The Translocation of Recreationally Desirable Fishes Is Detrimental to the Maintenance of Local Biodiversity: Sleepy Cod (oxyeleotris Lineolatus) and Other Translocated Species in the Burdekin River, Australia

The Burdekin River contains a distinctive fish fauna characterised by endemic species and species of biogeographic significance, and by a distinct disjunction in the distribution of many species due to the presence of a large waterfall (now the site of a very large impoundment) located in the lower quarter of the river's length. Downstream of the falls, large estuarine and catadromous piscivores such as barramundi (Lates calcarifer) are common. In contrast, large piscivorous fishes are all but absent from the river upstream of the falls. Sleepy cod (Oxyeleotris lineolatus), a piscivore, was first introduced into the upper reaches of the Burdekin River by 1980 and other releases, both official and unofficial, have occurred subsequently. The population remained small and restricted to the site of introduction for a decade, but subsequently expanded in size and distribution such that sleepy cod are now present in every available tributary system of the Burdekin basin. A number of studies, although not designed to examine the impact of translocated species, are used here to examine the spread and impact of sleepy cod. Despite the occurrence of substantial temporal variation in fish abundance due to a highly irregular flow regime, negative impacts on one species, a gudgeon of elevated conservation status (Mogurnda adspersa), are evident. It is unknown whether impacts such as localised extinctions are transitory or permanent. Additional species have been introduced to the upper Burdekin River to satisfy recreational fishing demand: some deliberately, others accidentally. Such species are typified by large size and piscivorous habitat, characteristics alien and inimical to the native fish fauna. It is hypothesised that these species are likely to have even greater impact than sleepy cod in some tributary systems of the upper Burdekin River.