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Salmon Bycatch Reduction through Temperature Studies in the Bering Sea Pollock Fishery 2007-2009.
Introduction
The Alaska pollock fishery is one of the largest sustainable fisheries in the world. Pollock represents a major component of Alaska’s commercial catch: 62%. Bering Sea pollock fishing is quite selective, with the total bycatch of all non-target species at only 1.2% (of the total removals by weight). But, the priority to reduce bycatch is especially high with the iconic Chinook salmon, important throughout rural Alaska villages as an important commercial fishery as well as a central component for the subsistence way of life and Alaska Native cultures.
Chinook salmon bycatch rates climbed to a record high in 2007, when around 120,000 Chinook were caught in the Pollock fishery. Pollock fishermen, Alaska villagers and Native leaders, fisheries managers, educators and many others were interested in finding solutions to this problem. |
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In this study funded by the North Pacific Research Board (NPRB), John Gauvin of the Marine Conservation Alliance Foundation (MCAF) partnered with Dr. Jim Ianaelli of the Alaska Fisheries Science Center and pollock vessel operators to collect bottom temperature data during the Bering Sea Pollock fisheries in 2007 and 2008. The instruments used to collect these data were scientific-grade “temperature at depth” devices to ensure that instruments were calibrated. This data were compared with Chinook and Chum salmon bycatch rates collected by the extensive North Pacific observer data. The results of this study were released in March 2010.
Results
This study found that temperature was the third most important factor for determining Chinook salmon bycatch rates in the Bering Sea pollock fishery; following year, and season.
Pollock were found to primarily stay within the 2-4°C temperature range, and within that, Chinook salmon bycatch is generally higher nearing 4 °C.
Had the relationship between temperature and salmon bycatch been more direct, it could be used by the pollock fishing cooperatives for “in-season” management to proactively avoid high bycatch zones. The pollock industry currently manages bycatch by closing areas to pollock fishing when salmon bycatch rates are relatively high. It was hoped that temperature data could make this process more effective by identifying areas before high bycatch rates are triggered. But given the lack of a strong relationship between temperature and salmon bycatch rates, more data and analysis would be needed to see if this management method could be put into place.
Separate analyses on Chum salmon bycatch also appeared to have a similar, but generally weaker relationship with temperature.
Study
This NPRB funded study coordinated by John Gauvin of MCAF brought together experts from multiple disciplines for this Cooperative Research project to address Chinook salmon bycatch in the Bering Sea Pollock fishery.
Pollock vessel operators working in the Bering Sea were asked to deploy scientific-grade temperature at depth (TDR) recorders on their nets over several pollock seasons. Coupled with survey bottom-temperature data and fishery observer data, experts were able to compare bycatch rates against a variety of factors to determine what had the biggest impact.
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For this project, SBE39 Seabird Electronics temperature collection recorders (TDR) were attached to the codends (end of the net where catch is collected) of pollock trawl nets of catcher vessel and catcher processor vessels during 2007 B season and 2008 A and B seasons. Over twenty pollock vessels volunteered for the project and deployed the temperature collection devices during some or all of the three separate seasons of deployments. |
The data were analyzed using general additive models (GAMs), this analysis showed that while temperature appears to be related to Chinook bycatch, the other factors including year, month, week, and geographical location were important factors to determine bycatch.
In the spring of 2008 and 2009 workshops took place to present the data collected and to gain the advice of individuals involved in the Bering Sea Pollock fisheries. These outreach opportunities were essential in determining more advanced methods of data collection.
Overall, Dr. Ianelli’s analysis confirms the conclusion of the 2009 Environmental Impact Assessment for Chinook salmon bycatch. Specifically, annual differences in salmon bycatch are the predominant factor to explain differences between rates. This likely indicates that the relative abundances of pollock and Chinook salmon varies between years. Also, time of year tends to be a significant factor for Chinook bycatch with higher bycatch rates occurring later in the season (October). To a lesser degree, combined with these factors, the fishing area matters for the level of Chinook bycatch. This study adds to these prior findings by indicating the temperature is also a relevant factor.
Lessons Learned
Additional temperature studies would provide invaluable information for several purposes:
- Confirming and expanding on the temperature bycatch results from this study.
- Evaluating the development and evolution of the Bering Sea cold pool. The extent and migrations of the cold pool could help provide information to help models predict recruitment of key groundfish species.
- Improving the understanding of the dynamics of the Bering Sea Ecosystem.
Future projects would need:
- More fishing vessels to obtain better spatial coverage,
- More robust temperature recording devices and modified deployment procedures,
- A longer time series because year-to-year variability was substantially higher than temperature effects.
Partners
This North Pacific Research Board (NPRB) funded project was coordinated by John Gauvin from the Marine Conservation Alliance Foundation (MCAF) with significant scientific and analytical assistance from Dr. James Ianelli of the Alaska Fisheries Science Center. Phyllis Stabeno of the Pacific Marine Ecosystem Laboratory and Karl Haflinger of Sea State made important contributions to the project. Diana Stram of the North Pacific Fishery Management Council assisted with designing the study and final reporting. A deployment strategy to help ensure the temperature data collection units were distributed across the pollock fishing grounds was undertaken by John Gruver of the United Catcher Boat Association.
This report was prepared by the MCA Foundation with funding provided by the North Pacific Research Board under agreement number 731 of award number NA05NMF4721198 from the National Oceanic and Atmospheric Administration, U.S. Department of Commerce. The statements, findings, conclusions, and recommendations are those of the author(s) and do not necessarily reflect the views of the National Oceanic and Atmospheric Administration, U.S. Department of Commerce, or the North Pacific Research Board.
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