Bradley P. Harris

Chapter 17 - Fisheries Sea Scallop, Placopecten magellanicus

Abstract The sea scallop ( Placopecten magellanicus ) fisheries in the United States and Canada have experienced unprecedented rebuilding over the past 15 years. Several factors have led to the successful rebound of these industries, including revised management approaches, investments in improved survey technologies, data-rich stock assessments, favourable environmental conditions and some luck. There is no comprehensive understanding of the stock–recruitment relationship for scallops, which complicates management of the species. Through the use of spatial and temporal management strategies, large recruitment events have been identified and juvenile scallops can be protected until they reach a harvestable size. Identification and protection of such anomalous, large recruitment events in Canada and the United States over the past 15 years have rebuilt the stocks and sustained the fisheries. This chapter describes sea scallop life history, the ecosystem inhabited by sea scallops, the composition of the Canadian and US fishing fleets, sea scallop stock assessments, resource surveys and sea scallop fisheries management.

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.

High Densities of Juvenile Sea Scallop (Placopecten magellanicus) on Banks and Ledges in the Central Gulf of Maine

ABSTRACT A video survey was conducted from August 10–14, 2009, to estimate sea scallop density, abundance, and size distribution on Platts Bank, Fippennies Ledge, Jeffreys Bank, Jeffreys Ledge, and Cashes Ledge in the central Gulf of Maine. Of the 298 km2 surveyed, 134 km2 (45%) had scallops present. Scallop density was estimated using only stations containing at least 1 scallop. High densities of small scallops occurred on all but Jeffreys Bank, where no scallops were observed. Densities ranged from 1.56 scallops/m2 on Jeffreys Ledge to 4.70 scallops/m2 on Platts Bank, equaling an estimated abundance of 470 million scallops. Less than 1% of scallops were larger than 100 mm. Explanations for the lack of large individuals may include sporadic recruitment, high natural mortality from predation, or environmental influences. If these scallops were to survive to harvestable size (approximately 102 mm), they could provide an important commercial resource worth approximately USS124 million.

Dynamic occupancy modeling of temperate marine fish in area-based closures

Abstract Species distribution models (SDMs) are commonly used to model the spatial structure of species in the marine environment, however, most fail to account for detectability of the target species. This can result in underestimates of occupancy, where nondetection is conflated with absence. The site occupancy model (SOM) overcomes this failure by treating occupancy as a latent variable of the model and incorporates a detection submodel to account for variability in detection rates. These have rarely been applied in the context of marine fish and never for the multiseason dynamic occupancy model (DOM). In this study, a DOM is developed for a designated species of concern, cusk (Brosme brosme), over a four‐season period. Making novel use of a high‐resolution 3‐dimensional hydrodynamic model, detectability of cusk is considered as a function of current speed and algae cover. Algal cover on the seabed is measured from video surveys to divide the study area into two distinct regions: those with canopy forming species of algae and those without (henceforth bottom types). Modeled estimates of the proportion of sites occupied in each season are 0.88, 0.45, 0.74, and 0.83. These are significantly greater than the proportion of occupied sites measured from underwater video observations which are 0.57, 0.28, 0.43, and 0.57. Individual fish are detected more frequently with increasing current speed in areas lacking canopy and less frequently with increasing current speed in areas with canopy. The results indicate that, where possible, SDM studies for all marine species should take account of detectability to avoid underestimating the proportion of sites occupied at a given study area. Sampling closed areas or areas of conservation often requires the use of nonphysical, low impact sampling methods like camera surveys. These methods inherently result in detection probabilities less than one, an issue compounded by time‐varying features of the environment that are rarely accounted for marine studies. This work highlights the use of modeled hydrodynamics as a tool to correct some of this imbalance.

Ichthyophonus in sport-caught groundfishes from southcentral Alaska

This report of Ichthyophonus in common sport-caught fishes throughout the marine waters of southcentral Alaska represents the first documentation of natural Ichthyophonus infections in lingcod Ophiodon elongates and yelloweye rockfish Sebastes ruberrimus. In addition, the known geographic range of Ichthyophonus in black rockfish S. melanops has been expanded northward to include southcentral Alaska. Among all species surveyed, the infection prevalence was highest (35%, n = 334) in Pacific halibut Hippoglossus stenolepis. There were no gross indications of high-level infections or clinically diseased individuals. These results support the hypothesis that under typical conditions Ichthyophonus can occur at high infection prevalence accompanied with low-level infection among a variety of fishes throughout the eastern North Pacific Ocean, including southcentral Alaska.