Publication Abstract

Size-spectra as indicators of the effects of fishing on coral reef fish assemblages

N.A.J. Graham, N.K. Dulvy, S. Jennings and N.V.C. Polunin

The data requirements and resources needed to develop multispecies indicators of fishing impacts are often lacking and this is particularly true for coral reef fisheries. Size-spectra, relationships between abundance and body-size class, regardless of taxonomy, can be calculated from simple size abundance data. Both the slope and the mid-point height of the relationship can be compared at different fishing intensities. Here, we de­velop size-spectra for reef fish assemblages using body size- abundance data collected by underwater visual census in each of ten fishing grounds across a known gradient of fishing intensity in the Kadavu Island group, Fiji. Slopes of the size-spectra became steeper (F_9,69=3.20, p< 0.01) and the height declined (F_9,69=15.78, p< 0.001) with increasing fishing intensity. Regressions of numbers of individuals per size class across grounds were negative for all size classes, although the slope was almost zero for the smallest size class. Response to ex­ploitation of each size class category was greatest for larger fish. Steepening of the slope with increasing fish­ing intensity largely resulted from reductions in the relative abundance of large fish and not from the eco­logical release of small fish following depletion of their predators. The slope and height of the size-spectrum appear to be good indicators of fishing effects on reef fish assemblages.

Reference:

N.A.J. Graham, N.K. Dulvy, S. Jennings and N.V.C. Polunin (2005). Size-spectra as indicators of the effects of fishing on coral reef fish assemblages. Coral Reefs, 24: 118-124.