Mining pollution and the diet of the purple-striped gudgeon Mogurnda mogurnda Richardson (Eleotridae) in the Finniss River, Northern Territory, Australia

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Journal Article
Ecological Monographs, 1980, 50 (4), pp. 457 - 485
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During the dry season of 1974, collections of the purple-striped gudgeon Mogurnda mogurnda were taken from the Finniss River of the Northern Territory; during the wet season, this river receives acidic and metallic pollutants from the formerly mined area of Rum Jungle. The fish consumed a great variety of foods, with high abundances of Dytiscidae, Chironomidae, Ceratopogonidae, Trichoptera, Odonata, Copepoda, Decapoda, and Pisces. Within polluted and unpolluted zones of the river, the dietary abundances of some foods varied with the size of the consuming fish and with habitat descriptors. For no food was there a significant regression against habitat descriptors in both of the zones; this emphasizes that pollution effects are more complex than simply depressing or raising the abundances of the dietary species. Five foods were more abundant in the diets of the polluted zone, and three in those of the unpolluted zone. The dietary abundances of two foods, both crustacean, increased in the polluted zone, compared to the unpolluted zone, through the dry season. Two categories of foods: (1) those obtaining oxygen directly from the atmosphere or via a film or bubble of air; and (2) the converse set (aquatic respirers), were contrasted for their usefulness in distinguishing between the zones, by both hierarchical agglomerative and discriminant function analyses. Aquatic respirers were the more effective. The polluted collections were more heterogeneous than the unpolluted ones in both the hierarchical and the discriminant analyses. One collection from the polluted zone was reclassified as unpolluted on the basis of its grouping behavior. The relevance for pollution studies of dietary analysis of euryphagous fish, rather than sampling aquatic fauna directly, is discussed in terms of food substitution, switching, strategies for abundance and recovery by the fauna, and possible effects of the pollutants on the fish as an intervening collector. Downstream patterns of abundance of the invertebrate fauna in this study are broadly similar to those of other studies in which such chemically diverse metals as Pb, Zn, and Cu are the pollutants, but there are differences for some faunal components. Difficulties in the comparison and causal interpretation of results of pollution studies in the field stem from a lack of experimental data on tolerances to pollutants and causes of abundance of stream invertebrates. However, because of the great detail required in such data, more profit for purposes of prediction may derive from experimental multivariate studies on faunal assemblages.
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