LINKAGES BETWEEN NEW ENGLAND DOLPHIN STRANDING FREQUENCY AND NORTH ATLANTIC OSCILLATION VARIABILITY

Abstract

The North Atlantic Oscillation (NAO) is a dominant climatic driver that influences hydrographic and ecological parameters at multiple spatial scales and several trophic levels. To date, linkages between NAO variability and dolphin strandings on a regional scale have not been investigated. Stranding records of short-beaked common dolphins (Delphinus delphis) and Atlantic white-sided dolphins (Lagenorhynchus acutus) during 1990–2014 between Maine and New York were correlated against the winter NAO index at several time lags in order to explore the link between stranding variability and NAO. The stranding frequencies of the two species were positively correlated to one another. When analyzed against the winter NAO index, the stranding time-series for both species yielded statistically significant inverse correlations at time lags of one and/or two years. Dolphin strandings were lower during the two years after winters when the NAO was positive and were higher during the two years after a negative NAO. Linear regression modeling confirmed a significant relationship between strandings and winter NAO at both 1- and 2-year lags for common dolphins, but not for white-sided dolphins. The hypothesized mechanism underlying the relationship is that NAO-linked hydrographic changes during winter in outer shelf and slope waters affect the abundance and/or availability of prey, leading to changes in the inshore-offshore distribution patterns of the dolphins. Increased occurrence and foraging closer to shore increases the dolphin’s susceptibility to stranding caused by other localized or short-term factors. This study represents the first attempt at linking NAO variability to dolphin mortality within New England waters.