Placopecten Magellanicus Research Articles

Accounting for Rents in the U.S. Atlantic Sea Scallop Fishery

The Current Rent Method II (CRMII) of environmental accounting was used to estimate resource rent and the asset value of resource biomass in the U.S. Atlantic sea scallop fishery during 1977-2002. High levels of surplus and profit masked negative asset values for about two decades, as low as -$100 million a year during 1989-91 after many years of resource depletion and degradation by the overcapitalized fishery. Regulatory policies implemented in 1994 involving limited entry, vessel effort quotas, and area closures fostered stock recovery and greatly improved resource accounts to where the value of the sea scallop asset has recently averaged $128 million. Despite these recent improvements, there is no evidence that asset value is growing at any benchmark interest rate. The importance of adjusting fishery resource accounts for inframarginal rent as well (as the value of vessel capital) is discussed, as are property rights to the resource income component of so-called producer surplus.

Linear mixed-effects models for weight–length relationships

Abstract Length and weight data are often analyzed in fisheries science to derive a parametric weight–length relationship for estimating biomass and to develop indices of condition for comparing the ‘wellness’ of different populations of fish. However, analysis of such data often ignores the inherent spatial and temporal grouping of the observations, and hence, the data hierarchy. This paper proposes the use of linear mixed-effects models as an effective means of analyzing and comparing weight–length relationships and indices of condition when there are many groups. The use of simple linear regression (where grouping is ignored), ANCOVA (where group effects are incorporated as fixed-effects), and linear mixed-effects models (where group effects are random-effects) are compared using data for Atlantic sea scallops (Placopecten magellanicus). The group means of residuals is proposed as a measure of relative weight or index of population condition. Linear mixed-effects models should be used to analyze grouped data because the variability among groups is ignored in simple linear regression and ANCOVA. Also, it is important that explanatory variables be incorporated in analyses of grouped data because their influence may mask the true differences among groups.

Depth and timing of settlement of veligers from different populations of giant scallop, Placopecten magellanicus (Gmelin), in thermally stratified mesocosms

The present study was conducted to evaluate the relative roles that water column stratification intensity and possible inter-population behaviour differences play in determining depth of larval settlement of giant scallops, Placopecten magellanicus, in relation to thermoclines. Differences in timing of settlement of larvae from various populations were also examined. Two separate experiments were conducted in a 10.5-m-deep, 3.7-m-diameter, thermally stratified tank with larvae spawned from scallops collected from several adult beds located in areas with differing oceanographic regimes (Georges Bank, Mahone Bay, Passamaquoddy Bay). Previous mesocosm experiments had shown that veligers from these various populations differ in their vertical migration patterns. In the first experiment (December 1992–February 1993), larvae from all three populations were held in separate 9.5-m-deep tubes and exposed to a 1.5 °C temperature differential established over a depth interval of 1 m. The number of settled juveniles (spat) of each population collected at the end of the experiment increased with depth and showed no peak at or above the thermocline. This depth distribution of spat was most likely driven by preferential larval settlement. In the second experiment (February–May 1994), larvae spawned from Georges Bank and Passamaquoddy Bay stocks were held in 9.0-m-deep tubes and exposed to a 5 °C temperature differential established over a depth interval of 1 m. The number of settled spat of both populations was greater above this thermal boundary and increased with decreasing depth. This depth distribution was most likely driven by preferential settlement above the thermocline followed by upward post-settlement migration. The results from the two experiments indicate that larvae from various populations show similar trends in settlement patterns in response to similar thermal stratifications. Stratification intensity, however, does affect depth of larval settlement. In the second experiment, both populations of larvae settled throughout the time interval of collector deployment (larvae 32–82 days old). These results extend the range of planktonic developmental times generally reported in the literature and may be more indicative of natural planktonic development in the field. While Georges Bank larvae settled in consistent numbers through time, Passamaquoddy Bay larvae showed peaks in settlement at certain time periods, indicating that pulses of larval settlement may occur even from an individual spawning event.

Atlantic sea scallop management: an alternative rights-based cooperative approach to resource sustainability

Abstract The effectiveness of the US Atlantic sea scallop fishery regulations has resulted in recovery from a biological standpoint. However, due to excessive harvest capability and regulatory inefficiencies, the industry is facing substantial harvesting costs and, hence, economic inefficiency. The main reason is that most regulations or restrictions do not take into account the fundamental importance of the property rights for inducing behavior more consonant with aggregate as well as individual rationality. This article conceptualizes the role and importance of property rights structures in their application to Atlantic sea scallop fishery management. Additionally, embryonic industry efforts in developing an enhancement program for this fishery may point to the need for more cooperative, area-based management strategies. By doing so, two important elements for achieving greater production and value from the scallop fishery are identified. First, establishing an ownership structure of private property rights in the form of Territorial User Rights in Fishing (TURFs) and second, having fishermen cooperate under an organizational structure, such as a harvesters’ cooperative. These elements imply that an alternative, rights-based cooperative approach may become a compatible governance arrangement and provide an incentive for the rational management of the scallop fishery.

Biological reference points for sea scallops (Placopecten magellanicus): the benefits and costs of being nearly sessile

In this paper, we concentrate on spatial aspects of growth and reproduction for sea scallops (Placopecten magellanicus) to advance the general theory for development of reference points for sessile animals and to illustrate the general points with several specific examples. Nonlinear mixed effects models can be used to define the spatial distribution of growth rates and their implications for the definition of growth overfishing. We develop a basin model to illustrate that the typical "boom and bust" effects, often attributed to environmental factors, are explained equally well by spatial variations in habitat quality, spatial concentration of fisheries, and dispersal of larvae among areas. Results suggest that incentives to concentrate fishing effort in lower productivity areas may be an effective tool for reducing recruitment variation and improving yields. Reductions in fishing mortality might be possible with closed areas as they can be used to reduce the concentration of effort on high scallop densities. Further, rotational area management strategies can offer the promise of balancing demands for increased yield, prevention of recruitment overfishing, maintaining spawning reserves, and reducing habitat damage and bycatch.

Effects of sex steroids on gonadal development and gender determination in the sea scallop, Placopecten magellanicus

Previous work has demonstrated the presence of various sex steroids in molluscs and suggested their possible functions in the control of reproduction. However, their potential roles in early sexual development have remained unexplored. The results of the present study showed that injections of estradiol, testosterone, progesterone, and dehydroepiandrosterone (DHEA) all accelerated gonadal differentiation and shifted sex ratios toward more males in the sea scallop. Morphological changes were also observed in the females of steroid-injected groups. Estradiol appeared to stimulate oocyte growth while testosterone appeared to induce degeneration of oocytes. No parallel changes were noted in males of steroid-injected groups. Hermaphroditic animals were also found in the progesterone- and DHEA-injected groups. Together, these results support the hypothesis that sex steroids are involved in invertebrate reproduction and may be exploited for gender manipulation in bivalve aquaculture.

Effect of varying levels of dietary essential fatty acid during early ontogeny of the sea scallop Placopecten magellanicus

This study investigated the biological effects of various dietary essential fatty acids levels to sea scallop larvae, Placopecten magellanicus. Scallop larvae were fed three diets from D-veliger to settlement. Diet A consisted of Isochrysis sp. and Pavlova lutheri, diet B was a mix of Isochrysis sp. and Chaetoceros muelleri and diet C consisted of the same two species, but C. muelleri was grown under silicate deprivation to alter the fatty acid composition. Pediveligers (28 days old) were sampled prior to settlement for fatty acid analysis, growth measurement and survival assessment. Survival and settlement success were measured at the end of the experiment (day 40). Our results show that feeding regime greatly influenced larval size, settlement and fatty acid composition. Diet A was severely deficient in arachidonic acid (20:4n-6, AA), leading to the poorest larval growth, survival and lipid content. Nevertheless, larvae fed diet A selectively accumulate AA by a factor three compared to the dietary amount. Shell size of 28-day-old larvae was positively correlated with AA content and negatively correlated with eicosapentaenoic acid (20:5n-3, EPA)–AA ratio, thus suggesting that these two variables are of major interest for the optimisation of larval growth in sea scallops. Finally, larvae fed diet C displayed 20% higher shell size at day 28 than larvae fed diet A and B, likely in relation to the dietary amount of saturated fatty acid (SFA). However, the moderate survival and settlement success of these groups of larvae might be associated with a relative deficiency in docosahexaenoic acid (22:6n-3, DHA). This study underlines that the overall balance between polyunsaturated fatty acid (PUFA) needs to be considered to adequately fed sea scallop larvae.

Effect of varying levels of dietary essential fatty acid during early ontogeny of the sea scallop Placopecten magellanicus

This study investigated the biological effects of various dietary essential fatty acids levels to sea scallop larvae, Placopecten magellanicus . Scallop larvae were fed three diets from D-veliger to settlement. Diet A consisted of Isochrysis sp. and Pavlova lutheri , diet B was a mix of Isochrysis sp. and Chaetoceros muelleri and diet C consisted of the same two species, but C. muelleri was grown under silicate deprivation to alter the fatty acid composition. Pediveligers (28 days old) were sampled prior to settlement for fatty acid analysis, growth measurement and survival assessment. Survival and settlement success were measured at the end of the experiment (day 40). Our results show that feeding regime greatly influenced larval size, settlement and fatty acid composition. Diet A was severely deficient in arachidonic acid (20:4n-6, AA), leading to the poorest larval growth, survival and lipid content. Nevertheless, larvae fed diet A selectively accumulate AA by a factor three compared to the dietary amount. Shell size of 28-day-old larvae was positively correlated with AA content and negatively correlated with eicosapentaenoic acid (20:5n-3, EPA)–AA ratio, thus suggesting that these two variables are of major interest for the optimisation of larval growth in sea scallops. Finally, larvae fed diet C displayed 20% higher shell size at day 28 than larvae fed diet A and B, likely in relation to the dietary amount of saturated fatty acid (SFA). However, the moderate survival and settlement success of these groups of larvae might be associated with a relative deficiency in docosahexaenoic acid (22:6n-3, DHA). This study underlines that the overall balance between polyunsaturated fatty acid (PUFA) needs to be considered to adequately fed sea scallop larvae.

A Spatially Explicit Open‐Ocean DeLury Analysis to Estimate Gear Efficiency in the Dredge Fishery for Sea Scallop Placopecten magellanicus

AbstractThe translation of survey data into estimates of absolute abundance hinges on the availability of an accurate estimate of gear efficiency. In many fisheries, however, a wide range of estimates exists and research directed at quantifying this critical parameter has focused on relatively small, fishery‐independent data sets. In the present study, a technique was developed to utilize the copious amounts of data available from an open‐ocean fishery for sea scallops Placopecten magellanicus in a spatially explicit depletion model. In June 1999, Georges Bank Closed Area II was opened to the commercial scallop fleet after a 5‐year multispecies fishing ban. During the 5‐month opening, the spatial distribution and magnitude of fishing effort was tracked through vessel monitoring systems, and a relatively small but still substantial number of catch observations were made aboard vessels from the commercial fleet. A spatial analysis of both catch and effort data was utilized to select areas consistent with the assumptions of a DeLury analysis. Maximum likelihood estimation was then used to generate a single estimate of the catchability coefficient (and thus efficiency), while simultaneously estimating the initial abundance in each area. The gear efficiency of the New England‐style scallop dredge used during the fishing season was estimated to be 42.7%. A sensitivity analysis of model results shows a potential range of 35.5–52.5%, depending on model assumptions.

Growth of postlarval sea scallops, Placopecten magellanicus, on microalgal diets, with emphasis on the nutritional role of lipids and fatty acids

Culture of the sea scallop, Placopecten magellanicus, is constrained by a reliable supply of high-quality postlarvae, yet little is known about the diets and essential nutrients required to maximize growth and survival during these vulnerable stages. Therefore, post-settlement sea scallops were exposed to binary microalgal diets consisting of a flagellate: Pavlova lutheri, Pavlova sp. (Pav, CCMP 459) or Tetraselmis striata (Plat-P) and a diatom: Chaetoceros muelleri, Thalassiosira weissflogii or Fragilaria familica for 28–30 days. The combination Pav 459/C. muelleri provided a superior diet for sea scallop postlarvae, yielding a growth rate of up to 28 μm day−1. However, when these algae were offered singly, a 32% (Pav 459) and 64% (C. muelleri) decrease in growth rates was observed, indicating that both species made a significant contribution to the success of the mixed diet. The two species are characterized by unique signatures of n−6 polyunsaturated fatty acids (PUFAs): C. muelleri has high levels of arachidonic acid (AA), and Pav 459 (in contrast to P. lutheri) has high levels of n−6 docosapentaenoic acid (DPA). DPA was selectively incorporated into tissues of scallops fed all binary diets except the one rich in DPA (Pav 459/C. muelleri). These results, coupled with a marked increase in n−6/n−3 ratios between the diet and tissues, provide evidence that n−6 PUFAs may play an important and previously underestimated role in scallop nutrition. The diet of T. striata and C. muelleri, which yielded the lowest growth rate (8.1 μm day−1) contained dietary docosahexaenoic acid (DHA; 22:6n−3) concentrations 4.5–7× lower than any other binary treatment. Low DHA levels may thus explain the poor performance of this diet. Tissue protein and triacylglycerol concentrations reflected diet performance, with higher values generally associated with more successful diets. This work suggests that DHA, as well as the n−6 PUFAs AA and DPA, may be essential for optimizing growth of sea scallop postlarvae.

Differences between epilithic and epizoic hydroid assemblages from commercial scallop grounds in the Bay of Fundy, northwest Atlantic

Hydroid assemblages from the shells of 104 live scallops Placopecten magellanicus and 136 cobbles were sampled from 39 sites on heavily dredged commercial scallop grounds in the Bay of Fundy, northwest Atlantic. The scallop shells were considered pseudo-controls, representing undisturbed 'island habitats' naturally interspersed amongst the cobbles. Cobbles were expected to represent disturbed habitat. Samples yielded 51 taxa from 24 genera across substrata. The number of taxa was significantly lower on cobbles. Multidimensional scaling plots and statistical analyses on presence-absence data discriminated 2 divergent assemblages consistent with substratum. Cobble assemblages were characterized by Campanularia volubilis, Clytia hemisphaerica and Clytia sp., while those on the live scallop shells were characterized by the small auto-epizoite Calycella syringa and its hosts Sertularia cupressina and Obelia dichotoma. Species discriminating between the sub- strata are considered substrate generalists. Fishing effort was introduced as a factor in an analysis of similarity and accounted for a significant proportion of the variance within and between substrata, with larger R 2 values associated with the cobble assemblages, as expected. Runner-like forms with small, unbranched colonies and medusa life stages were more frequently found on cobbles than on live scallop shells. Assemblage and life history divergence associated with fishing effort, widespread substrate generalism amongst the principle taxa, and observations from other studies suggest that these observed differences could be related to chronic disturbance of cobbles caused by fishing.

Localization of qualitative particle selection sites in the heterorhabdic filibranch Pecten maximus (Bivalvia: Pectinidae)

Particle-processing, and specifically qualitative particle selection, was studied in Pecten maximus using intact and empty versions of the naturally occurring diatom Coscinodiscus perforatus. Endoscope-directed sampling allowed comparison of particle proportions or numbers in the experi- mental medium, dorsal and ventral gill tracts, and labial palp pseudofeces. The general processing of particles was closely similar to that previously described for the more primitive scallop Placopecten magellanicus, despite the large phylogenetic distance between these 2 species. The gill and the labial palps of Pecten maximus each effected particle selection (rejection of empty, cleaned frustules), both in the presence of intact C. perforatus particles, and when only empty, cleaned frustules were pre- sented. Particle selection operated even when small proportions (approx. 10%) of empty, cleaned C. perforatus frustules were present in the particle mixture. This represents the first direct experimental demonstration of the sites of qualitative particle selection in a heterorhabdic filibranch bivalve, and shows the process to be located in both the gills and the labial palps. The qualitative selection capac- ity of the heterorhabdic gill could be the result of either early evolution in turbid environments, or an adaptation which avoids overloading qualitative selection of the palps in this gill type.

Effects of sex steroids on in vitro gamete release in the sea scallop, Placopecten magellanicus

Summary Effects of estradiol, testosterone and progesterone on 5-HT-induced gamete release were studied in vitro in both sexes of the sea scallop. The results showed that estradiol (10−5–10−8 M in females and 10−5–10−7 M in males) and progesterone (10−7–10−8 M in females and 10−5–10−7 M in males) potentiated gamete release in both sexes, whereas testosterone (10−5–10−7 M) had a facilitatory effect only in males. Pharmacological studies suggested that these effects may be achieved through activation of sex steroid receptors because they were abolished by receptor antagonists (tamoxifen, 1.25 μM; flutamine, 2.5 μM; RU486, 1 μM) and by RNA and protein synthesis inhibitors (actinomycin D, 8 μM; cycloheximide, 10 μM). These findings support a growing body of literature which suggests physiological roles of sex steroids in invertebrates. Furthermore, the results also suggest possible applications in the environmental monitoring of endocrine disrupting chemicals and in bivalve aquaculture.

Modelling potential effects of petroleum exploration drilling on northeastern Georges Bank scallop stocks

A set of numerical models was used along with laboratory and field observations to evaluate the potential risk of exploratory oil and gas drilling on northeastern Georges Bank to sea scallop ( Placopecten magellanicus) stocks. The models were used to predict the drilling waste zone of influence and the impact of chronic exposure on scallop growth and reproduction. Growth and reproduction are generally considered to be the most important sublethal effects of chronic contaminant exposure. The highest near-bottom concentrations of drilling waste (water-based mud) from a hypothetical 92-day exploration well was predicted to occur along the side of the bank (>100 m depth). Laboratory information on drilling mud toxicity threshold concentrations indicated a potential for 0–48 days of growth inhibition depending upon the site, settling velocity of the mud, and area over which results are averaged. Scallop stocks on the side of the bank are relatively sparse, but dense aggregations are found in some areas and it is possible that changes in reproductive output could have detectable effects at the population level. Growth inhibition in the tidal front region, which has the densest scallop stocks, was predicted to be more localised and confined to a range of 0–15 days. Growth loss in the central mixed region (<65 m) was predicted to be negligible (<2 days). These results illustrate the importance of site location and waste settling velocity on potential effects. The magnitude of effects predicted at each site was closely related to bottom stress ( u ∗) as this determines how rapidly drilling mud reaching the seabed are redistributed and diluted both horizontally and vertically.

Ontogenetic changes in gill morphology and potential significance for food acquisition in the scallop Placopecten magellanicus

Sources of mortality in both wild and cultured populations of marine bivalves during postlarval stages remain largely unknown, but may be partly associated with the inability to meet energetic demands during intense morphogenesis. The development of the gills in postsettlement scallops (Placopecten magellanicus) from 0.35 to 14 mm in shell height (SH) was investigated using scanning electron microscopy to determine the degree of size-specific differentiation of the gills and evaluate potential ontogenetic constraints in food acquisition. Key transitional stages in morphogenesis, likely to exert pronounced effects on feeding function, were identified and correlated with scallop size. The gill was initially homorhabdic, with unreflected inner demibranchs forming a basket-like structure maintained by ciliary junctions. Gill reflection, immediately followed by accelerated proliferation of gill filaments and formation of outer demibranchs, occurred at ~1 mm SH. Outer demibranchs were fully formed at ~2 mm SH. Suspension-feeding is probably rather inefficient prior to attaining 1–2 mm sizes. The onset of the heterorhabdic, adult form of the gill, which allows bidirectional particle transport and the potential for selection and for volume regulation of ingested material on the gill, occurred fairly late in development, at ~3.3–5.0 mm SH. Full development of gill plication was delayed until scallops attained ~7 mm. Gill differentiation in this species is thus relatively protracted and punctuated by critical transitional stages, which may be important in determining feeding and growth capacity of postlarval wild and cultured populations.

Postingestive sorting of living and heat-killed Chlorella within the sea scallop, Placopecten magellanicus (Gmelin)

Suspension-feeding bivalves may enhance the energy value of their food supply by sorting particles both before and after ingestion. Previous research has indicated that the sea scallop ( Placopecten magellanicus (Gmelin) (Mollusca: Bivalvia)) is capable of sorting particles within the gut both on the basis of physical properties (particle size and density) as well as chemical properties. In this study, the ability of the sea scallop to sort living from dead material solely on the basis of chemical properties was tested. The microalga Chlorella (Chlorophyta: Chlorophyceae) was chosen as the test particle because its thick cell wall remains physically intact following heat treatment, while its carbon, nitrogen, and chlorophyll a content declines. Scallops were fed a mixture of radiolabelled live and heat-killed Chlorella. We demonstrate that P. magellanicus can distinguish between living and dead algae, retaining live Chlorella cells longer than heat-killed cells. This ability to detect the subtle chemical differences between living algal material and detrital material would enhance the digestive efficiency of this species by reducing the amount of energy expended, digesting poor-quality materials. This paper presents the first study of the ability of a bivalve to distinguish between two physically identical but nutritionally different forms of the same species of microalgae.

Effects of substrate on interactions between juvenile sea scallops ( Placopecten magellanicus Gmelin) and predatory sea stars ( Asterias vulgaris Verrill) and rock crabs ( Cancer irroratus Say)

We investigated the effect of substrate (glass bottom, sand, granule, pebble) on predation of juvenile sea scallops ( Placopecten magellanicus) by sea stars ( Asterias vulgaris) and rock crabs ( Cancer irroratus) at two prey sizes (11–15 mm and 24–28 mm shell height), and two prey densities (10 and 30 scallops per aquarium) in laboratory experiments. Specifically, we quantified predation rate and underlying behaviours (proportion of time a predator spent searching for and handling prey, encounter rate between predators and prey, and various outcomes of encounters). We detected a significant gradual effect of particle size of natural substrates on sea star predation: specifically, predation rate on and encounter rate with small scallops tended to decrease with increasing particle size (being highest for sand, intermediate for granule, and lowest for pebble). Substrate type did not significantly affect predation rates or behaviours of sea stars preying on large scallops or of rock crabs preying on either scallop size classes. Other factors, such as prey size and density, were important in the scallop-sea star and scallop-rock crab systems. For example, predation rate by sea stars and crabs and certain sea star behaviours (e.g. probability of consuming scallops upon capture) were significantly higher with small scallops than with large scallops. As well, in interactions between small scallops and sea stars, predation rate and encounter rate increased with prey density, and the proportion of time sea stars spent searching was higher at low prey density than high prey density. Thus, substrate type may be a minor factor determining predation risk of seeded scallops during enhancement operations; prey size and prey density may play a more important role. However, substrate type still needs to be considered when choosing a site for scallop enhancement, as it may affect other scallop behaviours (such as movement).

Mobile fishing gear reduces benthic megafaunal production on Georges Bank

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 260:97-108 (2003) - doi:10.3354/meps260097 Mobile fishing gear reduces benthic megafaunal production on Georges Bank Jerome M. Hermsen1,3,*, Jeremy S. Collie1, Page C. Valentine2 1University of Rhode Island, Graduate School of Oceanography, Narragansett, Rhode Island 02882, USA 2US Geological Survey, 384 Woods Hole Road, Woods Hole, Massachusetts 02543, USA 3Present address: Fishery Statistics Office, Northeast Regional Office, National Marine Fisheries Sevice, 1 Blackburn Drive, Gloucester, Massachusetts 01930, USA *Email: jerome.hermsen@noaa.gov ABSTRACT: This study addresses the effect of mobile fishing gear disturbance on benthic megafaunal production on the gravel pavement of northern Georges Bank. From 1994 to 2000, we sampled benthic megafauna with a 1 m Naturalists¹ dredge at shallow (47 to 62 m) and deep (80 to 90 m) sites. The cessation of fishing in large areas of Georges Bank in January 1995 allowed us to monitor changes in production at a previously disturbed site. Production at a shallow disturbed site varied little over the sampling period (32 to 57 kcal m-2 yr-1) and was markedly lower than production at the nearby recovering site, where production increased from 17 kcal m-2 yr-1 in 1994 before the closure to 215 kcal m-2 yr-1 in 2000. Atlantic sea scallops Placopecten magellanicus and green sea urchins Strongylocentrotus droebachiensis dominated production at the recovering site. The community production:biomass ratio decreased over time at the recovering site as the sea scallop population matured. At the deep sites, production remained significantly higher at undisturbed sites (174 to 256 kcal m-2 yr-1) than at disturbed sites (30 to 52 kcal m-2 yr-1). The soft-bodied tube-building polychaete Thelepus cincinnatus dominated production at the undisturbed site, while hard-shelled bivalve molluscs Astarte spp. and P. magellanicus were prevalent at the disturbed site. Mobile fishing gear disturbance has a conspicuous effect on benthic megafaunal production in this hard-bottom habitat. Cessation of mobile fishing has resulted in a marked increase in benthic megafaunal production. These findings should help fishery managers to gauge the costs and benefits of management tools such as area closures and low-impact fishing gears. KEY WORDS: Benthic communities · Benthic production · Fishing impacts · Habitat disturbance · Scallop dredging Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 260. Online publication date: September 30, 2003 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2003 Inter-Research.

Comparison of cultured and wild sea scallops Placopecten magellanicus, using behavioral responses and morphometric and biochemical indices

As the survival of juvenile scallops released onto the seabed is of critical importance in programs seeking to enhance scallop populations, the basis of the vulnerability of seeded cultured scallops needs to be understood. High mortality rates following seeding operations could reflect weaker predator escape responses by cultured scallops. Thus, we compared behavioral responses as well as morphometric and biochemical measurements of cultured and wild sea scallops Placopecten magellanicus (35 to 45 mm shell height) sampled in August 1999 in the Gulf of St. Lawrence, eastern Canada. Cultured scallops had larger somatic tissues and higher muscle energetic contents than their wild counterparts. This may reflect the more favorable temperatures and better food supply during suspension culture. When faced with the starfish predator Asterias vulgaris, cultured scallops re- sponded with a greater number of claps, longer clapping period and faster recuperation of clapping performance. However, wild scallops had stronger shells and showed more intense escape responses (higher clapping rate) to the starfish. These differences contribute to making cultured scallops more vulnerable to predation by grasping predators (crabs) and asteroids.

Ontogenetic changes in gill morphology and potential significance for food acquisition in the scallop Placopecten magellanicus

Ontogenetic changes in gill morphology and potential significance for food acquisition in the scallop Placopecten magellanicus