Kerstetter and Graves: Survival of Tetrapturus albidus after release from longline gear 



441 



cally exclude tags that do not transmit data from subse- 

 quent analyses. Because it was not possible to estimate 

 how many such tags in this study could have been due 

 to malfunction versus individual mortality events, we 

 chose to conservatively estimate two postrelease mortal- 

 ity rates: one that includes all nontransmitting tags as 

 mortalities and another that excludes nontransmitting 

 tags. The expensive nature of PSAT technology resulted 

 in relatively small sample sizes and hence large confi- 

 dence intervals for the estimated postrelease mortality 

 rates. However, as with Horodysky and Graves (2005), 

 simulations with the observed rates in the present study 

 have shown that very large sample sizes (over 200 tags 

 for each hook type) under ideal conditions would be 

 required to reduce these estimates to within ±5% of 

 the true value. The advent of newer tag models with 

 features such as an emergency release will presumably 

 result in lower nontransmitting rates for PSATs and 

 hence more accurate estimates of postrelease survival. 



In this study, PSATs attached to some white marlin 

 in marginal physical condition at the time of release re- 

 turned data consistent with postrelease survival. These 

 included fish MA-04-03, which was hooked through 

 the right eyeball, and fish WP-04-01, which displayed 

 poor, faded color and was moving so little at haulback 

 that it initially appeared dead until careful inspec- 

 tion. Both internal hooking and stomach eversion have 

 been suggested as predictors of subsequent mortality 

 for billfishes (Domeier et al., 2003). Horodysky and 

 Graves (2005) found a 40% mortality rate for inter- 

 nally hooked white marlin, and Domeier et al. (2003) 

 found a 63% mortality rate for similarly hooked striped 

 marlin. We tagged four internally hooked animals, and 

 the one reporting tag (GB-02-01) indicated mortality 

 shortly after release for that fish. Three white marlin 

 with everted stomachs at haulback were tagged in this 

 study, but only one (MA-03-04) remained attached for 

 the duration of the deployment period and transmitted 

 data consistent with mortality. However, the survival 

 of a white marlin (Horodysky and Graves, 2005) and a 

 striped marlin (Holts and Bedford, 1990) with everted 

 stomachs indicates that billfish with everted stomachs 

 can survive if released. 



White marlin captured with circle hooks demonstrat- 

 ed a trend of lower postrelease mortality than those 

 hooked with J-style hooks, but this relationship was 

 not significant. This trend in mortality rate versus hook 

 type was independent of whether nontransmitting tags 

 were included as mortalities or excluded from analyses. 

 Horodysky and Graves (2005) observed a significant 

 decrease in mortality for white marlin caught on circle 

 hooks than on J-style hooks (0% versus 35% for J-style 

 hooks). Domeier et al. (2003) also noted a trend for a 

 lower mortality rate among animals hooked with non- 

 offset circle hooks (12.5% versus 29.4% for offset J-style 

 hooks), although this relationship was not significant. 

 The lower mortality-rate trend for white marlin caught 

 by circle hooks than by J-style hooks presented in the 

 present study is also consistent with the results in sev- 

 eral other studies of pelagic fishes, such Prince et al. 



(2002b) for recreationally caught billfish and Skomal 

 et al. (2002) with recreationally caught Atlantic blue- 

 fin tuna (Thunnus thynnus), which based predictions 

 of postrelease survival on likely injury resulting from 

 specific hooking locations on the animals. 



The majority of white marlin caught with circle hooks 

 in the present study were hooked in the mouth or jaw 

 (?2=23) rather than internally or by foul hooking on 

 the body (n = ^), as was also noted by Horodysky and 

 Graves (2005) for white marlin caught in the directed 

 recreational fishery. In the present study, low num- 

 bers of animals caught on either hook types prevented 

 robust comparisons of postrelease survival rates by 

 hook type. More balanced comparisons of postrelease 

 survival among hook types were precluded by both a 

 limited number of expensive PSATs and the imposition 

 of a domestic management measure that prohibited the 

 use of J-style hooks in the U.S. pelagic longline fish- 

 ery as of 5 August 2004 (FR, 2004). Although beyond 

 the scope of this study, any additional changes in the 

 fishing practices of this fishery, such as the varying 

 lengths of "soak time" between overnight sets (sword- 

 fish) and daylight sets (tunas), may also affect the rates 

 of postrelease survival of white marlin. 



Ultimately, hooking location may be a more important 

 factor than hook type for predicting postrelease sur- 

 vival. Three of the four PSATs attached to internally 

 hooked animals in this study did not transmit data, 

 although Prince et al. (2002b) reported encapsulated 

 hooks from istiophorid viscera, indicating that inter- 

 nal hooking events are not necessarily fatal. The large 

 percentage of white marlin (35.7%) hooked through the 

 upper lateral palate into the eye or eye socket raises 

 some concern. Istiophorid billfishes are considered to 

 be primarily visual predators (Rivas, 1975) and dam- 

 age to an eye would be expected to negatively affect 

 the foraging ability of the animal. Billfish are known 

 to have specialized muscle tissue that allows individu- 

 als to maintain elevated brain and eye temperatures 

 (Block, 1986), and recent work has revealed color vision 

 in some istiophorids (Fritsches et al., 2003). Dissections 

 of sailfish have revealed that bookings in the eye socket 

 often cause damage to the optic nerve and surrounding 

 ocular musculature (Jolley^). The one fish caught with 

 a circle hook through the eye socket in Horodysky and 

 Graves (2005) survived for the entire 10-day deploy- 

 ment period, and in the present study, the seven ani- 

 mals hooked through the eye socket also all survived 

 for their entire deployment periods, as did one white 

 marlin caught with a circle hook through the eyeball. 

 A tagged striped marlin in Domeier et al. (2003) with 

 a punctured eye also survived for ten days, suggesting 

 that this condition is not necessarily fatal over short 

 durations, and healthy swordfish have been observed 



■• JoUey, J. W. 1977. The biology and fishery of Atlantic 

 sailfish Istiophorus platypterus, from southeast Florida, 

 31 p. Fla. Mar. Res. Pub., contribution no. 298. Florida 

 Dep. Natural Resources, Marine Research Laboratory, 100 

 Eighth Avenue SE, St. Petersburg, FL 33701. 



