Effects of trawling on the diets of common demersal fish by‐catch of a tropical prawn trawl fishery

Abstract

The ecological effect of prawn trawling on the benthos of the Gulf of Carpentaria, northern Australia, was investigated by examining stomach contents of common demersal fishes incidentally caught as by-catch in the fishery. Fishes were collected from high and low fishing intensity sites in three regions based on vessel monitoring system data. The diets of eight species of benthic fish predators were compared between regions and fishing intensities. A regional effect on diet was evident for seven species. Only one generalist species had no significant difference in diet among the three regions. For the comparisons within each region, five predator species had significantly different diet between high and low fishing intensities in at least one region. Across the three regions, high fishing intensity sites had predators that consumed a greater biomass of crustaceans, molluscs and echinoderms. At low fishing intensity sites, predators had diets comprising a greater biomass of cnidarians and teleosts, and a different assemblage of molluscs, crustaceans and fishes. These changes in diet suggest that there may have been a shift in the structure of the benthic community following intensive fishing. Analysis of predator diets is a useful tool to help identify changes in the benthic community composition after exposure to fishing. This study also provided valuable diet information on a range of abundant generalist benthic predators to improve the ecosystem modelling tools needed to support ecosystem-based fisheries management.

Trawling disturbance effects on the trophic ecology of two co-generic Astropectinid species

“…In relation to trawl intensity the two species showed a highly opportunistic feeding strategy and co-occurred at all sites by showing differences in their diet preferences (Ribi et al, 1977) and shifting in size-frequency distributions. Our results support the hypothesis that bottom trawling affects the fitness of benthivorous organisms by altering the food availability and generating a positive response of facultative scavengers to carrion (Demestre et al, 2000;Link, 2004;Dell et al, 2013;Johnson et al, 2015).…”

“…Here, we tested the hypothesis that bottom trawling affects the diet of benthivorous organisms by altering food availability and generating a positive response of facultative scavengers to carrion. Benthic scavengers feeding on the benthic community that results from the effects of trawling might represent costeffective samplers, hence diet studies may provide insights into the trophic consequences of such community changes for other components of the ecosystem (Link, 2004;Dell et al, 2013;Johnson et al, 2015).…”

Indirect effects of bottom fishing on the productivity of marine fish

“…However, these fish had reduced body condition, which is most likely explained by the additional energetic costs of searching for food in a reduced prey field. Dell et al (2013) also found differences in the composition of the diet of eight fish species between low and high fishing intensity areas in a tropical prawn fishery, and also found that stomach fullness did not differ between low and high trawling areas.…”

“…Dell et al . () also found differences in the composition of the diet of eight fish species between low and high fishing intensity areas in a tropical prawn fishery, and also found that stomach fullness did not differ between low and high trawling areas.…”

“…This may be one reason that stomach fullness does not vary for fish caught in disturbed and undisturbed areas (Dell et al . ; Johnson et al . ).…”