Publication Abstract

Metals and organochlorines in small cetaceans stranded on the east coast of Australia

R.J. Law, R.J. Morris, C.R. Allchin, B.R. Jones and M.D. Nicholson

As top predators, marine mammals can accumulate high concentrations of some contaminants from their diet. It has been suggested that some of these contaminants may act to compromise the immune function of seals and dolphins, thereby rendering them more likely to infection, and this may have been a factor in a number of epizootics which have affected these animals in recent years (de Swart et al., 1996). Recent studies in the UK have also shown statistically significant associations between tissue concentrations of both mercury and chlorobiphenyls in harbour porpoises (Phocoena phocoena) and death from infectious disease (Bennett et al., 2001; Jepson et al., 1999). Contaminant concentrations in cetaceans are related both to the composition of their diet, and to its source relative to inputs from both natural and anthropogenic inputs. It is useful therefore to benchmark levels found in cetaceans from the UK against those found elsewhere, and, although some data are available from Arctic waters and the Pacific Ocean, few recent data have been published for small cetaceans from Australian waters (Kemper et al., 1994; Vetter et al., 2001). Although lower contaminant levels are generally found in remote sites, there seem to be no entirely pristine areas remaining as transport mechanisms operate globally via the atmosphere, especially for organochlorine compounds (Bignert et al., 1998). In this study we present the analyses of tissue samples taken opportunistically from three species of small cetaceans either stranded, or caught in shark nets, on the east coast of Australia. The three species involved have different behaviours and different patterns of feeding, illustrating varying patterns of uptake of anthropogenic pollutants in these waters. Groups of the inshore form of the bottlenose dolphin (Tursiops truncatus aduncus) found off the east coast of Australia tend to be resident in a particular coastal area. They live and feed close inshore, often spending considerable time in the numerous coastal bays which are partly enclosed by sand islands and sand spits. Their diet comprises a wide range of inshore species; benthic and midwater fish, benthic invertebrates, squid and octopi. In contrast, common dolphins (Delphinus delphis) are mainly pelagic but are often seen close inshore in these waters, sometimes coming right into the coastal bays. Whilst they may be regular visitors to the inshore areas they could not be considered as even semi-residents. Their diet would be mainly near surface pelagic, probably dominated by schooling fish and squid. Much less is known of the melon-headed whales (Peponocephala electra). They are rarely seen in the inshore waters of East Australian coast, being almost entirely pelagic and feeding on oceanic squid and fish species from a variety of depths (Evans, 1987; Martin, 1990).

Reference:

R.J. Law, R.J. Morris, C.R. Allchin, B.R. Jones and M.D. Nicholson. 2003. Metals and organochlorines in small cetaceans stranded on the east coast of Australia. Marine Pollution Bulletin, 46: 1206-1211