Management and conservation of billfishes

Billfishes (Family Istiophoridae) such as blue, black, white, and striped marlin are among the largest and most highly prized marine sportfish. Yet much of their basic biology and ecology is poorly known and their populations in many parts of the world appear to have declined substantially over the past 50 years. These declines may be the result of overfishing by commercial longliners. Our research has focused on understanding the ecological role of billfishes within the pelagic marine ecosystem and on evaluating conservation measures such as releasing hooked billfish and closing some areas to commercial longline fishing. Much of our work has focused on striped marlin in the area near Baja California, Mexico.

While striped marlin are known to occasionally undergo long distance movements (1000s of kilometers), recent tagging studies by Michael Domeier show that movements of individuals tagged off of Baja California are remarkably limited for a large pelagic fish. This area appears to be a hot spot in which striped marlin aggregate, a fact that’s been known to anglers for many decades. Our research on striped marlin has looked at the effects of recreational catch-release and longline area closures (essentially marine reserves) on population dynamics of striped marlin. Temporary closures of Mexico’s EEZ to longlining from 1977 – 1980 and 1984 – 1985 had a rapid effect on striped marlin abundance. Regional striped marlin abundance likely increased by 12% – 22% following the four-year closure and 6% – 12% 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 2.8 – 7.5% relative to no recreational release.

Related publications:

Jensen, O.P., S. Ortega-Garcia, S.J.D. Martell, R. Ahrens, M.L. Domeier, C.J. Walters, and J.F. Kitchell. 2010. Local management of a “highly migratory species?” The effects of longline closures and recreational catch-and-release for Baja California striped marlin fisheries. Progress in Oceanography. 86:176-186. PDF

Pine, W.E., S.J.D. Martell, O.P. Jensen, C.J. Walters, J.F. Kitchell. 2008. Effects of release mortality on the efficacy of length limits and catch-and-release policies: a case study of blue, white, and striped marlin. Canadian Journal of Fisheries and Aquatic Sciences 65: 975-988. PDF

Kitchell, James F., S. J. D. Martell, C. J. Walters, O. P. Jensen, I. C. Kaplan, J. R. Watters, T. E. Essington and C. H. Boggs. 2006. Billfishes in an ecosystem context. Bulletin of Marine Science 79: 669-682. PDF