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



435 



recommendations requiring reductions in commercial 

 landings by both pelagic longline and purse seine gears 

 (ICCAT, 2000, 2001a). However, these reductions in 

 landings by themselves may ultimately be insufficient 

 to rebuild these two marlin stocks. Goodyear (2G02a) 

 found that a reduction of 60% would be necessary to 

 halt the decline of blue marlin, a species which is more 

 abundant, larger, and presumably more robust to the 

 trauma associated with commercial capture (Kerstet- 

 ter et al., 2003). Given that white marlin are smaller 

 animals, and that the stock is more depleted than that 

 of blue marlin, even more drastic measures are likely 

 necessary to achieve the same management goal for 

 this species. 



Because the pelagic longline fishery accounts for the 

 majority of white marlin mortality, understanding the 

 nature of billfish interactions with this gear is criti- 

 cal to developing effective strategies to reduce fishing 

 mortality. Jackson and Farber (1998) reported that 

 56% of white marlin caught in the Venezuelan longline 

 fishery between 1987 and 1995 were alive at the time 

 of haulback. Data from the U.S. observer program and 

 mandatory pelagic longline logbook records indicate 

 that 71% of white marlin were released alive from U.S. 

 commercial pelagic longline gear between 1996 and 

 1998 (Cramer'). ICCAT has long been encouraging the 

 release of live white marlin through both binding and 

 nonbinding resolutions (ICCAT, 1995, 1996). More re- 

 cently, the commission has approved binding recommen- 

 dations that require the release of all live white marlin 

 caught by purse seine and pelagic longline vessels (IC- 

 CAT, 1997, 2001b). However, those animals released 

 alive must have a reasonable probability of survival for 

 such management measures to be ultimately effective. 



The assessment of postrelease survival presents spe- 

 cial problems for large pelagic fishes, which are rarely 

 capable of being held in captivity (de Sylva et al., 2000). 

 In general, recovery rates of billfish tagged with con- 

 ventional streamer tags by commercial and recreational 

 fishermen have been quite low (0.4-1.83%: Prince et al., 

 2003; Ortiz et al., 2003). Although this observation is 

 consistent with high postrelease mortality, low recovery 

 rates could also result from tag shedding and from tags 

 that fail to transmit data (Bayley and Prince, 1994; 

 Jones and Prince, 1998). The results of acoustic track- 

 ing studies of various billfish species (e.g., striped mar- 

 lin [Tetrapturus audax]: Brill et al., 1993; blue marlin: 

 Block et al., 1992; and black marlin [Makaira indica]: 

 Pepperell and Davis, 1999) captured on recreational 

 gear indicate that postrelease survival over periods of 

 a few hours to a few days is relatively high, although 

 mortalities have been observed in short-term tracking 

 studies. Recently, pop-up satellite archival tag (PSAT) 

 technology has proven especially useful to study postre- 



' Cramer, J. 2000. Species reported caught in the U.S. com- 

 mercial pelagic longline and gillnet fisheries from 1996-1998. 

 NMFS Sustainable Fisheries Division publication, SFD- 

 99/00-78:1-33. NOAA/NMFS Southeast Fisheries Science 

 Center, SFD, 75 Virginia Beach Dr., Miami, FL 33149. 



lease survival in several larger istiophorid species, in- 

 cluding blue marlin in the Atlantic (Graves et al., 2002; 

 Kerstetter et al., 2003) and striped marlin in the Pacific 

 (Domeier et al., 2003). Only recently have PSATs been 

 attached to smaller (<40 kg) istiophorid billfishes. Horo- 

 dysky and Graves (2005) used PSATs to evaluate the 

 postrelease survival of white marlin from recreation- 

 al (rod-and-reel) fishing gear and demonstrated that 

 smaller billfish (2I6 kg estimated weight) can carry 

 PSATs. Their work also suggested high postrelease 

 survival rates in the recreational fishery, especially for 

 fish caught on circle hooks. However, pelagic longline 

 gear presents a different suite of stressors during cap- 

 ture of an animal than does recreational gear. These 

 differences, including long "soak times" (the length of 

 time in each deployment of the gear that the longline 

 is fishing), may also affect postrelease survival rates. 

 In our study, we applied PSAT technology to estimate 

 the short-term mortality of white marlin released alive 

 after capture on pelagic longline gear. 



Materials and methods 



Fishing operations 



White marlin tagging took place off the east coast of 

 Florida (FL), the southwest edge of Georges Bank (GB), 

 the Yucatan Channel (YC), the Windward Passage (WP), 

 and the Mid-Atlantic Bight (MA). These locations are all 

 waters traditionally fished by the U.S. pelagic longline 

 fleet. All tagging operations occurred opportunistically 

 aboard the commercial pelagic longline fishing vessel 

 FV Carol Ann (54' length-over-all) between June 2002 

 and August 2004. This vessel is typical in size and is 

 equipped for targeting swordfish, mixed swordfish, and 

 tuna within the U.S. coastal pelagic longline fishery. 

 Hook types and sizes were also typical for the fishery 

 and included 7/0 and 9/0 offset J-style hooks (ca. 15° 

 offset; Eagle Claw model no. 9016 or Mustad model no. 

 7698), 16/0 non-offset circle hooks (Mustad models no. 

 39660 or no. 39666), and 18/0 non-offset circle hooks 

 (Lindgren-Pitman, Inc., Pompano Beach, FL). Adjusted 

 seasonally, individual leader lengths were 7.5 fathoms 

 (ca. 13.7 m) in the fall northern fishery targeting tuna 

 and 15 fathoms (ca. 27.4 m) in the spring southern fish- 

 ery for swordfish; this adjustment is standard practice 

 within the fleet (O'Neill-). Individual leader lengths 

 comprised a two-fathom "tail" separated from the rest 

 of the leader by a 28-g leaded swivel — a configuration 

 commonly used in this fishery to reduce tangles with 

 other leaders or the mainline. Varying the length of the 

 lines ("buoy drops") connecting the mainline with the 

 small buoy floats on the surface also allows the gear 

 to fish at different depths. Many captains will use two 

 buoy drop lengths in the beginning of a trip to ascertain 



2 O'Neill, G. 2003. Personal commun. Carol Ann Sword 

 Corporation. 629 NE 3rd Street, Dania Beach, FL 33004. 



