Oceanic Environmental Effects on American Eel Recruitment to the East River, Chester, Nova Scotia

Abstract

The effect of oceanic environmental conditions on the recruitment of American Eel Anguilla rostrata to coastal waters is poorly understood. This study examined correlations between the annual elver count index of the East River, Chester, Nova Scotia, seasonal oceanic environmental conditions associated with the larval and glass eel stages, and larval and glass eel migration times between the spawning area and continental recruitment. In recent years, the elver fishery of the East River has started earlier in conjunction with increasing inshore, continental shelf, and Gulf Stream water temperatures, with the strength of the correlation decreasing with distance from shore. A northward shift of the Gulf Stream may also have contributed to earlier arrival dates. Annual elver index values increased over the study period but were not significantly correlated with any atmospheric or oceanic environmental conditions, perhaps due to a relatively short time series, although effect sizes (correlation coefficient r) were often medium, a level potentially considered of biological importance. Elver mean lengths varied annually with no trend and were not significantly correlated with the elver index. Significant correlations occurred between the North Atlantic Oscillation and Sargasso Sea primary productivity (lag of 0) and Emerald Basin (Scotian Shelf) water temperatures (lag of –5), while Scotian Shelf chlorophyll values decreased with increasing water temperatures (lag of –3). The mean migration period from spawning to stream entrance at the East River was estimated at 1.2 years, mostly spent growing in and ultimately leaving the Sargasso Sea, then crossing oceanic and continental shelf waters between the Gulf Stream and coastal streams, with a short period of transport along the Gulf Stream. The estimate of total migration period based on observed recruitment times at various sites and the mean of the estimated spawning period averaged 45.5% greater than those estimated from otolith methods, perhaps due to the effect on otolith daily ring deposition during glass eel migration in oceanic water temperatures <10ºC between the Gulf Stream and coast.