Environmental heterogeneity and species responses to fishing disturbance: are the effects of clam harvesting spatially consistent?

GUTIERREZ, J,L.; PALOMO, M. G.; IRIBARNE, O.

FISHERIES RESEARCH

ELSEVIER SCIENCE BV

Año: 2004 vol. 67 p. 55 - 70

0165-7836

Small-scale artisanal fisheries of the stout razor clam Tagelus plebeius are currently developing in intertidal habitats ofseveral southwestern Atlantic estuaries (36–39◦S) in many cases conflicting with habitat conservation. We evaluated theeffects of this harvesting on non-target benthic species with replicated experiments conducted simultaneously at six differentlocations. Given the tendency of burrowing crabs Chasmagnathus granulata to rapidly colonize disturbed plots and excavatenew burrows, our a priori prediction was that local effects of clam harvesting would vary depending on the local densityof burrowing crabs because it may determine contrasting levels of burrowing disturbance after clam harvesting. To test thishypothesis, experimental plots were distributed equally between habitats characterized by contrasting levels of burrowingcrab density. Contrary to our expectation, burrowing crabs recolonized all the disturbed plots at similar rates. The effectsof clam harvesting on burrowing crabs, however, varied temporally from positive at low-density mosaics to negative athigh-density mosaics, probably due to temporal variations in crab wandering behavior. Juveniles of the crab Cyrtograpsusangulatus showed location-dependent positive responses to the clam harvesting treatment associated with increases in theamount of shell material exposed at the surface during harvesting. Harvesting significantly affects the density of the polychaeteLaeonereis acuta in a few particular locations and sampling dates. Location-dependent increases of this species in disturbedplots were observed after recruitment events, suggesting recruitment enhancement by bottom roughness interacting withdifferences among locations in larval supply. These results demonstrate that extrapolation of results from a single locationmay be inaccurate even for nearby areas.We strongly advocate that the occurrence and nature of location-dependency shouldbe integrated in the design of management programs.