Smooth Dogfish Mustelus Canis Research Articles

Size Changes within a Southeastern United States Coastal Shark Assemblage: 1975–2018

AbstractHarvest may have myriad effects on target species, including a change in population size structure. To assess whether size shifts have occurred among managed coastal species of shark (superorder Selachimorpha), we examined the population size structure of 12 species caught during a nearly five‐decade‐long fishery‐independent survey conducted in Onslow Bay, North Carolina, using standardized longline gear. We evaluated trends in mean fork length (FL), median FL, and index of maximum FL (L90%) for each species separately across time using linear regression models. We also examined trends in size‐classes (200‐mm bins) and catch per unit effort for each species over time. For 10 of the 12 species (excluding sample‐size‐constrained Tiger Shark Galeocerdo cuvier and Bull Shark Carcharhinus leucas), size structure metrics indicated decreasing sizes over time, although statistical confidence for these patterns varied across species and metrics. Strongest statistical support for declining sizes was observed for Blacknose Shark Carcharhinus acronotus (mean FL, median FL, L90%), Dusky Shark Carcharhinus obscurus (L90%), Smooth Dogfish Mustelus canis (L90%), and Atlantic Sharpnose Shark Rhizoprionodon terraenovae (L90%). Magnitude of decreases in L90% among these 10 species during the survey ranged from roughly 9% (Silky Shark Carcharhinus falciformis; 83‐mm decrease) to 35% (Sandbar Shark Carcharhinus plumbeus; 541‐mm decrease). Our findings indicate a potential for fishing pressure to exert directional selection on these coastal shark species, although further research is needed regarding the nature of size‐dependent catchability and species‐specific vital rates to adequately evaluate these dynamics. Furthermore, in addition to the removal of “great sharks,” decreasing sizes of small coastal sharks, such as Blacknose Shark, Smooth Dogfish, and Atlantic Sharpnose Shark (i.e., “mesopredators”), suggest that harvest may have pervasive effects on species throughout this assemblage.

A Hierarchical Bayesian Modeling Approach for the Habitat Distribution of Smooth Dogfish by Sex and Season in Inshore Coastal Waters of the U.S. Northwest Atlantic

AbstractThe Smooth Dogfish Mustelus canis is an abundant, small coastal shark occurring along the U.S. Atlantic coast. Despite being targeted by a directed fishery and having recently undergone a stock assessment that found the population neither overfished nor experiencing overfishing, little is known about the spatial and temporal distribution of this species. Here, we used catch data from the spring and fall Northeast Area Monitoring and Assessment Program's fishery‐independent trawl surveys conducted between 2007 and 2016 and various environmental factors to perform hierarchical Bayesian modeling as a first attempt to spatially predict adult Smooth Dogfish CPUE in U.S. northwest Atlantic Ocean waters by sex and season. Relevant environmental variables differed between both sexes and seasons. Male and female CPUEs were similarly associated with lower salinity and shallower depth in the spring. During fall, male CPUE was associated with sea surface temperature and bottom rugosity, and female CPUE was associated with chlorophyll‐a concentration, bottom rugosity, and year. Habitat modeling results predicted that areas of high male and female CPUEs would overlap during spring but strongly diverge during fall, when greater predicted CPUEs for males were distributed considerably farther north. These results suggest sexual segregation among Smooth Dogfish during fall, with the springtime overlap in distribution coinciding with the pupping and mating season in this population. This difference in distribution during fall may allow for a male‐only directed fishery for Smooth Dogfish in the northern extent of the species’ range in waters near southern New England and Georges Bank.

Identification and Distribution of Morphologically Conserved Smoothhound Sharks in the Northern Gulf of Mexico

AbstractIdentification of sharks within the genus Mustelus (smoothhound sharks) is problematic because of extensive overlap in external morphology among species. Consequently, species‐specific management of smoothhound shark resources is difficult when multiple species inhabit the same geographic region. The species identification and distribution of smoothhound sharks in the northern Gulf of Mexico (the Gulf) were assessed using sequences of mitochondrial DNA, nuclear‐encoded microsatellites, and catch data. Phylogenetic analysis of 1,047 base pairs of mitochondrially encoded ND‐2 sequences and Bayesian clustering of multilocus genotypes at 15 microsatellites revealed three genetically distinct monophyletic lineages (clades) of smoothhound sharks in the Gulf. Examination of external morphology revealed characters that distinguished each genetically distinct clade, and based on species descriptions and comparisons with the type and other specimens in established collections, the lineages were identified as Smooth Dogfish Mustelus canis, Florida Smoothhound Mustelus norrisi, and Gulf Smoothhound Mustelus sinusmexicanus. Two hundred and eighty‐seven smoothhound sharks sampled from across the Gulf were then assigned unequivocally, based on genetic data, to one of the three species. Multifactorial analysis and homogeneity tests of species‐specific means versus grand means of spatiotemporal factors (depth, longitude, and month) at capture indicated significant differences among the three species with respect to all three factors. On average, the Smooth Dogfish is found in deeper waters than the Gulf Smoothhound, whereas the Florida Smoothhound inhabits relatively shallow waters. A diagnostic key for the field identification of adult specimens of each species is provided.

Dynamics of residency and egress in selected estuarine fishes: evidence from acoustic telemetry

In an attempt to determine the extent and periodicity of several large juvenile and adult fishes (smooth dogfish Mustelus canis, black drum Pogonias cromis, hickory shad Alosa mediocris) in a temperate estuary, we tracked acoustically tagged individuals with passive and active telemetry techniques during the summer, fall and winter. This approach confirmed summer residency for all of these species and species-specific and individual patterns of egress ranging from summer through fall. Other species (striped bass Morone saxatilis, summer flounder Paralichthys dentatus, bluefish Pomatomus saltatrix) that were previously tracked in the same estuary with the same techniques were reanalyzed for the same characteristics. There were species-specific and individual differences in residency and egress of these species as well, but all species left the estuary by the end of December. Together, these observations confirm the importance of temperate estuaries in the summer and fall, but not during the winter for the juveniles and adults of these migratory species. However, the duration of residency and timing of egress may vary if warming of estuarine waters continues.

Trophic Resource Overlap Between Small Elasmobranchs and Sympatric Teleosts in Mid-Atlantic Bight Nearshore Habitats

Small, abundant elasmobranchs use shallow marine areas (<20 m depth) of the US Middle Atlantic coast as nurseries and adult foraging habitat, an area also used by a diverse assemblage of economically important juvenile and adult teleost species. Specimens of three small elasmobranch species (smooth dogfish Mustelus canis, clearnose skate Raja eglanteria, and bullnose ray Myliobatis freminvillii) were collected in August 2007 and 2008 from a study area of ∼150 km2, extending 22 km south from Ocean City, Maryland, USA (38° 19′ N) and offshore from 5- to 20-m depth. Stomach contents indicated that fish were part of the diets of smooth dogfish and clearnose skate at a level comparable with sympatric piscivorous teleosts. However, stable isotope data suggest that piscivory is likely an opportunistic foraging behavior in this habitat. Studied elasmobranchs were secondary-tertiary consumers with diets composed primarily of decapod crustaceans, fish, and mollusks. There was significant overlap in diet composition, spatial distribution, and diel stomach fullness patterns between clearnose skate, southern kingfish Menticirrhus americanus (teleost) and, to a lesser extent, smooth dogfish. Despite this evidence for piscivory, their relatively low densities suggest that predation by these elasmobranchs is unlikely to affect teleost populations in shallow coastal ocean habitats. If shared prey were to become scarce, then competitive interactions are possible.

Using Species Composition Data from a Trawl Survey to Determine Potential Bycatch of the Commercial Trawl Fishery for Horseshoe Crab Limulus polyphemus in the Middle Atlantic Bight

AbstractThe National Marine Fisheries Service has encouraged regional management councils to develop fisheries ecosystem plans that, among other things, identify the bycatch species within each fishery and describe each species' spatial and temporal distribution. Horseshoe crabs Limulus polyphemus have been harvested along the eastern coast of the USA since the 1800s; however, a fishery management plan was only recently created for this species, and bycatch in the horseshoe crab trawl fishery has not been quantified. We identified species likely to be caught as bycatch in the commercial fishery by using species composition data from a fishery‐independent horseshoe crab trawl survey conducted in 2005 and 2006. Seventy‐six taxa were caught, including 47 finfish species from 33 families. Skates (family Rajidae) comprised more than one‐half of the total biomass caught, and horseshoe crabs comprised one‐third of the total biomass. Catch per unit effort (kg/km towed) was greatest for little skate Leucoraja erinacea, winter skate Leucoraja ocellata, horseshoe crab, and clearnose skate Raja eglanteria. We also caught species that are currently on the World Conservation Union's Red List (e.g., Atlantic sturgeon Acipenser oxyrinchus) and unmanaged within U.S. waters (e.g., cownose ray Rhinoptera bonasus and smooth dogfish Mustelus canis). Nonmetric multidimensional scaling was used to cluster sites based on species abundance. The sites strongly clustered into two distinct groups, suggesting that species composition differs between northern and southern sites. Bottom water temperature was a significant factor in determining species composition, explaining almost 70% of the variation in species composition among sites. The results of this study provide managers with a better understanding of which nontarget populations may be affected by the horseshoe crab trawl fishery, a first step in understanding the broader ecosystem‐level effects of this fishery.

Sharks need the lateral line to locate odor sources: rheotaxis and eddy chemotaxis

Odor plumes are complex, dynamic, three-dimensional structures used by many animals to locate food, mates, home sites, etc. Yet odor itself has no directional properties. Animals use a variety of different senses to obtain directional information. Since most odor plumes are composed of dispersing odor patches and dissipating vorticity eddies, aquatic animals may localize odor sources by simultaneous analysis of chemical and hydrodynamic dispersal fields, a process referred to as eddy chemotaxis. This study examines the contributions of olfaction, mechanoreception and vision to odor source localization in a shark, the smooth dogfish Mustelus canis. Two parallel, turbulent plumes were created in an 8 m flume: squid rinse odor and seawater control. Minimally turbulent ;oozing' sources of odor and seawater control were physically separated from sources of major turbulence by placing a brick downstream from each oozing source, creating two turbulent wakes, one or the other flavored with food odor. This created four separate targets for the sharks to locate. Animals were tested under two light conditions (fluorescent and infrared) and in two sensory conditions (lateral line intact and lateral line lesioned by streptomycin). Intact animals demonstrated a preference for the odor plume over the seawater plume and for the source of odor/turbulence (the brick on the odor side) over the source of the odor alone (the odor-oozing nozzle). Plume and target preference and search time were not significantly affected by light condition. In the light, lesioning the lateral line increased search time but did not affect success rate or plume preference. However, lesioned animals no longer discriminated between sources of turbulent and oozing odor. In the dark, search time of lesioned animals further increased, and the few animals that located any of the targets did not discriminate between odor and seawater plumes, let alone targets. These results demonstrate for the first time that sharks require both olfactory and lateral line input for efficient and precise tracking of odor-flavored wakes and that visual input can improve food-finding performance when lateral line information is not available. We distinguish between rheotaxis: orientation to the large-scale flow field (olfaction, vision and superficial lateral line), eddy chemotaxis: tracking the trail of small-scale, odor-flavored turbulence (olfaction and lateral line canals), and pinpointing the source of the plume (lateral line canals and olfaction).

Ecological Interactions between Elasmobranchs and Groundfish Species on the Northeastern U.S. Continental Shelf. I. Evaluating Predation

Abstract Elasmobranchs are an important component of the northeastern U.S. continental shelf ecosystem in terms of both biomass and abundance. It has been hypothesized that because of their high biomass these species have a significant negative impact on commercially valuable groundfish via ecological interactions. One of these hypotheses posits that elasmobranchs directly remove such groundfish by predation. We analyzed data from the stomachs of 40,756 spiny dogfish Squalus acanthias, 3,806 smooth dogfish Mustelus canis, 17,618 little skate Raja erinacea, 11,593 winter skate R. ocellata, and 2,571 thorny skate R. radiata collected in bottom trawl surveys conducted principally during spring and autumn 1973–1998 in waters from Cape Hatteras, North Carolina, to Nova Scotia. Except for silver hake Merluccius bilinearis, most groundfish are not common in the diets of the elasmobranchs. Estimates of consumption indicate that both the number and the total biomass of the groundfish that are removed are generally...

The boundary layer of swimming fish.

Tangential and normal velocity profiles of the boundary layer surrounding live swimming fish were determined by digital particle tracking velocimetry, DPTV. Two species were examined: the scup Stenotomus chrysops, a carangiform swimmer, and the smooth dogfish Mustelus canis, an anguilliform swimmer. Measurements were taken at several locations over the surfaces of the fish and throughout complete undulatory cycles of their propulsive motions. The Reynolds number based on length, Re, ranged from 3x10(3) to 3x10(5). In general, boundary layer profiles were found to match known laminar and turbulent profiles including those of Blasius, Falkner and Skan and the law of the wall. In still water, boundary layer profile shape always suggested laminar flow. In flowing water, boundary layer profile shape suggested laminar flow at lower Reynolds numbers and turbulent flow at the highest Reynolds numbers. In some cases, oscillation between laminar and turbulent profile shapes with body phase was observed. Local friction coefficients, boundary layer thickness and fluid velocities at the edge of the boundary layer were suggestive of local oscillatory and mean streamwise acceleration of the boundary layer. The behavior of these variables differed significantly in the boundary layer over a rigid fish. Total skin friction was determined. Swimming fish were found to experience greater friction drag than the same fish stretched straight in the flow. Nevertheless, the power necessary to overcome friction drag was determined to be within previous experimentally measured power outputs. No separation of the boundary layer was observed around swimming fish, suggesting negligible form drag. Inflected boundary layers, suggestive of incipient separation, were observed sporadically, but appeared to be stabilized at later phases of the undulatory cycle. These phenomena may be evidence of hydrodynamic sensing and response towards the optimization of swimming performance.

The aryl hydrocarbon receptor in early vertebrates

The Ah receptor (AhR), which mediates effects of dioxins and related halogenated aromatic hydrocarbons, belongs to the emerging bHLH-PAS family of transcription factors. A reverse-transcription-polymerase chain reaction (RT-PCR) method using degenerate primers was used to search for the AhR in early vertebrates, including bony, cartilaginous, and jawless fish. AhR cDNA sequences were obtained for the killifish Fundulus heteroclitus, smooth dogfish Mustelus canis, the little skate Raja erinacea and the sea lamprey Petromyzon marinus. Further studies revealed evidence for a second AhR gene (AHR2) in Fundulus and Mustelus. The fish AhR1 and AhR2 genes are as different from each other as each is from mammalian AhRs, suggesting that they are the result of an ancient gene duplication, possibly occurring prior to the divergence of lineages leading to present-day mammals and fish. These studies demonstrate the conservation of AhR structure over more than 500 million years of vertebrate evolution. A search of the GenBank protein sequence database revealed a possible AhR homolog in the nematode Caenorhabditis elegans. Phylogenetic analysis of fish AhR sequences in comparison to mammalian AhRs and other members of the bHLH-PAS gene family provides an evolutionary perspective to the study of dioxin toxicity and Ah receptor function.

Aryl hydrocarbon receptor function in early vertebrates:: Inducibility of cytochrome P450 1A in agnathan and elasmobranch fish

The mammalian aryl hydrocarbon receptor (AHR) is a ligand-activated transcription factor that controls the expression of cytochrome P450 1A (CYP1A) genes in response to halogenated aromatic hydrocarbons such as 2,3,7,8-tetrachlorodibenzo- p-dioxin (TCDD). The natural ligand and normal physiologic function of this protein are as yet unknown. One approach to understanding AHR function and significance is to determine the evolutionary history of this receptor and of processes such as CYP1A induction that are controlled by the AHR in mammals. In these studies, AHR function was evaluated in representative cartilaginous fish (little skate, Raja erinacea) and jawless fish (sea lamprey, Petromyzon marinus and Atlantic hagfish, Myxine glutinosa), using CYP1A induction as a model AHR-dependent response. Treatment of skate with β-naphthoflavone (BNF) caused an 8-fold increase in hepatic ethoxyresorufin O-deethylase (EROD) activity as well as a 37-fold increase in the content of immunodetectable CYP1A protein. Evidence of CYP1A inducibility was also obtained for another cartilaginous fish, the smooth dogfish Mustelus canis. In contrast, hepatic EROD activity was not detected in untreated lamprey nor in lamprey treated with 3,3′,4,4′-tetrachlorobiphenyl (TCB), a potent AHR agonist in teleosts. A possible CYP1A homolog was detected in lamprey hepatic microsomes by one of three antibodies to teleost CYP1A, but expression of this protein was not altered by TCB treatment. CYP1A protein and catalytic activity were measurable in hagfish, but neither was induced after treatment with TCB. These results suggest that the AHR-CYP1A signal transduction pathway is highly conserved in gnathostomes, but that there may be fundamental differences in AHR signaling or AHR-CYP1A coupling in agnathan fish. Agnathan fish such as hagfish and lamprey may be interesting model species for examining possible ancestral AHR functions not related to CYP1A regulation.

Levels of ethanolamine intermediates in the human and rat visual system structures: Comparison with neural tissues of a lower vertebrate ( Mustelus canis) and an invertebrate ( Loligo pealei)

Levels of ethanolamine intermediates in the retina and optic nerves of autopsied human donors and in the rat visual system (retina, optic nerve, lateral geniculate body, superior colliculus) were measured. Amounts were also obtained from the retina, optic nerve, and optic tectum of a primitive elasmobranch, the smooth dogfish Mustelus canis, and from the related nervous structures (retina, optic lobe, fin nerve, and stellate ganglia) of a marine invertebrate, the squid Loligo pealei. In all regions of the human and rat nervous system, the pool size of CDP-ethanolamine (values ranging between 10–31 nmol/g wet wt) was much smaller than that of free ethanolamine (values ranging between 197–395 nmol/g wet wt), whereas glycerophosphorylethanolamine was present in relatively high content (values ranging between 125–280 nmol/g wet wt). In nervous system regions of the dogfish and squid, the distribution of values followed the same general trend as observed for humans and rats, even if all regions had less ethanolamine intermediates compared to the mammalian counterpart. In dogfish and squid retina, glycerophosphorylethanolamine showed the highest pool size among the ethanolamine derivatives analyzed (16 and 44 nmol/g wet wt, respectively). The present study confirms the basic similarity of ethanolamine intermediate pool size patterns in the nervous system structures (with the exception of the retina) of animal species which have widely different phylogenetic positions. The data support the proposal that the levels reached by ethanolamine and its derivatives in the nervous tissue is the result of an ancient evolutionary development of metabolic pathways for the maintenance of phosphatidylethanolamine membraneous content.

Levels of choline intermediates in the visual system structures and in peripheral nerve of the rat: Comparison with neural tissues of a lower vertebrate (Mustelus canis) and an invertebrate (Loligo pealei)

The levels of choline intermediate endogenous pools in structures of the visual system (retina, optic nerve, lateral geniculate body, superior colliculus) and in sciatic nerve of adult (4-month-old) and young (30-day-old) rats were measured. The amounts were also obtained from retina, optic nerve, optic tectum and cranio-spinal nerves of a primitive elasmobranch, the smooth dogfish Mustelus canis, and from related nervous structures (retina, optic lobe, fin nerve, stellar nerve and stellate ganglia) of a marine invertebrate, the squid Loligo pealei. In all regions of rat nervous system, the pool size of CDP-choline was much smaller than that of free choline, whereas GroPCho was present in a relatively higher content. The pool sizes of choline intermediates in 30- and 120-day-old rats were nearly the same. In nervous system regions of the dogfish and squid, the values followed the same general trend as observed for rat. Squid nervous tissues had the lowest choline and GroPCho contents. The rat retina showed the lowest glycerophosphorylcholine phosphodiesterase activity. The chemical studies described here confirm the basic similarity in the pattern of choline intermediate pool sizes among animal species widely different in phylogenetic position. The data highly reinforce the idea that the precursor role of choline and catabolic pathways for the maintenance of the PtdCho membraneous pool seem highly conserved during evolution.

The Topography of the Superficial Roots and Ganglia of the Anterior Lateral Line Nerve of the Smooth Dogfish, Mustelus canis

The topographic relationships of the superficial roots and ganglia of the anterior lateral line nerve (NLLa) to each other and to cranial nerves V, VII and VIII were studied, in the smooth dogfish Mustelus canis, by dissection of Sudan Black B stained specimens. NLLa consists of four branches: namely, superficial ophthalmic, buccal, otic and external mandibular. Each branch carriers lateral line neurons exclusively and forms a dorsal root and a ventral root which enter the anterior lateral line lobe and posterior lateral line lobe of the medulla respectively. It is estimated that slightly more than 50% of the fibers of the superficial ophthalmic, approximately 60% of the fibers of the buccal, at least 35% of the fibers of the otic and about 20% of the fibers of the external mandibular constitute the dorsal root. The ventral root is comprised of less than 50% of the fibers of the superficial ophthalmic, 40% of the fibers of the buccal, at least 50% of the fibers of the otic, and 80% of the fibers of the external mandibular. These results are correlated with the peripheral distribution and central termination of NLLa and it is concluded that the dorsal root carries axons from ampullary receptors and the ventral root carries fibers that innervate ordinary lateral line sense organs.

Retinal structure in the smooth dogfish Mustelus canis: electron microscopy of serially sectioned bipolar cell synaptic terminals.

AbstractPortions of axons of bipolar cells in the retina of the smooth dogfish Mustelus canis were sectioned serially and examined by electron microscopy. The studied axons generally could be related to a bipolar cell sub‐type identified by light microscopy. Bipolar cell axons make ribbon synapses onto amacrine processes and ganglion cell dendrites, and onto ganglion cell perikarya. Bipolar cell ribbon synaptic complexes varied as to the number of post‐synaptic processes (1–3) and the orientation of the ribbon with respect to the post‐synaptic membrane. Amacrine processes made numerous conventional synapses onto bipolar cell axons, but reciprocal synapses between amacrine and bipolar cells constituted only 3–25% of all synapses observed.The number of ribbon synapses per unit area of bipolar cell axon membrane differed little among bipolar cell sub‐classes. However, the density of amacrine cell conventional synapses was markedly lower for thin, horizontally‐oriented bipolar cell axons than for axons of other bipolar cell types.Gap junctions were noted between bipolar cell axons of the same sub‐type. They are structurally similar to gap junctions between horizontal cells in Mustelus retina and to those found elsewhere in the nervous system.