NOAA Technical Memorandum NMFS-AFSC-93

U.S. DEPARTMENT OF COMMERCE

National Oceanic and Atmospheric Administration

National Marine Fisheries Service

Alaska Fisheries Science Center

August 1998

by

J. M. Murphy, N. E. Maloney, and B. L. Wing

Distribution and Abundance of

Zooplankton in the North Pacific

Subarctic Frontal Zone and

Adjacent Water Masses
NOAA Technical Memorandum NMFS

The National Marine Fisheries Service’s Alaska Fisheries Science Center uses

the NOAA Technical Memorandum series to issue informal scientific and

technical publications when complete formal review and editorial processing

are not appropriate or feasible. Documents within this series reflect sound

professional work and may be referenced in the formal scientific and technical

literature.

The NMFS-AFSC Technical Memorandum series of the Alaska Fisheries

Science Center continues the NMFS-F/NWC series established in 1970 by the

Northwest Fisheries Center. The new NMFS-NWFSC series will be used by

the Northwest Fisheries Science Center.

This document should be cited as follows:

Murphy, J. M., N. E. Maloney, and B. W. Wing. 1998. Distribution and

abundance of zooplankton in the North Pacific Subarctic Frontal Zone

and adjacent water masses. U. S. Dep. Commer., NOAA Tech. Memo.

NMFS-AFSC-93,31 p.

Reference in this document to trade names does not imply endorsement by

the National Marine Fisheries Service, NOAA.
August 1998

NOAA Technical Memorandum NMFS-AFSC-93

by

J. M. Murphy, N. E. Maloney, and B. L. Wing

Distribution and Abundance of

Zooplankton in the North Pacific

Subarctic Frontal Zone and

Adjacent Water Masses

Auke Bay Laboratory

Alaska Fisheries Science Center

11305 Glacier Highway

Juneau, AK 99801-8626

U.S. DEPARTMENT OF COMMERCE

William M. Daley, Secretary

National Oceanic and Atmospheric Administration

D. James Baker, Under Secretary and Administrator

National Marine Fisheries Service

Rolland A. Schmitten, Assistant Administrator for Fisheries
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111

ABSTRACT

Zooplankton was collected from two depth strata (0-75 m and 75-150 m) with

oblique tows of a Tucker trawl at 40 stations across the Subarctic Frontal Zone of the

North Pacific Ocean and adjacent water masses in October and November 1989. Thirteen

taxonomic groups were identified, and their vertical and spatial distributions were

compared and summarized by three water-mass types: 1) Subarctic Domain (SD), 2)

Subarctic Frontal Zone (SAFZ), and 3) Transition Zone (TZ). Chaetognaths and mysids

were the only taxa that were more abundant in the deeper stratum, primarily due to the

overlapping distributions of the two predominant chaetognath species, Sagitta elegans and

Eukrohnia hamata, and the abundant deeper-dwelling mysid Euchaetomeropsis merolepis

in our samples. Abundances of the predominant taxa (gastropods, polychaetes, ostracods,

copepods, amphipods, euphausiids, and chaetognaths) were highest in the SD. Cirripede

larvae, decapod shrimp larvae, fish eggs, and squid larvae were most abundant in the

SAFZ. Fish larvae and mysids were most abundant in the TZ. Mysids were found only

in the SAFZ and the TZ. Overall, the most significant change in the zooplankton

community occurred between the SD and the SAFZ.

V

CONTENTS

INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

METHODS ................................................... 1

Zooplankton Collection and Sample Processing ...................... 1

Statistical Methods ......................................... 2

RESULTS .................................................... 3

Oceanographic Regions ...................................... 3

Dawn and Evening Effects .................................... 3

Vertical Distribution ........................................ 3

Distribution by Oceanographic Region ............................ 3

Community Ordination ...................................... 4

DISCUSSION .................................................

5

Vertical Distribution ........................................ 5

Distribution by Oceanographic Region ............................ 6

ACKNOWLEDGMENTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

CITATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

TABLES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

FIGURES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

APPENDICES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

INTRODUCTION

Zooplankton is an important food source in the pelagic ecosystem of the North

Pacific Ocean and is the basis for seasonal feeding migrations of many pelagic nekton

species (Shimazaki 1986). Hence, those who interpret the zoogeography and migratory

strategies of predators at higher trophic levels need to understand the distribution and

abundance patterns of zooplankton. Because distribution and abundance of zooplankton

are often linked to primary production and mixing dynamics associated with different

water-mass types (McGowan and Williams 1973, Miller et al. 1991), zooplankton can be

an important link between water-mass type and zoogeography of pelagic nekton.

The Subarctic Frontal Zone (SAFZ)-a large-scale, semipermanent frontal region

separating the Subarctic Domain (SD) and the Transition Zone (TZ) (Fig. 1)-is the

primary zoogeographic feature of the subarctic North Pacific Ocean. The SD is identified

by its permanent halocline, which forms as a result of precipitation exceeding evaporation.

The SD is typically bounded by the 33.0 and 33.8 isohalines (Roden and Robinson 1988).

The SAFZ delineates the southern limit of the subarctic water mass and is identified by

the surfacing of the permanent halocline (Roden and Robinson 1988).

In this paper we examine zooplankton community structure in the SAFZ and

adjacent water masses and quantify differences in these zooplankton communities.

METHODS

Zooplankton Collection and Sample Processing

Zooplankton was collected from 40 stations with a 0.5-mm mesh, l-m2 messengertripped Tucker trawl (Davies and Barham 1969) aboard the NOAA ship Miller Freeman

along five meridional transects during October and November 1989 (Fig. 2). The Tucker

trawl was equipped with General Oceanics Model 2030 flowmeters and a Benthos Model

1170-E bathykymograph. Before each trawl, salinity and temperature profiles were taken

to 1,000 m with a Seabird Model 19 SEACAT mini-CTD (Wing et al. 1993).

Line speeds were set at 45-50 m min-1 during deployment and 30-35 m min-1

during retrieval. Wire angles were monitored with an inclinometer, and vessel speed

(approximately 1.5 knots) was adjusted to maintain a 45° wire angle during retrieval.

Trawl samples were collected during the twilight periods after sunset (between

1930 and 2130 hours) and around sunrise (between 0500 and 0830 hours). Full-daylight

hours were devoted to visual census of marine mammals and seabirds and to hydroacoustic

surveys of the deep-scattering layer. Evening samples were collected as the acoustic

scattering layer was rising, but before it started to disperse. Morning samples were

collected as the scattering layer began its descent and before there was light enough for a

visual census of birds and mammals.

Three zooplankton samples were collected during each trawl deployment. The first

sample was taken during the descent of the trawl to 150 m, the second during the upward

oblique tow between 150 m and 75 m, and the third during the upward oblique tow

between 75 m and the surface. Volumes filtered for the stratified samples ranged from

200 to over 700 m3. We chose the 0-75 m (shallow) and 75-150 m (deep) strata to most
2

effectively sample acoustic scattering layers observed during the cruise. Appendix 1

summarizes the station information.

Samples were preserved in 4% formaldehyde solution buffered with sodium

tetraborate and transferred to alcohol after shipment to the Auke Bay Laboratory near

Juneau, Alaska. All samples were scanned for large or rare specimens such as squid

larvae, fish eggs, and fish larvae. Small samples were counted in entirety, and larger

samples were split with a Folsom plankton splitter (McEwen et al. 1954). The fraction

examined ranged from 0.12 to 1.0. All samples were processed, but only samples from

the 0-75 m and 75-150 m strata were included in this analysis. Thirteen taxa were

identified and counted: gastropods, squid larvae, polychaetes, ostracods, copepods,

cirripede larvae, amphipods, mysids, euphausiids, decapod shrimp larvae, chaetognaths,

fish eggs, and fish larvae (Appendix 2). Gelatinous zooplankton species (e.g., medusa,

siphonophores, ctenophores, heteropods, doliolids, salps, larvaceans) were not counted, due

to their colonial nature and their tendency for fragmentation, but were included in the

measurements of displacement volume for each sample. Appendix 3 contains qualitative

abundance levels of gelatinous zooplankton species.

Statistical Methods

Wilcoxon rank sum tests (Lehmann 1975) were used to test for significant

differences’ between dawn and evening abundance at each depth stratum, and paired

Wilcoxon rank sum tests were used to test whether zooplankton abundances differed

significantly between the shallow and deep samples.

Average abundances and coefficients of variation for the 13 taxa were computed

for each oceanographic region. To test for significant differences between oceanographic

regions, a Kruskal-Wallis rank sum test (Lehmann 1975) was used. The Kruskal test was

selected because of its ability to test for significant differences between multiple groups of

data.

We computed coordinates for both species and station ordinations of the

zooplankton community using principal component analysis (PCA). In species ordination,

a sample is placed into a hyperspace with a dimension for each species. This hyperspace

is then rotated to find projections (components) that result in the least amount of spread

(variability) in the data. In PCA, this is accomplished by partitioning a resemblance

matrix into a set of orthogonal linear axes (components) that explain the greatest amount

of variability (Pielou 1984, Ludwig and Reynolds 1988). We refer to the direction and

magnitude each axis is rotated in species hyperspace as the loading of the species, and the

rotation of an axis in station hyperspace as the scale (Statistical Sciences 1995). The

principal components were computed using a correlation matrix, and all computations were

completed in the S-plus statistical language (Statistical Sciences 1995).

1

p < 0.05, throughout this paper.
3

RESULTS

Oceanographic Regions

An obvious subsurface horizontal front was present in all transects and formed as

the permanent halocline began to surface (Fig. 3); however, the latitude where the

permanent halocline reached the surface depended on the strength of the seasonal halocline

and mesoscale frontal dynamics of the mixed layer. Stations with a permanent halocline

were clearly cooler and less saline at 75 m depth than stations lacking a permanent

halocline (Fig. 4). This temperature and salinity property was used to separate the SD

stations from the SAFZ stations.

Unlike Lynn (1986), we did not find an obvious gradient in the physical properties

associated with the southern limit of the SAFZ. Lacking this gradient, we used the 33.8

(Practical Salinity Scale) isohaline to separate the SAFZ stations from the TZ stations.

Dawn and Evening Effects

No taxon differed significantly in abundance between dawn and evening samples

(Table 1A). Hence, we pooled the data from the two periods in the subsequent analysis.

Vertical Distribution

All zooplankton taxa except chaetognaths and mysids were more abundant in the

shallow stratum (Table 1B). However, not all taxa differed significantly. Abundances of

polychaetes (Polychaeta), ostracods (Ostracoda), decapod shrimp (Decapoda)larvae, fish

(Osteichthys) eggs, fish larvae, and squid (Cephalopoda) larvae did not differ significantly

between the two depth strata (Table 1B). When each oceanographic region was

considered separately, most taxa also had higher abundances in the shallow stratum.

However, abundances were higher in the deep stratum for chaetognaths in all regions; for

decapods, fish eggs, and fish larvae in the SD; and for mysids and ostracods in the SAFZ

(Table 2).

Distribution by Oceanographic Region

The abundance of most taxa in both depth strata declined from north to south

(Table 2). Chaetognaths were most abundant in the SD and least abundant in the TZ, and

their abundances differed significantly in both depth strata. The low p-values for

chaetognaths (0.002 and <0.00l) were largely due to the abrupt decline in their abundance

between the SD and SAFZ. Amphipods were also more abundant in the SD and least in

the TZ, but their abundances differed significantly only in the shallow stratum.
4

Euphausiids and gastropods had the same pattern, but their abundances did not differ

significantly in either depth stratum.

Copepods were the most abundant zooplankton taxon, and in both depth strata they

were more abundant in the SD and least in the SAFZ. Their coefficients of variation were

similar in each oceanographic region, but were highest in the SAFZ, indicating that

copepod abundance was more variable in the SAFZ.

Squid larvae, cirripede larvae, decapod shrimp larvae, and fish eggs were most

abundant in the SAFZ. However, the abundance of squid larvae did not differ

significantly in either depth stratum, and the abundance of decapod shrimp larvae and fish

eggs differed significantly only in the shallow stratum. The abundance of cirripede larvae

was more than 10 times as great in the SAFZ as in the SD or TZ.

Mysids and fish larvae were most abundant in the TZ, and their abundances

differed significantly in both depth strata. The predominant mysid species in our samples

were Euchaetomeropsis merolepis and a Siriella sp.; however, the E. merolepis occurred

almost exclusively in the deep samples of the SAFZ, whereas the Siriella sp. were in the

shallow samples in the TZ. Fish larvae were predominantly myctophids. Stenobrachius

spp. were the most common myctophids, and Pacific viperfish, Chauliodus macouni, were

the most common nomnyctophid larvae.

Ostracods had the most uniform abundance levels across water-mass types and

depth strata, which reflects the cosmopolitan nature of Conchoecia spp., the common

ostracods of the subarctic North Pacific Ocean (Angel 1972).

Displacement volumes were highest in the SD in both depth strata and were higher

in the shallow stratum in all oceanographic regions. However, the difference in

displacement volume was greatest between the SD and the SAFZ.

Community Ordination

Taxa that reached their highest abundance in the subarctic water mass (gastropods,

polychaetes, ostracods, copepods, amphipods, euphausiids, chaetognaths; Table 2) were

separated from the other taxa by the sign of their loadings (Table 1C). The separation of

the subarctic taxa (taxa more abundant in the subarctic water mass) was more apparent in

the shallow stratum than in the deep stratum. In the shallow stratum, these taxa were

separated from other zooplankton taxa by the first principal component (PCl), which

accounted for 21% of the variation in species composition. In the deep stratum, these taxa

were separated by the second principal component (PC2), which accounted for only 16%

of the variation in species composition. The loading for ostracods was considerably lower

than for other taxa with negative loadings on PC1 and PC2, which reflects the more

uniform distribution of ostracods in our samples. The separation of subarctic taxa can also

be seen in the biplots (Gabriel 1971) of species and station ordinations (Figs. 5 and 6).

Station scores (Figs. 5 and 6) were consistent with abundance patterns found in Table 2

and loadings in Table 1C. Scores of the SD and SAFZ stations were separated by PC1 in

the shallow stratum and by PC2 in the deep stratum. The scores of the three TZ stations

in the deep stratum overlapped both SD and SAFZ stations (Fig. 6).
5

The second principal component split the scores of the shallow stratum in both the

SD and SAFZ. The shallow SD scores were split into a group with higher abundances of

gastropods, polychaetes, copepods, amphipods, euphausiids, and chaetognaths and a group

with higher displacement volumes (Fig. 5). Due to the colonial nature of the gelatinous

zooplankton in our samples (predominantly salps and doliolids), the variability in

displacement volume was determined primarily by their abundance. As a result, the two

groups could be defined as a gelatinous and a nongelatinous zooplankton assemblage.

PC2 also separated the shallow SAFZ samples into a group with higher abundances of

squid larvae, cirripede larvae, decapod shrimp larvae, and fish eggs and a group with

higher abundances of mysids and lower abundances of gastropods, polychaetes, copepods,

amphipods, euphausiids, and chaetognaths. Squid larvae, cirripede larvae, decapod shrimp

larvae, and fish eggs were also the taxa that reached their peak abundances in the SAFZ

(Table 2). Decapod shrimp larvae abundances in the SAFZ and the SD were much more

similar than those of cirripede larvae and fish eggs (Table 2), and this pattern is reflected

in the decapod shrimp larvae loadings (Fig. 5). The scores of the six TZ stations in the

shallow stratum overlapped the scores of the SAFZ stations.

DISCUSSION

The Tucker trawl was designed to capture macroplankton (2-20 mm) and

micronekton (20-200 mm) (Davies and Barham 1969). The 1 -m2 net is an effective

sampler for macroplankton and smaller micronekton in the coastal water of the eastern

Gulf of Alaska. Although the slow tow speed and relatively small mouth may allow some

net avoidance by the larger micronekton, we do not believe that net avoidance was a

significant factor contributing to the low abundance of macroplankton in many of our

samples. Our samples had few adult euphausiids, sergestid shrimp, myctophids, or other

micronekton over 20 mm compared with similar sampling in coastal areas of the eastern

Gulf of Alaska.

Vertical Distribution

Most zooplankton taxa were more abundant in the shallow stratum; however,

chaetognaths and mysids were significantly more abundant in the deeper stratum (Table

1B). Overlapping distributions of the two predominate chaetognath species (Eukrohnia

hamata and Sagitta elegans) can explain the higher abundance of chaetognaths found in

the deep stratum. E. hamata reaches its maximum abundance near 150 m and is typically

rare in surface samples (0-50 m), whereas S. elegans reaches its peak abundance at the

surface and is rare below 300 m (Kotori 1972). The higher abundance of mysids in the

deep stratum can be explained by the higher overall abundance of E. merolepis, which

occurred almost exclusively in the deep stratum. The other predominate mysid, Siriella

sp., was found only in the shallow stratum and in numbers significantly less than E.

merolepis.
6

Distribution by Oceanographic Region

Abundances of predominate taxa (gastropods, polychaetes, ostracods, copepods,

amphipods, euphausiids, and chaetognaths) were higher in the SD and lower in the SAFZ

and TZ, which is consistent with McGowan and Williams (1973) and Taniguchi (1981).

The association of these taxa with the SD was also apparent in the principal component

analysis. However, only polychaetes, copepods, and chaetognaths had significantly higher

abundances in the SD. The decline in polychaete abundance to the south was probably

due to the absence of the common subarctic species Tomopteris septentrionalis in the

SAFZ and TZ stations (Tebble 1962). The decline in abundance of amphipods to the south

can be explained by the absence of the common subarctic amphipod Themisto pacifica

(Bowman 1960) in the SAFZ and TZ. The decline in the abundance of chaetognaths to

the south can be attributed to the absence of Sagitta elegans and submergence of

Eukrohnia hamata-the predominate chaetognaths in the subarctic (Hida 1957, Alvarino

1964).

Stations where gelatinous zooplankton were the most abundant (stations with the

largest displacement volumes) occurred most frequently in the SD, and based on principal

component scores, appeared to have a zooplankton community that differed from the

nongelatinous community. At a species level, gelatinous zooplankton provide a habitat

and a food base for a unique zooplankton community. Most hyperiid amphipod species

and some copepods are directly associated with and feed on gelatinous zooplankton

(Hamner et al. 1975, Lava1 1980). Several nekton species are also associated with

gelatinous zooplankton (e.g., smalleye squaretail, Tetragonurus cuvieri, feed exclusively on

gelatinous zooplankton [Hart 1973], and chum salmon, Oncorhynchus keta, feed

extensively on gelatinous zooplankton [Pearcy et al. 1988, Welch et al. 19951). Gelatinous

zooplankton may provide a basis for a unique pelagic community with trophodynamics

distinctly different from that of the nongelatinous community.

The SAFZ appeared to support a zooplankton community of its own beyond a

simple transition from a SD community to a TZ community. Taxa associated specifically

with the SAFZ included squid larvae, cirripede larvae, fish eggs, and, to a lesser extent,

decapod shrimp. Stations with relatively high numbers of these taxa had principal

component scores that differed from scores at other SAFZ stations. Decapod shrimp were

most abundant in the SAFZ, but still were found in significant numbers in the SD. This

distribution was consistent with the known distribution of Sergestes similis, the common

subarctic decapod shrimp (Omori et al. 1972, Krygier and Pearcy 1981) and the

predominant decapod shrimp in our samples. Although S. simdis occurs throughout the

subarctic North Pacific Ocean, it reaches its peak abundance and forms dense swarms in

the SAFZ (Omori et al. 1972).

Mysids were the only taxon not found in the SD. Their absence in the SD is

typical of north Pacific meso- and epipelagic mysids, which are found primarily in the

lower latitudes (Mauchline and Murano 1977). The coefficients of variation for mysids

were high, indicating that their spatial distribution was patchy and is consistent with the

patchy distribution found in neuston samples (Ebberts and Wing 1997).
7

Due to the loss of taxonomic resolution inherent in species aggregation, we were

not able to incorporate the true complexity of the zooplankton community; however, the

taxa identified in our analysis differed significantly by depth stratum and oceanographic

region. The most significant change in the zooplankton community appeared to occur

between the SD and SAFZ, suggesting that the presence or absence of a permanent

halocline may be important in defining the distribution and abundance of zooplankton in

the subarctic.

ACKNOWLEDGMENTS

We wish to thank Shannon Fitzgerald and Bryan Herczeg of the National Marine

Mammal Laboratory for their assistance with oceanographic data collection during the first

leg of the cruise and for taking full responsibility for oceanographic data collection during

the second leg of the cruise. We thank the crew and officers of the NOAA ship Miller

Freeman for assistance and hospitality during the field operations, especially William

Floring and John Greenwalt, who assisted in all sampling activities. Also, we wish to

thank Blaine Ebberts for his assistance in processing the zooplankton samples.
8

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(Oncorhynchus spp.) in the spring. Can. J. Fish. Aquat. Sci. 52: 489-503.

Wing, B. L., B. D. Ebberts, M. A. Masters, and H. E. Garcia.

1993. Physical oceanographic observations in the northeastern Pacific transition zone,

October-November 1989. U.S. Dep. Commer., Proc. Rep. AFSC 93-09, 269 p.
TABLES

Table l.--(A) Wilcoxon rank sum probabilities of difference between morning and evening samples; (B) mean paired differences

between the 0-75 m (shallow) and 75-150 m (deep) depth strata and paired Wilcoxon rank sum probabilities (paired

differences were computed by subtracting the zooplankton abundance in the deep stratum from that in the shallow

stratum for each station); and (C) coordinates of the species ordination (loadings) for the first two principal component

axes (PC1 and PC2), and the variance explained by each component. Displacement volume is the whole sample, less

osteichthys larvae and cephalopod larvae. Asterisk indicates significant difference (p < 0.05).
14

Table 2.--Comparisons of mean abundance and coefficients of variation (CV) between

oceanographic regions with the Kruskal-Wallis test of significance. Shallow =

0-75 m depth; deep = 75-150 m depth. Displacement volume is the whole

sample less osteichthys larvae and cephalopod larvae. Asterisk indicates

significant difference (p < 0.05).
FIGURES

17

Figure l.--Schematic diagram showing the locations of the Subarctic and Subtropical

Domains, the Transition Zone, and the associated Subarctic Frontal Zone

(SAFZ) and Subtropical Frontal Zone (STFZ). Black arrows indicate boundary

current intrusions (from Roden 1991).
18

Figure 2.--Oceanographic regions and Tucker trawl sample locations and numbers, October

and November 1989.
19

Figure 3.--Salinity along 161°W in October 1989. Oceanographic domains are labeled on

top as TZ (Transition Zone), SAFZ (Subarctic Frontal Zone), and SD (Subarctic

Domain). Dotted lines indicate station locations.
20

Figure 4.--Temperature and salinity at 75 m depth. Station numbers label each point.
21

Figure 5.--Biplot of the zooplankton community ordinations using principal component

analysis (PCA). Zooplankton were collected between 0 and 75 m depths.

Vector coordinates are the species loadings on the first (x-axis) and second (yaxis) principal components of the species ordination. Letter (D, S, and T)

coordinates are the station scores from the station ordination. Volume refers to

displacement volume.
22

Figure 6.--Biplot of the zooplankton community ordinations using principal component

analysis (PCA). Zooplankton were collected between 75 and 150 m depths.

Vector coordinates are the species loadings on the first (x-axis) and second (yaxis) principal components of the species ordination. Letter (D, S, and T)

coordinates are the station scores from the station ordination. Volume refers to

displacement volume.
APPENDICES

25

Appendix l.--Station information, including the station number, sample number, depth of

sample, time and location of sample, and volume of seawater filtered during

collection. Times are Alaska Daylight Saving Time.
26

Appendix 1 .--Continued.
Appendix 2.--Zooplankton sample counts and displacement volumes. Counts are the number of individuals per sample.

CHAETOGMOLLUSCA ANNELIDA CRUSTACEA NATHA VERTEBRATA

Depth DisplaceStation stratum squid Cirripedia Decapoda Fish Fish merit

volume

number (m) Gastropoda larvae Polychaeta Ostraccda Copepoda larvae Amphipoda Mysidacea Euphausiacea larvae Sagittoidea eggs larvae (ml)
Appendix 2.--Continued.

CHAETOGMOLLUSCA ANNELIDA CRUSTACEA NATHA VERTEBRATA

Depth DisplaceStation stratum Squid Cirripedia Decapoda Fish Fish ment

volume

number ON Gastropoda larvae Polychaeta Ostracoda Copepoda larvae Amphipoda Mysidacea Euphausiacea larvae Sagittoidea eggs larvae (ml)
Appendix 2.--Continued.
30

Appendix 3.--Qualitative summary of the abundance of gelatinous zooplankton in the

Tucker trawl samples. The codes used are - = absent, 2 = few, 4 =

some, 6 = many, 10 = >98% of sample.
31
RECENT TECHNICAL MEMORANDUMS

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AFSC92 FRITZ, L. W., and S. A. LOWE. 1998. Seasonal distributions of Atka mackerel 

(Pleurogrammus monopterygius) in commercially-fished areas of the Aleutian Islands and Gulf of Alaska,

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91 WING, B. L., and J. J. PELLA. 1998. Time series analyses of climatological records from Auke Bay,

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90 PACUNSKI, R. E., P. A. LIVINGSTON, and B. S. MILLER. 1998. Food of flathead sole 

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89 WILKINS, M. E., M. ZIMMERMANN, and K. L. WEINBERG. 1998. The 1995 Pacific west coast bottom

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composition, 138 p. plus Appendices. NTIS No. PB98-136252.

88 FRITZ, L. W., A. GREIG, and R. F. REUTER. 1998. Catch-per-unit-effort, length, and depth distributions

of major groundfish and bycatch species in the Bering Sea, Aleutian Islands, and Gulf of Alaska regions

based on groundfish fishery observer data, 179 p. NTIS No. PB98-139298.

87 SINCLAIR, E. H. (editor) 1997. Fur seal investigations, 1996, 115 p. NTIS No. PB98-131790.

86 SINCLAIR, E.H. (editor). 1997. Fur seal investigations, 1995, 188 p. NTIS No. PB98-131808.

85 KINOSHITA, R. K., A. GREIG, and J. M. TERRY. 1998. Economic status of the groundfish fisheries off

Alaska, 1996, 91 p. NTIS No. PB98-126170.

84 LAAKE, J., D. RUGH, and L. BARAFF. 1998. Observations of harbor porpoise in the vicinity of acoustic

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83 RUTECKI, T. L., M. F. SIGLER, and H. H. ZENGER JR. 1997. Data report: National Marine Fisheries

Service longline surveys, 1991-96, 64 p. NTIS No. PB98-108822.

82 MARTIN, M. H. 1997. Data report: 1996 Gulf of Alaska bottom trawl survey, 235 p. NTIS No. PB98-

103930.

81 LAUTH, R. R. 1997. The 1996 Pacific West Coast upper continental slope trawl survey of groundfish

resources off Washington and Oregon: Estimates of distribution, abundance, and length composition, 

156 p. NTIS No. PB97-208912.

80 LAUTH, R. R. 1997. The 1995 Pacific West Coast upper continental slope trawl survey of groundfish

resources off southern Oregon and northern California: Estimates of distribution, abundance, and length

composition, 110 p. NTIS No. PB97-208920.

79 LAUTH, R. R., M. E. WILKINS, and P. A. RAYMORE JR. 1997. Results of trawl surveys of groundfish

resources of the West Coast upper continental slope from 1989 to 1993, 342 p. NTIS No. PB97-208904.

78 HILL, P. S., D. P. DEMASTER, and R. J. SMALL. 1997. Alaska marine mammal stock assessments,

1996, 150 p. NTIS No. PB97-203277.

77 CHUMBLEY, K., J. SEASE, M. STRICK, and R. TOWELL. 1997. Field studies of Steller sea lions

(Eumetopias jubatus) at Marmot Island, Alaska, 1979 through 1994, 99 p. NTIS No. PB97-203376.