Summer spatial patterns of the fish community in a large, shallow, turbid coastal lake

Abstract

Several water quality parameters, marginal vegetation, and the fish community in Lake Ellesmere, a large, shallow, turbid lake situated on the east coast of the South Island, New Zealand, were sampled along selected transects in late summer to determine species spatial patterns. Thirteen species of fish were caught, with seven of them comprising major populations, although only four of these were adequately sampled by the method used - they included inanga (Galaxias maculatus), common smelt (Retropinna retropinna), shortfinned eel (Anguilla australis), and common bully (Gobiomorphus cotidianus). Inanga were almost exclusively confined to areas on the western side of the lake which has a convoluted shoreline with a variety of small embayments with scattered vegetation along the margins. Common smelt occupied both marginal and offshore areas, but they too were more abundant along the margins particularly on the western side. Both the common bully and shortfinned eel were widespread and abundant in the lake, although their abundance and biomass were higher within the vicinity of the lake outlet, major inflowing tributaries, and other marginal habitats. All three species of flounders of the genus Rhombosolea were poorly represented in our samples. However, in commercial catches they were reasonably abundant, with the sand flounder (R. plebeia) and yellowbelly (R. leporina) being more common in offshore than inshore catches, whereas the black flounder (R. retiaria) showed no difference in the catches between areas. Our overall findings are consistent with the hypothesis that bottom-dwelling species (eels, bullies, flounders) are more widely distributed than free-swimming forms (inanga, common smelt), which were largely confined to areas sheltered from prevailing winds. The highly turbid nature of the lake, primarily because of re-suspension of fine bottom sediments by frequent winds, is considered an important factor in the distribution of the fish fauna.