Scallop Placopecten Magellanicus Research Articles

Evaluating bycatch avoidance in the U.S. Atlantic sea scallop Placopecten magellanicus fishery

AbstractObjectiveThe effectiveness of bycatch avoidance programs relies on changes in fishing behavior in response to spatiotemporal information on bycatch patterns. A voluntary bycatch avoidance program in the U.S. sea scallop Placopecten magellanicus fishery designed to prevent triggering bycatch allocation of Yellowtail Flounder Limanda ferruginea was implemented and maintained concurrently with other management measures. Detecting bycatch avoidance behavior and relative effectiveness for bycatch mitigation presents an analytical challenge.MethodsWe evaluated effectiveness of the bycatch avoidance program over the course of 4 years based on fishing behavior relative to bycatch advisories. Using loglinear models to compare frequencies, we examined the relationship between bycatch reports from participating vessels and bycatch advisories throughout the year in each of the 4 years. We compared results from self‐reported catch to data from a mandatory observer program for participating and nonparticipating vessels in the bycatch avoidance program.ResultSignificant associations between bycatch advisories and fishing locations indicated bycatch avoidance behavior, while accounting for the effect of sea scallop density on fishing location decisions. Evidence of avoidance behavior was stronger in earlier years of the program and varied spatially. Decreasing avoidance behavior coincided with revised bycatch management measures, which appear to have altered the incentives for bycatch avoidance.ConclusionWe found differences in the fishing behavior of fishing captains who participated in the bycatch avoidance program when Yellowtail Flounder bycatch was perceived to threaten economic yield due to fishery closures. Bycatch mitigation program evaluations should consider the program objectives as well as incentives (and disincentives) in interpreting behavior.

Chromosome-level genome assembly of sea scallop Placopecten magellanicus provides insights into the genetic characteristics and adaptive evolution of large scallops

Placopecten magellanicus (Gmelin, 1791), a deep-sea Atlantic scallop, holds significant commercial value as a benthic marine bivalve along the northwest Atlantic coast. Recognizing its economic importance, the need to reconstruct its genome assembly becomes apparent, fostering insights into natural resources and generic breeding potential. This study reports a high-quality chromosome-level genome of P. magellanicus, achieved through the integration of Illumina short read sequencing, PacBio HiFi sequencing, and Hi-C sequencing techniques. The resulting assembly spans 1778 Mb with a scaffold N50 of 86.71 Mb. An intriguing observation arises – the genome size of P. magellanicus surpasses that of its Pectinidae family peers by 1.80 to 2.46 times. Within this genome, 28,111 protein-coding genes were identified. Comparative genomic analysis involving five scallop species unveils the critical determinant of this expanded genome: the proliferation of repetitive sequences recently inserted, contributing to its enlarged size. The landscape of whole genome collinearity sheds light on the relationships among scallop species, enhancing our broader understanding of their genomic framework. This genome provides genomic resources for future molecular biology research on scallops and serves as a guide for the exploration of longevity-related genes in scallops.

Discard Mortality of Sea Scallops Placopecten magellanicus Following Capture and Handling in the U.S. Dredge Fishery

AbstractDiscard mortality can represent a potentially significant source of uncertainty for both stock assessments and fishery management measures. While the family Pectinidae is considered to be robust to the capture and handling process, understanding species‐specific discard mortality rates is critical to characterize both population dynamics and to develop regulatory measures to meet management objectives. The discard mortality rate for the U.S. dredge fishery of sea scallop Placopecten magellanicus was estimated empirically via a retention study aboard industry vessels under commercial conditions. Over 16,000 sea scallops were assessed via a composite index of scallop vitality that consisted of semiqualitative measures of both overt trauma (shell damage) and response to stimuli. Results indicate that overall sea scallop discard mortality was 21% and consistent with the values currently assumed in the stock assessment. Survival mixture models support the utility of a simple metric of physical trauma as an effective predictor of mortality. Exposure time was also identified as a positively correlated factor that was important in describing the discard mortality process. Application of experimental results highlight the need to consider some operational characteristics of the fishery to reduce potential discard mortality.

Seasonal Trends in Groundfish Discards on Georges Bank: Implications for Adaptive Quota Management

AbstractFor fisheries to be sustainable, management should account for all major sources of fishing mortality. On the Canadian side of Georges Bank, landings and discards of transboundary stocks of Atlantic Cod Gadus morhua, Haddock Melanogrammus aeglefinus, and Yellowtail Flounder Limanda ferruginea are monitored against quotas that are shared by the Canadian groundfish and scallop (sea scallop Placopecten magellanicus) fisheries to limit fishing mortality. The shared quota allocations are managed using an adaptive quota management system; quota can be redistributed between the fisheries during the season to maximize fishing opportunities, while still respecting the overall catch limits. However, the redistribution relies on estimates of the total end‐of‐year discards of Atlantic Cod, Haddock, and Yellowtail Flounder from the scallop fishery. Here, we evaluated and compared two approaches for projecting end‐of‐year discards within season: an empirical method based on scallop fishery landings and a seasonal modeling approach. Seasonal trends in discards were identified, with discards of all three groundfish species highest in April or May. The seasonal models out‐performed the empirical landings‐based projection method, and our results demonstrate that accounting for seasonal patterns in discards better informs risk‐based fishery management decisions.

Sensitivity to oil dispersants: Effects on the valve movements of the blue mussel Mytilus edulis and the giant scallop Placopecten magellanicus, in sub-arctic conditions.

In response to accidental oil spills at sea, chemical oil dispersants are utilized to limit negative impacts on nearby littoral zones. However, current evidence suggests that such dispersants may be toxic to aquatic organisms. Blue mussels (Mytilus edulis) and giant scallops (Placopecten magellanicus) were exposed to different environmentally relevant concentrations of oil dispersant and their behavioural responses were closely monitored using high frequency (10Hz) valvometry. Behavioural valve responses included rapid closures when oil dispersant was added to the experimental tanks. At higher concentrations, the mussels remained closed throughout the exposure period. The giant scallop displayed escape behaviours (clapping) prior to mortality, suggesting toxicity of the oil dispersant. Relationships between different behavioural indicators and oil dispersant concentrations were observed for both species, but with different trends. While scallops demonstrated positive correlations between gaping behaviours and dispersant concentration, mussels exhibited a concentration threshold beyond which the gaping behaviour was characteristic of longer closure periods. This study highlights behavioural response differences consistent with bivalve-specific biological traits: the continuous valve closure of an intertidal species, M. edulis, firmly attached to the substrate, and the escapement behaviours of a semi-mobile subtidal species, P. magellanicus. From these observations, it appears that valvometry could be used as a tool for environmental assessments.

The Effects of Scallop Dredge Fishing Practices on Physical, Behavioral, and Physiological Stress in Discarded Yellowtail Flounder, Windowpane, and Fourspot Flounder

AbstractThe Atlantic sea scallop Placopecten magellanicus dredge fishery is one of the most lucrative commercial fishing industries in the northeastern United States, and fish bycatch can comprise up to ~42% of the total catch. Benthic species, such as flatfish, are particularly susceptible to unintended capture in scallop dredge gear, and mitigating bycatch and associated mortality has been mandated a priority for fisheries management. Based on this management need, the present study evaluated the physical, physiological, and behavioral stress responses of Yellowtail Flounder Limanda ferruginea, Windowpane Scophthalmus aquosus, and Fourspot Flounder Paralichthys oblongus to capture in the scallop dredge fishery. More specifically, we used generalized additive models and linear regression models to assess the influence of various fishing practices, environmental conditions, and biological factors on injury condition, physiological parameters, and reflex indicators. Although these flatfish species appeared to be physically resilient to capture based on an observable injury assessment, dredge capture and handling factors proved stressful, with the degree of immediate mortality, physiological disturbances, and reflex impairment varying by species. While multiple factors influenced the degree of stress in these species, based on our results the reduction of tow duration and limiting air exposure/sorting duration would likely be the most effective strategies to mitigate the impact of scallop dredge fishing on these flatfish species.

Not only greening: The effects of marennine produced by Haslea ostrearia on physiological traits of three bivalve species

The marine diatom Haslea ostrearia is known for its ability to produce marennine, a blue-green water-soluble pigment, which is responsible for the oyster greening phenomenon in the French Atlantic Coast. Marennine can be considered a bioactive extracellular compound (BEC) as it exhibits activities against detrimental pathogens in bivalve aquaculture. However, marennine could also be toxic to animals. The aim of this experimental study was to assess the effect of marennine produced by H. ostrearia upon three commercially important bivalve species, the American oyster Crassostrea virginica, the blue mussel Mytilus edulis and the giant scallop Placopecten magellanicus. Effect of this BEC was also assessed on different ontogenic stages of scallops. The animals were exposed to 3 mg L−1 of marennine and physiological response associated with clearance rates (CR), oxygen consumption and condition index (CI) were measured after 16 h of exposure (day 0), and after one subsequent week of recovery (day 7). In the short term, CR and oxygen consumption on mussels and oysters were significantly altered by marennine but not for scallops. CR recovery was observed in oysters after seven days, but no depuration was observed in mussels. Nevertheless, oxygen consumption in both mussels and oysters recovered on day 7. CI in the marennine-exposed group for both adult oysters and scallops was not significantly different, yet CI of mussels was lowered by 18.2 % compared to control. Scallop adults seemed largely resistant to marennine, but juveniles were more susceptible with a reduced CR and oxygen consumption by 71.9 % and 24.5 %, respectively, and no depuration activity observed until day 7. Additionally, CI in marennine-exposed juvenile scallops was 27 % lower than that of control. This study demonstrates species- and age-specific effect of marennine on bivalves, thus highlighting the importance of further assessment on the utilization of this pigment as a natural product decreasing pathogenicity of bacteria in shellfish aquaculture systems.

Verification of authenticity: A rapid identification method for commercial scallop species through multiplex real-time PCR

Seafood products are particularly vulnerable to food fraud and mislabelling, which may have negative implications on fisheries resources, economy, consumer health and trust. This is a considered problem for scallops, since these high-valued seafood products are usually sold without their morphologically characteristic shells. Scallop products differ in taste and value and usually species of the genus Pecten spp. are especially expensive in many European countries. The aim of the present study was the development of a multiplex TaqMan real-time PCR assay that allows a rapid and reliable authentication of the three commercially important species/genera Pecten spp. (usually King scallop P. maximus), Atlantic sea scallop Placopecten magellanicus, and Japanese scallop Mizuhopecten yessoensis. The design of primers and probes was based on mitochondrial 16S rRNA gene amplifying fragments of 138–198 bp. Following the optimization of the multiplex real-time PCR assay, analyses on efficiency, limit of detection, specificity, robustness, and crosstalk were conducted for validation purpose. Average Cq values of 20 ng DNA obtained for Pecten spp. were 17.64 ± 0.89, for P. magellanicus 18.42 ± 0.83, and for M. yessoensis 17.08 ± 0.79. Non-target species produced either no fluorescence signal or the Cq differed significantly from those of target species (p < 0.01). Finally, the newly developed real-time PCR assay was tested on commercial samples from German supermarkets and fishmongers accompanied by simultaneous verification through Sanger sequencing, which revealed a high mislabelling rate of 48%, especially for products purchased at fishmongers. The results emphasize the need of a control method that allows the rapid analysis of sufficient sample quantities. The study is one of the first which presents a multiplex TaqMan real-time PCR approach for the authentication of commercially important seafood species.

Convergence of a Disease and Litigation Leading to Increased Scallop Discard Mortality and Economic Loss in the Georges Bank Fishery

AbstractRotational management in the Atlantic sea scallop Placopecten magellanicus fishery has focused on closing areas to fishing when a high proportion of small scallops is observed in a discrete area, but less attention has been paid to reopening closed areas to prevent poor meat quality. In this fishery there are several large marine protected areas, including Closed Area I of Georges Bank. Intense drop camera surveys of Closed Area I in 1999 led to incorporating a 700‐km2 area into the rotational management scheme. There was a larger abundance of scallops to the south of this area, and these were made available for harvest in 2005, but this fishery was closed in 2006 when the management plan was overturned by a federal court decision. When the area was reopened again in 2011, however, the expected harvest was not achieved. Although fishermen harvested the scallops and opened the shells to extract the meat, they found that many of the meats were gray and not of marketable quality and so they discarded them. The gray meats were linked to a highly pathogenic apicomplexan infection. There was a 52% decline in exploitable biomass between 2011 and 2013 (7,300 metric tons, representing a gross revenue of US$170 million) that could not be attributed to a reduction in landings, resulting in a failure to complete the allotted trips. The scallop rotation management plan has been extremely successful overall, with 69 of the access area trips harvesting over 80% of the allocation; however, increased monitoring of meat quality would further improve management.

A spatiotemporal Evaluation of Atlantic Sea Scallop Placopecten magellanicus Habitat in the Gulf of Maine Using a Bioclimate Envelope Model

AbstractA bioclimate envelope model was developed to evaluate the impacts of climate variability on spatiotemporal availability of suitable habitat for the Atlantic sea scallop Placopecten magellanicus in the Gulf of Maine (GOM). Bioclimate envelopes were established through habitat suitability indices (HSIs) based on bottom temperature, bottom salinity, current velocity, depth, and bottom composition. The relationship between Atlantic sea scallop abundance and each environmental variable was quantified using suitability indices, which were generated based on standardized scallop abundance sampled over 10 years of dredge survey data. Boosted regression tree models were used to determine the relative importance of each environmental variable to scallop abundance, thereby establishing a weighting scheme within the HSI. A regional circulation model was coupled with the weighted HSI to hindcast spatiotemporal dynamics of suitable habitat for Atlantic sea scallop in coastal and offshore waters of the GOM from 1978 to 2013. Higher habitat suitability was found along inshore areas compared with offshore areas. Model predictions indicated an increasing trend in habitat suitability in inshore waters since 1978 and decreasing habitat suitability in offshore waters. This research provides a novel modeling framework with which to enhance research and management of commercially valuable Atlantic sea scallop stocks over broad spatiotemporal scales in the climatically altered GOM.

Growth optimization of marine diatom Amphora sp. by tailoring silica and nitrate concentration

Growth optimization of marine diatom Amphora sp. by tailoring silica and nitrate concentration

Reducing Discards of Flatfish in the Sea Scallop Dredge Fishery by Dredge Pause

Flatfishes are routine bycatch in the Atlantic sea scallop Placopecten magellanicus (Gmelin) dredge fishery but must be discarded at sea. Despite release, a 90% mortality rate is assumed for overfished species such as yellowtail flounder Limanda ferruginae and windowpane Scophthalmus aquosus.When the scallop fishery exceeds the annual catch limit for yellowtail flounder, accountability measures may be triggered and seasonal closures of the scallop fishery can occur in specific areas. Flatfish bycatch is potentially reduced by stopping the scallop dredge in midwater to allow escape. This technique has been voluntarily practiced, but not widely adopted, owing to a lack of knowledge about its efficacy relative to collateral scallop loss. In a test of 122 scallop dredge tows on a commercial vessel using otherwise standard procedures, pausing the dredge during retrieval significantly reduced flatfish bycatch relative to pause length (0, 5, 10, or 15 min) but also allowed some scallop escapement. Flatfish were more likely to escape from paused dredges if there were fewer scallops in the dredge. Video provided evidence that flatfish do escape through the tickler chains and over the lip during pauses, and also showed the benefit of time in allowing them to work free of the suspended scallop load. During rough weather, vessel heave winnowed the dredge contents, increasing scallop loss. Captains can judge the practice as a cost-benefit calculation to avoid loss of revenue from early closure, but it appears to offer only a weak return on the time investment. Escaped fish may still suffer mortality.

Evaluating the interaction of the invasive tunicate Didemnum vexillum with the Atlantic sea scallop Placopecten magellanicus on open and closed fishing grounds of Georges Bank

Abstract An invasive colonial tunicate (Didemnum vexillum) was initially observed on Georges Bank in 1998, and it has since spread in benthic environments on fishing grounds and areas closed to bottom-fishing. It can form dense mats on gravel substrates that are also a preferred habitat for the Atlantic sea scallop (Placopecten magellanicus), which supports one of the most valuable commercial fisheries in the United States. We used HabCam, a vessel-towed underwater imaging system, to investigate the spatial distributions of P. magellanicus and D. vexillum in a region that includes fishing grounds and an area protected from bottom-fishing. We found a negative relationship between P. magellanicus and D. vexillum, even after controlling for substrate and management status, suggesting that D. vexillum competes for habitat with P. magellanicus. We also applied the geostatistical method of universal kriging to interpolate the distribution of D. vexllium based on the covariables gravel, depth and area. Our results indicate that D. vexillum is more common in areas open to fishing than in the areas closed to fishing, even taking bottom substrate effects into account. Didemnum vexillum appears to have spread over portions of the northern edge of Georges Bank. This research evaluates potential fish and invertebrate habitat degradation caused by an invasive species.

Identifying patterns of dispersal, connectivity and selection in the sea scallop,Placopecten magellanicus,usingRADseq‐derivedSNPs

Understanding patterns of dispersal and connectivity among marine populations can directly inform fisheries conservation and management. Advances in high‐throughput sequencing offer new opportunities for estimating marine connectivity. We used restriction‐site‐associated DNA sequencing to examine dispersal and realized connectivity in the sea scallop Placopecten magellanicus, an economically important marine bivalve. Based on 245 individuals sampled rangewide at 12 locations from Newfoundland to the Mid‐Atlantic Bight, we identified and genotyped 7163 single nucleotide polymorphisms; 112 (1.6%) were identified as outliers potentially under directional selection. Bayesian clustering revealed a discontinuity between northern and southern samples, and latitudinal clines in allele frequencies were observed in 42.9% of the outlier loci and in 24.6% of neutral loci. Dispersal estimates derived using these clines and estimates of linkage disequilibrium imply limited dispersal; 373.1 ± 407.0 km (mean ± SD) for outlier loci and 641.0 ± 544.6 km (mean ± SD) for neutral loci. Our analysis suggests restricted dispersal compared to the species range (>2000 km) and that dispersal and effective connectivity differ. These observations support the hypothesis that limited effective dispersal structures scallop populations along eastern North America. These findings can help refine the appropriate scale of management and conservation in this commercially valuable species.

Prophylactic effect ofHaslea ostreariaculture supernatant containing the pigment marennine to stabilize bivalve hatchery production

This paper explores the possibility of using the supernatant of Haslea ostrearia culture containing marennine, a natural microalgal pigment, as an antimicrobial in bivalve hatcheries. The blue mussel Mytilus edulis and the scallop Placopecten magellanicus were used as model animals, and the pathogenic marine bacteria Vibrio splendidus was used to induce larval mortality. The hypothesis tested was that V. splendidus pathogenicity in larval rearings can be controlled by using marennine-containing culture supernatants. The effect of three marennine concentrations was tested on a larval rearing over 20 days for M. edulis and 9 days for P. magellanicus. At a low dose (0.1 mg L-1), survival and physiological condition were both higher than in the control. In bacterial challenges, larvae were exposed to V. splendidus for 72 h, with or without marennine. The bacterial challenge caused significant mortality when compared to controls, while the marennine-treated larvae showed significantly higher survival. Results show that marennine is an interesting molecule for pathogen control in hatcheries as it is active at low concentrations and significantly enhanced larval survival and physiological condition. -- Keywords : Bivalve hatcheries ; microalgal by-products ; Haslea ostrearia ; Mytilus edulis ; Placopecten magellanicus ; Vibrio splendidus.

Mortality Assessment of Atlantic Sea Scallops (Placopecten magellanicus) from Gray-Meat Disease

ABSTRACT The sea scallop Placopecten magellanicus (Gmelin, 1791) fishery is the most valuable wild scallop fishery in the world. Landings are primarily adductor muscles, which are ideally creamy white and firm. Recently, an increasing number of dark brown to gray, flaccid, and stringy meats have been caught in areas of Georges Bank and the mid-Atlantic, causing concern in industry and management. The mortality of gray-meat scallops was investigated, and an anesthetization procedure was developed allowing assessment of meat color in live scallops for laboratory experiments. The mortality rate of gray-meat scallops compared with white-meat scallops was tested. Gray-meat infection was swift and fatal; 26 of the original 28 gray-meat scallops died, whereas only 1 of 28 white-meat scallops died. The gray-meat condition was clearly associated with apicomplexan parasite infection intensity. Gray-meat scallops were identified visually, with image analysis computer software, and cell counts of apicomplexan nuclei....

Measuring scallop fertilization success in the field: chamber design and tests

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 551:141-154 (2016) - DOI: https://doi.org/10.3354/meps11684 Measuring scallop fertilization success in the field: chamber design and tests Skylar R. Bayer*, Richard A. Wahle, Peter A. Jumars, Damian C. Brady Darling Marine Center, University of Maine, 193 Clark’s Cove Road, Walpole, ME 04573, USA *Corresponding author: skylar.bayer@maine.edu ABSTRACT: We developed and tested a method to field test fertilization success, measured as the proportion of eggs fertilized, in the giant sea scallop Placopecten magellanicus, a commercially valuable and sedentary broadcast spawner in the northwest Atlantic. A laboratory sperm dilution series determined maximum fertilization success expected in the field and assessed gamete longevity. We also developed and flume-tested a fertilization chamber to assess ambient water-column sperm loads near field populations. We then conducted a series of dockside field trials using these chambers over the course of the late summer spawning season in coastal Maine, USA. Chambers were deployed among manipulated populations of scallops to assess effects of local spawner abundance and location on time-integrate fertilization success. In dilution-series experiments, maximum fertilization success occurred at sperm concentrations >107 sperm ml-1. Egg longevity fell to zero between 8 and 24 h at ambient temperatures of 12°C, and sperm half-life shortened from 2 h to 9 min with a 10-fold dilution from a sperm concentration of 107 cells ml-1. Flume trials demonstrated chamber artifacts: fertilization was lower inside the chamber and the effect was greater at higher flow rates, but chamber orientation to flow had no effect. Increasing the numbers of eggs tended to reduce fertilization efficiency. In dockside tests, a 30-fold difference in spawner numbers had a significant effect on fertilization success. Notwithstanding acknowledged chamber artifacts due to flow impedance, this study establishes the feasibility of time-integrated fertilization experiments with scallops and sets the stage for further investigations of fertilization dynamics in natural scallop populations. KEY WORDS: Giant sea scallop · Placopecten magellanicus · Fertilization success · Fertilization ecology · Population density effect · Allee effects · Fisheries · Depensation Full text in pdf format PreviousNextCite this article as: Bayer SR, Wahle RA, Jumars PA, Brady DC (2016) Measuring scallop fertilization success in the field: chamber design and tests. Mar Ecol Prog Ser 551:141-154. https://doi.org/10.3354/meps11684 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 551. Online publication date: June 09, 2016 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2016 Inter-Research.

Identification of a Mycobacterium sp. as the causative agent of orange nodular lesions in the Atlantic sea scallop Placopecten magellanicus.

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.

Effects of spatial heterogeneity in growth and fishing effort on yield-per-recruit models: an application to the US Atlantic sea scallop fishery

Abstract Conventional yield-per-recruit (Y/R) and spawning-stock biomass-per-recruit (SSB/R) models make no allowance for spatial heterogeneity in fishing mortality, natural mortality, or growth across the stock area, although variability in these processes can affect model results. For example, areas with higher growth and/or lower natural mortality rates should be fished at a lower rate to maximize Y/R; however, these areas may be especially attractive to fishers and are often fished harder. Here, Y/R and SSB/R models are developed that simultaneously account for spatial heterogeneity in growth and fishing effort. These models are applied to the US Atlantic sea scallop (Placopecten magellanicus) fishery. The spatial variability in growth uses depth-integrated models from the literature and variability in effort is based on, alternatively, uniform, observed, and relative-optimal spatial harvesting distributions. The observed effort patterns are derived from vessel monitoring system positions, and illustrate one application for these widely collected but underutilized spatial data. In this example, the distribution of observed fishing effort reduces Y/R compared with the relative-optimal, or the uniform effort distribution implicitly assumed by conventional Y/R analysis. SSB/R was in some cases considerably higher under the relative-optimal distribution of effort than when calculated using observed or uniform effort patterns. Such more realistic spatially integrated Y/R and SSB/R models can help to evaluate the impact of effort patterns on fishery yield and stock egg production. These models demonstrate that the spatial distribution of effort can be as important as the overall average fishing mortality when managing fisheries to optimize Y/R, SSB/R, and yield.

Scallops caught in the headlights: swimming escape behaviour of the Atlantic sea scallop (Placopecten magellanicus) reduced by artificial light

AbstractQuantifying the distribution and abundance of the Atlantic sea scallop (Placopecten magellanicus) is a fishery management priority, and stock assessments increasingly rely on video surveys. Interpreting the results of these surveys requires understanding the inherent biases introduced as a result of target animal behaviour. Our study investigated the effect of artificial lights on the behaviour of Atlantic sea scallops during a video survey using a towed benthic sled. Swimming and stationary scallops were counted in survey videos using event logging software. In addition, the locations, orientations, and swimming directions of the scallops were noted in a subset of the videos. The proportion of scallops that swam when an artificial light was turned on was significantly smaller than the proportion that swam when the light was off. Further analysis using a logistic model showed that only light state (off or on) predicted the likelihood of scallop swimming responses. Possible reasons for this unexpected behaviour are discussed, with a focus on the scallop visual system.