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The Salmon Purse Seine - Competition And Information Among
By Max Ledbetter, Sat Dec 10th
In British Columbia, Canada, salmon purse seiners line up atfishing access points, forming well defined queues. These queueswere measured over time, using a one-dimensional recordingscale. Sixty-one overflights of Johnstone Strait and QueenCharlotte Strait were attempted; 51 flights were completed. Two models were presented for exploitation rates in relation toqueuing patterns. The overflight model was fit to the line-updistributions. One underlying assumption was that the skipperspossessed fairly accurate information regarding the distributionof catches (analysis of variance methods utilizing skippers'logbook data showed that line-up lengths reflected catch rates).The model fit well and the parameter estimates reflectedanecdotal and statistical information about fish behavior. Theexploitation rates saturated at an effort level of 100 vessels(whereas the maximum effort observed was 363 boats) andindicated that (at saturation) the fleet caught 80% to 90% ofthe vulnerable migrating salmon present in Johnstone and QueenCharlotte Straits during what were commonly 48- or 72-hourfishing openings. (Note: Salmon successfully migrating throughthe strait on days that were closed to seiners and salmon thatwere not vulnerable to the gear--e.g., below the depth of thenets--escaped the purse-seine fleet.) In general, traditional
assumptions were rejected. Vessels didnot operate independently. Boats were not distributed in arandom fashion. The overflight model provided predictedexploitation rates. The exploitation response to effort wasqualitatively distinct from the forms incorporated intraditional models.
In partial summary, the question is one of power--theability of gear, boats, or fleets, in the B.C. and P.E.I. casesand others, to exploit or overexploit fish stocks. Without ahistorical perspective based on quantitative (and innovative)field research, we are doomed to repeat our work loads: In theabsence of extensive (and often necessarily alternative) timeseries of effort and effectivity (fishing power), stockassessment and fisheries management become absurd. Like theysaid on P.E.I., a fleet (or transient cluster) of purse seinerscan wipe out a stock (anywhere in the world).http://freehosting.hostrave.com/p/ledbetter/http://freehosting.hostrave.com/p/ledbetter/ About the author:Max Ledbetter is a published aquatic ecologist who is now addingoriginal fiction to his body of work. For more past an currentfisheries information, seehttp://freehosting.hostrave.com/p/ledbetter/.
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