NOAA Technical Memorandum NMFS-AFSC-132

U.S. DEPARTMENT OF COMMERCE

National Oceanic and Atmospheric Administration

National Marine Fisheries Service

Alaska Fisheries Science Center

December 2002

by

M. J. Doyle, M. S. Busby, J. T. Duffy-Anderson,

S. J. Picquelle, and A. C. Matarese

Aspects of the Early Life History of

Capelin (Mallotus villosus) in the

Northwest Gulf of Alaska: A Historical

Perspective Based on Larval Collections

October 1977 - March 1979
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:

Doyle, M. J.., M. S. Busby, J. T. Duffy-Anderson, S. J. Picquelle, 

and A. C. Matarese. 2002. Aspects of the early life history of capelin

(Mallotus villosus) in the northwestern Gulf of Alaska: A historical

perspective based on larval collections October 1977- March 1979. 

U. S. Dep. Commer., NOAA Tech. Memo. NMFS-AFSC-132, 32 p.

 

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

the National Marine Fisheries Service, NOAA.
Joint Institute for the Study of the Atmosphere and Ocean

University of Washington

Seattle, WA 98195

Alaska Fisheries Science Center

7600 Sand Point Way N.E.

Seattle, WA 98115

www.afsc.noaa.gov

December 2002

NOAA Technical Memorandum NMFS-AFSC-132

by

M. J. Doyle, M. S. Busby, J. T. Duffy-Anderson,

S. J. Picquelle, and A. C. Matarese

Aspects of the Early Life History of

Capelin (Mallotus villosus) in the

Northwest Gulf of Alaska: A Historical

Perspective Based on Larval Collections

October 1977 - March 1979

U.S. DEPARTMENT OF COMMERCE

Donald L. Evans, Secretary

National Oceanic and Atmospheric Administration

Vice Admiral Conrad C. Lautenbacher, Jr., U.S. Navy (ret.), Under Secretary and Administrator

National Marine Fisheries Service

William T. Hogarth, Assistant Administrator for Fisheries

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ABSTRACT

Analyses of historical ichthyoplankton data collected in the vicinity of Kodiak Island

Gulf of Alaska, provide new infonnation on the spawning strategy and early life history

characteristics of capelin (Mallotus villosus) in the northeast Pacific. Ichthyoplankton surveys

have been conducted by the Alaska Fisheries Science Center (AFSC) in the northwest Gulf of

Alaska from 1977 to the present, primarily during spring. Time series data (1977-98) from these

cruises indicate that a peak in capelin larval abundance occurs in late summer and early autumn

(September-October) on the continental shelf. Capelin larvae occur in the plankton throughout

the rest of the year in low numbers, with a minimum observed from March-May. The most

intensive seasonal collections of larvae were made during a 17-month period from 1977 to 1979

within four Kodiak Island bays and over the adjacent continental shelf and slope. More extensive

analyses of these data concur with observed long-tenn seasonal patterns of abundance on the

shelf and also indicate a summer peak (July-August) in larval abundance in Kodiak Island bays.

Seasonal variation in abundance, length, and distribution of capelin larvae from the 1977-

collections indicates that in 1978, capelin populations in this area spawned during the summer

and autumn in inshore waters, with a peak in spawning activity during June-July. The

distribution patterns for these years suggest that subsequent to hatching and emergence into the

plankton, larvae are transported from the bays and coastal zone around Kodiak Island into

adjacent shelf waters, probably by tidal flushing and wind-induced surface currents. Mixing

processes on the shelf seaward of Kodiak Island, reflecting variable current patterns in this area

are likely to enhance the dispersal of larvae as indicated by the unifonnity observed among

distribution patterns of several length categories of larvae. A comparison of larval abundance

and lengths between bongo and neuston samples suggests that capelin larvae, mostly greater than

30 mm standard length, actively migrate to the surface layer. Although enhanced net avoidance

by the larvae during daylight hours is a confounding factor, the observed diel variation in

abundance of capelin larvae in the neuston implies that the migration to the surface layer is

largely nocturnal. Our observations represent a picture of capelin early life history during a

periQd of high adult abundance that has been linked to a cold phase in the oceanographic

environment of the Gulf of Alaska.

111
CONTENTS

ABSTRACT................................................................. iii

CONTENTS..................................................................

INTRODUCTION .............................................................

METHODS ..................................................................

FieldCollections ........................................................

LaboratoryProcedures ....................................................

AnalyticalMethods ......................................................

RESULTS ...................................................................

Larval Identification and Development .......................................

Seasonal Variation in Abundance and Size of Larvae . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Distribution and Dispersal of Larvae .........................................

Neustonic Occurrence and Diel Variation in Catches of Larvae . . . . . . . . . . . . . . . . . . . . 5

Sea Surface Temperature and Salinity ........................................

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

ACKNOWLEDGMENTS ......................................................

CITATIONS..................................................................

TABLES....................

................................................

Table 1. List of cruises, dates and numbers of stations sampled by bongo and neuston

nets during UW and AFSC cruises, Kodiak Archipelago, 1977- 1979. ........ 15

Table 2. Habitat and spawning times of fi ve species of Osmeridae from the Northeast

Pacific .........................................................

Table 3. Developmental landmarks of capelin larvae. .......................... 17

Table 4. Mean sea surface temperatures and salinities ( SD) for stations sampled from

within bays around Kodiak Island in spring (March-May), summer (June-August),

and autumn (November), and from the shelf seaward of Kodiak Island in spring

(March-April), summer (June-July), and autumn (September-November). .... 18

FIGURES ...................................................................

Figure 1. Map of the Kodiak Archipelago and adjacent study area. . . . . . . . . . . . . . . . . 19

Figure 2. Seasonal variation in mean abundance (+SE) (top panel), and sampling effort

and percent occurrence (bottom panel) of Mallotus villosus larvae in bongo

samples collected in the Gulf of Alaska 1977-98. . 

. . . . . . . . . . . . . . . . . . . . . . .

Figure 3. Seasonal variation in sampling effort and mean abundance (+SE) of Mallotus

villosus larvae in bongo and neuston samples collected in bays and over the

continental shelf and slope near Kodiak Island, October 1977 - March 1979.

Labels 7801 , 4MF77 etc. are cruise numbers (see Table 1). ................ 21
Figure 4. Seasonal variation in mean standard length ( SE) of Mallotus villosus larvae

collected in bongo (top panel) and neuston (bottom panel) tows in bays and over

the continental shelf and slope near Kodiak Island, October 1977 - March 1979

and regression of larval length with sampling date for summer through autumn of

1978 ...........................................................

Figure 5. Seasonal variation in length frequency of Mallotus villosus larvae collected in

bongo tows in bays and over the continental shelf and slope near Kodiak Island

1977 - 79. n = number of fish larvae measured. .......................... 23

Figure 6. Seasonal variation in distribution and abundance (number per 10 m ) of

Mallotus villosus larvae collected in bongo tows in bays and over the continental

shelf and slope near Kodiak Island, 1977-79. ........................... 24

Figure 7. Seasonal variation in length frequency of Mallotus villosus larvae collected in

neuston tows in bays and over the continental shelf and slope near Kodiak Island

1977 -79. n = number of fish larvae measured. ......................... 25

Figure 8. Seasonal variation in distribution and abundance (number per 1000 m ) of

Mallotus villosus larvae collected in neuston tows in bays and over the continental

shelf and slope near Kodiak Island, 1977-79. ........................... 26

Figure 9. Distribution of four size-categories of Mallotus villosus larvae in bongo

samples collected during early autumn 1978. ........................... 27

Figure 10. Distribution of four size-categories of Mallotus villosus larvae in bongo

samples collected during late autumn 1978. ............................

Figure 11. Distribution of four size-categories of Mallotus villosus larvae in neuston

samples collected during early autumn 1978. ...........................

Figure 12. Distribution of four size-categories of Mallotus villosus larvae in neuston

samples collected during late autumn 1978. ............................ 30

Figure 13. Comparison of length frequencies for Mallotus villosus larvae collected in

bongo (top panel) and neuston tows (bottom panel) - data from all cruises

combined. n = number of fish larvae measured. . . . . . . . . . . . . . . . . . . . . . . . . . 

Figure 14. Diel variation (hourly intervals) in mean stratified abundance (+SD) of

Mallotus villosus larvae in bongo samples (top panel - data combined from cruises

4MF77, 2MF78, lWE78 and IMF79), and neuston samples (bottom panel- data

combined from cruises 4MF77, 4DI78, lWE78 and IMF79). ..............
INTRODUCTION

Capelin (Mallotus villosus) is a boreoarctic member of the smelt family (Osmeridae) that

occurs. in the North Atlantic and Arctic Oceans, Chukchi and Bering Seas, Gulf of Alaska, and

northeast Pacific Ocean as far south as the waters off Washington State. They are known to

spawn throughout most of their range (Hart 1973, Garrison and Miller 1982). The ecological

importance of capelin as a forage species utilized by marine birds and mammals has been well

documented in the Gulf of Alaska (Piatt and Anderson 1996, Merrick et al. 1997) and declines in

abundance of forage species, including capelin, have been observed following a dramatic change

in ocean climate (regime shift) that occurred in the late 1970s (Anderson et al. 1997 , Anderson

and Piatt 1999). Warner and Shafford (1978), Blackburn et al. (1981) and Pahlke (1985) give

preliminary infonnation on the spawning biology of capelin in Alaskan waters based on aerial

and beach spawning surveys conducted in the eastern Bering Sea and Gulf of Alaska. The

biology of capelin has been extensively studied in the North Atlantic for many years, but despite

its importance in the trophic web of Alaskan coastal waters, there have been few studies

pertaining to capelin early life history in the North Pacific. Capelin larvae have been observed in

the ichthyoplankton of the eastern Bering Sea shelf (Waldron 1981), and Kendall and Dunn

(1985) reported on the abundance and distribution of capelin larvae as part of the

ichthyoplankton assemblage near Kodiak Island. Doyle et al. (1995) documented the occurrence

of capelin larvae in spring neuston collections in the western Gulf of Alaska, and Norcross and

Fransden (1996) and Brown et al. (1999) included capelin larvae in investigations of forage

fishes in Prince William Sound. None of these early life history studies , however, focused

exclusively on capelin.

Ichthyoplankton surveys, designed to describe aspects of the distribution and abundance

of fish eggs and larvae in the Gulf of Alaska, have been conducted annually by the National

Oceanic and Atmospheric Administration s (NOAA) Alaska Fisheries Science Center (AFSC)

and its predecessor agencies from 1977 to the present. Since 1981 , sampling has been restricted

to spring and early summer months when capelin larvae are relatively scarce in sub-surface

plankton samples (Matarese et aI., in press). From late 1977 to early 1979, however, a series of

research cruises supported primarily by the Outer Continental Shelf Environmental Assessment

Program (OCSEAP) was conducted seasonally by the AFSC and the University of Washington

(UW) Fisheries Research Institute to assess potential effects of offshore oil development on

Alaskan marine resources (Rogers et al. 1979, Kendall et al. 1980, Kendall and Dunn 1985).

These cruises sampled ichthyoplankton over a 17-month period in four Kodiak Island bays and

along the adjacent continental shelf and slope. The resulting data provided an opportunity to

examine aspects of the early life history of capelin, in particular temporal and spatial patterns in

larval abundance, during a period when adult capelin abundance was high, prior to the observed

decline in forage fishes in the Gulf of Alaska.

In this study, we examine seasonal and spatial patterns in the abundance and size of

capelin larvae in the water column and neuston, in the vicinity of Kodiak Island, Alaska, from

autumn 1977 through winter/early spring 1979. The purpose of this study is to use these data to

describe likely capelin spawning patterns and larval dispersal in this area and also to interpret our

observations of capelin early life history in relation to physical and biological characteristics of

the pelagic ecosystem of the northwest Gulf of Alaska.
METHODS

Field Collections

Ichthyoplankton were collected from 31 October 1977 to 16 March 1979 during a series

of 20 AFSC and UW cruises (Table 1). AFSC cruises primarily sampled areas on the continental

shelf and slope southeast of Kodiak Island while UW cruises sampled within four Kodiak Island

bays (Fig. 1). A neuston net (Sameoto sampler; Sameoto and Jaroszynski 1969) and a 60 cm

bongo net (Posgay and Marak 1980) fitted with flowmeters and 505 jlm mesh plankton nets and

cod ends, were used to collect ichthyoplankton samples. Tow procedures generally followed

survey guidelines in Smith and Richardson (1977). Sea surface temperature and salinity data

were collected at irregular intervals throughout the sampling area. Plankton samples were

preserved in a 5% fonnalin-seawater mixture buffered with sodium tetraborate. Conductivity,

temperature, and bottom depth (CTD) data were collected using a Seabird CTD profiler.

Laboratory Procedures

Ichthyoplankton were identified and Mallotus villosus larvae were removed, enumerated

and measured to the nearest 0. 1 mm standard length (SL). At the time of initial examination of

the larvae, smaller individuals with incomplete fin ray development, particularly pectoral-fin

rays, were identified at the family level (Osmeridae). Larger individuals with complete

complements of fin rays were identified as M. villosus. After identification, larvae were

transferred to 70% ethanol and stored in the University of Washington Larval Fish Collection

(UWLFC). Data relevant to sample collection for AFSC samples (e. , geographic coordinates

date/time collected, gear used) were archived in a database (ICHBASE) at AFSC. Data for UW

samples were obtained with the assistance of the National Oceanographic Data Center (NODC).

We examined and reidentified a subset of small larvae, by comparing our specimens with

descriptions of taxonomic characters of other osmerid species from Hearne (1983, 1984), Young

(1984), and Moser (1996) that were not available at the time of original sorting, to detennine

whether larvae historically characterized and archived as "Osmeridae" were M. villosus. 

addition, we compiled and compared published data on adult distributions, early life history, and

spawning habitat characteristics of other osmerid fishes reported to occur in the Gulf of Alaska

with capelin. We also differentially cleared and stained a developmental series of 24 capelin

specimens 4. 90.0 mm SL using the method of Potthoff (1984) to detennine length ranges for

each developmental stage and identify developmental landmarks as reported by Kendall et al.

(1984).

Analytical Methods

Numbers of larvae from each tow were standardized for bongo (number per 10 m ) and

neuston (number per 1 000 m ) tows using tow depth and volume filtered (Kendall and Dunn

1985). Variation in larval abundance with season (six periods from October 1977 through

March 1979) and geographic strata (bay, continental shelf, continental slope) was examined by

mapping standardized catches by season and by using two-way ANOV As. Data were fourth-root

transfonned prior to analyses to reduce heteroscedasticity and increase symmetry (Downing

1979).
Length- frequency histograms were created for each sampling gear and season to examine

seasonal variation in larval size and to compare length distributions between gears. Data were

included from the shelf strata only because there were no larval lengths measured from the

neuston samples in the bays and there were very few larvae caught by either gear in the slope

strata. Spatial variation in the distribution patterns of different sizes of larvae was investigated

for autumn 1978 by plotting on maps the abundance of four length categories of larvae; less than

10 mm standard length (SL) (newly hatched and preflexion), 10-20 mm SL (flexion), 20-40 mm

SL (post flexion), and greater than 40 mm SL (late larvae/transfonnation). Placement in

developmental categories is based on data for sequence of fin fonnation from Fahay (1983).

Growth was examined by plotting mean standard length against mean date for each cruise. 

regression of these data over summer and autumn 1978 provided an average change in length of

the population per day.

Diel variation in abundance of larvae in the bongo and neuston samples was investigated

by examining data from five AFSC cruises (4MF77, 4DI78, 2MF78, lWE78 and IMF79) that

included both day and night samples. Diel catch data were combined for these cruises to

calculate a stratified mean larval abundance, and standard deviation, in one hour intervals.

Cruise 4DI78 was omitted from the bongo calculations and cruise 2MF78 from the neuston

calculations due to the absence or scarcity of larvae in the samples from these cruises.

For cruises when CTDs were not deployed, temperature-salinity-depth profiles were

obtained from the online, 20+ year EPIC database developed by NOAA' s Pacific Marine

Environmental Laboratory. In these cases, profiles were obtained for cruises carried out in the

same geographic region and time period. In several cases, however, no CTD data from the

appropriate time and location were available (i.e. , Cruises 3MF78, 4MF78, 5MF78, IMF79).

The CTD data were more limited for the UW cruises. Surface temperatures and salinities

measured at each station were pooled to provide infonnation on the seasonal characteristics of

each Kodiak bay and the shelf area east of Kodiak Island.
RESUL TS

Larval Identification and Development

Examination of a subset of small larvae (prior to attainment of a full complement of fin

rays) initially identified and archived as "Osmeridae" led us to conclude that these larvae were, in

all likelihood Mallotus villosus. Comparison of published infonnation on adult distributions

and spawning times and habitat characteristics of other osmerid fishes likely to occur in the Gulf

of Alaska (Table 2) supported this conclusion. Six other osmerid fishes reported to occur in

Alaskan waters spawn in different habitats at different times of year with minimal overlap (Table

2). Three species are reported as being uncommon or rare and are unlikely to spawn in the study

area. Consequently, data for these two taxa (Osmeridae and Mallotus villosus) were pooled for

anal yses in this study.

From our cleared and stained developmental series of capelin larvae (Table 3), we

detennined that notochord flexion begins at 8.5 mm SL and is complete at 25.5 mm SL.

Transfonnation from the postflexion to juvenile stage begins at approximately 60.0 mm SL when

ossification of vertebrae and fins is complete. The juvenile stage begins between 75.0 and 80.

mm SL when the cranium, pterygiophores and bones supporting fins are ossified, lateral line

scales begin to fonn, palatine teeth are present, and the skin has a silvery sheen characteristic of

adult coloration. Using these criteria and developmental landmarks, all capelin collected for this

study are considered larvae.

Seasonal Variation in Abundance and Size of Larvae

Based on an extensive set of bongo samples collected throughout the Gulf of Alaska from

1977 through 1998 (sampling coverage and methodology described in Matarese et aI., in press),

Figure 2 illustrates the general pattern of monthly variation in mean abundance and percent

occurrence of capelin larvae in this region. Lack of sampling in January, August, and December

and the concentration of sampling during spring means that observed seasonal patterns in

abundance in this region is incomplete. Nevertheless, a peak in abundance appears to occur

during late summer-early autumn. Larvae occur in the plankton throughout the rest of the year 

low numbers, with a minimum in March-May. The proportion of samples yielding capelin larvae

was highest (40-45%) in September-October and lowest (~3%) in April-May.

Seasonal variation in larval abundance for the 1977-79 collections was statistically

significant (bongo, P ~ 0.001; neuston, P ~ 0.05) and these data concur with but expand on the

above general seasonal pattern. Figure 3 shows the monthly patterns by geographic strata and

sampling gear. Within the bays, the peak abundance of larvae occurred in the summer months.

A peak in larval abundance was apparent on the continental shelf during autumn, SeptemberNovember 1977 and 1978, whereas abundance was at a minimum during spring 1978, MarchMay, in all geographic strata. These data indicate a summer-autumn spawning season for capelin

in the vicinity of Kodiak Island.

Seasonal variation in mean standard length of larvae in bongo and neuston samples from

the Kodiak area also suggests a summer peak in capelin spawning activity and hatching of larvae

into the plankton (Fig. 4). Mean larval size increased from less than 10 mm SL in the summer

of 1978 to greater than 30 mm SL in the winter/early spring of 1979, with intennediate values for

early and late autumn of 1978. The mean standard length of the few larvae caught in bongo and

neuston tows during spring of 1978 was greater than 40 mm SL indicating that they were
spawned during summer-autumn of 1977. During autumn cruises when capelin larvae are most

abundant in continental shelf samples, mean larval size was consistently greater in neuston than

in bongo samples (Fig. 4). Using data from bongo collections in the summer through autumn of

1978 , the rate of change in the average length of the larval population was 0. 11 mm per day C:t

011 SE). This was estimated from the slope of a length/time regression for this larval year

class and can be considered as a proxy for larval growth rate (Fig. 4). Seasonal progression in

larval standard length is also apparent in length-frequency distributions of larvae from sampling

cruises grouped into six seasonal periods from October 1977 through March 1979 (Figs. 5 and 7).

Distribution and Dispersal of Larvae

The statistical comparison of larval abundance between bays, shelf, and slope yielded a

significant difference among the three geographic strata (bongo and neuston P ~ 0.001), as well

as the significant effect of season mentioned previously (bongo P ~ 0.001 , neuston P ~ 0.05) on

capelin abundance for both sampling gears. A significant interaction between the two factors

(geographic strata and season) was also detected (bongo and neuston P ~ 0.001).

Seasonal variation in horizontal patterns of distribution of capelin larvae collected in the

bongo tows indicates that the smallest larvae (~ 10 mm SL), that were most abundant during

summer 1978 (Figs. 3 and 4), are associated primarily with the Kodiak bays and adjacent coastal

zone in water less than 100 m deep (Figs. 6 and 8). During autumn of 1978 and winter/early

spring of 1979, when larvae were mostly 10-40 mm SL, the larvae were more evenly distributed

throughout the shelf zone, northeast to southwest of Kodiak Island (Figs. 6 and 8), suggesting a

seaward dispersal of larvae with development. A comparison of the distribution patterns of four

size categories of larvae (~ 10, 10- , 20-40 and ~ 40 mm SL), for early and late autumn 1978

when larval size range was greatest, indicated a substantial difference only between larvae less

than 10 mm SL (coastal distribution) and those greater than 10 mm SL (dispersed on the shelf) in

early autumn (Figs. 9- 12). Very few larvae were caught over the continental slope, in water

greater than 200 m deep, during any season (Figs. 6 and 8).

Neustonic Occurrence and Diel Variation in Catches of Larvae

As stated above, seasonal variation in abundance and patterns of horizontal distribution of

capelin larvae in the neuston collections mirrored those observed for the bongo collections

including the occurrence of the smallest larvae (~ 10 mm SL) close to the coast in summer (Figs.

12). Larvae less than or equal to 10 mm SL were equally well represented in both the neuston

and bongo samples (Fig. 13) suggesting that when the newly hatched larvae are in shallow

coastal waters, they are as likely to occur in the surface layer as deeper in the water column. 

substantial difference between proportions of larger larvae (~30 mm SL) in the neuston and

bongo samples, however, was observed (Fig. 13). For larvae greater than 10 mm SL, 63% of

those in the neuston samples were greater than 30 mm SL in contrast to only 7.9% in the bongo

samples.

Diel catch data were combined to calculate a stratified mean larval abundance in one-hour

intervals for each sampling gear (Fig. 14). For both bongo and neuston samples a reduction in

catches of capelin larvae was apparent during most of the daylight hours, suggesting enhanced

gear avoidance during the day. In addition, larvae were absent from the neuston tows during six
of the daylight hours implying that diel variation in catches at the surface was influenced by diel

vertical migration of larvae. The high level of variance (illustrated by the standard error values)

for the stratified hourly abundance values, especially for the bongo samples, however, prevents

an accurate estimate of the actual level of reduction in catches during daylight.

Sea Surface Temperature and Salinity

Temperature and salinity data for the study area and period are presented in Table 4.

Mean sea surface temperatures in the Kodiak bays varied seasonally with a recorded maximum

of 9.40 10.40 C in the summer when spawning and larval hatching are most intense in the coastal

zone. Summertime mean temperature was slightly lower (8.20 C) on the shelf, and in autumn

when capelin larvae were most abundant on the shelf, the mean temperature was 6.90 C. Mean

salinities ranged from 31.4 to 34.2 psu among the Kodiak bays but remained relatively constant

with season. A slight decrease in the mean value (maximum difference of 2.2 psu for Kiliuda

Bay) was observed during summer, possibly reflecting a seasonal peak in fresh water runoff. 

seasonal variation in mean salinity (32.2 psu) was apparent for the shelf.
DISCUSSION

This study provides new infonnation on the early life history characteristics of capelin in

the northeast Pacific, specifically in the vicinity of Kodiak Island in the northeast Gulf of Alaska.

Although we have provided new infonnation on length at stage of development and

associated osteological and morphological landmarks in capelin, identification of osmerid larvae

from the Gulf of Alaska remains difficult. Of the six anadromous and marine species reported to

occur in Alaskan waters (Table 2), only larvae of Mallotus villosus have been described at all

stages of development (Templeman 1948, Fahay 1983). These descriptions, however, are based

on specimens from the Atlantic Ocean. Unfortunately, larval stages of the other five species

have been incompletely described and few illustrations are available (Barraclough 1964, Fahay

1983 , Hearne 1983, Young 1984, Moser 1996). Larvae of the Alaskan osmerids are slender

bodied and have long guts (approx. 75% SL) with rows of melanophores on the dorsal and/or

ventral margins. One to several post-anal ventral melanophores are also present in all species.

Because the osmerid larval stages currently known are so strikingly similar in appearance, future

taxonomic studies of this group would greatly benefit from genetic analyses. Ichthyoplankton

sampling in nearshore areas of the northeast Pacific will be needed to collect larvae of these

anadromous and beach spawning osmerids.

In the vicinity of Kodiak Island, it appears that capelin populations spawn during the

summer and autumn in inshore waters. A peak in spawning activity during June-July in the

Kodiak bays results in a summer peak in abundance of recently hatched (~ 10 mm SL) capelin

larvae in coastal waters and a September-October peak in abundance of well-developed larvae

(10-50 mm SL) in adjacent shelf waters. This seasonal pattern in spawning activity appears

consistent with beach and aerial spawning surveys in the North Pacific which found that capelin

spawning runs occurred in late spring and early summer (Blackburn et al. 1981 , Pahlke 1985). It

is similar to the spawning season (June-July) observed for capelin in the Newfoundland-Labrador

region of the northwest Atlantic (Templeman 1948, Carscadden et al. 1997), but later than the

March-April peak observed for the capelin populations in the Barents Sea and Iceland-Greenland

regions of the northeast Atlantic (Vilhjalmsson 1997).

The dominant fish populations in the Gulf of Alaska are spring spawners and a spring

peak (April-May) in larval abundance is observed for most species (Matarese et al. in press),

coinciding with a late April to early May peak in phytoplankton production in coastal and shelf

waters (Cooney 1986, Napp et al. 1996). The contrasting, later occurrence of capelin larvae

actually coincides with a summer peak in production of copepod nauplii (Cooney 1986), a

suitable food for first-feeding larvae.

Carscadden et al. (1997) conclude that the timing of capelin spawning in the

Newfoundland region is related primarily to water temperature. The pre-spawning water

temperature and size and age structure of the adult capelin population, however, also seem to

exert significant influence on timing of spawning in the northwest Atlantic (Carscadden et al.

1997). These factors are also likely to influence capelin pre-spawning and spawning dynamics

in the Gulf of Alaska but we lack the data in this area, especially from the spawning beaches, to

explore such a relationship. Our 1977-79 data, however, suggest that larval hatching and

emergence into the plankton occurred in water temperatures ranging approximately from 80 to

11O

An average daily growth rate of 0. 11 mm per day estimated for the 1978 larval year class

appears low in comparison with mean rates of 0. 15- , and 0. 18- 25 mm per day

reported for larval capelin populations in the Gulf of St. Lawrence, Icelandic waters, and

Newfoundland waters, respectively (Jacquaz et al. 1977). Rather than expressing the true growth
rate (i. , the change of length with age), however, these estimates represent the change in

average length of the larval population over time and are a function of growth, mortality, larval

production and larval transport into and out of the survey area. Furthennore, a direct comparison

between our data and those from the Atlantic Ocean seems inappropriate without further

exploration of larval growth rates in relation to temperature and plankton characteristics (food

conditions) of water massses containing capelin larvae, among these different ocean regions.

Similarly, a more thorough investigation of environmental conditions is needed in the Gulf of

Alaska pelagic ecosystem, and adjacent coastal and beach zones where pre-spawning adult

capelin occur, for a meaningful comparison to be made between spawning strategies and early

life history characteristics of capelin here and in the Atlantic Ocean.

Our observations of capelin larval distribution patterns suggest that subsequent to

hatching and emergence into the plankton, larvae are dispersed from the bays and coastal zone

around Kodiak Island into adjacent shelf waters. The mechanism for seaward transport of capelin

larvae in this area is unknown but is likely to involve both tidal flushing and wind-induced

surface currents as is the case in Newfoundland waters (Frank and Leggett 1982, Fortier and

Leggett 1982). Salinities in the Kodiak bays were relatively homogeneous and similar to those

on the shelf and slope, implying that the bays experience regular tidal flushing. As such, larvae

may be transported from bays onto the shelf with tidal currents. It is likely that subsequent to

seaward drift, larvae are subject to mixing processes on the shelf. The unifonnity in distribution

patterns observed among four length categories of larvae greater than 10 mm SL on the shelf

outside Kodiak Island reflects such a process. Reed and Schumacher (1986) showed that current

patterns in this area are variable, including onshore and offshore flow on the shelf that is likely to

enhance the dispersal of larvae. Along the outer shelf and slope, the Alaska Stream flows in a

steady southwesterly direction, parallel to the slope, probably contributing to the retention of

larvae on the shelf and the southwesterly transport of larvae over the slope.

The high proportion of larvae greater than 30 mm SL in the neuston samples relative to

. the bongo samples implies a facultative association of larger capelin larvae with the surface layer.

Given the absence or scarcity of capelin larvae in samples taken during daylight hours, it seems

that these larger larvae are likely to migrate vertically into the neuston at night. The confounding

factor of enhanced gear avoidance by the larvae during daylight hours, as indicated by a reduction

in larval abundance in daytime bongo samples, must also be taken into consideration in the

interpretation of these results. Nevertheless, Doyle et al.(1995) documented a high fraction

(57%) of large capelin larvae (~ 25 mm SL) in the neuston relative to bongo collections in the

Gulf of Alaska during spring and diel variation in their abundance in the neuston samples 

suggested that they migrate into the neuston at night. In addition, Haldorson et al. (1993) report

that osmerid larvae in Auke Bay, southeast Alaska, spent most of their time in the mixed layer

rising to the surface at night and returning to shallow depths during the day. This association 

large capelin, and other fish larvae, with the neustonic layer is considered to be a feeding

adaptation that allows the large larvae to exploit a wide variety and size range of food organisms

that accumulate at the surface, particularly at night (Neilson and Perry 1990, Doyle et al. 1995).

Although the data analyzed for our study were collected slightly later than the 1976-

oceanographic regime shift documented in the Gulf of Alaska, adult capelin abundance remained

high until the early 1980s (Anderson et al. 1997, Anderson and Piatt 1999). Thus, our findings

represent a picture of capelin early life history during the period of high adult abundance that has

been linked to a cold phase in the oceanographic environment of the Gulf of Alaska. Our

observations could fonn the basis for a future comparative study of early life history

characteristics of capelin in the Gulf of Alaska during the warm water and transitional phases of

the oscillating oceanographic regime in this region. In order to investigate capelin population
fluctuations and early life history variability in the Gulf of Alaska, relative to oceanographic

regime shifts or other temporal changes, annual ichthyoplankton and oceanographic surveys are

crucial during summer and autumn months when capelin larvae are most abundant in the

plankton.
ACKNOWLEDGMENTS

J an Benson (AFSC) assisted with mapping. Theodore Pietsch and Erin Macdonald (UW)

provided larvae from the UW Fish Collection and assisted with data compilation. Mary

Hollinger (NODC) provided archived data from UW collections. Rachael Cartwright and

Beverly Vinter (AFSC) measured additional specimens. This publication was supported by the

Joint Institute for the Study of the Atmosphere and Ocean (JISAO) under NOAA Cooperative

Agreement # NA67RJO155, Contribution # 932. This research is contribution FOCI-0454 to

NOAA' s Fisheries-Oceanography Coordinated Investigations.
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Table 1. List of cruises, dates , and numbers of stations sampled by bongo and neuston nets for University of

Washington (UW) Alaska Fisheries Science Center (AFSC) OCSEAP and other cruises, Kodiak

Archipelago. 1977-79.

UW OCSEAP bay stations AFSC OCSEAP continental shelf and slope stations

Crui se Dates Bongo Neuston Cruise Dates Bongo Neuston

7801 Mar 29-Apr 8 4MF77 Oct 31-Nov 14

7802 Apr 10-Apr 17 4DI78 Mar 29-Apr 20 113

7803 Apr 21-May 2MF78 Jun 20-July 5 1127804 May 3-May 28 3MF78* Sep 9-

7805 May 31-Jun 6 4MF78 * Sep 26-0ct 7

7806 Jun 14-Jun 24 5MF78* Oct 19-Nov 7807 Jun 28-Ju118 WE7 8 Oct 31-Nov 14

7808 Jul 21-Jul 29 1MF79 Feb 14-Mar 87809 Aug 1-Aug 9 totals 519 573

7810 Aug 15-Aug 21 *Not OeSEAP grid stations, occupied as piggyback on APSe7811 Nov 3-Nov 13 groundfish surveys.

7901 Mar 6-Mar 16

totals 289 313
Table 2. Summary of published infonnation on environment, spawning habitat, and spawning season for the osmerid

fishes of Alaska. Sources: Hart (1973), Morrow (1980), Mecklenburg et al. (2002).

Taxon Environment Spawning habitat Spawning season

Jun

0'\

Hypomesus olidus freshwater ponds or streamsHypomesus pretiosus manne beaches

Mallotus villosus marine beaches (small gravel), offshore?

Osmerus mordax anadromous lakes, rivers, streams, estuaries

Spirinchus starksi manne beachesSpirinchus thaelichthys anadromous lakes, rivers, streams

Thaelichthys pacificus anadromous rivers triburaries of large river systems

earscadden et al. (1989) northwest Atlantic, undetermined in Pacific.Uncommon or rare and unlikely to spawn in study area.

Mar-May

late May-Oct

early spring

May

Oct - Dec

Mar-May
Table 3. Developmental landmarks of capelin (Mallotus villosus) detennined from

examination of a cleared and stained developmental series 4. 90.0 mm

standard length (SL).

-...J

Length (mm SL)

25.60.

75. 80.

StageYolksac

Preflexion

Flexion

Postflexion

Transfonning

Juvenile

Landmarks

Hatch

Yolk absorbed

Notochord flexion begins.Notochord flexion ends.

All vertebrae and fin rays ossified.

Entire cranium, pterygiophores, andbones supporting fins ossified.Palatine teeth present, lateral line

scales beginning to fonn, skin

exhibits a silvery sheen similar to

adults.
Table 4. Mean sea surface temperatures and salinities (:tSD) for stations sampled from within bays around Kodiak

Island (1977-79) in spring (March-May), summer (June-August), and autumn (November), and from the shelf seaward

of Kodiak Island in spring (March-April), summer (June-July) and autumn (September-November).

Location Spring Summer Autumn

Izhut Bay C (:t 1.3) C (:t 1.3) 6.2O

33.6 psu (:t 1.1) 33.4 psu (:to. 33.9 psu

Chiniak Bay C (:t 1.4) 9.4 oC (:t 1.6)

33.6 psu (:to. 33.3 psu (:to. 34.2 psu

Kiliuda Bay C (:t 1.8) 10.4OC (:t 1.6)

33.0 psu (:t 1.3) 31.4 psu (:to. 33.6 psu

Kaiugnak Bay C (:t 1.5) C (:t2.

33.5 psu (:to. 33.0 psu (:to.4) 33.9 psu

Kodiak Shelf C (:to. C (:to. C (:to.

32.2 psu (:to. 32.2 psu (:to. 32.2 psu (:to.4)
1570 1530 1560 1550 1540 1520 1500 1490 1510

590

Cook Inlet

If,,,,

Bering Sea

580

Continental

Shelf

570 (J' '\ Kaiugnak Bay

50 km

1570 1520 1510 1560 1500 1550 1540 1530

Figure 1, -- Map of the Kodiak Archipelago and adjacent study area,

590

580570
500

C\J

T"'"

Q) .c ~ 

E 0 300

::J Ic: 0 200

CtI a..

::J

CtI

CtI

CtI

-.J

400

100

100

a..

(ft.

Figure 2, --

6000

5000

4000 ~

3000 

::J 2000 Z

Month

1000

Seasonal variation in mean abundance (+SE) (top panel), and sampling effort and

percent occurrence (bottom panel) of Mal/otus villosus larvae in bongo samples

collected in the Gulf of Alaska 1977-98.
Bongo Neuston

2000 100 1200 100

1000

1500

800

Bay 1000 600

400

500

200

..... C\J C") -:t to CD I'- co 0) 0 ... 

.....

..... C\J C") -:t to CD I'- co 0) 0 

..........

000000000........0 000000000..........0 co co co co co co co co co co co 0) co co co co co co co co co co co 0) I'- I'- I'- I'- I'- I'- I'- I'- I'- I'- I'- I'- I'- I'- I'- I'- I'- I'- I'- I'- I'- I'- I'- I'-

CJ) c: CJ) CJ) c: CJ)

L:; E c:

..

L:; E c: :J"L:; C') L:;

..

C\I C/) - Q. C/) ~C/) :J C/)

C/) C/) c::(

;::...

Q)~ Q) C/)

(1j (1j (1j (1j

T"'" .....Jw .....Jw

1::: T"'" 1:::

c: 

2000 100 1200 100

'E 1000

::J Shelf 1500

::J 800 ::J

1000 600

Ctj 400

500 Ctj

200 ::J

::J

Ctj

Ctj

2000 100 Ctj 100

Ctj

Ctj 1500 -.J Ctj

Slope -.J

1000

500

!::: 

I'- co co co co co co 0) I'- I'- I'- I'- I'- I'- I'- I'- LLLLLL LLLLLL :2 -:t :2 :2 :2 :2 ~ :2 -:t :2 :2 :2 :2 ~ 

-:t

..:::...:!... 

to ..... -:t C\J C") -:t to 

..... ...

CJ) '- c: CJ) '-

c: Q) CJ) c: Q) CJ) E 'L:; E E 'L:; E

:J Q. E L:; :J Q. L:;

"5 C/)

C/) "5 C/)

C/) c::( C/) c::( c::( c::( C/) c::( c::(

;::... ;::...

Q) 

;::;::...

1:: 1:: 1:: 1::

(1j (1j (1j (1j (1j (1j (1j (1j

.....J .....J .....J .....J

1::: 1:::

Figure 3. -- Seasonal variation in sampling effort and mean abundance (+SE) of Mallotus villosus

larvae in bongo and neuston samples collected in bays and over the continental shelf

and slope near Kodiak Island, October 1977 - March 1979. Labels 7801 , 4MF77 etc.

are cruise numbers (see Table 1),
2 = 0.763

....

.c: :1:

:.:

C, 30

..

CJ)

....

.c:

C, 30

..

CJ)

L.. L.. L..

::J i:: ::J i::

c.. c..

::J ::J

c::( ::J

c::(

1977 1978 1979

Figure 4, -- Seasonal variation in mean standard length ( SE) of Mallotus villosus larvae collected

in bongo (top panel) and neuston (bottom panel) tows in bays and over the continental

shelf and slope near Kodiak Island, October 1977 - March 1979, and regression of

larval length with sampling date for summer through autumn of 1978.
Late Autumn 1977 Spring 1978

n = 79 n = 4

Summer 1978 Early Autumn 1978

J:: n = 1828 n=1115

...

c...

Late Autumn 1978 Winter/Early Spring 1979

n = 929 n = 184

Standard length (mm)

Figure 5, -- Seasonal variation in length frequency of Mallotus villosus larvae collected in

bongo tows in bays and over the continental shelf and slope near Kodiak Island

1977 - 79. n = number of fish larvae measured
Figure 6. --

Late Autumn 1977

Summe! 1978

Late Autumtl 1978

Spring 1978

Early Autu mn 1978

inter/Early Spring 1979

Larval abundance (number per 10 m

0 - 10

10 - 50

50 - 100

100 - 500

500 - 1 000

~ 1000

Seasonal variation in distribution and abundance (number per 10 m ) of Mallotus

villosus larvae collected in bongo tows in bays and over the continental shelf and slope

near Kodiak Island, 1977-79.
Spring 1978

n = 13

Summer 1978 Early Autumn 1978

n = 51 n = 121

CtS

D....

Late Autumn 1978 Winter/Early Spring 1979

n = 174 n =24

Standard length (mm)

Late Autumn 1977

n = 18

Figure 7. -- Seasonal variation in length trequency of Mal/o/us vil/osus larvae collected in

neuston tows in bays and over the continental shelf and slope near Kodiak Island

1977 - 79. n = number of fish larvae measured
Figure 8. --

Late Auturvn 1977

Summer 1978

Late Autumn 1978

SpriJ)g 1978

Early Autumn 1978

Winter/Early Spriog 1979

Larval abundance (number per 1000 m

0 -

10 - 50

50 - 100

100 - 500

500 - 1000

~ 1000

Seasonal variation in distribution and abundance (number per 1000 m ) of Mallotus

villosus larvae collected in neuston tows in bays and over the continental shelf and

slope near Kodiak Island, 1977-79.
Length c:: 10 

Length 20 - 40 mm

Length 1 0 - 20 mm

Length 

:::

40 mm

larval abundance (number per 10 m

0 - 10

10 - 50

50 - 100

100 - 500

500 - 1000

:::

1000

Figure 9, -- Distribution of four size-categories of Mallotus villosus larvae in bongo samples

collected during early autumn 1978.
larval abundance (number per 10m 2

0 -

10 - 50

50 - 100

100 - 500

500 - 1000

~ 1 000

Length c:: 10 

Length 20 - 40 mm

Figure 10. --

Length 10 - 20 mm

Length ~ 40 mm

Distribution of four size-categories of Mal/a/us vil/osus larvae in bongo samples

collected during late autumn 1978.
larval abundance (number per 1000 m

0 - 10

10 - 50

50 - 100

100 - 500

500 - 1000

:::-1000

Length ~ 1 0 mm

Length 20 - 40 mm

Figure 11, --

Length 10 - 20 mm

b!~

Length ~ 40 mm

Distribution of four size-categories of Mal/otus vil/osus larvae in neuston samples

collected during early autumn 1978.
larval abundance (number per 1000 m

0 - 10

10 - 50

50 - 100

100 - 500

500 - 1000

~ 1000

Length c:: 1 0 

Length 20 - 40 mm

Figure 12. --

Length 10 - 20 mm

Length ~ 40 mm

Distribution of four size-categories of Mallo/us villosus larvae in neuston samples

collected during late autumn 1978. 
..c

.9 

~ 20

a...

Bongo

n = 2366

Neuston

n = 398

10 20 30 40 

Standard length (mm)

Figure 13. -- Comparison of length frequencies for Mallotus villosus larvae collected in bongo (top

panel) and neuston tows (bottom panel) - data ftom all cruises combined. n = number

of fish larvae measured.
Figure 14, --

......

C\J

::J

CtI

::J

CtI

CtI

CtI

.....J

......

C\J

::J

CtI

::J

CtI

CtI

CtI

.....J

IffNIJiWlf&WI Stratified Mean Abundance & Standard Deviation

Total No, Tows

160

20 

:s:

15 ~

::J 10 Z

20 

:s:

15 ~

::J 10 Z

Diel variation (hourly intervals) in mean stratified abundance (+SD) of Mallotus

villosus larvae in bongo samples (top panel- data combined from cruises 4MF77

2MF78, 1WE78 and 1MF79), and neuston samples (bottom panel- data combined

from cruises 4MF77, 4DI78 , 1 WE78 and 1MF79).

100

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

Alaska Standard Time (Hours)
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