Assessing the Vulnerability of Marine Benthos to Fishing Gear Impacts

The Magnuson-Stevens Fishery Conservation and Management Act (MSA) requires US fishery management plans to minimize, to the extent practicable, the adverse effects of fishing on essential fish habitats (EFHs). To meet this requirement, fishery managers would ideally be able to quantify such effects and visualize their distributions across space and time. Here, we develop a framework to quantify and assess benthic impacts of the six most common bottom-tending gears (>99% of bottom-tending fishing effort) in New England: otter trawls, scallop dredges, hydraulic clam dredges, gillnets, longlines, and traps. We first conducted a comprehensive review of the habitat impacts literature relevant to Northeast USA fishing gears and seabed types. We then used this information to develop a framework for generating and organizing quantitative susceptibility (based on percent loss of structural habitat from a single interaction with the gear) and recovery (i.e., the time required for recovery of lost structure) parameters for each biological (e.g., sponges, ascidians, mollusks) and geological (e.g., mud burrows, sand ripples, cobble, and boulder piles) feature common to the following five substrates: mud, sand, granule-pebble, cobble, and boulder in low-and high-energy environments. In general, we found that both susceptibility and recovery scores were highest for hydraulic dredges, slightly lower for otter trawls and scallop dredges, and much lower for fixed gears (i.e., gillnets, longlines, and traps). For bottom trawls and scallop dredges, geological features in mud, sand, and cobble-dominated substrates were more susceptible to gear impacts than features found in granule-pebble and boulder substrates. Meanwhile, biological features were largely equally susceptible to impacts across the five substrate types. Average susceptibility scores for both biological and geological substrate features were not affected by energy level. Average recovery times for geological features affected by bottom trawls and dredges were much longer in low-energy granule-pebble, and low-and high-energy cobble and boulder than in mud and sand substrates. Meanwhile, there was no difference among substrates or energy levels for biological feature recovery times. These results collectively suggest that cobble and boulder substrates are the most vulnerable to impacts from mobile bottom-tending gear. Recovery from the relatively minor impacts caused by fixed gear required slightly longer in the three coarser substrate types than in mud and sand. Our findings highlight the importance of considering the resilience of specific components of habitat such as emergent epifauna or geological formations that serve as EFH by providing shelter and a source of food for fish. When coupled with the distribution of geological substrates and energy environments that exist in a particular region, our framework offers fisheries resource managers a tool to assess gear-specific spatial impacts on benthic substrates and identify benthic habitat vulnerability hotspots.