The Distribution and Ecology of Ariosoma Balearicum (Congridae) Leptocephali in the Western North Atlantic

A total of 4589 leptocephali of the congrid eel, Ariosoma balearicum, were examined from 17 cruises in the western North Atlantic Ocean. Myomere counts made on 915 of these indicated there were two ranges of number of myomeres that appear to be associated with separate spawning populations. Those with the higher range (high count: 128–137) were consistently 70–100mm in length in the Sargasso Sea from February to April and 20–80mm in length in the northern Sargasso Sea and Gulf Stream from September to October. Those with the lower range (low count: 120–130) were rare in the northern and eastern Sargasso Sea where they had consistently greater lengths than high count leptocephali and were most abundant in the Florida Current and Providence Channel. The geographic distributions of size and myomere ranges in relation to hydrography provide strong support for the hypothesis that high count eels found along the South Atlantic Bight (SAB) migrate across the Florida Current to spawn in the northwest Sargasso Sea. This migratory pattern is similar to those of Anguilla rostrata and Conger oceanicus, which use the southern Sargasso Sea for development as larvae. However, the distribution of high count leptocephali suggests that they use the entire Sargasso Sea gyre as a development area as larvae before crossing the Florida Current and recruiting to the SAB. The low count eels inhabiting the Bahamas appear to spawn near the banks and their abundance in the Providence Channel and southwest Sargasso Sea suggests most are retained close to the Bahamas. These two distinct styles of spawning, distribution and recruitment of larvae are hypothesized to be related to the different hydrographic regimes of the two juvenile habitats and the resulting constraints on growth and recruitment of larvae. Vertebral and myomere counts reported from other areas suggest there are distinct populations in other regions of the North Atlantic Ocean.