721 



Abstract— Bycatch studies have largely 

 ignored population level efTects on fish 

 species of little commercial interest. 

 Here we analyze bycatch of the lined 

 seahorse ^Hippocampus erectus) in the 

 bait-shrimp trawl fishery in Hernando 

 Beach, Florida, providing the first 

 fisheries data for this species. Based 

 on catch per unit of effort (CPUE), 

 size, sex, and reproductive status of 

 trawled H. erectus, 1) approximately 

 72,000 seahorses were caught annu- 

 ally by this fleet, from a population of 

 unknown size, 2) trawling affected pop- 

 ulation cohorts differentially because of 

 temporal and spatial variation in CPUE 

 and population size, and 3) a greater 

 proportion of females than males was 

 removed in trawling. Our findings sug- 

 gest that trawling may affect seahorse 

 populations through direct mortality, 

 social disruption, and habitat damage. 

 However, the lack of specific abundance 

 or catchability estimates for H. erectus 

 means that the precise impact of trawl- 

 ing on this fish remains uncertain. This 

 paper focuses attention on the need 

 for research and monitoring of small 

 fishes that are caught incidentally in 

 nonselective gear. 



Bycatch of lined seahorses (Hippocampus erectus) 

 in a Gulf of Mexico shrimp trawl fishery 



Julia K. Baum 



Jessica J. Meeuwig 



Amanda C. J. Vincent 



Proiect Seahorse 



Department of Biology 



McGill University, 



1205 Dr Penfield Ave. 



Montreal, Quebec, H3A 1B1, Canada 



Present address (for J. K Baum); Department of Biology 



Dalhousie University 



1355 Oxford St. 



Halifax, Nova Scotia, B3H 4J1, Canada 

 E-mail address (for J K Baum) baum@mathstat.dal.ca 



Manuscript approved for publication 

 2 June 2003 by Scientific Editor 



Manuscript received 26 June 2003 at 

 NMFS Scientific Publications Office. 



Fish. Bull 101:721-731 (2003). 



The incidental capture of marine or- 

 ganisms is now recognized as a seri- 

 ous problem in fisheries management 

 and marine conservation (Alverson et 

 al., 1994; lUCN, 1996; Alverson, 1997; 

 Jennings and Kaiser, 1998; FAO, 1999). 

 Shrimp trawl fisheries are the single 

 greatest source of bycatch, accounting 

 for 35% of the world's total bycatch 

 (Alverson et al., 1994). Bycatch research 

 has focused on marine megafauna, sea- 

 birds, and commercially important fish 

 species (see as examples Polacheck, 

 1989; Graham, 1995; Weimerskirch 

 et al., 1997; Julian and Beeson, 1998; 

 Pikitch et al., 1998; Galloway and Cole, 

 1999; Diamond et al., 2000). The conser- 

 vation impacts of bycatch for noncom- 

 mercial fishes and invertebrate species 

 remain largely unstudied (but see 

 Chan and Liew, 1986; Pettovello, 1999; 

 Milton, 2001). The few studies that 

 have evaluated incidental capture of 

 these species have focused on survival 

 rates of individuals (Hill and Wassen- 

 berg, 1990, 2000; Kaiser and Spencer, 

 1995; Probert et al., 1997; Mensink et 

 al., 2000) without addressing popula- 

 tion level effects of bycatch. However, 

 even species that comprise only a small 

 portion of the bycatch in a fishery may 

 experience significant impacts of inci- 

 dental harvest on their population size 

 and structure. 



Seahorses are among those spe- 

 cies inferred to be greatly affected by 

 nonselective fishing gear, both because 

 intense trawling often covers seahorse 



habitat and because their life history 

 traits likely render these fishes vul- 

 nerable to overexploitation (Vincent, 

 1996). Most studied seahorse species 

 are strictly monogamous (i.e. sexually 

 and socially), meaning that removal can 

 disrupt pairs and may reduce reproduc- 

 tive output (e.g. Vincent, 1995; Vincent 

 and Sadler, 1995; Kvarnemo et al., 

 2000; Perante et al., 2002). Obligatory 

 parental care by males, combined with 

 relatively low fecundity, may reduce the 

 potential for population recovery from 

 overexploitation, although potentially 

 high survival of young may also offset 

 this apparent cost. In addition, sparse 

 distributions and low mobility suggest 

 that seahorses will be slow to recolonize 

 depleted areas (Perante et al., 2002; 

 Vincent et al.^). 



Seahorses derived from bycatch ap- 

 pear to be contributing greatly to the 

 large and growing international trade 

 in these fishes (Vincent, 1996; Vincent 

 and Perry2). Consumer demand for 

 seahorses — both dried for traditional 

 medicine and curiosity trades, and, 

 less frequently, live for the aquarium 

 trade — is very high (Vincent, 1996). 

 Global demand for seahorses has sur- 

 passed supply and therefore trade has 

 increased and expanded geographically 



' Vincent, A. C. J., K. L. Evans, and A. D. 

 Marsden. 2003. Home range behaviour 

 of the monogamous Australian seahorse. 

 Hippocampus whitei. Manuscript in 

 review. 



