Atlantic white marlin (Tetrapterus albidus) are severely overexploited, and the stock is currently at historically low levels. The species is a highly prized sportfish targeted by a directed recreational fishery in which 99% fish are released after capture. The major source of mortality for white marlin is believed to occur through incidental catch in commercial pelagic longline fisheries targeting swordfish and tunas. The degree to which management measures including the release of live billfishes will decrease marlin fishing mortality is uncertain because little is known of the fate of istiophorid billfishes released alive.
My thesis research entails the use of pop-up satellite archival tag (PSAT) technology to estimate the survival and elucidate the habitat preferences of white marlin released from the western North Atlantic recreational fishery. Goals of this study are: (1) establish an experimentally-derived estimate of post-release survival, (2) address the performance of circle and straight shank J hooks and their effects on survival, and (3) examine how white marlin exploit the water column and elucidate their habitat preferences.
To date, a total of 22 white marlin have been tagged offshore of the Dominican Republic (5 fish in May 2002), the US Mid-Atlantic Coast (11 fish in August-September 2002) and Venezuela (6 fish in November 2002). Twenty-one of the twenty-two tags deployed have reported. Preliminary data suggest that the mortality of white marlin caught on dead ballyhoo rigged on straight shank “J” hooks is higher than for blue marlin caught on high-speed trolled lures, but similar to that of striped marlin caught on live bait. Hook-induced trauma appears to be a good predictor of mortality in J hook caught white marlin: 75% of moribund fish were deep hooked and bleeding. Minimizing fishing mortality is especially important in light of increasingly pessimistic assessments and heightened concern for the status of Atlantic white marlin. Preliminary data for six white marlin caught on circle hooks suggests reduced deep hooking, no bleeding, and no mortality. Will this trend hold? Stay tuned through the 2003 sampling season, when I plan to tag at least 20 more white marlin.
McBride, R.S. and A.Z. Horodysky. Mechanisms maintaining sympatry of two ladyfish (Elopidae: Elops) morphs in the Gulf of Mexico and western North Atlantic. (In prep.)
Horodysky, A.Z. and R.S. McBride. 2000. Growth and mortality of two populations of ladyfish (Elops) in east-central Florida. 20th Annual meeting of the Florida Chapter of the American Fisheries Society. 28-30 March 2000.
McBride, R.S., A.Z. Horodysky, D. Adams, and J. Whittington. 2001. Mechanisms maintaining sympatric distributions of two ladyfish (Elops) morphs in the Gulf of Mexico and western North Atlantic. 25th Annual Larval Fish Conference, Sandy Hook, NJ. 8-13 August 2001.
McBride, R.S., A.Z. Horodysky, and B. Bowen. 2002. Allopatric and sympatric distributions of ladyfish (Elops spp) in the Gulf of Mexico and western North Atlantic. 26th Annual Larval Fish Conference, Bergen, Norway. 22-26 July 2002.