Analysis of Indices of Abundance for Important Groundfish Species in the Northern Gulf of Mexico From 1987-2008, Relative to Shrimp Bycatch

Shrimp harvest is one of the most important fisheries in the United States.  In the Gulf of Mexico and South Atlantic (GSA), warm-water shrimp fisheries have been a dominant economic driver since the early twentieth century, representing the majority of the shrimp harvest in the United States. Effort data for shrimp harvest in the Gulf of Mexico was obtained through National Marine Fisheries Service (NMFS) for the years 1960-2008 shows that harvest peaked in 1987. Harvest began a drastic decline in 2002 and, by 2008, had declined to 26% of peak effort. Several factors have led to this drastic decrease in effort, which began in the late 1990’s and has continued. Three major economic impacts to the shrimp industry includes 1) an increase in imported shrimp products, 2) increased vessel operational costs, and 3) the recent devastating impact of hurricanes Rita and Katrina in 2005. Such a large reduction in effort has undoubtedly had some effects on the species harvested, both target and bycatch species. The goal of this study is to examine the impacts shrimp harvest has had on the Gulf of Mexico ecosystem via bycatch removal over a 22 year time series with large changes in shrimping effort. According to NMFS data, bycatch accounts for 95.09% of harvest in the shrimp fishery. It is, therefore, very important to determine what ecosystem level effects have occurred with various levels of harvest. SEAMAP (Southeast Area Monitoring and Assessment Program) groundfish data was analyzed from 1987-2008, to determine the most abundant species caught by weight during the time series. Thirty species/species groups of great ecological and commercial/recreational importance were selected to develop indices of abundance using the delta-lognormal method (DLM). These indices of abundance were visually assessed for trends in the data from the time periods before (1987-2001) and after (2002-2008) the drastic reduction in effort.  Simple linear regression was conducted for each species to analyze the relationship between shrimp effort and DLM indices of abundance. A correlation matrix was also created to determine the relationship of abundance indices of each species to the others and to shrimping effort. These analyses were used in relation to life history characteristics of each species obtained through literature review. By examining life history characteristics, we can make inferences about the responses of each species to the various levels of shrimping effort over time.