346 



Fishery Bulletin 98(2) 



55 W 



Figure 1 



Proposed migration circuits for northern and southern stocks of dolphinfish, Coryphaena hip- 

 purus. SoHd arrows indicate proposed migration route, open arrows indicate proposed migra- 

 tion route where catch data are not available. Letter symbols indicate months of peak catch. 

 Redrawn from Oxenford and Hunte ( 1986). 



peak in November. Assuming the migration circuit 

 of the two-stock hypothesis (Oxenford and Hunte, 

 1986), we interpret the major peak in Puerto Rico as 

 coinciding with the presence of the northern stock, 

 whereas the minor peak coincides with the appear- 

 ance of the southern stock in the Virgin Islands. The 

 two-stock hypothesis is based on three main obsei-va- 

 tions. First, there are differences in life-history para- 

 meters between dolphinfish from the southeast United 

 States (North Carolina and Florida) and those from 

 Barbados. Southern dolphinfish grow faster, attain 

 sexual maturity at a larger size, have lower fecun- 

 dity for size, and have smaller eggs than northern 

 dolphinfish (Oxenford and Hunte, 1986). Second, the 

 gene flow between both groups is slight. The dif- 

 ference in allele frequencies of the IDH-2 locus in 

 heart extracts and in phenotypic frequencies at the 

 IDH-2, 3 loci in liver extracts indicates infrequent 

 breeding between the stocks (Oxenford and Hunte, 

 1986). Third, the seasonality of catch between regions 

 is different (Oxenford and Hunte, 1986). Because 

 Puerto Rico lies along the boundary for the two pro- 

 posed stocks, it is an ideal location to test the two- 

 stock hypothesis. 



The purpose of our study was to determine age 

 and gi-owth of dolphinfish in Puerto Rico. Compari- 

 son of growth rates between Puerto Rico and other 

 areas (Florida, Barbados) was used to test the two- 

 stock hypothesis. Of specific interest was the com- 

 parison of growth between fish from the north and 

 fish from the south coasts. All fish from the north 

 coast were caught during the period when abun- 

 dance first peaked, whereas 92% of the fish from 

 the south coast were caught during the period of the 

 second peak in abundance. 



Materials and methods 



Dolphinfish were collected from sportfishing tourna- 

 ments and commercial fishing villages from Septem- 

 ber 1991 to April 1992. Twelve dolphin tournaments 

 were held in Puerto Rico, five on the north coast and 

 seven on the south coast. Fifteen billfish tournaments 

 were visited for additional samples. Purchased fish 

 or fish heads supplemented samples when necessary. 

 Fish were caught by trolling lines. Data on date and 

 site of collection, standard, fork, and total lengths, 



