Long-Term Seasonal and Interannual Patterns of Marine Mammal Strandings in Subtropical Western South Atlantic

摘要

Understanding temporal patterns of marine mammal occurrence is useful for establishingconservation strategies. We used a 38 yr-long dataset spanning 1976 to 2013 to describetemporal patterns and trends in marine mammal strandings along a subtropical stretch ofthe east coast of South America. This region is influenced by a transitional zone betweentropical and temperate waters and is considered an important fishing ground off Brazil. GeneralizedAdditive Models were used to evaluate the temporal stranding patterns of the mostfrequently stranded species. Forty species were documented in 12,540 stranding events.Franciscana (n = 4,574), South American fur seal, (n = 3,419), South American sea lion (n =2,049), bottlenose dolphins (n = 293) and subantarctic fur seal (n = 219) were the most frequentlystranded marine mammals. The seasonality of strandings of franciscana and bottlenosedolphin coincided with periods of higher fishing effort and strandings of SouthAmerican and subantarctic fur seals with post-reproductive dispersal. For South Americansea lion the seasonality of strandings is associated with both fishing effort and post-reproductivedispersal. Some clear seasonal patterns were associated with occurrence of cold-(e.g. subantarctic fur seal) and warm-water (e.g. rough-toothed dolphin) species in winterand summer, respectively. Inter-annual increases in stranding rate were observed for franciscanaand South American fur seal and these are likely related to increased fishing effortand population growth, respectively. For subantarctic fur seal the stranding rate showed aslight decline while for bottlenose dolphin it remained steady. No significant year to year variationin stranding rate was observed for South American sea lion. The slight decrease infrequency of temperate/polar marine mammals and the increased occurrence of subtropical/tropicalspecies since the late 1990s might be associated with environmental changeslinked to climate change. This long-term study indicates that temporal stranding patterns ofmarine mammals might be explained by either fishing-related or environmental factors.