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Auke Bay Laboratory

(Quarterly Report for Jul-Aug-Sep 2000)
  

Distribution and Habitat of Rockfish in Nearshore Waters of Southeast Alaska

From 1998 to 2000, a remotely operated vehicle (ROV) was used to record in situ observations of juvenile and adult rockfish (Sebastes spp.) in nearshore waters (<90 m deep) of Southeast Alaska; 210 ROV dives were completed at 37 sites.  Habitat types sampled included eelgrass meadows, kelp beds, vertical bedrock walls, soft-bottom basins, and complex bottoms of boulder or rock.  Of the 32 species of rockfish found in the Gulf of Alaska, 13 species were observed in this study.  Most observations of rockfish were at sites closer to the outer coast. Quillback rockfish (S. maliger) were observed at more sites than any other rockfish species, whereas China rockfish were observed at only one site.  Most observations (>70%) of rockfish were in complex and vertical wall habitats with numerous ledges, holes, and crevices for cover.  No rockfish were observed over soft bottoms with no relief.  Black, copper, and unidentified juvenile rockfish were commonly observed in or near vegetation (e.g., eelgrass).  Median depth of observations ranged from 16 m for black rockfish (S. melanops) to 62 m for rosethorn rockfish (S. helvomaculatus).  Information from this study will help managers identify and protect essential fish habitat.  This is especially important because nearshore habitats are susceptible to impacts from shoreline development.

By Scott Johnson.


Residence, Diet, Growth, And Condition of Juvenile Rockfish in Subtidal Vegetated Habitats of Southeast Alaska

A 2-year study on juvenile rockfish was completed in September 2000. In summer 1999, movement of age-1 copper rockfish (S. caurinus) and quillback rockfish was investigated in Sitka Sound, Alaska, to determine residence time in eelgrass and kelp habitats (Habitat Areas of Particular Concern). Results from a mark-recapture experiment in the first year of the study showed that juvenile rockfish move into shallow eelgrass and kelp habitats in May and remain in the same local area through late summer.

In summer 2000, growth and diet of age-1 copper and quillback rockfish within two small semi-enclosed  bays sampled in 1999 were investigated by mark-recapture methods. Eelgrass and understory kelp sites from each bay were sampled with a beach seine monthly from May to September 2000. Fish were marked with injected elastomer tags to distinguish month and site and with sequential coded wire tags (CWT) to obtain unique identification. A total of 4,636 juvenile rockfish were captured, of which 2,969 were tagged, and 720 were recaptured.  In addition, 64 age-2+ copper, quillback, and brown rockfish were recaptured from fish marked the previous year, 72% of which were recaptured at the same site where they were tagged.  Growth rates will be compared between the two habitat types.  Also, fish were collected for diet description and diel sampling to calculate diet ration within each habitat.

By Scott Johnson.


Study of Spot Shrimp Decline in Prince William Sound

The goal of the ABLs Prince William Sound (PWS) spot shrimp (Pandalus platyceros) project  is to determine the extent to which spot shrimp abundance in western PWS has recovered since the population decline which began just prior to 1989. Our objectives in FY2000 were:

  1. to estimate the abundance of spot shrimp at 12 sites in western PWS

  2. to determine the sex and size composition of spot shrimp at the study sites

  3. to estimate spot shrimp fecundity and relative number of egg-bearing females at the study sites

  4. to compare abundance data and data on population structure obtained for this project with that collected by the Alaska Department of Fish and Game (ADF&G).

We accomplished these objectives by sampling six sites traditionally included in ADF&Gs annual survey using a methodology similar to ADF&Gs. In addition, we added six new sites selected during a preliminary cruise in August 1999. We sampled spot shrimp using two strings of 11 pots each at each site in October 1999. Our methods differed from those of ADF&G only in the type of pot used. We used a conical pot identical to that used by ADF&G in southeastern Alaska. In PWS ADF&G uses a rectangular pot.

In a side-by-side comparison of the conical and rectangular pots we found the rectangular pot to be less effective than the conical pot in catching spot shrimp. However, our pot was somewhat smaller and had larger mesh openings in the entrance tunnels. Subsequent comparison of our data with a summary of ADF&Gs data at the same sites also collected in October 1999 revealed no significant difference between our estimate of the number of spot shrimp per pot or weight of the shrimp catch per pot and that of ADF&G. Nevertheless, in the interest of standardization within the ADF&G as a whole, we recommended that the ADF&G in Cordova change to the conical pot as soon as resources become available to do so. Statistical comparison of the summarized ADF&G annual survey data from 1998 and 1999 provided to us by ADF&G revealed no significant increase in the number of spot shrimp per station or weight of the shrimp catch per station between 1998 and 1999. Although examination of the mean values for these variables appeared to suggest that population recovery may have been starting in 1999, we do not have the evidence to indicate an increase in spot shrimp abundance between 1998 and 1999.  We found no significant differences between ADF&Gs traditional six sites and our six new sites in October 1999 for several variables related to the spot shrimp populations at those sites including: mean number of spot shrimp per pot, mean weight of spot shrimp per pot, mean carapace length of males, transitional shrimp and females, and fecundity. This suggests that our 6 new sites could be added to the traditional sites of ADF&G to form a suite of 12 or more sites from which 6 sites could be randomly chosen for the ADF&G annual survey, thereby precluding statistical difficulties from lack of independence that follows from sampling the same sites each year.

Our estimates of spot shrimp fecundity were frequently substantially higher than previously published estimates for the ADF&G traditional sites from 1989 to1991. We were unable to test the difference between those estimates and ours because we lacked the raw data on fecundity used to calculate the ADF&G estimates. If the differences were real, they may represent true interannual differences in the mean fecundity of the shrimp populations at these sites suggesting that spot shrimp fecundity may be an important variable to monitor on a periodic basis.

By Chuck OClair.


Examination of Lipid Class and Fatty Acid Composition of Northern Fur Seals from St. Paul Island

Lipid and fatty acid analyses provide a basis for evaluating the nutritional condition of animals by measuring the relative concentration of triacylglycerides (TAG). This is a direct index of the amount of surplus energy stored as lipid in animal tissues as a result of diet.  Otariids are likely to be especially amenable to these analyses because their blubber is easily sampled, metabolically active, and is an important site for fat storage.  Of particular interest is the northern fur seal (Callorhinus ursinus), which has been suffering recent population declines posited to result from changes in the nutritional quality of their prey. Consequently, lipid class and fatty acid analysis may offer significant advantages over existing biased or invasive methods for examining diet content and quality in these mammals.  However, for blubber to be useful in the analysis of the nutritional well-being of these marine mammals, the homogeneity of lipid and fatty acids must be assessed between specific sites on the body, as well as between metabolically active proximate blubber layers and relatively inert distal layers.

Blubber samples for  lipid class and fatty acid analysis were taken by the National Marine Mammal Laboratory (NMML) from 3 female and 16 male northern fur seals harvested on St. Paul Island, Alaska in 1997.  Samples were collected from locations near the neck, shoulder, and pelvis from each seal. The blubbers were divided longitudinally, and one of the resulting sections was further divided latitudinally to provide an inner, outer, and complete section of blubber from each body location, for a total of 164 samples. The nonpolar lipid and fatty acid composition of each sample was evaluated at the ABL by high performance liquid chromatography and mass spectrometry, after which ANOVA was used to compare the nonpolar lipid content and principal components analysis (PCA) to compare fatty acid compositions. Comparisons were drawn between samples to determine if fatty acid and nonpolar lipid content differed among body locations, blubber layers, sexes, and individuals.

Nonpolar lipid content varied widely among individuals ranging from 148 to 1,189 mg/g blubber. Nonpolar lipid content also varied between the sexes primarily as a result of the inclusion of a primiparous female in the data set. Within individuals, body locations also differed in nonpolar lipid content, but no body location was consistently greater than the others. Blubber layers did not differ in nonpolar lipid content. Comparison of  individuals and sexes revealed large differences in the 29 fatty acids analyzed. PCA models could not reliably distinguish differences in the fatty acid composition of blubber in different body locations or blubber layers. These data indicate that individual differences in blubber fatty acids are a driving feature in the overall variation of blubber  fatty acid composition. Future sample collections of  blubber from fur seals can be taken from any body location, but that location should be consistent from individual to individual.  Future studies in cooperation with the NMML will utilize results presented here to examine differences in the lipid class and fatty acid composition of two distinct populations of northern fur seals, and compare those compositions to that of potential prey.

By Johanna Vollenweider.


Decomposing Salmon Carcasses are Important Nutrition Source for Juvenile Salmon

Returning adult salmon are known to represent an important source of nitrogen and phosphorous to their natal streams. The arrival of these nutrients results in increased productivity at lower trophic levels because the organisms can rapidly assimilate the nutrients.  However, decaying carcasses also contain macromolecules such as essential fatty acids, which can be of vital importance to resident fishes. Top level predators may obtain the macromolecules by consuming the flesh of decaying adults or by consuming other scavengers.  Consequently, the annual arrival of adult salmon may have a quantitative impact on the nutritional status of resident fish populations. This is likely to be seen as changes in the amount of stored lipids which are called triacylglycerides (TAG). In addition, the composition of the TAG should represent a more marine signature if the bulk of the stored lipids are derived from decaying adults.

In a cooperative study  with the U.S. Forest Service, ABL scientists tested these hypotheses by constructing simulated coho salmon (Oncorhynchus kisutch) streams, loading them with various amounts of pink salmon carcasses and, after 60 days, evaluating the lipid class and fatty acid composition of resident coho salmon.  Carcass loads in the streams ranged from 0 to 4 carcasses per square meter. The TAG concentrations in coho salmon increased with carcass load from 0.78 mg/g lipid in unloaded streams to 28.9 mg/g in the most heavily loaded streams.  Increases in TAG  resulted from the storage of marine-
derived Omega-3 fatty acids. Juveniles from unloaded streams averaged one tenth the Omega-3 fatty acid content of coho salmon from the most heavily loaded streams.  Coho salmon are unable to synthesize Omega-3 fatty acids but depend on them for maintaining cell membrane integrity and osmoregulation during smolting.  Thus, overwinter survival and smolting success of resident juveniles are influenced by the availability of these compounds as provided by the biomass of returning adults.

By Ron Heintz.


Hatchery Pink Salmon in Prince William Sound: Enhancement or Displacement?

Total pink salmon (O. gorbuscha) production in Prince William Sound (PWS) is currently at historic highs; catches over the past decade have averaged 27.0 million fish annually.  Over 85% of this production is from a system of large hatcheries.  The hatcheries are considered by some to be a tremendous success;  protection of the hatcheries from oil contamination was one of the highest priorities in the response to the Exxon Valdez oil spill in 1989.  However, there has also been concern that hatchery production may have been deleterious to wild pink salmon in PWS, complicating the achievement of escapement goals and reducing productivity.  A recent analysis published in Transactions of the American Fisheries Society asserts that hatcheries have caused a decline in the productivity and escapements of wild pink salmon and that hatchery fish to a large degree have replaced, not enhanced, pink salmon returns in PWS, resulting in an average net gain of only 2.0 million pink salmon annually.

The ABL, in collaboration with the University of Alaska and ADF&G, prepared an alternative analysis of the changes in pink salmon production in PWS.  By comparing catches from historical and current peak production regimes, they showed that numbers of pink salmon in PWS have increased to a much greater degree than in three other regions of Alaska: Southeast Alaska, Kodiak, and south Alaska Peninsula.  They did find that wild stock abundance has declined over a time period in which wild stock abundances have generally increased in other regions; hatchery interactions were a possible contributing factor to this asynchronous decline.  However, they also found asynchrony in previous increases and declines of wild stock production in PWS relative to other regions, which may indicate that other biophysical changes concurrent with increased hatchery production have caused density-independent decline in wild stock productivity in the recent past.  Based on these temporal comparisons, they estimated that average net gain in catch of pink salmon in PWS due to hatcheries has been 17.5-23.7 million fish for the decade of the 1990s.  They showed that the estimates of net gain of only 2.0 million pink salmon were based on a model that produces highly unrealistic estimates of wild stock production potential.  They also found that management resolution for meeting escapement goal ranges has improved in PWS and is the likely explanation for the decline in wild stock escapements from a time period when escapements were chronically above the escapement goal range, to a time period when escapements were generally closer to or within the management range.

By Alex Wertheimer.


Ocean Survival of Wild Coho Salmon

Research at ABL's Auke Creek hatchery and weir is conducted to evaluate the long-term ocean survival of wild coho salmon.  While ocean survival of coho salmon throughout much of its southern range has declined  in Southeast Alaska over the previous three decades, including the Auke Creek stock, survivals have been in an increasing trend since at least 1980.

Coho salmon studies at Auke Creek are conducted under a long-term cooperative project between the ABL and ADF&G.  The Auke Creek coho salmon stock is one of four wild stocks used as index systems in Southeast Alaska..  Ocean survival rates of wild coho salmon at Auke Creek are known from 1977, when CWTs were first used on smolts leaving Auke Creek, through 2000, except 1979 (Figure 1).  The research at Auke Creek relies heavily on the permanent fish weir and includes the annual capture and tagging of seaward-migrant smolts and capture and enumeration of  fish returning to the creek.  Auke Creek is the only index site where all smolts are captured and marked.  Ocean survival of each smolt cohort is estimated by summing the fishery harvest of adults and the number adults that return to the weir. Fishery harvest is estimated by the ADF&G from the number of tagged fish recovered during rigorous sampling of the commercial and sport fisheries.

Although the 2000 coho returns to some areas of Southeast Alaska were depressed, the ocean survival of Auke Creek coho was close to the long-term average of 19%.  The ocean survival of the 1999 smolts that returned as adults in 2000 from Auke Creek was 17 %.  The harvest of about 250 coho in the fishery accounted for a 5% return of smolts, and the return of 623 coho to the weir represented 12% of the smolts.  Scales and size data on the fish returning to Auke Creek are being collected and archived.  A major retrospective analysis using the data on scale growth patterns and ocean survival is being planned.   We propose to use data on Auke Creek coho salmon adults and past and proposed coastal sampling studies to retrospectively examine ocean growth and survival.  We will compare interannual marine growth, as reflected in adult scales, to document the range of scale growth patterns, and compare theses patterns with marine survival, smolt-to-adult, for coho salmon at Auke Creek.

By Jerry Taylor.


Hook Spacing Studies

A sablefish (Anoplopoma fimbria) hook spacing experiment was conducted in the Gulf of Alaska off Yakutat Bay 25-26 July 2000 aboard the fishing vessel Alaskan Leader.  Four hook spacings of 0.5, 1, 2, and 4 m were tested using standard survey longline gear. Results were consistent with two previous hook spacing experiments conducted by ABL scientists; catch per hook increased as hook spacing increased.  These data are being used to improve an equation for standardizing catch rate differences associated with hook spacing.  This relationship is being used to standardize the catch rates of commercial longline vessels, and the standardized rates will be included in the sablefish stock assessment.

By Chris Lunsford.


Seamounts

NMFS exploratory trawl and trap fishing on nine Gulf of Alaska seamounts in June and July 1979 found that sablefish were the dominant finfish on each of the seamounts. Of the sablefish sampled,  nearly all were ripe, spawning, or recently spent, and there was a total absence of younger, immature fish, indicating that the populations of sablefish on seamounts are maintained by the migration of mature fish from the continental slope rather than by local recruitment. Tagged fish released at different areas of the slope have been recovered on Gulf of Alaska seamounts, verifying that slope to seamount migration does occur.  It is not known if emigration from the seamounts or exchange between seamounts occurs.

Seamount sampling during the annual sablefish longline survey was initiated in 1999 and continued in 2000.  During the 1999 survey, Giacomini, Surveyor, and Pratt seamounts were sampled.  A total of 2,400 sablefish were caught.  About 800 fish were tagged and released, and otoliths were taken from 140 fish.  Length, sex, and maturity were recorded for almost all sablefish caught.

During the 2000 longline survey, we revisited Surveyor and Pratt seamounts and fished Welker seamount for the first time.  Catches were down slightly from 1999 at Surveyor seamount and about the same as last year at Pratt.  A total of 930 fish were tagged and released from the three seamounts.  Otoliths and length and sex data were collected as in 1999.  Seven tagged fish were recovered from the same seamounts where they were released last year, and one tagged fish, released off Kodiak in 1989, was recovered on Welker Seamount.  Seamount sampling will continue on the 2001 annual longline survey.

By Nancy Maloney.


Rockfish and Sablefish Stock Assessment

Survey data from the 2000 longline survey have been processed and incorporation of results into assessment models are in the preliminary stages.  Work was done to improve the new age-structured model for northern rockfish, first previewed at last years Groundfish Plan Team meeting; the model will be finalized in October. Longline survey data also will be incorporated into an assessment model for shortraker (Sebastes borealis) and rougheye (S. aleutianus) rockfish, and we are developing a preliminary assessment model for dusky rockfish.

By Jeff Fujioka.


Alaska Longline Survey Completed

The AFSC  completed the twenty-second annual longline survey of the upper continental slope of the Gulf of Alaska and eastern Aleutian Islands region on 5 September 2000.  One hundred-forty-eight longline hauls (sets) were completed.  Sablefish  was the most frequently caught species, followed by giant grenadiers (Albatrossia pectoralis), Pacific cod (Gadus macrocephalus), arrowtooth flounder (Atheresthes stomias), and Pacific halibut (Hippoglossus stenolepis).  A total of 76,351 sablefish were taken during the survey.  A total of 3,098 sablefish, 492 shortspine thornyhead (Sebastolobus alascanus), and 37 Greenland turbot (Reinhardtius hippoglossoides) were tagged and released during the survey.  Length-weight data and otoliths were collected from 2,079 sablefish. Twenty-seven surface gillnet sets were completed to assess the abundance of juvenile sablefish.  A low number of sablefish (138 young-of-the year) were caught in the small mesh gillnets during the 2000 survey.  Killer whales preying on sablefish and Greenland turbot retrieved on the gear were observed at one Aleutian Islands station and one Gulf of Alaska station.

By Mike Sigler.


Rockfish Genetics

Genetic samples of Pacific ocean perch were collected from the Aleutian Islands region and the Bering Sea during AFSC trawl surveys to examine the population structure of Pacific ocean perch throughout Alaska.  An additional study in under way to examine the potential for a genetic basis underlying the different color morphs of rougheye rockfish. Genetic samples of rougheye rockfish were collected during the 2000 longline survey. Both light and dark color morphs and intermediates have been observed, and two quite different genetic forms have been identified, often in the same catches. The large genetic differences suggest the possibility of two species. These studies are being done under sponsorship of the AFSC's Rockfish Working Group in cooperation with the University of Alaska Fairbanks, Juneau Center School of Fisheries and Ocean Sciences .

By Jon Heifetz.


Growth and Recruitment of Shallow-water Alaskan Gorgonian

At least 20 species of gorgonian corals inhabit Alaskan waters. Specimens of all but one species have been incidentally entangled in fishing gear (e.g., hook and line, longlines, trawls, crab pots, and fish traps) and detached from the seafloor.  Several species attain large size and provide essential habitat in the form of structure and refuge for species of demersal fishes and invertebrates.  The effects of coral habitat alteration on benthic communities are unknown but may be substantial due to the reported longevity and slow growth rates of cold-water corals.  The North Pacific Fishery Management Council is considering measures to establish several marine protected areas where gorgonian corals are abundant.

We examined growth and recruitment of a shallow-water Alaskan gorgonian (Calcigorgia spiculifera) in an effort to elucidate the effects of fishing activities on coral habitat. We used computer image analysis tools to measure the linear length of colony branches from digitized video images collected on tagged specimens in situ.  Length of a branch was measured along the medial axis from the point opposite its origin.  This method provides a permanent record of colony morphometry.  Highly accurate measurements are possible with proper colony orientation with respect to the calibration grid and parallel alignment of the camera lens with the grid.

Thirty five colonies were tagged at two sites in July 1999.  We relocated 32 (91%) of those colonies in July 2000.  The missing colonies were presumably detached from the seafloor.  Growth measurements were possible for 16 colonies.  Growth rate was variable for branches from the same colony and also between colonies.  Mean branch growth rate at both sites ranged from -1.82 to 14.83 mm yr-1.  Growth rates (mean = 5.81 mm yr-1, SD = 4.99) measured during this study were generally much lower than those reported for other gorgonians worldwide, including  (Primnoa sp.), a deep-water Alaskan species.  Recruitment of new colonies had not occurred at either study site for a minimum of several years.

The slow growth rates measured during the first year of this study, although preliminary, are noteworthy since shallow-water corals are widely believed to have faster growth rates and shorter life spans than deep-water corals.  Additionally, recruitment appears to be a rare, sporadic event.  Shallow-water gorgonian communities may therefore exhibit slow recovery rates from seafloor perturbations.  Our future research priorities are to focus on growth of smaller colonies and to establish a third study site where colonies are more numerous and more variable in size (i.e., age).

By Robert Stone.


First International Deep Sea Corals Symposium

Robert Stone and Ken Krieger attended The First International Symposium on Deep Sea Corals held 30 July to 3 August 2000 at Halifax, Nova Scotia, Canada.  Robert presented a poster titled "Growth and Recruitment of an Alaskan Shallow-water Gorgonian" and a paper for Jon Heifetz titled "Coral in Alaska: Distribution, abundance, and species associations."  Ken Krieger presented a paper titled "Observations of megafauna that associate with Primnoa spp. and damage to Primnoa by bottom fishing."

  

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