Estuarine predator—prey interactions in the early life history of two eels (Anguilla rostrata and Conger oceanicus)

Abstract

Field observations (timing of larval ingress from 1989 to 2010) and laboratory experiments (habitat preference, predation, cannibalism by glass eels and elvers) were conducted to better understand the interactions between the early life history stages of two eel species, Anguilla rostrata and Conger oceanicus, which both ingress annually to Great Bay/Little Egg Harbor, New Jersey. A 21-year weekly time series revealed that these species generally overlap in occurrence in spring, but the degree of overlap may be changing over time: the peak in A. rostrata glass eel abundance occurring later and the peak in C. oceanicus leptocephali abundance occurring earlier. During this overlap period and subsequent settlement, the two species show differences in habitat use patterns, with both preferring shelter, but only A. rostrata burying in substrate. In one-on-one trials, cannibalism was infrequent (A. rostrata 1 % of 59 trials, C. oceanicus 16 %, of 51 trials). Predation by C. oceanicus elvers on A. rostrata glass eels and elvers was frequent (45 % of 165 trials), but never occurred for the opposite interaction. This order presumably is related to the larger size of C. oceanicus at ingress, metamorphosis and settlement compared to A. rostrata and the aggressive piscivory of C. oceanicus even extending to cannibalism. Together, these observations of predation and the change in timing of C. oceanicus occurrence in the estuary may influence the success of A. rostrata immediately after ingress and thus contribute to the decline of the latter. Further, these interactions provide another example of predation in estuaries (presumed refugia) and the contributing role of predation on and among the early life history stages of fishes—a relatively underexplored phenomenon.