Abstract
The genus Kogia, which comprises only two extant species, Kogia sima and Kogia breviceps, represents one of the least known groups of cetaceans in the global ocean. In some coastal regions, however, stranding events of these species have been relatively common over the last decades. Stranding provides the opportunity to investigate the biology of these cetaceans and to explore the epidemiological aspects associated with the mortality of the organisms found on the beach. A number of disturbances (including pelagic fisheries, chemical pollution, boat strikes, and noise pollution) have been confirmed to pose a particular threat to the Kogia species. However, no study has yet investigated potential relationships between environmental conditions and stranding events. Here we analyse how a collection of environmental, physical, and biological variables, such as wind, sea surface temperature (SST), water depth, and chlorophyll-a, correlate to Kogia stranding events along the Brazilian coast. The results of our statistical analyses suggest that K. sima is more likely found in warm tropical waters, which provide an explanation for the high frequency of stranding in northeastern Brazilian coast. In contrast, K. breviceps appears to have a preference for temperate and productive waters. Wind speed results to be also an important factor for predicting Kogia strandings in Brazilian coast. Additionally, literature information in combination with our own data and analyses of stomach contents confirms that oceanic cephalopods constitute the primary nutritional source of both Kogia species. By using the available information as a qualitative proxy for habitat preference and feeding ecology, our study provides a novel and comprehensive assessment of Kogia stranding data in relation to environmental conditions along the Brazilian coast.
Highlights
The genus Kogia comprises only two extant species, the pygmy sperm whale (Kogia breviceps, de Blainville 1838) and the dwarf sperm whale (Kogia sima, Owen 1866)
We evaluated which combination of environmental variables best described the observed number of strandings by fitting different probabilistic models and by selecting the preferred one using the Akaike’s Information Criterion (AIC)
In the time period from 1965 to 2014, 100 stranding events of the genus Kogia were recorded along the Brazilian coast
Summary
The genus Kogia comprises only two extant species, the pygmy sperm whale (Kogia breviceps, de Blainville 1838) and the dwarf sperm whale (Kogia sima, Owen 1866). These two species are considered different since 1966 after extensive morphological analyses of cranium, skeleton and external characteristics have pinpointed relevant taxonomic dissimilarities between them [1]. Dwarf and pygmy sperm whales inhabit offshore tropical, subtropical and temperate waters of the world ocean [4]. According to Caldwell and Caldwell [5], both Kogia species inhabit oceanic waters near continental shelves and slopes, albeit K. breviceps can be found further off shore
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