Horodysky and Graves: Estimation of survival of Tetrapturus albidus caught and released in the North Atlantic recreational fishery 93 



—I 1 1 1 1 1 r 1 1 1 1 1 1 r- 



10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 190 200 



Number of tags 



Figure 6 



Effect of sample sizes ranging from 10 to 200 PSATs on the 959c confidence intervals 

 for estimates of release mortality. Estimates were derived from 10,000 simulations of 

 hypothetical experiments with increasing numbers of tags (by using software developed 

 by Goodyear [2002]). The dashed line represents the underlying true value of 0.35. 



to revive any of the exhausted or tailwrapped white 

 marlin in this study would have biased the mortality 

 estimate upwards if any of these animals perished as 

 a result of exhaustion. 



It is unlikely that trauma induced by boatside han- 

 dling or tagging contributed to the difference between 

 the mortality of white marlin caught on circle hooks and 

 those caught on "J" hooks. Holts and Bedford (1990) and 

 Domeier et al. (2003) suggested that striped marlin in 

 their studies may have died as a result of striking the 

 tagging vessel rather than from hook-induced injury. 

 We observed only one white marlin (DR02-01) strike the 

 side of a tagging vessel; this fish survived and exhibited 

 behavior similar to other healthy white marlin for the 

 full five-day tag deployment duration. 



The implications for stomach eversion on billfish sur- 

 vival are unclear because of fairly few observations in 

 studies assessing survival. Stomach eversion appears 

 to be a natural behavioral mechanism by which unde- 

 sired food items and remnants may be expelled, and 

 stomachs quickly retracted (Holts and Bedford, 1990). 

 In addition, the generally weakened condition of some 

 marlin with everted stomachs indicates that this condi- 

 tion may occur in response to stress (Holts and Bedford, 

 1990; Pepperell and Davis, 1999). A striped marlin 

 with an everted stomach tracked by Holts and Bed- 

 ford (1990) survived, whereas a black marlin with an 

 everted stomach tracked by Pepperell and Davis (1999) 

 and a white marlin in this condition tagged by Ker- 

 stetter et al. (2004) were both attacked by sharks and 

 died. In the present study, two white marlin (DR02-03 

 and MA01) everted their stomachs during the fight. 

 White marlin DR02-03 showed behavior consistent with 

 survival until the tag was prematurely released after 

 2.5 days. In contrast, white marlin MA01 was hooked 



in its everted stomach and bled profusely during the 

 fight. Depth data recovered from the PSAT attached 

 to this animal indicated that it died less than 10 min- 

 utes after release. The survival of some istiophorids 

 with everted stomachs supports the release of fish in 

 this condition; however, without further observations 

 of animals in this condition, the relevance of stomach 

 eversion in predicting mortality of released billfishes 

 remains uncertain. 



The majority of mortalities observed in our study 

 occurred within the first six hours of release; however 

 two mortalities (DR02-04 and VZ03-13) occurred more 

 than 24 hours after tagging. Insights into the behavior 

 of VZ03-13 prior to mortality are compromised by large 

 sections of missing data; however, it should be noted 

 that the final four hours prior to death were associated 

 with surface waters. Likewise, white marlin DR02-04 

 (Fig. 3A) spent the majority of the first day almost 

 entirely within nearsurface waters following release. 

 Similar prolonged surface associations have been docu- 

 mented in blue marlin (Block et al., 1992) and striped 

 marlin (Brill et al., 1993) — a behavioral pattern that 

 has been attributed to that of a badly injured fish (Brill 

 et al., 1993). White marlin DR02-04 resumed diving 

 behavior similar to that observed in healthy tagged fish 

 (Fig. 3B) after 20 hours, indicating possible recovery 

 from catch-and-release procedures. This white marlin 

 again returned to the surface for four hours prior to its 

 death 64 hours after release. 



The two white marlin that had the longest fight times 

 in our study, DR02-04 and VZ03-11 (83 and 46 min, 

 respectively), may have experienced delayed postrelease 

 mortality associated with physiological stress, such 

 as intracellular acidosis following exhaustive exercise 

 (Wood et al., 1983) or haemodilution (Bourke et al., 



