MEPS 495:219-231 (2014)  -  DOI: https://doi.org/10.3354/meps10579

ABSTRACT: Recent studies suggest that fishing and climate change can lead to a decrease in body size of fishes. While the effect of fishing on marine ecosystems has been widely explored, much less is known about the ecosystem effects of fish body size decrease. Here we used a marine ecosystem model to compare how fishing and small (<0.1% yr ^-1) but continuous (50 yr) decreases in the average body sizes of 5 Australian demersal fish species affect ecosystem indicators, biomasses and diets of different species. We found that decreasing growth rate of the 5 species had similar and comparable impact as the introduction of fishing of these 5 species at fishing mortality rate of F = 0.2 yr ^-1. The same applied when impacts of decrease in size were compared to those of increasing fishing from F = 0.2 to F = 0.4. This suggests that declines in body size alone can lead to ecosystem responses similar in magnitude to those caused by moderate fishing. On average, body size decrease alone caused more qualitative changes in diets of all species and larger changes in the predation mortality of slower growing species than the introduction or intensification of fishing. The overall ecosystem response to fishing and slower growth of fish was largely similar and additive, suggesting that decreasing sizes of harvested fishes are likely to amplify the effects of fishing.

KEY WORDS: Diets · Ecosystem indicators · Ecosystem models · Fisheries induced evolution · Growth · Predator–prey interactions