Dogfish Squalus Acanthias Research Articles

Mophological description of the parasitic copepod Pandarus boscii (Siphonostomatoida: Pandaridae) found on the Picked dogfish Squalus acanthias (Squaliformes: Squalidae) in Turkish waters

Pandarus boscii was previously reported in Mustelus mustelus (basionym: Squalus mustelus), but the original description of P. boscii was incomplete and inadequate. P. boscii is currently accepted as a synonym of Pandarus bicolor. Females of P. boscii differ in that the body is colorless or pale (in P. bicolor the cephalothorax is brown and the dorsum is yellow), the first and distal segments of the antennule have 23-25 plumose setae and 12 setae, respectively (in P. bicolor are 24-26 plumose setae and 13 setae), mandibular blade with 7-8 teeth (in P. bicolor are 8 teeth), maxilliped with one seta (in P. bicolor absent), proximal exopodal segment of the second leg with 5 spines (in P. bicolor are 6 spines). Significant differences were observed between male individuals of the two species, such as: smaller total body measuring 3.5 mm in length (in P. bicolor 3.9 mm), first and distal segments of the antennule with 15-17 plumose setae and 14 setae, respectively (in P. bicolor 26-27 plumose setae and 12 setae), mandibular blade with 7 teeth (in P. bicolor are 8), first antennal segment with one process and maxilliped with one seta (in P. bicolor absent), leg 5 with one naked and one plumose seta (in P. bicolor 3 plumose setae and a robust seta), distal exopodal segment of 3 and 4 legs with 2 spines (in P. bicolor 4 spines), distal endopodal segment of 3 and 4 legs with 4 and 3 setae, respectively (in P. bicolor with 5 and 4 setae). A detailed description of P. boscii is provided from individuals found on the body surface and fins of the spiny dogfish Squalus acanthias, recently collected in the Sea of Marmara, Turkey. Therefore, according to the results Pandarus boscii and P. bicolor are different species.

Leopard Seals (Hydrurga leptonyx) in New Zealand Waters Predating on Chondrichthyans

Leopard seals (Hydrurga leptonyx) are top-order predators that prey on a wide variety of species including crustaceans, cephalopods, fishes, birds, and pinnipeds. While multiple diet studies have been conducted worldwide, there are no previous accounts of leopard seals predating on chondrichthyans. As part of a wider study on the diet of leopard seals in New Zealand (NZ) waters, researchers and citizen scientists recorded 39 observations of predation and collected 127 scats (166 total records) between 1942 and 2019. Predation on chondrichthyans was detected in 23.1% (n = 9) of observations of predation and 7.1% (n = 9) of scats (the latter via morphological examination and DNA sequencing). From both observations of predations and scats, three chondrichthyan species or genus were identified; elephantfish (Callorhinchus milii), ghost sharks (Hydrolagus spp.) and spiny dogfish (Squalus acanthias). While this is the first published record of leopard seals feeding on chondrichthyans, the relatively high frequency of occurrence within our NZ records, and that certain individuals appeared to target this type of prey, indicates that these species could constitute a substantial, or important, part of the diet for some leopard seals in this region. As chondrichthyans form an important part of the NZ marine ecosystems, our recognition of an additional top-order predator of these species contributes to understanding the overall health of, and future impacts of predators on, the wider NZ marine ecosystem.

Gastric Evacuation Rates of Spiny Dogfish, Goosefish, and Summer Flounder: Implications for Multispecies Models

AbstractThe gastric evacuation rates of Spiny Dogfish Squalus acanthias, Summer Flounder Paralichthys dentatus and Goosefish Lophius americanus held at two different temperatures were determined in the laboratory by gastric lavage. Overall, exponential models provided the best fit for the evacuation rates. The Spiny Dogfish, an elasmobranch, evacuated more slowly than the Summer Flounder (a teleost) but the Goosefish, also a teleost, had the slowest evacuation rate of the three species. The Goosefish evacuation rate was nearly ten times slower than that of Summer Flounder. Evacuation was more rapid at the higher temperature tested in all three species. At 15°C, Summer Flounder had the highest average evacuation rate (0.094 exponential rate of decline), followed by Spiny Dogfish (0.063 exponential rate of decline), and then Goosefish (0.018 exponential rate of decline). Among the three species, activity levels and feeding behaviors are also very different, contributing to differences in evacuation rate. Species‐specific parameters of evacuation rate should be considered to better inform multispecies and ecosystem models and to more accurately estimate consumption and prey removal rather than using broad taxonomic groupings as in current common practice.

Observations on Bycatch Rate for Vulnerable Fish Species on the Romanian Coast

"Living marine resources obviously contribute to the survival of humanity. Unfortunately, numerous studies highlighted that marine biological diversity faces various threats related to overfishing and illegal fishing, pollution (marine and terrestrial), invasive species, marine litter and climate change. In this context, the incidental catch of vulnerable species (i.e., elasmobranchs, marine mammals, seabirds) is considered one of the main threats to good environmental condition of the marine fauna.The aim of the study conducted in 2020, was to highlight the impact of fishing activities on aquatic resources, especially on vulnerable fish species as picked dogfish Squalus acanthias), thornback ray (Raja clavata) and common stingray (Dasyatis pastinaca), marine mammals and seabirds. The background information was collected by observations from scientific trawl surveys by pelagic and demersal trawl gears, observations from stationary fishing points, observations from commercial beam-trawl fishing operations. The analysis of logbooks of several economic operators and data collected by observers on board vessels, highlighted the low bycatch rate for vulnerable species in most fishing gear. Key Words: vulnerable species, by-catch, fishing gear "

Spiny Dogfish (Squalus Acanthias): Changes in Structural and Mechanical Properties Under Storage

Fresh histological sections of the Black Sea spiny dogfish have been examined using a 500xSDM electron microscope. Experimental histological sections of the Black Sea spiny dogfish have been made along and across muscle fibers. Sections of skin and adipose tissue between the skin and the muscle have also been examined. PH value in the spiny dogfish muscle layers has been measured using a Kelilong Electron pH-150MI device. Thus, there are three zones determined: the first one is within 24-42 hours of storage with a pH ranging from 6,77; the second one – 46-78 hours with a pH in the range of 6,55; the third one – from 85 to 97 hours of storage with a pH of 6,41. The study of the elastic properties of fish is a study of the deformation properties. Regularities of change of rheological properties of fish depending on term and temperature mode of storage have been established. Graphs of values of deforming force of samples of different shelf life have been obtained, comparison of deformation time and size of deforming values have been made. Results of physical properties are placed in the process of optimizing the parameters of shelf life of the spiny dogfish. Mathematical models describing changes in the basic physicochemical properties of spiny dogfish in different storage parameters are.

Seasonal Presence of Atlantic Sturgeon and Sharks at Cape Hatteras, a Large Continental Shelf Constriction to Coastal Migration

AbstractCape Hatteras is a major topographic feature on the continental shelf of the U.S. eastern seaboard that changes the dynamics of nearshore large ocean currents, including the Labrador Current and Gulf Stream. Cape Hatteras constricts shelf habitat and restricts the migratory corridors of highly migratory species through this area. Our objective was to describe the seasonal patterns of presence for three species—the Spiny Dogfish Squalus acanthias, Atlantic Sturgeon Acipenser oxyrinchus oxyrinchus, and Sandbar Shark Carcharhinus plumbeus—and analyze environmental conditions associated with fish presence near this feature. These species are managed under the Magnuson–Stevens Act, and two of them are also listed as species of concern under the Endangered Species Act. Transmitter detections from tagged fish recorded by the Cape Hatteras acoustic array, which was deployed just south of the cape, indicated that these species are present year‐round. The greatest number of detections occurred from November through April. This simple baseline of seasonal presence can provide insights for regional offshore development activities, which have the potential to affect movement patterns of migratory species through the Cape Hatteras constriction. Our results show the value of strategically placed acoustic arrays for observing fish habitat use and provide presence/absence data to enhance our understanding of species ecology and distribution.

Methylmercury Levels in Commercially Harvested Spiny Dogfish Captured off the Coast of Massachusetts

Abstract Spiny Dogfish Squalus acanthias are small sharks that are harvested for seafood, primarily off the Eastern Seaboard of the United States. For the purposes of establishing seafood consumption advisories with regard to methylmercury (MeHg) content, the U.S. Food and Drug Administration (FDA) classifies Spiny Dogfish as “sharks,” an overly broad taxonomic grouping with a mean MeHg content of 0.98 μg/g wet weight. Because the FDA mean includes fishes of different species that have been collected internationally over the last four decades, there is reason to believe that the FDA mean value is not reflective of the fish harvested in the Spiny Dogfish fishery. To evaluate how closely Spiny Dogfish match the values in the FDA’s generic shark category, we collected muscle samples from 102 commercially harvested Spiny Dogfish caught off Cape Cod, Massachusetts, during the 2018 fishing season. Among the fish we sampled, 100% had MeHg concentrations lower than the FDA mean for sharks and 77.5% had MeHg concentrations that the FDA considers safe for consumption at a frequency of once per week. The mean MeHg concentration in our samples was 0.378 μg/g wet weight, less than half of the value for the generic shark category. Moreover, through a comparison with data from the 1970s, we documented a 30% decline in MeHg concentrations for select size categories of Spiny Dogfish captured off the coast of New England. Exposure simulations indicated that to minimize risk, Spiny Dogfish should be consumed no more than twice per month by most people.

Sugar uptake, metabolism, and chloride secretion in the rectal gland of the spiny dogfish Squalus acanthias.

The rectal gland of the spiny dogfish Squalus acanthias secretes a salt solution isosmotic with plasma that maintains the salt homeostasis of the fish. It secretes salt against an electrochemical gradient that requires the expenditure of energy. Isolated rectal glands perfused without glucose secrete salt, albeit at a rate about 30% of glands perfused with 5 mM glucose. Gradually reducing the glucose concentration is associated with a progressive decrease in the secretion of chloride. The apparent Km for the exogenous glucose-dependent chloride secretion is around 2 mM. Phloretin and cytochalasin B, agents that inhibit facilitated glucose carriers of the solute carrier 2 (Slc2) family such as glucose transporter 2 (GLUT2), do not inhibit the secretion of chloride by the perfused rectal glands. Phloridzin, which inhibits Slc5 family of glucose symporters, or α-methyl-d-glucoside, which competitively inhibits the uptake of glucose through Slc5 symporters, inhibit the secretion of chloride. Thus the movement of glucose into the rectal gland cells appears to be mediated by a sodium-glucose symporter. Sodium-glucose cotransporter 1 (SGLT1), the first member of the Slc5 family of sodium-linked glucose symporters, was cloned from the rectal gland. No evidence of GLUT2 was found. The persistence of secretion of chloride in the absence of glucose in the perfusate suggests that there is an additional source of energy within the cells. The use of 2-mercapto-acetate did not result in any change in the secretion of chloride, suggesting that the oxidation of fatty acids is not the source of energy for the secretion of chloride. Perfusion of isolated glands with KCN in the absence of glucose further reduces the secretion of chloride but does not abolish it, again suggesting that there is another source of energy within the cells. Glucose was measured in the rectal gland cells and found to be at concentrations in the range of that in the perfusate. Glycogen measurements indicated that there are significant stores of glucose in the rectal gland. Moreover, glycogen synthase was partially cloned from rectal gland cells. The open reading frame of glycogen phosphorylase was also cloned from rectal gland cells. Measurements of glycogen phosphorylase showed that the enzyme is mostly in its active form in the cells. The cells of the rectal gland of the spiny dogfish require exogenous glucose to fully support the active secretion of salt. They have the means to transport glucose into the cells in the form of SGLT1. The cells also have an endogenous supply of glucose as glycogen and have the necessary elements to synthesize, store, and hydrolyze it.

Genetic characterisation of the spiny dogfish Squalus acanthias in the Adriatic Sea: evidence for high genetic diversity and an Atlantic–South Pacific origin

Spiny dogfish Squalus acanthias is a widely distributed, highly migratory mesopredatory shark that is extremely sensitive to overexploitation. Because of unregulated targeted and incidental capture and a lack of enforceable management in the Mediterranean Sea, the spiny dogfish subpopulation has declined by at least 50% in the Mediterranean Sea over the past 75–105 years, and is regionally classified as endangered. In this study we sampled 124 spiny dogfish in the northern-most part of the Mediterranean (i.e. the Adriatic Sea) to: (1) assess levels of genetic diversity using 13 microsatellite loci and mitochondrial (mt)DNA (NADH dehydrogenase subunit 2 (ND2) gene); and (2) infer its evolutionary placement while assessing further possible genetic divergence across the Atlantic and Pacific Ocean basins based on ND2. Analysis of mtDNA revealed 12 unique haplotypes and a high level of genetic variation in the Mediterranean region, whereas results from microsatellite markers showed significant genetic heterogeneity and a fine-scale stock structuring involving both sexes. The findings support an Atlantic–South Pacific origin for the spiny dogfish in the Adriatic Sea, with little or no present-day connectivity with the Atlantic population. Consequently, this commercially exploited and regionally endangered coastal shark in the Adriatic Sea should be considered as a separate management unit, with implementation of regional protective management plans.

Life-history traits of the spiny dogfish Squalus acanthias in the Adriatic Sea

Pivotal life history traits concerning age structure and reproduction of the spiny dogfish (Squalus acanthias, Linnaeus 1758) were investigated in the Adriatic Sea from mid February 2012 to mid July 2013 and in 2016. The whole sample consisted of 176 females and 150 males, ranging between 217–1025 mm and 219–875 mm, respectively. The individual age, which was estimated using a cross-sectioning technique of the second dorsal-fin spine, ranged from 0 to 13+ years for females and from 0 to 9+ years for males. Based on the length-at-age estimates, the Gompertz growth parameters were L∞ = 1130 mm, k = 0.18 and L∞ = 920 mm, k = 0.24 for females and males, respectively. The size at sexual maturity (L50) was 659 mm for females and 575 mm for males, corresponding to 7.5 and 5.5 years of age (A50), respectively. Mean biennial fecundity was approximately 11 embryos/female and 12 ripe oocytes/female. Mature males occurred during much of the sampling period, while mature females with nearly full-term embryos were exclusively recorded in May 2013 and July 2016. Monitoring of catches conducted in a sample port of the north Adriatic (Chioggia) over the past 20 years has shown fluctuating trends in landings, with peaks during the summer reproductive season.

Ultrastructure of Intestinal Epithelium in Cartilaginous Fish

By means of electronic microscopy, the structural distinctions of epithelial cells are revealed in three species of cartilaginous fish differing in their foraging: spiny dogfish Squalus acanthias (a typical fish predator), common stingray Dasyatis pastinaca, and thornback ray Raja clavata (benthos eaters-facultative fish predators). In the spiny dogfish, the length of microvillu in the brush border of enterocytes in the medial region of the spiral intestine is smaller than in Dasyatis pastinaca and Raja clavata (0.66 ± 0.05 vs. 1.16 ± 0.07 and 1.04 ± 0.10 μm) and their diameter, on the contrary, is greater (0.10 vs. 0.08 and 0.07 μm). In Dasyatis pastinaca, there is a well-developed glycocalix and the distal decrease of microvilli length. The role of the brush border enetocytes in the increase of digestive and transport surface of the intestine, as well as the role of particular organelles in digestions and transport of nutrients in the investigated fish, is discussed.

An Analysis of Extraocular Muscle Forces in the Piked Dogfish (Squalus acanthias).

Vertebrates utilize six extraocular muscles that attach to a tough, protective sclera to rotate the eye. The goal of the study was to describe the maximum tetanic forces, as well as the torques produced by the six extraocular muscles of the piked dogfish Squalus acanthias to understand the forces exerted on the eye. The lateral rectus extraocular muscle of Squalus acanthias was determined to be parallel fibered with the muscle fibers bundled into discrete fascicles. The extraocular muscles attach to the sclera by muscular insertions. The total tensile forces generated by the extraocular muscles ranged from 1.18 N to 2.21 N. The torques of the extraocular muscles ranged from 0.39 N to 2.34 N. The torques were greatest in the principal direction of movement for each specific muscle. The lateral rectus produced the greatest total tensile force, as well as the greatest torque force component, while the medial rectus produced the second greatest. This is likely due to the constant rotational movement of the eye anteriorly and posteriorly to stabilize the visual image, as well as increase the effective visual field during swimming. Rotational forces in dimensions other than the primary direction of movement may contribute to motion in directions other than the principal direction during multi-muscle contraction that occurs in the vertebrate eye. Anat Rec, 2018. © 2018 Wiley Periodicals, Inc. Anat Rec, 302:837-844, 2019. © 2018 Wiley Periodicals, Inc.

Fecundity and Embryonic Development of Spiny Dogfish in the Northwest Atlantic Ocean

AbstractWe investigated the fecundity and embryonic development of Spiny Dogfish Squalus acanthias (68.8–88.4 cm TL; n = 49) caught in the northwest Atlantic Ocean off Long Island, New York, between October 2014 and January 2015. Ovarian fecundity ranged from 0 to 6 eggs, whereas uterine fecundity ranged from 0 to 7 embryos. The average ovarian fecundity and uterine fecundity were equal at 4.1, and fecundity increased with maternal body length. All ovarian eggs and embryos in an individual female were at the same stage of development. Ovarian eggs (n = 200) ranged from 1.4 to 4.9 cm in diameter and weighed between 1.3 and 39 g. Embryos (n = 200) ranged from 8.6 to 27.5 cm TL and weighed between 2 and 74 g. The sex ratio of the embryos (female : male) was 1.17:1.00; however, within individual females, one sex dominated over the other. The development of ovarian eggs was concurrent with embryo development. The data collected in this study can be used in future stock assessments for the northwest Atlantic Spiny Dogfish population.

A pilot study of multiple paternity in three litters of spiny dogfish (Squalus acanthias) off the South Carolina/Georgia coast

The spiny dogfish (Squalus acanthias) is the target of the largest U.S. shark fishery where stock size is monitored and assessed. Understanding and defining regional populations is essential to conservation efforts. Previous work on spiny dogfish in U.S. waters has concentrated on sampling from New England and the North Carolina/Virginia coast. The migratory habits and reproductive traits of these sharks have been described, but little can be found about the southernmost part of the population, including those occupying the coast of South Carolina and Georgia. This pilot study investigated the reproductive biology of the spiny dogfish in the southernmost region. Three family groups of spiny dogfish were sampled and five microsatellite loci were used to screen for multiple paternity. Both litter size and overall genetic diversity were consistent with values reported in other parts of the range. In addition, no evidence of multiple paternity or parthenogenesis was found in the three family groups. The analysis of additional samples will provide clarity about the southern population and contribute to effective population management.

Habitat partitioning and diurnal-nocturnal transition in the elasmobranch community of a North Carolina estuary

In marine communities, resource partitioning can be as important as abiotic environmental preferences in determining habitat use patterns. Elasmobranchs are generally assumed to be crepuscular or nocturnal, but diel temporal habitat partitioning is poorly studied in this group. We attempted to identify habitat preferences and find evidence of resource partitioning among the elasmobranch community in Back and Core Sounds, North Carolina, using a multi-gear, fishery-independent survey with a temporal focus on the diurnal-nocturnal transition. Gillnet, longline, drumline, and rod-and-reel sampling captured a total of 160 elasmobranchs, representing 12 species within the estuary, and differences between the seven most abundant species were assessed in terms of temporal, environmental, and spatial habitat factors. The elasmobranch community was broadly divided into cool and warm temperature assemblages. Most species showed evidence of generalist habitat preferences, but spatial overlap between species was generally low. Blacknose sharks [Carcharhinus acronotus (Poey,1860)] appeared to be nocturnal, and aggregations of smooth dogfish [Mustelus canis (Mitchill,1815)] and spiny dogfish (Squalus acanthias Linnaeus, 1758) were found during mid-afternoon hours. Blacknose sharks and blacktip sharks [ Carcharhinus limbatus (Muller and Henle,1839)] showed evidence of spatial resource partitioning based on distance from the nearest inlet. Temperature appears to be a strong influence on the presence of elasmobranch species within Back and Core Sounds, but behavioral interspecific avoidance may be a greater influence on fine-scale habitat use by elasmobranchs in this estuarine system.

Life history aspects of two species of the Squalus genus in the Eastern Ionian Sea

Data on life history aspects of two species of Squalus genus were collated from five different studies carried out in the Eastern Ionian Sea from 1995 to 2014. Data were collected from 948 longnose spurdogs Squalus blainville (Risso, 1827) and 65 spiny dogfish Squalus acanthias Linnaeus, 1758 caught by trawl and longlines. The mean length of both species increased with depth. Sexual segregation was observed for S. blainville, whereas a segregation of immature and mature individuals was detected for S. acanthias. The length–weight relationship for S. blainville indicated positive allometry (b > 3) for both sexes, whereas a negative allometry (b < 3) was found for S. acanthias for the combined sexes. The sex ratio of both species was in favour of males. For S. blainville, the gonadosomatic and hepatosomatic indices differed significantly between sexes but not between seasons with the maturity data supporting the hypothesis of continuous reproduction throughout the year. Length at first maturity (L50) for female and male S. blainville was 603 and 413 mm respectively. For S. acanthias, males collected in autumn had finished their spawning activity; the single specimen caught in summer was reproductively active. Females, caught only in summer, were all gravid. Prey identified in the stomachs of S. blainville belonged to three major groups: fish, cephalopods and shrimps. Other groups such as echinoderms and ascidians were also found. Identified prey in the stomachs of S. acanthias belonged to two main groups, fish and cephalopods, although other groups (including echinoderms and polychaetes) were also present.

Potential role of spiny dogfish in gray and harbor seal diets in the Gulf of Maine

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 550:249-270 (2016) - DOI: https://doi.org/10.3354/meps11718 Potential role of spiny dogfish in gray and harbor seal diets in the Gulf of Maine Carrie Byron*, Alexia Morgan Marine Science Center, University of New England, 11 Hills Beach Road, Biddeford, ME 04005, USA *Corresponding author: cbyron@une.edu ABSTRACT: Harbor seal Phoca vitulina and gray seal Halichoerus grypus populations have increased by 28.7% (1997-2001) and 8.6% (1999-present), respectively, in the Gulf of Maine. Here, we investigated what seals are eating and how their diet influences the food web in the Gulf of Maine. There is suggestion, but little evidence, that seals are eating spiny dogfish Squalus acanthias, currently an abundant species (standing stock biomass = 235000 t) in the Gulf of Maine and surrounding areas. We used an Ecopath food web model to explore the potential of dogfish being a primary food source for seals and how this may be impacting the ecosystem. We explored various plausible diets for seals and the implications for other non-prey species in the ecosystem. In addition, white sharks Carcharodon carcharias have increased in abundance regionally, and shark predation on seals is documented in the southern Gulf of Maine. We therefore also explored top-down impacts of white shark predation on seals and lower trophic level fish species. Our results suggest that (1) dogfish could be contributing to the recovery of seal populations by providing an alternative prey base, (2) there is a tipping point between 10 and 20% of dogfish in seal diet that elicits a linearly increasing trend in seal biomass over time, and (3) seals as prey will have a continued impact on the projected increase in white shark biomass. This work advances our understanding of top-down control and may help to inform fisheries and resource management. KEY WORDS: Food web · Ecopath with Ecosim · Phoca vitulina · Halichoerus grypus · Squalus acanthias · Cod · White shark · Carcharodon carcharias Full text in pdf format Supplementary material PreviousCite this article as: Byron C, Morgan A (2016) Potential role of spiny dogfish in gray and harbor seal diets in the Gulf of Maine. Mar Ecol Prog Ser 550:249-270. https://doi.org/10.3354/meps11718 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 550. Online publication date: May 25, 2016 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2016 Inter-Research.

Reproductive and population parameters of spiny dogfish Squalus acanthias in the south-western Atlantic Ocean.

The objective of this study was to estimate reproductive and population parameters of the spiny dogfish Squalus acanthias for the south-western Atlantic Ocean. In total, 2714 specimens (1616 males and 1098 females) were collected from surveys carried out using research vessels. Males ranged from 225 to 861 mm total length (LT ) and females from 235 to 925 mm LT . The size at maturity of females (651 mm) was significantly greater than that of males (565 mm). The maximum proportion of mature individuals (Pmax ) of the gestation ogive was <1, which indicates that a proportion of mature females was not in gestation. This inactivity may be explained by the occurrence of resting periods between cycles or by the asynchrony of the reproductive cycle. The estimated Pmax for the maternity ogive suggested that about one third of mature females were in the maternity stage (i.e. with embryos >156 mm). The temporal and spatial co-occurrence of non-gravid adult females at different stages of ovarian development, as well as gravid females at all embryonic development stages would indicate that the female reproductive cycle in the south-western Atlantic Ocean is asynchronous. The results indicate that S. acanthias is susceptible to fishing pressure on account of its length at maturity, extended reproductive cycles and low fecundity.

Diel Variations in Survey Catch Rates and Survey Catchability of Spiny Dogfish and their Pelagic Prey in the Northeast U.S. Continental Shelf Large Marine Ecosystem

This study examines the potential uncertainty in survey biomass estimates of Spiny Dogfish Squalus acanthias in the Northeast U.S. Continental Shelf Large Marine Ecosystem (NES LME). Diel catch-per-unit-effort (CPUE) estimates are examined from the Northeast Fisheries Science Center bottom trawl surveys conducted during autumn (1963–2009) and spring (1968–2009). Influential environmental variables on survey catchability are identified for Spiny Dogfish life history stages and five pelagic prey species: Butterfish Peprilus triacanthus, Atlantic Herring Clupea harengus, shortfin squid Illex spp., longfin squid Doryteuthis spp., and Atlantic Mackerel Scomber scombrus. Daytime survey catchability was significantly higher than nighttime catchability for most species during autumn and for mature male Spiny Dogfish, shortfin squid, and longfin squid during spring in the NES LME. For most stages and species examined, breakpoint analyses identified significant increases in CPUE in the morning, peak CPUE during the day, and significant declines in CPUE in the late afternoon. Seasonal probabilities of daytime catch were largely driven by solar zenith angle for most species, with stronger trends identified during autumn. Unadjusted CPUE estimates appear to overestimate absolute abundance, with adjustments resulting in reductions in absolute abundance ranging from 41% for Spiny Dogfish to 91% for shortfin and longfin squids. These findings have important implications for Spiny Dogfish regarding estimates of population consumption of key pelagic prey species and their ecological footprint within the NES LME. Received February 25, 2015; accepted December 16, 2015

Population structure of the piked dogfish Squalus acanthias (Elasmobranchii: Squalidae), with preliminary reproductive observations

Squalus acanthias has been poorly studied in Uruguay, though reproductive studies have been carried out in Argentina in the decades of 1970–1980. The aim of this work was to analyze the population structure and the reproductive biology of S. acanthias along the Uruguayan continental shelf (south-western Atlantic Ocean) between 1995 and 2010. Total length (TL) ranged from 30–95 cm for females (n = 1,323) and 25–81 cm for males (n = 999). Significant differences in the TL frequency distributions between sexes and among seasons were detected, with abundances in the magnitude of up to 5,000 individuals/nm2. Length at first maturity (TL50) was 58.3 cm in males and 70.4 cm in females. Ovarian and uterine fecundity were 2–14 and 1–14, respectively, and both were positively correlated with maternal TL. Females with candled embryos were recorded in autumn. Embryo TL was significantly greater in winter, which is when parturition is likely occurring. Full-term embryos had a TL of 22–25 cm. Sex ratio of embryos was close to parity. Ovarian vitellogenesis was observed to be occurring concomitantly with gestation.