Author Method Area Results 

Nakano et al. (1991) otolith chemistry: 

adults, whole otolith 

homogenates 

Mulligan et al. (1989) otolith chemistry: juveniles, inner early life 

otolith increments 

Severin et al. (1995) otolith chemistry: juveniles, outer otolith increments 

Arthur (1983) parasites 

Avdeev and Avdeev parasites 

(1989) 

Misc. Authors, see Tagging studies 

eastern Bering Sea, western Bering Sea, Donut hole 

eastern Bering Sea, (SE 

Shelf, NW Shelf, Aleutian 

Basin) 

eastern Bering Sea (Bristol 

Bay), Gulf of Alaska 

British Columbia-Strait 

of Georgia, West side of 

Vancouver Island, Queen 

Charlotte Sound, and 

Dixon Entrance 

Sea of Okhotsk, Kommader Is., Kamachatka 

Penin. 

western and eastern Bering 

differences in 3 areas, little mixing 

differences in 3 areas, some mixing 

distinguish 5 areas, some mixing 

3 stocks in this area; Strait of 

Georgia, Vancouver Island and 

Queen Charlotte Sound/ Dixon 

Entrance 

Seven distinct groups within 

the NE Sea of Okhotsk, distinct groups in Kommander I., 

E. Kamchatka, and Shirshov 

Ridge 

Broad movements, homing miFigs. 2.17, 2.18. Sea, Japan grations to spawning site 

sus the Bering Sea showed significant genetic differentiation between these 

populations (Fig. 2.19). 

More recently, using sequences of mtDNA cytochrome-b and ATPase-8, 

Powers (1996) and his colleagues (J. Quattro and D. Powers, unpublished 

data, Hopkins Marine Station, Stanford University, Pacific Grove, CA 93950; 

see Appendix.2a) identified haplotype differences between Asian and North 

American pollock. The unique DNA sequences allowed them to develop 

an enzyme method to rapidly identify individuals by RFLP. An analysis of 

molecular variance on the combined data identified sharp distinctions between Asian and North American fish and considerable substructure within 

the American and Asian clusters (Fig. 2.20). 

A promising technique for examining genetic variance among fish populations is the study of genomic DNA microsatellites. Microsatellites are nuclear 

DNA sequences comprising tandem arrays of di-, tri-, or tetranucleotide repeats such as (GT)n or (CAC)n that usually extend over less than 300 base 

pairs (bp) (Wright and Bentzen, 1994). Microsatellites are dispersed at intervals of 10-30 kilobase (kb) intervals throughout eukaryotic genomes, and 

alleles exhibit high levels of size variation associated with variation in the 

number of repeating units. Hence, microsatellites constitute an extremely 

abundant class of highly polymorphic genetic markers. Allelic variation in 
38 S.A. Macklin (ed. ) 

Gulf of Alaska 

Donut Bering Hole 

- 

Bogoslof Island 

I Adak Island 

Divergence 

Figure 2.19: UPGMA clustering of genetic distances among walleye pollock stocks in the eastern Bering 

Sea and Shelikof Strait (from Mulligan et al., 1992). 

microsatellites can be detected by using oligonucleotide primers specific to 

DNA sequences flanking the satellite and amplifying between the primers 

using the polymerase chain reaction. Alleles are discriminated by using 

electrophoresis to separate the PCR products according to size in polyacrylamide gels. Studies of microsatellite markers in Atlantic cod populations 

(Bentzen et al., 1996) have yielded finer genetic discrimination of geographic 

subpopulations than had been possible previously. Powers and his colleague 

Gary Villa (unpublished data, Hopkins Marine Station, Stanford University, 

Pacific Grove, CA 93950; see Appendix 2a) screened populations for DNA 

microsatellite loci that allowed the discrimination between pollock populations on a finer scale than was possible by mtDNA analysis. Using PCR 

primers that allow amplification of microsatellites in Atlantic cod (Bentzen et 

al., 1996), pairwise comparisons from the first two microsatellite loci examined, Gmo145 and Gmo2, confirmed differences between Asian and American 

pollock stocks, and further resolved differences between Gulf of Alaska and 

Bering Sea stocks (Fig. 2.21). However, in the case of Gmo145 there was a 

null allele scored for this primer that was responsible for the major east-west 

differences. The presence of a null allele indicates that nucleotide sequences 

in the flanking regions of microsatellite markers are not homologous between 

these populations, resulting in no scorable PCR product. 

Microsatellite alleles may be "the most powerful Mendelian markers ever 

found" (Jarne and Logoda, 1996). Microsatellites have a number of valuable 
r Northea

Southe

Northe

- Aleutia

- Southe

Gulf of 

Figure 2.20: UPGMA dendogram of walleye pollock stocks from mt-DNA RFLP data utilizing the 

Distance Method of analysis (from Powers). 

- East K

? 

- Sea of 

- West 
UPGMA Tree TCH 1 and Tch 2 

ci NE Be

L~leutian 

5 

I IGulf Of A'as

4 3L South Kamc

I I West Bering 

Figure 2.21: UPGMA dendogram of walleye pollock stocks from microsatellite polymorphism frequencies fr

Gmo2 and Gmo145 (from Powers). 
BERING SEA FOCI FINAL REPORT 41 

Table 2.4: Summary studies of pollock stock structure using acquired characteristics. 

Author Method Area Results 

Mulligan et al. (1992) mtDNA RFLP eastern Bering Sea basin, 2 distinct stocks in Aleutian Is. 

Aleutian Is. and Donut Hole/Bogoslof, Gulf 

and Gulf of Alaska and Donut Hole/Bogoslof have 

informative differences 

Shields and Gust 

(1995) 

Grant and Utter (1980) 

Johnson (1977) 

Iwata (1973) 

Iwata (1975a, b) 

Efremov et al. (1989) 

Powers (1996) 

mtDNA sequencing across Bering Sea and Gulf significant differences between 

of Alaska eastern and western Bering Sea 

allozy me 

allozyme 

allozyme 

allozyme 

allozyme 

southeastern Bering Sea minor genetic differences beand Gulf of Alaska tween the two areas. No differences within the areas. 

eastern Bering Sea and No significant differences found 

Gulf of Alaska 

northern Sea of Japan No differences found 

and north Pacific coast of 

Japan 

northern Sea of Japan and Highly significant differences 

eastern Bering Sea found between the two areas 

northern Sea of Okhotsk Allozyme variability suggesting 

that aconitase could be genetic 

marker 

mtDNA RFLP and Bering Sea and Gulf of eastern and western Bering Sea 

DNA microsatellite Alaska distinguished using mtDNA, 

Gulf of Alaska and eastern 

Bering Sea stocks have informative differences using microsatellite DNA 

attributes as tools in stock discrimination. First, they typically exhibit much 

higher levels of variability than other conventional genetic markers, such as 

allozymes or mitochondria1 DNA. In marine fishes and invertebrates they 

typically have 10 or more alleles, and heterozygosities of 50-95% (Wright 

and Bentzen, 1994; Bentzen et al., 1996; Garcia de Le6n et al., 1997). This 

higher level of polymorphism may confer greater resolution in surveys of 

population structure than that obtained with either allozymes or mtDNA, a 

generalization supported both by theoretical analyses and several empirical 

studies in which microsatellite surveys have revealed population structure 

not evident with either allozymes or mtDNA (Bentzen et al., 1996; Ruzzante 

et al., 1996a, b). As well, rates of change of microsatellites appear to be on 

the order of lo4 greater than those for coding DNA. These rates of change are 

due to replication errors causing size polymorphisms rather than mutation 

rates resulting in base pair changes. Second, microsatellites are more likely 

to be selectively neutral than either allozymes or mtDNA, which increases 
42 S.A. Macklin (ed.) 

their value for estimating gene flow (migration) rates. Third, the DNA basis 

of microsatellites, their small size and the use of PCR in their assay present 

logistical advantages in sample acquisition (minimal tissue requirements and 

no need for frozen storage) and makes possible the use of archival materials 

such as scales and otoliths as tissue sources, hence making retrospective 

studies a possibility. 

An emerging view of genetic structure in walleye pollock suggests a more 

complex pattern of stock structure than recognized previously. Studies to 

date indicate varying degrees of genetic differentiation between pollock in 

the Gulf of Alaska and Bering Sea. Phenotypic differences between stocks, 

elemental composition of otoliths, and parasite studies are consistent with 

this interpretation. Distinction between adjacent putative stocks at the subbasin scale, for example in the eastern Bering Sea, is currently lacking but 

is more likely to be observed when higher-resolution molecular techniques 

are used. Therefore, more pollock-specific microsatellite primers need to 

be developed and tested to survey a greater number of microsatellite loci. 

Although the microsatellite analyses presented here are tentative, they are 

generally supportive of data from life history characteristics and phenotypic 

patterns that indicate considerable population heterogeneity. 

2.4.5 Discussion of Gene Flow and Larval llansport 

Among the major basin regions of the Sea of Japan, Sea of Okhotsk, Bering 

Sea, and Gulf of Alaska there is good evidence of genetic structure in pollock that is supported by genetic, phenotypic, and life history data. Probably 

these major basin regions were largely isolated from each other during the 

last major glaciation, as well as at other times during pollock's ancient history in the North Pacific. Considering the colonizing ability of pollock the 

potential limited degree of genetic mixing between populations is somewhat 

surprising, but perhaps can be attributed to larval retention mechanisms, 

differences in reproductive characteristics (timing and temperature adaptations), natal homing, or outbreeding depression of vagrants that reproduce 

with historical local populations. 

In spite of substantial opportunities for gene flow through larval transport 

and dispersal of juveniles and adults within a major region like the Bering 

Sea, there appears to be genetic differentiation of populations across a wide 

distance, such as the eastern versus western Bering Sea. The inhospitable 

nature of the Aleutian Basin as a nursery for larvae and juveniles may act 

as a barrier to population mixing. Among adjacent spawning regions in 

the eastern Bering Sea, the potential for gene flow during larval drift is 

high. However, since there appears to be an unresolved degree of structuring 

within the Bering Sea, reduced gene flow due to larval retention mechanisms 

or strong natal homing and philopatry may be indicated. 

Genetic differentiation between the Gulf of Alaska and Bering Stocks 

presents an interesting scenario. The Alaska Peninsula presents an obvious 

land barrier to mixing. Larvae spawned in Shelikof Strait are frequently retained in the sea valley region by fronts and eddies, and larvae transported 

onto the shallow continental shelf between the Shumagin Islands and the 
BERING SEA FOCI FINAL REPORT 43 

Shelikof sea valley have a long residence time there due to slow and meandering currents. Years with conditions that favor transport into the Alaska 

Stream are also years of high larval mortality. When larvae do enter the 

Alaskan Stream, where they could be transported into the Bering Sea, they 

encounter conditions that are poor for survival. Furthermore, the transit 

time is usually greater than the 50 d planktonic life of larvae. If larvae did 

survive the journey in the Alaskan Stream, they would enter the Bering Sea 

through the relatively deep western island passes. To mix with the gene pool 

on the eastern Bering Sea shelf, they would have to cross the Aleutian Basin 

region, where feeding conditions are poor and mortality is high. Unimak 

Pass is the only conduit between the shelf of the North Pacific and eastern 

Bering Sea. While several drifters deployed in Shelikof Strait have entered 

the Bering Sea through Unimak Pass, the transit time exceeded 60 d in each 

case. Consequently, it appears that vagrants from the Shelikof Strait spawning have a high mortality, limiting gene flow and population homogenization 

between the Gulf and Bering populations. These populations could have 

become differentiated during isolation by glaciation and founder effects, or 

alternatively, during recent periods of bottlenecks and genetic drift. Whereas 

the Bering Sea pollock population is extremely large and unlikely to experience genetic drift, the Gulf of Alaska population is smaller and is known to 

fluctuate widely, perhaps experiencing periods of enhanced genetic drift. 

2.4.6 Metapopulation Summary 

A summary view of genetic structure in walleye pollock suggests a pattern 

of considerable geographic stock structure in walleye pollock. Phenotypic 

differences between stocks, elemental composition of otoliths, and parasite 

studies indicate restricted mixing of juveniles and adults. Genetic differences 

appear between broad regions, but resolution between adjacent stocks, especially within the eastern Bering sea, is currently lacking. All of the genetic 

studies to date indicate a varying degree of genetic differentiation between 

pollock in the Gulf of Alaska and Bering Sea. The potential for gene flow 

during larval drift is high between adjacent stocks. However, since there 

appears to be an unresolved degree of structuring within the Bering Sea, reduced gene flow due to larval retention mechanisms or strong natal homing 

and philopatry is indicated. 

The standard metapopulation models of Harrison (1991; Fig. 2.2) do not 

fit the apparent population structure of pollock as known to date. A strawman metapopulation structure can be proposed that represents an intermediate model. This metapopulation model of pollock is made of several large 

populations separated by long distances and geographical barriers (such as 

the eastern Bering Sea and Sea of Okhotsk populations) with little gene flow 

between them, and numerous smaller populations with potential linkages 

among each other and the larger populations (Fig. 2.22). Some populations 

may show local adaptations to their specific habitat, minimizing gene flow 

through reliance on larval retention features and natal homing. 

In spite of the importance of this resource, and the importance of stock 

structure to its management, we don't have a comprehensive genetic sur- 
44 S.A. Macklin (ed.) 

Figure 2.22: Hypothetical nondimensional pictogram representing the population structure of walleye pollock. Closed ellipses represent habitat patches; filled = occupied, unfilled = vacant. Dashed lines indicate 

boundaries of populations. Arrows indicate relative gene flow through migration or larval transport. Probable main populations for pollock are Sea of Okhotsk and eastern Bering Sea shelf. 
BERING SEA FOCI FINAL REPORT 45 

vey across the whole range using modern genetic techniques. Nor is there 

a finescale genetic survey, within a region where different stocks have been 

identified. Such a survey would need to be adequate to determine if there 

are clines that represent differences by distance, or a sudden transition representing a barrier. Many of the smaller fjord populations represent an 

opportunity to examine founder effects on genetic differentiation within the 

pollock metapopulation. However, these populations have not been included 

in past genetic surveys. Future work should concentrate on genetic structures with high mutation rates, such as microsatellites, capable of resolving 

genetic structure that may have evolved recently. Stock mixing problems can 

be better addressed using these techniques in conjunction with applied tags 

and natural environmental tags, such as elemental composition of otoliths. 

2.5 Management Implications 

The question of whether fisheries fluctuations result from local populations 

waxing and waning independently or movements among populations has 

been a central issue in fisheries since the time of Hjort (1914). Since that 

time, most fisheries research has assumed that local populations are closed 

and homogeneous systems. However, many scientists are currently suggesting that we reexamine the large-scale patterns underlying the dynamics of 

fish populations (Frank, 1992). For example, prior to the collapse of the 

northern cod population in the Northwest Atlantic Ocean it was believed 

that there was no genetically based population structure due to extensive 

egg and larval drift, followed by opportunistic and nonphilopatric recruitment of juveniles to adult assemblages (deYoung and Rose, 1993). Studies 

of allozymes and mtDNA studies had little success in discriminating among 

Northwest Atlantic cod stocks. However, Bentzen et al. (1996) examined 

nuclear DNA microsatellite distributions and found that the northern cod 

population does not represent a single panmictic assemblage, but is comprised of genetically distinguishable subunits, each of which is affiliated with 

a distinct spawning area. It is of great interest that considerable finestructure has been found in Atlantic cod populations, because cod and pollock 

have taxonomic as well as life history similarities. 

There are several issues especially relevant to pollock stocks when genetically or geographically discrete subpopulations are lumped as single management units. Daan (1991) indicates that if catch-at-age analysis is applied to 

a heterogeneous unit stock (a metapopulation), then fishing effort is underestimated and fishing mortality deviates from the recent true trend, leading 

to the possibility of overfishing. Pawson and Jennings (1996) indicated that 

lumping of stocks may lead to reductions in short-term yields. The depletion 

of unidentified local subpopulations and their possible extinction is another 

issue (Ovenden, 1990). The rate of recovery of geographically but not genetically discrete populations will depend on the level of gene flow between 

subpopulations. Genetically distinct subpopulations, by definition, have low 

levels of gene flow among them, and specific stock adaptations to local habitat conditions can impede recovery from extrinsic source populations. 

There are some other key areas where high-resolution stock identification 
46 S.A. Macklin (ed.) 

would be extremely useful in management of pollock harvests. A central issue 

in the case of pollock management is whether broad-scale migrations occur 

that result in seasonal mixing of subpopulations. For example, if eastern 

or western Bering Sea fish migrate across or around the Basin (as believed 

by Dawson, 1994), they may be harvested on both sides of the Bering Sea 

basin. Therefore, a migratory population would experience two independent 

sources of fishing mortality in two management regions. 

Recently, new local populations of pollock have been discovered. Whether 

they will be maintained as self-sustaining populations or whether they are 

ephemeral stocks is a question that depends upon the mechanism of natal 

spawning and local adaptation for reproductive success. For example, in 

recent years a spawning population of 300,000 tons has been found around 

the Shumagin Islands in the western Gulf of Alaska (C. Wilson, Alaska Fisheries Science Center, 7600 Sand Point Way NE, Seattle, WA 98115, personal 

communication, October 1996). This population is largely composed of the 

1989 year class, which was strong in the Bering Sea, but weak in the rest of 

the Gulf of Alaska. It is unknown whether this population originated from 

density-dependent dispersal from the Bering Sea, or whether it represents an 

increase in a previously unknown local subpopulation. Another explanation 

may be that vagrants from the Bering Sea could have joined a small local 

spawning population. 

Research on spawner-recruitment relationships is also dependent on the 

definition of stock structure among populations. For example, consider the 

following hypothetical but realistic example: if two genetically distinct and 

asynchronously fluctuating populations, A and B, are lumped together in a 

VPA analysis, dominance shifts could result in a spawner-recruit relationship where recruits from population A are compared to egg production from 

population B. Shifts in dominance between putative stocks appears to be a 

situation particularly applicable to pollock in the Bering Sea (Francis and 

Bailey, 1983). In this case, knowledge of the underlying population structure would vastly improve the understanding of spawner-recruit relationships. Alternatively, different spatial scales can be a problem when early life 

dynamics in the juvenile nursery of population A are compared to recruits 

derived from VPA analysis of lumped populations; this type of comparison 

is common in fisheries research. Other confounding cases may occur where 

there is vagrancy of recruits or an exogenous source of recruits, such as might 

occur with pollock in the Gulf of Alaska. All of these circumstances can re 

sult in misinterpretations of the factors underlying the dynamics of these 

populations. 

The mechanism of natal-site fidelity has broad implications to fisheries 

management and sustainable harvesting of these populations. For example, 

if fish learn their migration routes from older fish, currently thought to be 

important for cod (Rose, 1993) and herring (Corten, 1993), then removing 

older fish from the population can lead to increased straying of younger fish 

due to loss of social tradition. Furthermore, this mechanism implies that 

larvae dispersed from the range of adults can adopt new local populations. 

The mechanism of "innate" or "genetic memory" implies that removal of 

any fish is of equal importance to the population, but it is essential not 
BERING SEA FOCI FINAL REPORT 47 

to drive a population into extinction, because recolonization will depend on 

the process of natural selection and adaptation to local conditions. Vagrants 

from other populations are unlikely to spawn with local populations in the 

same region. Imprinting implies that harvesting will not have an impact 

on migratory routes, and heavily depleted populations can be re-seeded. In 

fact, marine fish species probably use a combination of all of these mechanisms for natal fidelity, and the response to any one stimulus is graded 

against others. It is not known which homing mechanisms are utilized by 

pollock during spawning migrations; however, the existence of genetic structure in the population, which is maintained in spite of larval drift and highly 

dispersed feeding migrations, tends to indicate a genetic-based mechanism. 

Based on the complex range of behaviors pollock are capable of exhibiting 

(Olla et al., 1996) it should not be surprising that they show considerable 

flexibility in their homing behavior. 

New paradigms for managing fisheries in a sustainable manner are urgently needed, and these concepts are largely dependent upon better definition of stock distributions and interrelationships. In a review of stock structure methods, Pawson and Jennings (1996) suggest that despite widespread 

application of genetic techniques, there are only a few cases where these studies have provided information to managers that could have been adopted, 

except for salmon. Certainly, information indicating multiple genetic-based 

stocks adds another element of concern to fisheries managers and makes their 

task more complex (Lincoln, 1994). As noted by Carvalho and Hauser (1994) 

good communication between fisheries managers and geneticists is needed for 

effective implementation of stock structure information, including clear objectives for proposed work and utilization of appropriate techniques. Future 

work on stock structure of walleye pollock should be closely coordinated with 

scientists responsible for establishing pollock harvest policies. 

Given the high potential for gene flow in marine species including pollock, genetic approaches alone may not completely resolve stock structure 

issues at the level of harvest stocks or ecological populations; tagging studies 

offer another way to study linkages between fish populations. Gauldie (1991) 

suggests that tagging studies and monitoring catch statistics are methods to 

assess how much fishing in one placeltime affects groups of fishes in other 

places (harvest stocks). Pawson and Jennings (1996) are also proponents 

of tagging studies for providing evidence of stock separation and migration, 

and indicate that carefully planned tagging experiments, or experiments utilizing naturally acquired tags, are needed to establish a relationship between 

fishes in different regions. Although not necessarily showing levels of gene 

flow between areas, well thought out and executed tagging and/or transplant experiments would offer a powerful approach to studying migration 

mechanisms. Tagging pollock has been problematic in the past due to issues of barotrauma, tag recovery bias, and distribution of effort, and the 

large number of tags necessary to characterize such large populations. New 

technologies should be developed to minimize these problems, including environmental tags, such as otolith chemical fingerprints, and in situ tagging. 

Studies of fish dispersal that are coordinated with modern genetic studies 
48 S.A. Macklin (ed.) 

should contribute significantly to understanding linkages between population 

dynamics and structure of marine fish populations. 

2.6 Acknowledgments 

Arthur Kendall, Paul Bentzen, Carol Sibley, Robin Waples, Stew Grant, Ric 

Brodeur, Phyllis Stabeno, and Mike Canino reviewed sections, or in some cases all of 

an earlier version of this manuscript. I also thank Dennis Powers, Phyllis Stabeno, 

Steven Porter, Annette Brown, Akira Nishimura, Jim Traynor, Gary Villa, Joseph 

Quattro, Allen Macklin, and Susan Picquelle for contributing information used in 

this report. 

2.7 References 

Andrewartha, H.G., and L.C. Birch (1954): The Distribution and Abundance of 

Animals. University of Chicago Press, Chicago. 

Arthur, J.R. (1983): A preliminary analysis of the discreteness of stocks of walleye pollock, Theragra chalcogramma, from the northeastern Pacific Ocean off 

Canada based on their parasites. Can. Tech. Rep. Fish. Aquat. Sci., 1184, 15 

PP . Avdeev, V.V., and G.V. Avdeev (1989): A study of walleye pollock population 

structure and migration routes using parasitological indicators. In Proceedings 

of the International Symposium on the Biology and Management of Walleye 

Pollock, Alaska Sea Grant Rept. No. 89-1, University of Alaska, Fairbanks, 

569-590. 

Avise, J.C. (1994): Molecular Markers, Natural History and Evolution. Chapman 

and Hall, NY. 

Bailey, K.M. (1989): Interaction between the vertical distribution of juvenile walleye 

pollock Theragra chalcogramma in the eastern Bering Sea, and cannibalism. 

Mar. Ecol. Prog. Ser., 53, 205-213. 

Bailey, K.M., R.D. Brodeur, and A.B. Hollowed (1996a): Cohort survival patterns 

of walleye pollock, Theragra chalcogramma, in Shelikof Strait, Alaska: A critical 

factor approach. Fish. Oceanogr., 5, 179-188. 

Bailey, K.M., S.J. Picquelle, and S.M. Spring (199613): Mortality of larval walleye 

pollock Theragra chalcogramma in the western Gulf of Alaska, 1988-91. Fish. 

Oceanogr., 5, 124-136. 

Bailey, K.M., M.F. Canino, J.M. Napp, S.M. Spring, and A.L. Brown (1995): Contrasting years of prey levels, feeding conditions and mortality of larval walleye 

pollock Theragra chalcogramma in the western Gulf of Alaska. Mar. Ecol. Prog. 

Ser., 119, 11-23. 

Bailey, K.M., and S.A. Macklin (1994): Analysis of patterns in larval walleye pollock 

Theragra chalcogramma survival and wind mixing events in Shelikof Strait, Gulf 

of Alaska. Mar. Ecol. Prog. Ser., 113, 1-13. 

Bakkala, R.G. (1993): Structure and historical changes in the groundfish complex 

of the eastern Bering Sea. NOAA Tech. Rept. NMFS-114, 91 pp. 

Bentzen, P., C.T. Taggart, D.E. Ruzzante, and D. Cook (1997): Microsatellite 

polymorphism and the population structure of Atlantic cod (Gadus morhua) in 

the northwest Atlantic. Can. J. Fish. Aquat. Sci., 53, 2706-2721. 

Bernatchez, L., and S. Martin (1996): Mitochondria1 DNA diversity in anadromous 

rainbow smelt, Osmems mordm Mitchill: A genetic assessment of the membervagrant hypothesis. Can. J. Fish. Aquat. Sci., 53, 424-433. 

Bograd, S.J., P.J. Stabeno, and J.D. Schumacher (1994): A census of mesoscale 

eddies in Shelikof Strait, Alaska, during 1989. J. Geophys. Res., 99, 18,243- 

18,254. 
BERING SEA FOCI FINAL REPORT 49 

Boorman, S.A., and P.R. Levitt (1973): Group selection on the boundary of a stable 

population. Theor. Pop. Biol., 4, 85-128. 

Brown, J.H. (1984): On the relationship between abundance and distribution of 

species. American Naturalist, 123, 253-279. 

Brown, J.H. (1995): Macroecology. Univ. Chicago Press, Chicago. 

Canino, M.F., K.M. Bailey, and L.S. Incze (1991): Temporal and geographic differences in feeding and nutritional condition of walleye pollock larvae Theragra 

chalcogramma in Shelikof Strait, Gulf of Alaska. Mar. Ecol. Prog. Ser., 79, 

27-35. 

Carr, S.M., A.J. Snellen, K.A. Howse, and J.S. Wroblewski (1995): Mitochondrial 

DNA sequence variation and the genetic stock structure of Atlantic cod (Gadus 

morhua) from bay and off shore locations on the Newfoundland continental 

shelf. Mol. Ecol., 4, 79-88. 

Carvalho, G.R., and L. Hauser (1994): Molecular genetics and the stock concept in 

fisheries. Rev. Fish. Biol. Fisheries, 4, 326-350. 

Corten, A. (1993): Learning processes in herring migrations. ICES C.M. 1993/H:18. 

Daan, N. (1991): Bias in virtual population analysis when the unit stock assessed 

consists of sub-stocks. ICES C.M. 1991/D:17. 

Dawson, P. (1994): The stock structure of Bering Sea walleye pollock (Theragra 

chalcogramma). Master of Science Thesis, University of Washington, Seattle, 

220 pp. 

DelllArciprete, O.P. (1992): Growth, mortality, and transport of walleye pollock 

larvae (Theragra chalcogramma) in the eastern Bering Sea. Master of Science 

Thesis, University of Washington, Seattle, 105 pp. 

deYoung, B., and G.A. Rose (1993): On the recruitment and distribution of Atlantic 

cod (Gadus morhua) off Newfoundland. Can. J. Fish. Aquat. Sci., 50, 2729- 

2741. 

Doherty, P.J., S. Planes, and P. Mather (1995): Gene flow and larval duration in 

seven species of fish from the Great Barrier Reef. Ecology, 76, 2373-2391. 

Efremov, V.V., E.V. Mikhajlova, and V.B. Molokanov (1989): Aconitase, a new 

and promising marker to be used in genetic studies of Theragra chalcogramma 

populations. Genetika, 25, 2263-2265 (English abstract only). 

Francis, R.C., and K.B. Bailey (1983): Factors affecting recruitment of selected 

gadoids in the northeast Pacific and east Bering Sea. In From Year to Year, 

W. Wooster (ed.), Washington Sea Grant, University of Washington, Seattle, 

35-60. 

Frank, K.T. (1992): Demographic consequences of age-specific dispersal in marine 

fish populations. Can. J. Fish. Aquat. Sci., 49, 2222-2231. 

Garcia de Le6n, L. Chikhi, and F. Bonhomme (1997): Microsatellite polymorphism 

and population subdivision in natural populations of European sea bass Dicentrarchus labrax (Linnaeus, 1758). Mol. Ecol., 6, 51-62. 

Gauldie, R.W. (1991): Taking stock of genetic concepts in fisheries management. 

Can. J. Fish. Aquat. Sci., 48, 722-731. 

Gonzalez-Villasenor, L.I., and D.A. Powers (1990): Mitochondrial DNA restriction site polymorphisms in the teleost Fundulus heteroclitus support secondary 

intergradation. Evolution, 44, 27-37. 

Gong, Y., Y.H. Hur, and S.S. Kim (1990): Comparison of meristic characters of 

Alaska pollock, Theragra chalcogramma, from seven geographic areas of the 

North Pacific. In Compilation of Papers Presented at the International Symposium on Bering Sea Fisheries. Alaska Fisheries Science Center, Seattle, WA, 

77-82. 

Grant, W.S., and F.M. Utter (1980): Biochemical genetic variation in walleye pollock Theragra chalcogramma: population structure in the southeastern Bering 

Sea and Gulf of Alaska. Can. J. Fish. Aquat. Sci., 37, 1093-1100. 
50 S.A. Macklin (ed. ) 

Hanski, I., and M. Gilpin (1991): Metapopulation dynamics: Brief history and 

conceptual domain. In Metapopulation Dynamics, M. Gilpin and I. Hanski 

(eds.), Academic Press, Inc., San Diego, CA, 3-16. 

Harrison, S. (1991): Local extinction in a metapopulation context: An empirical 

evaluation. In Metapopulation Dynamics, M. Gilpin and I. Hanski (eds.), Academic Press, Inc., San Diego, CA, 73-88. 

Hashimoto, R., and S. Koyachi (1969): Biology of the Alaska pollock, Theragra 

chalcogramma (Pallas), distributed on the fishery grounds of the Tohoku districts and the Pacific coast of Hokkaido, southward from the Erimo ground, I, 

The morphological differentiation of the three types and the comparison with 

the other fishery ground's groups. Bull. Tohoku Reg. Fish. Res. Lab., 29, 37-92 

(in Japanese with English summary). 

Hashimoto, R., and S. Koyachi (1977): Geographical variation of relative growth of 

walleye pollack Theragra chalcogramma (Pallas). Bull. Tohoku Reg. Fish. Res. 

Lab., 38, 41-74 (in Japanese with English summary). 

Hedgecock, D. (1994): Temporal and spatial genetic structure of marine animal 

populations in the California Current. CalCOFI Rept., 35, 73-81. 

Hillgruber, N., L.J. Haldorson, and A.J. Paul (1995): Feeding selectivity of larval 

walleye pollock Theragra chalcogramma in the oceanic domain of the Bering 

Sea. Mar. Ecol. Prog. Ser., 120, 1-10. 

Hinckley, S. (1987): The reproductive biology of walleye pollock, Theragra chalcogramma, in the Bering Sea, with reference to spawning stock structure. Fish. 

Bull. U.S., 85(3), 481-498. 

Hinckley, S., K.M. Bailey, S. Picquelle, J.D. Schumacher, and P.J. Stabeno (1991): 

Transport, distribution and abundance of larval and juvenile walleye pollock 

(Theragra chalcogramma) in the western Gulf of Alaska. Can. J. Fish. Aquat. 

Sci., 48, 91-98. 

Hjort, J. (1914): Fluctuations in the great fisheries of northern Europe. Rapp. 

Proc. Verb. Cons. Int. Explor. Mer, 20, 1-228. 

Ishida, T. (1954): On the age determination and morphometrical differences of the 

otolith of Alaska pollock in the Hokkaido coast. Bull. Hokkaido Reg. Fish. Res. 

Lab., 11, 36-67 (in Japanese with English summary). 

Iwata, M. (1973): Genetic polymorphism of tetrazolium oxidase in walleye pollock. 

Jpn. J. Genet., 48, 147-149. 

Iwata, M. (1975a): Population identification of walleye pollock, Theragra chalcogramma (Pallas), population in the vicinity of Japan. Memo. Fac. Fish. Hokkaido 

Univ., 22, 193-258. 

Iwata, M. (1975b): Genetic identification of walleye pollock, Theragra chalcogramma (Pallas), populations on the basis of tetrazolium oxidase polymorphism. 

Comp. Biochem. Physiol., 50B, 197-201. 

Iwata, M., and I. Hamai (1972): Local forms of walleye pollock, Theragra chalcogramma (Pallas) classified by number of vertebrae. Bull. Jpn. Soc. Sci. Fish., 

38(10), 1129-1142. 

Janusz, J. (1994): How many pollock (Theragra chalcogramma) stocks support the 

fishery in the Sea of Okhotsk. Bull. Sea Fish. Inst. Gdynia, 132, 67-68 (English 

abstract). 

Janusz, J., T.B. Linkowski, and M. Kowalewska-Pahlke (1989): Results of the population studies of walleye pollock Theragra chalcogramma in the Bering Sea. In 

Proceedings of the International Scientific Symposium on Bering Sea Fisheries, 

NOAA Tech. Memo. NMFS F/NWC-163, Alaska Fisheries Science Center, Seattle, WA, 216-230. 

Jarne, P., and P.J.L. Logoda (1996): Microsatellites, from molecules to populations 

and back. Trends Ecol. Evol., ill, 424-429. 
BERING SEA FOCI FINAL REPORT 51 

Johnson, A.G. (1977): A survey of biochemical variants found in groundfish stocks 

from the North Pacific and Bering Sea. Anim. Blood Groups Biochem. Genet., 

8, 13-19. 

Kendall, A.W., J.D. Schumacher, and S. Kim (1996): Walleye pollock recruitment 

in Shelikof Strait: Applied fisheries oceanography. Fish. Oceanogr., 5, 4-18. 

Kennedy, P.K., M.L. Kennedy, E.G. Zimmerman, R.K. Chester, and M.H. Smith 

(1986): Biochemical genetics of mosquito fish, V, Perturbation effects on genetic 

organization of populations. Copeia, 1986, 937-945. 

Kim, S., and A.W. Kendall, Jr. (1989): Distribution and transport of larval walleye 

pollock (Theragra chalcogramma) in Shelikof Strait, Gulf of Alaska, in relation 

to water movement. Rapp. P.-v. Reun. Cons. Int. Explor. Mer, 191, 127-136. 

Koyachi, S., and R. Hashimoto (1977): Preliminary survey of variations of meristic 

characteristics of walleye pollock Theragra chalcogramma (Pallas). Bull. Tohoku 

Reg. Fish. Res. Lab., 38, 17-40 (in Japanese with English summary). 

Lawton, J.H., S. Nee, A.J. Letcher, and P.H. Harvey (1994): Animal distributions: 

Patterns and processes. In Large-Scale Ecology and Conservation, P.J. Edwards, 

R.M. May, and N.R. Webb (eds.), Blackwell Sci. Publ., Oxford, 41-58. 

Levins, R. (1970): Extinction. In Some Mathematical Problems in Biology, M. 

Gersternhaber (ed.), American Mathematical Society, Providence, RI, 77-107. 

Lincoln, R. (1994): Molecular genetics applications in fisheries: Snake oil or restorative? Rev. Fish. Biol. Fish., 4, 389-392. 

Lynde, C.M., M.V.H. Lynde, and R.C. Francis (1986): Regional and temporal 

differences in growth of walleye pollock (Theragra chalcogramma) in the eastern 

Bering Sea and Aleutian Basin with implications for management. Unpublished 

manuscript, 48 pp., Northwest and Alaska Fish. Cent., Natl. Mar. Fish. Serv., 

NOAA, 7600 Sand Point Way NE, Seattle, WA 98115. 

MacArthur, R.H., and E.O. Wilson (1967): The Theory of Island Biogeography. 

Princeton University Press, Princeton, N.J., 203 pp. 

McConnaughey, R.A. (1995): Changes in geographic dispersion of eastern Bering 

Sea flatfish associated with changes in population size. In Proceedings of the 

International Symposium on North Pacific Flatfish, Alaska Sea Grant Program, 

Fairbanks, 385-406. 

Matthews, K.R. (1990): An experimental study of the habitat preferences and 

movement patterns of copper, quillback, and brown rockfishes (Sebastes spp.). 

Env. Biol. Fish., 29, 161-178. 

Mulligan, T.J., K.M. Bailey, and S. Hinckley (1989): The occurrence of larval and 

juvenile walleye pollock, Theragra chalcogramma, in the eastern Bering Sea with 

implications for stock structure. In Proceedings of the International Symposium 

on the Biology and Management of Walleye Pollock, Alaska Sea Grant Rept. 

No 89-1, University of Alaska, Fairbanks, 471-490. 

Mulligan, T.J., R.W. Chapman, and B.L. Brown (1992): Mitochondria1 DNA analysis of walleye pollock, Theragra chalcogramma, from the eastern Bering Sea 

and Shelikof Strait, Gulf of Alaska. Can. J. Fish. Aquat. Sci., 49, 319-326. 

Nakano, H., M. Takahashi, and K. Kikuchi (1991): Geographical differences of 

walleye pollock caught from three Bering Sea areas from standpoint of metal 

and amino acid contents of otoliths. Int. Pac. Fish. Comm. Doc. 3668, Fisheries 

Agency of Japan, National Res. Inst. of Far Sea Fisheries, 7-1 Orido 5 chome, 

Shimizu, Shizuoka, Japan 424, 14 pp. 

Napp, J.M., L.S. Incze, P.B. Ortner, D.L.W. Siefert, and L. Britt (1996): The plankton of Shelikof Strait, Alaska: Standing stock, production, mesoscale variability 

and their relevance to larval fish survival. Fish. Oceanogr., 5, 19-38. 

National Research Council (1996): The Bering Sea Ecosystem. National Academy 

Press, Wash., D.C. 307 pp. 
S.A. Macklin (ed.) 

Nitta, A., and T. Sasaki (1990): Study of stock identification of walleye pollock 

based on morphometric data. In Compilation of Papers Presented at the International Symposium on Bering Sea Fisheries, Alaska Fisheries Science Center, 

Seattle, WA, 74-76. 

Ogata, T. (1959): Population studies of the Alaska pollock in the Sea of Japan, I, 

On the variation in the vertebral count. Ann. Rept. Jap. Sea Reg. Fish. Res. 

Lab., 5, 119-125 (in Japanese with English summary). 

Olla, B.L., M.W. Davis, C.H. Ryer, and S.M. Sogard (1996): Behavioral determinants of distribution and survival in early stages of walleye pollock, Theragra 

chalcogramma: a synthesis of experimental studies. Fish. Oceanogr., 5, 167-178. 

Ovenden, J.R. (1990): Mitochondria1 DNA and marine stock assessment: A review. 

Aust. J. Mar. Freshwater Res., 41, 835-853. 

Palsson, W.A., K. Hoeman, G.G. Bargmann, and D. Day (1996): Draft report, 

Puget Sound bottomfish status of stocks. Wash. Dept. Fish. 

Pawson, M.G., and S. Jennings (1996): A critique of methods for stock identification 

in marine capture fisheries. Fish. Res., 25, 203-217. 

Powers, D.A. (1996): The use of molecular techniques to dissect the genetic architecture of pollock populations. Report to the Coastal Ocean Program. 

Quinn, T.P. (1993): A review of homing and straying of wild and hatchery-produced 

salmon. Fish. Res., 18, 29-44. 

Quinn, T.P., and R.D. Brodeur (1991): Intra-specific variations in the movement 

patterns of marine animals. Amer. Zool., 31, 231-241. 

Rand, D.M. (1996): Neutrality test of molecular markers and the connection between DNA polymorphism, demography, and conservation biology. Cons. Biol., 

10, 665-671. 

Rose, G.A. (1993): Cod spawning on a migration highway in the north-west Atlantic. Nature, 366, 458-461. 

Ruzzante, D.E., C.T. Taggart, D. Cook, and S. Goddard (1996a): Genetic differentiation between inshore and offshore Atlantic cod (Gadus morhua L.) off 

Newfoundland: Microsatellite DNA variation and antifreeze level. Can. J. Fish. 

Aquat. Sci., 53, 634-645. 

Ruzzante, D.E., C.T. Taggart, and D. Cook (1996b): Spatial and temporal variation 

in the genetic composition of a larval cod (Gadus morhua) aggregation: Cohort 

contribution and genetic stability. Can. J. Fish. Aquat. Sci., 53, 2695-2705. 

Saunders, M.W., G.A. McFarlane, and W. Shaw (1989): Delineation of walleye 

pollock (Theragra chalcogramma) stocks off the Pacific coast of Canada. In 

Proceedings of the International Symposium on the Biology and Management 

of Walleye Pollock, Alaska Sea Grant Rept. No. 89-1, University of Alaska, 

Fairbanks, 379-401. 

Serobaba, 1.1. (1977): Data on the population structure of the walleye pollock, 

Theragra chalcogramma (Pallas), from the Bering Sea. Vopr. Ikhtiol., 17, 247- 

260 (in Russian) (English translation 1978, J. Ichthyol., 17, 219-231). 

Severin, K.P., J. Carroll, and B.L. Norcross (1995): Electron microprobe analysis of 

juvenile walleye pollock, Theragra chalcogramma, otoliths from Alaska: A pilot 

stock separation study. Env. Biol. Fish., 43, 269-283. 

Schumacher, J.D., and A.W. Kendall, Jr. (1995): An example of fisheries oceanography: Walleye pollock in Alaskan waters. Rev. Geophys. (suppl.), 1153-1163. 

Schumacher, J.D., P.J. Stabeno, and S.J. Bograd (1993): Characteristics of an eddy 

over a continental shelf: Shelikof Strait, Alaska. J. Geophys. Res., 98, 8395- 

8404. 

Schumacher, J.D., and P.J. Stabeno (1994): Ubiquitous eddies of the eastern Bering 

Sea and their coincidence with concentrations of larval pollock. Fish. Oceanogr., 

3, 182-190. 
BERING SEA FOCI FINAL REPORT 53 

Schumacher, J.D., and P.J. Stabeno (1997): The continental shelf of the Bering 

Sea. In The Sea, Vol. 10 (in press). 

Shaw, W., and G.A. McFarlane (1986): Biology, distribution and abundance of 

walleye pollock (Theragra chalcogramma) off the west coast of Canada. Int. 

North Pac. Fish. Comm. Bull., 45, 262-283. 

Shields, G.F., and J.R. Gust (1995): Lack of geographic structure in mitochondria1 

DNA sequences of Bering Sea walleye pollock, Theragra chalcogramma. Mol. 

Mar. Biol. Biotech., 4, 69-82. 

Sinclair, M. (1988): Marine populations: An essay on population regulation and 

speciation. Washington Sea Grant Press, Seattle. 

Slatkin, M. (1987): Gene flow and the geographical structure of natural populations. 

Science, 236, 787-792. 

Smith, P.J., A. Jamieson, and A.J. Birley (1990): Electrophoretic studies and the 

stock concept in marine teleosts. J. Cons. Int. Explor. Mer, 47, 231-245. 

Somerton, D. (1978): Competitive interaction of walleye pollock and Pacific Ocean 

perch in the northern Gulf of Alaska (abstract). In Fish Food Habit Studies, 

S.J. Lipovsky, and C.A. Simenstad (ed.), Washington Sea Grant, University of 

Washington, Seattle, 163. 

Sogard, S.M., and B.L. Olla (1996): Food deprivation affects vertical distribution 

and activity of a marine fish in a thermal gradient: Potential energy-conserving 

mechanisms. Mar. Ecol. Prog. Ser., 133, 43-55. 

Stabeno, P. J., R.K. Reed, and J.D. Schumacher (1995): The Alaska coastal current: 

Continuity of transport and forcing. J. Geophys. Res., 1OO(C2), 2477-2485. 

Stepanenko, M.A. (1997): Variations from year to year in the spatial differentiation 

of the walleye pollock, Theragra chalcogramma, and the cod, Gadus macrocephalus, in the Bering Sea. J. Ichthyol., 37, 14-20. 

Svetovidov, A.N. (1948): Fauna of USSR fishes. Gadiformes, 9(4). Moscow, Zool. 

Inst. Acad. Sci. USSR, 304 pp. 

Swain, D.P., and E. J. Wade (1993): Density-dependent geographic distribution of 

Atlantic cod (Gadus morhua) in the southern Gulf of St. Lawrence. Can. J. 

Fish. Aquat. Sci., 50, 725-733. 

Swain, D.P., and R. Morin (1996): Relationship between geographic distribution 

and abundance of American plaice (Hippoglossoides platessoides) in the southern 

Gulf of St. Lawrence. Can. J. Fish. Aquat. Sci., 53, 106-119. 

Swartzman, G., W. Stuetzle, K. Kulman, and M. Powojowski (1994): Relating the 

distribution of pollock schools in the Bering Sea to environmental factors. ICES 

J. Mar. Sci., 51, 481-492. 

Taylor, A.D. (1991a): Studying metapopulation effects in predator-prey systems. 

In Metapopulation Dynamics, M. Gilpin and I. Hanski (eds.), Academic Press, 

Inc., San Diego, CA, 305-323. 

Taylor, B. (1991b): Investigating species incidence over habitat fragments of different areas-a look at error estimation. In Metapopulation Dynamics, M. Gilpin 

and I. Hanski (eds.), Academic Press, Inc., San Diego, CA, 177-191. 

Temnykh, O.S. (1991): The population structure of Alaska pollock in the Okhotsk 

Sea. Rybn. Khoz., 6, 28-31 (English abstract only). 

Temnykh, O.S. (1994): Morphological differentiation of Alaskan pollock, Theragra 

chalcogramma, in the west Bering Sea and Pacific waters of Kamchatka. J. 

Ichthyol., 34, 204-211. 

Theilacker, G.H., K.M. Bailey, M.F. Canino, and S.M. Porter (1996): Variations in 

larval walleye pollock feeding and conditions: A synthesis. Fish. Oceanogr., 5, 

112-123. 

Thompson, J.M. (1981): Preliminary report on the population biology and fishery 

of walleye pollock (Theragra chalcogramma) off the Pacific coast of Canada. 

Can. Tech. Rep. Fish. Aquat. Sci., 1031, 157 pp. 
54 S.A. Macklin (ed.) 

Tsuji, S. (1989): Alaska pollock population, Theragra chalcogramma, of Japan and 

its adjacent waters, I, Japanese fisheries and population studies. Mar. Behav. 

Physiol., 15, 147-205. 

Vastano, A.C., L.S. Incze, and J.D. Schumacher (1992): Observation and analysis 

of fishery processes: Larval pollock at Shelikof Strait. Alaska. Fish. Oceanogr., 

1, 20-31. 

Waples, R.S. (1987): A multispecies approach to the analysis of gene flow in marine 

shore fishes. Evolution, 41, 385-400. 

Wespestad, V.G. (1996): Trends in North Pacific pollock and cod fisheries. In Norfish '96,15-16 August 1996, Trondheim, Norway (see http: //www . af sc. noaa. 

gov/refm/norfish/norfish.htm). 

Wilimovsky, N.J., A. Peden, and J. Peppar (1967): Systematics of six demersal 

fishes of the North Pacific Ocean. Fish. Res. Board Can. Tech. Rep., 34,95 pp. 

Wright, J.M., and P. Bentzen (1994): Microsatellites: Genetic markers for the 

future. Rev. Fish. Biol. Fisheries, 4, 384-388. 
BERING SEA FOCI FINAL REPORT 55 

Part 2A 

The use of molecular techniques to dissect the 

genetic architecture of pollock populations 

(Dennis A. Powers') 

One of the main goals of fisheries biologists is to understand the mechanisms 

that regulate the distribution and abundance of marine fish. Elucidation of 

these mechanisms requires an understanding of the genetic architecture of 

the fish species, including the ability to discriminate between stocks and determine the relative contributions of these stocks to the fishery. During the 

initial phase of our project, we developed pollock-specific polymerase chain 

reaction (PCR) methods to test the hypothesis that "there are distinct Pollock stocks in the Bering Sea." After these methods were developed, we 

analyzed 164 individual pollock samples that represented populations sampled from the Gulf of Alaska, Bering Sea, and Sea of Japan. Using 47 individuals as population representatives, we initially sequenced 300 base pairs 

of DNA for each of two mitochondria1 genes (i.e., cytochrome-b and ATPase) for each individual fish. Our sequencing results identified 14 mtDNA 

haplotypes, three of which were in high enough frequency to be informative 

for tests of population subdivision. These three haplotypes were defined by 

base substitutions at two different DNA sequence sites: Haplotype 3 - AA; 

Haplotype 7 - GA, and Haplotype 13 - GG. 

Forty-seven individuals were sequenced for approximately 600 base pairs; 

300 base pairs each for cytochrome-b and ATPase. Individuals represented 

all populations sampled from the Gulf of Alaska, Bering Sea, and Sea of 

Japan. Fourteen mtDNA haplotypes were found, three of which were in 

high enough frequency to be informative for tests of population subdivision. 

These three haplotypes were defined by base substitutions at two sites. 

Haplotype 3 - AA 

Haplotype 7 - GA 

Haplotype 13 - GG 

where the first position is found in cytochrome-b, and the second in ATPase8. Substitutions at both sites were silent, the first a third-position substitution in a threonine codon, the second a third-position substitution in a 

glutamic acid codon. A restriction enzyme assay was developed to score 117 

additional individuals for these three haplotypes (a total of 164 individuals) 

(Table 2A.1). 

An analysis of molecular variance (AMOVA) was performed on the aggregate data (164 individuals) representing nine populations. Most of the 

variation was found to be within populations (85.5%), although a small but 

significant proportion was among populations (14.5%). A UPGMA den- 

'Hopkins Marine Station, Stanford University, Pacific Grove, CA 93940, U.S.A. 
56 S.A. Macklin (ed.) 

Table 2A.1: Cytochrome-b and ATPase-8 haplotypes from different areas of the Bering Sea. 

Haplotype Pairs 

AA GO GA 

America 

Northeastern Shelf 

Aleutian Basin 

Southeastern Aleutian 

Northeastern Aleutian 

Gulf of Alaska 

Southeastern Shelf 

Asia 

East Kamchatka 

West Bering Sea 

Sea of Japan 

Table 2A.2: Tests for temporal variation. 

Locality Years Compared Probability Significance 

Gulf of Alaska 1988 vs 1994 0.3866 ns 

Southeast Shelf 1988 vs 1991 0.1648 ns 

Northeast Aleutians 1988 vs 1991 0.9021 ns 

drogram (Fig. 2A.1) using among-population genetic distances revealed evidence for a distinct split between American (Gulf of Alaska and Eastern 

Bering Sea) and Asian (Sea of Japan and Western Bering Sea) populations, 

primarily in the distribution of the GG and GA haplotypes. An AMOVA 

revealed that haplotype frequencies within each group differed significantly 

(P < 0.0002). An analysis of these data using the Neighbor Joining Method 

was consistent with the distinct division between American and Asian pop 

ulations. As was the case for the dendogram derived by the DA genetic 

distance analysis (Fig. 2A.2), the Neighbor Joining Method also revealed 

considerable substructure within the larger American and Asian clusters. 

Some of the smaller clusters were consistent with the substructure derived 

by the UPGM genetic distance dendogram illustrated in Fig. 2A.2, while 

others were slightly different. If we could significantly expand the sample 

size for each of the nine populations involved in this study and provide data 

for these populations between year classes, there is a very high likelyhood 

that we could discriminate between all nine populations on the basis of RFLP 

analysis of mtDNA haplotypes. 

Based on the DNA sequence data of these 47 individuals, we developed a 

restriction enzyme assay that allowed the rapid identification of mtDNA hap 

lotypes based on restriction fragment length polymorphisms (RFLP) using 

gel electrophoresis. Employing this RFLP analysis, 117 additiond individual 

pollock were analyzed for the three mtDNA haplotypes identified by DNA se 

quence analyses. After the methods were developed, we analyzed 164 pollock 

DNA samples representing nine populations from the Gulf of Alaska, Bering 
BERING SEA FOCI FINAL REPORT 57 

I - SE Aleutian 

SE Shelf 

NE Aleutian 

Gulf of Alaska 

NE Shelf 

I 1 leut ti an Basin 

W. Bering Sea - 1s. 

I 

Japan 

E. Kamchatka 

Figure 2A.1: UPGG Dendogram utilizing the Standard Genetic Distance Method of analysis. 

NE Shelf 

NE Aleutian 

Gulf of Alaska 

Aleutian Basin 

SE Aleutian 

SE Shelf 

S. Japan 

E. Kamchatka 

I 

W. Bering Sea 

Figure 2A.2: UPGM Dendogram utilizing the DA-Genetic Distance Method of analysis. 

Sea, and Sea of Japan. An analysis of molecular variance (AMOVA) was 

performed on the aggregate data of 164 individuals representing nine populations. Most of the variation was found to be within populations (85.5%), 

although a small but significant proportion was among populations (14.5%). 

In order to better define those populations, we expanded the sample size and 

analyzed samples from an earlier year to determine if the greater variation 

within populations was the result of pooling samples collected from different year classes. We developed the following specific goals for October 1995 

through September 30, 1996 in order to attack this problem: 

(i) analyze samples collected from populations in 1988, 

(ii) analyze new samples collected from nine populations in 1994, 

(iii) compare the results of the 1988 and 1994 samples with those collected 

and analyzed early, 
58 S.A. Macklin (ed.) 

r NE Aleutians (2) 

1 

7 

r L NE Shelf (3) 

2L Aleutian 

I 3 Basin (7) 

1 Shelikof 

Strait (8) 

I I S. Kamchatka (5) 

I 4 

I W. Bering (6) 

Sea 

Figure 2A.3: UPGMA dendrogram of Bering Sea and Gulf of Alaska walleye pollock, based on genetic 

distances at the microsatellite locus Gmo-2. Number in parentheses correspond to the population numbers 

on the map (Figure 4). 

(iv) do an analysis of variance of the temporal and spatial data sets. 

By the end of 1995 we had already made substantial progress toward 

achieving these specific goals. For example, we had expanded the sample size 

from 164 individuals to 262 samples. In an attempt to determine if there was 

a temporal component of the data that could help explain the larger variation within populations than between populations that we reported last year, 

we analyzed samples collected in 1988 from the Gulf of Alaska, the Northeast Aleutians, and the Southeast Shelf and compared them with samples 

collected in 1994 and 1991 from those sites. However, tests for temporal 

variation between 1988 samples and samples collected later did not identify significant differences between year classes (Table 2A.2). Consequently, 

we reject the hypothesis that the larger variation that we observed within 

populations was derived from temporal variation between year classes. 

Since our previous report, we have identified a small proportion (i.e., 

four) of the AG haplotype. This haplotype is probably a rare convergent 

change. The distribution of the haplotypes between geographical regions for 

1988, 1991, and 1994 are shown in Table 2A.3. 

Even though there was still greater variation within than between pop 

ulations, the additional data maintained the same small but significant difference between populations that we previously reported. There remained 

a sharp discrimination between Asian and American groups. However, expanding the sample size did not provide better discrimination between populations. 

Since expanding the sample size of the populations did not dramatically 

improve our ability to discriminate between populations, we undertook an 

analysis of minisatellite elements (i.e., "DNA Fingerprinting") of pollock 

populations. However, none of the minisatellite loci screened yielded useful 

information. We surveyed some of the pollock nuclear genome for variation in 

the number of tandemly repeated microsatellite elements. We screened seven 
BERING SEA FOCI FINAL REPORT 59 

Table 2A.3: Distribution of haplotypes between geographical regions for 1988, 1997, and 1994. 

America 

Northeastern Shelf 1991 

Aleutian Basin 1991 

Southeastern Aleutian 1991 

Northeastern Aleutian 1988 

Northeastern Aleutian 1991 

Gulf of Alaska 1988 

Gulf of Alaska 1994 

Southeastern Shelf 1988 

Southeastern Shelf 1991 

Haplotype 

AA GG GA AG 

41240 

6730 

61121 

10 23 6 1 

3920 

32061 

32050 

62150 

49100 

Asia 

East Kamchatka 1991 4890 

West Bering Sea 1991 49100 

Sea of Japan 1994 0120 

microsatellite primers for the polymerase chain reaction (PCR) that have 

been previously shown to amplify regions in several gadid species (Brooker 

et al., 1994). These primers were used to analyze 221 individual pollock representing seven pollock populations. Of those primers, three pairs (Gmo2, 

Gmog, Gmo145) gave detectable product, and two (Gmo2 and Gmo145) 

showed genetic variation. Using the Gmo145 primer, we identified 19 detectable alleles and one allele that appeared that did not yield a PCR product (Table 2A.4). 

Since there was a lack of detectable PCR product, conditions of the template DNA were tested with two universal PCR primers (ACT1 and ACT4). 

Because all the individuals that did not yield a PCR product with Gmo145 

primers gave detectable PCR products when amplified with the ACT1 and 

ACT4 primers, these data suggest that the absence of product for Gmo145 

may be due to a "null allele" at this locus resulting from one or more sequence differences in the priming region of Gmo145. When the putative 

"null allele" is scored as a separate allele, it is clear that the vast majority of the Asian populations have much higher frequencies than American 

populations. 

The microsatellite data in Table 2A.5 appears to give the same general 

discrimination between Asian and American populations as was obtained by 

the haplotypes described earlier in this report. Moreover, there is a suggestion for further subdivisions in Table 2A.5 but a proper statistical analysis 

must be done before we can be sure if the apparent trend is significant. 

The statistical analysis of haplotype and microsatellite data is one of 

our major goals for the remainder of our funding period after which we will 

publish the results in internationally refereed journals. For the haplotype 

data, an analysis of molecular variance (AMOVA) like that performed last 

year on the aggregate data (164 individuals) representing nine populations 

will be done on the expanded data set. Dendograms utilizing DA genetic 
Table 2A.4: Alleles for Gmo 145 microsatellite locus. 

Alleles 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 18 Nul

NE Aleutians 1032 5 7023 61 0 0 0 0 0 0 0 0 0 0 

NE Shelf 0001321831000100000 0 

AleutianBasin 001 16 6029 4 2 10 0 0 0 0 0 0 0 0 

S. Kamchatka 000000000000000000068 

W.BeringSea 0000 0 00 0 0 0 0 0 0 0 0 0 0 0 0 34 

Shelikof Strait 11631912048429 3 12 2 4 12 11 0 

Table 2A.5: Frequencies of microsatellite alleles of pollock populations. 

Alleles 1 2 3 4 5 6 7 8 9 10 11 13 14 15 16 17 

NE Aleutians .020 .OOO .063 ,042 .lo4 .I46 .OOO .479 .I25 .020 .OOO .OOO .OOO .OOO .OOO .OOO 

NE Shelf .ooo .000 .OOO .050 .I50 .lo0 .050 ,400 .15O .050 ,000 .OOO .050 .OOO ,000 ,000 

Aleutian Basin .000 .000 .020 .020 .I20 .I20 .000 .580 .080 .040 .020 .000 .000 .000 .OD0 .000 

S. Kamchatka .000 .OOO .OOO .OOO .OOO .OOO .OOO .OOO ,000 .OOO .OOO .OOO .OOO .OOO .OOO .OOO 

W. Bering Sea .000 .000 .000 .000 .000 .000 .000 .000 .000 .000 ,000 .000 .000 .000 .000 .000 

Shelikof Strait .006 .006 .038 .019 .I20 .076 .OOO ,304 .266 .057 .019 .006 .013 .013 .006 .OX3 
BERING SEA FOCI FINAL REPORT 6 1 
62 S. A. Macklin (ed.) 

distances, standard genetic distance, and the Neighbor Joining Method will 

be used. The DNA sequences from individuals will be aligned and compared 

with software written to handle large numbers of sequences, and analyzed 

using parsimony (PAUP), maximum likelihood (PHYLIP), and neighborjoining methods to construct phenograms as we have in our earlier analyses. Gene flow will be estimated using the phylogenetic approach of Slatkin 

and Madison (1989). Population structure will be measured using the GSt 

statistic (Takahata and Palumbi, 1985) which has been modified for DNA sequence analysis and tested against a random null model using bootstrapping 

(Palumbi and Wilson, 1990). In the event that recombination within alleles 

is detected, allele phylogenies will be constructed with genetic distance techniques (Slatkin and Madison, 1989). Coding regions will be examined for 

patterns of amino acid versus silent nucleotide changes among individuals 

(Hughes and Nei, 1988). 

Although the mtDNA data was sufficient to differentiate between Asian 

populations and American populations, it did not adequately detect more 

finescale structure within these groups. As stated above, we therefore began 

using DNA microsatellites to study this smaller scale population structure 

of pollock. 

Microsatellites are segments of DNA that consist of a small (2-5 bases) 

motif repeated in tandem several times, such as GTGTGTGT. They have 

been found to be useful for population studies in many organisms. Microsatellites often give a finer scale of resolution than other molecular genetic 

markers. 

Several microsatellite loci have already been found in pollock and other 

related fishes. While we are still screening pollock populations for these loci 

to determine which of them will be useful in this study, one microsatellite 

locus, Gmo2, has been optimized for pollock, and yielded useful data. We 

have studied 315 individual pollock from six localities at this locus. Our 

results so far have identified 11 alleles ranging in length from 1 to 13 units. 

Information derived from this one microsatellite locus revealed the same 

detectable difference between Asian and American areas of the Bering Sea 

that was detected by using the combined data from the sequences of the two 

mitochondial loci, i.e., cytochrome-b, and ATPase-8. Moreover, this single 

microsatellite locus also revealed a difference between the Gulf of Alaska 

and Eastern Bering Sea populations that was not detectable using the two 

mtDNA loci sequence data. Pairwise ANOVA comparisons (Table 2A.6) 

suggest that the Aleutian Islands block some gene flow between the Pacific 

and the Bering Sea. The consequence of this is that Gulf of Alaska fishes 

appear to be mixing with western Pacific fishes nearly as much as with 

Eastern Bering Sea fishes. A UPGMA dendrogram (Fig. 2A.3) shows the 

relationship of the six localities according to genetic distance at the Gmo2 

locus. 

We have identified 13 more microsatellite loci that could provide the 

discrimination between populations within each region that we have tried to 

find for the past 3 years. We have already found that at least four of these 

(pTCR-1, Gmo-1, Gmo-9, and Gmo-145) appear to be detectable in pollock 

and highly variable. 
BERING SEA FOCI FINAL REPORT 63 

Table 2A.6: Pairwise ANOVA comparisons of Bering Sea and Gulf 

of Alaska pollock populations based on polymorphism at the Gmo-2 

microsatellite locus. Three distinct groups emerge: Eastern Bering 

Sea, Western Bering Sea, and Gulf of Alaska. 

Aleutian Shelikof 

NE Shelf S. Kamchatka W. Bering Sea Basin Strait 

NE Aleutians P=0.847 P=0.029 P=0.0002 P=0,700 P=0.0195 

NE Shelf P=0.031 P=9.8E5 P=0.831 P=0.030 

S. Kamchatka P=0.308 P=0.025 P=0.056 

W. Bering Sea P=0.0002 P=O.OOOl 

Aleutian Basin P=0.036 

If we can obtain additional funding, we would construct primers for PCR 

(polymerase chain reaction) that are optimized to amplify these loci in pollock. Also, we would continue screening the other nine loci in order to 

increase the number of usable markers for this study which could not only 

provide finescale discrimination between pollock from each of the three geographical regions we have already identified, but these additional markers 

would also allow us to calculate gene flow between populations. 

References 

Brooker, A.L., D. Cook, P. Bentzen, J.M. Wright, and R.W. Doyle (1994): Organization of microsatellites differs between mammals and cold-water teleost fishes. 

Can. J. Fish. Aquat. Sci., 51, 1959-1966. 

Hughes, A.L., and M. Nei (1988): Pattern of nucleotitle substitution at major 

histocompatibility complex class I loci reveals over dominant selection. Nature, 

335, 167-170. 

Palumbi, S.R., and A.C. Wilson (1990): Mitochondria1 DNA diversity in the sea 

urchins Strongylocentrotus Purpuratus and S. Droebachiensis. Evolution, 44(2), 

403-415. 

Slatkin, M., and W.P. Maddison (1989): A cladistic measure of gene flow inferred 

from the phylogenics of alleles. Genetics, 123, 603-613. 

Takahata, N., and S.R. Palumbi (1985): Extranuclear differentiation and gene flow 

in the finite island model. Genetics, 109, 441-457. 
BERING SEA FOCI FINAL REPORT 65 

Part 2B 

Trends in north Pacific pollock and 1998 harvest 

prognosis (Vidar G. Wespestadl) 

Pollock 

Walleye, or Alaska pollock, has been the basis of the largest groundfish 

harvests since the early 1980s. The majority of the harvest is taken in 

the U.S. and Russian EEZs, and relatively small amounts are harvested 

off Canada, Japan, and Korea. However, in recent years there has been a 

downward trend in harvest, primarily in the Russian EEZ. Pollock harvests 

peaked in 1986 at 6.8 million t, declined until 1994, and in recent years 

has been stable near 4 million t (Table 2B.1). One reason for the high 

harvest levels in the 1980s was the advent of high seas fisheries in the Bering 

Sea Donut Hole and in the Okhotsk Sea Peanut Hole (Fig. 2B.1). These 

fisheries have been halted by international agreements, and are not expected 

to resume operation in the near future. 

North American catch has been stable, varying annually only slightly 

from the 1981-1997 average of 1.3 million t. In Asia, on the other hand, 

catch decreased significantly over the same time period, decreasing from a 

peak of 5 million t in 1981 to 2.2 million t in 1994. Part of the decline 

was due to overfishing, principally in Japan and Korea, and some in Russia, 

including the Peanut Hole Fishery. A partial reason for the very low catches 

observed in 1994 was the collapse of the Russian fishing industry, and their 

inability to fully exploit pollock and other fish in the Russian EEZ. However, 

harvesting capacity has increased in Russia and catch has been increasing in 

recent years. In other areas of Asia, catches appear to remain at relatively 

low levels, and where data are available, there do not appear to be any 

prospects for near-term increases in stocks or harvest. 

North American Pollock 

The principal fisheries in North America are off Alaska, in the eastern Bering 

Sea, and in the western Gulf of Alaska (Table 2B.1). Minor fisheries occur 

in the eastern Gulf of Alaska and off Canada (Table 2B.1). 

The eastern Bering Sea pollock fishery is the largest fishery in North 

America, and has averaged a harvest of 1.2 million t since the early 1980s 

(Fig. 2B.2, Table 2B.1). While catch has been stable, biomass has fluctuated 

greatly in response to strong variation in recruitment. In the late 1970s and 

early 1980s three strong year classes occurred which increased the population to very high levels in the mid-1980s (Fig. 2B.3). In the late 1980s to 

early 1990s only one strong year-class occurred, 1989, and the population 

declined to lower levels of abundance. This year, 1997, trawl surveys and 

hydroacoustic-midwater trawl surveys of the eastern Bering Sea found that 

the overall biomass of eastern Bering Sea pollock decreased slightly from 

'Alaska Fisheries Science Center, NOAA, Seattle, WA 98115, U.S.A. 
Table 2B.1: Alaska pollock catch by area, 1981-1986, 1997 preliminary catch estimates, and 1998 preliminary catch recommendations. 

Russia: Russian Catch Only to 1993 

Gulf of Eastern Donut Western Kamchatka North East South W. Sakhalin Peanut 

Canada Alaska Bering Seaa ~ole-ering Sea East West Okhotsk Sakhalin Kuril I. Japan Sea Hole JapanC So

0 

0 

0 

181 

363 

1040 

1704 

1484 

1484 

1069 

558 

10 

3 

0.6 

0.3 

0.4 

trace 

0.1 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

297 

698 

264 

124 

N A 

Closed 

Closed 

Mean 120 1201 494 742 162 807 573 61 175 38 99 466 

aIncludes Aleutian Islands 

b~ncludes Bogoslof Island catch in US. EEZ 

'Japan catch: Fisheries Agency of Japan catch statistics: Local catch to 1986, 1987-1994 includes catch from Russian EEZ 

*~ollock fishing prohibited since 1989 due to low stock abundance 

Gulf of Alaska and Bering Sea catches include discards in 1990-1996 

Russian data from Fedeev, N.S. and V. Wespestad (in press), Harvest history of pollock (in Russian), and TINRO, Vladivostok, and KoTINRO, Petropavlovsk, Russ

S. Korea catch: Jank Uk Lee, Natl. Fish. Res. Dev. Ag. (personal communication) 

N. Korea catch: C. Zhang Kunsan, Natl. U. (personal communication), estimated from ratio of north-south catch 1926-1940 
BERING SEA FOCI FINAL REPORT 67 

Figure 2B.1: Pollock catch in the Gulf of Alaska and regions of the Bering Sea, 1981-1997. 

1996, as expected, with a preliminary estimate of about 5.5 million t. However, the survey confirmed the presence of a very large 1996 year-class, which 

was first noted by fishers during the 1997 pollock A season. The analysis is 

not complete, but it appears that this year-class may be of similar size to 

the 1978 year-class which initiated the high abundance of the 1980s. The 

1997 survey also found the 1985 year-class to be much bigger than previously 

estimated. In 1996 Russian surveys reported 1995 to be a strong year-class 

based on results from the northwest Bering Sea, but the same year-class was 

not found to be abundant in U.S. waters. The large numbers of juvenile 

fish suggest that the exploitable pollock stock will begin to increase in 1999- 

2000. It should be noted that although eastern Bering Sea pollock are at a 

relatively low level, the level of exploitation is currently less than 20%, much 

below that of other major gadid stocks. 

The western Gulf of Alaska is also increasing in abundance due to a 

strong 1994 year-class. This year-class is entering the fishable population, 

and the recommended allowable catch has been raised for 1998 to 98,000 t, 

up from 76,000 in 1997. 

Aleutian Islands pollock, which appear to be a geographic extension of 

eastern Bering Sea pollock, are stable or increasing. A 1997 survey indicates 

that biomass has increased from a 1994 survey. The pollock size frequency 

obtained in the survey indicates that the 1989 year-class is the dominant 

age group. Aleutian Islands pollock quotas were halved in 1996 to 28,000 t. 

Based on survey abundance estimates, the catch may remain at the current 

level of 28,000 t. The Aleutian Islands pollock biomass may be an underestimate of actual abundance due to the lack of an estimate of the pelagic 

portion of the population. 

Adjacent to the Aleutian Islands is the Bogoslof Island area, which is the 
68 S.A. Macklin (ed.) 

Gulf of Alaska 

.East. Bering Sea 

Donut Hole 

$North. Bering Sea 

West. Berlng Sea 

Figure 2B.2: Eastern Bering Sea pollock abundance trend, 1964-1996. 

primary spawning area of the Aleutian BasinIDonut Hole "stock." These 

pollock also continue to decline. In the 1997 survey the biomass was estimated to be near 300,000 t, down from 2.4 million t in 1988. Until the 

"stock" increases to 1.1 million t no fishery will occur in the Bogoslof Island 

area or in the Donut Hole. This level of biomass is not expected to occur 

until 5-10 years from now, at the earliest, since it appears that Donut Hole 

pollock mainly accrue from strong year-classes from the eastern and western 

Bering Sea. 

Asian Pollock 

Pollock fisheries occur in the Japan Sea within the EEZs of Japan, Korea, 

and Russia, on the Pacific side of Hokkaido. Stocks in these waters are 

currently small, primarily due to overfishing. Recent official catch data is 

scant (Table 2B.1). The greatest amount of catch is by Japan where the 

catch quota was established as 258,000 t in 1997. South Korea has had very 

small harvests in its EEZ in recent years, and the catch from North Korea is 

unknown, although it is reported to have been closed since 1989 due to low 

abundance. Russia also harvests relatively small amounts of pollock from 

the Japan Sea and South Kurile Islands. The expected 1998 harvest from 

these and other minor stocks in Russian waters is estimated to be less than 

300,000 t. 

The primary harvest areas for pollock in Asia are in the Sea of Okhotsk 

and northwestern Bering Sea. The Okhotsk Sea is the primary Asian harvest 

area, and contains two main stocks, the northern Okhotsk, and west Kamchatka stocks. The preliminary estimate of the 1997 pollock catch in west 

Kamchatka is 1.18 million t, about equal to 1996. In the Northern Okhotsk 
BERING SEA FOCI FINAL REPORT 69 

Figure 2B.3: Catch of pollock in Asia, North America, and the Donut Hole, 1981-1997. 

the catch decreased slightly between 1996 and 1997, dropping to 650,000 t 

from 756,000 t. For 1998, Russian biologists are recommending sharp reductions that would decrease the west Kamchatka catch to 800,000 t, and the 

northern Okhotsk to 460,000 t. The 1998 Russian pollock quotas are not 

yet finalized, and it is possible that the final quotas may be different from 

those recommended by scientists. 

Scientists are concerned that the over-harvest in 1995-1996 reduced the 

amount of mature pollock available in 1997, leading the fishery to harvest 

small pollock. The problem of small fish also may have been caused by 

regulations that prohibit trawling in the coastal spawning areas where adult 

pollock congregate, forcing trawl vessels to fish immature pollock in offshore 

areas. 

The 1997 fishery was also reported to be affected by large area fishery 

closures of areas with high bycatch of herring and undersized pollock. Adult 

pollock abundance in Okhotsk Sea is expected to continue to decline in 

1998. Russian data indicates that the 1995 year-class is a large year-class, 

and 1992-1993 are near average. The oldest of these year-classes are just 

reaching maturity, and the 1995 year-class will not mature until 2000. 

The western-northern Bering Sea is the second largest producer in the 

Russian EEZ. The catch of western Bering Sea stock used to average about 

250,000 t, but in recent years has decreased to 50,000-70,000 t due to decrease in stock abundance and concentration of fishing effort in more productive areas such as the Okhotsk and northern Bering Sea. The recommended 

catch quota for the western Bering Sea in 1998 is up, increasing to 150,000 t. 

The northern Bering Sea has the second largest quota in the Russian 

EEZ, with a recommended 1998 quota of 600,000 t. Pollock in this area 

originate from the western Bering Sea and eastern Bering Sea stocks, and 
70 S.A. Macklin (ed. ) 

Table 2B2: Estimated 1998 harvest of walleye pollock by major 

areas of the north Pacific. 

Gulf of Bering Sea Kamchatka North South West 

Alaska Eastern Western Northern West East Okhotsk Kurils Sakhalin Japan Korea Total 

98 1000 150 600 800 45 460 300 3453 

little to no spawning is observed in the area. Russian vessels have fished the 

area since the early 1970s, and the catch has average near 500,000 t, with a 

peak of 900,000 t in 1981. 

This fishery is problematic for several factors, which include that the fish 

are primarily of U.S. origin in recent years, the area (and the harvest) is 

dominated by juvenile pollock that will recruit to U.S. fisheries at maturity, 

there is little dialogue between the U.S. and Russia in developing a coherent 

management plan, and there are questions on the level of Russian fisheries 

monitoring in the area. 

The magnitude of the harvest of small pollock in the Russian northern 

Bering Sea is not fully known, but from reports of masters of vessels fishing 

the area it may be significant. The effect on eastern Bering Sea stocks cannot 

be fully determined at the present. Simulation of the catch and population 

time series using likely scenarios of pollock movement suggests that the worst 

case effect of the current levels of Russian fishing in the northern Bering Sea 

is that harvest levels in the eastern Bering Sea may have to be reduced. This 

will not lead to stock collapse in the eastern Bering Sea. 

Russian scientists had been concerned that the percentage of undersized 

pollock would increase in the 1998 west Kamchatka fishery. However, they 

believe new regulations may decrease the anticipated problems. In 1998, 

for the first time, trawlers will be able to fish in selected coastal spawning 

areas which will allow a harvest of large pollock. Secondarily, mesh size and 

minimum retention size increases have been proposed which should further 

reduce the harvest of juvenile fish. The mesh size and minimum retention 

size increases also apply to the Bering Sea, so that catch of juvenile pollock 

should also decrease in this area as well. 

Prognosis Summary for 1998 

The estimated projected harvest of pollock for 1998 is shown in Table 2B.2. 

The projected harvest is 3.4 million t. This is about 600,000 t less than 

in 1997. A large part of the projected decrease is in the Sea of Okhotsk. 

However, since quotas have not been finalized, it is not certain that these 

reductions will occur. At last year's Groundfish Forum, the 1997 pollock 

harvest was forecast to be 3.8 million t, slightly less than the actual harvest 

of 4 million plus t. It is equally likely that this year's pollock projection may 

be on the conservative side. 
BERING SEA FOCI FINAL REPORT 71 

Biophysical processes relevant to recruitment 

dynamics of walleye pollock (Theragra chalcogramma) 

in the Eastern Bering Sea (J.M. Napp,' A.W. 

Kendall, Jr. ,' and J.D. Schumacher2) 

Abstract 

Walleye pollock is a nodal species in the Bering Sea ecosystem (NRC Report 

1996): juvenile pollock are the dominant prey of fishes, seabirds, and marine 

mammals in this productive ecosystem. The estimated adult pollock biomass 

in the eastern Bering Sea and central basin exceeds 9 MMT, and is the target 

of an ~$1 billion fishery. 

We constructed a conceptual model for larval pollock dynamics using 

factors we found to influence their distribution and feeding success in the 

southeastern Bering Sea. These factors may have a strong influence on 

recruitment success by modifying larval survival. The model is based on 

relevant biophysical variables and pollock early life history traits. Pollock 

spawning occurs in discrete concentrations during winter and spring in a 

variety of habitats which include oceanic (basin and slope) and shelf waters. 

Biophysical phenomena that affect conditions for larval survival and eventual recruitment exhibit marked differences between the Oceanic and Shelf 

Regimes. In the Oceanic Regime eddies are a common feature. While their 

genesis is not well known, eddies have unique biophysical characteristics and 

occur with such regularity that they likely affect larval survival. High concentrations of larval pollock often are associated with eddies. Some of these 

eddies are transported onto the shelf, thereby providing larvae to the Outer 

Shelf Domain. Observations from biophysical instrument platforms moored 

over the basin demonstrated that advection rather than local production 

dominated the observed springtime increase in chlorophyll (often a correlate 

of larval food). Over most of the southeastern shelf eddies are absent and 

other phenomena are important. Seasonal sea-ice and the associated cold 

pool of bottom layer water are striking features of the Middle Shelf Domain. 

Interannual variability in sea-ice and cold-pool extent affects developmental rate of larvae, timing of the phytoplankton bloom (and potentially the 

match/mismatch of larvae and prey), and abundance and distribution of 

juvenile pollock. 

3.1 Introduction 

3.1.1 Description of the Area 

The Bering Sea (Fig. 3.1) is a semi-enclosed portion of the North Pacific 

Ocean that lies between the northernmost land masses of the North Amer- 

'Alaska Fisheries Science Center. NOAA, Seattle, WA 98115, U.S.A. 

'Pacific Marine Environmental Laboratory, NOAA, Seattle, WA 98115, U.S.A. 
72 S. A. Macklin (ed.) 

Figure 3.1: Southeast Bering Sea and associated biophysical domains. The solid circle indicate locations of 

the BS FOCI biophysical platforms. 
BERING SEA FOCI FINAL REPORT 73 

ican and Asian continents. It is divided almost equally between a deep 

basin (maximum depth 3,500 m) and a continental shelf (<200 m) which 

are separated by a steep convoluted continental slope (Hood, 1981; Macklin, 

in press). The Bering Sea is bounded to the south by the Aleutian Island 

chain with its many passes and to the north by the shallow (<60 m) Bering 

Strait, providing the only connection from the Pacific to the Arctic Ocean. 

Water exchange between the North Pacific Ocean and the Bering Sea occurs mainly through the deeper western passes, although transport through 

the eastern passes is important to regional circulation and water properties. The broad (>500 km) eastern shelf is the second broadest continental 

shelf in the world. The southeastern Bering Sea consists of an Oceanic and 

Shelf Regime (Fig. 3.1). Within the Shelf Regime, three distinct Domains 

exist which are characterized by contrasts in water column structure, currents, and biota (Iverson et al., 1979a; Coachman, 1986; Schumacher and 

Stabeno, in press). These Domains include the Coastal (<50 m deep with 

weak stratification), Middle Shelf (50-100 m deep with strong stratification), 

and Outer Shelf (100-200 m deep with mixed upper and lower layers sep 

arated by slowly increasing density). The zooplankton community in the 

two shallower Domains is comprised primarily of the small copepods and 

euphausiids whereas in the Outer Shelf Domain and in the Oceanic Regime 

large open-ocean copepods are numerically dominant (Cooney and Coyle, 

1982; Vidal and Smith, 1986). 

Being a high-latitude sea, seasonal extremes occur in solar radiation 

(length of daylight), meteorological forcing, and ice cover (Niebauer, 1981; 

Overland, 1981). Interannual variations in ice extent (Mysak and Manak, 

1989; Wyllie-Echeverria, 1995a) and its associated phenomenon, the cold 

pool, are marked and interdecadal changes (sometimes called regime shifts 

or Decadal Climate Oscillations: DCO) in the atmosphere above the North 

Pacific Ocean affect the surface wind stress, Sverdrup transport, surface 

ocean heat flux (Trenberth and Hurrell, 1995), and likely have significant 

implications for the biota (Mantua et al., 1997). 

3.1.2 Description of the Problem 

The Bering Sea is the site of some of the most productive fisheries on Earth. 

Besides the lucrative king crab, halibut, and salmon fisheries, most of the 

world catch of walleye pollock comes from the Bering Sea. Pollock is the 

most abundant species harvested in the Bering Sea, accounting for 80% of 

the total weight of the harvest. Pollock, with a total biomass in the Bering 

Sea approaching 20 MMT, is harvested in Bering Sea waters of the exclusive 

economic zones (EEZ) of Russia and the U.S. Formerly there was a large 

pollock fishery in international waters of the Bering Sea basin (known as the 

"donut hole"), but it is now closed by international agreement. The annual 

U.S. catch of pollock in the Bering Sea in recent years has amounted to 

1.3 MMT, with an ex-vessel value of $210 million. Pollock also dominate the 

ecosystem of the Bering Sea, providing most of the food for the extensive 

marine mammal and bird populations found there (e.g., Springer and Byrd, 

1989; Lowry et al., 1996; Sinclair et al., 1996). 
74 S.A. Macklin (ed. 

Pollock spawning, 1984-1 989 

Figure 3.2a: Distribution of selected walleye pollock life history stages in the southeastern Bering Sea. (a) 

pollock spawning areas, 1984-1989 as defined by the fishery; fishing areas are the dark squares and the black 

dots are where spawning fish were found (from Dell'Arciprete, personal communication). 

Pollock in the Bering Sea do not form one homogeneous population, but 

the actual stock structure is not well known. For example, distributions 

of spawning adults, eggs, and larvae show a broad geographic range (Dell' 

Arciprete, in preparation; Fig. 3.2). Research using spawning and juvenile 

distributions and elemental composition of otoliths suggested that four pop 

ulations were identifiable in the eastern Bering Sea (Mulligan et al., 1989). 

More recent genetic studies, conducted as part of Bering Sea FOCI, indicate that there are differences between pollock from the eastern and western 

parts of the Bering Sea (Bailey, this report). Within the eastern Bering 

Sea, there are several spawning areas, and these may also be discrete stocks. 

However, presently used genetic techniques are unable to detect significant 

differences between spawning areas-genetic variability within subjectively 

defined spawning areas is large relative to that between areas. 

In the eastern Bering Sea there are large interannual variations in recruitment of pollock (more than one order of magnitude), and these drive 

population size and thus harvest levels. Without reliable forecasts of recruit- 
BERING SEA FOCI FINAL REPORT 75 

Historical Distribution of Pollock Eggs 

Maximum Number Number Depth of Eggs per 10m2 ,- - of . Hauls Contours 

50,001 - 300,000 

from Dell-Arciprete 

Figure 3.2b: Distribution of selected walleye pollock life history stages in the southeastern Bering Sea. (b) 

pollock eggs; fishing areas are the dark squares and the black dots are where spawning fish were found (from 

DelllArciprete, personal communication,). 
76 S. A. Macklin (ed. ) 

Historical Distribution of Pollock Larvae 

Maximum Number Number 

of Hauls Depth of Larvae per IOm* Contours 

5,001 -200,000 

from Dell-Arciprete 

Figure 3.2~: Distribution of selected walleye pollock life history stages in the southeastern Bering Sea. 

pollock larvae; fishing areas are the dark squares and the black dots are where spawning fish were fo 

(from DelllArciprete, personal communication). 

(c> 

und 
BERING SEA FOCI FINAL REPORT 77 

ment, based on an understanding of the processes that determine recruitment 

variability, harvest levels must be set very conservatively. In order to understand recruitment variations, we must understand the relatidnships among 

the various spawning populations, and the contribution of each to recruitment to the total stock. Recruitment in Bering Sea pollock, as in most other 

marine fish, is thought to be largely set during their egg and larval stages. 

Studies on causes of mortality of these early life history stages of pollock are 

needed to understand recruitment variation. 

3.2 Physical Oceanographic Setting 

3.2.1 Marine Climatology and Sea Ice 

Complex interactions among ocean, ice, and atmosphere dominate the physics 

of the Bering Sea. The migration of storms results in a statistical feature 

known as the Aleutian Low, one of the two main low pressure systems in 

the high latitude northern hemisphere. During summer with its long periods 

of daylight and high insolation, the Aleutian Low is typically weak and the 

weather is benign. During the darkness of winter, a marked change occurs 

in atmospheric pressure fields. The Asian continent is dominated by high 

sea level pressure (Siberian High) while the Aleutian Low intensifies and 

dominates weather over the North Pacific and Bering Sea. The juxtaposition of these features results in strong, frigid winds from the northeast. 

The frequency and intensity of storms in the southern Bering Sea decreases 

from winter to summer and frequency also decreases with increasing latitude (averland and Pease, 1982). In the winter, an average of three to five 

storms per month move eastward along the Aleutian Island Chain forming 

the primary storm track, while less than two storms per month cross the 

northern Bering Sea. A secondary storm track curves northward along the 

Asian coast. A difference in the number of storms also occurs across the 

broad eastern shelf, with more activity occurring over the Outer Shelf than 

the Coastal Domain (Schumacher and Kinder, 1983). 

Seasonal sea ice extent in the eastern Bering Sea fluctuates over 1000 km 

between the Bering Strait in summer and south to the Alaska Peninsula and 

shelf break in winter. The actual mechanism of ice formation for the eastern 

shelf has been described by a "conveyor belt" analogy (Overland and Pease, 

1982). Ice is produced along leeward (south-facing) coasts primarily located 

in the northern region of the shelf, and driven by wind to its thermodynamic 

limit where it melts. Brine rejection occurs as water freezes and regions of 

open water, or polynyas, are created by downwind advection of ice. The sea 

ice limit advances southward as ice-melt cools and freshens the upper ocean. 

The amount of production and advection of ice depends upon which storm 

track dominates in a given winter, with greatest ice production occurring in 

years when the Aleutian Low is well developed and storms migrate along the 

primary storm track. 

Variations in overall ice coverage (Fig. 3.3), time of advection over the 

open shelf, and subsequent melt-back are striking features of the physical 

environment. Formation of sea ice generally begins in November, with max- 
78 S.A. Macklin (ed. ) 

Year 

Figure 3.3: Time series of annual maximum sea ice extent, 1972 to 1997 (Wyllie-Echeverria and Wooster, 

submitted). The index is the southernmost latitude of seasonal sea ice extent along longitude 16g0W in the 

Bering Sea. The 26-year mean (57O15'N) and standard deviation (f 22') are shown as solid horizontal lines. 

imum ice extent occurring in late March. Ice-free conditions typically exist from June through October. Observations of ice cover over the eastern 

Bering Sea shelf show a nearly 40% interannual variation about the mean 

(Niebauer, 1988). Other characteristics of ice cover that exhibit great variability include duration of ice at its southern extent (3-15 weeks), time of 

retreat from the southernmost extent (between mid-March and June), and 

number of weeks that ice remains over the Middle Shelf Domain (3-28 weeks 

with a mean of 20 weeks; Wyllie-Echeverria, 1995b). 

Ice formation, brine rejection, advection, and eventual melting play a 

critical role in fluxes of heat and salt and generation of both baroclinic flow 

and the cold pool located over the Middle Shelf Domain (Schumacher and 

Stabeno, in press; Wyllie-Echeverria, 1995b). The positive buoyancy from 

melting ice initiates both baroclinic transport along the marginal ice zone 

(-0.3 x lo6 m3 s-l) and stratification. Cooling and mixing associated with 

ice advance help to condition the entire water column over the Middle Shelf 

Domain and as seasonal heating occurs, the lower layer becomes insulated, 

often with temperatures remaining below 2.0°C (Reed, 1995). It is these 

waters that are commonly called the "cold pool" and whose area varies by 

-20 x lo4 km2 between maximum and minimum extent. Also associated 

with ice-melt is a bloom of phytoplankton that accounts for 10-65% of the total annual primary production over the eastern shelf (Niebauer et al., 1990). 
BERING SEA FOCI FINAL REPORT 79 

Ice production and the cold pool also influence distributions of higher trophic 

level biota (Ohtani and Azumaya, 1995; Wyllie-Echeverria, 1995a). 

3.2.2 Oceanic Circulation 

The major objectives for BS FOCI research on circulation over the basin 

were to identify potential pathways which could connect the various pollock 

stocks in the Bering Sea and to identify features and mechanisms which could 

provide habitats that favor survival of larval fish and/or transport onto the 

shelf. Prior to BS FOCI research many schematics existed of circulation in 

the Bering Sea. In these, wind stress was considered to provide the primary 

forcing (Hughes et al., 1974). Using observations (Stabeno and Reed, 1994; 

Leben, personal communication; Stabeno et al., in press a) and model studies (Bond et al., 1994; Overland et al., 1994) conducted during BS FOCI, we 

have greatly enhanced knowledge of currents and meteorological forcing. A 

cyclonic gyre dominates circulation with a western boundary current (Kamchatka Current) along the Asian side of the basin (Fig. 3.4; Reed et al., 

1993; Cokelet et al., 1996) and the Bering Slope Current (BSC) forming the 

eastern boundary (Stabeno and Reed, 1994; Stabeno et al., in press a). This 

gyre is mainly an extension of the Alaskan Stream with the majority of volume transport (6-12 x lo6 m3 s-l) entering through the eastern passes and 

exiting via the Kamchatka Current (Stabeno and Reed, 1994). When instabilities in the Alaskan Stream inhibit flow into the Bering Sea through Near 

Strait (Stabeno and Reed, 1992), transport in the Kamchatka Current can be 

reduced by -50% and the alteration of flow can persist for months to years 

(Reed and Stabeno, 1993). A climatology of the wind forcing shows that 

eastward- and northward-propagating storm systems dominate the surface 

stress at short periods (<1 month), which serves principally to mix the upper 

ocean (Bond et al., 1994). At longer periods (>1 month), the wind-driven 

transports estimated by the Sverdrup method account for roughly one-half 

of the observed transport within the Kamchatka Current. The interannual 

variations in the Sverdrup transports are ~25% of the mean. Thus, while 

wind driven transport contributes significantly to circulation, the Alaskan 

Stream is the dominant circulation feature in the Bering Sea. 

Results from BS FOCI studies described the previously unknown Aleutian North Slope Current (ANSC: Reed and Stabeno, in press) and a refined 

view of the Bering Slope Current (BSC: Leben, personal communication; 

Stabeno et al., in press a). Northward inflows of the Alaskan Stream through 

Near Strait, Amchitka Pass, and Amukta Pass produce the ANSC, which is 

an eastward flow along the north side of the Aleutian Islands. The ANSC is 

often fairly narrow (<50 km) and shallow (upper 500 m) with peak speeds 

>40 cm s-l. Eddy-like features occur in this region and some are formed 

by flow through Amukta Pass (Schumacher and Stabeno, 1994). The ANSC 

typically transports 2-4 x lo6 m3 S-l, providing the main source of the BSC 

and having a profound impact on regional water properties and circulation 

(Schumacher and Stabeno, 1994; Reed and Stabeno, in press; Reed and 

Stabeno, submitted). BS FOCI research also synthesized satellite altimetry, hydrographic, and satellite-tracked drifter data to elucidate features 
80 S.A. Macklin (ed.) 

~ANSC - Aleutian North Slope Current 1 

Figure 3.4: Major current features and general circulation of the upper 50 m of the Southeast Bering Sea. 

of the BSC. The BSC exists in two modes: an ill-defined, highly variable 

flow interspersed with eddies, meanders, and instabilities, or a more regular 

northwestward flowing current. It is likely that shelf/slope exchange differs 

significantly depending upon which mode dominates in the BSC. The potential importance of both the ANSC and BSC to pollock larvae is twofold: 

they can provide transport from the Oceanic Regime (including the important spawning region near Bogoslof Island) to the Outer Shelf Domain, and 

their inherent eddies may provide a habitat that favors survival. 

3.2.3 Eddies 

Eddies are a ubiquitous feature of the southeastern Bering Sea (Schumacher 

and Stabeno, 1994; Stabeno et al., in press a). During 3 years of BS FOCI 

(1992, 1993, 1994) a moored instrument platform, named Peggy, was located in 2200 m of water over the southeastern Oceanic Regime (54'48'N, 

168'34'W; Fig. 3.1). Data from this biophysical platform provided the most 

complete time series of water properties and currents over the southeastern 
BERING SEA FOCI FINAL REPORT 8 1 

basin available to date. The results showed the marked influence of eddies on water properties, current velocity, and chlorophyll concentration and 

permitted a characterization of the eddies as often being anti-cyclonic, 20- 

100 km in diameter, and extending to a depth of 400-1000 m with rotational 

speeds >20 cm s-' (Fig. 3.5 and 3.6; Cokelet and Stabeno, 1997). Eddies 

are also common at the eastern shelf break (Schumacher and Reed, 1992) 

and shoreward to depths of -150 m. A recent interpretation of hydrographic 

observations (Reed, submitted) suggests anticyclonic eddies exist in the region between 100 and 122 m <20% of the time. Shoaler than 100 m, eddies 

are uncommon. Until recently, eddies were not considered to play a role in 

Outer Shelf Domain dynamics. Between 1986 and 1994, 45 satellite-tracked 

buoys were deployed in support of studies of pollock and their environment. 

In three of these years, satellite-tracked buoys were deployed in areas where 

larval pollock were abundant. In all four cases trajectories of the buoys defined eddies (Fig. 3.6). Conversely, the buoys (33) which were not deployed 

in a larval patch did not indicate eddies. This association of pollock larvae 

and eddies may have significant impact on larval survival (Schumacher and 

Stabeno, 1994). 

3.2.4 Exchange Between the Oceanic and Shelf Regimes 

Shelf-slope exchange can occur virtually anywhere along >I200 km of shelf 

break north of Unimak Pass; however, preferential transport onto the shelf 

has been observed in two regions: Bering Canyon (along the Aleutian Islands near Unimak Pass) and west of the Pribilof Islands. The enhanced 

concenkation of nutrients observed near Unimak Pass likely originates from 

ANSC waters interacting with canyon topography and coming onto the shelf 

(Schumacher and Stabeno, in press). South of the Pribilof Islands the outer 

shelf narrows and accelerates the flow along the 100 m isobath which then 

turns northward (Stabeno et al., in press). This phenomenon likely results 

in slope water being entrained onto the shelf from Pribilof Canyon (Schumacher and Stabeno, in press) and thereby provides a somewhat continuous 

source of nutrients to the vicinity of the Pribilof Islands. Evidence for this 

flow near the Pribilof Canyon is the on-shelf trajectories of satellite-tracked 

drifters released over the canyon and the presence of Outer Shelf Domain 

mesozooplankton taxa on the eastern side of the islands in the Middle Shelf 

Domain (Stabeno et al., in press b; Napp et al., submitted). 

Episodic events of onshelf flow have been observed resulting from both 

eddy-topography interactions and instabilities in the BSC (VanMeurs and 

Stabeno, in press). Along the slope of the central shelf (--56.7"N), current 

records reveal that eddies are common and estimates of salt and temperature fluxes indicate that significant onshore fluxes exist (Schumacher and 

Reed, 1992). In 1992 an excellent set of data was collected when an eddy 

translated onto the shelf (Schumacher and Stabeno, 1994). Three satellitetracked drifters had been deployed in the center of an eddy. The drifters 

remained in the eddy for weeks until the eddy translated onto the shelf. The 

drifters were deposited onto the shelf as the eddy disintegrated. Both of' 

these episodic events of onshelf flow were related to the stability of the BSC 
82 S. A. Macklin (ed. ) 

(~pq Mp (m) wdaa 
BERING SEA FOCI FINAL REPORT 83 

Satellite-tracked drifter trajectory of an eddy near 

Peggy Bering Sea in 1992 

I I I I I I L I 

@ 

Pribilof Is. I' 

Cokelet and Stabeno (1 997) 

NOANPMEL 

Figure 3.6: A mesoscale eddy detected in the Bering Slope Current using Lagrangian drifters (Cokelet and 

Stabeno, 1997). The satellite-tracked drifter was released in the vicinity of Peggy Bering Sea, spring 1992. 
84 S.A. Macklin (ed.) 

and are mechanisms that could transport both nutrients and pollock larvae 

onto the shelf. 

3.3 Production of Prey for Larval Pollock-Variability in 

the Timing and Magnitude of the Spring Phytoplankton Bloom 

Two of the Program's hypotheses were (I) interannual variability in the 

timing of prey production limits larval survival, and (2) prey densities in 

the Oceanic Regime are generally less than those encountered in the Shelf 

Regime. We assumed that production of most larval prey was initiated by the 

spring phytoplankton bloom. Thus, the lower trophic level research component of BS FOCI had two main objectives: describe interannual variability 

in the timing of spring phytoplankton blooms, and compare variability in 

springtime standing stocks of larval pollock prey between the Oceanic and 

Shelf Regimes. Variability in the timing and magnitude of the spring bloom 

are reported in this section and variations in prey density are presented in 

the larval feeding section. 

Knowledge of spring phytoplankton bloom dynamics and the mesozooplankton community that produces prey for larval pollock is greatest for the 

Shelf Regime (e.g., Iverson et al., 1979a; Dagg et al., 1984; Sambrotto et 

al., 1986; Vidal and Smith, 1986). Knowledge of the phytoplankton dynamics and pollock prey densities in the Oceanic Regime are less well known, 

although the mesozooplankton community, in general, is well known (e.g., 

Motoda and Minoda, 1974; Iverson et al., 1979b; Coyle et al., 1996). The 

waters in the vicinity of the shelf break, between the two regimes, are thought 

to be a region of sustained productivity during the spring and summer (a 

"green belt") due to continuous flux of nutrients into the euphotic zone 

(Springer et al., 1996). 

3.3.1 Oceanic Regime 

Bering Sea FOCI'S major contribution to the study of plankton dynamics 

and interannual variability in the Oceanic Regime resulted from the use 

of moored biophysical platforms to obtain continuous time-series of phytoplankton biomass, measurements of associated physical forcing functions 

(e.g., winds for mixing and incident radiation), and acoustically derived zooplankton biomass. Time-series of phytoplankton biomass were obtained using chlorophyll absorbance meters (ChlAM) attached at discrete depths in 

the euphotic zone. During our long-term deployments contamination of the 

signal due to instrument biofouling was minimized using new technologyless hazardous chemical biocides and subtraction of absorbance in several 

wavebands outside the peak absorbance of chlorophyll (Davis et al., 1997). 

Seasonal changes in zooplankton biomass and vertical distribution were estimated from continuous records of 150 kHz ADCP backscatter (Cokelet et 

al., in preparation). 

In the spring of 1993 a slow and gradual increase in chlorophyll was interrupted by a sharp (four-fold), rapid (<1 day) increase (Fig. 3.7a; Cokelet 
BERING SEA FOCI FINAL REPORT 85 
86 S. A. Macklin (ed .) 

et al., in preparation). A simultaneous increase in the mixed layer depth 

and appearance of warmer surface water (3.75OC) suggest that the large increase in phytoplankton biomass was due to advection rather than in situ 

growth. Currents were weak (-10 cm s-l) during this period, but rotated 

from southwestward to eastward. Elevated concentrations at the mooring 

persisted for -20 days before gradually returning to lower pre-event levels. The same pattern was observed in the spring of 1994, although the 

rapid increase in chlorophyll was somewhat slower. Note that during the 

1993 event, die1 vertical migration of the zooplankton community radically 

changed (Fig. 3.7b). Without net samples we are unable to say whether this 

was due to a change in behavior by the pre-event assemblage or whether 

a new assemblage of zooplankton with different behavior arrived with the 

high chlorophyll waters. These Eulerian biological measurements support 

the previous point that mesoscale physical variability over the continental 

slope is important, and demonstrates that at times biological and physical 

variability are strongly linked in this system. The Bering Slope Current is 

eddy-rich and pollock larvae are sometimes found in association with these 

eddies (Schumacher and Stabeno, 1994). To the extent that phytoplankton 

biomass is a surrogate for increased production and standing stock of larval 

prey, larvae that find themselves in these dynamic features may have a lower 

probability of starvation than those outside such features. 

3.3.2 Shelf Regime 

BS FOCI'S major contributions to our knowledge of spring bloom dynamics 

in the Shelf Regime resulted from our combined use of moored biophysical platforms and Lagrangian drifters equipped with optical sensors. The 

platforms enabled us to observe previously unreported under-ice spring phytoplankton bloom dynamics. In 1995, when sea ice extent was much further 

south than usual, we measured a single, large, early phytoplankton bloom 

over the Middle Shelf Domain (-72 m of water) that continued to develop 

despite an unstable water column (Fig. 3.8; Stabeno et al., in press c). Note 

the low water temperatures (-0.5OC). Previous researchers have described 

an initial ice-edge bloom stimulated by increased water column stability (ice 

melt) followed by a main spring bloom that occurs when wind mixing from 

storms erode the thin fresh surface layer and restore nutrients (e.g., McRoy 

and Goering, 1974; Niebauer et al., 1990). In 1995, however, the bloom occurred despite an unstable water column and Lagrangian drifters equipped 

with optical sensors did not detect a subsequent "main" bloom. Springtime 

winds were not strong enough to erode the pycnocline that year and surface 

nutrients were never replenished after the under-ice bloom. 

In 1996, a year with minimal ice extent, the spring bloom was first detected by aircraft in the Outer, rather than Middle Shelf Domain as in the 

previous year, but not until the first week of May (Cullen, personal communication). Thus, the presence or absence of sea ice and springtime winds 

influence the timing, location, and number of spring blooms. 
BERING SEA FOCI FINAL REPORT 87 
88 S. A. Macklin (ed.) 

MAR APR MAY 

Figure 3.8b: Dynamics of a spring phytoplankton bloom under sea ice on the southeastern Bering Sea 

shelf during an extremely heavy ice year, 1995 (Stabeno et al., in press). Both panels show temperature 

and currents as a function of depth and time (upper panel) and chlorophyll concentration (mg mP3) or 

fluorescence, salinity (PSU), and sea-ice presence as a function of time. (b) Outer Shelf Domain. 
BERING SEA FOCI FINAL REPORT 89 

3.4 Larval Pollock Feeding 

Much of the information on walleye pollock larval feeding is based on studies 

done in Shelikof Strait, Gulf of Alaska (Theilacker et al., 1996). There they 

found that starvation can be a significant source of mortality (up to 32% 

per day) for first-feeding larvae, up to about 6.5 mm in length. Larval 

condition is closely related to the amount of food in the water; at prey 

concentrations of less than 20 I-', condition indices are low and mortality 

elevated. Numbers of prey per gut is positively correlated with numbers 

of prey in the water at prey densities of less than about 20 1-I (Canino, 

personal communication). First-feeding pollock larvae ingest particles of 

maximum dimension 100-400 pm. Maximum prey size increases with the size 

of fish, while the minimum prey size remains more or less constant (Nakatani, 

1988). Our dietary studies are presently limited to prey items that leave 

some sort of hard body part in the digestive tract. Pollock larvae ingest 

items of known (e.g., copepod nauplii, rotifers) and unknown nutritional 

value where inefficient or ineffectual digestion is suspected (e.g., copepod 

eggs and phytoplankton). Laboratory studies have shown that pollock larvae 

modify their swimming behavior in the presence of food: in prey they turn 

more frequently, swim slower, and spend more time in a horizontal rather 

than vertical orientation (Spring, 1996). Vertical movements in the absence 

of food may facilitate locating concentrations of prey in a highly stratified 

water column or in thin microlayers of food (Iverson et al., 1979b; Owen, 

1981). 

3.4.1 " Oceanic Regime 

As in other areas, copepod nauplii were the most common food item in the 

guts of first-feeding pollock larvae in the Oceanic Regime (bottom depth 

1900 m) in April 1992 (Hillgruber et al., 1995). A suite of ca. 5 genera 

of copepod nauplii (Eucalanus, Metridia, Pseudocalanus, Microcalanus, and 

Oithona) were available in the water, 1992-1995. Concentrations ranged 

from <5 to >40 liter-' (Paul et al., 1996; Napp et al., in preparation). 

Cyclopoid nauplii (Oithona spp.) tended to dominate the assemblage in all 

years and most depths. Larval pollock, however, preferred the later stages 

(NIII-NV) of calanoid nauplii over the more abundant cyclopoid nauplii and 

earlier stages of calanoid nauplii (Hillgruber et al., 1995). In particular, they 

selected for the older stages of the genera Metridia and Microcalanus, but 

against Oithona. Late stage Oithona and Microcalanus nauplii are approximately the same size; therefore, this demonstrates prey selection on a basis 

other than size. Copepod eggs were also prevalent in the guts, but they are 

probably of little nutritional value, may have inordinately long gut residence 

times, and may indicate a generally poor feeding environment (Flinkman et 

al., 1994). 

In 1992, larvae and their prey were most abundant at 30 m, where light 

was sufficient for feeding (Fig. 3.9). At that depth, 97.5% of the larvae 

were feeding, and they contained an average of 4.6 prey per larva. Densities 

of copepod nauplii were 26.3 1-I at 30 m; however, >80% of the available 
90 S. A. Macklin (ed. 

Larval Pollock and Prey, 

Oceanic Regime, April 1992 

Larvae 100 m-3 

- Feeding Incidence (%) 

.I. Oifhona nauplii '-' 

tam Calanoid nauplii 1-I 

- Prey per gut 

- - Larval length (mm) 

Figure 3.9: Vertical distributions of larval pollock, larval length, prey concentration, feeding incidence, and 

prey per larval gut for larvae collected in the Oceanic Regime, April 1992 (Hillgruber et al., 1995). 
BERING SEA FOCI FINAL REPORT 9 1 

nauplii were Oithona spp. (Hillgruber et al., 1995). Naupliar densities and 

feeding incidence were much lower at other depths, leading to the conclusion 

that overall, prey were below saturation densities at that station. This, along 

with modeling results (Bollens et al., in preparation) leads us to explore the 

possibility that protozoans could be an additional source of nutrition for 

pollock larvae. Microzooplankton abundance (protozoans >20 pm) in the 

Oceanic Regime in April 1992 ranged from 300-6233 organisms 1-I (0.58- 

9.7 pg C I-'; Howell-Kiibler et al., 1996). Thus, in some situations, first 

feeding pollock larvae could potentially meet their maintenance ration by 

grazing on both protozoa and nauplii. Whether or not significant ingestion 

of protozoa occurs in the field is not yet known, but a new technique for live 

staining protists was developed and used to show that pollock larvae ingest 

protozoa in the laboratory (Lessard et al., 1996; cf. Last, 1978). 

3.4.2 Shelf Regime 

The feeding environment of larval pollock in the Shelf Regime was investigated using samples collected at 2-week intervals in an area of high concentration of pollock larvae in late April and mid and late May 1995 (Brase, 1996). 

The highest densities of pollock larvae were found in mid May (Fig. 3.10). 

Mean standard lengths of larvae were 6.13 mm in iate April, 6.40 mm in mid 

May, and 7.37 mm in late May. The temperatures at the depths of maximal 

larval abundance were 2.5"C in late April, 3.5OC in early May, and 3.75"C 

in late May (Fig. 3.10). Total copepod naupliar densities were always less 

than 8 I-'; maximum water column integrated abundance was in late May. 

In most samples, 100% of the larvae were feeding. Copepod eggs were usually the most numerous prey item, with Pseudocalanus spp. nauplii being 

the second most abundant item (Fig. 3.11). In late April 41% of the diet 

by numbers, excluding copepod eggs, was rotifers, in mid May euphausiid 

nauplii made up a significant fraction of the diet (24% by number, 64% by 

volume), and in late May copepod nauplii (Pseudocalanus spp. and Acartia 

spp.) were abundant in the larval diets (25% by number, 35% by volume). 

First-feeding larvae (5.0-6.9 mm), however, had very few prey items in their 

guts when copepod eggs were excluded from the analysis (April, 1 larva-'; 

mid May 0.5-1 larva-'; late May, 3-5 larva-'). 

In conclusion, it seems that in 1995 there was a mismatch between the 

period of maximal first feeding larval abundance (the period of greatest 

vulnerability to starvation) and the maximum standing stock of copepod 

nauplii. During the period of maximal abundance of first feeding larvae 

prey densities were much less than 20 1-', the critical value determined from 

research in Shelikof Strait. Evidence for a deleterious effect of low prey 

concentrations on larvae was contrary to expectations. We lack specific estimates of larval mortality; however only 1% of the larvae sampled during mid 

May 1995 were starving (Porter and Theilacker, in preparation). In Shelikof 

Strait, at comparable prey densities (but slightly higher water temperatures) 

ca. 34% of the first feeding larvae were starving. A late larval/early juvenile 

survey of the Shelf Regime during the summer of 1995 revealed much lower 
Temperature (OC) 

2 3 4 

1L _ 

0 10 

Copepod Nauplii 1-I 

Larvae m-3 

Temperature (OC) 

2 3 4 

Temperature 

2 3 

- -- 

0 10 

Copepod Nauplii 1-1 

Larvae m-3 

Figure 3.10: Springtime vertical distributions of larval pollock (horizontal bars), copepod nauplii (filled c

water temperature (solid line; "C) at three stations over the southeastern shelf during a year of maxima

(1995). Shown are the mean concentrations f SE (pollock; Brase, 1996) and f 95% confidence interval (na

et al., in preparation). Station 1, late April; Station 2, early May; Station 3, late May. 
BERING SEA FOCI FINAL REPORT 93 
94 S.A. Macklin (ed.) 

late larval/age-0 juvenile abundances than found in 1996, a minimal ice year 

(Brodeur, this volume). 

3.5 Implications: Shelf and Oceanic Regimes as Feeding Environments for Pollock Larvae 

Now that we know what pollock larvae eat and which prey they prefer, we 

can compare the two Regimes (Shelf and Oceanic) and examine interannual 

differences in the timing of the spring phytoplankton bloom and prey standing stocks. Note that our investigations of prey density and spring bloom 

dynamics were geographically and temporally limited. Prey density and larval feeding measurements were limited to places and times where pollock 

larvae were very abundant and feeding studies were conducted. Spring phytoplankton bloom dynamics data were limited to the locations of the biophysical platforms which were initially chosen to be representative of particular 

regions. In addition, our ability to resolve sources of interannual variability 

is tempered by the short duration of the Program and the emphasis on two 

large oceanographic regimes. We spent only two full field seasons in each 

region with a transition year between. Thus our intra-Regime interannual 

comparisons are limited to two adjacent years. 

3.5.1 Timing of Prey Production 

Egg production of many calanoid copepods is generally thought to be initiated by increased food availability (i.e., coincident with the spring phytoplankton bloom; e.g., Hirche, 1996). Our time-series observations of chlorophyll concentration (1993-1996) at the biophysical platforms suggest that 

the onset of larval prey production was less variable over the basin than over 

the shelf, despite the importance of mesoscale variability over the slope. 

The presence or absence of sea-ice was the physical factor most responsible 

for variability in timing over the shelf; variability in wind mixing may be 

important, but only when ice is absent (cf. Sambrotto et al., 1986). 

The assumption that production of prey is initiated by the spring bloom 

remains to be tested for the Bering Sea. Recent examination of one species 

of shelf prey producer (Calanus marshallae) revealed no correspondence between gonadal maturity (a proxy for egg production) and sea surface chlorophyll in April of 1995 (Baier and Napp, in preparation). In this species, 

most of the sampled population was sexually mature females with well developed eggs in their oviducts ready for release, despite very low sea surface 

chlorophyll values (0.5-1 pg 1-I). 

The timing of egg production relative to the appearance of first-feeding 

larvae is also important. At 3OC, a typical springtime temperature for the 

Outer Shelf and Slope Domains, Metridia paclifica needs ca. 12 days to develop from egg to the fourth naupliar stage (NIV; Pinchuk and Paul, 1998) 

and Pseudocalanus spp. require ca. 15 days to do the same (Corkett and 

McLaren, 1978). The "critical period" of first feeding larvae is ca. 7-14 days 

at 5°C; therefore prey production must be initiated several weeks before first 

feeding larvae appear. 
BERING SEA FOCI FINAL REPORT 95 

3.5.2 Amount of Prey Produced 

Production of preferred prey involves two steps: egg production and development to the preferred developmental stage. Both are affected by variability in the physical environment. Total production of prey items may be 

decoupled from the absolute level of primary production depending on the 

amount of food required for maximal reproduction by the dominant calanoid 

copepods in the system (Runge, 1988). Egg production rates by one of the 

copepod genera responsible for prey production (Pseudocalanus spp.) would 

not be food-limited in either region (slope or shelf) during periods of maximal phytoplankton standing stock. This may not be true for the larger 

prey-producing copepods Metridia, Calanus, and Eucalanus. 

Variability in prey densities within the Oceanic Regime and between 

the Oceanic and Shelf Regimes was found to be much larger than initially 

thought. We did find low densities over the Oceanic Regime of <10 nauplii 1-I in April of all years (Paul et al., 1996; Napp et al., in preparation), 

but also found several incidences where densities were >20 I-', the critical 

value determined for larvae from Shelikof Strait. Naupliar abundances over 

the shelf in April 1994 and 1995 and May 1995 were 510 1-I at almost all 

sampled depths. Our Oceanic Regime prey densities are comparable to the 

slope values from PROBES with the exception of low values found in their 

cold year, 1980 (Dagg et al., 1984; Walsh and McRoy, 1986). Shelf Regime 

naupliar densities sampled during cold years are comparable between the 

two programs, but BS FOCI did not sample the Shelf Regime in May and 

June of "warm" years. One important distinction between the results of the 

two programs is that BS FOCI has direct measurements of larval condition. 

Even at low prey densities found during cold years by both programs, larvae 

did not appear to be starving (Porter and Theilacker, in preparation). 

Determination of prey density during the critical first feeding period is 

only one part of the recruitment story. Exposure to high prey concentrations 

is advantageous for rapid growth and potentially lower predation risk during 

the larval and early juvenile stages. Over the Middle Shelf Domain, in the 

absence of wind mixing, a rapid increase, then decline of phytoplankton and 

nutrients is observed. Springtime water column stratification separates the 

phytoplankton from their nutrient source. When nutrients become depleted 

the bloom sinks and continued prey production by copepods must rely on 

lower levels of phytoplankton standing stock sustained by regenerated nutrients. Thus, variability in insolation (heat flux) and wind mixing determines 

the absolute or annual level of larval prey production over parts of the shelf. 

3.5.3 Taxonomic Composition of Prey 

Since we know that pollock larvae are selective feeders, we must take into 

account the type of prey as well as the concentration of all available prey. A 

major difference between the Oceanic Regime and Shelf Regime is the ratio 

of calanoid to cyclopoid nauplii. At most depths sampled over the Oceanic 

Regime in April of 1994, 20-30% of the copepod nauplii were calanoids, while 

at the Outer Shelf Domain station on the same cruise, 50-60% were calanoid 
96 S.A. Macklin (ed.) 

nauplii. The exception to this generalization for the slope region was at the 

depths where large concentrations of nauplii were found; they were 70% 

calanoid, i.e., more similar to the Shelf Regime, than the Oceanic Regime 

prey assemblage. Thus, when we take preferential feeding into account, 

starvation was not apparent even at very low effective prey concentrations. 

3.5.4 Larval Condition 

In the above discussion we noted that we have little or no evidence to support 

the hypothesis that starvation was an important source of mortality for 

larval pollock in the Bering Sea (one might argue that these data refute the 

hypothesis). Our limited measurements of larval condition were made in 

patches of water where larvae were abundant. Few larvae showed symptoms 

of recent food deprivation in these patches. However, these same larvae 

were feeding under prey-poor conditions and had few prey items in their 

guts. This contradiction, low prey levels, yet low incidence of starvation, is 

one of the more significant findings of BS FOCI. Investigations are underway 

to determine the affect of temperature on both prey production and larval 

feeding and metabolism. 

3.6 Conclusions 

Pollock spawn in two distinct Regimes in the Southeast Bering Sea: the 

Oceanic Regime and the Shelf Regime. At present, molecular genetic techniques are unable to distinguish between spawning fish in either regime or 

among the fish regularly found spawning at different times and locations on 

the southeastern shelf. Conditions for the emerging larvae can be very different for the two regimes as are the factors that affect variability in survival of 

early larvae between regimes (Fig. 3.12). In the Oceanic Regime advection 

is strong, but variable, and mesoscale features (eddies) are common. Conditions outside mesoscale features show very low interannual variability. Over 

the shelf advection is generally low, but there are large fluctuations in the 

environment due to interannual variability in the presence or absence of sea 

ice. This affects the stability and temperature of the water column. Spring 

phytoplankton bloom dynamics vary between the two regimes as a result 

of the differences in their physical characteristics. Variability in observed 

plankton standing stocks may be largely due to advective rather than local 

processes in the Oceanic Regime. In the Shelf Regime interannual variability 

in a complex set of forcing functions (sea ice, wind mixing, temperature, and 

insolation) result in phytoplankton blooms with different timing, magnitude, 

and transfer efficiencies to the zooplankton and nekton (or benthos). The 

two Regimes provide different feeding environments for larval pollock. In the 

Oceanic Regime prey concentrations are generally low and are dominated by 

less preferable prey items. This may necessitate the larvae supplementing 

their diet with protists. Mesoscale features of unknown origin, when present, 

may contain much higher prey densities with a larger proportion of the prey 

being the type preferred by first-feeding larvae. In the Shelf Regime, preferred prey constituted a larger fraction of the available prey, but copepod 
BERING SEA FOCI FINAL REPORT 97 
98 S.A. Macklin (ed.) 

nauplii were still at minimal levels for growth and survival. There was no 

evidence to suggest, however, that these larvae were starving. Low temperatures associated with early sea-ice-associated spring phytoplankton blooms 

resulted in a mismatch between the maximal concentrations of first feeding 

larvae and their prey (cf. Walsh and McRoy, 1986; Townsend et al., 1994). 

Thus the key to interannual variation in food for first feeding pollock larvae 

in the Oceanic Regime is advection, and in the Shelf Regime it is the coupled 

dynamics of the atmosphere-ice-ocean system. 

3.7 Acknowledgments 

We thank the Principal Investigators of BS FOCI for allowing us use of their published and unpublished results, and the FOCI Coordinator, S.A. Macklin, for facilitating the Program's research. We also express our thanks to the officers and crew 

of the NOAA Ships Miller neeman and Surveyor for their field support during the 

Program. 

3.8 References 

Aron, W., and J. Balsiger (1989): Proceedings of the International Scientific Symposium on Bering Sea Fisheries. NOAA Tech. Memo. NMFS-F/NWC-163, 424 

PP . Baier, C.T., and J.M. Napp. Springtime distribution and gonadal maturity of 

Calanus marshallae over the southeastern Bering Sea shelf (in preparation). 

Bollens, S.M., M.C. Landsteiner, B.W. Frost, K.M. Bailey, and C.S. Davis. A model 

of the upper ocean production dynamics of zooplankton and larval pollock in 

the Bering Sea (in preparation). 

Bond, N.A., J.E. Overland, and P. Turet (1994): Spatial and temporal characteristics of the wind forcing of the Bering Sea. J. Clim., 7, 1119-1130. 

Brase, A.L.J. (1996): Temporal variation in feeding of larval walleye pollock, Theragra chalcogramma, in the southeastern Bering Sea. Master of Science Thesis, 

University of Alaska, Fairbanks, 87 pp. 

Coachman, L.K. (1986): Circulation, water masses, and fluxes on the southeastern 

Bering Sea shelf. Cont. Shelf. Res., 5, 23-108. 

Cokelet, E.D., R.F. Davis, and J.M. Napp. Springtime biophysical observations over 

the southeastern Bering Sea continental slope: advection versus local changes 

in chlorophyll and derived zooplankton biomass (in preparation). 

Cokelet, E.D., J.M. Napp, and D. Dougherty. ADCP backscatter calibration for 

Bering Sea zooplankton (in preparation). 

Cokelet, E.D., M.L. Schall, and D. Dougherty (1996): ADCP-referenced geostrophic 

circulation in the Bering Sea basin. J. Phys. Oceanogr., 26, 1113-1128. 

Cokelet, E.D., and P.J. Stabeno (1997): Mooring observations of the thermal structure, density stratification and currents in the SE Bering Sea basin. J. Geophys. 

Res., 102(C10), 22,947-22,967. 

Cooney, R.T., and K.O. Coyle (1982): Trophic implications of cross-shelf copepod 

distributions in the southeastern Bering Sea. Mar. Biol., 70, 187-196. 

Corkett, C.J., and I.A. McLaren (1978): The biology of Pseudocalanus. Adv. Mar. 

Biol., 15, 1-231. 

Coyle, K.O., V.G. Chavtur, and A.I. Pinchuk (1996): Zooplankton in the Bering 

Sea: A Review of Russian-Language Literature. In Ecology of the Bering SeaA Review of the Russian Literature, O.A. Mathisen and K.O. Coyle (eds.), 

Alaska Sea Grant Report No. 96-01, Fairbanks, AK, 97-133. 
BERING SEA FOCI FINAL REPORT 99 

Dagg, M.J., M.E. Clarke, T. Nishiyama, and S.L. Smith (1984): Production and 

standing stock of copepod nauplii, food items for larvae of the walleye pollock 

Theragra chalcogramma in the southeastern Bering Sea. Mar. Ecol. Prog. Ser., 

19, 7-16. 

Davis, R.R., C.C. Moore, J.R.V. Zaneveld, and J.M. Napp (1997): Reducing the 

effects of fouling on chlorophyll estimates derived from long-term deployments 

of optical instruments. J. Geophys. Res., 102(C3), 5851-5856. 

Flinkman, J., I. Vuorinen, and M. Christiansen (1994): Calanoid copepod eggs 

survive passage through fish digestive tracts. ICES J. Mar. Sci., 51, 127-129. 

Hillgruber, N., L.J. Haldorson, and A.J. Paul (1995): Feeding selectivity of larval 

walleye pollock Theragra chalcogramma in the oceanic domain of the Bering 

Sea. Mar. Ecol. Prog. Ser., 120, 1-10. 

Hirche, H.-J. (1996): The reproductive biology of the marine copepod, Calanus 

finmarchicus-A review. Ophelia, 44, 111-128. 

Hood, D.W. (1981): Introduction. In The Eastern Bering Sea Shelf: Oceanography and Resources, D.W. Hood and J.A. Calder (eds.), Vol. 1, University of 

Washington Press, Seattle, xiii-xviii. 

Howell-Kubler, A.N., E.J. Lessard, and J.M. Napp (1996): Springtime protozoan 

abundance and biomass in the southeastern Bering Sea and Shelikof Strait, 

Alaska: Its potential role as prey for planktivorous fish larvae. J. Plankton 

Res., 18, 731-745. 

Hughes, F.W., L.K. Coachman, and K. Aagaard (1974): Circulation, transport and 

water exchange in the western Bering Sea. In Oceanography of the Bering Sea, 

D.W. Hood, and E.J. Kelley (eds.), Occasional Publ. No. 2, Institute of Marine 

Science, University of Alaska, Fairbanks, 3-37. 

Iverson, R.L., L.K. Coachman, R.T. Cooney, T.S. English, J.J. Goering, G.L. Hunt, 

Jr., M.C. McCauley, C.P. McRoy, W.S. Reeburg, and T.E. Whitledge (1979a): 

Ecological significance of fronts in the southeastern Bering Sea. In Ecological 

Processes in Coastal and Marine Systems, R.J. Livingston (ed.), Plenum Press, 

New York, 437-466. 

Iverson, R.L., T.E. Whitledge, and J.J. Goering (1979b): Chlorophyll and nitrate 

fine structure in the southeastern Bering Sea shelf break front. Nature, 281, 

664-666. 

Last, J.M. (1978): The food of three species of gadoid larvae in the Eastern English 

Channel and Southern North Sea. Mar. Biol., 48, 377-386. 

Lessard, E.J., M.P. Martin, and D.J.S. Montagnes (1996): A new method for livestaining protists with DAPI and its application as a tracer of ingestion by 

walleye pollock (Theragra chalcogramma (Pallas)) larvae. J. Exp. Mar. Biol. 

ECOL, 204,43-57. 

Lowry, L.F., V.N. Burkanov, and K.J. Frost (1996): Importance of walleye pollock, Theragra chalcogramma, in the diet of phocid seals in the Bering Sea and 

northwestern Pacific Ocean. In Ecology of Juvenile Walleye Pollock, Theragra chalcogramma, R.D. Brodeur, P.A. Livingston, T.R. Loughlin, and A.B. 

Hollowed (eds.), NOAA Tech. Report NMFS 126, 141-152. 

Macklin, S.A. Bering Sea FOCI. In The Bering Sea: A Summary of Physical, Chemical and Biological Characteristics and a Synopsis of Research, T.R. Loughlin and 

K. Ohtani (eds.), North Pacific Marine Science Organization, PICES, Alaska 

Sea Grant Press (in press). 

Mantua, N.J., S.R. Hare, Y. Zhang, J.M. Wallace, and R.C. Francis (1997): A Pacific interdecadal climate oscillation with impacts on salmon production. Bull. 

Amer. Met. Soc., 78, 1069-1079. 

McRoy, C.P., and J. J. Goering (1974): The influence of ice on the primary productivity of the Bering Sea. In Oceanography of the Bering Sea with Emphasis on 
100 S. A. Macklin (ed.) 

Renewable Resources, D.W. Hood, and E.J. Kelley (eds.), Occasional Publ. No. 

2, Institute of Marine Science, University of Alaska, Fairbanks, 403-421. 

Motoda, S., and T. Minoda (1974): Plankton of the Bering Sea. In Oceanography 

of the Bering Sea with Emphasis on Renewable Resources, D.W. Hood, and E.J. 

Kelley (eds.), Occasional Publ. No. 2, Institute of Marine Science, University of 

Alaska, Fairbanks, 207-241. 

Mulligan, T.J., K. Bailey, and S. Hinckley (1989): The occurrence of larval and 

juvenile walleye pollock, Theragra chalcogramma, in the eastern Bering Sea with 

implication to stock structure. In Proceedings of the International Symposium 

on the Biological Management of Walleye Pollock, Alaska Sea Grant Report 

NO. 89-1, 471-489. 

Mysak, L.A., and D.K. Manak (1989): Arctic sea-ice extent and anomalies, 1953- 

1984. Atmos. Ocean, 27, 376-405. 

Nakatani, T. (1988): Studies on the early life history of walleye pollock, Theragra 

chalcogramma, in Funka Bay and vicinity, Hokkaido. Mem. Fac. Fish. Hokkaido 

Univ., 35, 1-46. 

Napp, J.M, R.D. Brodeur, D. Demer, R. Hewitt, P.J Stabeno, G.L Hunt, Jr., and 

J.D. Schumacher. Determination of nekton, zooplankton and seabird concentrations at tidally generated shelf fronts in the eastern Bering Sea. Mar. Ecol. 

Prog. Ser. (submitted). 

Napp, J.M., A.J. Paul, L.J. Haldorson, and M.K. Cohen. Interannual variability 

of larval pollock feeding and prey in the southeastern Bering Sea, I, Copepod 

naupliar distributions and effective prey concentrations (in preparation). 

National Research Council Committee on the Bering Sea Ecosystem (1996): The 

Bering Sea Ecosystem. National Academy Press, Washington, D.C., 324 pp. 

Niebauer, H.J. (1981): Recent short-period wintertime climatic variations and their 

effect on sea-surface temperatures in the eastern Bering Sea. In The Eastern 

Bering Sea Shelf: Oceanography and Resources, D.W. Hood, and J.A. Calder 

(eds.), Vol. 1, University of Washington Press, Seattle, WA, 23-30. 

Niebauer, H.J. (1988): Effects of El Niiio-Southern Oscillation and North Pacific 

weather patterns on interannual variability in the subarctic Bering Sea. J. 

Geophys. Res., 93, 5051-5068. 

Niebauer, H.J., V.A. Alexander, and S. Henrichs (1990): Physical and biological 

oceanographic interaction in the spring bloom at the Bering Sea marginal ice 

edge zone. J. Geophys. Res., 95, 22,229-22,242. 

Ohtani, K., and T. Azumaya (1995): Interannual change of the sea conditions on 

the continental shelf and its influence on abundance of walleye pollock in the 

eastern Bering Sea. Can. J. Fish Aquat. Sci., Special Pub. 121, 87-95. 

Overland, J.E. (1981): Marine climatology of the Bering Sea. In The Eastern 

Bering Sea Shelf: Oceanography and Resources, D.W. Hood, and J.A. Calder 

(eds.), Vol. 1, University of Washington Press, Seattle, 15-22. 

Overland, J.E., and C.H. Pease (1982): Cyclone climatology of the Bering Sea and 

its relation to sea ice extent. Mon. Weather Rev., 110, 5-13. 

Overland, J.E., M.C. Spillane, H.E. Hurlburt, and A. J. Wallcraft (1994): A numerical study of the circulation of the Bering Sea basin and exchange with the 

North Pacific Ocean. Phys. Oceanogr., 24, 736-758. 

Owen, R.W. (1981): Microscale plankton patchiness in the larval anchovy environment. Rapp. P.-v. Reun. Cons. Int. Explor. Mer., 178, 364-368. 

Paul, A.J., J.M. Paul, and K.O. Coyle (1996): Abundance and taxa composition of 

copepod nauplii over southeastern Bering Sea deep water spawning grounds of 

walleye pollock, Theragra chalcogramma. Cmstaceana, 69, 494-508. 

Pinchuk, A.I., and A.J. Paul (1998): Growth of Metridia pacifica (Copepoda: 

calanoida) nauplii in the laboratory. Plankton Bid. Ecol., 45(2) (in press). 
BERING SEA FOCI FINAL REPORT 101 

Porter, S.M., and G.H. Theilacker. Physiological condition of walleye pollock larvae, Theragra chalcogramma, in the southeastern Bering Sea using histological 

techniques (in preparation). 

Reed, R.K. (1995): Water properties over the Bering Sea shelf: climatology and 

variations. NOAA Tech. Rept. ERL 452-PMEL 42, 15 pp. 

Reed, R.K. Confirmation of a convoluted flow over the southeastern Bering Sea 

Shelf. Cont. Shelf Res. (in press). 

Reed, R.K., G.V. Khen, P.J. Stabeno, and A.V. Verkhunov (1993): Water properties 

and flow over the deep Bering Sea basin, summer 1991. Deep-sea Res., 40, 

2325-2334. 

Reed, R.K., and P.J. Stabeno (1993): The return of the Alaskan Stream to Near 

Strait. J. Mar. Res., 51, 515-527. 

Reed, R.K., and P.J. Stabeno (1996): On the climatological mean circulation over 

the eastern Bering Sea shelf. Cont. Shelf Res., 16, 1297-1305. 

Reed, R.K., and P.J. Stabeno. The Aleutian North Slope Flow. In The Bering Sea: 

A Summary of Physical, Chemical and Biological Characteristics and a Synopsis 

of Research, T.R. Loughlin, and K. Ohtani (eds.), North Pacific Marine Science 

Organization, PICES, Alaska Sea Grant Press (in press). 

Reed, R.K., and P.J. Stabeno. Magnitude and time scales of inflow through Unimak 

Pass, Alaska. Geophys. Res. Lett. (submitted). 

Runge, J.A. (1988): Should we expect a relationship between primary production 

and fisheries? The role of copepod dynamics as a filter of trophic variability. 

Hydro biolgia, l6'?/l68, 61-71. 

Sambrotto, R.N., H.J. Niebauer, J.J. Goering, and R.L. Iverson (1986): Relationship among vertical mixing, nitrate uptake, and phytoplankton growth during 

the spring bloom in the southeast Bering Sea middle shelf. Cont. Shelf Res., 5, 

161-198. 

Schumacher, J.D., and A.W. Kendall, Jr. (1995): An example of fisheries oceanography: walleye pollock in Alaskan waters. Rev. Geophys. Suppl., 33, 1153-1163. 

Schumacher, J.D., and T.H. Kinder (1983): Low-f-requency current regimes over the 

Bering Sea shelf. J. Phys. Oceanogr., 13, 607-623. 

Schumacher, J.D., and R.K. Reed (1992): Characteristics of currents over the continental slope of the eastern Bering Sea. J. Geophys. Res., 97, 9423-9433. 

Schumacher, J.D., and P.J. Stabeno. The continental shelf of the Bering Sea. In 

The Sea, Vol. XI, The Global Coastal Ocean: Regional Studies and Synthesis. 

John Wiley, Inc., New York (in press). 

Schumacher, J.D., and P.J. Stabeno (1994): Ubiquitous eddies of the eastern Bering 

Sea and their coincidence with concentrations of larval pollock. Fish. Oceanogr., 

3, 182-190. 

Sinclair, E.H., G.A. Antonelis, B.W. Robson, R.R. Ream, and T.H. Loughlin (1996): 

Northern fur seal, Callorrhinus ursinus, predation on juvenile walleye pollock, 

Theragra chalcogramma. In Ecology of Juvenile Walleye Pollock, Theragra 

chalcogramma, R.D. Brodeur, P.A. Livingston, T.R. Loughlin, and A.B. Hollowed (eds.), NOAA Tech. Report NMFS 126, 167-178. 

Spring, S. (1996): Swimming behavior of walleye pollock larvae Theragra chalcogramma in relation to food. Master of Science Thesis, University of Washington, 

Seattle, 123 pp. 

Springer, A.M., and G.V. Byrd (1989): Seabird dependence on walleye pollock in 

the southeastern Bering Sea. In Proceedings of the International Symposium on 

the Biology and Management of Walleye Pollock, Alaska Sea Grant, AK-SG89-01. 

Springer, A.M., C.P. McRoy, and M.V. Flint (1996): The Bering Sea Green Belt: 

shelf-edge processes and ecosystem production. Fish. Oceanogr., 5, 205-223. 
102 S.A. Macklin (ed.) 

Stabeno, P.J., and R.K. Reed (1992): A major circulation anomaly in the western 

Bering Sea. Geophys. Res. Letters, 19, 1671-1674. 

Stabeno, P.J., and R.K. Reed (1994): Circulation in the Bering Sea basin observed 

by satellite-tracked drifters: 1986-1993. J. Phys. Oceanogr., 24, 848-854. 

Stabeno, P. J., J.D. Schumacher, R.F. Davis, and J.M. Napp. Under-ice observations of water column temperature, salinity and spring phytoplankton dynamics: 

Eastern Bering Sea shelf, 1995. J. Mar. Res. (in press c). 

Stabeno, P.J., J.D. Schumacher, K. Ohtani, and S. Gladychev. Overview of the 

Bering Sea. In The Bering Sea: Physical, Chemical, and Biological Dynamics, 

T.R. Loughlin, and K. Ohtani (eds.), Alaska Sea Grant Press (in press a). 

Stabeno, P.J., J.D. Schumacher, S.A. Salo, G.L. Hunt Jr., and M. Flint. The 

Pribilof Islands: Physical environment. In The Bering Sea: Physical, Chemical, 

and Biological Dynamics, Loughlin, T.R., and K. Ohtani (eds.), Alaska Sea 

Grant Press (in press b). 

Theilacker, G.H., K.M. Bailey, M.F. Canino, and S.M. Porter (1996): Variations 

in larval walleye pollock feeding and condtion: A synthesis. Fish. Oceanogr., 5 

(suppl. I), 112-123. 

Townsend, D.W., L.M. Cammen, P.M. Holligan, D.E. Campbell, and N.R. Pettigrew (1994): Causes and consequences of variability in the timing of spring 

phytoplankton blooms. Deep-sea Res., 41, 747-765. 

Trenberth, K.E., and J.W. Hurrell (1995): Decadal coupled atmosphere-ocean variations in the North Pacific Ocean. Can. Spec. Publ. Fish. Aquat. Sci., 121, 

15-24. 

VanMeurs, P., and P.J. Stabeno. Evidence of episodic onshelf flow in the southeast 

Bering Sea. J. Geophys. Res. (in press). 

Vidal, J., and S.L. Smith (1986): Biomass, growth, and development of populations 

of herbivorous zooplankton in the southeastern Bering Sea during spring. DeepSea Res., 33, 523-556. 

Walsh, J.J., and C.P. McRoy (1986): Ecosystem analysis in the southeastern Bering 

Sea. Cont. Shelf. Res., 5, 259-288. 

Wyllie-Echeverria, T. (1995a): Sea-ice conditions and the distribution of walleye 

pollock (Theragra chalcogramma) on the Bering and Chukchi Sea Shelf. Can. 

Spec. Pub. Fish. Aquat. Sci., 121, 131-136. 

Wyllie-Echeverria, T. (1995b): Seasonal sea ice, the cold pool and gadid distribution 

on the Bering Sea shelf. Ph.D. Dissertation, University of Alaska, Fairbanks, 

281 pp. 

Wyllie-Echeverria, T., and W.S. Wooster. Year-to-year variations in Bering Sea ice 

cover and some consequences for fish distribution. Fish. Oceanogr. (submitted). 
BERING SEA FOCI FINAL REPORT 103 

Part 3A 

Juvenile pollock studies (R.D. Brodeurl) 

Summary 

Analysis of summer survey data from several years indicate that age-0 pollock are more likely to be found in the waters surrounding the Pribilof Islands 

than the Bering Sea shelf in general and this area may represent an important nursery ground for juvenile pollock. The frontal zones that surround 

each island exhibit elevated levels of phytoplankton and small zooplankton 

compared to those found on either side of the front. Acoustic and trawl 

catch data show that age-0 pollock are concentrated at these fronts, as are 

many piscivorous fishes, seabirds, and marine mammals. Age0 pollock and 

large jellyfish dominate by number and biomass, respectively, the catches 

of midwater trawls in the Pribilof Island area. In situ videos have demonstrated that these age-0 pollock are found in the same layer as the jellyfish 

during the day and are found to actually associate with these medusae, perhaps to gain protection from visual predators during the day. Age0 pollock 

were larger offshore of the fronts, but an analysis of otoliths of these fish 

indicates that the offshore fish are older, suggesting an ontogenetic offshore 

movement. Analysis of hatch-date distributions suggests that the Pribilof 

fish were spawned on the southeastern Bering Sea shelf and slope. No indication was found of any size-selective predation on age-0 pollock by older 

age classes of pollock or other fish predators in any region, although fish predation overall was much greater offshore of the front due to high abundances 

of adult pollock in this region. 

Summer Distribution of Age-0 Pollock on the 

Eastern Bering Sea Shelf 

Pelagic trawling was done in 1995 and 1996 aboard a Japanese research vessel 

to study the mid-summer distribution of age0 pollock and associated taxa. 

A similar set of grid stations was sampled both years using a rectangular 

fine-mesh beam trawl. Bottom temperatures in the Pribilof Island area 

were mostly between 3' and 4°C in 1995 and between 4" and 5°C in 1996. 

Thermocline depth was centered near 30 m depth in 1995 and around 40 m 

in 1996. In both years, standardized catches of age-0 walleye pollock, based 

on rough counts at sea, were the highest in the northwest part of the grid 

and in the area closest to the Pribilof Islands (Fig. 3A.1). The catch of 

juvenile walleye pollock in 1996 was over five times greater than in 1995. 

Relatively fewer fish were caught in the southern and eastern portions of the 

grid. Noticeably larger age-0 walleye pollock tended to occur in the eastern 

part of the survey area, although the actual length measurements will not be 

available until the 1996 samples are processed. Larvae of Greenland turbot 

'Alaska Fisheries Science Center, NOAA, Seattle, WA 98115, U.S.A. 
Oshoro Maru 1995 

G' 

-, Pribilof a 0 

\, Islands fed-- .-. \ -=s // 

-- . \,-c- a-x,- a -/ H--ZOO-~ \ \ '- \ \ 

1 .'‘\\a 

\ ' . (No.11000 m3) \ \ look \ 

\ / 

I' 

\,e l--_ 

l 

= 10-25 .--x. , 

Oshoro Maru 1996 

\ 

170 168 166 164 172 170 168 1

Latitude Latitude 

57 - 

56 - 

Figure 3A.1: Location of stations sampled in 1995 and 1996 by the Oshoro Maw for age-0 walleye po

relative size of the dots correspond to the density of age-0 pollock according to the legend. 

\ 

\;*\ 0 a 

\ Pribilof /---., 

\\Islands 1 -. - 

-\ \l ~7-4 - 7 0 , e\\ 

\\ \ 

,'286-m -, \ 

\-/\ , \ 

\r \ 

I 0 

I 

I 

\ 

\ 

\ 
BERING SEA FOCI FINAL REPORT 105 

(Reinhardtius hippoglossoides), a common circum-arctic flatfish species, were 

frequently collected in 1995 beam trawl samples but were absent from 1996 

samples. 

There were also some interannual differences in the zooplankton collected 

during the 2 years. Both densities and biomass were much higher in 1996 

than in 1995. Gelatinous zooplankton (chaetognaths and cnidarians) were 

predominant during 1995 whereas euphausiids dominated the 1996 invertebrate catches. In fact, five of the top seven most abundant species collected 

in 1996 were euphausiids. There were day/night differences in the catches 

of most crustaceans but not of the gelatinous zooplankton. 

Distribution and Species Associations of Juvenile 

Pollock and Forage Fishes 

This project analyzed archival data on abundance and distribution of juvenile pollock and other important forage fishes in the Bering Sea. Forage fish are currently a topic of active research due to recent declines of 

marine mammal and seabird populations which have historically depended 

upon them. At the "International Symposium of the Role of Forage Fish in 

Marine Ecosystems" held in 1996, many of our findings of this project were 

presented. This project allowed collaborative research with the Russian fisheries laboratory (TINRO) in Vladivostok whereby a Russian scientist was 

able to bring data from the western Bering Sea to Seattle and analyze it 

using similar analytical methods for both the eastern and western data sets. 

Our study is the first to examine the large-scale distribution patterns 

of juvenile pollock and several dominant forage fish species throughout the 

Bering Sea. We analyzed new data on the association of these forage fishes 

with other taxa that may compete with these forage fishes and, in some 

cases, prey upon them. In this study, we examined survey data on some 

dominant pelagic forage fishes (herring Clupea pallasi and capelin Mallotus villosus) and the juvenile stages of major commercial groundfish species 

(walleye pollock and Pacific cod Gadus macrocephalus). Age-0 pollock had 

the highest biomass and were the most widely distributed forage fish on the 

eastern Bering Sea shelf (Fig. 3A.2), although jellyfish and age-2+ pollock 

dominated the biomass overall. Several geographically distinct assemblages 

were recognized in both the eastern and western Bering Sea. Age-0 pollock 

were associated with warmer bottom temperatures and capelin with colder 

bottom temperatures compared with other species. 

Habitat Characteristics of Juvenile Pollock in the 

Eastern Bering Sea 

Data from a midwater trawl survey of the eastern Bering Sea shelf and 

southern Bering Sea basin conducted in 1987 aboard the Russian research 

vessel Damin was analyzed in detail to study the spatial relationships of 

juvenile pollock to other pelagic species and to begin to address how these 
106 S. A. Macklin (ed.) 
BERING SEA FOCI FINAL REPORT 107 

(number per hour) 

1,000-9,999 

10,000-49,999 

50,000- 100,000 

*++ 

.++++.+ 

++..+++++* 

++...++.+++ +..... ++++ 

+.. . ... . 

++. 

.++ 

.++++.+. 

++..+++++. 

++...++.+ r+ +..... ++++ 

170 W 175 180 175 170 165 160 E 

Figure 3A.3: Age-0 walleye pollock densities and the locations of four different taxonomic groups based 

on (top) catch composition and (bottom) optimal habitat of age-0 pollock based on optimal bottom depth, 

temperature, and dissolved oxygen, and salinity at 45 m depth. It was found that these were the combination 

of variables that were significantly associated with age-0 pollock distribution. 
108 S.A. Macklin (ed.) 

fish may respond to environmental variability. The availability of pollock 

length data made it possible to study the juveniles separately from the 

adults. Catch composition and hydrographic data (temperature, salinity, 

and dissolved oxygen) were collected during this survey making both a community and a single species approach possible. A synecological approach was 

first used assuming that an ordination of the ecological amplitudes of the 

various taxa collected may more effectively reflect influential environmental 

gradients than considering taxa singly. Cluster and ordination techniques, 

incorporating environmental constraints, revealed four bio-types and several 

prominent environmental gradients. A basin group and three major shelf 

groups were identified as having distinct catch compositions, environmental attributes, and geographic locations (Fig. 3A.3). Juvenile pollock were 

mostly found on the shelf. The principle environmental gradients were salinity and dissolved oxygen; temperature was less important. Juvenile pollock 

were intermediate in position along these gradients but differences between 

age-0 and age-1 cohorts were apparent. 

Distribution of Juvenile Pollock and Other Biota 

in Relation to Fronts 

Using midwater trawl observations from September 1994 and 1995, the abundance, distribution, and size composition of age-0 walleye pollock were examined in relation to the physical oceanography and biology of the structural 

front along a transect north of St. Paul Island (Fig. 3A.4). The frontal 

region occurred 12-20 km offshore in both years, but the thermocline was 

much shallower in 1995 (25 m) than in 1994 (45 m). The isothermal (<8"C) 

inner domain had low chlorophyll, and relatively low small (>I53 pm) and 

large (>505 pm) fraction zooplankton concentrations. The highest chlorophyll and small zooplankton concentrations occurred at the front and were 

lower both inshore and farther offshore of the front. Large zooplankton 

(mainly euphausiids and cnidarians) were most abundant in the stratified 

offshore waters. By number, age-0 walleye pollock dominated the catches of 

midwater trawls (>99% and >95% in 1994 and 1995, respectively). Overall, 

however, large medusae dominated the total biomass. Age-0 walleye pollock 

densities were the highest at the front or inshore of the front. Age-0 pollock 

densities averaged about three times higher in 1994 than in 1995. Age-0 

pollock were significantly smaller in 1994 inshore and at the front (mean = 

43.4 and 44.6 mm, respectively) than in 1995 (52.2 and 51.7 mm; Fig. 3A.5). 

Commensal Associations of Juvenile Pollock with 

Schyphomedusae 

In September 1995, dense aggregations of large scyphomedusae (mainly 

Chrysaora melanaster and Cyanea capillata) were observed in 27 midwater 

deployments of a remotely operated vehicle (ROV) near the Pribilof Islands 

in the Bering Sea. Age-0 walleye pollock appeared to be frequently associ- 
BERING SEA FOCI FINAL REPORT 109 

B Middle Shelf Structural Front Coastal 

38 kHz 

Figure 3A.4: (top) Location of sampling transects around the Pribilof Islands, (middle) cross-shelf section of 

temperature and identification of different habitats, and (bottom) acoustic backscatter, in the three diierent 

habitats along Transect A in 1994. 
110 S.A. Macklin fed. 1 

11 

Inshore Inshore 

11 52.2 mm 

Middle ll 51.7mm 

Standard Length (mm) 

Figure 3A.5: Size distributions of age-0 pollock in the three habitats during 1994 and 1995. 
BERING SEA FOCI FINAL REPORT 111 
112 S.A. MacMin (ed.) 

ated with these gelatinous zooplankton. During daytime, up to 30 pollock 

were observed swimming within the tentacles of these medusae, but when 

approached by the ROV, the pollock generally left the vicinity of the jellyfish. 

At night, few such associations were observed and juvenile pollock moved 

closer to the surface (Fig. 3A.6), apparently feeding in loose aggregations, 

while the medusae remained close to the thermocline (35-40 m). Trawl collections during the day showed a strong association between age0 pollock 

and medusae density, whereas at night no such association was observed. 

The lack of gelatinous material in the stomachs of the pollock suggests that 

juvenile pollock associate to gain shelter from predation. This commensal 

behavior with gelatinous zooplankton may have important implications relevant to pollock recruitment dynamics in the Eastern Bering Sea if these 

juvenile pollock substantially decrease their vulnerability to predation by 

seeking shelter within jellyfish tentacles. 

Variability in Feeding and Condition of Age-0 

Pollock in Relation to Fronts 

Dietary composition, feeding intensity, and condition index of age0 walleye 

pollock were examined for variations related to time of day, location, size 

of predator, and year. Stomach contents of pollock collected at a hydrographic front near the Pribilof Islands during September 1994 through 1996 

were compared with those from pollock collected on either side of the front. 

Diets were dominated in all three regions by small zooplankton, mainly copepods, pteropods, euphausiids, and chaetognaths, but fish and some epibenthic crustaceans were also consumed. Copepods and pteropods dominated 

the diet in all years and areas by number but the diet was more mixed by 

weight with chaetognaths, euphausiids, and fish (smaller pollock) also being 

important (Fig. 3A.7). Copepods were more abundant in the diet during the 

day. No significant day/night differences in weight composition were noted. 

Stomach fullness was highly variable by year and habitat and no significant 

differences were observed. Stomach fullness peaked at around sunset for fish 

<50 mm and at night for the larger fish, implying that feeding chronology 

changed with ontogeny. Age-0 pollock condition factor (Fulton's K) varied 

from 0.45 to 1.20 (mean = 0.767 f 0.09 (SD)). Year was not found to be an 

important factor in determining condition although location with respect to 

the front was important. 

Age and Growth of Juvenile Pollock in Relation to 

the Fronts 

The hatch-date distributions for the fish taken at ten stations in the 1994 

sampling area showed that hatching occurred from mid April through early 

July with a peak occurring in June. Allowing approximately 1 month from 

spawning to hatching, at water temperatures of 1-3"C, it can be presumed 

that these fish were spawned from late March through early June with a 
BERING SEA FOCI FINAL REPORT 113 

Inshore Front Offshore 

60 60 50 

Inshore Front Offshore 

20 - ~uphausiids e] copepods Pteropods 

69 Ostracods Curnaceans Decapods 

Chaetognaths 0 Fishes Other 

0 I - 

Inshore Front Offshore 

Figure 3A.7: Interannual and habitat differences in the percentage weight composition of the diet of age-0 

pollock on Transect A north of St. Paul Island. Stomach contents are grouped into major prey categories. 

The number of stomachs examined in each category is given at the top of each figure. 
114 S.A. Macklin (ed.) 
BERING SEA FOCI FINAL REPORT 115 

peak in spawning during May. This spawning period coincides with the 

spawning period for pollock on the southeastern continental shelf and slope 

of the Bering Sea. Age in days after hatching ranged from 76 to 152 and was 

predominantly less than 120 days (Fig. 3A.8). Some geographical distinction 

is noticeable in the age-length relationship, particularly among the larger 

fish. The possibility of variability in growth rates was investigated using 

growth among individual fish backcalculated using otolith microincrement 

measurements. Even though sampling was limited at and inshore of the 

tidal fronts around the Pribilof Islands, it seems from the data that fish 

were smaller and younger at these locations than those sampled offshore of 

the fronts. 

Covariation of Plankton, Juvenile Fish, and 

Seabirds at Tidal Fronts 

Tidally generated shelf frontal systems around the Pribilof Islands offer a 

unique setting where the effects of ocean dynamics on the production and 

distribution of plankton, nekton, and seabirds can be observed. During a pilot study in late summer 1994, the frontal zone between inshore and offshore 

regimes northeast of St. Paul Island was sampled by continuous underway 

transects of hydroacoustics (38, 120, and 200 kHz) and seabird counts to determine the distributions of juvenile fish and their predators. Net sampling 

of juvenile fish and their planktonic prey followed. Echograms of volume 

backscatter (S,) at all frequencies showed a correspondence between scatterer density and hydrography. By rendering differences in volume backscatter (Fig. 3A.9) at two frequencies as echograms (Sv200-Sv120), we were able to 

discriminate between layers of fish (with or without zooplankton) and layers 

of zooplankton (without fish). Juvenile walleye pollock comprised >90% of 

fish biomass captured with a pelagic trawl. The dominant zooplankton scatterers had different vertical distribution patterns in different hydrographic 

regimes (inshore, frontal, and offshore). In the offshore regime, fish were 

aggregated around the thermocline (ca. 40 m) during the day, and migrated 

to the surface at night. Biomass of large zooplankton was highest in this 

regime (250 ml mV3), and some of the potential prey populations remained 

below the thermocline at night after the distribution of fish shoaled. Juvenile walleye pollock were more abundant in the front (>200-1000 m-3) than 

either of the other regimes. Biomass of small zooplankton was highest in 

the frontal zone (>700 ml m-3). Seabirds (murres, Uria spp.), whose diet is 

strongly dependent on the availability of juvenile fish, were most abundant 

just offshore of, rather than in, the front. 

Predation on Juvenile Pollock by Major Teleost 

Predators 

Spatial and temporal variation in the consumption of age0 walleye pollock 

by arrowtooth flounder (Atherethes stomias) and older age classes of pollock 
116 S.A. Macklin (ed.) 

FOCI 1994 Transect A, Daytime, Sv Difference Smoothed 

0 5 10 15 20 25 30 35 40 45 

Distance (km) 

-20246810 

Sv @200kHz-Sv @ 120kHz (dB) 

FOCI 1994 Transect A, Nighttime, Sv Difference Smoothed 

0 5 10 15 20 25 30 35 40 45 

Distance (km) 

Sv@2001;Hz - SV@ 120kHz (dB) 

Figure 3A.9: Acoustic backscatter difference between 120 kHz and 200 kHz during the (top) day and 

(bottom) night along Transect A in 1994. Note the layering of what is apparently zooplankton at the 

thermocline around 40 m. 
BERING SEA FOCI FINAL REPORT 117 
118 S.A. Macklin (ed.) 

was examined at the tidal front located north of St. Paul Island, Alaska. Age0 walleye pollock were the primary prey of arrowtooth flounder throughout 

the day, but were least digested in the late day, indicating a diurnal feeding 

pattern. A similar diurnal pattern was not seen in the vertical distribution 

of age-0 walleye pollock, suggesting that the feeding pattern exhibited by 

arrowtooth flounder was based upon their migratory behavior. Lengths of 

age-0 walleye pollock consumed by arrowtooth flounder were similar to those 

sampled from mid-water trawls. Walleye pollock cannibalism was examined 

along a transect that included samples collected at the front and offshore 

of the front. Age-0 walleye pollock were the primary prey (by weight) of 

walleye pollock at all locations (Fig. 3A.10). Adjacent cohort cannibalism 

was prevalent (age-0 walleye pollock were 79% of the diet by weight) at the 

frontal region. Age0 walleye pollock cannibalism removal estimates were 

highest at the front for age-1 walleye pollock and offshore for the adults. 

The much higher removal rate of age-0 by age-1 walleye pollock at the front 

compared to the offshore region is due to an order of magnitude larger predator biomass at the front and nearly double the percent by weight of age-0 

walleye pollock in the diet. Adults cannibalizing age-0 walleye pollock at a 

much higher rate offshore than at the front is also a result of higher adult 

walleye pollock biomass offshore than at the front. Prey selectivity analysis 

indicated that age-0 walleye pollock were more highly selected offshore than 

at the front. 

Seabird Distributions Relative to F'rontal Regions 

Data on the distribution and abundance of seabirds were collected in 1994 

aboard the R/V Surveyor (950 nautical miles surveyed), in 1995 aboard the 

Surveyor (250 nm) and R/V Miller Freeman (230 nm), and in 1996 aboard 

Miller Freeman (135 nm). Continuous counts of birds were made from the 

flying bridge while the ship was underway and all birds within an arc from 

300 m ahead of ship to 90' off the port side were recorded using a standard 

strip transect method. 

Murres (Uria lomvia and U. aalge) and puffins (Fkatercula cirrhata and 

F. comiculata), whose diets consist of primarily juvenile pollock, breed in 

large numbers on the Pribilof Islands. High concentrations of murres foraged 

on the seaward edge of the front north of St. Paul Island. Murres were 

observed in these stratified waters in 1994 and 1995. In particular, the 

abundance of feeding murres was greatest in 1995 over stratified water 30 

to 42 km north of St. Paul Island where acoustic sign was dense and close 

to the surface. South of St. Paul Island, relatively large numbers of feeding 

murres were found in the transition zone between stratified and mixed water. 

In addition to the area north of St. Paul Island, consistent aggregations of 

foraging piscivores were also observed along the first 12-15 km south of St. 

George Island. Murres and puffins were relatively abundant in the inshore, 

vertically mixed waters south of St. George in the fall of 1995, as was the case 

for murres in 1996 (Fig. 3A.11). North of St. George, murres and puffins 

were relatively abundant nearshore over a shallow (~25 m) pycnocline in 
BERING SEA FOCI FINAL REPORT 119 

LlNE A 

0 3 6 9 12 15 18 21 24 27 30 33 36 39 42 

Distance (km) 

LlNE D 

Dista nce (km) 

Figure 3A.11: The density of foraging murres observed on Line A (top) north of St. Paul Island. No more 

than 2.2 murres km-2 were observed on Line A in 1996; therefore, these observations were omitted. The 

density of foraging murres observed on Line D (bottom), south of St. George Island. Comparable area not 

sampled in 1994. 
120 S.A. Macklin (ed.) 

1996. Perhaps vertical mixing enhances production here and thus foraging 

birds are attracted to this location. Farther offshore during this same cruise, 

the depth of the pycnocline increased to 50 m and the pycnocline was no 

longer apparent at the northern end of the line. Despite the presence of 

dense acoustic sign near the Pribilof Canyon, we observed very few murres 

and puffins feeding in this location. 

Fur Seal Distributions Relative to Frontal Regions 

Marine mammal observations were conducted in 1994-96 from the flying 

bridge during daylight hours when the vessel was underway. Transects and 

ship movements were designed for oceanographic and trawling effort, so marine mammal observations were opportunistic and not conducted for abundance estimates. In 1995 and 1996, shipboard survey efforts were coordinated with concurrent studies on female fur seal movements using satellite 

telemetry. The vessel detoured for special prey trawling effort in areas of 

high fur seal density, as indicated by shipboard observations and satellite 

records. 

The overall number of marine mammal sightings was quite low (n = 

273). However, a preliminary analysis indicates that the highest density of 

fur seals sighted from the ship corroborate satellite records of female movement patterns during feeding bouts, and generalized areas of high pollock 

density. The greatest number of on-effort hours and the greatest number of 

sightings per unit effort were in 1995. In October of 1995, satellite tracked 

female fur seals from St. Paul Island concentrated their foraging efforts to 

the north and northwest of St. Paul Island. Fur seal females tracked from 

St. George Island foraged south of St. George Island exclusively. These 

patterns are very similar to the distribution of fur seals observed from the 

ship in September 1995, with the exception that relatively high densities 

of seals were also observed along the transect southeast of St. Paul Island 

(running between St. Paul and St. George). Correlation between observed 

and recorded movements of fur seals in 1996 are currently being analyzed as 

well as the larger question of the relationship between fur seal movements 

and the concentration of their prey along. frontal boundaries. 

References 

Brodeur, R.D. In situ observations of the association between juvenile fishes and 

scyphomedusae in the Bering Sea. Mar. Ecol. Prog. Ser. (in press). 

Brodeur, R.D., P.A. Livingston, T.R. Loughlin, and A.B. Hollowed (1996): Ecology 

of juvenile walleye pollock, Theragra chalcogramma. NOAA Tech. Rep. NMFS 

126, 227 pp. 

Brodeur, R.D., M.T. Wilson, and L. Ciannelli. Spatial and temporal variability in 

feeding and condition of age-0 walleye pollock in frontal regions of the Bering 

Sea. ICES J. Mar. Sci. (submitted). 

Brodeur, R.D., M.T. Wilson, J.M. Napp, P. J. Stabeno, and S. Salo (1997): Distribution of juvenile pollock relative to frontal structure near the Pribilof Islands. 
BERING SEA FOCI FINAL REPORT 121 

In Proceedings of Forage Fishes in Marine Ecosystems, Alaska Sea Grant AKSG-97-01. 

Brodeur, R.D., M.T. Wilson, G.E. Walters, and I.V. Melnikov. Forage fishes in 

the Bering Sea: Distribution, species associations, and biomass trends. In The 

Bering Sea: Physical, Chemical, and Biological Dynamics, T.R. Loughlin, and 

K. Ohtani (eds.), University of Alaska Sea Grant (in press). 

Ciannelli, L., R. Brodeur, and T. Buckley. Development and application of a bioenergetics model for juvenile walleye pollock. J. Fish Biol. (in revision). 

Lang, G.M., R.D. Brodeur, J.M. Napp, and R. Schabetsberger. Variation in fish 

predation on juvenile walleye pollock relative to hydrographic structure near 

the Pribilof Islands, Alaska. ICES J. Mar. Sci. (submitted). 

Napp, J.M., R.D. Brodeur, D. Demer, R. Hewitt, P.J. Stabeno, G.L. Hunt, Jr., and 

J.D. Schumacher. Observations of nekton, zooplankton, and seabird distributions at tidally generated shelf fronts in the eastern Bering Sea. Mar. Ecol. 

Prog. Ser. (submitted). 
BERING SEA FOCI FINAL REPORT 123 

Part 3B 

Modeling the upper ocean production dynamics of 

plankton and larval pollock in the Bering Sea 

(Stephen M. Bollens1 and Bruce W. .Frost2) 

Introduction 

We constructed and applied a coupled multi-species biological-physical model 

to investigate the production dynamics of the pelagic ecosystem in the Bering 

Sea, especially in regards to the early life history stages of pollock. In addition, our work focused on assimilating into our model newly generated 

physical (e.g., PEGGY) and, to a lesser degree, biological (e.g., zooplankton) field observations. We then used this model and data to address several 

key questions regarding how and why different processes-namely, protozoan dynamics, short-term mixed layer depth variability, and species-specific 

copepod dynamics-affect growth of larval pollock on the shelf of the southeastern Bering Sea. This work will continue to aid the BS FOCI and the 

SEBSCC programs in identifying specific hypotheses to be tested in the field 

and laboratory, as well as generally lead to a better understanding of how 

and why variable physical and biological processes regulate dynamics of biological production in upper ocean ecosystems. This latter point has obvious 

implications for management of the pollock fishery in the Bering Sea, as 

discussed below. 

Background 

The eastern Bering Sea can be divided into four distinct oceanographic domains (Coachman, 1986). For the purposes of the current discussion, we focus on the deep (>3500 m) open basin and the mid-continental shelf. These 

two domains differ dramatically in both physical (e.g., Coachman, 1986) and 

biological (e.g., Smith and Vidal, 1986) oceanographic dynamics. In a general sense, different planktonic production dynamics in each domain would 

be expected to result in different levels of production of larval fish, with 

copepods and other zooplankton acting as "filters" of primary production 

(Runge, 1988). However, while such a linkage between larval fish production 

and lower-level planktonic production in the Bering Sea has obvious intuitive 

appeal, the exact nature of this linkage, and the role played by site-specific 

physical processes in regulating it, have yet to be determined. This was the 

fundamental problem we wished to address with the proposed research. 

'San Francisco State University, California 

'university of Washington, Seattle 
124 S. A. Macklin (ed. ) 

Results 

Model Construction and Elaboration 

We have adapted the nutrient-phytoplankton-zooplankton model of Frost 

(1987) to include stage-structured dynamics of copepod populations and 

growth of larval pollock as a function of abundance of appropriately sized 

prey. Input data were taken from the Bering Sea (e.g., the PROBES study 

and other historical data) whenever possible, but were at other times taken 

from Ocean Station Papa in the North Pacific, as described below. Model 

output consists of daily concentrations of nutrient, phytoplankton, and all 

developmental stages of copepods, as well as growth rate of larval pollock. 

Protozoan microplankton and dynamically modeled mixed-layer depths were 

also added to the model as described below. 

The dynamics of phytoplankton (P) in the mixed layer is modeled using the equation of Frost (1987) modified to include two types of grazers, 

a population of protistan herbivorous microzooplankton (M) and a stagestructured population of suspension feeding copepods (Cj): 

dP aPAR, N 

dt zm P(PMAX) tanh [$PMAX] - T~(PMAX)P} - d+N 

- e~ (P - Po) M - ec(P + M - Po) 

f,+P-P0 f, + P + M - poCjW,0'75 +v (P*m+l - P) 

where 

PMAX = (eDln2 - 1.0) DL/24, 

with 

D = doublings d-' = 0.851 (10°.02750) and DL = day length, 

and 

PAR, = 0.51, = 

where I. is daily incident solar radiation, z is depth, and k is the attenuation 

coefficient for irradiance. It is assumed that irradiance is absorbed by both 

the water and phytoplankton; thus k = upy-' + b{a = 0.02 m2 (mg Chla)-I 

and b = 0.1 m-I). All other variables and parameters are defined in Table 3B.1. Phytoplankton production is integrated over the mixed layer (z,), 

and then homogenized to calculate the change in phytoplankton stock due 

to production, grazing, and mixing. A constant phytoplankton carbon-te 

chlorophyll a ratio (y) was assumed. Grazing mortality of the phytoplankton 

is due to both microzooplankton and copepods. 

The dynamics of herbivorous protistan microzooplankton is described as: 

It is assumed that the source(s) of predation mortality is not exclusively due 

to copepod ingestion, and thus mortality is parameterized with a MichaelisMenten function. Also, microzooplankton behave as passively mixed particles (the third term). 
BERING SEA FOCI FINAL REPORT 125 

Table 3B.1: Multi-species model variables and standard values. 

Parameter description [units] 

Physical Environment 

maximum mixed-layer depth (MLD) [m] 75 

time of initial MLD shoaling ljulian day] 90 

minimum MLD [m] 30 

time of initial minimum MLD ljulian day] 135 

minimum temperature [OC] 

maximum temperature [OC] 

mixing rate (v) [d-'1 

Phytoplankton Diatoms Dinoflagellates 

initial nitrate concentration N(t=O) [mM mP3] 10.8 10.8 

intial chlorophyll concentration P(t=0)$-' 

[mg chla mP3] 

carbon:chlorophyll ($) [mgC (mg ch1a)-'1 

half-saturation of N uptake (d) [mM mP3] 

photosynthetic efficiency (a) 

[mgC (mg ch1a)-' ly-'1 

maximum doublings per day (@lO°C) [Dl 

respiration as % phytosynthesis [~p] 

Protozoa 

initial biomass M(t=O) [mgC m-3] 

maximum ingestion rate (e~) [d-'1 

half-saturation ingestion (f~) [mgC md3] 

feeding threshhold (PO) [mgC mF3] 

respiration as % of grazing (TM) 

assimilation efficiency (a~) 

maximum mortality rate (g~) [d-'1 

half-saturation of mortality (h~) [mgC m-3] 

Copepods 

initial biomass C(t=O) [mgC mP3] 

time of initial biomass ljulian day] 

period of introduction to the surface [days] 

maximum ingestion rate (ec) [d-'1 

half-saturation of ingestion (fc) [mgC md3] 

feeding threshhold (Po) [mgC m-3] 

respiration as % of grazing (rc) 

assimilation efficiency (ac) 

maximum mortality rate (gc) [d-'1 

half-saturation of mortality (hc) [mgC mP3] 

minimum egg development time [days] 

fema1e:male to recruits 

power dependence of weight on growth 

egg weight [KC1 

adult weight [P~C] 

Larval Pollock 

maximum ingestion rate (eF) [d-'1 

half-saturation of ingestion (f~) [mgC m-3] 

intial larval weight [pgC] 

maximum size of food as % of larval weight 

Calanus 

.0238 

90 

1 

1.25 

50 

10 

.40 

0.8 

.10 

1000 

4 

0.8 

0.75 

0.25 

100 

Neocalanus 

.26 

30 

60 

.55 

50 

10 

.40 

0.8 

.10 

1000 

4 

0.8 

0.75 

1 .o 

416 

Pseudocalanus 

.0238 

30 

1 

.75 

25 

5 

.40 

0.8 

.10 

1000 

4 

0.8 

0.75 

.08 

8 

Metridia 

.26 

30 

1 

1.5 

50 

10 

.40 

0.8 

.10 

1000 

4 

0.8 

0.75 

0.1 

55 

power dependence of weight on growth 
126 S.A. Macklin (ed.) 

The dynamics of copepod populations are simulated as the production 

of daily cohorts of eggs, and the subsequent changes in numbers and masses 

of individuals in those daily cohorts (e.g., Steele and Frost, 1977). The 

production of cohorts of eggs on day j was determined by the growth rate 

of adult female copepods: 

(ac - rc) ec (P + M - Po) 

fc+P+M-Po w:~~~} /W(t = 0) 

where the summation is over 1 day for the broadcast spawner. The initial 

individual mass on day j [W(t = O)] is the mass of the egg. It is assumed 

that copepods feed indiscriminately on phytoplankton and protistan microzooplankton. The subsequent change in individual mass (Wj) and numbers 

(Cj) in cohort j are described as: 

Predation closure of the model is parameterized as a Michaelis-Menten function without a threshold abundance since it is assumed that larval fish do 

not significantly impact their prey populations. It was assumed that the 

copepods maintain their abundances in the mixed layer through vertical migration. That is, as the mixed-layer shoals, the concentration of copepods 

in the mixed-layer increases, and similarly decreases with mixed-layer deepening, thus conserving the actual number of animals in the mixed-layer. 

Dissolved nitrogenous nutrient is described as: 

&PAR, N 

dt z, 

P(PMAX) tanh [cPMAX] - rP(~~Ax)~} - d+N 

Where the first term represents the photosynthetic utilization of nitrate. 

A constant nitrogen-to-carbon ratio (x) is used to convert phytoplankton 

carbon uptake rate to an equivalent rate of nitrogen utilization. The second 

and third terms describe the nitrogen reintroduced into the system due to 

microzooplankton and copepod respiration. Finally, sub-mixed-layer nitrate 

(Nzrn+l) mixed (diffused) into the mixed layer. 

Growth rate of larval pollock was modeled as a function of availability of 

copepod prey biomass (Cj Wj), including eggs, in the appropriate size range 

(j,k) and protozoan biomass (M): 
BERING SEA FOCI FINAL REPORT 127 

Each model is initialized with a standing stock concentration of phytoplankton (P) and protozoa (M). An initial biomass of adult female Calanus 

appear in the surface water in early spring over a period of 1 day. Neocalanus, on the other hand, is initialized as C1 copepodites appearing in the 

surface waters over a period of 2 months starting in mid-winter. Note the 

food web structure was simplified by initializing protozoa abundance to zero. 

The physical characteristics of the basin and midshelf environment were 

simulated using idealized mean seasonal mixed-layer depths (Z,), temperatures (T), and solar insolation (I,). Wintertime conditions in the Bering Sea 

result in deep mixed-layer depths (150 m) in the basin (Dodimead, 1963); 

whereas Z, of the shelf is limited by the depth of the bottom (75 m). Due 

to solar heating and decreasing winds, mixed-layer depths in both regions 

shoal in (the late) spring. 

To evaluate the effect of daily mixed-layer depth variability on the food 

web dynamics, daily mixed-layer depth was simulated using the Price et al. 

(1986) mixed-layer model (PWP). The model has been successfully used to 

model daily mixed-layer variability in a variety of regions (e.g., Davis and 

Steele, 1994). Given the limited pertinent observations in the Bering Sea, 

the physical model was forced using representative meteorological data (i.e., 

1977) from Ocean Station Papa in the north Pacific (50°N, 145OW). The 

initial subsurface density structure was prescribed to simulate mixed-layer 

depth and temperature in the Bering Sea (Dodimead et al., 1963; Favorite 

et al., 1976). The resulting daily mixed-layer depths were then used to force 

the biological model described above. Since this version of the biological 

model is limited to two layers, and thus the subsurface structure is poorly 

resolved, we have constrained the model not to dilute the passive constituents 

(eg., phytoplankton and protozoa) with rapid deepening of the mixed layer 

(otherwise extreme and unrealistic dilution occurs). 

We recently extended this model to include stage-structured dynamics 

of four copepod populations (Calanus, Pseudocalanus, Metridia, and Neocalanus), two functional groups of phytoplankton (diatoms and dinoflagellates), and larval pollock feeding and growth. Model variables and standard 

values for the multi-species model are given in Table 3B.1. This extended 

model was for the most part driven by extremely simplified physical oceanographic dynamics, with the water column consisting of two layers (mixed 

layer and deep layer), and exchange between layers occurring as a result of 

mixed layer shoalingldeepening (detrainmentlentrainment) and turbulent 

vertical mixing. Model output consists of simulated daily abundances of 

nitrogenous nutrients, diatoms, dinoflagellates, protistan microzooplankton, 

copepod developmental stages of each of four species, sizes (weight) of larval 

pollock, and instantaneous growth rates of larval pollock. 

Model Results-Generic Seasonal Cycles 

Early model results highlight several important phenomena. (Note that 

these results have appeared elsewhere, i.e., numerous presentations at scientific meetings and previous annual reports, as well as manuscripts soon 

to be published (e.g., Francis et al., in press; Bollens et al., in prepara- 
128 S.A. Macklin (ed.) 

tion). What follows is only a very brief summary of these results). First 

is the species composition and dynamics of meso/macrozooplankton: larval 

pollock dependent on Calanus (e.g., on the shelf) should experience much 

better growth conditions later in the spring, whereas those dependent on 

Neocalanus (e.g., in the deep basin) are likely to grow more slowly, generally, 

although somewhat better earlier in the year when young Neocalanus are 

first recruited to the surface layer. Second is the role of protozoans: larval 

pollock in this model are highly dependent on these organisms for sustaining high growth rates, especially during times of year when young copepods 

are not abundant (i.e., early spring on the shelf and late spring/summer in 

the basin). A third process, short-term mixed-layer depth variability, has 

significant impacts on lower trophic levels (phytoplankton and protozoans) 

but less effect on copepods and larval pollock growth rate. We are in the 

process of examining this last point in much greater detail by fully coupling 

our biological model to the Price-Weller-Pinkel mixed-layer physical model 

(Price et al., 1986). 

These modeling results point to several data gaps and processes/ 

phenomena that need to be addressed through further modeling, field, and 

laboratory studies. The first is the functional response of larval pollock (ingestion vs. prey concentration), the parameterization of which could only 

be crudely approximated in this study, but to which the model is very sensitive. Second is the distribution and abundance of protozoans (of which 

we know virtually nothing in the Bering Sea) and the degree to which these 

organisms provide nutrition for larval pollock. Third is the field collection of 

time series data on basic biological, physical, and meteorological variables, 

especially early in the year (winter/early-spring). 

Multi-Species Model and Assimilation of 1992-1994 Physical 

Oceanographic Data 

Results of the multi-species model-including the dynamics of Calanus, 

Pseudocalanus, Metridia, and Neocalanus, as well as two functional groups 

of phytoplankton (diatoms and dinoflagellates), and larval pollock feeding 

and growth rates-need to be evaluated in light of recent field data on zooplankton abundance and composition. (Note: these field data, from the 

1992-1994 field seasons, were only made available to us in September 1997). 

Nevertheless, preliminary model results (Fig. 3B.1) indicate that there are 

significant differences in the dynamics of the main mesozooplankton taxa, 

and that Metridia may in particular be a key link between primary producers 

and larval pollock growth rate. More work is needed in this area, however. 

We have also run the multi-species model using the physical oceanographic data collected by the PEGGY mooring during 1992-1994 (Figs. 3B.2- 

4). Clear differences are evident between years. For instance, larval pollock 

growth rate is very low in late June of 1993 (0.03-0.06 per day) compared 

with rates predicted for either 1992 or 1994 (0.12-0.15 per day). This low 

rate of growth seems to be due to the rapid deepening of the mixed layer in 

1993, and would be expected to have the effect of diluting concentrations of 
BERING SEA FOCI FINAL REPORT 129 

(- . _) Protozoa, (. . .) Calanus, d- J Pseudocalanus, (...) MeaidiaL2, (ooo) Neocalanus 

0.12 1 I i , ( 120 

75 

h 

&o5 

345 b. 

0 

p 

7' 30 3 

15 

" 

Feb Mar *Pr May Jun Jul 

Larval Food: (. . .) Calanus*4, (- , J Pseudocaianus*4, (...) Metridia, (om) Neocalanus*4 

Figure 3B.1: Multi-species plankton-larval fish model on the shelf. 

I - - 

- - ............................. 

- ......... .\ ......................... 

- /. /. 0 - '. .,.-.- ./. \ --dd '. -. \ -.-.-.& 

-.-.-.-.-.+*O . --- . ----- ' - -,- - - - - 

25 

m" 

-20 

w 

1s g C 

s 

C 

#lo 8 

5 

0 

5 

O' Feb Mar AP~ May Jun Jul 

- 0 

(. . .) Nitrate, d, J Diatoms, (...) Dinoflagellates, C . J Protozoa 
130 S. A. Macklin (ed.) 

25 

m^ 

20 E 2 w 

........... l5 -1 

10 3 

8 0 

5 

0 

(. . .) Nitrate. (-, J Diatoms, (...) Dinoflagellates, C. 3 Rotozoa 

Larval Food: (. . .) Calmus*4, (, -3 Pseudocalmus, (...) Metridia, (ooo) Neocalanus*4 

Figure 3B.2: Multi-species plankton-larval fish model on the shelf, 1992. 
BERING SEA FOCI FINAL REPORT 131 

(. . .) Nitrate, C - 3 Diatoms, (...) Dinoflagellates, C . J.Protozoa 

~25 1 I 1 1 I 1 i d75 

3 /'3 . 

520- 

4 

5 

8 10- 

a 

(, . 3 Protozoa (. . .) Calanus, C -3 Pseudocalanud2, (...) Metridia/2, (ooo) Neocalanus. 

Larval Food: (. . .) Calanus*4, d, 3 Pseudocalanus, (...) Metridia, (om) Neocalanus*4 

Figure 3B.3: Multi-species plankton-larval fish model on the shelf, 1993. 

c;;0.15 

4 

a - 

% 0.12 

4 

3 0.09 5 

n 

- 8 0.06 

2 3 0.03 

- a 

I I I I I 

- li 

- 125 

- 

- 

- 

- 

O' Feb Mar Jun Jul 
132 S.A. Macklin (ed.) 

(. . .) Ni-, C -3 Diatoms, (...) Dinoflagellates, C .3 Protozoa 

V Feb 

" 

Mar Jun Jul 

Larval Food: (. . .) Calmus*4, (- , 5 Pseudocalmus. (...) Metridia, (ooo) Neocalanus*4 

Figure 3B.4: Multi-species plankton-larval fish model on the shelf, 1994. 
BERING SEA FOCI FINAL REPORT 133 

larval pollock prey (nauplii and protozoans). Here too more work is needed 

to fully assimilate the field data and otherwise validate the model. 

Future Activities and Anticipated Milestones 

We plan to continue our modeling work with emphasis on data assimilation from the 1992, 1993, and 1994 field studies (particularly zooplankton 

data and physical and meteorological data from the PEGGY moorings). We 

anticipate producing one or more manuscripts detailing the results of our 

multi-species model and data assimilation for publication in Marine Ecology Progress Series, FiBheries Oceanography, Journal of Marine Science, or 

related peer-reviewed journal; submission of such manuscript(s) would be 

expected in late 1997 or early 1998. 

Management Implications 

As noted above, this work will continue to aid current (e.g., SEBSCC) and 

future scientific programs in identifying specific hypotheses to be tested in 

the field and laboratory. Moreover, our modeling work has led to a better 

understanding of how and why variable physical and biological processes regulate dynamics of biological production in upper ocean ecosystems generally, 

and the Bering Sea in particular. 

This has obvious implications for management of the pollock fishery in 

the Bering Sea. For instance, if appropriate physical oceanographic data 

could be collected in "real time," via moorings (e.g., PEGGY) or satellites, 

a model such as described above could be implemented and predictions generated of larval pollock growth rate. When coupled with other models concerned with larval mortality and/or juvenile growth and mortality, such a 

model could generate predictions of pollock recruitment strength. While 

such a series of coupled models may not yet be in hand, it is a very reasonable short-term to medium-term (2-5 yrs.) goal, and would provide managers 

another tool with which to manage the Bering Sea pollock fishery. 

References 

Archer, D., T.M. Powell, and B.W. Frost (1990): Results from a coupled mixed 

layer physics-ecosystem process model in the N. Pacific. Eos, Trans. AGU, 

71(2), 180. 

Bollens, S.M., M.C. Landsteiner, B.W. Frost, K. Bailey, and C.S. Davis. A model 

of the upper ocean production dynamics of zooplankton and larval pollock in 

the Bering Sea. Mar. Ecol. Prog. Ser. (in preparation). 

Coachman, L.K. (1986): Circulation, water masses, and fluxes on the southeastern 

Bering Sea shelf. Cont. Shelf Res., 5, 23-108. 

Cooney, R.T., and K.O. Coyle (1982): Trophic implications of cross-shelf copepod 

distributions in the southeastern Bering Sea. Mar. Biol., 70, 187-196. 

Davis, C.S. (1984): Interaction of a copepod population with the mean circulation 

on Georges Bank. J. Mar. Res., 42, 573-590. 
134 S.A. Macklin (ed.) 

Dodimead, A.J., F. Favorite, and T. Hirano (1963): Salmon of the North Pacific 

Ocean, Part 11: Review of Oceanography of the Subarctic Pacific Region. Int. 

North Pac. Fish. Comm. Bull., 13, 195 pp. 

Favorite, F., A.J. Dodimead, and K. Nasu (1976): Oceanography of the Subarctic 

Pacific Region, 1960-1971. Int. North Pacific Fish. Comm. Bull., 33, 187 pp. 

Francis, R.C., R. Merrick, S.M. Bollens, and K. Aydin. Modeling and Management 

of the Bering Sea Ecosystem. In The Bering Sea Ecosystem, R.C. Francis (ed.), 

University of Washington Press, Seattle (in press). 

Frost, B.W. (1982): Modeling effects of environmental perturbations on marine 

plankton dynamics. In Second US/USSR Symposium: Biological Aspects of 

Pollutant Effects on Marine Organisms, D.J. Baumgartner, and A.I. Siminov 

(eds.), U.S. Environmental Protection Agency document EPA-60013-82-034, 

1-15. 

Frost, B.W. (1987): Grazing control of phytoplankton stock in the open subarctic 

Pacific Ocean: a model assessing the role of mesozooplankton, particularly the 

large calanoid copepods, Neocalanus spp. Mar. Ecol. Prog. Ser., 39, 49-68. 

Frost, B.W. (1993): A modelling study of the processes regulating plankton standing 

stock and production in the subarctic Pacific Ocean. Prog. Oceanogr., 32, 17- 

56. 

Heinrich, A.K. (1962): The life histories of plankton animals and seasonal cycles of 

plankton communities in the oceans. J. Cons. Int. Explor. Mer., 24, 455-464. 

Hood, D.W. (1986): Processes and resources of the Bering Sea Shelf (PROBES). 

Cont. Shelf Res., 5, 1-288. 

Price, J.F., R.A. Weller, and R. Pinkel (1986): Diurnal cycling: observations and 

models of the upper ocean response to diurnal heating, cooling, and wind mixing. J. Geophys. Res., 91, 8411-8427. 

Runge, J.A. (1988): Should we expect a relationship between primary production 

and fisheries? The role of copepod dynamics as a filter of trophic variability. 

Hydrobiologia, 167, 61-71. 

Smith, S.L., and J. Vidal (1986): Variations in the distribution, abundance, and 

development of copepods in the southeastern Bering Sea in 1980 and 1981. 

Cont. Shelf Res., 5, 215-239. 

Steele, J.H., and B.W. Frost (1977): The structure of plankton communities. Phil. 

Trans. Roy. Soc. Lond. B, 280, 485-534. 
BERING SEA FOCI FINAL REPORT 135 

Part 3C 

Seasonal sea ice in the Eastern Bering Sea (James 

D . Schumacherl and Tina Wyllie-Echeverria2) 

A striking feature of the physical environment of the eastern Bering Sea 

is the occurrence of seasonal sea ice. The extent fluctuates over 1000 km 

between waters north of the Bering Strait in the summer south to the Alaska 

Peninsula and southeastern shelf break in winter. The actual mechanism of 

ice formation for the eastern shelf has been described by a "conveyor belt" 

analogy (Pease, 1980; Overland and Pease, 1982). Ice is produced along 

leeward (south-facing) coasts primarily located in the northern region of the 

shelf, and driven by wind to its thermodynamic limit where it melts. As 

water freezes brine rejection occurs and the salinity of the ice varies between 

5-12 psu. Regions of open water, or polynyas, are created by downwind 

advection of ice. The sea ice limit advances southward as ice-melt cools and 

freshens the upper ocean. During winter, a climatological average of 3 to 

5 storms per month move eastward along the Aleutian Chain forming the 

primary storm track, while less than two storms per month cross the northern 

Bering Sea. The amount of sea ice production and advection depends upon 

which atmospheric conditions dominate in a given winter. The greatest ice 

production occurs in years when the Aleutian Low is well developed and 

storms migrate along the primary storm track. 

For the Bering Sea; variations in overall ice cover (Fig. 3C.1), time of advection over the open shelf, and subsequent melt-back are important features 

of the physical environment. Formation of sea ice generally begins in November with maximum ice extent occurring in late March. Ice-free conditions 

typically exist from June through October. Observations of ice cover over 

the eastern Bering Sea shelf show a nearly 40% variation about the mean 

(Niebauer, 1988). Other characteristics of ice cover that show great variability include duration of ice at its southern extent (3-15 weeks), time of retreat 

from the southernmost extent (between mid-March and June), and number 

of weeks that ice remained over the middle shelf domain (3-28 weeks with 

a mean of 20 weeks) (Wyllie-Echeverria, 1995b). The differences in these 

characteristics vary greatly between years with maximum and minimum ice 

extent (Fig. 3C.2). 

Ice formation, brine rejection, advection and eventual melting play a critical role in fluxes of heat and salt (Aagaard et al., 1985; Hendricks et al., 

1985; Coachman, 1986) and in generation of baroclinic flow (Schumacher et 

al., 1983; Muench and Schumacher, 1985). The production of dense (cold 

saline) water has a marked impact on the halocline of the Arctic Ocean with 

water from the Anadyr and Anadyr Strait polynyas providing a substantial 

fraction of the total (Cavalieri and Martin, 1994). From 9-25 m of ice formation occurs over the winter season depending on location and meteorological 

'Pacific Marine Environmental Laboratory, NOAA, Seattle, WA 98115, U.S.A. 

2~oint Institute for the Study of the Atmosphere and Ocean (JISAO), University of 

Washington, Seattle 
136 S.A. Macklin led. 

Figure 3C.1: Approximate location of the maximum sea ice extent in a year with extreme ice cover (1976) 

and in a year with minimal ice cover (1979). 

conditions (Cavalieri and Martin, 1994). A growth rate of -6 cm d-l was 

estimated from changes in salinity (Schumacher et al., 1983; Roach et al., 

1995). The average thickness of ice at any given instant over most of the 

open southeastern shelf, however, is only -0.5 m (Coachman, 1986). The 

positive buoyancy flux from melting ice initiates both baroclinic transport 

along the marginal ice zone (-0.3 x lo6 m3 s-l) and stratification of the 

water column. 

Sea ice also exerts an important influence on the biota. Associated with 

ice-melt is a bloom of phytoplankton that accounts for 10-65% of the total annual primary production over the eastern shelf (Niebauer et al., 1990, 

1995). More recent observations (Stabeno et al., 1998) demonstrate that 

chlorophyll concentrations begin to increase concomitant with the presence 

of sea ice even though the water column is not stratified. Sea ice plays a 

central role in the timing of primary secondary production cycles which can 
BERING SEA FOCI FINAL REPORT 137 

JASONDJFMAMJ I 

- 

- Point Barrow 

D 

- - 

Bering Strait - 

n 

Figure 3C.2: Characteristics of sea ice extent measured along 169"W each week for atmospheric conditions 

during a cold year (1975-1976: shown as dark line and dots) and a warm year (1978-1979: shown as light 

line and dots). Note the differences in time of advance, southern limit, duration over the Middle shelf and 

time of retreat (after Wyllie-Echeverria, 1995b). 

influence food availability for first feeding pollock larvae. Ice production 

and formation of cold bottom water (the cold pool) also influences the distributions of higher trophic level biota over the eastern shelf (Ohtani and 

Azumaya, 1995; Wyllie-Echeverria, 1995a, b). This latter effect may influence the overlap of young of the year pollock and older fish, thereby providing 

a physical determinant for the extent of cannibalism in a given year. 

References 

Aagaard, K., L.K. Coachman, and E. Carmack (1985): On the halocline of the 

Arctic Ocean. J. Geophys. Res., 90, 4833-4846. 

Cavalieri, D.J., and S. Martin (1994): The contribution of Alaskan, Siberian, and 

Canadian coastal polynyas to the cold halocline layer of the Arctic Ocean. J. 

Geophys. Res., 99, 18,343-18,362. 

Coachman L.K. (1986): Circulation, water masses, and fluxes on the southeastern 

Bering Sea shelf. Cont. Shelf. Res., 5, 23-108. 

Hendricks, P.J., R.D. Muench, and G.R. Stegen (1985): A heat balance for the 

Bering Sea ice edge. J. Phys. Oceanogr., 15, 1747-1758. 

Muench, R.D., and J.D. Schumacher (1985): On the Bering Sea ice edge front. J. 

Geophys. Res., 90, 3185-3197. 

Niebauer, H.J. (1988): Effects of El Niiio-Southern Oscillation and North Pacific 
138 S.A. Macklin (ed. ) 

weather patterns on interannual variability in the subarctic Bering Sea. J. 

Geophys. Res., 93, 5051-5068. 

Niebauer, H. J., V.A. Alexander, and S. Hendricks (1990): Physical and biological 

oceanographic interaction in the Spring Bloom at the Bering Sea marginal ice 

edge zone. J. Geophys. Res., 95, 22,229-22,242. 

Niebauer H.J., V. Alexander, and S.M. Henrichs (1995): A time-series study of the 

spring bloom at the Bering Sea ice edge, I, Physical processes, chlorophyll and 

nutrient chemistry. Cont. Shelf Res., 15, 1859-1878. 

Ohtani, K., and T. Azumaya (1995): Interannual change of the sea conditions on 

the continental shelf and its influence on abundance of walleye pollock in the 

eastern Bering Sea. Can. J. Fish. Aquat. Sci., Special Pub., 121, 87-95. 

Overland, J.E., and C.H. Pease (1982): Cyclone climatology of the Bering Sea and 

its relation to sea ice extent. Mon. Weather Rev., 110, 5-13. 

Pease, C.H. (1980): Eastern Bering Sea ice processes. Mon. Weather Rev., 108, 

2015-2023. 

Roach, A.T., K. Aagaard, C.H. Pease, S.A. Salo, T. Weingartner, V. Pavlov, and 

M. Kulakov (1995): Direct measurements of transport and water properties 

through Bering Strait. J. Geophys. Res., 100, 18,443-18,457. 

Schumacher, J.D., K. Aagaard, C.H. Pease, and R.B. Tripp (1983): Effects of a shelf 

polynya on flow and water properties in the northern Bering Sea. J. Geophys. 

Res., 88, 2723-2732. 

Stabeno, P.J., J.D. Schumacher, R.F. Davis, and J.M. Napp (1998): Under-ice 

observations of water column temperature, salinity and spring phytoplankton 

dynamics: Eastern Bering Sea shelf. J. Mar. Res., 56, 239-255. 

Wyllie-Echeverria, T. (1995a): Sea-ice conditions and the distribution of walleye 

pollock and the Bering and Chukchi Sea shelf. In Climate Change and Northern 

Fish Populations, R.J. Beamish (ed.), Can. Spec. Publ. Fish. Aquat. Sci., 121, 

87-95. 

Wyllie-Echeverria, T. (1995b): Seasonal sea ice, the cold pool and gadid distribution 

on the Bering Sea shelf. Ph.D. Thesis, University of Alaska, Fairbanks, 281 pp. 
BERING SEA FOCI FINAL REPORT 139 

Part 4 

Administration and management of the Bering Sea 

FOCI Program (S. Allen Macklin) 

4.1 Beginning of the Project 

Bering Sea Fisheries-Oceanography Coordinated Investigations (BS FOCI) 

developed from the need to better understand environmental characteristics 

and processes affecting the rapidly developing walleye pollock fishing industry in the Bering Sea. NOAA previously had funded a study in the Gulf of 

Alaska, Shelikof Strait FOCI (Kendall et al., 1996), that had established an 

understanding of processes affecting survival of young pollock. Although the 

Shelikof Strait pollock fishery was of commercial importance, it was dwarfed 

by the catch of pollock in the Bering Sea. 

A chronology of BS FOCI is provided in Table 4.1. In May of 1990 BS 

FOCI published an implementation plan (BS FOCI, 1990) for a FisheriesOceanography Coordinated Investigation of Pollock in the Bering Sea. This 

plan was in response to the establishment of a coastal fisheries ecosystems (CFE) project by NOAA's Coastal Ocean Program (COP; Boyles and 

Scavia, 1993; Wenzel and Scavia, 1993). The goal of CFE was to reduce 

uncertainty in resource management decisions through ecological research. 

The premise of BS FOCI was that the Bering Sea was among the most 

productive of northern high-latitude seas. The primary commercial resource 

was walleye pollock, prevalent on the continental shelves of the Bering Sea 

and in the basin. With the passage of the Magnuson Fisheries Conservation 

and Management Act of 1976, the coastal fishery came under management 

control of the United States. By the 1980s, a domestic fishery industry 

developed to replace foreign industry in the U.S. Exclusive Economic Zone 

(EEZ). However, over-exploitation in the international deep basin was an 

important issue in the management of the fishery, as basin pollock stocks 

were thought to be linked to stocks in the EEZ. Despite biological assessment 

of the southeast Bering Sea shelf through a number of research programs 

provided by the National Science Foundation and NOAA with the Bureau 

of Land Management, the information base for the region, especially the 

deep basin and its ties to the shelf, was almost nonexistent. 

BS FOCI'S implementation plan called for examination of the hypothesis 

that transport of larval pollock from the deep Aleutian basin to the continental shelf contributes to the viability of U.S. fisheries. Four objectives 

were established, based on research recommendations from an International 

Scientific Symposium on Bering Sea Fisheries held in Sitka, Alaska during 

July 1988 (Aron and Balsiger, 1989): 

1. Determine the differences between pollock spawning aggregations 

through techniques of molecular biology. 

2. Determine circulation of the Bering Sea, including the deep basin and 

the extensive eastern continental shelf. 
140 S.A. Macklin (ed.) 

Table 4.1: A chronology of significant Bering Sea FOCI events. 

Year Month Event 

1990 June 

1991 March 

August 

November 

1992 April 

September 

1993 March 

April 

August 

September 

October 

November 

1994 January 

February 

April 

September 

November 

1995 March 

April 

May 

AugustSeptember 

1996 February 

1996 April 

May 

September 

October 

December 

1997 January 

March 

June 

Implementation Plan with hypothesis that transport of larval pollock from the deep Aleutian Basin to the southeastern shelf contributes to the viability of U.S. fisheries 

Project Study Plan 1991-1996 

Cruise: large scale CTD and ADCP survey of the Bering Sea basin 

Principal investigators organizational meeting, Seattle, Washington 

Cruise: first deployment of Peggy Bering Sea, larval survey 

Cruise: recover Peggy Bering Sea 

Cruise: deploy Peggy Bering Sea 

Cruise: larval survey 

Principal investigators meeting in Portland, Oregon 

Cruise: recover Peggy Bering Sea, CTD survey 

Sponsored Juvenile Pollock Symposiym, Seattle, Washington 

Reviewed by National Research Council, Washington, D.C. 

Reviewed by National Research Council with Technical Advisors present, Seattle, Washington 

Cruise: deploy Peggy Bering Sea 

Cruise: larval survey 

Cruises: CTD survey, acoustics; Pribilof juvenile pollock studies, mooring recoveries 

Principal investigators meeting, Seattle, Washington 

Cruise: deploy moorings 

Cruise: larval studies 

Cruise: larval studies 

Cruises: moorings, Pribilof juvenile pollock studies 

Cruise: deploy moorings 

Cruise: moorings, CTD and larval survey 

Joint cruise and aircraft flights: moorings, groundtruth, primary productivity survey 

Cruises: Pribilof juvenile pollock studies; mooring recoveries 

Juvenile studies principal investigators synthesis meeting, Seattle, Washington 

Biophysical interactions principal investigators synthesis meeting, Seattle, Washington 

Biophysical interactions investigators synthesis meeting, Seattle, Washington 

Juvenile studies principal investigators synthesis meeting, San Diego, California 

Publication of Bering Sea and North Pacific Ocean Theme Page on the Worldwide Web 

September Larval ecology principal investigators synthesis meeting, Juneau, AK 

3. Determine patterns and processes involved in vertically mixing the 

water column. 

4. Study how different oceanographic domains in the Bering Sea contribute to larval growth and mortality. 

After the implementation plan was reviewed by the CFE Advisory Committee in January 1991, BS FOCI was asked to submit a Project Study Plan 

(BS FOCI, 1991) to describe research from 1991 through 1996. The Project 

Study Plan, submitted in March 1991, identified two goals for the project. 

The first goal was to address the issues of pollock stocks in the Bering Sea 

based on objectives 1 and 2. The second goal dealt with the processes that 

affected the survival of basin pollock in their earliest life stages and their 

subsequent recruitment, and was based on objectives 3 and 4. During the 

last 2 years of BS FOCI, the arena for recruitment studies was shifted to the 
BERING SEA FOCI FINAL REPORT 141 

Table 4.2: Bering Sea FOCI Executive Committee 

William Aron (ex officio) Allen Macklin (coordinator) 

NOAA/Alaska Fisheries Science Center NOAA/Pacific Marine Environmental Laboratory 

Eddie Bernard (ex officio) Jeffrey M. Napp 

NOAA/Pacific Marine Environmental Laboratory NOAA/Alaska Fisheries Science Center 

Stephen Bollens 

San Francisco State University 

Lewis Haldorson 

University of Alaska Fairbanks 

James E. Overland 

NOAA/Pacific Marine Environmental Laboratory 

James D. Schumacher 

NOAA/Pacific Marine Environmental Laboratory 

Arthur Kendall Jr. Gary L. Stauffer 

NOAA/Alaska Fisheries Science Center NOAA/Alaska Fisheries Science Center 

southeastern shelf. A component examining juvenile pollock near the Pribilof Islands during the late summer and fall of their birth year was added 

in 1994. 

4.2 Project Management 

The Project Study Plan designated co-project managers from the Alaska 

Fisheries Science Center (AFSC; G. Stauffer) and the Pacific Marine Environmental Laboratory (PMEL; J. Overland). The co-managers, together 

with senior scientists from each laboratory and the laboratory directors, 

formed an Executive Committee (Table 4.2). This committee was responsible for directing BS FOCI consistent with COP'S guidelines, coordination 

of BS FOCI with other NOAA base programs concerned with Bering Sea 

pollock, and evaluation of proposals from academic institutions. A project 

coordinator was added to the Executive Committee in August 1993, and two 

academic members were added in 1994 in response to a suggestion by the 

National Research Council (1994). 

The plan further identified an intramural research team of scientists from 

the Alaska Fisheries Science Center and the Pacific Marine Environmental 

Laboratory. These scientists brought expertise on Bering Sea pollock stocks, 

circulation, and recruitment processes, including the collected wealth of Shelikof Strait FOCI established in 1985. To provide balance and expertise in 

needed areas, extramural contracts were established in September 1991 for 

genetic studies, satellite remote sensing of circulation, and studies on vertical distribution of zooplankton. A Principal Investigator group consisted 

of the two project managers and all the principal participating scientists. 

This group met at least quarterly, published a quasi-annual Progress and 

Plans document, coordinated all contracts with academic research institutions, and obtained peer review of scientific results at national meetings and 

in refereed journal publications. 

At the end of the first year, COP conducted a review of the project. As a 
142 S.A. Macklin (ed.) 

Table 4.3: Bering Sea FOCI Technical Advisory Committee 

Dr. Michael Dagg Dr. Thomas Royer 

Louisiana University Marine Consortium Old Dominion University 

Chauvin, LA 70344 Norfolk, VA 23505 

Mr. Bart Eaton Dr. A1 Tyler 

Trident Seafoods Corporation University of Alaska Fairbanks 

Seattle, WA 98107 Fairbanks, AK 99775-1080 

Dr. Eileen Hofmann 

Old Dominion University 

Norfolk, VA 23505 

Dr. Warren Wooster 

University of Washington 

Seattle, WA 98195-5685 

Dr. William Leggett 

Queens University 

Kingston, Ontario 

Canada K7L 3N6 

result of this review, BS FOCI implemented a Technical Advisory Committee 

(Table 4.3) to help guide the project. 

4.3 Budget 

Funds for BS FOCI were allocated in the first year at just under a million 

dollars. The project was level funded through 1995, then funds tapered off 

during the final 2 years. The funding profile for BS FOCI was 

4.4 Competitive Process and Research Cycles 

For the first round of research (FY 1991 through FY 1993), AFSC and 

PMEL FOCI scientists submitted work statements addressing the objectives 

of Phase I and Phase I1 research. These were evaluated by the co-managers 

and a team of intramural scientists was established. To provide academic balance, proposals were solicited from the outside community in a competitive 

process for $260K. These were evaluated by the co-managers and Executive 

Committee. From the evaluations, extramural contracts were established in 

September 1991 for genetic studies, satellite remote sensing of circulation, 

and studies on vertical distribution of zooplankton to last through FY 1993. 

In FY 1993, proposals for FY 1994 and FY 1995 research were solicited 

from the scientific community at large. Proposals were evaluated by the 

Executive Committee and the Technical Advisory Committee. Finally, the 

Executive Committee solicited work statements from specific researchers for 
BERING SEA FOCI FINAL REPORT 143 

FY 1996 to complete objectives of the project. Funds in FY 1997 were used 

to support publications, analysis of samples and data, synthesis meetings, 

and development of data access through the World Wide Web. Table 4.4 

lists all BS FOCI research components. 

BS FOCI developed collaborations with Russian, Korean, and Japanese 

scientists. These associations provided scientific leverage through the sharing 

of data and research vessels. 

4.5 Meetings and Workshops 

BS FOCI intramural researchers met monthly at a FOCI Principal Investigators meeting. An electronic bulletin board was established to share notice 

and agenda of these meetings, and to publish their minutes, so that extramural researches could be represented and informed. 

The Executive Committee met several times a year to establish procedure, evaluate proposals, and provide guidance. 

During October 1993, BS FOCI hosted a 3-day international workshop 

in conjunction with the second annual meeting of the North Pacific Marine 

Science Organization. The subject of the workshop was the importance of 

prerecruit walleye pollock to the Bering Sea and North Pacific ecosystems 

(Brodeur et al., 1996). 

The full suite of principal investigators met on several occasions to discuss 

research plans and progress and to implement field plans. 

Small working groups of principal investigators associated with juvenile 

pollock ecology and biophysical processes held synthesis meetings in the fall 

and winter of 1996-1997. 

4.6 Field Experiments 

BS FOCI conducted more than 20 cruises and one aircraft expedition during 

its 7-year lifetime. Because the project was focused on the early life history 

of pollock and determining circulation and stock structure of pollock, the 

field season developed a recurring routine. In general, the earliest cruises of 

the year were conducted during February and March. Their purpose was to 

deploy moorings for the late winter, spring, summer, and early fall observation period, to ascertain ground truth for the moorings, and to sample water 

conditions prior to spawning of pollock in the spring. During spring, cruises 

worked to sample larval pollock distributions as well as their prey and predators, to monitor the progress of the nutrient-phytoplankton-zooplankton cycle, and to document biophysical processes important to survival of larval 

pollock. Fall cruises observed the ecosystem associated with juvenile pollock 

in the Pribilof Islands habitat and recovered moorings. 

The project utilized a number of research vessels. The primary carrier 

was the NOAA Ship Mzller Freeman. Other vessels supporting BS FOCI 

were the NOAA Ship Surveyor and the Japanese Fishery Research Vessel 

Oshoro Maru. 
144 S.A. Macklin (ed.) 

Table 4.4: Bering Sea FOCI research components and principal 

investigators. 

Larval feeding mechanisms of walleye pollock 

U.S./Japan cooperative studies 

Population ecology of walleye pollock 

Component Principal Investigator 

Kevin M. Bailey 

NOAA/Alaska Fisheries Science Center 

Kevin M. Bailey 

NOAA/Alaska Fisheries Science Center 

Kevin M. Bailey 

NOAA/Alaska Fisheries Science Center 

Dennis A. Powers 

Stanford University 

Modeling the upper ocean production dynamics of 

plankton and larval pollock in the Bering Sea 

Spatial and temporal characteristics of wind forcing of 

the Bering Sea 

Impact of invertebrate predators on walleye pollock 

larvae 

Juvenile pollock studies 

Larval pollock nutritional condition assay 

Basin vertical processes: mixed-layer dynamics from 

the Peggy Bering Sea mooring 

Determining chlorophyll concentration from ocean 

color measurement in the Bering Sea 

Bimodal distribution of juvenile pollock in the southeastern Bering Sea 

Growth, transport, and mortality studies of larval 

walleye pollock 

Feeding ecology of larval walleye pollock in oceanic and 

neritic domains of the Bering Sea: effects of variation 

in prey 

An aggregated ecosystems model for the southeastern 

Bering Sea 

Ichthyoplankton collections in the eastern Bering Sea 

A retrospective analysis of GEOSAT altimeter data in 

the Bering Sea 

Role of protozoa in the diet of larval pollock in the 

Bering Sea 

Stephen Bollens 

San Francisco State University 

Nicholas A. Bond 

JISAO/University of Washington 

Richard D. Brodeur 

NOAA/Alaska Fisheries Science Center 

Richard D. Brodeur 

NOAA/Alaska Fisheries Science Center 

Michael Canino 

NOAA/Alaska Fisheries Science Center 

Edward D. Cokelet 

NOAA/Pacific Marine Environmental Laboratory 

John Cullen and Richard Davis 

Dalhousie University 

Miriam Doyle 

JISAO/University of Washington 

Robert C. Francis 

University of Washington 

Lewis J. Haldorson 

University of Alaska Fairbanks 

Albert J. Hermann 

JISAO/University of Washington 

Arthur W. Kendall, Jr. 

NOAA/Alaska Fisheries Science Center 

Robert Leben 

University of Colorado 

Evelyn J. Lessard 

University of Washington 
BERING SEA FOCI FINAL REPORT 145 

Table 4.4: (continued). 

Com~onent Principal Investigator 

Monitoring of mesoscale ocean processes by synthetic 

aperture radar (SAR) 

Food chain dynamics: spring bloom hypothesis and 

larval survival 

Otolith technique for tracing geographic life history of 

pollock 

Modeling Bering Sea circulation 

Microcrustacean production potential during the onset 

of feeding by walleye pollock larvae in the Aleutian 

Basin and Bering Sea shelf 

The use of molecular techniques to dissect the genetic 

architecture of pollock populations: analysis of mitochondrial and nuclear genes by the polymerase chain 

reaction 

Circulation of the eastern Bering Sea: Aleutian North 

Slope Flow 

Larval transport and mesoscale circulation 

Shelf-slope exchange along the eastern Bering Sea shelf 

break 

Data integration system and theme page for the Bering 

Sea 

Nutritional condition of larval walleye pollock 

Relationships between pollock distribution and extent 

of seasonal sea ice on the Bering Sea shelf 

Phytoplankton dynamics from moored optical instruAntony K. Liu 

NASA/Goddard 

Jeffrey M. Napp 

NOAA/Alaska Fisheries Science Center 

Brenda L. Norcross 

University of Alaska Fairbanks 

James E. Overland 

NOAA/Pacific Marine Environmental Laboratory 

A.J. Paul 

University of Alaska Fairbanks 

Dennis A. Powers 

Stanford University 

Ronald K. Reed and Phyllis J. Stabeno 

NOAA/Pacific Marine Environmental Laboratory 

James D. Schumacher 

NOAA/Pacific Marine Environmental Laboratory 

James D. Schumacher and Phyllis J. Stabeno 

NOAA/Pacific Marine Environmental Laboratory 

Nancy Soreide 

NOAA/Pacific Marine Environmental Laboratory 

Gail H. Theilacker 

NOAA/Alaska Fisheries Science Center 

Tina Wyllie-Echeverria 

JISAO/University of Washington 

J. Ronald V. Zaneveld 

ments in the southeastern Bering Sea Oregon State University 
146 S.A. Macklin (ed.) 

4.7 Data Dissemination 

In order to facilitate data exchange between investigators and to make BS 

FOCI data available to the scientific community, the project underwrote 

creation of the Bering Sea and North Pacific Ocean Theme Page, a World 

Wide Web resource at http : //www . pmel . noaa. gov/bering. The theme 

page provides pathways to much of the physical and biological data collected 

by BS FOCI, as well as other information grouped by scientific discipline. 

The Bering Sea Ecosystem Biophysical Metadatabase, an annotated index 

of data holdings, is available through the theme page. 

4.8 Project Reviews 

BS FOCI was reviewed formally on two occasions. The first was an internal 

review by COP in the spring of FY 1992. As a result of this review, the 

project convened its Technical Advisory Committee. 

A more extensive review was conducted by the National Research Council 

(1994) during FY 1994. There were two phases of this review of accomplishments and plans of the NOAA Coastal Ocean Program. The first phase was 

a briefing of the panel by senior project scientists in Washington D.C. The 

second was held in Seattle with BS FOCI'S technical advisors present. At 

this meeting, project principal investigators gave a series of presentations to 

the panel. Administrative changes suggested by the panel and adopted by 

BS FOCI were the expansion of the Executive Committee to include academic investigators, formalization of the competitive process, and formation 

of small working groups based on the scientific structure of the project. 

The importance of the Bering Sea's commercial resources and the success of BS FOCI in addressing questions pertaining to walleye pollock in the 

Bering Sea have helped generate increased interest in the Bering Sea ecosystem. New programs such as COP'S Southeast Bering Sea Carrying Capacity 

and NOAA's Arctic Research Initiative, as well as ongoing research by FOCI, 

build on these concepts developed by BS FOCI, and continue to advance our 

understanding of the complex, productive ecosystem of the Bering Sea. 

4.9 References 

Aron, W., and J. Balsiger (1989): Proceedings of the International Scientific Symposium on Bering Sea Fisheries. NOAA Tech. Memo. NMFS F/NBC-163,424 pp. 

(available from Alaska Fisheries Science Center, 7600 Sand Point Way N.E., 

Seattle, WA 98115-0070). 

Boyles, R., Jr., and D. Scavia (1993): Innovative coastal ocean science at NOAA. 

Sea. Tech., 34, 10-16. 

Brodeur, R.D., P.A. Livingston, T.R. Loughlin, and A.B. Hollowed (eds.) (1996): 

Ecology of juvenile walleye pollock, Theragra chalcogramma. U.S. Department 

of Commerce, NOAA Technical Report NMFS 126, 227 pp. (available from 

Alaska Fisheries Science Center, 7600 Sand Point Way N.E., Seattle, WA 98115- 

0070). 

BS FOCI (1990): Bering Sea FOCI Implementation Plan FY 1991-1996. U.S. 

Department of Commerce, National Oceanic and Atmospheric Administration, 

16 pp. (available from Pacific Marine Environmental Laboratory, 7600 Sand 

Point Way N.E., Seattle, WA 98115-0070). 
BERING SEA FOCI FINAL REPORT 147 

BS FOCI (1991): Bering Sea FOCI Project Study Plan FY 1991-1996. U.S. Department of Commerce, National Oceanic and Atmospheric Administration, 28 pp. 

(available from Pacific Marine Environmental Laboratory, 7600 Sand Point Way 

N.E., Seattle, WA 98115-0070). 

Kendall, A.W., Jr., R.I. Perry, and S. Kim (1996): Fisheries oceanography of walleye 

pollock in Shelikof Strait, Alaska. Fish. Oceanogr., 5(Suppl. I), 203 pp. 

National Research Council (1994): A Review of the Accomplishments and Plans 

of the NOAA Coastal Ocean Program. National Academy Press, Washington, 

D.C., 115 pp. 

Wenzel, L., and D. Scavia (1993): NOAA's Coastal Ocean Program. Oceanus, 36, 

85-92. 
BERING SEA FOCI FINAL REPORT 149 

Part 5 

Selected monitoring, modeling, and technical 

achievements (compiled by S. Allen Macklin) 

The development and application of new technology allows the field of fisheries oceanography to move forward. During BS FOCI's 64-year lifetime, 

its scientists and technicians made numerous and significant technological 

contributions to the field. Some of these achievements were specific to the 

Bering Sea region, some were specific to walleye pollock, and some were 

more wide-ranging in their applications. In the following sections, selected 

achievements are discussed under the headings of monitoring, modeling, and 

technology. 

5.1 Monitoring 

BS FOCI used moorings, satellite-tracked drifters, and shipboard measurements to monitor physical and biological oceanographic conditions in the 

several distinct domains of the Bering Sea basin and the eastern Bering Sea. 

a. refined understanding of circulation in the Bering Sea basin through 

observations with vessel-mounted acoustic Doppler current profiler 

(Cokelet et al., 1996) and satellite-tracked drifters (Stabeno and Reed, 

1994) : 

A month-long circumnavigation of the Bering Sea basin in August 1991 

was one of BS FOCI's first field operations. During the cruise, scientists 

made the first use of an acoustic Doppler current profiler in the Alaskan 

Stream and Bering Sea. Observations of three-dimensional current velocity led to an increased knowledge of circulation and transport in 

the Bering Sea basin and improved the ability to compute geostrophic 

circulation from hydrographic casts. 

From 1986 through 1996 (and continuing since then under sponsorship from other research funding), BS FOCI deployed more than 120 

satellite-tracked drifters in the North Pacific Ocean and Bering Sea. 

Most drift buoys were drogued at 40 m. A composite current pattern was derived from data telemetered by these drifters. This pattern 

helped identify large- and mesoscale features of circulation and led to 

discovery of a new current, the Aleutian North Slope Current (Reed 

and Stabeno, 1998). 

b. unique time series of water column temperature, salinity, estimated 

chlorophyll-a, and phytoplankton fluorescence during ice advance and 

retreat (Stabeno et al., 1998): 

During 1995 three surface moorings were deployed over the southeast 

Bering Sea shelf. Each mooring had instruments that measured temperature, salinity and fluorescence. After the moorings were deployed 
150 S.A. Macklin (ed.) 

in February, the most severe ice conditions in the last 20 years developed. Two of the moored platforms were struck by the sea ice but 

continued to function. They provided unique time series of watercolumn temperature, salinity, chlorophyll-a and fluorescence under an 

advancing and retreating ice field. One platform was located in the 

weakly advective middle shelf regime. Here, contrary to earlier findings, chlorophyll-a concentrations increased prior to the formation of 

a well-defined two-layer system. Events of strong advection, rather 

than vertical fluxes, dominated changes in water column structure and 

properties. These advective events provide a mechanism for nutrients 

(required to support the rich blooms that occur over the middle shelf 

during spring) to be transported onto the middle shelf. A second mooring was located in the more advective outer shelf. The ice also reached 

this site, and chlorophyll-a concentrations increased with the advent 

of ice. The final mooring was deployed to the east of Unimak Pass. 

Sea ice was not advected this far south, and the spring bloom did not 

occur until May. 

c. upper ocean phytoplankton survey (Davis et al., 1997a): 

For its last field experiment, in spring 1996, BS FOCI conducted a 

survey of sea surface chlorophyll over the southeastern Bering Sea using a research aircraft and ship. The project documented the spatial 

and temporal evolution of chlorophyll concentration during the spring 

bloom in the Bering Sea and how this concentration related to the 

ocean's physical characteristics. Chlorophyll concentration was estimated from the aircraft using remote color-sensing instrumentation 

designed to detect upwelling radiance from the ocean. The ocean's 

physical characteristics were assessed using air-expendable bathythermographs deployed from the plane; instrumented, moored buoys; and 

by CTD casts and ADCP transects aboard ship. Preliminary results 

showed higher chlorophyll concentrations in the northern portion of 

the domain where sea ice was melting, and a prominent 100 x 200 km 

patch southeast of the Pribilof Islands with concentrations an order of 

magnitude greater than background levels. This patch was in a region 

of the shelf where pollock spawning occurs. 

5.2 Modeling 

BS FOCI used models to conceptualize program strategies, to expand the 

time-space domain of field observations, to guide program direction through 

hypothesis generation, and to understand features of biophysical processes. 

a. numerical model of circulation of the Bering Sea basin and exchange 

with the North Pacific Ocean (Overland et al., 1994): 

At the beginning of the Bering Sea FOCI project, use was made of 

a high-resolution, 118'-grid, numerical model to investigate the circulation of the Bering Sea basin and the adjacent North Pacific Ocean. 
BERING SEA FOCI FINAL REPORT 151 

The modeling was based on the Navy Layered Ocean Model, one of 

the highest-resolution ocean circulation models at the time, and run 

on the University of Alaska Fairbanks' supercomputer. There was a 

generally cyclonic, but spatially complex and non-stationary, circulation within the Bering basin, fed by flow through the Aleutian passes. 

The numerical study demonstrated that internal flow instabilities, and 

not just external forcing such as wind and inflow current, contribute 

to substantial interannual variability in the circulation of the Bering 

Sea and adjacent northwestern Pacific Ocean. 

coupled, one-dimensional, biophysical model investigating production 

dynamics of the pelagic ecosystem with respect to growth of larval 

pollock (Francis et al., 1998; Bollens et al., in preparation): 

A coupled, one-dimensional, biophysical model investigated production dynamics of the pelagic ecosystem with respect to growth of larval pollock. The approach used field observations to determine rates 

and appropriate species composition for several of the distinct physical 

and biological domains in the eastern Bering Sea. The model included 

stage-structured dynamics of copepod populations (Calanus and Neocalanus) and larval pollock feeding and growth. The temporal behavior 

of the mixed layer was obtained from observations from Peggy Bering 

Sea, a moored biophysical platform. Model results showed that the 

species composition of zooplankton has a strong influence on growth 

of larval pollock, and the presence of protozoan prey becomes important when young copepods are scarce, i.e., during early spring over the 

slope. Results from the model also suggested that variability of the 

mixed-layer depth has significant impact on larval growth by affecting 

lower trophic level production. These results led to the addition of a 

field research component that developed a new method for live-staining 

protists and showed that microprotozoan biomass levels are sufficient 

to augment prey levels and support estimated metabolic needs of firstfeeding larval pollock. 

Technology 

At the beginning of the project, there was scant knowledge of processes that 

affect recruitment of walleye pollock in the Bering Sea. Some findings from 

FOCI'S Shelikof Strait project were applicable, but steps had to be taken to 

develop new methods to address specifics of the Bering Sea environment and 

ecosystem. BS FOCI made nearly 20 significant technological developments 

that furthered understanding of general and regional physical and biological 

oceanography. 

a. a modified PROTEUS mooring that withstands the arctic marine climate of the Bering Sea and measures winds, insolation, air temperature, humidity, salinity, and temperature at ten depths, currents from 

acoustic Doppler current profiler and acoustic current meters, acoustic 

backscatter, and chlorophyll absorption (Cokelet and Stabeno, 1997): 
152 S.A. Macklin (ed.) 

Because there were no continuous time series of biophysical conditions 

from pre-spring bloom conditions through the summer, BS FOCI developed and deployed a surface mooring, Peggy Bering Sea, in the southeast basin at 2195 m depth in the spring and summer of 1992-1994 

and the winter of 1994. It recorded the first long-term oceanographic 

time series in the basin. The winter observations are particularly valuable due to the lack of wintertime measurements in this region. The 

platform was a PROTEUS (PROfile TElemetry of Upper ocean currents) similar to moorings deployed in the tropical Pacific Ocean, but 

modified to withstand the arctic marine climate of the Bering Sea. 

Included in its suite of measurements were winds, insolation, air temperature, humidity, salinity, and temperature at ten depths, currents 

from acoustic Doppler current profiler and acoustic current meters, 

acoustic backscatter, and chlorophyll absorption. Some of the observations were telemetered real time via satellite and System ARGOS. 

Useful information for understanding the Bering Sea ecosystem was deduced from Peggy Bering Sea measurements. At that part of the basin 

there is a weak background flow of a few cm s-I and little density 

variation with internal tides superimposed. Anticyclonic (clockwise) 

eddies pass by sporadically, inducing currents up to 430 cm s-I and 

depressing isopycnals by as much as ~200 m. The thermal structure 

in the upper 400 m shows a deep temperature maximum from warm 

Alaskan Stream inflows and a minimum above due to winter cooling. 

A sea surface cooling event was observed in the late winter of 1994, 

with cold water penetrating to -120 m depth. Spring warming begins 

in late April to early May of each year, marked by the arrival of the 

3.75"C isotherm. The local wind plays little role in forcing ocean currents at the site except at the inertial frequency. Because some data 

were telemetered in real time, Peggy Bering Sea permitted direction of 

field sampling to provide in situ measurements by ship. The mooring 

design later was modified for shallow-water use, and two moorings were 

deployed during early March 1995--one over the outer and one over 

the middle southeastern Bering Sea shelf. They were inundated by sea 

ice, providing unique time series of water column temperature, salinity, estimated chlorophyll-a, and phytoplankton fluorescence during ice 

advance and retreat. 

b. remote methods for determining mesoscale ocean circulation and features using high resolution synthetic aperture radar (Liu et al., 1994) 

and radar altimetry (Stabeno et al., in preparation) from satellites, 

and shipboard acoustics (Brodeur et al., 1996): 

Results from the slope waters of the eastern Bering Sea indicated that 

the highest abundances of pollock larvae often reside in eddies. To 

examine the nature of biophysical processes present in these features 

and determine their influence upon survival required in situ observations. Finding a reliable method to locate an eddy for field studies 
BERING SEA FOCI FINAL REPORT 153 

was a challenge. Although infrared imagery has proved useful, cloud 

cover and generally weak sea surface temperature gradients limit this 

approach for the Bering Sea. High-resolution synthetic aperture radar 

(SAR) eliminates both of these constraints. Mesoscale features are imaged by SAR through several possible mechanisms that are not well 

understood, including current-induced wave refraction. SAR images 

were examined for mesoscale features in Alaskan coastal waters, and 

BS FOCI maintained an image library. A new method for time-varying 

signal analysis, called the Wavelet Transform was developed (Liu et al., 

1997) and gives spectral decompositions via the scale concept. A twodimensional wavelet transform is a highly efficient band-pass-filter that 

can be used to separate various scale processes and show their relative 

phase and location as a matched filter detector. A two-dimensional 

Gaussian wavelet transform of a SAR image can be used with threshold 

as an edge detector for small-scale features. The evolution of mesoscale 

features such as oil slicks, fronts, eddies, and internal waves can be 

tracked by wavelet analysis using satellite data from repeating paths. 

Real-time, remote tracking of eddies enabled BS FOCI to guide sampling by a Japanese research vessel working cooperatively with project 

scientists during summer 1993. 

A new technology, near real-time altimetry, was employed in the Bering 

Sea to help locate an anticyclonic eddy for field surveys. Near realtime data from TOPEX/POSEIDON (TIP) and ERS-2 were processed 

at the University of Colorado's Center for Astrodynamics Research 

(CCAR) to map sea surface height anomalies in the southeast Bering 

Sea basin, and these maps were posted daily on the CCAR website 

(http: //www-ccar . colorado. edu/-leben/bering/). This method 

came to fruition for Bering Sea research in the year following BS 

FOCI'S final field operations. In May 1997, the development of an 

8-cm high at 55"N, 169"W was monitored by a BS FOCI scientist 

using maps posted on the CCAR website. Using the near real-time information supplied by the satellite altimetry, she was able to direct the 

NOAA ship Mzller Freeman to the location of the eddy. Subsequent 

surveys and satellite tracked drifters confirmed eddy circulation. 

Acoustic backscatter signals from hull-mounted echo sounders also 

were used to identify and characterize mesoscale biophysical features 

in the ocean. Higher frequency transponders are able to scatter their 

acoustic energy from zooplankton and other smaller marine life that 

are contained by eddy circulation. 

c. method for measuring the growth and retreat of seasonal sea ice along 

a longitudinal meridian (Wyllie-Echeverria, 1996): 

Data for the position of the ice edge along 169"W longitude were extracted from products of the Navy/NOAA Joint Ice Center's data base 

presenting weekly concentration and position of sea ice cover. This lon- 
154 S.A. Macklin (ed.) 

gitude was chosen because it lies over open water for the entire extent 

of the Bering and Chukchi shelves and intersects the shelf break at 

the shelf's southernmost reaches. Data were verified using weekly ice 

charts for the western Arctic provided by the Naval Polar Oceanography Center. Comparison with areal ice coverage between 160°W and 

180°W (Chapman and Walsh, 1993) revealed that the southernmost 

latitude reached by ice along 169"W is significantly correlated with icecovered shelf area (r = 0.91). This method developed by BS FOCI for 

measuring the growth and retreat of seasonal sea ice along a longitudinal meridian was also adopted for application by NMFS to evaluate 

sea ice conditions in the western Bering Sea. 

d. development of digitally recording chlorophyll absorption meters and 

an anti-fouling system to enable their long-term deployment (Davis et 

al., 1997b): 

BS FOCI has played an instrumental role in the ongoing development 

and deployment of digitally recording chlorophyll absorption meters. 

These instruments enable accurate, long-term, in situ monitoring of 

phytoplankton standing stock, and are unique in the world. Absorption data from the meters are used to calculate accurate estimates of 

chlorophyll concentration by the simple subtraction of a baseline value 

for background absorption. Time series of phytoplankton biomass coupled with hydrographic properties can then be used to validate biophysical algal growth models and investigate ecological processes on 

several time scales. BS FOCI was one of the first programs to make 

use of these meters. Peggy Bering Sea served as a test platform for 

this developing technology. The development of a simple, low-cost, 

low-toxicity antifoulant system has made it possible to collect longterm, high-quality data on in situ light absorption, even in remote 

environments such as the Bering Sea. The ability to deploy optical 

instruments for extended periods of time produces considerable savings in resources since periodic servicing of instruments may be made 

at longer intervals. First-generation optical instrumentation for the 

detection of spectral absorption and attenuation of light was included 

as part of the 1993 Peggy Bering Sea mooring. For this deployment, a 

chemical method was developed to reduce the extent of the biofouling. 

To prevent biofouling in the sample chamber of the absorption meters, 

a novel system was implemented that utilized the enclosed flow tube 

of the instruments. A perforated inner canister was filled with solid 

bromine tablets and then placed into a vented outer canister. The 

holes in the inner canister allow the slow dissolution of the bromine 

tablets into the sea water within the outer canister, with the rate of 

bromine dissolution being determined by the size of the holes. A dissolution was chosen such that a concentration of -30 parts per million 

(ppm) built up in the enclosed flow tube of the optical instrument 

within 15 min after a sampling period, a concentration about 10 times 

the minimum toxic level determined from tests on natural waters from 
BERING SEA FOCI FINAL REPORT 155 

Newport, Oregon. The sample chamber was flushed for 5 s prior to 

data collection using a Sea-Bird pump model 5T, which provided more 

than three full volume exchanges in the flow tube. This flushing insured that the bromine did not compromise absorption measurements. 

e. relationships between ADCP acoustic backscatter and zooplankton 

abundance (Cokelet et al., in preparation) : 

The Peggy Bering Sea surface mooring contained, along with other 

meteorological and oceanographic instruments, a downward-looking 

153-KHz acoustic Doppler current profiler (ADCP) to measure vertical profiles of ocean currents. The ADCP computes ocean currents by 

measuring the Doppler frequency shift of sound of a known transmitted frequency as it reflects off scatterers carried by the moving water. 

The scatterers themselves are usually zooplankton whose concentration and time-dependent behavior are valuable for biological studies. 

One BS FOCI research objective was to determine the zooplankton 

biomass from ADCP measurements. To do so involved a two-step process: determining the volume backscattering strength (Sv in dB) from 

ADCP-measured quantities and relating Sv to the zooplankton concentration. 

The volume backscattering strength at a fixed acoustic frequency is 

a physical property of the scattering medium and represents its ability 

to reflect sound. It cannot be measured directly by the ADCP. As a 

byproduct of the current measurements, the ADCP records automatic 

gain control counts that can be related to Sv via factory-specified relationships utilizing the thermally induced circuit noise to which the 

signal is referenced. This circuit noise was determined by tank-testing 

the ADCPs. Tracking the noise calibrations over time gave an indication of calibration variability and has been used to determine the 

overall error in the zooplankton biomass via a new error analysis. 

To relate the volume backscattering strength to the zooplankton biomass, BS FOCI collected zooplankton from 23 MOCNESS (Multiple 

Opening Closing Net Environmental Sampling System) hauls with up 

to nine nets each, giving a total of 111 samples. Computer software 

was developed to integrate the ADCP backscatter along the same timedepth trajectories as the net tows. Trajectory-averaged acoustic volume backscattering strength was then compared to zooplankton displacement volume which in turn was related to biomass via published 

relationships. Not all of the MOCNESS tows were near the mooring, but all tows were made from a ship with an ADCP of the same 

frequency as the mooring. Therefore, to provide the largest possible 

sample size, Sv-zooplankton comparisons were also made for the shipboard ADCP whose noise level was calibrated at sea. 

Results show that the logarithm of the zooplankton dry weight concen- 
156 S.A. Macklin (ed.) 

tration (DW mg mP3) is linearly related to the volume backscattering 

strength (r2 = 0.61). The error analysis shows that the inferred biomass is correct to within a factor of two. The variance is probably 

due to the size, orientation, and relative species composition of the 

scatterers which were dominated by copepods (Neocalanus spp., Eucalanus bungii and Metridia pacifica). Observations give zooplankton 

dry weight concentrations varying from vanishingly small at 300 m 

depth to 400 mg mP3 at 14 m during the spring bloom. Rapid behavioral changes have been observed in which the zooplankton cease 

their usual diel vertical migration from below 300 m to the surface 

and concentrate in the upper 100 m during a phytoplankton bloom. 

These quantitative, long-term time series of zooplankton biomass and 

behavior are useful for understanding the Bering Sea ecosystem. 

f. a dual-frequency hydroacoustic analytical procedure that pioneered visualization of distributions of upper-trophic-level predators and their 

prey in marine ecosystems (Napp et al., submitted): 

BS FOCI researchers collaborated with bio-acousticians from the Southwest Fisheries Science Center, La Jolla, California, to apply a dual 

frequency hydroacoustic analytical procedure to examine distribution 

patterns of predators (age-0 pollock) and prey (zooplankton) in structural fronts around the Pribilof Islands. The fronts are hypothesized to 

be important habitat for age-0 pollock in the eastern Bering Sea. The 

technique exploits the difference in volume backscattering measured at 

two acoustic frequencies, 200 and 120 kHz. A 50-km transect from a 

cruise during September 1994 near the Pribilof Islands was analyzed. 

The differencing technique (Greenlaw, 1977; Mitson et al., 1996) assumes that only two different types and sizes of organisms dominate 

the acoustic backscatter at these frequencies. Low differences indicate 

that scattering is dominated by fish; high values are interpreted to be 

primarily invertebrate zooplankton such as copepods and euphausiids, 

the main prey of juvenile fish. During daytime conditions, the upper 

layer to about 20 m is dominated by zooplankton. Juvenile fish are 

distributed at mid depth and show a preference for the thermocline. 

This could be a strategy for avoiding predators during daylight. At 

night, there is a strong upward migration by fish over the inner front 

and middle shelf, presumably to feed on the zooplankton in the upper 

layer. After the fish migrate upwards, the bottom layer is dominated 

by invertebrates. Juvenile pollock in the Gulf of Alaska have been 

shown to be night feeders. This visualization of the diel pattern in 

and around the structural front suggests how physics affects the distribution and behavior of fish and their prey through the tidal mixing 

process. When coupled with net samples and physical measurements, 

this dual-frequency technique has the potential to reveal important 

information about the ecosystem. 

g. a mitochondria1 DNA probe to discern pollock population differences 
BERING SEA FOCI FINAL REPORT 157 

between the eastern and western Bering Sea (Bailey et al., 1998): 

The genetics component of BS FOCI surveyed mitochondria1 DNA 

(mtDNA) sequence variation in pollock throughout a major portion of 

its range. A total of 512 nucleotides were examined in 45 individuals 

from populations representing the eastern and western portions of the 

Bering Sea. Fourteen haplotypes were uncovered, of which three were 

frequent enough to be of use in population differentiation. Testing of 

an additional 119 samples allowed determination of significant differences among populations within the eastern and western portions of 

the Bering Sea. A rapid restriction enzyme assay for mtDNA surveying 

of a large number of pollock from all populations allows near real-time 

analysis of genetic material from fish collected at sea, and also permits 

retrospective analysis of samples that have been preserved in alcohol. 

h. a microsatellite primer technique for pollock DNA that can discriminate sub-populations (Villa and Powers, in press): 

In order to detect distinct pollock stocks within the Bering Sea, primers 

were developed for the polymerase chain reaction that would amplify 

microsatellite loci in pollock. Working from primers developed for Atlantic cod (Brooker et al., pollock-specific primers were developed for two microsatellites. Individual fish from six sites in the eastern 

and western Bering Sea were screened. The microsatellite loci showed 

a significant difference between eastern and western fish. Analysis of 

additional samples collected northwest of the Pribilof Islands indicate 

that there may also be a distinct stock structure between northern and 

southern Bering Sea pollock. 

i. methods for analyzing chemical deposition in pollock otoliths as a 

record of the environment experienced by the larvae at various times 

during their development (Severin et al., 1995): 

The incorporation of dissolved oceanic constituents in the otoliths of 

pollock has potential as a chemical tracer for reconstructing their early 

life history. Wavelength dispersive spectrometers on an electron microscope were used to measure Na, Mg, P, S, C1, K, Ca, and Sr concentrations on the outer margins of 57 juvenile walleye pollock otoliths 

from five locations in the Gulf of Alaska and Bering Sea. Discriminant analyses that used various combinations of Na, P, K, Sr, and fish 

standard length and/or age showed that 60-80% of the samples could 

be assigned to the correct capture locality. While the concentrations 

of some of the measured elements correlated with standard length of 

age of the fish, there are measurable differences among localities when 

concentrations are length of age corrected, mainly due to differences 

in Na and K concentrations. Elemental composition of otoliths potentially could be used to assign fish from a mixed stock fishery to original 
158 S.A. Macklin (ed.) 

stocks, information that is greatly needed for the effective management 

of fish stocks. 

j. sophisticated 3D video cinematography to examine how larvae find 

patches of prey and maintain themselves in these patches (Spring 

1996): 

Two synchronized CCD cameras were used with time-lapse video 

recorders to film larvae under experimental laboratory conditions. A 

shadowgraph filming technique was used with light provided by infrared diodes. Direct Linear Translation was used to retrieve 3D coordinates from the video images. The techniques developed were successfully applied to examine larval swimming speed, path aspect and 

tortuosity in relation to the presence of food particles. 

k. a new method for live-staining protists (Lessard et al., 1996): 

A method was developed to live-stain protists with the fluorescent 

nuclear stain, DAPI, for use in tracing ingestion of protists by larval 

pollock. DAPI was shown to effectively live-stain eight species of protists and showed no toxic effects. The stain is simple to apply, easy 

to visualize in larval guts using epifluorescence microscopy, and does 

not appear to adversely affect the swimming behavior or growth rate 

of protists. With this stain, it was shown that larval walleye pollock 

are able to ingest a relatively small (60 pm) aloricate ciliate. This new 

method provides a means for visually following the ingestion of previously undetectable, but potentially important, prey in larval pollock. 

It provides a simple laboratory tool that can be used to determine 

larval pollock gut evacuation rates and functional feeding responses to 

different types and sizes of protists. Such laboratory measurements 

would help to provide the information needed to predict the importance of heterotrophic protists in the diets of pollock larvae. 

1. an antibody to protist-specific protein for an immunoassay to detect 

ingestion by pollock larvae in the field (Howell-Kubler et al., 1996): 

BS FOCI researchers used SDS-PAGE to survey the protein signatures of a large number of protists to identify a protein that would 

be protist-specific for use in the development of an immunoassay for 

ingestion of protists in pollock larvae. A 21-kD protein was found in 

all heterotrophic protists, but not photosynthetic protists, copepods, 

or pollock larvae. Antibodies to this protein have been developed and 

purified, and are now available for immunoassay development. When 

fully tested, the immunoassay will be used to detect the presence and 

quantity of protist proteins in the guts of field-caught pollock larvae. 

As protists generally do not leave visible remains after digestion, the 

immunoassay method will provide a means for detecting otherwise undetectable food items in the guts of pollock larvae and allow the determination of the prevalence of protist ingestion in wild pollock larvae. 
BERING SEA FOCI FINAL REPORT 159 

m. a simple procedure for sampling and releasing a suspension of nuclei 

from larval pollock muscle cells and for storage of the nuclei for subsequent analyses of larval condition (Theilacker et al., 1996): 

IvIuscle cell nuclei were examined by marking them with fluorescent 

dyes and submitting them to laser flow cytometry for cell cycle analysis. These methods were applied successfully to assess the nutritional 

condition of pollock larvae in field studies. 

n. techniques for determining larval pollock health by cytological examination of brain cells (Theilacker and Shen, 1993a, b): 

This method includes marking RNA and DNA from a suspension of 

brain cells with a fluorescent dye and quantifying the amounts of each 

nucleic acid using laser flow cytometry. 

o. techniques for distinguishing between Stage I and Stage I1 nauplii of 

the copepods Metridia and Pseudocalanus (Siefert, 1998): 

Food availability for pollock larvae is one of the key factors controlling larval growth and survival. To determine the role of the copepods 

Metridia and Pseudocalanus in the ecosystem and to learn specifically 

more about their role as prey of larval pollock, it is necessary to understand their life history and identify all their developmental stages. 

Because the developmental stage'of the prey changes with the ontogeny 

of the fish, recent studies have stressed the importance of identifying 

copepod nauplii of Metridia and Pseudocalanus to the lowest possible taxon. Past attempts to distinguish between the younger stages of 

these dominant taxa have been unsuccessful. Recent work by BS FOCI 

has enabled identification of the developmental stages of Metridia and 

Pseudocalanus in field samples. Stage I nauplii of Metridia pacifica, 

Stage I and I1 nauplii of Metridia lucens and the equivalent stages 

of Pseudocalanus minus were reared from eggs to find morphological 

characters for separating the genera at these stages. Differences in 

naupliar body shape and caudal armature permit the differentiation 

of Stage I and I1 Metridia from Pseudocalanus in southeastern Bering 

Sea plankton. These characters are potentially useful for distinguishing 

Metridia and Pseudocalanus nauplii from other regions, contributing 

to the understanding of their role in various ecosystems. 

p. Bering Sea and North Pacific Ocean Theme Page (http: //www . pmel . noaa. gov/bering): 

Funding from BS FOCI was used to support the creation of a Bering 

Sea and North Pacific Ocean Theme Page. The theme page provides 

pointers to information and images generated by NOAA, universities, 

and other governmental sources and other information grouped by scientific discipline. This page includes links to up-to-date satellite imagery, new research, and educational material related to the Northern 
160 S. A. Macklin (ed.) 

Pacific Ocean and the Bering Sea. Efforts included the design of the 

pages, location of resources to be included in the pages, prototyping 

of the theme page family of pages, interaction with PMEL and AFSC 

researchers to refine the page, and production of a public version of the 

page that became available in June 1997. The primary page includes 

sub-pages covering physical and biological sciences in the North Pacific; 

research, monitoring, and assessment information; a subject index; and 

a What's New section providing direct access to both new links on the 

pages and information on technical changes in the pages. With completion of the public version of the page, efforts turned to development 

of data access routines and pages to bolster data access. Routines for 

the display of drifter data and for the overlaying of biological data on 

physical oceanographic properties have been developed. The drifter 

data page allows selection of a single drifter or a set of drifters, and 

plotting of either the current location or the history of the drifter. Development of data displays for biological data has included: design of 

EPIC data formats for biological bottle data; development of routines 

to take bottle data from original database format and transform it 

into EPIC format files; routines to locate concurrent bottle and CTD 

data files; and routines to plot biological data as an overlay on a plot of 

physical data. Information is also available on user access to the theme 

page; during winter 1998 there were about 20,000 hits each month on 

the site. An up-to-date summary of access statistics is available from 

http://corona.pmel.noaa.gov/~rees/stats/bering/no_pmel. 

5.4 References 

Bailey, K.M., D. Powers, J. Quattro, G. Villa, A. Nishimura, J. Traynor, and G. 

Walters (1998): Population ecology and structural dynamics of walleye pollock, 

Theragra chalcogramma. In Dynamics of the Bering Sea, Loughlin, T.R., and 

K. Ohtani (eds.), Alaska Sea Grant Press, in press. 

Brodeur, R.D., J.M. Napp, M.T. Wilson, S. J. Bograd, E.D. Cokelet, and J.D. Schumacher (1996): Acoustic detection of mesoscale biophysical features in the Shelikof Sea valley, and their relevance to pollock larvae in the Gulf of Alaska. Fish. 

Oceanogr., 5 (Suppl. I), 71-80. 

Brooker, A.L., D. Cook, P. Bentzen, J.M. Wright, and R.W. Doyle (1994): Organization of microsatellites differ between mammals and cold-water teleost fishes. 

Can. J. Fish. Aquat. Sci., 51, 1959-1966. 

Chapman, W.L., and J.E. Walsh (1993): Recent variations of sea ice and air temperature in high latitudes. Bull. Am. Meteorol. Soc., 74, 33-47. 

Cokelet, E.D., J.M. Napp, and D.M. Dougherty: Acoustic Doppler current profiler backscatter calibration for Bering Sea zooplankton. ICES J. Mar. Sci., in 

preparation. 

Cokelet, E.D., M.L. Schall, and D. Dougherty (1996): ADCP-referenced geostrophic 

circulation in the Bering Sea basin. J. Phys. Oceanogr., 26, 1113-1128. 

Cokelet, E.D., and P. J. Stabeno (1997): Mooring observations of the thermal structure, salinity and currents in the SE Bering Sea basin. J. Geophys. Res., 102, 

22,947-22,964. 

Davis, R.F., G. Lazin, J. Bartlett, A. Ciotti, and P. Stabeno (1997a): Remote 

sensing of a pigment patch in the southeastern Bering Sea. In Ocean Optics 

XIII, Proc. Soc. Photo-Opt. Instrum. Eng., 2963, 654-657. 
BERING SEA FOCI FINAL REPORT 161 

Davis, R.F., C.C. Moore, J.R.V. Zaneveld, and J.M. Napp (1997b): Reducing the 

effects of fouling on chlorophyll estimates derived from long-term deployment 

of optical instruments. J. Geophys. Res., 102, 5851-5856. 

Francis, R.C., R. Merrick, K. Aydin, and S.M. Bollens (1998): Modeling and management of the Bering Sea ecosystem. In The Bering Sea: Physical, Chemical 

and Biological Dynamics Loughlin, T.R., and K. Ohtani (eds.), University of 

Alaska Sea Grant Press, in press. 

Greenlaw, C.F. (1979): Acoustical estimation of zooplankton populations. Limnol. 

Oceanogr., 24, 226-242. 

Howell-Kubler, A.N., E.J. Lessard, and J.M. Napp (1996): Springtime protozoan 

abundance and biomass in the southeastern Bering Sea and Shelikof Strait, 

Alaska: Its [sic] potential role as prey for planktivorous fish larvae. J. Plankton 

Res., 18, 731-745. 

Lessard, E.J., M.P. Martin, and D.J.S. Montagnes (1996): A new method for livestaining protozoa with DAPI for use as a tracer of ingestion by walleye pollock 

(Theragra chalcogramma) larvae. Mar. Ecol. Prog. Ser., 204, 43-57. 

Liu, A.K., C.Y. Peng, and S.Y.-S. Chang (1997): Wavelet analysis of satellite images 

for Coastal Watch. IEEE J. Oceanic Eng., 22(1), 9-17. 

Liu, A.K., C.Y. Peng, and J.D. Schumacher (1994): Wave-current interaction study 

in the Gulf of Alaska for detection of eddies by SAR. J. Geophys. Res., 99, 

10,075-10,085. 

Mitson, R.B., Y. Simard, and C. Goss (1996): Use of a two-frequency algorithm 

to determine size and abundance of plankton in three widely spaced locations. 

ICES J. Mar. Sci., 53, 209-215. 

Napp, J. M., R.D. Brodeur, D. Demer, R. Hewitt, J.D. Schumacher, P.J. Stabeno, 

and G.L. Hunt, Jr.: Acoustic determination of zooplankton and nekton distributions at tidally generated shelf fronts in the eastern Bering Sea. Mar. Ecol. 

Prog. Ser., submitted. 

Overland, J.E., M.C. Spillane, H.E. Hurlburt, and A.J. Wallcraft (1994): A numerical study of the circulation of the Bering Sea basin and exchange with the 

North Pacific Ocean. J. Phys. Oceanogr., 24, 736-758. 

Reed, R.K., and P.J. Stabeno: The Aleutian North Slope Current. In Physical 

Characteristics of the Bering Sea. In Dynamics of the Bering, Loughlin, T.R., 

and K. Ohtani (eds.), Alaska Sea Grant Press, in press. 

Severin, K.P., J. Carroll, and B.L. Norcross (1995): Electron microprobe analysis of 

juvenile walleye pollock, Theragra chalcogramma, otoliths from Alaska: A pilot 

stock separation study. Env. Biol. Fish., 43, 269-283. 

Siefert, D.L.W. (1998): Distinguishing between Stage I and Stage I1 nauplii of the 

copepods Metridia and Pseudocalanus from the Bering Sea. J. Plankton Res., 

20, 1061-1072. 

Spring, S. (1996): Swimming behavior of walleye pollock larvae Theragra chalcogramma in relation to zooplankton. Master of Science Thesis, University of 

Washington, Seattle. 

Stabeno, P.J., J.J. Cullen, R.F. Davis, and R. Leben: Dynamics and productivity 

of an eddy in the southeastern Bering Sea. J. Geophys. Res., in preparation. 

Stabeno, P.J., and R.K. Reed (1994): Circulation in the Bering Sea basin observed 

by satellite-tracked drifters: 1986-1993. J. Phys. Oceanogr., 24, 848-854. 

Theilacker, G.H., and W. Shen (1993a): Calibrating starvation-induced stress in 

larval fish using flow cytometry. Am. Fish. Soc. Symp., 14, 85-94. 

Theilacker, G.H., and W. Shen (1993b): Fish larval condition analyzed using flow 

cytometry. In Physiological and Biochemical Aspects of Fish Development, 

Walther, B.T., and H.J. Fyhn (eds.), Norway: University of Bergen, 346-355. 

Theilacker, G.H., K.M. Bailey, M.F. Canino, and S.M. Porter (1996): Variations in 
162 S.A. Macklin (ed.) 

larval walleye pollock feeding and condition: A synthesis. Fish. Oceanogr., 5, 

112-123. 

Villa, G.W., and D.A. Powers: Stock structure of walleye pollock, Theragra chalcogramma, in the Bering Sea region based on nuclear microsatellites. Env. Biol. 

Fish, in press. 

Wyllie-Echeverria, T. (1996): The relationship between the distribution of one-yearold pollock and sea ice characteristics. In Ecology of Juvenile Walleye Pollock, 

Theragra chalcogramma. NOAA Tech. Report., NMFS 126, 47-56. 
BERING SEA FOCI FINAL REPORT 163 

Part 6 

Bering Sea FOCI Publication List 

Bailey, K.M., 1997: Structural ecology of marine flatfish populations. J. Sea Res., 

37, 269-280. 

Bailey, K.M., W.S. Grant, T. Quinn, and P. Bentzen: Population ecology of walleye 

pollock. Advances in Marine Biology, submitted. 

Bailey, K.M., D. Powers, J. Quattro, G. Villa, A. Nishimura, J. Traynor, and G. 

Walters: Population ecology and structural dynamics of walleye pollock, Theragra chalcogramma. In: The Bering Sea: Physical, Chemical and Biological 

Dynamics, T.R. Loughlin and K. Ohtani (eds.), University of Alaska Sea Grant, 

Fairbanks, Alaska 99775, in press. 

Bailey, K.M., P. Stabeno, and D. Powers, 1997: The role of larval retention and 

transport features in mortality and gene flow of walleye pollock, Theragra 

chalcogramma. J. Fish Biol., 51, 135-154. 

Bollens, S.M., B.W. Frost, H.R. Schwaninger, C.S. Davis, K.J. Way, and M.C. 

Landsteiner, 1992: Seasonal plankton cycles in a temperate fjord, and comments 

on the match-mismatch hypothesis. J. Plankton Res., 14, 1279-1305. 

Bond, N.A., J.E. Overland, and P. Turet, 1994: Spatial and temporal characteristics 

of the wind forcing of the Bering Sea. J. Clim., 7, 1119-1130. 

Brodeur, R.D. 1998: In situ observations of the association between juvenile fishes 

and scyphomedusae in the Bering Sea. Mar. Ecol. Prog. Ser., 163, 11-20. 

Brodeur, R.D., M.T. Wilson, and L. Ciannelli: Spatial and temporal variability in 

feeding and condition of age-0 walleye pollock in frontal regions of the Bering 

Sea. ICES J. Mar. Sci., in press. 

Brodeur, R.D., M.T. Wilson, J.M. Napp, P.J. Stabeno, and S. Salo, 1997: Distribution of juvenile pollock relative to frontal structure near the Pribilof Islands, 

Bering Sea. Proc. Int. Symp. on the Role of Forage Fishes in Marine Ecosystems, Alaska Sea Grant AK-97-01, 573-589. 

Brodeur, R.D., M.T. Wilson, G.E. Walters, and I. Melnikov: Forage fishes in the 

Bering Sea: Distribution, species associations, and biomass trends. In: The 

Bering Sea: Physical, Chemical and Biological Dynamics, T.R. Loughlin and 

K. Ohtani (eds.), University of Alaska Sea Grant, Fairbanks, Alaska 99775, in 

press. 

Cokelet, E.D., M.L. Schall, and D. Dougherty, 1996: ADCP-referenced geostrophic 

circulation in the Bering Sea basin. J. Phys. Oceanogr., 26(7), 1113-1128. 

Cokelet, E.D., and P.J. Stabeno, 1997: Mooring observations of the thermal structure, salinity and currents in the SE Bering Sea basin. J. Geophys. Res., 102, 

22,947-22,964. 

Cullen, J.J., A.M. Ciotti, F. Davis, and M.R. Lewis, 1997: Optical detection and 

assessment of algal blooms. Limnol. Oceanogr., 42(5, part 2), 1223-1239. 

Davis, R.F., J.J. Cullen, and A.M. Ciotti, Ocean color of the southeastern Bering 

Sea: Remotely sensed and in situ results. Inter. J. Rem. Sens., in preparation. 

Davis, R.F., G. Lazin, J. Bartlett, A Ciotti, and P. Stabeno, 1997: Remote sensing 

of a pigment patch in the southeastern Bering Sea. In: Ocean Optics XIII, 

Proc. Soc. Photo-Opt. Instmm. Eng., 2963, 654-657. 

Davis, R.F., C.C. Moore, J.R.V. Zaneveld, and J.M. Napp: Reducing the effects of 

fouling on chlorophyll estimates derived from long-term deployment of optical 

instruments. J. Geophys. Res., in press. 

Francis, R.C., R. Merrick, K. Aydin, and S.M. Bollens: Modeling and management 

of the Bering Sea ecosystem. In: The Bering Sea: Physical, Chemical and 
164 S.A. Macklin (ed.) 

Biological Dynamics, T.R. Loughlin and K. Ohtani (eds.), University of Alaska 

Sea Grant, Fairbanks, Alaska 99775, in press. 

Hillgruber, N., L.J. Haldorson, and A.J. Paul, 1995: Feeding selectivity of larval 

walleye pollock Theragra chalcogramma in the oceanic domain of the Bering 

Sea. Mar. Ecol., 120, 1-10. 

Howell-Kubler, A.N., E. J. Lessard, and J.M. Napp, 1996: Springtime protozoan 

abundance and biomass in the southeastern Bering Sea and Shelikof Strait, 

Alaska: Its [sic] potential role as prey for planktivorous fish larvae. J. Plankton 

Res., 18, 731-745. 

Kendall, A.W., Jr.: Fisheries Oceanography Coordinated Investigations (FOCI) in 

the Bering Sea. Presented at: Comparisons between the Oyashio Region and 

the Bering Sea Ecosystems, Hokkaido University, January 1998. Mem. Fac. 

Fish. Hokkaido University, in press. 

Lang, G.M., R.D. Brodeur, J.M. Napp, and R. Schabetsberger: Variation in groundfish predation on juvenile walleye pollock relative to hydrographic structure near 

the Pribilof Islands, Alaska. ICES J. Mar. Sci., in press. 

Lazin, G., R.F. Davis, A.M. Ciotti, and M.R. Lewis, 1997: Ocean color measurements from low flying aircraft: Atmospheric and surface glint correction. In: 

Ocean Optics XIII, Proc. Soc. Photo-Opt. Instrum. Eng., 2963, 703-707. 

Lessard, E.J., M.P. Martin, and D.J.S. Montagnes, 1996: A new method for livestaining protozoa with DAPI for use as a tracer of ingestion by walleye pollock 

(Theragra chalcogramma) larvae. Mar. Ecol. Prog. Ser., 204, 43-57. 

Liu, A.K., C.Y. Peng, and S.Y.-S. Chang, 1997: Wavelet analysis of satellite images 

for coastal watch. IEEE J. Oceanic Eng., 22, 9-17. 

Luchin, V.A., V.A. Menovschikov, V.M. Lavrientiev, and R.K. Reed: Thermohaline 

structure and water masses in the Bering Sea. In: The Bering Sea: Physical, 

Chemical and Biological Dynamics, T.R. Loughlin and K. Ohtani (eds.), University of Alaska Sea Grant, Fairbanks, Alaska 99775, in press. 

Macklin, S.A.: Bering Sea FOCI. In: The Bering Sea: Physical, Chemical and 

Biological Dynamics, T.R. Loughlin and K. Ohtani (eds.), University of Alaska 

Sea Grant, Fairbanks, Alaska 99775, in press. 

Megrey, B.A., 1991: Pollock recruitment and reproduction. In: Discussion Summaries from the International Workshop on Bering Sea Pollock Stock Assessment; J.E. Pearce (compiler), AFSC Processed Report 91-06, NOAA/NMFS, 

Seattle, WA 98115, 53 pp. 

Napp, J. M., R.D. Brodeur, D. Demer, R. Hewitt, J.D. Schumacher, P.J. Stabeno, 

and G.L. Hunt, Jr.: Acoustic determination of zooplankton and nekton distributions at tidally generated shelf fronts in the eastern Bering Sea. Mar. Ecol. 

Prog. Ser., submitted. 

Napp, J. M., A.W. Kendall, Jr., and J.D. Schumacher: Biophysical processes relevant to recruitment dynamics of walleye pollock (Theragra chalcogramma) in 

the eastern Bering Sea. Fish. Oceanogr., submitted. 

Napp, J.M., K. Mier, and M.K. Cohen: Estimation of larval fish prey volume: 

Mensuration formulae for copepod nauplii. J. Plankton Res., submitted. 

Overland, J.E., and L.H. Kantha: Mixing and stratification on the Bering Sea shelf. 

J. Geophys. Res., submitted. 

Overland, J.E., M.C. Spillane, H.E. Hurlburt, and A. J. Wallcraft, 1994: A numerical 

study of the circulation of the Bering Sea basin and exchange with the North 

Pacific Ocean. J. Phys. Oceanogr., 24, 736-758. 

Overland, J.E., P.J. Stabeno, and S.A. Salo, 1996: Direct evidence for northward 

flow on the northwestern Bering Sea shelf. J. Geophys. Res., 101, 8971-8976. 

Paul, A.J., J.M. Paul, and K.O. Coyle, 1996: Abundance and taxa composition of 

copepod nauplii over southeastern Bering Sea deep water spawning grounds of 

walleye pollock, Theragra chalcogramma. Crustaceans, 69, 494-508. 
BERING SEA FOCI FINAL REPORT 165 

Pinchuk, A.I., 1997: Early life history of Metridia pacifica Brodsky (Copepoda: 

Calanoida) from the southeastern Bering Sea and Gulf of Alaska. M.S. Thesis, 

University of Alaska Fairbanks, 65 pp. 

Pinchuk, A.I., 1997: Naupliar development of Metridia pacifica Brodsky, 150 (Copepoda: Calanoida) reared in the laboratory. J. Crustacean Biol., 17, 343-351. 

Pinchuk, A.I., and A. J. Paul (1998): Growth of Metridia pacifica (Copepoda:calanoida) 

nauplii in the laboratory. Plankton Biol. Ecol., 45(2) (in press). 

Reed, R.K., 1995: On geostrophic reference levels in the Bering Sea basin. J. 

Oceanogr., 51, 489-498. 

Reed, R.K., 1995: On the variable subsurface environment of fish stocks in the 

Bering Sea. Fish. Oceanogr., 4, 317-323. 

Reed, R.K., 1995: Water properties over the Bering Sea shelf: Climatology and 

variations. NOAA Tech. Report ERL 452-PMEL 42, 15 pp. 

Reed, R.K.: Confirmation of a convoluted flow over the southeastern Bering Sea 

shelf. Cont. Shelf Res., in press. 

Reed, R.K., G.V. Khen, P.J. Stabeno, and A.V. Verkhunov, 1993: Water properties 

and flow over the deep Bering Sea basin, summer 1991. Deep-sea Res., 40, 

2325-2334. 

Reed, R.K., J.D. Schumacher, C.H. Pease, P.J. Stabeno, A.W. Kendall, Jr., and 

P. Dell'Arciprete, 1994: Bering Sea circulation explored. Eos Trans. AGU, 75, 

342. 

Reed, R.K., and P.J. Stabeno, 1993: The recent return of the Alaskan Stream to 

Near Strait. J. Mar. Res., 51, 515-527. 

Reed, R.K., and P.J. Stabeno, 1994: Flow along and across the Aleutian ridge. J. 

Mar. Res., 52, 639-648. 

Reed, R.K., and P. J. Stabeno, 1996: On the climatological mean circulation over 

the eastern Bering Sea shelf. Cont. Shelf Res., 16, 1297-1305. 

Reed, R.K., and P.J. Stabeno, 1997: Long-term measurements of flow near the 

Aleutian Islands. J. Mar. Res., 55, 565-575. 

Reed, R.K., and P.J. Stabeno: The Aleutian North Slope Current. In: The Bering 

Sea: Physical, Chemical and Biological Dynamics, T.R. Loughlin and K. Ohtani 

(eds.), University of Alaska Sea Grant, Fairbanks, Alaska 99775, in press. 

Reed, R.K., A.V. Verkhunov, G.V. Khen, E.D. Cokelet, J.E. Overland, and T.E. 

Whitledge, 1992: Recent U.S.-U.S.S.R. cruise in Bering Sea. Eos Trans. AGU, 

73, 16, p. 184. 

Roach, A.T., K. Aagaard, C.H. Pease, S.A. Salo, T. Weingartner, M. Kulakov, 

and V. Pavlov, 1995: Direct measurements of transport and water properties 

through Bering Strait. J. Geophys. Res., 100, 18,443-18,457. 

Royer, T.C., and P.J. Stabeno: Polar Ocean Boundaries. The Sea, Vol. 10, in press. 

Schumacher, J. D., and V. Alexander: Variability and role of the physical environment in the Bering Sea ecosystem. In: The Bering Sea: Physical, Chemical and 

Biological Dynamics, T.R. Loughlin and K. Ohtani (eds.), University of Alaska 

Sea Grant, Fairbanks, Alaska 99775, in press. 

Schumacher, J.D., and R.K. Reed, 1992: Characteristics of currents over the continental slope of the eastern Bering Sea. J. Geophys. Res., 97, 9423-9433. 

Schumacher, J.D., and P.J. Stabeno, 1994: Ubiquitous eddies of the eastern Bering 

Sea and their coincidence with concentrations of larval pollock. Fish. Oceanogr., 

3, 182-190. 

Schumacher, J.D., and P.J. Stabeno: The continental shelf of the Bering Sea. The 

Sea, Vol. 10, in press. 

Schumacher, J.D., P.J. Stabeno, N.A. Bond, and J.M. Napp, 1998: Ecosystem 

anomalies in the eastern Bering Sea during 1997. NPAFC Workshop, in press. 

Severin, K.P., J. Carroll, and B.L. Norcross, 1995: Electron microprobe analysis of 
166 S.A. Macklin (ed.) 

juvenile walleye pollock, Theragra chalcogramma, otoliths from Alaska: A pilot 

stock separation study. Env. Biol. Fish., 43, 269-283. 

Siefert, D.L.W., 1998: Distinguishing between stage I and stage I1 nauplii of the 

copepods Metridia and Pseudocalanus from the Bering Sea. J. Plankton Res., 

20, 1061-1072. 

Spring, S., 1997: Swimming behavior of walleye pollock larvae Theragra chalcogramma in relation to food. M.S. Thesis, University of Washington, Seattle, 

Washington 98195, 123 pp. 

Stabeno, P.J., J. Napp, and R. Reed: Magnitude and time scales of inflow through 

Unimak Pass, Alaska. Geophys. Res. Lett., in preparation. 

Stabeno, P.J., and R.K. Reed, 1992: A major circulation anomaly in the western 

Bering Sea. Geophys. Res. Lett., 19, 1671-1674. 

Stabeno, P.J., and R.K. Reed, 1994: Circulation in the Bering Sea basin observed 

by satellite-tracked drifters: 1986-1993. J. Phys. Oceanogr., 24, 848-854. 

Stabeno, P.J., and R.K. Reed: Drifters on the Bering Sea shelf: Kinematics and 

diffusivity. J. Phys. Oceanogr., in preparation. 

Stabeno, P.J., R.K. Reed, and J.E. Overland, 1994: Lagrangian measurements in 

the Kamchatka Current and Oyashio. J. Oceanogr., 50, 653-662. 

Stabeno, P.J., J.D. Schumacher, R.F. Davis, and J.M. Napp, 1998: Under-ice observations of water column temperature, salinity and spring phytoplankton dynamics: Eastern Bering Sea shelf, 1995. J. Mar. Res., 56, 239-255. 

Stabeno, P. J., J.D. Schumacher, and K. Ohtani: Overview of the Bering Sea. In: 

The Bering Sea: Physical, Chemical and Biological Dynamics, T.R. Loughlin 

and K. Ohtani (eds.), University of Alaska Sea Grant, Fairbanks, Alaska 99775, 

in press. 

Stabeno, P.J., J.D. Schumacher, S.A. Salo, G.L. Hunt, and M. Flint: The physical 

environment around the Pribilof Islands. In: The Bering Sea: Physical, Chemical and Biological Dynamics, T.R. Loughlin and K. Ohtani (eds.), University 

of Alaska Sea Grant, Fairbanks, Alaska 99775, in press. 

Sugisaki, H., R. Brodeur, and J. Napp: Summer distribution and abundance of 

macrozooplankton in the western Gulf of Alaska and the Bering Sea. Proceedings of Comparison Between the Oyashio Region and Bering Sea Ecosystem 

Symposium, submitted. 

Swartzman, G., R. Brodeur, J. Napp, D. Walsh, R. Hewitt, D. Demer, G. Hunt, 

and E. Logerwell: Relating predator and prey spatial distributions in the Bering 

Sea using acoustic backscatter data. Can. J. Fish. Aquat. Sci., in press. 

U.S. GLOBEC, 1996: Report on climate change and carrying capacity planning 

meeting. (A.B. Hollowed, ed.; Contributions by R. Brodeur, N. Bond, E.D. 

Cokelet, A. Hermann, B. Megrey, J. Napp, J. Overland, R. Reed, J. Schumacher, 

P. Stabeno, et al.). U.S. GLOBEC Rep. 15, University of California, Berkeley. 

Vance, T., and S.A. Macklin, 1998: What the heck is a coccolithophore? Alaska 

Fisherman's Journal, 21(3), 36-37. 

Van Meurs, P., and P. Stabeno: Evidence for episodic on-shelf flow. J. Geophys. 

Res., in press. 

Villa, G.W., and D.A. Powers: Stock structure of walleye pollock, Theragra chalcogramma, in the Bering Sea region based on nuclear microsatellites. Env. Biol. 

Fish., in press. 

Wyllie Echeverria, T., 1995: Sea-ice conditions and the distribution of walleye 

pollock (Theragra chalcogramma) on the Bering and Chukchi Sea Shelf. Can. 

Spec. Pub. Fish. Aquat. Sci., 121, 131-136. 

Wyllie Echeverria, T., 1996: The relationship between the distribution of one year 

old pollock and sea ice characteristics. NOAA Tech. Report, NOAA NMFS-126, 

47-56. 
BERING SEA FOCI FINAL REPORT 167 

Wyllie-Echeverria, T.: Remotely sensed seasonal sea ice and oceanology of the 

Bering Sea. In: Satellite Sensing of the North Pacific Ocean, Earth, Ocean and 

Space Pty. Ltd., Sydney, Australia, in press. 

Wyllie-Echeverria, T., and K. Ohtani: Seasonal sea ice variability in the Bering Sea 

ecosystem. In: The Bering Sea: Physical, Chemical and Biological Dynamics, 

T.R. Loughlin and K. Ohtani (eds.), University of Alaska Sea Grant, Fairbanks, 

Alaska 99775, in press. 

Wyllie-Echeverria, T. and W.S. Wooster: Sea ice as an indicator of interannual and 

decadal climatic variability in the Bering Sea ecosystem. Fish. Oceanogr., in 

press. 
OTHER TITLES IN THE 

DECISION ANALYSIS SERIES 

No. 1. Able, Kenneth W. and Susan C. Kaiser. 1994. Synthesis of Summer Flounder Habitat 

Parameters. 

No. 2. Matthews, Geoffrey A. and Thomas J. Minello. 1994. Technology and Success in Restoration, Creation and Enhancement of Spartina Alterniflora Marshes in the United States. 2 vols. 

No. 3. Collins, Elaine V., Maureen Woods, Isobel Sheifer, and Janice Beattie. 1994. Bibliography 

of Synthesis Documents on Selected Coastal Topics. 

No. 4. Hinga, Kenneth R., Heeseon Jeon, and Noelle F. Lewis. 1995. Marine Eutrophication 

Review. 

No. 5. Lipton, Douglas W., Katherine Wellman, Isobel C. Sheifer, and Rodney F. Weiher. 1995. 

Economic Valuation of Natural Resources: A Handbook for Coastal Policymakers. 

No. 6. Vestal, Barbara, Alison Reiser, et al. 1995. Methodologies and Mechanisms for Management 

of Cumulative Coastal Environmental Impacts. Part I - Synthesis with Annotated Bibliography, 

Part I1 - Development and Application of a Cumulative Impacts Assessment Protocol. 

No. 7. Murphy, Michael L. 1995. Forestry Impacts on Freshwater Habitat of Anadromous 

Salmonids in the Pacific Northwest and Alaska - Requirements for Protection and Restoration. 

No. 8. William F. Kier Associates. 1995. Watershed Restoration - A Guide for Citizen Involvement in California. 

No. 9. Valigura, Richard A., Winston T. Luke, Richard S. Artz, and Bruce B. Hicks. 1996. 

Atmospheric Nutrient Inputs to Coastal Areas - Reducing the Uncertainties. 

No. 10. Boesch, Donald F., et al. 1997. Harmful Algal Blooms in Coastal Waters: Options for 

Prevention, Control and Mitigation. 

No. 11. McMurray, Gregory R., and Robert J. Bailey, editors. 1998. Change in Pacific Northwest 

Coastal Ecosystems. 

No. 12. Fonseca, Mark S., W. Judson Kenworthy, and Gordon W. Thayer. 1998. Guidelines for 

the Conservation and Restoration of Seagrasses in the United States and Adjacent Waters. 
US Department of Commerce 

National Oceanic and Atmospheric Administration 

Pacific Marine Environmental Laboratory 

7600 Sand Point Way NE 

Seattle, WA 98115