Dramatic declines in red abalone populations after opening a “de facto” marine reserve to fishing: Testing temporal reserves

Red abalone (Haliotis rufescens) were assessed inside and outside a “de facto” reserve before fishing, after 3 and then 6 years of fishing. In just 3 years, there was a 65% decline (p < 0.001) in the subtidal and a 78% decline (p < 0.001) in the intertidal abalone populations. Size frequency distributions differed significantly following fishing and there was a sharp decrease in the potential egg production (>72% decline). Before fishing began, the intertidal density at the reserve was 86% greater (p = 0.001) than at a nearby fished site, however after 3 years of fishing there was no difference (p = 0.764). Abalone fishing report cards revealed a 950% increase in local catch once the reserve site was opened, however after just 1.5 years of fishing, catch declined sharply (59%) compared to the previous year. In 3 years, mean abalone catch per hour declined significantly (p < 0.001) from 7.01 (SD 6.14) to 2.44 (SD 1.98) as did abalone catch/picker from 2.83 (SD 0.47) to 2.38 (SD 0.92, p < 0.01). Estimates of illegal take inside the former reserve were 2.5 times greater than the legal catch. We demonstrate that for areas with high value, slow growing species such as red abalone, temporarily opening reserves may lead to density, size structure and egg production similar to heavily fished areas in just 3 years. These results caution against the use of temporal (rotating) reserves for abalone and emphasize the importance of marine spatial planning.