Potential Implications of Excluding Live‐Bottom Habitat from a Bottom‐Trawl Survey in the Eastern Gulf of Mexico

Abstract

AbstractData provided by the Southeast Area Monitoring and Assessment Program (SEAMAP) shrimp/groundfish trawl survey have long been used in assessing diverse managed taxa, including several reef fishes; however, there are rising concerns over the impacts of trawling on live‐bottom habitats. Using data collected from summer SEAMAP trawl surveys (2009–2016; N = 1,103), we examined how avoiding areas of live‐bottom habitat might affect the survey's ability to assess interannual changes in abundance of managed reef fish taxa. Trawl samples at 48% of sampling sites contained <50 kg of sponge, and 12% of sampling sites contained at least 50 kg of sponge, while 40% of sites had zero sponge bycatch. Mean number of taxa, taxonomic richness, and taxonomic diversity were significantly higher as sponge bycatch increased, while the total number of individuals remained the same. To examine interannual variability of managed reef fish taxa, annual indices of relative abundance were calculated on different subsets of data (all data, data excluding sites with sponge bycatch ≥50 kg, and data excluding all sites with sponge bycatch). For Red Snapper Lutjanus campechanus and pink shrimp Farfantepenaeus duorarum, indices and general trends were largely unaffected by excluding sites with sponge, but for most selected taxa (e.g., Gray Triggerfish Balistes capriscus and Red Grouper Epinephelus morio), overall trends were affected by excluding sites that contained sponge bycatch, and in some cases the frequency of occurrence did not meet the requirement to calculate an index of abundance (i.e., <5%) when sponge sites were excluded (e.g., Hogfish Lachnolaimus maximus). Efforts to mitigate survey interactions with live‐bottom habitats will likely alter the utility of survey data and the ability to assess managed species, so careful consideration is needed to evaluate any trade‐offs between the benefits of the trawl survey for fishery assessments and the benefits of protecting the habitat.