Environmental correlates of historic abalone catch in the State of California and Baja California, Mexico

Background/Question/Methods

Abalone (Haliotis spp.) and other benthic invertebrates are ecologically and economically important to communities in the California Current Large Marine Ecosystem. Commercial harvesting is an important driver of abalone population decrease, causing thinning populations and removing larger, more fecund size classes. Even after strong reduction in fishing mortality, many abalone populations failed to recover, suggesting influence of other factors on abalone survival and recruitment. We sought to determine if there is a correlation between abalone catch, human harvesting, and environmental factors and, if so, which factors had the greatest impact on abalone populations.

Our data included 5 datasets of historic abalone catch per unit effort (CPUE) in Baja California and one dataset of historic commercial abalone landings in the State of California.

We used generalized additive modeling and time series analysis to determine the relationship between abalone CPUE and potential environmental drivers. The full model included CPUE as a function of time caught, location landed, El Nino Southern Oscillation (ENSO) conditions, sea surface temperature (SST), and upwelling index. Backward model selection was used to choose the best fitting model.

Results/Conclusions

All datasets had a significant relationship between CPUE and time. For the majority of Baja California studies, the best model included upwelling index as a predictor variable and there was a significant one year time lag.

There were three best fitting models for the California CPUE when considered on a monthly basis. All 3 models showed a significant relationship between CPUE and time and CPUE and latitude. All three models included ENSO conditions as a significant predictor and two models included SST as a significant predictor. In all cases, there was a significant time lag at 6 years.

These results suggest that environmental conditions are an important factor for determining abalone catch. Large impacts by temperature changes and more extreme weather phenomena, such as ENSO events, in the California Current Large Marine Ecosystem are predicted for organisms, including abalone, and these trends are expected to continue over the next century. Little is known about the effects of variability in temperature and ENSO events on these species. However, effective management of marine invertebrates requires an understanding of how fishing, temperature and ENSO events combine to affect population levels.