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Marine Ecology and Stock Assessment Program

Alaska Sockeye Salmon Scale Patterns as Indicators of Climatic and Oceanic Shifts in the North Pacific Ocean, 1922–2000

Climate regime shifts can alter the community structure of marine species in the North Pacific Ocean. In this study, we used a regime shift detection algorithm to determine whether regime shifts are recorded as shifts in the mean fish length indices at the smolt, juvenile, immature, and mature life stages based on measurements of increments on scales of adult age-2.2 sockeye salmon that returned to the Karluk River, Alaska, over a 77-year time period (1924–2000).

Fish length was expected to increase with cool-to-warm climate shifts (1926, 1958, 1977, and 1998) and decrease with warm-to-cool climate shifts (1943, 1947, 1971, and 1989). Regime shifts were not consistently observed as statistical shifts in the time series of fish length indices.

At contemporaneous lags, shifts in the mean temperature of the North Pacific were detected as shifts in length in 1958 (+), but not in 1926 (+), 1943 (-), 1971 (-), and 1977 (+). Shifts in the atmospheric circulation and sea level pressure of the North Pacific were detected as negative shifts in length in 1989 (-), but not in 1926 (+), 1947 (-), 1977 (+), 1998 (+).

Shifts in length indices were associated with the 1957-58 El Niño, the warm-to-cool shift in 1989, and preceded the 1976–77 climate shift in the North Pacific Ocean. Fish length indices from salmon scales may be useful predictors for major and more recent shifts in the status of the ecosystem of the North Pacific Ocean.

By Ellen Martinson

Groundfish Stock Assessments

Scientists from ABL's MESA Program completed eight full stock assessments and updated one assessment for nine species/species groups of Alaska groundfish. Full assessments included Alaska sablefish, Bering Sea/Aleutian Islands sharks, and the following assessments for the Gulf of Alaska: Pacific ocean perch, northern rockfish, pelagic shelf rockfish, rougheye and blackspotted rockfish, shortraker rockfish and “other slope rockfish,” and sharks. A short stock assessment update was also done for Alaska grenadiers. Stock assessment and fishery evaluation (SAFE) reports or executive summaries were prepared for each assessment, and results were presented to the North Pacific Fishery Management Council’s Groundfish Plan Teams in November and also were reviewed by the Council’s Scientific and Statistical Committee in December. The Council used these assessments as the primary source for determining catch quotas (levels of total allowable catch) for these species in 2010. More information about these assessments is available in the Resource Ecology and Fishery Management (REFM) Division's "Groundfish Stock Assessments for 2010 Fishery Quota Recommendations" report in this issue.

By Dave Clausen

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