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Auke Bay Laboratories (ABL)

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July-Aug-Sept 2007
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Marine Salmon Interactions Program

Surface Trawl Calibration Completed to Maintain SECM Data Time Series

From 1997 to present, the Southeast Alaska Coastal Monitoring (SECM) project at ABL has used the NOAA ship John N. Cobb to accrue a time series of biophysical data in the Southeast Alaska region. These data, which include surface trawl catches in the northern region of Southeast Alaska, are used to gain a better understanding of factors affecting year-class strength of salmonids and other fishes.

Currently the data are being used to forecast pink salmon run strength to Southeast Alaska (see companion article above on forecasting). However, the Cobb is scheduled to be decommissioned after 2008, and there is no time line set for a replacement vessel. Because of this uncertainty, ABL contracted the ADF&G research vessel Medeia to develop intervessel calibration data for the Nordic 264 surface trawl used for the SECM fish collections in July 2007. The Medeia has previously been used by ABL to conduct research with the Nordic 264 surface trawl in the coastal waters of the Gulf of Alaska. (More information on that research effort is available on the North Pacific Anadromous Fish Commission website at http://www.npafc.org/new/publications/Documents/PDF%202006/956(USA).pdf).

Catch statistics were compared between the two vessels to determine if correction factors would have to be applied. A total of 28 trawl hauls were fished by each vessel alongside one another over a 6-day period in Icy and Chatham Straits from 26 to 31 July. Catches of juvenile salmon were significantly higher for the Medeia, averaging 1.7 times the catch of the Cobb. These higher catches were probably due to the faster towing speed of the Medeia, resulting in a significantly longer trawling distance by this vessel over the 20-minute haul durations. Although catch rates were higher for the Medeia, the species composition of the juvenile salmon catch did not differ significantly between the two vessels. Sizes of juvenile salmon captured also did not differ significantly between vessels.

The ratio of the catch of juvenile pink salmon between the two vessels (1.6 times higher by the Medeia) was similar to that of total juvenile salmon caught. However, the paired-differences for juvenile pink salmon were not statistically significant. The catches of juvenile pink salmon were the lowest ever recorded for July over the 11-year SECM time series, which resulted in lower statistical power. To increase statistical power and to develop a calibration factor applicable to higher catch-per-set observations, we plan to repeat the paired comparison in 2008, pending funding support from the Pacific Salmon Commission Northern Fund. The 2007 and 2008 data will enhance the feasibility of using the Medeia as a contractual option during the time period between Cobb decommissioning and replacement, and as a standard for future calibration of a Cobb replacement vessel or contracted trawler.

By Alex Wertheimer, Joe Orsi, Molly Sturdevant, and Emily Fergusson


Genetic Analysis Of Wild Coho Populations Before And After Local Coho Enhancement

The Marine Salmon Interactions Program (MSI) staff have initiated a study on the effects of large-scale coho salmon enhancement on the population structure of nearby wild coho salmon populations. The field research will be based from ABLís Little Port Walter (LPW) research station, located on the southern tip of Baranof Island in Southeast Alaska. The project is supported with funding obtained from the Southeast Sustainable Salmon Fund.

Coho enhancement using Sashin Creek coho salmon as brood stock started at LPW in the early 1970s and ended in the late 1980s. Sashin Creek is the watershed draining into LPW. Subsequently, the Deer Lake coho enhancement project, located 9 miles north of LPW, and Port Armstrong hatchery, located 7 miles south of LPW, started culturing and releasing coho salmon and continue to release them to this day. Brood stock for both hatcheries originated from Sashin Creek and Deep Creek (located 15 miles north of Sashin Creek). Nakvassin Creek is located 5 miles north of LPW, midway between LPW and Deer Lake. Coho salmon from Nakvassin Creek have not been used as brood stock for any enhancement projects. The enhancement projects produce returns of adult coho salmon in the tens of thousands; Sashin Creek and Nakvassin Creek have wild adult escapements numbering in the hundreds.

This summer MSI staff collected samples from Port Armstrong hatchery, Sashin Creek, and Nakvassin Creek coho salmon for analysis with single nucleotide polymorphisms (SNPs) and microsatellite DNA assays to analyze the population structure. We will repeat the analysis on samples collected from the Deer Lake coho salmon enhancement project in the spring. The DNA results will be evaluated to determine the current degree of population differentiation among the enhanced and wild stocks. We will then extract DNA from archived Sashin Creek and Nakvassin Creek coho salmon scales collected by researchers at LPW in the 1960s, before any coho salmon enhancement was initiated on Baranof Island. The results from the scale assays will be compared to the current population structure to evaluate whether the genetic structure of the wild populations has been affected by the local enhancement efforts.

The combined data will help assess the effect of enhancement practices (i.e., selection, drift, or stock transfers) on the genetic structure of hatchery populations and the degree of gene flow to nearby wild populations. This will help to determine whether current culture practices and the Alaska genetic policy are providing adequate protection for sustaining the genetic integrity of wild coho stocks.

By Andrew Gray and Alex Wertheimer
 

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