UW Aquatic & Fishery Sciences Quantitative Seminar

Olaf Jensen

UW School of Aquatic & Fishery Sciences

Local management of a "highly migratory species?" The effects of longline closures and recreational catch-and-release for Baja California striped marlin fisheries

 

Abstract

Management of highly migratory fish species is generally assumed to require complicated international agreements.  The effects of spatial closures for such species are thought to be diluted by their extensive movements.  We tested these assumptions using a case study of striped marlin (Kajikia audax) fisheries off of Baja California, Mexico. Beginning in 1977, Mexico instituted a series of
longline fishery closures and closed areas designed to reduce commercial fishing mortality rates on billfishes.  Using data from the Japanese longline fishery and the recreational billfish fishery in a stock reduction analysis (SRA) model, we show that temporary closures of Mexico's EEZ to longlining from 1977 - 1980 and 1984 - 1985 had a rapid effect on local striped marlin abundance.Regional striped marlin abundance likely increased by 17% - 27% following the four-year closure and 7% - 10% following the two year closure.  Increases near Baja California may have been larger.  Recreational catch-release appears to have a more modest effect because catches in the recreational fishery are substantially smaller than historic longline catches.  A 100% release rate over the 10-year period for which recreational catch data were available would likely have increased regional abundance by 1.4 - 7% relative to no recreational release.  There is also evidence for a small effect of the El Nino - Southern Oscillation on recruitment or net immigration, with stronger recruitment or net immigration during the cooler La Nina phase.