Commercial trawling in seagrass beds: Bycatch and long-term trends in effort of a major shrimp fishery

Abstract

Fisheries for penaeid shrimp have historically represented one of the largest in the Gulf of Mexico (GOM). Fishing grounds include both deeper, offshore areas, which have received considerable attention from scientists and managers, as well as shallow, nearshore areas. In the eastern GOM, the nearshore fishing grounds are in highly productive seagrass beds, which serve as nursery, temporary and permanent habitats to a multitude of fishes and invertebrates, including many of economic importance. Despite concerns regarding high levels of bycatch often observed in penaeid shrimp fisheries that use trawling gears, studies of potential gear impacts to seagrass ecosystems are surprisingly limited. We combined fishery-independent and -dependent methods to examine the temporal trends in bycatch rates and catch composition for the trawling gears used by the inshore fishery as well as the intra- and inter-annual patterns in fishing effort. The proportion of bycatch was consistently high (0.74 to 0.93) across the late spring through fall months, corresponding to the period of highest primary and secondary productivity in eastern GOM seagrass beds. Fifty species were captured by the rollerframe trawls, including several species of economic concern as well as abundant fishes that serve as linkages between primary and secondary production in seagrass ecosystems. Using 24 yr of fishery data, we found long-term evidence of an intraannual shift from offshore grounds to seagrass beds during the spring through fall period of high productivity. Moreover, the proportion of total effort in seagrass beds during this period has increased in recent years, largely due to unprecedented declines in offshore effort. Extraction of both bycatch and targeted fauna from this highly productive ecosystem represents an impact that has largely been ignored. Understanding the effects of this extraction on seagrass-associated populations and communities should be considered in future ecosystem-based management and conservation efforts.