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Fishery Bulletin 101(4) 



size to H. erectus have found varied densities: H. comes, an 

 exploited species associated with coral reefs in the tropics, 

 had localized densities of 0.019/m- in a marine protected 

 area, and much less elsewhere (Perante et al., 2002), and 

 an unexploited species, H. whitei, had localized densities 

 of 0.088-0. 215/m^ in a study area, and no seahorses were 

 found over large adjacent areas (Vincent et al.'). Our study 

 also suggests very patchy distributions of//, erectus (549f 

 of the trawls had no seahorses at all and the number of 

 seahorses per trawl set ranged from to 16). 



Although variation in CPUE may reflect differential 

 catchability by habitat, we suggest that in areas where 

 seahorses were caught, temporal rather than spatial ef- 

 fects drove CPUE. It is difficult to make conclusions about 

 variation in CPUE because data were unbalanced, in that 

 the areas trawled differed between years and among lu- 

 nar phases. However, analysis of variance on a subset of 

 data for three sites (Nl, N2, N3) on three lunar phases 

 (1^' quarter, full moon, 3'''' quarter) for which we had data 

 in both years («=149 trawls), indicated that there was a 

 strong effect of year, a weaker effect of lunar phase, and no 

 effect of site. These results suggest that CPUE was mainly 

 affected by temporal variation. Lunar patterns in CPUE 

 as a result of fish behavior and ecology are common (e.g. 

 Parrish, 1999). This would be consistent with observations 

 for other species of seahorses; H. comes in the Philippines 

 (Vincent et al.-*) and H. spinosissimus and H. trimaculatus 

 in Vietnam (Meeuwig et al.**) exhibited patterns in CPUE 

 with respect to lunar phase, although these species were 

 also distributed in patches in space. 



Data from this study suggest that the H. erectus popu- 

 lation was spatially structured. In 1999, the mean size of 

 incidentally caught adult seahorses decreased, reflecting 

 the absence of the largest size class of males and an in- 

 crease in smaller females that year (Fig. 5). We attribute 

 this difference to spatial structuring: the shallower areas 

 (12, S2) where the largest male and female seahorses were 

 caught in 1998 were not fished during the 1999 sampling 

 season. Most of the seahorse bycatch were adult H. erectus; 

 the dearth of juvenile H. erectus (and dwarf seahorses, H. 

 zosterae) in the trawls reflects low catchability or retention 

 due to mesh size. Similar proportions of juvenile seahorses 

 were caught over the two sampling seasons. The ratio of 

 juveniles to adults appears to be temporally influenced 

 I proportionally more juveniles were caught on new moons), 

 but this variation probably also reflects spatial structuring 

 because these trawls occurred primarily in deeper offshore 

 areas (N2, N3) that were fished almost exclusively during 

 this lunar phase. Perhaps//, erectus undergoes ontogenetic 

 movement, between juvenile and adult life history stages, 

 and adults maintain site fidelity. Spatial size structuring 

 probably also occurs in other seahorse species, for the en- 

 tire population and for adults alone (//. comes, Meeuwig'''; 



H. guttulatus, Curtis''). A better understanding of the 

 spatial structuring of populations could allow for spatial 

 control of fishing effort to minimize bycatch. 



We found a consistent, female-biased sex ratio in the 

 catch across the two years of our study, with only 42% 

 males. This bias may reflect the sex ratio of the H. erectus 

 population: a similar sex ratio (40% males) was found in a 

 population of//, erectus in Chesapeake Bay, Virginia (Teix- 

 eira and Musick, 2000). Female-biased sex ratios have also 

 been found in H. zosterae (33% males) when sampled by 

 pushnet (Strawn, 1958), and in H. abdominalis studied 

 underwater in Australia (Martin-Smith^). Many other 

 wild populations of seahorses studied underwater, however, 

 have documented equal numbers of males and females (//. 

 breviceps: H. comes: Moreau and Vincent*; Perante et al., 

 1998; H. reidi: Dauwe, 1993; H. whitei: Vincent and Sadler, 

 1995). Sexual dimorphism in H. erectus was too slight to 

 explain different catchability of the two sexes and would, 

 in any case, have favored the capture of males. The dispro- 

 portionate catch of females could have arisen from spatial 

 segregation by sex; the greater catches of reproductively 

 active males in shallower areas suggests that males may 

 spend most of their time inshore of the trawled area. We 

 also cannot discount the possibility that some seahorses 

 classified as females may have been immature males, and 

 the sex ratio in the population could in fact be 1:1. 



The proportion of reproductively active seahorses in the 

 bycatch was lower than expected, particularly in 1999. Our 

 study occurred during summer, within the breeding season 

 for the congeneric and sympatric //. zosterae in Florida (Feb- 

 ruary to October; Strawn, 1958), and for H. erectus in Ches- 

 apeake Bay (May to October; Teixeira and Musick, 2000; 

 Vincent, personal obs.). Males of all studied seahorse species 

 were reproductively active almost continuously throughout 

 the breeding season (Dauwe, 1993; Nijhoff, 1993; Vincent 

 and Sadler, 1995; Perante et al., 2002), often remating the 

 same day that they release their young (Vincent and Sadler, 

 1995). In our study, trawling may have occurred outside the 

 primary breeding areas for male H. erectus, but catches of re- 

 productively nonactive adult males during the breeding sea- 

 son also suggest that repeated trawling may have disrupted 

 breeding in the population. A further indication of possible 

 spatial structuring in the population (by reproductive sta- 

 tus and size) is that almost half of the reproductively active 

 males caught in 1998 were found in S2, the shallowest area; 

 this area was not sampled in 1999 when few reproductively 

 active males were found. Such spatial structuring offers the 

 possibility of trawling outside the breeding area. 



^ Vincent, A. C. J., J. J, Meeuwig, M. G. Pajaro, and N. C. I'eranto. 



Seahorse catches in the central Philippines: characteristics and 



conservation implications. Manuscript in prep. 

 " Meeuwig, J. J., D. H. Hoang, T S. Ky, S.D. Job, and A. C. J. Vincent. 



Bycatch landings of seahorses in central Vietnam. Manuscript 



in prep. 



•'' Meeuwig, J. J. Life history parameters of the exploited seahorse 



Hippocnmpus comes: a length based analysis. Manuscript in 



prep. 

 ^ Curtis, J. 2002. Unpubl. data. Project Seahorse. Fisheries 



Center, The University of British Columbia, 2204 Main Mall, 



Vancouver, BC, V6T 1Z4, Canada. 

 " Martin-Smith, K. 2002. L'npubl. data. Project Seahorse, 



Fisheries Center. The University of British Columbia, 2204 



Main Mall, Vancouver, BC, V6T 1Z4, Canada. 

 8 Moreau, M-A., and A. C. J. Vincent. 2000. Unpubl. data. 



Project Seahorse, Fisheries Center, The University of British 



Columbia, 2204 Main Mall, Vancouver, BC,V6T 1Z4, Canada. 



