International Pacific Halibut Commission, P. O. Box 95009, University
of Washington, Seattle, WA 98145-2009 Manuscript accepted (March 98) for publication the North American Journal
of Fisheries Management
Abstract
Since the 1960s, fisheries for other species of groundfish have caused
an average of about 9,000 metric tons (mt) of Pacific halibut Hippoglossus
stenolepis bycatch mortality every year, while directed catches have varied
from 13,000 to almost 50,000 mt (both measured in round weight). Around
half of the bycatch consists of juvenile fish caught in Alaska, some of
whom would otherwise migrate south and contribute to the fishery in British
Columbia. These interceptions have long been a difficult issue for the
United States and Canada. At recent high levels of juvenile abundance,
juvenile bycatch reduces coastwide recruitment by about 10%. The resulting
yield loss, plus bycatch of adult fish, reduces yield to the directed fishery
by about 11,000 mt per year. Migration modeling indicates that the yield
loss due to bycatch occurs almost entirely in the area where the bycatch
is taken. In particular, bycatch in Alaska reduces Pacific halibut yields
in British Columbia by at most a few percent. During the 1980s and early
1990s, annual quotas in the directed Pacific halibut fishery were reduced
by an amount equal to (or sometimes greater than) the amount of total Pacific
halibut bycatch mortality, and the quota reduction was distributed among
regulatory areas in proportion to Pacific halibut biomass. At present,
the Pacific halibut quota in each regulatory area is reduced by the amount
of adult Pacific halibut bycatch mortality in that area, and the target
exploitation rate is adjusted downward (slightly) to offset the bycatch
mortality of juveniles.