Age, growth, and reproductive biology, of the winter skate, Leucoraja ocellata, in the western Gulf of Maine

This study describes the age, growth and reproductive biology of the winter skate, Leucoraja ocellata, in the Western Gulf of Maine. Age was estimated by enumerating annular bands within the vertebral centra. Precision of the age estimates was evaluated using the Index of Average Percent Error and the annual nature of growth band formation was documented using marginal increment analyses. Growth was assessed with the use of the von Bertalanffy growth equation. Age and size at maturity was estimated by measuring morphological and histological changes in the reproductive tract and circulating steroid hormone concentrations. Maturity ogives for males predict that 50% maturity occurs at a total length of 730 mm and at 11 years. For females, maturity ogives predict that 50% maturity occurs at a total length of 760 mm and between 11 and 12 years of age. To elucidate the reproductive cycle of the winter skate, plasma concentrations of the sex steroids testosterone (T), 17beta-estradiol (E2), and progesterone (P4) were determined by radio immunoassay and compared to morphological and histological changes occurring in the reproductive tract over a complete reproductive cycle for mature individuals. Overall, when the results of my dissertation are combined, they indicate that the winter skate is a late maturing, slow growing, long lived species, with an apparent succinct reproductive cycle. Like many other elasmobranchs, these characteristics make L. ocellata \u27s populations highly susceptible to exploitation by commercial fisheries

A Preliminary Abundance Estimate Of An Atlantic Sturgeon (Acipenser Oxyrinchus Oxyrinchus) Contingent Within An Open Riverine System

Abundance estimates are essential for fisheries management, but estimating the abundance of open populations with low recapture rates has historically been unreliable. However, by using mark-recapture data modulated with survivability parameters obtained from analysis of acoustic telemetry data, more accurate abundance estimates can be made for species that exhibit these characteristics. One such species is the Atlantic sturgeon, for which abundance estimates were designated a research priority following precipitous population declines throughout the 20th century. We addressed this research need in the Saco River Estuary (SRE), a system where the Atlantic sturgeon has been extensively studied using mark-recapture and acoustic telemetry methods since 2009. These data were analyzed using Bayesian analysis of a Lincoln-Peterson estimator, constrained with parameters from a Cormack-Jolly-Seber model, to provide an initial abundance estimate for the system. The resulting estimate indicated that approximately 3 299 (95% Credible Interval: 1 462–6 828) Atlantic sturgeon utilize the SRE yearly, suggesting that the SRE provides critical foraging habitat to a large contingent of the species within the Gulf of Maine. The present study demonstrated the method utilized herein was effective in generating a reasonable estimate of abundance in an open system where recapture events are rare, and therefore may provide a valuable technique for supplying initial estimates of fish abundance in additional systems that display similar characteristics

The reproductive cycle of the thorny skate (Amblyraid radiata) in the western Gulf of Maine

The thorny skate (Amblyraja radiata) is a large species of skate that is endemic to the waters of the western north Atlantic in the Gulf of Maine. Because the biomass of thorny skates has recently declined below threshold levels mandated by the Sustainable Fisheries Act, commercial harvests from this region are prohibited. We have undertaken a comprehensive study to gain insight into the life history of this skate. The present study describes and characterizes the reproductive cycle of female and male thorny skates, based on monthly samples taken off the coast of New Hampshire, from May 2001 to May 2003. Gonadosomatic index (GSI), shell gland weight, follicle size, and egg case formation, were assessed for 48 female skates. In general, these reproductive parameters remained relatively constant throughout most of the year. However, transient but significant increases in shell gland weight and GSI were observed during certain months. Within the cohort of specimens sampled monthly throughout the year, a subset of females always had large preovulatory follicles present in their ovaries. With the exception of June and September specimens, egg cases undergoing various stages of development were observed in the uteri of specimens captured during all other months of the year. For males (n=48), histological stages Ill through VI (SIII-SVI) of spermatogenesis, GSI, and hepatosomatic index (HSI) were examined. Although there appeared to be monthly fluctuations in spermatogenesis, GSI, and HSI, no significant differences were found. The production and maintenance of mature spermatocysts (SVI) within the testes was observed throughout the year. These findings collectively indicate that the thorny skate is reproductively active year round

The effect of capture and handling stress in Lophius americanus in the scallop dredge fishery

Capture and handling stress studies are considered a primary research priority, particularly for species and fisheries where discard rates are high, and/or for overfished stocks and species of concern. Lophius americanus, a commercially valuable finfish in New England, constitutes the second highest bycatch species within the sea scallop dredge fishery. Despite its commercial importance, no data exists on the capture and handling stress of monkfish for any gear type. Given these shortcomings, our goals were to evaluate the stress response of monkfish captured in scallop dredge gear by evaluating physical, behavioural and physiological responses to scallop fishing practices. While 80% of monkfish displayed little to no physical trauma, behavioural and physiological assessment indicated high levels of stress, especially as air exposure and tow duration increased. This finding suggests that the manifestation of stress in monkfish may be a cryptic response necessitating further research in addition to estimates of post-release mortality rates to appropriately advise fisheries management regarding the mortality of monkfish bycatch in the sea scallop fishery

The reproductive cycle of the thorny skate (Amblyraja radiata) in the western Gulf of Maine

The thorny skate (Amblyraja radiata) is a large species of skate that is endemic to the waters of the western north Atlantic in the Gulf of Maine. Because the biomass of thorny skates has recently declined below threshold levels mandated by the Sustainable Fisheries Act, commercial harvests from this region are prohibited. We have undertaken a comprehensive study to gain insight into the life history of this skate. The present study describes and characterizes the reproductive cycle of female and male thorny skates, based on monthly samples taken off the coast of New Hampshire, from May 2001 to May 2003. Gonadosomatic index (GSI), shell gland weight, follicle size, and egg case formation, were assessed for 48 female skates. In general, these reproductive parameters remained relatively constant throughout most of the year. However, transient but significant increases in shell gland weight and GSI were obser ved during certain months. Within the cohort of specimens sampled monthly throughout the year, a subset of females always had large preovulatory follicles present in their ovaries. With the exception of June and September specimens, egg cases undergoing various stages of development were observed in the uteri of specimens captured during all other months of the year. For males (n=48), histological stages III through VI (SIII−SVI) of spermatogenesis, GSI, and hepatosomatic index (HSI) were examined. Although there appeared to be monthly fluctuations in spermatogenesis, GSI, and HSI, no significant differences were found. The production and maintenance of mature spermatocysts (SVI) within the testes was observed throughout the year. These findings collectively indicate that the thorny skate is reproductively active year round

Age and growth estimates of the winter skate (Leucoraja ocellata) in the western Gulf of Maine

Age and growth estimates for the winter skate (Leucoraja ocellata) were estimated from vertebral band counts on 209 fish ranging in size from 145 to 940 mm total length (TL). An index of average percent error (IAPE) of 5.8% suggests that our aging method represents a precise approach to the age assessment of L. ocellata. Marginal increments were significantly different between months (Kruskal-Wallis P<0.001) and a distinct trend of increasing monthly increment growth began in July. Estimates of von Bertalanffy growth parameters suggest that females attain a slightly larger asymptotic TL (L∞=1374 mm) than males (L∞=1218 mm) and grow more slowly (k=0.059 and 0.074, respectively). The oldest ages obtained for the winter skate were 19 years for males and 18 years for females, which corresponded to total lengths of 932 mm and 940 mm, respectively. The results indicate that the winter skate exhibits the characteristics that have made other elasmobranch populations highly susceptible to exploitation by commercial fisheries

Evaluating the Condition and Discard Mortality of Monkfish, Lophius americanus, Following Capture and Handling in the Sea Scallop Dredge Fishery

The incidental capture of nontarget organisms, known as bycatch, remains an unavoidable occurrence for all fisheries (Kirby and Ward, 2014). One of the most challenging issues facing fisheries management is the post-release mortality of these bycaught species due to its difficulty to predict and the variability among species and gear type (Benoit et al., 2010, 2013; Depestele et al., 2014), which makes it inherently difficult to conduct proper stock assessments. Since there have been few studies conducted on post-release mortality across species, fisheries managers typically assign conservative estimates of mortality which limits total allowable catch and may negatively impact the economic contribution of fisheries (Knotek et al., 2018). Due to the continued increase in global fishing efforts and the economic and ecological impact of the post-release mortality of bycatch, there is a growing need for research in this arena. To this end, this research is required across a wide range of species due to the inherent species-specific differences in how animals physiologically and behaviorally cope with the stressors of capture

Discard Mortality of Sea Scallops Following Capture and Handling in the Sea Scallop Dredge Fishery - Final Report

The focus of sea scallop, Placopecten magellanicus, management over the past 20 years has been to encourage the harvest of larger animals. This has been accomplished through a series of management measures including gear modifications, effort controls, crew size limitations and spatial management to protect juvenile scallops. While these measures have been effective in reducing the harvest of small scallops, their capture does still occur. Central to fully understanding the impact of the fishery on the resource, is a comprehensive estimate of the non-harvest mortality associated with commercial operations. Non-harvest mortality can be broken down into a number of different processes, with discard mortality being a major category. Discard mortality (DM) is the rate of mortality associated with animals that are captured and subsequently released due to primarily market factors. The latest stock assessment for sea scallops assumes that 20% of all animals discarded will die. There is considerable uncertainty associated with this estimate that is based on a single older tagging study and studies examining a non-Placopecten species under different biotic and abiotic conditions