The influence of individual transferable quotas on discarding and fishing behavior in multispecies fisheries.

摘要

Under individual transferable quotas (ITQs), participants receive a share of the total allowable catch (TAC), can choose when to fish, and can sell or lease their share. ITQs generally increase fishing flexibility, improve profitability, reduce overcapitalization, and may improve sustainability of the resource through increased stewardship incentives. However, ITQs may increase high-grading and discarding, and create social problems because quota owners have increased control compared to other stakeholders. The U.S. West Coast groundfish trawl fishery is managed under two-monthly landing limits (not ITQs) for each species and has generally high discard levels. The British Columbia groundfish trawl fishery (B.C. fishery) is an ITQ fishery with full observer coverage, where marketable discard mortality is deducted from quotas. Under this system, total discards declined for most species, and marketable discards declined from 0.20% to 0.10%, after an adjustment period. The B.C. system would likely reduce discards in the West Coast fishery, although severe catch restrictions on overfished West Coast species may limit these reductions. To predict fishing changes under fishery regulations, a method was developed for defining "fishing opportunities" for each vessel---groups of trawls over the same portion of a fishing ground. This method uses simple clustering method on Euclidean distances between trawls, offers a more realistic way of defining fishing opportunities than grid cells, and is able to correctly classify simulated trawls into fishing opportunities. The top vessels in the B.C. fishery frequented a wide variety of fishing opportunities (mean 38, range 20--69), in which trawls generally caught similar species. The B.C. fishery is a multispecies fishery with TACs imposed on 22 species. Despite these constraints, skippers were able to adjust the species mixture in their catches to match changes in TACs. Skippers reduced catches of rougheye, shortraker, and yelloweye rockfish by more than 50% when TACs for those species were reduced. However, there was only weak evidence that skippers changed their fishing patterns based on the species mixture of all of the most important species. Instead, a variety of other factors were likely important in determining which fishing opportunities are preferred and avoided in the B.C. fishery.