Size-selective Mortality of Juvenile Bristol Bay Sockeye Salmon
We tested the hypothesis that larger juvenile sockeye salmon (Oncorhynchus nerka) in Bristol Bay, Alaska, have higher marine-stage survival rates than smaller juvenile salmon. This study used archived scales from returning adults (33 years of data) and trawl samples of juveniles (n = 3,572) collected along the eastern Bering Sea shelf during August through September 2000-02. The size of juvenile sockeye salmon mirrored indices of their marine stage survival rate (i.e., smaller fish had lower indices of marine stage survival rate). However, there was no relationship between the size of sockeye salmon after their first year at sea as estimated from archived scales and brood year survival; size was relatively uniform over the time series, possibly indicating size-selective mortality on smaller individuals during marine residence.
Variation in size, relative abundance, and marine stage survival rate of juvenile sockeye salmon is likely related to ocean conditions affecting their early marine migratory pathways along the eastern Bering Sea shelf.
By Edward Farley
North Pacific Salmon Survey
The North Pacific salmon survey was conducted from the Japanese trawler Kaiyo maru on 24 May to 23 June 2006. The survey transect area was from lat. 53.00°N, long. 160.00°W to lat. 46.00°N, long. 164.00°E. Kristin Cieciel participated on behalf of ABL’s Ocean Carrying Capacity Program on Leg 2 of the survey, from Kodiak, Alaska, to Kushiro, Japan. The highlight of the second half of the survey was the continuation of a North Pacific Anadromous Fish Council tagging project funded by the National Pacific Research Board. The tagging project uses data from line- and trawl-caught salmon for a tag-and-recapture study that examines salmon migration ecology.
Hook and line fishing for salmon was performed every day after the last station from 26 May to 10 June aboard the Kaiyo maru. Fishing effort consisted of up to 14 lines in the water for 1 to 3.5 hours; total time was weather and schedule dependent. Trawl-caught salmon were tagged dependent on scale condition and overall health of fish. Data storage tags (DST) used to measure temperature and depth were attached to sockeye, chum, coho, and Chinook salmon. United States and Japanese disk tags were used on all species of salmon, and a single CTD (conductivity, temperature and depth) tag was attached to a Chinook salmon. The tagging summary is shown in Table 1 below.
Table 1. Tagging summary for North Pacific Salmon
Survey Cruise, 24 May to 23 June 2006.
Species
Total number tagged
Japan Disk tag
U.S. Disk tag
DST tag
CTD tag
Chinook
4
3
3
3
1
Chum
46
40
46
5
0
Coho
1
1
1
0
0
Pink
24
23
24
0
0
Sockeye
47
33
47
15
0
Three tags have been recovered in Alaska since the survey’s end in June. Tag 10650 (DST) was tagged at lat. 54.00°N, long. 175.00°W on 8 June 2006 and was recovered in the Egegik fishing district on 5 July 2006. Tag 10638 (DST) was also tagged at lat. 54.00°N, long. 175.00°W on 8 June 2006 and was recovered in Nushagak fishing district on 5 July 2006. The single CTD tag, used on a trawl-caught, 85-cm Chinook salmon tagged on 8 June 2006 at lat. 175°08'W long. 54°50'N, was recaptured on 30 June 2006, 20 miles downstream from Mountain Village (lat. 163°43'46"W, long. 62°05'08"N). Trey Walker of the University of Washington believes this may be the first recovered high-seas-applied tag from a maturing Yukon Chinook salmon.
