Horodysky and Graves: Estimation of survival of Tetrapturus albidus caught and released in the North Atlantic recreational fishery 85 



measures for U.S. recreational anglers include a mini- 

 mum size of 66 inches lower jaw fork length (NMFS, 

 1999) and mandatory reporting of landed billfishes 

 (NMFS, 2003). White marlin landings by U.S. recre- 

 ational anglers ranged between 40 and 110 t from 1960 

 to the mid-1980s (Goodyear and Prince, 2003) and have 

 decreased to about 2 t in recent years. At present, over 

 99% of the 4000-8000 white marlin estimated to be 

 caught annually by U.S. recreational fishermen are 

 released (Goodyear and Prince, 2003). 



The benefit of current management measures that 

 rely on the release of white marlin cannot be evaluated 

 because levels of postrelease survival are not known for 

 this species. Recapture rates of billfishes tagged with 

 conventional tags are very low (0.4-1.83%; Prince et 

 al., 2003; Ortiz et al., 2003), which may result from 

 high postrelease mortality, tag shedding, or a failure 

 to report recaptures (Bayley and Prince, 1994; Jones 

 and Prince, 1998). Little acoustic tracking has been 

 conducted on white marlin (Skomal and Chase, 2002; 

 n=2 tracks), but similar work on other istiophorid spe- 

 cies indicates relatively high postrelease survival for 

 periods ranging from a few hours to a few days for fish 

 released from recreational fisheries (e.g., sailfish: Jolley 

 and Irby, 1979; blue marlin: Holland et al, 1990; Block 

 et al., 1992; black marlin: Pepperell and Davis, 1999). 

 However, data from acoustic tracking studies bear limi- 

 tations and biases that preclude their use in estimating 

 billfish postrelease survival (Pepperell and Davis, 1999; 

 Graves et al., 2002). In the absence of better data, all 

 recreationally released billfishes have been assumed 

 to survive (Peel, 1995), and estimates of white marlin 

 postrelease mortality are currently not incorporated 

 into ICCAT landing statistics or assessments (White 

 Marlin Status Review Team, 2002). 



Developments in pop-up satellite archival tag (PSAT) 

 technology have greatly improved scientific under- 

 standing of the behavior, movements and postrelease 

 survival of highly migratory marine fishes, including 

 bluefin tuna (Block et al., 2001), swordfish (Sedber- 

 ry and Loefer, 2001), white sharks (Boustany et al., 

 2002), blue marlin (Graves et al., 2002; Kerstetter 

 et al., 2003), black marlin (Gunn et al., 2003), and 

 striped marlin (Domeier et. al, 2003). To estimate the 

 postrelease survival of billfishes, researchers have 

 used PSAT deployment durations ranging from five 

 days to seven months (Graves et al., 2002; Domeier 

 et al., 2003; Kerstetter et al., 2003). Goodyear (2002) 

 cautioned that longer duration deployments increase 

 the potential for tag shedding, tag malfunction, and 

 data corruption, and may bias postrelease survival 

 estimates by including additional sources of mortality 

 other than the capture event. Graves et al. (2002) con- 

 sidered five days to be an appropriate window to detect 

 mortality in blue marlin released from recreational 

 gear in offshore waters of Bermuda, citing recaptures 

 of blue marlin tagged with conventional tags within 

 five days of the initial tagging event as evidence that 

 some istiophorids may recover sufficiently to resume 

 feeding shortly after capture. 



Survival estimates for other istiophorid species re- 

 leased from recreational fishing gear may not be ap- 

 plicable to white marlin. One reason may involve body 

 size: recreationally caught blue marlin and striped 

 marlin are generally larger than white marlin. Inter- 

 and intra-specific differences in body size may affect 

 feeding behavior, fight time, handling time, as well as 

 postrelease recovery (Kieffer. 2000). Another reason 

 may involve the different angling techniques used to 

 catch certain istiophorid species. Blue marlin often hook 

 themselves in the mouth and head while aggressively 

 pursuing high speed trolled lures (Graves et al., 2002). 

 In contrast, as white and striped marlin approach a 

 specific baitfish in the trolling spread, many anglers 

 free-spool (i.e., "drop-back") rigged natural baits to 

 feeding marlin to imitate stunned baitfish (Mather 

 et al., 1975). This process increases the probability 

 that straight-shank ("J") hooks rigged with natural 

 baits will damage vital internal areas such as the gills, 

 esophagus, and stomach (Prince et al., 2002a). Recently, 

 several studies have documented a reduction in hook- 

 induced trauma associated with the use of circle hooks 

 in fisheries targeting estuarine and pelagic fishes (Lucy 

 and Studholme, 2002). However, there is little research 

 specifically comparing levels of postrelease survival of 

 pelagic fishes caught on circle and straight-shank ("J") 

 hooks. Prince et al. (2002a) and Skomal et al. (2002) 

 examined hooking locations and injuries in sailfish 

 and bluefin tuna caught on both hook types but lacked 

 postrelease survival data from study animals. Domeier 

 et al. (2003) did not detect a significant difference be- 

 tween striped marlin caught on circle and straight- 

 shank ("J") hooks, although the authors did observe 

 significantly decreased rates of deep-hooking and tissue 

 trauma with circle hooks compared to straight-shank 

 ("J") hooks. 



We used data recovered from PSATs to estimate 

 the survival of 41 white marlin caught on circle and 

 straight-shank ("J") hooks in the recreational fishery 

 and released in the western North Atlantic Ocean dur- 

 ing 2002-2003. In addition, differences in hooking 

 locations and hook-induced trauma for white marlin 

 caught on circle and straight-shank ("J") hooks were 

 assessed. 



Methods 



Tags 



The Microwave Telemetry, Inc. (Columbia, MD) PTT-100 

 HR model PSAT tag was used in our study. This tag is 

 slightly buoyant, measures 35 cm by 4 cm, and weighs 

 <70 grams. The body of the tag contains a lithium com- 

 posite battery, a microprocessor, a pressure sensor, 

 a temperature gauge, and a transmitter, all housed 

 within a black resin-filled carbon fiber tube. Flotation 

 is provided by a spherical resin bulb embedded with 

 buoyant glass beads. This tag model is programmed to 

 record and archive a continuous series of temperature, 



