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 vesselís 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
AFSC Quarterly Research Reports Jan-March 2004