Squalus Acanthias Research Articles

The use of satellite tags to redefine movement patterns of spiny dogfish (Squalus acanthias) along the U.S. east coast: implications for fisheries management.

Spiny dogfish (Squalus acanthias) are assumed to be a highly migratory species, making habitual north-south migrations throughout their northwestern Atlantic United States (U.S.) range. Also assumed to be a benthic species, spiny dogfish stock structure is estimated through Northeast Fisheries Science Center (NEFSC) bottom-trawl surveys. Recent anomalies in population trends, including a recent four-fold increase in estimated spawning stock biomass, suggest alternative movement patterns could exist for this shark species. To obtain a better understanding of the horizontal and vertical movement dynamics of this species, Microwave Telemetry pop-up satellite archival X-Tags were attached to forty adult spiny dogfish at the northern (Gulf of Maine) and southern (North Carolina) extents of their core U.S. geographic range. Reconstructed geolocation tracks ranging in lengths from two to 12 months suggest that the seasonal migration patterns appear to be local in nature to each respective northern and southern deployment site, differing from previously published migration paradigms. Differences in distance and direction traveled between seasonal geolocations possibly indicate separate migratory patterns between groups. Kernel utilization distribution models also suggest strong separate core home ranges. Significant differences in seasonal temperature and depths between the two regions further substantiate the possibility of separate regional movement patterns between the two groups. Vertical utilization also suggests distinct diel patterns and that this species may not utilize the benthos as previously thought, potentially decreasing availability to benthic gear.

Age at maturity of Mediterranean marine fishes

In this review we collected data on the age at maturity (tm) and maximum reported age (tmax) for 235 stocks of Mediterranean marine fishes, belonging to 82 species, 37 families, 12 orders and 2 classes (Actinopterygii and Elasmobranchii). Among Actinopterygii (mean tm ± SD = 2.20 ± 1.43 y, n = 215), tm ranged from 0.3 y, for the common goby Pomatoschistus microps, to 12 y, for dusky grouper Epinephelus marginatus, while among Elasmobranchii (mean tm ± SD = 5.94 ± 2.47 y, n = 20), tm ranged between 2.7 y, for brown ray Raja miraletus, and 12 y for picked dogfish Squalus acanthias. Overall, the tmax ranged between 1 y, for transparent goby Aphia minuta, and 70 y, for wreckfish Polyprion americanus. The mean tmax of Actinopterygii (tmax ± SD = 10.14 ± 9.42 y) was lower than that of Elasmobranchii (tmax ± SD = 14.05 ± 8.47 y). The tm exhibited a strong positive linear relation with tmax for both Actinopterygii (logtm = 0.58 ´ logtmax – 0.25, r2 = 0.51, P < 0.001) and Elasmobranchii (logtm = 0.67 ´ logtmax – 0.006, r2 = 0.51, P = 0.007). The mean tm/tmax did not differ significantly with sex within Actinopterygii (ANOVA: F = 0.27, P = 0.60, n = 90; females: mean ± SD = 0.276 ± 0.143; males: mean ± SD = 0.265 ± 0.138) and Elasmobranchii (ANOVA: F = 1.44, P = 0.25, n = 10; females: mean ± SD = 0.499 ± 0.166; males: mean ± SD = 0.418 ± 0.133). Finally, the dimensionless ratio tm/tmax was significantly lower (ANOVA: F = 31.04, P < 0.001) for Actinopterygii (mean ± SD = 0.270 ± 0.135, n = 180) than for Elasmobranchii, (mean ± SD = 0.458 ± 0.152, n = 20), when stocks with combined sexes were excluded from the analysis.

The influence of anthropogenic pollution on several indicators of congenital immunity and oxidizing processes in the liver of Squalus acanthias Linnaeus, 1758 (Pisces: Squalidae) that inhabit coastal waters of the Black Sea

The results of a study on several parameters of congenital immunity and oxidative processes in the liver of spiny dogfish Squalus acanthias that inhabit the Caucasus coastal waters of the Black Sea with various anthropogenic loads are described. The antimicrobial properties of serum, the content of non-specific immune complexes in the liver, the total lipid value, and antioxidant activity were studied. It was determined that the ratio of immunodeficient individuals was much higher in samples from the polluted areas than in samples from the clean ones. The fish sampled in areas of high anthropogenic load contained higher contents of products of lipid peroxidation and immune complexes, as well as lower values of antioxidants.

Sharks modulate their escape behavior in response to predator size, speed and approach orientation

Escape responses are often critical for surviving predator–prey interactions. Nevertheless, little is known about how predator size, speed and approach orientation impact escape performance, especially in larger prey that are primarily viewed as predators. We used realistic shark models to examine how altering predatory behavior and morphology (size, speed and approach orientation) influences escape behavior and performance in Squalus acanthias, a shark that is preyed upon by apex marine predators. Predator models induced C-start escape responses, and increasing the size and speed of the models triggered a more intense response (increased escape turning rate and acceleration). In addition, increased predator size resulted in greater responsiveness from the sharks. Among the responses, predator approach orientation had the most significant impact on escapes, such that the head-on approach, as compared to the tail-on approach, induced greater reaction distances and increased escape turning rate, speed and acceleration. Thus, the anterior binocular vision in sharks renders them less effective at detecting predators approaching from behind. However, it appears that sharks compensate by performing high-intensity escapes, likely induced by the lateral line system, or by a sudden visual flash of the predator entering their field of view. Our study reveals key aspects of escape behavior in sharks, highlighting the modulation of performance in response to predator approach.

Managing a Marine Stock Portfolio: Stock Identification, Structure, and Management of 25 Fishery Species along the Atlantic Coast of the United States

AbstractIn this review, stock identification methods used, resulting stock numbers and boundaries, and assessment and management context were explored for all 25 species managed by the Atlantic States Marine Fisheries Commission (ASMFC). This included invertebrates and vertebrates distributed between Maine and Florida, with a few species ranging across all these states and some ranging into the Gulf of Mexico and the Canadian Maritimes. The effects of larval dispersal or mixing of adults in the marine environment were evident. Marine and catadromous spawners were recognized and treated as a unit stock (e.g., northern shrimp Pandalus borealis, American Eel Anguilla rostrata, Atlantic menhaden Brevoortia tyrannus, Bluefish Pomatomus saltatrix, Tautog Tautoga onitis), a metapopulation (American lobster Homarus americanus, Atlantic Herring Clupea harengus), or two stocks, north and south of Cape Hatteras, a major biogeographic boundary, (Black Sea Bass Centropristis striata, Scup Stenotomus chrysops, Red Drum Sciaenops ocellatus, Summer Flounder Paralichthys dentatus). Estuarine and anadromous spawners were structured and managed at a finer spatial scale (horseshoe crab Limulus polyphemus, Atlantic Sturgeon Acipenser oxyrinchus, American Shad Alosa sapidissima and the river herrings Blueback Herring A. aestivalis and Alewife A. pseudoharengus, and Spotted Seatrout Cynoscion nebulosus). A broad suite of stock identification methods have been applied to ASMFC species and reviewed here in five categories: life history traits, other phenotypic traits, genetic traits, natural marks, and applied marks. An interdisciplinary mix of methods has been achieved for a few species (Striped Bass Morone saxatilis, Winter Flounder Pseudopleuronectes americanus), but only a few or no stock identification methods have been applied to others (Spiny Dogfish Squalus acanthias, Hickory Shad A. mediocris, Spot Leiostomus xanthurus, Spanish Mackerel Scomberomorus maculatus). Clinal phenotypic variation has contributed to several long‐standing debates about stock structure; some of these have been recently reevaluated as a unit stock (Atlantic Croaker Micropogonias undulatus, Weakfish Cynoscion regalis), and others are still debated. For some ASMFC species, other priorities (e.g., bycatch) dominate the uncertainty of the assessment or management process. Otherwise, stock identification remains a research priority for most of these species. Continued research of this subject should consider (1) research priorities tabulated by ASMFC review panels, (2) strategic use of interdisciplinary stock identification methods, (3) use of experiments or reaction norms to separate phenotypes from genotypes, (4) genetic surveys at a seascape scale, (5) demonstration of contingent (nongenetic) structure and its implications for management, and (6) simulation modeling. Obstacles to adopting finer‐scale structure into assessments or management of ASMFC fisheries include: (1) multiple stock units are apparent but boundaries are not clear, (2) monitoring requirements for smaller areas or for mixed‐stock catches are not cost effective, or (3) mixing rates within a metapopulation or across biogeographic boundaries are poorly described.Received May 8, 2013; accepted March 3, 2014

Sexual Segregation of Spiny Dogfish in Fishery‐Dependent Surveys in Cape Cod, Massachusetts: Potential Management Benefits

AbstractCommercial gill‐net and longline surveys were conducted in the Cape Cod, Massachusetts, area to assess whether the proportion of male Spiny Dogfish Squalus acanthias in the catch changes throughout a normal fishing day (an event frequently observed by local commercial longliners) and to identify the associated potential benefits for fishery management in the study area. Sex ratio changes were examined with respect to location (north and south of 42°N), environment (depth, surface and bottom temperatures, and salinity) and fishing (type of gear and time of activity). Spiny Dogfish showed differences in sex ratios (the proportion of males in the catch [PM]) that were related to location and type of fishing gear as well as to depth and time. Higher numbers of fish were caught with longlines, and higher numbers of males were caught in the southern area in inshore shallower waters early in the day. In the northern area, the sex distribution found within sets indicated a higher presence of females and a lower presence of males in shallower inshore waters. Changes in environmental parameters (depth and bottom temperature) were correlated with PM only in the south. A consistent seasonal (summer and early fall) diurnal shift in the sex ratio was found within 10 mi (16.1 km) of the east coast of the Cape Cod peninsula. This shift suggests that the implementation of a seasonal, male‐only directed longline fishery be considered for this location. Such a fishery would enhance the sustainability of the U.S. Atlantic Spiny Dogfish stock by reducing fishing pressure on adult females. The sex ratios observed suggest that sexual segregation in Spiny Dogfish in the Cape Cod area corresponds to female avoidance of males coupled with specific mating and/or feeding behavior by males.Received March 19, 2013; accepted November 20, 2013

Application of generalized additive models to examine ontogenetic and seasonal distributions of spiny dogfish (Squalus acanthias) in the Northeast (US) shelf large marine ecosystem

Increased commercial importance of spiny dogfish (Squalus acanthias) combined with an often debated, and controversial, ecological impact has warranted an investigation of the relationship among distribution, environment, and prey to better understand the species ecology and inform management. To elucidate mechanisms behind distributional changes, we modeled seasonal occurrence and abundance of neonate, immature, and mature spiny dogfish as functions of abiotic and biotic factors using generalized additive models and Northeast Fisheries Science Center bottom trawl survey data. Significant nonlinear relationships were widespread throughout dogfish stages and seasons. Seasonal occurrence was tightly linked to depth and bottom temperature, with year and Julian day influential for some stages. While these factors also influenced abundance, ecological factors (e.g., squid abundances) significantly contributed to trends for many stages. Potential impacts of climate change were evaluated by forecasting distributions under different temperature scenarios, which revealed higher regional probabilities of occurrence for most stages during a warmer than average year. Our results can be used to better understand the relationship between sampling periods and movement drivers to survey catchability of the population in the Northeast (US) shelf large marine ecosystem.

Fine-scale spatial patterns in the demersal fish and invertebrate community in a northwest Atlantic ecosystem

The abundance, biomass, diversity, and species composition of the demersal fish and invertebrate community in Rhode Island Sound and Block Island Sound, an area identified for offshore renewable energy development, were evaluated for spatial and seasonal structure. We conducted 58 otter trawls and 51 beam trawls in the spring, summer and fall of 2009–2012, and incorporated additional data from 88 otter trawls conducted by the Northeast Area Monitoring and Assessment Program. We used regionally-grouped abundance, biomass, diversity, and size spectra to assess spatial patterns in the aggregate fish community, and hierarchical cluster analysis to evaluate trends in species assemblages. Our analyses revealed coherent gradients in fish community biomass, diversity and species composition extending from inshore to offshore waters, as well as patterns related to the differing bathymetry of Rhode Island and Block Island Sounds. The fish communities around Block Island and Cox's Ledge are particularly diverse, suggesting that the proximity of hard bottom habitat may be important in structuring fish communities in this area. Species assemblages in Rhode Island and Block Island Sounds are characterized by a combination of piscivores (silver hake, summer flounder, spiny dogfish), benthivores (American lobster, black sea bass, Leucoraja spp. skates, scup) and planktivores (sea scallop), and exhibit geographic patterns that are persistent from year to year, yet variable by season. Such distributions reflect the cross-shelf migration of fish and invertebrate species in the spring and fall, highlighting the importance of considering seasonal fish behavior when planning construction schedules for offshore development projects. The fine spatial scale (10 s of kms) of this research makes it especially valuable for local marine spatial planning efforts by identifying local-scale patterns in fish community structure that will enable future assessment of the ecological impacts of offshore development. As such, this knowledge of the spatial and temporal structure of the demersal fish community in Rhode Island and Block Island Sounds will help to guide the placement of offshore structures so as to preserve the ecological and economic value of the area.

Notes on the occurrence of a rare Cardinal Fish at Coral Bay, Southern Palawan, Philippines

A team of researchers led by Haribon Palawan and the author with staff from DENR-PENRO, assisted by Coral Bay Nickel Corporation (CBNC) staff conducted coastal habitat monitoring in several areas of Coral Bay, southern Palawan in March 2008 and 2014, under the auspices of CBNC. While diving in one of the survey stations (Maranto Point), the author observed an unusual solitary fish, of which he has seen for the first time in his three-decade work in marine fishes of Palawan. The author took photographs of the fish under water to document fish occurence (Figure 1). The fish was found in a shallow (2-3 meters deep) reef patch off the Maranto Point, located west of the mouth of Rio Tuba River in Coral Bay, Southern Palawan. The exact location of the site was: Latitude, 8.50400o; Longitude, 117.28290o. Although A. griffini might have been previously recorded in Palawan waters, it has not appeared in the pictorial guides of Palawan fishes (Schroeder 1980; Gonzales 2013) Seale also described this species from Bantayan Island, Philippines in 1910. In January 2009, the fish photograph was sent to Dr. Kent Carpenter of the Department of Biological Science of the Old Dominion University, Virginia, USA for identification. After about a month, Dr. Carpenter identified the fish as Apogon griffini (Seale, 1910), a rarely seen kind of cardinal fish called northern spiny dogfish. Seale described this species from Bantayan Island, Philippines in 1910. The genus of this species was renamed to Ostorhinchus (Fishbase 2014). This cardinal fish is found only from the Philippines to Northern Borneo (Malaysia, Indonesia and Brunei), which is a relatively limited range of distribution for a marine fish. Ostorhinchus griffini is a fish native to Philippines. One alarming issue is that during the period of five-year underwater survey in Coral Bay, only one living individual of this fish species was recorded, found in a very restricted area of Coral Bay, indicating that the population of this fish species is at high risk in the area. The author again went with the same monitoring team to Coral Bay on March 23-28, 2014 and observed most probably the same solitary fish in the very same area at Maranto reef. Through fish visual estimate, the fish has grown three times its original length in 2008. Although the CITES status of this fish has not yet been evaluated (FishBase 2014), this fish needs some degree of protection, especially in its local population. Its habitat is further threatened being only about 50 m distance from the shore, fronting a fishing village, open to human activities. Possible flush flood from Rio Tuba River and rampant dynamite fishing in the bay are other threats to the existence of this fish species. Basing from its population status, area occupied, the extent where it occurs, and the threats it is facing, it is apparent that this species needs immediate protection in order to ensure its survival and prevent its loss in Coral Bay. Something has to be done to save this population, like protection of the Maranto Point coral reefs.

Mercury bioaccumulation in cartilaginous fishes from Southern New England coastal waters: Contamination from a trophic ecology and human health perspective

This study examined total mercury (Hg) concentrations in cartilaginous fishes from Southern New England coastal waters, including smooth dogfish (Mustelus canis), spiny dogfish (Squalus acanthias), little skate (Leucoraja erinacea), and winter skate (Leucoraja ocellata). Total Hg in dogfish and skates were positively related to their respective body size and age, indicating Hg bioaccumulation in muscle tissue. There were also significant inter-species differences in Hg levels (mean ± 1 SD, mg Hg/kg dry weight, ppm): smooth dogfish (3.3 ± 2.1 ppm; n = 54) > spiny dogfish (1.1 ± 0.7 ppm; n = 124) > little skate (0.4 ± 0.3 ppm; n = 173) ∼ winter skate (0.3 ± 0.2 ppm; n = 148). The increased Hg content of smooth dogfish was attributed to its upper trophic level status, determined by stable nitrogen (δ15N) isotope analysis (mean δ15N = 13.2 ± 0.7‰), and the consumption of high Hg prey, most notably cancer crabs (0.10 ppm). Spiny dogfish had depleted δ15N signatures (11.6 ± 0.8‰), yet demonstrated a moderate level of contamination by foraging on pelagic prey with a range of Hg concentrations, e.g., in order of dietary importance, butterfish (Hg = 0.06 ppm), longfin squid (0.17 ppm), and scup (0.11 ppm). Skates were low trophic level consumers (δ15N = 11.9–12.0‰) and fed mainly on amphipods, small decapods, and polychaetes with low Hg concentrations (0.05–0.09 ppm). Intra-specific Hg concentrations were directly related to δ15N and carbon (δ13C) isotope signatures, suggesting that Hg biomagnifies across successive trophic levels and foraging in the benthic trophic pathway increases Hg exposure. From a human health perspective, 87% of smooth dogfish, 32% of spiny dogfish, and <2% of skates had Hg concentrations exceeding the US Environmental Protection Agency threshold level (0.3 ppm wet weight). These results indicate that frequent consumption of smooth dogfish and spiny dogfish may adversely affect human health, whereas skates present minimal risk.

Feeding Habits, Daily Ration, and Potential Predatory Impact of Mature Female Spiny Dogfish in North Carolina Coastal Waters

AbstractThough the feeding habits of Spiny Dogfish Squalus acanthias in the northwestern Atlantic Ocean have received much attention due to their potential interactions with fisheries, currently no estimate of daily ration specific to the northwestern Atlantic population has been determined. To assess the diet of these sharks in the southern extent of their range, stomach contents were collected from 255 Spiny Dogfish captured by bottom trawl in nearshore North Carolina waters; 244 were mature females. Prey items were identified and percent index of relative importance was calculated for each prey taxon and category. To determine daily ration, 15 mature female Spiny Dogfish were captured by hook and line in North Carolina waters and kept in captivity for 2 weeks of feeding trials. Dogfish were fed preweighed frozen Atlantic Menhaden Brevoortia tryannus and allowed to digest their prey for predetermined periods, after which remaining food was removed using stomach‐tube gastric lavage. Gastric evacuation rates determined by feeding trials were combined with data collected from sampling stomach contents to determine the daily ration and the amount of important prey taxa consumed during the Spiny Dogfish overwintering period. Teleost fishes were the dominant prey category, and Atlantic Menhaden and Bay Anchovy Anchoa mitchilli were the most important prey taxa. Daily ration estimates ranged from 0.26% to 0.56% of the shark's body weight per day. Spiny Dogfish potentially consumed an equivalent of 1.55–3.33% of the Atlantic Menhaden stock while overwintering in North Carolina waters.Received July 23, 2013; accepted March 5, 2014

Active removal of inorganic phosphate from cerebrospinal fluid by the choroid plexus.

The P(i) concentration of mammalian cerebrospinal fluid (CSF) is about one-half that of plasma, a phenomenon also shown here in the spiny dogfish, Squalus acanthias. The objective of the present study was to characterize the possible role of the choroid plexus (CP) in determining CSF P(i) concentration. The large sheet-like fourth CP of the shark was mounted in Ussing chambers where unidirectional (33)P(i) fluxes revealed potent active transport from CSF to the blood side under short-circuited conditions. The flux ratio was 8:1 with an average transepithelial resistance of 87 ± 17.9 Ω·cm(2) and electrical potential difference of +0.9 ± 0.17 mV (CSF side positive). Active P(i) absorption from CSF was inhibited by 10 mM arsenate, 0.2 mM ouabain, Na(+)-free medium, and increasing the K(+) concentration from 5 to 100 mM. Li(+) stimulated transport twofold compared with Na(+)-free medium. Phosphonoformic acid (1 mM) had no effect on active P(i) transport. RT-PCR revealed both P(i) transporter (PiT)1 and PiT2 (SLC20 family) gene expression, but no Na(+)-P(i) cotransporter II (SLC34 family) expression, in the shark CP. PiT2 immunoreactivity was shown by immunoblot analysis and localized by immunohistochemistry in (or near) the CP apical microvillar membranes of both the shark and rat. PiT1 appeared to be localized primarily to vascular endothelial cells. Taken together, these data indicate that the CP actively removes P(i) from CSF. This process has transport properties consistent with a PiT2, Na(+)-dependent transporter that is located in the apical region of the CP epithelium.

The opening and closing mechanism of the spiracle in the spiny dogfish shark, Squalus acanthias (918.20)

Benthic sharks ventilate their gills by using a dual pump mechanism. They take water in by sequentially opening their spiracle and mouth, and expel water through their gills by closing their mouth and spiracle and compressing their oropharyngeal cavity (Hughes 1960). However, the mechanism of opening and closing the spiracle and the possible role of the pseudobranch are not fully understood. Therefore, we analyzed the functional morphology of the spiracle in a Spiny Dogfish Shark by micro‐dissection and digital imaging. The immovable edges of the spiracle are held in place by radially arranged subcutaneous collagen fibers. The spiracle is opened and closed by the spiracular flap, which is formed by the underlying spiracular muscle. In the closed spiracle, the spiracular flap and muscle are contracted, wide, and flat. When the chondrocranium is raised to open the mouth, the spiracular flap and muscle are stretched, elongated, and narrowed to open the spiracle and break the watertight seal within the oropharyngeal cavity. The spiracle closes when the mouth is closed by the contraction of the levator palatoquadrati, rostral levator hyomandibulae and spiracular muscles. The pseudobranch serves as a hydraulic cushion that ensures a watertight seal in the closed spiracle.Grant Funding Source: Supported by LSU Foundation to DGH

Influence of environmental, spatial, and ontogenetic variables on habitat selection and management of spiny dogfish in the Northeast (US) shelf large marine ecosystem

Declines in abundance of commercially valuable groundfish have highlighted the ecological and commercial importance of previously underutilized elasmobranchs in the Northeast (US) shelf large marine ecosystem (NES LME). Seasonal distributions and ontogenetic habitats of one such species, spiny dogfish (Squalus acanthias), were investigated using Northeast Fisheries Science Center (NEFSC) bottom trawl survey data (1963–2009). Neonate, immature, and mature dogfish all selected warmer, more saline, and more southerly locations during spring compared with available locations. During autumn, larger dogfish occupied relatively warmer, shallower, and less saline waters while neonates selected higher salinities. There were strong ontogenetic patterns in habitats occupied. Contrary to expectation, geographic range contracted as abundance increased during autumn. This suggests that niche constraints override density-dependent effects, although detection of relationships within stages was limited by low statistical power. The proportion of mature female survey catch within the Mid-Atlantic Bight was significantly related to temperature, suggesting that environmental conditions surveyed may impact population trends. Collectively, these results highlight critical habitats, suggest mechanisms behind ontogenetic habitat selection, and provide insight into how changing environmental conditions may impact stock assessment.

Thermal stability and refolding capability of shark derived single domain antibodies

Single-domain antibodies (sdAb) from camelids and sharks represent the smallest immunoglobulin-based functional binding domains, and are known for their thermal stability and ability to refold after denaturation. Whereas target-binding sdAb have been derived from both immunized and naïve sharks and camelids, the stability of camelid-derived sdAb have been evaluated much more extensively. To address this disparity we characterized 20 sdAb derived from spiny dogfish shark and smooth dogfish shark in terms of their protein production, melting temperature and ability to refold after heat denaturation. Using the same expression system and protocol as we follow to produce camelid sdAb, production of the shark sdAb was quite poor, often resulting in less than a tenth of the typical yield for camelid sdAb. We measured the melting temperature of each of the sdAb. Similar to camelid sdAb, the shark-derived sdAb, showed a range of melting temperature values from 42°C to 77°C. Also similar to what has been observed in camelids, the sdAb from both shark species showed a range of ability to refold after heat denaturation. This work demonstrated that although shark sdAb can possess high melting temperatures and refolding ability, no clear advantage over sdAb derived from camelids in terms of thermostability and renaturation was obtained.

Comparative squamation of the lateral line canal pores in sharks

The current study collected the first quantitative data on lateral line pore squamation patterns in sharks and assessed whether divergent squamation patterns are similar to experimental models that cause reduction in boundary layer turbulence. In addition, the hypothesis that divergent orientation angles are exclusively found in fast-swimming shark species was tested. The posterior lateral line and supraorbital lateral line pore squamation of the fast-swimming pelagic shortfin mako shark Isurus oxyrinchus and the slow-swimming epi-benthic spiny dogfish shark Squalus acanthias was examined. Pore scale morphology and pore coverage were qualitatively analysed and compared. In addition, pore squamation orientation patterns were quantified for four regions along the posterior lateral line and compared for both species. Isurus oxyrinchus possessed consistent pore scale coverage among sampled regions and had a divergent squamation pattern with multiple scale rows directed dorsally and ventrally away from the anterior margin of the pore with an average divergent angle of 13° for the first row of scales. Squalus acanthias possessed variable amounts of scale coverage among the sampled regions and had a divergent squamation pattern with multiple scale rows directed ventrally away from the anterior margin of the pore with an average angle of 19° for the first row of scales. Overall, the squamation pattern measured in I. oxyrinchus fell within the parameters used in the fluid flow analysis, which suggests that this pattern may reduce boundary layer turbulence and affect lateral line sensitivity. The exclusively ventral oriented scale pattern seen in S. acanthias possessed a high degree of divergence but the pattern did not match that of the fluid flow models. Given current knowledge, it is unclear how this would affect boundary layer flow. By studying the relationship between squamation patterns and the lateral line, new insights are provided into sensory biology that warrant future investigation due to the implications for the ecology, morphology and sensory evolution of sharks.

Seasonal dynamics of the cestode fauna in spiny dogfish,Squalus acanthias(Squaliformes: Squalidae)

This study furthers understanding of cestode infections in a marine environment through time and space by following seasonal fluctuations in infection parameters of three cestode species (Gilquinia squali, Trilocularia gracilis and Phyllobothrium squali) parasitizing spiny dogfish (Squalus acanthias) in the northwest Atlantic and comparing them to work previously published from the northeast Atlantic on T. gracilis. For each cestode species, host size, season and presence of the other cestode species were analysed using generalized linear models to determine if they were good predictors of prevalence and intensity. Infection parameters differed across season for the three cestode species. However, within T. gracilis seasonal trends were found to be remarkably similar on both sides of the Atlantic, differing only in a somewhat delayed decline in prevalence in the northwest Atlantic. The differences seen in infection measures across cestode species likely reflect the unique life history strategies of different parasite species. While general trends appear to be maintained across disparate localities, variation seen is likely due to differences in accessibility to intermediate hosts and host diet across sites. The knowledge gained from understanding cestode infections in the vast ocean environment allows us to speculate about the factors driving fluctuations in parasite infections in elasmobranchs.

Time course of the acute response of the North Pacific spiny dogfish shark (Squalus suckleyi) to low salinity

Dogfish are considered stenohaline sharks but are known to briefly enter estuaries. The acute response of North Pacific spiny dogfish (Squalus suckleyi) to lowered salinity was tested by exposing sharks to 21‰ salinity for 48h. Temporal trends in blood pH, plasma osmolality, CO2, HCO3−, Na+, Cl−, K+, and urea concentrations, and in the rates of urea efflux and O2 consumption, were quantified. The rate of O2 consumption exhibited cyclic variation and was significantly depressed by lowered salinity. After 9h, plasma [Cl−] stabilized at 9% below initial levels, while plasma [Na+] decreased by more than 20% within the first 12h. Plasma [urea] dropped by 15% between 4 and 6h, and continued to decrease. The rate of urea efflux increased over time, peaking after 36h at 72% above the initial rate. Free-swimming sharks subjected to the same salinity challenge survived over 96h and differed from cannulated sharks with respect to patterns of Na+ and urea homeostasis. This high-resolution study reveals that dogfish exposed to 21‰ salinity can maintain homeostasis of Cl− and pH, but Na+ and urea continue to be lost, likely accounting for the inability of the dogfish to fully acclimate to reduced salinity.

Non-Genotoxic Assessment of a Natural Antimicrobial Agent: Squalamine

Squalamine, a natural aminosterol compound isolated from the dogfish shark Squalus acanthias, is reported to possess high antimicrobial activities. Herein, we assessed its in vitro genotoxic properties by using the Ames test and the micronucleus assay. All the experimental results demonstrate that squalamine is a non genotoxic molecule and call for further work to evaluate its potent human therapeutic use as a new class of antinfectious agents. Keywords: Ames test, antimicrobial agent, non-genotoxic, squalamine.

Bounds on Biomass Estimates and Energetic Consequences of Ctenophora in the Northeast U.S. Shelf Ecosystem

Previous descriptions have noted that the stomach samples of spiny dogfish, Squalus acanthias, showed a major increase in the overall occurrence and hence implied abundance of Ctenophora. This apparent and persistent gelatinous zooplankton outbreak is increasingly more common in the world’s oceans. We briefly explore the energetic ramifications of ctenophores in the spiny dogfish diet, inferring that the presence of gelatinous zooplankton represents an ambient feeding strategy. Relative to other prey, ctenophores are not a high energy density prey item. However, given varying assumptions of the amount of ctenophores consumed, they may be an important staple in the diet of spiny dogfish. We also examine the utility of using spiny dogfish as a gelatinous zooplankton sampling device. Using five calculation methodologies, we provide bounds on potential abundance and biomass estimates of ctenophores in the Northeast U.S. shelf ecosystem. We then contextualize these findings relative to the implications for the Northeast U.S. and any large marine ecosystem.