ENVIRONMENTAL CORRELATES OF CETACEAN MASS STRANDING SITES IN FLORIDA

Abstract

The cause(s) of cetacean strandings remain uncertain, and though numeroustheories abound, relatively few are supported by substantial evidence. Massstrandings (i.e., more than two animals of the same species) can span one or moredays and range over miles of shoreline (Walsh et al. 2001). Recent explanations forsuch strandings include bottom topography, coastal configuration, or geomagnetictopography; meteorological or oceanographic events; extreme conditions in theenvironment; auditory trauma; toxicity of pollutants in the environment; andparasitism (Perrin and Geraci 2002). Contributory factors may also include unusualtides, sea state, nature of the adjacent seafloor, and meteorological events such aselectrical storms (Warneke 1983). It is important not to make generalizations aboutthecauses of mass strandings(Odell1987). Althoughmany strandingsmaybe duetoa common cause, others may simply be a result of experiencing conditions for whicha group of animals was not prepared. A stranding may also reflect prior events whilethe animals were some distance out to sea (Best 1982; Walsh et al. 1991, 2001).One factor that has not been examined in depth is the effect of seasonalenvironmental parameters on the frequency of mass strandings. The effect of windon nearshore oceanic circulation is highly variable and also changes between andwithin seasons. The effects of wind-forcing on across-shelf ocean circulation havebeen noted as an important aspect of the ocean environment and shelf dynamics(Lentz 2001, Fiedler 2002). Although it is unlikely that wind alone could causea mass stranding, the wind does influence across-shelf exchange and water masscharacteristics. This may affect prey assemblages, and in turn influence cetaceans.Wind-driven transport in the near-surface water layer is deflected by the Coriolisforce at 908 to the right in the northern hemisphere (Ekman transport). Since the