Steven X. Cadrin

Discard Mortality Estimation of Yellowtail Flounder Using Reflex Action Mortality Predictors

Abstract The southern New England mid-Atlantic stock of yellowtail flounder Limanda ferruginea has a history of substantial discards, and the current stock assessment assumes 100% discard mortality. A controlled experimental trawl was used to test seven reflex actions, which in combination make up the reflex action mortality predictors (RAMPs), from stressed and unstressed yellowtail flounder. Tow time and air exposure were tested to identify their effects on mortality. Mortality was significantly related to reflex impairment. Exposure to air was the more influential stressor in the survivability of yellowtail flounder, suggesting that discard mortality in the fishery could be reduced by limiting the duration of on-deck air exposure for the fish. An example application of RAMP monitoring demonstrates a 42–73% range of discard mortality estimates from the southern New England trawl fishery. The reflex impairment–mortality relationship enables the estimation of discard mortality aboard commercial fishing ve...

Spawning Dynamics and Associated Management Implications for Atlantic Cod

AbstractMany stocks of Atlantic Cod Gadus morhua have been depleted due to interactions between overfishing and environmental variation. Stock declines were often accompanied by reductions in spawning diversity and collapses of population structure. Studying Atlantic Cod spawning activity can provide insights into the mechanisms involved in rebuilding. This paper reviews the existing literature on Atlantic Cod spawning dynamics, including habitat, timing, behavior, gamete production, larval survivorship, and fishery impacts. The associated implications for fisheries management are discussed, and critical information gaps are identified for inclusion in future research. Of primary importance for consideration by fisheries managers are the spatial and temporal extent of spawning, the behavior of spawners, and the reproductive contributions of older age-classes. The application of spawning closures as part of a multidisciplinary approach to fisheries management is advocated to prevent the disruption of spawn...

Evaluating the Effects of Two Coastal Mobile Gear Fishing Closures on Finfish Abundance off Cape Cod

Abstract A 16-year time series of research trawl catches, commercial landings, and effort data were used to evaluate two areas protected from mobile gear fishing off Cape Cod, Massachusetts, and assess effects of the spring otter trawl fishery for longfin squid Loligo pealeii on local abundance of finfish frequently caught as bycatch. Catch rates were compared between a seasonal closure, a permanent closure, and adjacent waters open to mobile gear fishing. Winter flounder Pleuronecles americanus and scup Stenotomus chrysops were more abundant in the two protected areas. Black sea bass Centropristis striata and windowpane Scophthalmus aquosus were more abundant in the seasonal closure but not in the permanent closure. Abundance indices of summer flounder Paralichthys dentatus and longfin squid were not significantly different between the seasonal closure and the exploited area but both species were less abundant in the permanent closure. Little skate Raja erinacea were more abundant in areas open to trawli...

Lessons learned from practical approaches to reconcile mismatches between biological population structure and stock units of marine fish

Recent advances in the application of stock identification methods have revealed inconsistencies between the spatial structure of biological populations and the definition of stock units used in assessment and management. From a fisheries management perspective, stocks are typically assumed to be discrete units with homogeneous vital rates that can be exploited independently of each other. However, the unit stock assumption is often violated leading to spatial mismatches that can bias stock assessment and impede sustainable fisheries management. The primary ecological concern is the potential for overexploitation of unique spawning components, which can lead to loss of productivity and reduced biodiversity along with destabilization of local and regional stock dynamics. Furthermore, ignoring complex population structure and stock connectivity can lead to misperception of the magnitude of fish productivity, which can translate to suboptimal utilization of the resource. We describe approaches that are currently being applied to improve the assessment and management process for marine fish in situations where complex spatial structure has led to an observed mismatch between the scale of biological populations and spatially-defined stock units. The approaches include: (i) status quo management, (ii) weakest link management, (iii) spatial and temporal closures, (iv) stock composition analysis, and (v) alteration of stock boundaries. We highlight case studies in the North Atlantic that illustrate each approach and synthesize the lessons learned from these real-world applications. Alignment of biological and management units requires continual monitoring through the application of stock identification methods in conjunction with responsive management to preserve biocomplexity and the natural stability and resilience of fish species.

Eyes In The Sky: Linking Satellite Oceanography And Biotelemetry To Explore Habitat Selection By Basking Sharks

BackgroundSatellite-based oceanographic data products are a valuable source of information on potential resource availability for marine species. Satellite oceanography data may be particularly useful in biotelemetry studies on marine species that feed at low trophic levels, such as zooplanktivorous whales, sharks, and rays. The basking shark, Cetorhinus maximus, is a well-documented zooplanktivore in the western North Atlantic, yet little is known of its movements and spatial ecology in this region. A combination of satellite tag technologies were used to describe basking shark movements with respect to concurrent satellite-observed oceanographic conditions in order to test for selection of these environmental variables.ResultsSatellite-linked ‘smart’ position only transmitting tags (SPOTs, Nu2009=u200910) were used to assess horizontal movements, activity space, and habitat selection, while pop-up satellite archival tags (PSATs, Nu2009=u20097) were used to describe depth preferences of basking sharks during summer and fall. The duration of SPOT tracks ranged from 5 to 45xa0days. Basking sharks used relatively small activity spaces in three focal areas off Massachusetts: Vineyard Sound, the Great South Channel, and Cape Cod Bay. These sharks appeared to select areas with shallow bottom depths, high primary production and chlorophyll concentrations, and steep surface gradients, but significant selection for these variables was only detected between mid-August and mid-October when the sharks were primarily located in Cape Cod Bay.ConclusionsBasking sharks in the southern Gulf of Maine during summer and fall focus their activities in discrete areas likely to support high primary and secondary productivity. Habitat selection may also be influenced by mating and social activity at times, but further research is needed to differentiate these behaviors from foraging activity. Satellite-based biotelemetry and oceanography are powerful tools that together can provide valuable new insights into habitat selection patterns of highly mobile marine species.

Using Fishermen’s Ecological Knowledge to map Atlantic cod spawning grounds on Georges Bank

Using Fishermen’s Ecological Knowledge to map Atlantic cod spawning grounds on Georges Bank Gregory R. DeCelles*, David Martins, Douglas R. Zemeckis, and Steven X. Cadrin School for Marine Science and Technology, University of Massachusetts Dartmouth, 706 South Rodney French Blvd, New Bedford, MA 02740, USA Massachusetts Division of Marine Fisheries, 1213 Purchase Street, New Bedford, MA 02740, USA *Corresponding author: tel: þ1 508 99

The Impact of the Second Seasonal Spawn on the Nantucket Population of the Northern Bay Scallop

Abstract Nantucket, Massachusetts, has one of the last remaining commercial fisheries of the bay scallop Argopecten irradians, which is based largely on natural recruitment. Though previously thought to spawn only once in early summer at age 1, individuals of the northern subspecies often spawn again in late summer or fall, and recruits from this second spawning can survive to reproduce again in their second summer. We formulated an age-based Leslie matrix model and estimated population growth rate with and without a second spawn based on data from 5 years of life history research. Elasticity analysis revealed that the population growth rate was most sensitive to juvenile survival, the major factor in recruitment rate, and year-1 adult fertility was a close second. We varied those two rates randomly in a stochastic matrix model, which represented the effect of environmental fluctuations on population growth. A life history modeled with a second spawn had a negligible effect on the deterministic population growth rate under constant conditions, but under variable conditions the second spawn increased the mean of the stochastic growth rates up to 58.3% over that of a single early-spawning life history. These results suggest that the second spawn is a successful bet-hedging strategy. The northern bay scallop increases its chances for successful recruitment in a variable environment by spreading reproductive effort over more than one period in a season. This strategy appears to have sustained the Nantucket scallop population in spite of severe annual fluctuations and the eventual collapse seen in other locations.

Towards an Improved System for Sampling New England Groundfish Using Video Technology

There is considerable controversy regarding abundance estimates of New England groundfish. Federal surveys sample randomly but are restricted to short tow lengths and minimal area covered at high daily expense. Working collaboratively with fishermen, we developed a video system that can be deployed in a commercial trawl net to improve the information on the abundance and distribution of groundfish stocks (focusing on Atlantic Cod Gadus morhua and Yellowtail Flounder Limanda ferruginea) by increasing the amount of sea floor sampled per sea day without killing more fish. Rather than being hauled to the surface for counting, fish are counted as they pass through the net. This results in continuous transect data that can be processed into sampling units, randomized, and used to estimate abundance. High-intensity sampling of important habitats can complement existing multispecies random and stratified random survey designs to reduce uncertainty, presenting a clearer picture of the resource.

Effects of epizootic shell disease on egg quality of the American lobster

Epizootic shell disease (ESD) of the American lobster, Homarus americanus Milne Edwards, 1837, is of increasing concern, particularly in the southern New England fishery where prevalence is highest. Egg-bearing female lobsters are more susceptible to the disease because many of them molt less frequently when carrying eggs. This study examines the effect of the disease on late-stage embryos through measures of egg quality. Egg samples were taken from ninety lobsters with varying levels of ESD in lower Buzzards Bay and Vineyard Sound off the coast of Massachusetts, USA. Egg quality was measured with biomass (egg area and dry weight) and biochemical (total carbon and total nitrogen) components. Each response variable was estimated using linear mixed-effects models that included potential covariates as measures of maternal adult lobster size and embryonic development. The effect of disease was significant for all of the response variables, indicating that the presence of the disease correlates with individual egg quality. Counterintuitively, results showed that as disease severity increased, measures of egg quality also increased. Trends showed that light cases of ESD produced similar responses to lobsters with no disease present. Moderate and severe levels of the disease also produced similar results. This could suggest that heavily diseased lobsters are exhibiting energetic trade-offs, investing more energy into reproduction. It is also possible that this trend is the result of other combined effects corresponding to lobster molt cycles, spawning timing, and environmental conditions that also result in the presence of ESD. Effects of the disease on early life history processes could be important considerations for future research on ESD and its effect on the lobster population.