NOTES 



A PRELIMINARY INVESTIGATION OF 



THE STOCK STRUCTURE OF 



THE DOLPHIN, CORYPHAENA HIPPURUS, 



IN THE WESTERN CENTRAL ATLANTIC 



Dolphin, Coryphaena hippurus, are fast swimming, 

 migratory, pelagic fish, which support commercial 

 and sport fisheries throughout the western central 

 Atlantic (Erdman 1956; Zaneveld 1961; Beardsley 

 1967; Rose and Hassler 1969; Sacchi et al. 1981; 

 Olsen and Wood 1982). In terms of weight and 

 revenue, they are the most important large pelagic 

 fish landed by the commercial fisheries in the south- 

 eastern Caribbean (Mahon et al. 1981). In the north- 

 west, they are the most important sport fish, being 

 taken on more trips and in greater numbers by 

 charter boats in Florida (Ellis 1957; Iversen 1962) 

 and in North Carolina (Hassler and Hogarth 1977; 

 Rose and Hassler 1969) than any other species. 

 Rapid expansion of the dolphin fishery fleets is cur- 

 rently underway in the eastern Caribbean, but the 

 biological data necessary for management have not 

 been gathered. For example, we remain ignorant of 

 the number and distribution of stocks of C. hippurus 

 in the western central Atlantic. 



Regional dolphin fisheries are markedly seasonal 

 and this presumably results from migration; but 

 migration patterns remain largely unknown (Palko 

 et al. 1982). However, Beardsley (1967) believed that 

 dolphin migrate northwards during spring and sum- 

 mer, and Gibbs and Collette (1959) suggested that 

 the spring abundance of C. hippurus in the Carib- 

 bean may be a prespawning migration, mostly by 

 females. A preliminary survey of regional catch 

 records indicates a staggering of the peak fish- 

 ing seasons, which supports the assumption 

 that migration is large-scale (Hunte and Mahon 

 1982). 



In the present paper, we take three approaches to 

 our investigation of C. hippurus in the western cen- 

 tral Atlantic: 1) We use commercial and sport fishing 

 data from several countries to examine seasonality 

 and size structure of catch throughout the region; 

 2) we compare growth, age/size at sexual maturity, 

 fecundity, and egg size of dolphin from different 

 parts of the region; 3) we use electrophoretic tech- 

 niques to compare dolphin sampled from Miami and 

 Barbados, two widely spaced fisheries in the region. 

 Electrophoretic techniques, combined with histo- 



FISHERY BULLETIN: VOL. 84, NO. 2, 1986. 



chemical staining for isozymes, are now widely 

 recognized as a useful tool for examining genetic af- 

 finities between fish stocks (Iwata 1975; Allendorf 

 1979; McGlade 1981; Ihssen et al. 1981; Ferris et al. 

 1982). By these means, we address the question of 

 whether the dolphin fisheries in the western central 

 Atlantic exploit a single stock migrating through the 

 region or distinct units located in geographically con- 

 tiguous areas. Resolution of this question will affect 

 the extent to which individual territories should ex- 

 pand their dolphin fisheries, will determine whether 

 management programs need be regional or territory- 

 specific, and will identify which territories need to 

 collaborate for joint management of stocks. 



Methods 



Dolphin monthly catch data, recorded by commer- 

 cial or sport fisheries, were obtained either by let- 

 ter, personal visit to fisheries departments, and/or 

 published literature (Table 1). The catch data, re- 

 corded as numbers, weights, catch per day or per 

 boat, and over time periods of 1 to 12 years, were 

 standardized and plotted as percentages of total an- 

 nual catch landed each month. Where more than 1 

 year's data were available, the average catch each 

 month was calculated. 



Tissue samples for the electrophoretic survey were 

 collected off Barbados between December 1982 and 

 March 1983, and off Miami in May and June 1983. 

 Samples of eye, heart, liver, gonad, and white mus- 

 cle were taken from a total of 1,669 freshly landed 

 dolphin and were deep frozen for later analysis. A 

 survey of 22 enzymes encoded by 55 presumptive loci 

 was conducted to identify polymorphic enzyme 

 systems. The allelic frequencies of the highly poly- 

 morphic isocitrate dehydrogenase, Idh-2, locus were 

 compared in Miami and Barbados dolphin. The 

 horizontal starch gel electrophoresis methodology 

 follows that of May et al. (1979) and McGlade et al. 

 (1983). Allelic nomenclature follows that of Allen- 

 dorf and Utter (1979). 



Life history data were obtained from the literature, 

 from records of length and weight of specimens 

 caught in the Bahamas, Bermuda, and North 

 Carolina, and from our own studies of 624 dolphin 

 landed during the peak of the sport fishery in Miami 

 and 3,126 dolphin landed by the commercial fishery 

 in Barbados. 



451 



