Applying Fishery Catch Data to Population Trends and Community Structures in Atlantic Pelagic Species

Abstract

Recent studies have shown that fishing can influence marine trophic networks, as larger, higher trophic level species are preferentially targeted by fishers. In this study, we investigate US Pelagic Longline catch dynamics of twenty-nine Atlantic species from 1986 to 2008 using information provided by the fishermen’s logbook data program. Two different analyses were performed on the data for this study. Data were cleaned and monthly catch per unit effort (CPUE) for each species within each of five fishing effort regions – the Mid Atlantic Bight and Northeast Costal area, The Caribbean area, the Florida East Coast and South Atlantic Bight area, the Gulf of Mexico area, and the Northeast Distant area – were calculated to examine trends in catch rates. Annual CPUE graphs were made for all areas combined, correcting for changes in fishing dynamics to examine changes in relative abundance of species over time. A regression was run through these annual graphs of CPUE over the study period in order to estimate increases or decreases in relative population abundance for each species. The slopes from these annual abundances regressions were further regressed versus trophic level, average generation length, and resiliency to test for significant correlations between these ecological factors and trends in population size. Though trends matched our predictions (species with higher trophic level, lower resiliency, and longer generation length showed greater declines in abundance), no significant p-values were found. It seems likely that ecosystem structural shifts similar to those seen in other recent studies are occurring, but the lack of significance makes it difficult to draw strong conclusions. The lack of significance between ecological factors and population trends observed in this study may be due to trophic shifts in fishing are not occurring or may be due to issues with the data used for regressions. Future studies using different methods of obtaining demographic factors and incorporating additional years of catch data could bring more clarity to this work.