Size structural change in lightly exploited coral reef fish communities: evidence for weak indirect effects

• Published in: Canadian journal of fisheries and aquatic sciences Vol. 61; no. 3; pp. 466 - 475
• Main Authors: Dulvy, N K, Polunin, N VC, Mill, A C, Graham, N AJ
• Format: Journal Article
• Language: English
• Published: Ottawa, Canada NRC Research Press 01.03.2004; National Research Council of Canada; Canadian Science Publishing NRC Research Press
• Subjects: Animal populations; Animal, plant and microbial ecology; Applied ecology; Biological and medical sciences; Biomass; Community structure; Coral reefs; Ecological effects; Exploitation; Exploitation and management of natural biological resources (hunting, fishing and exploited populations survey, etc.); Fish; Fishing; Fundamental and applied biological sciences. Psychology; Islands; Marine; Physical growth; Predation; ISEW, Pacific, Fiji; Population exploitation; Community structure; Coral reef; Corporal biometry; Impact study; Fishing; Marine environment; Aquatic environment; Vertebrata; Animal community; Pisces; Body size; Reef animal
• ISSN: 0706-652X; 1205-7533
• DOI: 10.1139/f03-169

Exploitation influences community structure directly through preferential removal of larger-bodied fishes and indirectly because larger-bodied fishes may exert top-down control upon other community members. We consider the direct and indirect effects of subsistence exploitation upon the size structure of coral reef fish communities along an island-scale spatial gradient of fishing intensity. We explored the effect of fishing intensity and sample date (three dates over a year) at six islands and the overall effect of fishing intensity averaged over sample dates at 13 islands. Fishing intensity consistently explained more of the variation in the size metrics than sample date. In response to exploitation, the mean weight of individuals declined by 52%, the weighted average maximum size (L max ) declined by 25%, and slopes of community size spectra steepened. The larger size classes (>26 cm) declined in relative numbers by 63% and relative biomass by 61% in response to exploitation. However, the numbers and biomass of the three smallest size classes (<25 cm) increased by 31% and 9%, respectively, in response to exploitation. This increased abundance is consistent with a weak compensatory response presumably from a reduction in predation upon smaller size classes as an indirect effect of exploiting larger size classes.