AUKE BAY LABORATORY (ABL)

Ocean Carrying Capacity Program

Fishing Power Models and Trawl Comparisons During the 2002 BASIS Survey

At the 2004 Marine Science Symposium in Anchorage, Jim Murphy of Auke Bay Laboratory (ABL) presented a poster on fishing power models and trawl comparisons of vessels used during the 2002 Bering-Aleutian Salmon International Survey (BASIS). The BASIS survey is a cooperative research program by member nations of the North Pacific Anadromous Fish Commission. The program was created to address critical information gaps for the marine phase of Pacific salmon (Oncorhynchus spp.), through seasonal pelagic trawl surveys to determine distribution, abundance, and stock origins of salmon in the Bering Sea.

A key factor in the ability of BASIS to accomplish this objective is ensuring that catches are comparable between different BASIS research vessels. Trawl comparisons were completed by the Japanese research vessel Kaiyo Maru, the U.S. chartered fishing vessel Northwest Explorer, and the Russian research vessel TINRO in the central Bering Sea between 14 and 17 September during the 2002 BASIS survey, and fishing power models were constructed accordingly.

Fishing power was highest for the Kaiyo Maru, followed by the TINRO, and the Northwest Explorer. Higher fishing power by the Kaiyo Maru reflects the larger vertical opening of this vessel’s trawl. Catch rates were based on area trawled rather than volume, and therefore do not account for differences in trawl height. The largest difference in fishing power between vessels was observed for juvenile Atka mackerel (Pleurogrammus monopterygius). The larger fishing power coefficients for Atka mackerel are primarily due to the deeper vertical distribution of these fish.

By Jim Murphy


Distribution of Juvenile Pink Salmon in the Gulf of Alaska Relative to Surface Salinity and Potential Implications for Foraging and Growth Opportunities

The NOAA ship Miller Freeman and the research vessel Alpha Helix participated in a coordinated oceanographic and fisheries sampling effort on the Alaskan continental shelf near the Seward Line during July 2003. On this occasion, the brackish Alaska Coastal Current (ACC) (27 psu (practical salinity unit) surface salinity) ran near shore and was separated from saltier midshelf water (31 psu) by a frontal region (29 psu) a few kilometers in width. Sampling in all three zones consisted of conductivity-temperature-depth (CTD) casts, multiple opening/closing net and environmental sensing system (MOCNESS) hauls, and juvenile salmon trawls. Juvenile pink salmon diet was quantified onboard the Miller Freeman, and potential zooplankton prey items were collected via MOCNESS onboard the Alpha Helix.

The observations were designed to determine how juvenile pink salmon are distributed relative to surface salinity and to assess the energetic costs and benefits associated with physical and biological conditions across a salinity gradient. The working hypothesis was that juvenile pink salmon would be confined to the ACC and would not be found farther offshore. However, juvenile pink salmon were found both in the ACC and offshore, thus negating the hypothesis. Juvenile pink salmon inhabiting the brackish core of the ACC had the highest diversity of zooplankton prey in their diet. The highest growth efficiencies were obtained in midshelf water and the lowest in the brackish core water of the ACC. The greatest variation in juvenile pink salmon consumption demand occurred in the brackish core water of the ACC.

By Jamal Moss


Juvenile Salmon, Water Characteristics, and Phytoplankton in the Southeastern Bering Sea

Lisa Eisner of ABL presented a poster at the 2004 winter meeting of the American Society of Limnology and Oceanography, on juvenile salmon distributions, water mass characteristics, and phytoplankton biomass in the southeastern Bering Sea. Surface fish trawls and oceanographic data were collected during fall 2003 as part of the BASIS program. Distributions of juvenile salmon and their primary prey (young-of-year pollock) were compared to temperature and salinity, and phytoplankton biomass (total and percentages within each size class) across frontal boundaries.

Different salmon species have different distributions, possibly due to variations in migration patterns or preferred prey species. Juvenile sockeye salmon, the most abundant salmonid in the southeastern Bering Sea, are located in the 2-layer system in the middle shelf and their distributions overlap young-of-year pollock distributions for a large part of the study area. In contrast, juvenile chinook salmon have the highest abundance within the low salinity nearshore waters in the coastal realm. This ongoing work provides information on interactions between physical and biological oceanographic parameters and juvenile salmon abundances and adds to our understanding of the climatic influences on marine ecosystems in the eastern Bering Sea.

By Lisa Eisner

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AFSC Quarterly Research Reports Jan-March 2004