939 



Use of pop-up satellite archival tags to demonstrate 

 survival of blue marlin (Makaira nigricans) 

 released from pelagic longline gear 



David W. Kerstetter 



Virginia Institute of Marine Science 

 The College of William & Mary 

 Rt 1208 Create Road 

 Gloucester Point, Virginia 23062 

 E-mail address bailey(a)vims edu 



Brian E. Luckhurst 



Division of Fisfieries 



Department of Agnculture and Fisfienes 



PO BoxCR 52 



Crawl CRBX, Bermuda 



Eric D. Prince 



National Manne Fisfienes Service 

 75 Virginia Beacfi Dnve 

 Miami, Flonda 33146 



John E. Graves 



Virginia Institute of Manne Science 

 Tfie College of William & Mary 

 Rt, 1208 Create Road 

 Gloucester Point, Virginia 23062 



Blue marlin (Makaira nigricans) sup- 

 port commercial and recreational 

 fisheries throughout the tropical and 

 subtropical waters of the Atlantic 

 Ocean. The species is taken in directed 

 recreational and artisanal fisheries 

 in several areas and constitutes an 

 incidental catch of the widespread 

 commercial pelagic longline fishery. 

 Although blue marlin comprise only a 

 small fraction of the catch of the pela- 

 gic longline fishery that targets tunas 

 and swordfish, this fishery accounts 

 for the majority of fishing mortality 

 on Atlantic blue marlm (ICCAT, 1997; 

 2001). 



Atlantic blue marlin were last as- 

 sessed in 2000 by the Standing Commit- 

 tee for Research and Statistics (SCRS) 

 of the International Commission for the 

 Conservation of Atlantic Tunas (IC- 

 CAT). The assessment indicated that 

 the total biomass of Atlantic blue mar- 

 lin is only about 40% of that necessary 

 to produce maximum sustainable yield 



(MSY) and that current harvests are 

 more than twice the replacement yield, 

 further contributing to the decline of 

 the stock (ICCAT, 2001). A reduction in 

 fishing mortality of approximately 60% 

 is needed simply to halt the decline in 

 stock abundance (Goodyear, 2000). 



One means of reducing fishing mor- 

 tality on blue marlin, without severely 

 impacting catches of target species of 

 the pelagic longline fishery, is to release 

 those blue marlin that are alive at the 

 time longline gear is retrieved (hauled 

 back). Jackson and Farber (1998) re- 

 ported that 48% of blue marlin caught 

 in the Venezuelan longline fishery are 

 alive at the time of haulback. Data from 

 the U.S. observer program between 

 1992 and 1996 indicate that 66% of 

 blue marlin were released alive from 

 the domestic longline fishery (Lee and 

 Brown, 1998) and U.S. National Marine 

 Fisheries Service (NMFS) data and 

 mandatory pelagic longline logbook 

 submissions between 1987 and 1991 



indicate that 59.8% of blue marlin are 

 released alive from commercial pelagic 

 longline gear (Cramer, 1998). 



ICCAT has been encouraging the 

 release of live blue marlin for several 

 years, and in 2000 the Commission 

 mandated that all live blue marlin and 

 white marlin be released from com- 

 mercial longline and purse seine ves- 

 sels. However, for such a management 

 measure to significantly reduce fishing 

 mortality, released animals must have 

 a reasonably high postrelease survival 

 rate. 



Little information exists about post- 

 release survival of blue marlin, espe- 

 cially of animals taken on pelagic long- 

 line gear. In general, recovery rates 

 of billfish tagged with conventional 

 (streamer) tags have been quite low 

 (<2%; Jones and Prince, 1998; Ortiz et 

 al., 1998). This observation is consis- 

 tent with high postrelease mortality, 

 although low recovery rates could also 

 result from tag shedding and a lack of 

 reporting recovered tags (Bayley and 

 Prince, 1994; Jones and Prince, 1998). 

 Results of acoustic tracking studies of 

 blue marlin captured on recreational 

 gear suggest that postrelease survival 

 over periods of a few hours to a few days 

 is relatively high, although mortalities 

 have been noted (reviewed in Pepperell 

 and Davis, 1999). More recently, pop- 

 up satellite archival tags (PSATs) have 

 been used to study postrelease survival 

 of blue marlin taken in a recreational 

 fishery. Graves et al. (2002) attached 

 nine PSATs to blue marlin caught on 

 recreational gear off Bermuda. Eight of 

 the tags detached from the animals and 

 reported as expected after five days; net 

 displacement and direction, tag incli- 

 nation, and temperature data for all 

 eight individuals were consistent with 

 postrelease survival for five days. 



In this note, we present the results 

 of a study evaluating the postrelease 

 survival of blue marlin from pelagic 

 longline fishing gear in the western 

 North Atlantic. We include analyses 

 of the movement and behavior of these 

 animals for tagging periods of both five 

 days and thirty days. 



Manuscript approved for publication 

 9 March 2003 by Scientific Editor. 



Manuscript received 12 July 2003 



at NMFS Scientific Publications Office. 



Fish.Bull. 101:939-948 (2003). 



