Abstract

Swordfish is one of the most economically important highly migratory species in the northwestern Atlantic. The high level of fishing and declining catches in recent years fish have prompted managers to impose regulatory measures to avoid recrutitment overfishing. The lack of adequate data has prevented the development of more precise management regulations. Spawning stock biomass is often used as a proxy for total egg production in spawner-per-recruit analysis, but this type of analysis does not take into consideration the dynamics of egg production. In highly fecund species, like swordfish, changes in egg production increase with age, thus the use of spawning stock biomass fails to recognize the higher seasonal fecundity of older fish. To demonstrate this, the effect of fishing on the reproductive potential of the northwestern Atlantic swordfish stock on a per-recruit basis was analyzed using the Spawning Potential Ratio (SPR) based in terms of spawning stock biomass-per-recruit (SPRssb/r ) and as egg production-per-recruit (SPRep/r). Pronounced differences were observed in the estimation of SPRssb/r and SPRep/r , due to the non-linear nature of the egg production curve over the lifetime of an individual swordfish. This results in a reduction of the SPRep/r with respect to the SPRssb/r and causes an overestimation up to 1.5 times of any target F%SPR (i.e., fishing mortality of a % of SPR). The effect on other highly fecund species, like billfish, is also discussed. Another aspect considered was the effect of fishing effort (deployed by the U.S. and Venezuelan longline fleet) spatial distribution on the spawning stock. It was observed that the seasonal fishing effort was clustered from January to May in the oceanic area, time when most of the spawning takes place in that area. It became evident that the reproductive output of the swordfish stock will be strongly affected by the high concentration of the fishing effort on the spawning grounds.

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