Kevin D. E. Stokesbury

Estimation of Sea Scallop Abundance in Closed Areas of Georges Bank, USA

Abstract A high-resolution video survey conducted from May to September 1999 in historic scallop fishing grounds that have been closed to mobile fishing gear since 1994 revealed some of the highest densities and largest sea scallops Placopecten magellanicus ever observed on Georges Bank. Sea scallop densities ranged from 0.25 to 0.59 scallops/m2 within the three surveyed areas and from 0.58 to 1.06 scallops/m2 at stations where at least 1 scallop was observed. Sea scallops were highly aggregated into patches (beds) on the scale of square kilometers, and the distribution was strongly associated with the distribution of coarse sand-granule-pebble substrate. The three areas surveyed (1,938 km2) contained approximately 650 million scallops representing 17 million kg of harvestable scallop meats. This is equivalent to 54% of the average harvestable scallop meat biomass from 1977 to 1988. The area surveyed covered 5% of the total scallop fishing grounds of Georges Bank. The video survey technique has several ad...

Spatial and Temporal Variability in Juvenile Pacific Herring, Clupea pallasi, Growth in Prince William Sound, Alaska

We examined the spatial and temporal variability of juvenile Pacific herring, Clupea pallasi, growth within Prince William Sound, Alaska. Pacific herring, ranging from post-larval to mature fish, were collected from four spatially segregated bays between October 1995 and March 1998. Linear growth equations from each bay were similar. However, growth rates and wet weight-at-length, reflecting condition, of juvenile Pacific herring cohorts varied seasonally and annually. The short term spatial variability in juvenile Pacific herring growth suggested that each bay was a unique nursery area. The physical and biological conditions within each bay appeared to dictate Pacific herring growth rate.

AN ASSESSMENT OF JUVENILE AND ADULT SEA SCALLOP, PLACOPECTEN MAGELLANICUS, DISTRIBUTION IN THE NORTHWEST ATLANTIC USING HIGH-RESOLUTION STILL IMAGERY

ABSTRACT Recent surveys using high-resolution imagery have enabled improved detection of Atlantic sea scallops, Placopecten magellanicus, between 10 mm and 65 mm in shell height, allowing the observation of juvenile scallops in the wild, which was previously difficult. Using these high-resolution images from 2008 and 2009 surveys of Georges Bank and the Mid-Atlantic Bight, the distribution and crowding levels of juvenile and adult scallops were examined. Mean crowding values revealed differences in small-scale distribution of scallops that were undetectable with density estimates. Juveniles on Georges Bank were 2.6–3.9 times more crowded than adults, and 2.9–7.4 times more crowded than juveniles and adults in the Mid-Atlantic Bight. The increased crowding of juvenile scallops on Georges Bank may be the result of differences in substrate, sea star interactions, and abundance of filamentous flora and fauna. The incorporation of high-resolution imagery into optical surveys represents an important development in the advancement of survey techniques because it has the potential (1) to quantify year class strength of 1-y-old scallops more accurately; (2) to improve growth, mortality, and biomass estimates in stock assessments; and (3) to advance our understanding of scallop ecology, including recruitment processes and population dynamics.

Spatial and Temporal Variation in the Shell Height/Meat Weight Relationship of the Sea Scallop Placopecten magellanicus in the Georges Bank Fishery

ABSTRACT Spatial and temporal variations in the meat weight of sea scallops were examined in the Georges Bank fishery. From 1998–2007, 31 commercial scallop vessels supplied 145 dissections from the last tow of their fishing trip. During the dissection process we recorded the shell height, meat weight, sex, gonad weight, and visceral tissue weight. Meat weight was regressed against shell height (Ln(MW) = &agr; + &bgr; ln SH). Predicted meat weight varied by up to 29% for a 120 mm shell height scallop among months. Scallop meat weight varied by 31% for a 120 mm shell height scallop between areas in the same month. The Southern Flank of Georges Bank had a different pattern of monthly variation in meat weight, possibly because of a spring spawning event observed in the gonadal indices. These spatial and temporal differences in meat weight could affect harvest, and harvest rate, with a 22% difference in scallops harvested between June and October calculated from a hypothetical fishery. Understanding these spatial and temporal variations in the shell height/meat weight relationship is important for optimal harvest, especially if a fully rotational area management strategy is implemented.

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.

Stock Definition and Recruitment: Implications for the U.S. Sea Scallop (Placopecten magellanicus) Fishery from 2003 to 2011

The United States sea scallop management plan applies fishing mortality in a uniform manner, assigning a single value of instantaneous fishing mortality (F) to the entire resource. Applying a single value of fishing mortality assumes the scallop resource is a single population. Dividing the resource into Georges Bank and Mid-Atlantic Bight reveals that each has been either excessively fished or underutilized based on the present definition of optimum yield. The sea scallop resource was highest in 2003 and has declined by about 50,000 metric tons, entirely from the Mid-Atlantic Bight. Abundance and the corresponding harvest levels will likely continue if the resource is a single population and scallops in the closed areas of Georges Bank populate the entire resource. Abundance and the corresponding harvest levels will likely decline if Georges Bank and the Mid-Atlantic Bight are separate populations in that scallops within these areas have a closed lifecycle. The depletion of the large number of small scallops in the Mid-Atlantic observed in 2003, and poor recruitment from 2009 to 2011, could lead to a rapid reduction in abundance, seriously impacting the fishery that was valued at US

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

455 million in 2010.

Characterization of River Herring Bycatch in the Northwest Atlantic Midwater Trawl Fisheries

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.

Bait and the susceptibility of American lobsters Homarus americanus to epizootic shell disease

AbstractIn the U.S. northwest Atlantic, the incidental catch of river herring (Alewife Alosa pseudoharengus and Blueback Herring A. aestivalis) by midwater trawl vessels targeting Atlantic Herring Clupea harengus and Atlantic Mackerel Scomber scombrus has become a concern for river herring conservation. Reduction of this incidental catch is a focus of fisheries managers, but information about river herring bycatch is limited. To improve the information available to fishery managers, we combined portside and at-sea observations to examine (1) the size of river herring, (2) the concentration of river herring with respect to the target species, and (3) the yearly contribution of different fishery areas to the total catch of river herring. We divided the fisherys spatial range into four nearshore areas and tested two null hypotheses: (1) length frequency distributions of river herring are similar between areas and between species and (2) bycatch ratios are similar among areas. We also used length frequency d...

Use of the SAFE Index to Evaluate the Status of a Summer Aggregation of Atlantic Sturgeon in Minas Basin, Canada, and the Implication of the Index for the USA Endangered Species Designation of Atlantic and Shortnose Sturgeons

Shell disease (SD) has been observed in lobster populations for almost a hundred years, but recently, rates of an epizootic form of shell disease (ESD) have increased in the southern New England (USA) area. A large proportion of fish in the diet of American lobsters Homarus americanus has been linked to increased rates of SD. Therefore, the use of fish as lobster bait may be linked to increased ESD rates in lobsters. Lobsters from the western portion of Marthas Vineyard, MA (41 degrees N, 71 degrees W), were randomly divided into 3 groups of 16 and exposed to dietary treatments (100% herring; 48% crab, 48% blue mussel and 4% plant matter; or 50% herring, 24% crab, 24% mussel, 2% plant matter) to determine if lobster tissue delta15N levels reflected diet. The results of the feeding experiment confirmed that differences in diet are observed in the delta15N levels of lobster muscle tissue. The delta15N levels of tissue samples from 175 wild lobsters with varying degrees of ESD were unrelated to ESD severity but did indicate lobsters were eating large amounts of fish (bait). This result does not support the speculation that fish used as bait is contributing to ESD outbreaks in portions of the southern New England area.