Shallow larval depth-distribution and life history characteristics of the tropical congrid eel Ariosoma scheelei in the Northwest Coral Sea

Abstract

Small-sized eels of the Tropical Conger, Ariosoma scheelei, appear to be common in shallow Indo-Pacific tropical sheltered-bay and lagoon-type habitats when they are sampled appropriately and their larvae are abundant offshore of these areas, but little is known about their biology. Collections of about 7800 likely A. scheelei larvae in May 1997 using a 2-mm mesh 70 m2 mouth-opening trawl with a multiple opening-and-closing codend system at 13 Northwest Coral Sea (NWCS) areas (5 upper-200 m sampling depth-layers, 2 nighttime trawl-deployments/area) and a surface net were used to examine the vertical and geographic distributions of abundance and size of the leptocephali and metamorphosing larvae. 76.5% of trawl-caught A. scheelei leptocephali (33–169 mm, 95.3 ± 22.9 mm) were collected in the 0–12 m depth-layer and 927 (43–151 mm, 83.6 ± 19.5 mm) were examined from surface catches. Some larvae were caught at 12–25 m (12.3%) and 25–50 m (10.1%), but few were caught at 50–100 m (0.77%) and 100–200 m (0.12%). Leptocephali were most abundant offshore in the southeast and metamorphosing larvae (N=532, 82–146 mm) were most abundant in the northwest near the large shelf areas of Torres Strait and the Gulf of Papua. Regional size variations, proportions of metamorphosing larvae, and currents entering/exiting the NWCS suggested that larvae experience transport among areas, and have potential for retention by the Coral Sea Gyre or other recirculations. The high larval abundance of this small-size eel that reaches reproductive maturity at sizes <200 mm suggest it is more abundant in shallow tropical areas than is widely known.