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Fishery Bulletin 103(1) 



or sampling error (or a combination of these factors). It 

 should be noted that Domeier et al. (2003) and the crew 

 of the present study both used non-offset and 5° offset 

 circle hooks. 



The survival rate observed for white marlin caught 

 on straight-shank ("J") hooks in our study (65%) is 

 slightly lower than that reported for other istiophorid 

 species (blue marlin 89%, Graves et al., 2002; striped 

 marlin 71%, Domeier et al., 2003) caught on this type 

 of hook. Differences in the recreational fishing practices 

 for these species may account for the variation in lev- 

 els of istiophorid postrelease survival. In recreational 

 fisheries that target striped marlin and white marlin, 

 longer drop-back durations with natural baits rigged 

 on "J" hooks increase the probability of deep-hooking 

 and internal damage, which influence mortality. The 

 postrelease mortality rates of white marlin and striped 



Hook 

 type 



Hook 

 location 



Bleeding 



Fate 



"J" hook 

 20 



< 



Circle 

 hook 



20 



< 



Figure 5 



Effects of circle and straight-shank ("J") hooks on hook- 

 ing location, trauma, and fate. Ext. = externally, n/a = 

 not applicable. 



marlin from drop-back fisheries are similar and are 

 notably higher than that of blue marlin caught on high- 

 speed trolled baits. 



The results of our study also agree with previous 

 research documenting increased deep-hooking and tis- 

 sue trauma associated with the use of straight-shank 

 ("J") hooks. In contrast to circle hooks, "J" hooks are 

 over 20 times more likely to cause bleeding in sailfish 

 (Prince et al., 2002a), five times more likely to cause 

 bleeding in striped marlin (Domeier et al., 2003), and 

 15 times more likely to cause bleeding in white marlin 

 (present study). Slightly more than half of the bleeding 

 white marlin and less than half of the deep-hooked fish 

 caught on "J" hooks died in our study. Observations of 

 rusted hooks encapsulated in the viscera of otherwise 

 healthy istiophorids (Prince et al., 2002a) have indicated 

 that wounds resulting from deep-hooking are not neces- 

 sarily lethal. Furthermore, the results of the present 

 study also indicate that jaw hooking locations are not 

 exclusively nonlethal. Straight-shank ("J") hooks can 

 cause lacerations to vital organs such as the eye, brain, 

 pharynx, esophagus, and stomach before detaching from 

 the initial hooking location and rehooking in regions 

 that are typically considered less lethal, such as the 

 jaw and bill (Prince et al., 2002a). These internal inju- 

 ries are difficult to record without additional handling 

 and internal examination and confound relationships 

 between hooking location and mortality in the absence 

 of other predictors. Regardless, the significantly higher 

 survival rate for white marlin caught on circle hooks, 

 coupled with reduced rates of deep-hooking and tissue 

 trauma, indicate that this terminal gear may decrease 

 postrelease mortality rates in drop-back fisheries that 

 currently use "J" hooks. 



None of the white marlin caught on circle hooks in 

 this study were hooked deeply. Despite documenting 

 significantly lower deep-hooking rates with circle hooks, 

 previous studies have nonetheless observed that both 

 non-offset and offset circle hooks may occasionally hook 

 fish deeply (Prince et al., 2002a; Skomal et al. 2002). 

 This is especially true of severely offset (e.g., 15°) circle 

 hooks, which are highly associated with increased levels 

 of deep hooking and which may mitigate any conserva- 

 tion benefits associated with the use of this terminal 

 gear (Prince et al., 2002a). 



Resuscitation of exhausted istiophorids is a common 

 practice in the recreational fishery. Five white mar- 

 lin that were tailwrapped and unable to ram-ventilate 

 during the fight were resuscitated in our study. For ex- 

 ample, white marlin MX03-03 was tailwrapped for the 

 final seven minutes of the 21-minute fight and appeared 

 to be severely exhausted at boatside. This fish was 

 unable to regulate its position in the water when the 

 PSAT was implanted, and required the longest resusci- 

 tation of any white marlin in this study (~5 min.). After 

 release, a diver confirmed that this marlin regained 

 color and actively swam away upon reaching cooler 

 water at a depth of about 20 m (G. Harvey 2 ). Depth 

 and temperature data showed that this fish survived 

 for the entire 10-day tag deployment duration. Failure 



