Here's an interesting report I came across on the topic of gillnet mortalities. Would be interesting to compare estimates of mortalities among gear types:
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Improving the Chances of Survival for Bycatch Fish
Patricia Gallaugher*, Anthony Farrell and Richard Routledge
Centre for Coastal Studies, Simon Fraser University, Burnaby
British Columbia, Canada V5A 1S6
One quarter of the world’s total commercial catch is discarded because it is not the right species or size (Cook 2001). It is generally assumed that, depending on species and fishery, most of these discarded fish do not survive after capture and release. However, recent experiments conducted in various locations on the British Columbia coast indicate that it is possible to revive commercially captured non-target salmon and significantly improve their chances of long-term survival after release.
In 1998, in response to conservation concerns regarding coho salmon (Oncorhynchus kisutch) on the west coast of Canada, Fisheries and Oceans Canada established a policy for Selective Fisheries, defined as “the ability to avoid known, non-target species and stocks or, if encountered, to release them alive and unharmed” (Anon 1999).
However, very little information exists with regard to whether it is possible to release commercially captured fish so that they are indeed ‘alive and unharmed’. Hence, over the course of three summers, a unique partnership of academic and government scientists, commercial fishermen, First Nations, members of the fishing industry, coastal communities and Fisheries and Oceans Canada collaborated on experiments to test how to improve the chances of survival of salmon when released after capture by the commercial fishing fleet.
Experiments on board gillnet vessels (Farrell et al., 2000, 2001; Buchanan et al., 2001, Gallaugher 2001), were funded both by the fishers themselves through a percentage of the Total Allowable Catch, Fisheries and Oceans Canada, the province of British Columbia, and Canada’s Natural Sciences and Engineering Research Council. A number of different physiological parameters of muscle metabolism and post-capture stress were measured as indicators of recovery and delayed mortality following capture. The results showed that the use of a laminar flow revival box on board the vessels promoted significant recovery as indicated by improved values for the physiological indicators, good swimming ability and low long-term mortality rates, even for fish that were observed as asphyxiated and considered to be ‘dead’. When combined with modifications in handling techniques, soak times and gear the result was a very significant reduction in mortality rate (ie., from 60% to
< 10%). Measured swimming velocities of the recovered fish after release suggested that these fish could swim well enough to avoid predators and successfully complete migration and reproduction. Similar experiments with the seine fleet using an adaptation of the gillnet laminar flow revival tank demonstrated significant reductions in long-term mortality rates for captured coho salmon after release (Berry et al. 2001). As well, experiments with salmon captured by the troll (hook and line) fleet have demonstrated near zero mortality when fish recover while slowly swimming alongside the vessel in a cage (Farrell et al. 2001).
To follow up on these findings, fishers took the initiative, and facilitated by Fisheries and Oceans Canada, developed and implemented a number of technology transfer workshops along the British Columbia coast prior to the 2001 fishing season. This led to the ‘buy in’ of more fishers. Those who complied by using these conservation-friendly methods were recognized by Fisheries and Oceans Canada through increased fishing opportunity in the 2001 British Columbia salmon fishing season.
These findings bring into question the practices of all commercial fisheries globally with regard to the treatment of bycatch and stress the importance of experimenting with methods that could increase the chances of the long-term survival of non-target, non-retention fish following release after capture. We suggest that if we are able to demonstrate significant improvement in survival for salmonids following capture and release, species known to be particularly sensitive to capture and handling, then there is significant room for improvement in fishing practices for many other species in global fisheries with regard to bycatch. In fact, recent experiments in Johnstone Strait, British Columbia, which examined the return of non-target quillback rockfish, Sebastes maliger, showed encouraging results with regard to release techniques that can reduce rates of mortality (Berry 2001).
References
Anon. 1999. A Policy for Selective Fisheries in Canada’s Pacific Fisheries. Fisheries and Oceans Canada
http://www-comm.pac.dfo-mpo.gc.ca/english/selective.
Berry, M. 2001. Area 12 (Inside) Rockfish Selective Fishery Study. Final Report prepared for Fisheries Renewal BC and Science Council of BC. (
http://www.icnrc.org).
Berry, M., Gallaugher, P., Farrell, A.P., Buchanan, S. and Pike, D. 2000. A Comparison of the standard recovery box and a re-designed laminar flow box in the recovery of coho salmon (Oncorhynchus kisutch) caught with commercial seine gear: Mortality rates and swimming performance. Report to Fisheries and Oceans Canada. 14pp.
http://www.sfu.ca/cstudies/science/selective.
Buchanan, S., Farrell, A.P., Fraser, J., Gallaugher, P., Joy, R. and Routledge, R. 2001. Dramatic Reductions in Gillnet Mortality for Incidentally Caught Coho. Under Review. N. Am. J. Fish. Manag.
Cook, Robin 2001.The magnitude and impact of by-catch mortality by fishing gear. In Proceedings of the Reykjavik Conference on Responsible Fisheries in the Marine Ecosystem. Reykjavik, Iceland. October 1-4, 2001. 18pp.
Farrell, Anthony P., Patricia E. Gallaugher and Richard Routledge. 2001. Rapid recovery of exhausted adult coho salmon after commercial capture by troll fishing. Submitted.
Farrell, A.P., Gallaugher, P.E., Fraser, J., Pike, D., Bowering, P., Hadwin, A.K.M., Parkhouse, W. and Routledge, R. 2001. Successful recovery of the physiological status of coho salmon on board a commercial gillnet vessel by means of a newly designed revival box. Can. J. Fish. Aquat. Sci. 58: 192-1946.
Farrell, A.P., Gallaugher, P., Clarke, C. Delury, N., Kreiberg, H., Parkhouse, W. and Routledge, R. 2000. Physiological status of coho salmon (Oncorhynchus kisutch) captured in commercial nonretention fisheries. Can. J. Fish. Aquat. Sci. 49: 1157-1162.
