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Auke Bay Laboratory

(Quarterly Report for Oct-Nov-Dec 2000)

NPAFC Annual Meeting and Workshop

The Eighth Annual Meeting of the North Pacific Anadromous Fish Commission (NPAFC) was held in Tokyo, Japan,  from 30 October to 2 November 2000, and included a 1-day workshop on 29 October entitled “Factors Affecting Production of Juvenile Salmon: Comparative Studies on Juvenile Salmon Ecology Between the East and West North Pacific Ocean.”  Auke Bay Laboratory (ABL) staff participating in these meetings included Ed Farley,  Bill Heard,  Jack Helle, and Dick Wilmot.  Helle coauthored a feature presentation on “Research conducted by the United States on the early ocean life history of Pacific salmon.” Heard presented an invited paper on “A synthesis of research on early marine ecology of juvenile Pacific salmon in Southeast Alaska.”  ABL  posters presentations were by Farley on “Factors affecting distribution, migration, and growth of juvenile sockeye salmon in the eastern Bering Sea (July-September 1999), and by Joe Orsi (with Heard as stand-in) on “Southeast Alaska coastal monitoring for habitat use and early marine ecology of juvenile Pacific salmon.” ABL staff also participated in the Committee on Scientific Research and Statistics review of a range of issues including the relationship between changes in ocean and atmospheric conditions and the abundance and other biological and ecological characteristics of salmonid production.   A new NPAFC Science Plan was adopted that will focus on three areas of cooperative marine research: Bering Sea, juvenile salmon research, and winter salmon research.

By Bill Heard.

U.S.- Japan Natural Resources (UJNR) Aquaculture Panel Meetings

Bill Heard participated in the U.S.-Japan (UJNR) Aquaculture Panel’s 29th Annual Meeting and Symposia at Ise in Mie Prefecture and Mini-Symposium at Ishigaki in Okinawa Prefecture, and as Secretary General of the U.S. Panel from 7 to 17 November 2000.   The symposium at Ise focused on “Pathogenic Organisms and Disease Prevention in Aquaculture Systems.” The Ishigaki symposium, held at the Ishigaki Tropical Station,  was  on “Present Status and Perspectives of Environmentally-Friendly Aquaculture and Resource Enhancement in Tropical Regions.” At the annual UJNR business meeting there was a general reluctance on the part of the Japanese scientists to jointly enter into new 5-year plan of themes for UJNR until after the major reorganization of governmental agencies is completed.

By Bill Heard

Pacific Aquaculture Caucus Meeting

In October, Alex Wertheimer of the Auke Bay Laboratory attended part of a 2-day meeting hosted by Pacific Aquaculture Caucus (PAC) at the NMFS Manchester Field Station that  featured the Advanced Technology Program (ATP) of the Department of  Commerce (DOC),   National Institute of Standards and Technology (NIST).  The meeting was designed to examine the Northwest aquaculture industry’s potential in utilizing ATP funding support for testing new aquaculture technologies and methods.  The ATP/NIST focus on applying new technologies to aquaculture is part of the DOC’s recent commitment to encourage development of an environmentally sound and economically viable U.S.-based aquaculture industry to help provide safe, wholesome, seafoods for the Nation.  A strong U.S. aquaculture industry is essential to help relieve pressures on depressed wild stocks of fish and other seafoods harvested in capture fisheries and to help reduce a major balance of payments deficit on imported sea food products.

By Bill Heard.

Stock Assessment of Slope Rockfish and Pelagic Shelf Rockfish in Gulf of Alaska

Updated stock assessments of slope rockfish and pelagic shelf rockfish in the Gulf of Alaska were completed during the quarter.  The completed assessments for Pacific ocean perch and northern rockfish (members of the slope rockfish assemblage) used age-structured models. The estimated exploitable biomass was 211,160 metric tons (t) for Pacific ocean perch and 93,850 t for northern rockfish.  The Pacific ocean perch (POP) stock is increasing. The northern rockfish stock is decreasing because of recent weak recruitment.  This was the first time that the stock assessment for northern rockfish was based on an age-structured model. The assessment of other species of slope rockfish and pelagic shelf rockfish in the Gulf of Alaska rely exclusively on biomass estimates provided by trawl surveys.  The most recently completed assessment indicates the following stock levels and stock trends: shortraker and rougheye rockfish exploitable biomass 70,890 t, trend unknown; other slope rockfish, exploitable biomass 102,510 t, trend unknown; pelagic shelf rockfish exploitable biomass 66,440 t, trend unknown.  The recommended Acceptable Biological Catches (ABC) for 2001 were the following: 13,510 t for POP; 1,730 t for shortraker and rougheye rockfish; 4,880 t for northern rockfish; 4,900 t for other slope rockfish; and 5,980 t for pelagic shelf rockfish. Compared with 2000, the 2001 ABC for POP increased approximately 500 t, slightly decreased for northern rockfish, and remained the same for the other species groups listed. These ABC values were all accepted by the North Pacific Fishery Management Council (NPFMC).

Alaska Sablefish Assessment

The final sablefish assessment was prepared by Mike Sigler (ABL), Jeff Fujioka (ABL), and Sandra Lowe (REFM) and presented to the NPFMC’s groundfish plan teams and Scientific and Statistical Committee (SSC).  The assessment shows that sablefish abundance increased during the mid-1960s due to strong year classes from the late 1950s and 1960s. Abundance subsequently dropped during the 1970s due to heavy fishing; catches peaked at 56,988 t in 1972.  The population recovered due to exceptional year classes from the late 1970s; spawning abundance peaked again in 1987. The population then decreased because these exceptional year classes are dying off.

For the combined stock in the GOA and Bering Sea/Aleutians Islands, the survey abundance index decreased 10% in numbers and 8% in weight from 1999 to 2000. These decreases follow survey abundance index increases from 1998 to 1999 of 10% in numbers and 5% in weight and in the fishery abundance index of 7% in weight, so that relative abundance in 2000 is similar to 1998.  Fishery abundance data for 2000 were not analyzed because the fishery was still ongoing.  Exploitable and spawning biomass are projected to increase 3% and 4%,  respectively, from 2000 to 2001.  Alaska sablefish abundance now appears low and stable.  This confirms the conclusion from last year’s assessment that the abundance trend has changed from low and slowly decreasing to low and stable.  Abundance is projected to continue to increase slowly; the size of the increase depends on the actual strength of the above-average 1997 and 1998 year classes.

A simple Bayesian analysis was completed by examining the effect of uncertainty in natural mortality and survey catchability on parameter estimation.  A decision analysis was completed using the posterior probability from the Bayesian analysis to determine what catch levels likely will decrease abundance.  The decision analysis indicates that a yield of 16,800 t will maintain spawning biomass.  The maximum permissible yield using an adjusted F40% strategy is 16,900 t.  Based on these results, we recommended a 2001 ABC of 16,900 t for the combined stock, similar to the 2000 ABC of 17,300 t. The recommended ABC for 2001 was accepted by the NPFMC.

By Michael Sigler

Electronically Tagged Sablefish Recovered

Auke Bay Laboratory scientists began tagging sablefish with electronic tags in 1998 in an effort to learn more about sablefish behavior and the marine environmental conditions in which they live.  The electronic tag records depth and temperature.  We are learning about the daily, seasonal, and age-related depth movements of sablefish from recovery of these tags.  Knowledge of these movements will help us understand what part of the population is susceptible to the fishery, and how this susceptibility changes during the life of the fish.  This information will help us improve recommended sustainable harvests.

During the 1998 longline survey of the Aleutian Islands region and Gulf of Alaska, electronic tags, measuring 3/4 inches diameter by 2 1/4 inches long, were surgically implanted in the abdominal cavity of 195 sablefish. The fish also were externally marked with a fluorescent pink and green tag.  During the 2000 longline survey, about 130 electronic tags were implanted.

Twenty electronic tags have been recovered so far: 1 during 1998, 8 during 1999, and 11 during 2000.  One tagged fish was at large 2 months, and the remainder 1-2 years.  The fish generally were shallower during summer and deeper during winter.  Average weekly depth for each recovered fish ranged  from 200 to 500 m during summer and 400 to 700 m during winter.  Average weekly temperature at depth ranged from 3.5° to 6.5°C, but no seasonal pattern was apparent.  Individual fish traveled a wide depth range, sometimes during 1 or 2 days.  For example, one fish rose from about 1,100 m to 670 m in 1.5 days and to 220 m in 9 days during October 1998.  Some fish also exhibited diel vertical migrations. For example, one fish rose from about 500 to 200 m at dusk and returned to 500 m at dawn. This cycle lasted  several months.

By Michael Sigler.

Gulf of Alaska Coastal Research on Juvenile Salmon

A research cruise was conducted by the Ocean Carrying Capacity Program during August 2000 to study the early marine distribution, migration, and growth of juvenile salmon in the coastal waters of the Gulf of Alaska. Emphasis of the August cruise was placed on determining migratory pathways for juvenile salmon around Kodiak Island. Initial results based on average size of juvenile salmon indicate that juvenile salmon captured in Shelikof Strait may be from localized stocks near Kodiak Island.  Future analysis of juvenile salmon otoliths for hatchery thermal marks and tissues using genetic stock identification techniques will shed additional light on the migratory pathways of juvenile salmon around Kodiak Island.

By Ed Farley.

Eastern Bering Sea Coastal Research on Juvenile Salmon

An eastern Bering Sea research cruise was conducted by the Ocean Carrying Capacity Program during August 2000 to study the early marine distribution, migration, and growth of juvenile sockeye salmon from Bristol Bay and early marine distribution and migration of juvenile chum salmon from the Kuskokwim River. Juvenile sockeye salmon were distributed in the middle domain of the eastern Bering Sea east of 166ºW. The distribution differed from our September 1999 survey where large numbers of juvenile salmon were found within both the coastal and middle domains. These differences in distribution (habitat) between years may have played a vital role in increased early marine growth for juvenile sockeye salmon caught during August 2000 when compared to those caught during September 1999. The largest catch of juvenile chum salmon occurred in the coastal domain of the eastern Bering Sea south and west of the Kuskokwim River between 163ºW and 164ºW. Further sampling north, south, and east of Nunivak Island will be needed to determine early marine distribution and migration of juvenile chum salmon leaving the Kuskokwim River and entering the Bering Sea.

By Ed Farley.

Distribution, Migration, and Growth of Juvenile Sockeye Salmon in the Eastern Bering Sea

The early marine ecology of juvenile sockeye salmon was compared between July and September 1999 in the eastern Bering Sea.  Most juvenile sockeye salmon were encountered northeastward of Port Moller during July and were distributed from nearshore to 74 km offshore.  The extent of offshore distribution of juvenile sockeye salmon may have been related to sea surface temperatures. Sea surface temperatures during this period indicated that a cold pool of surface water (<6ºC) was located offshore between Port Moller and Port Heiden.  Juvenile sockeye salmon were encountered shoreward of the cold pool, apparently preferring the warmer surface waters along the coast.  Most of the juvenile sockeye salmon encountered during September were southwestward of Port Moller and were distributed from nearshore to 150 km offshore.  The expanded offshore distribution of juvenile sockeye salmon encountered during September was associated with increased sea surface temperatures (>8.5ºC) within this area.

The 1999 surveys were unique in that they occurred after a cold spring in the eastern Bering Sea, which was characterized by a delay in the breakup of lake-ice in sockeye salmon nursery lakes and anomalously cold sea temperatures.  The cold spring may have delayed the seaward migration of juvenile sockeye salmon.  For example, during July we caught only one juvenile sockeye salmon west of Port Moller; whereas, past studies of juvenile salmon migration in the eastern Bering Sea that occurred after relatively warm springs, indicated that large catches of juvenile sockeye salmon could occur west of Port Moller during this time period.

Our 1999 survey results suggest that the anamolously cold spring and surface water temperatures possibly delayed offshore migration of juvenile sockeye salmon into areas of greater forage densities, affecting their early marine growth.  During July and September 1999, zooplankton densities (ml·m-2) were greatest within the middle domain and within the coastal domain west of Port Moller.  Differences in seasonal distribution of juvenile sockeye salmon (inhabiting areas with low zooplankton densities during July and high zooplankton densities during September) may explain the significantly higher growth and condition factor found for juvenile sockeye salmon captured during September than those captured during July.  Similar observations of early marine distribution, migration, and growth of juvenile sockeye salmon encountered within the coastal waters of the eastern Bering Sea during the summer of 1971 (which followed an anomolously cold spring) by Straty (1974) were followed by dramatically reduced adult sockeye salmon returns to Bristol Bay two (1973) and three (1974) years later.  If this qualitative comparison holds true, then we may expect lower than average returns of 2-ocean sockeye salmon to Bristol Bay during summer 2001.

By Ed Farley