Consequences of dispersal of subtropically spawned crevalle jacks, Caranx hippos, to temperate estuaries


McBride, Richard S., and Kim A. McKown
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Caranx hippos spawn at subtropical and tropical latitudes, but some of their propagules are dispersed hundreds of kilometers north of Cape Hatteras into temperate waters of the western North Atlantic. The effect that this northward dispersal pattern has upon the population depends on whether these juveniles return south during autumn to overwinter or whether they become expatriated from the spawning population and die from hypothermal winter conditions at temperate latitudes. We evaluated whether repatriation was possible by comparing C. hippos seasonal abundance and size-structure from New York to Florida. Young-of-the-year C. hippos occurred annually during summer and autumn but were uncommon in relation to other species in subtropical and temperate estuaries. Sizes of C. hippos at temperate latitudes were as large as conspecifics at subtropical latitudes and juveniles of other species that are known to migrate during autumn from temperate nursery grounds to subtropical latitudes. As C. hippos disappeared from estuaries of the middle Atlantic states in autumn, similar-size fish appeared on the inner continental shelf. We postulate that at least some of the C. hippos observed migrating from temperate estuaries during the autumn eventually overwinter at subtropical latitudes, where they can return to the spawning population. This is unusual, because individuals of many other species whose larvae are transported north of Cape Hatteras do not appear to successfully migrate back to subtropical overwintering habitats. This life-history pattern, in which fish begin their first year in the Carolinian biogeographic province, are dispersed to the Virginian province, and return to the Carolinian province before their first winter, has been demonstrated for only one other western North Atlantic finfish species: bluefish (Pomatomus saltatrix). A few other species are likely to occupy and reproduce within such large-scale oceanographic systems because they have a combination of spawning, larval, and juvenile traits that is similar to that of P. saltatrix and C. hippos.