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Article Excerpt
Introduction
Conservation of Atlantic white marlin, Tetrapturus albidus, has been a concern of U.S. fishery managers since the 1980's. In 1988, domestic regulations established by the Atlantic Billfish Fishery Management Plan (FMP) (NMFS, 1988) required the release, dead or alive, of all white marlin caught in U.S Atlantic commercial fisheries. Management measures for U.S. recreational fishermen include a minimum size of 66 inches lower jaw fork length (NMFS, 1999). These measures and increased voluntary release of white marlin by recreational fishermen reduced reported U.S. commercial dead discards of white marlin by commercial fishermen from 81 t in 1990 to 41 t in 2000 and reported landings by recreational fishermen from 17 t in 1990 to 1 t in 2000. (1) However, the success of these conservation measures depends, not only on reduction of landings, but reduction in total mortality. Post-release mortality may be significant, particularly in recreational fisheries, where over 99% of the estimated 4,000 to 8,000 white marlin caught are released (Goodyear and Prince, 2003). Recent studies indicate that a minor change in hook type, from "J" hooks to circle hooks, may affect the frequency of deep-hooking and associated tissue trauma and therefore have a profound effect on post-release mortality (Horodysky and Graves, 2005). Sea turtle mitigation measures require the use of circle hooks by the U.S. longline fishery (Federal Register, 2004). U.S. recreational marlin fisheries have traditionally used "J" hooks and are not required to use circle hooks (Prince et al., 2002).
Until recently, data available for estimation of post-release mortality of large pelagic species included other factors. Low conventional tag recaptures (0.4-1.83%) (Prince et al., 2002; Ortiz et al., 2003), are confounded with tag shedding, low exploitation rate, and failure to report recaptured tags so that they do not provide sufficient information to estimate post-release mortality (Bailey and Prince, 1994; Jones and Prince, 1998). Acoustical tagging studies suggest relatively low post-release mortality rates for periods ranging from a few hours to a few days (e.g. sailfish, Istiophorus albicans (Jolley and Irby, 1979); blue marlin, Makaira nigricans (Holland et al., 1990; Block et al., 1992); black marlin, Makaira indica (Pepperell and Davis, 1999)). However, acoustical tagging data on Atlantic white marlin are limited (Skomal and Chase, 2002; n = 2 tracks) and furthermore, limitations and biases of acoustic tracking study procedures may limit the accuracy of the billfish post-release mortality estimates (Pepperell and Davis, 1999; Graves et al., 2002). These procedures include additional handling required to apply the acoustical tag to these animals which would be expected to increase mortality compared to mortality of animals that were only caught and released. On the other hand, animals that are in poor shape upon capture might be selectively released without the tag compared to animals that were in good shape. Selection for animals that are robust rather than average would cause a positive bias in survival rates. The acoustical data show that some billfish survive the catch and release experience in the short term. In summary, existing acoustic data cannot be relied upon to accurately estimate the traction of fish that survive because of small sample sizes, biases due to handling, and limited observation time.
Pop-up satellite archival tag (PSAT) technology provides...
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