The Atlantic sea scallop Placopecten magellanicus is an economically important species in the offshore fisheries on the east coast of the USA. Recently, animals collected from waters ranging from Massachusetts to Maryland have shown variably sized (up to 1 cm in diameter) orange nodular foci, predominantly in the adductor muscle tissue, but also in other organs. Histological evaluation of the nodular lesions showed rod-shaped bacteria that stain acid-fast positive and Gram-positive. PCR methodology was employed to identify the causative organism of the nodules as a Mycobacterium sp. using analysis of the partial 16S gene and the 16S-23S internal transcribed spacer region. Based upon genotypic findings, the causative bacterium fits well into the genus Mycobacterium.
Direct age determination of crustaceans has remained a long-standing challenge because all calcified structures are shed with each molt. Cuticle bands in the ossicles of the gastric mill have shown promise as age indicators. We validated the one-to-one relationship between known-age and number of cuticle bands for fifteen hatchery raised juvenile American lobsters (Homarus americanus). Additionally, we applied this method to 308 lobsters from three contrasting thermal regimes in New England, USA. Band counts matched our expectations of differences in age-at-size across this thermal gradient: lobsters at harvestable size in southern New England were estimated to be 5.5 (卤1.5) years old, compared to 7.5 (卤1.6) years in the Gulf of Maine. We found 81% of our band count estimates of age fell within two years of independent, regionally specified growth model estimates of age-at-size for lobster. Notwithstanding remaining uncertainties regarding the mechanism of band formation, our findings indicate the method may provide an independent and direct means to determine the age of individual American lobsters, which will improve estimates of essential life history parameters.
Bycatch is a constraint to the Atlantic sea scallop fishery, the most valuable single-species fishery along the eastern coast of the United States. To characterize trends in the bycatch of three flatfish species, a fishery-independent scallop dredge survey was conducted in two sea scallop access areas (Closed Areas I and II) on Georges Bank from 2011 to 2014. Generalized additive mixed models were used to identify seasonal bycatch hotspots of yellowtail, winter, and windowpane flounder. In all cases, spatially explicit models best fit the data (deviance explained: 47-73%) and provided insight into the spatial distribution underlying the seasonal trends in each area. Modeled catch rates for the three flatfish species suggested localized catches at discrete times of the year. Catches of yellowtail and windowpane flounder were highest in Closed Area II in the fall and winter, respectively. Winter flounder were caught in the highest numbers in Closed Area I during the summer and fall, and were largely absent from catches in Closed Area II. Our results suggest consistent seasonal trends that may help managers identify the optimal times to open the access areas to the scallop fleet in order to reduce flatfish bycatch.
The American monkfish is an important commercial species that is widely distributed across a range of depths and temperatures from North Carolina to southern Nova Scotia, including on Georges Bank. We examined changes in the seasonal distribution and relative abundance of monkfish in the scallop access areas in Closed Area I and Closed Area II on Georges Bank using catch data from a three-year seasonal scallop dredge survey. Over the course of the survey, more than 6,000 monkfish were caught and measured, and clear seasonal changes in monkfish abundance were documented. Monkfish catch peaked in the summer and early fall when they were caught across the entire survey area, while they were caught only in deeper waters at the edges of the bank in the winter. Monkfish relative abundance was modeled using a generalized linear mixed model with a Tweedie distribution, and the final model, with month, depth, and bottom temperature as fixed effects, effectively explained the seasonal shifts in the location and relative abundance of monkfish observed during this study. The results suggest that monkfish movements are driven by seasonal changes in bottom temperature. Management measures for monkfish are determined primarily based on data collected during the Northeast Fisheries Science Center bottom trawl surveys, yet this survey catches few monkfish, adding uncertainty to stock assessments. Our research indicates that increasing the use of dredge surveys to collect data on monkfish would be a positive step toward improving monkfish assessments. If monkfish movements are impacted by changes in thermal habitat, their distributions may shift in response to climate change, increasing the need for improved monkfish assessment strategies to effectively manage the species in the future.
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