Harmful effects of sediment-induced turbidity on juvenile fish in estuaries

Estuaries are important nursery habitats for juvenile fishes of many species, but are under increasing pressure from anthropogenic stressors. We examined the impacts of suspended sediments/turbidity on the foraging success and health of juvenile snapper Pagrus auratus F. Sparidae, which are abundant in many northern New Zealand estuaries and comprise a major coastal fishery as adults. In the laboratory, short-term exposure to turbidity (range <10 to 160 NTU) reduced foraging success of juvenile snapper, while month-long exposure caused higher rates of gill ventilation, gill deformation (epithelial hyperplasia, fusion of the lamellae), weight loss and mortality. In 7 northern New Zealand estuaries with varying catchment land uses, total suspended sediments were negatively correlated with capture rates of juvenile snapper and the condition of individuals, and positively correlated with rates of gill deformation and gill parasite loads. Fish diets changed from zooplankton to benthic prey as turbidity increased. Collectively, our results indicate that elevated turbidity levels have strong negative effects on the health and abundance of juvenile snapper. These turbidity impacts compound the negative effects of sediments on important biogenic fish nursery habitats such as subtidal seagrass beds, likely reducing subsequent recruitment into the fishable adult stock. Management of exploited fish species that have an estuarine life stage must consider the effects of both fishing and sediment runoff from the catchment.