Squalus Acanthias Research Articles

Comparative Studies of Hepatic and Blood Biomarkers in Three Species of Black Sea Elasmobranchs

The investigations of elasmobranchs are very important for the understanding of evolutionary process and mechanisms of fish adaptation. Fishing pressure and global climate changes are affecting elasmobranch population size and structure. Baseline data of these taxa from different locations are useful for the evaluation of their health and for development of the methods of their preservation. In this study Aminotransferases (ALT and AST) activity, oligopeptides, albumin and hemoglobin concentrations were determined in the liver, red blood cells and blood serum of three Black Seaelasmobranch species: Atlantic spiny dogfish Squalus acanthias, buckler skate Raja clavata and stringray Dasyatis pastinaca. Interspecies differences of enzymatic activities depending on fish biology and ecology were shown. Hepatic aminotransferases level and serum oligopeptides concentration were greater in benthic/pelagic active shark, than in benthic sluggish rays. Oligopeptides concentration in red blood cells was the similar in tested elasmobranchs, while serum enzymatic activity and hepatic oligopetides level were higher in R. clavata than in D. pastinaca and S. acanthias inhabiting deeper waters. The results demonstrate that the complex of biochemical characteristics of elasmobranchs together with their ecological specificity can be used to indicate the main strategy of biochemical adaptation of fish evolutionary process.

CGMP inhibition of type 3 phosphodiesterase is the major mechanism by which C-type natriuretic peptide activates CFTR in the shark rectal gland

The in vitro perfused rectal gland of the dogfish shark (Squalus acanthias) and filter-grown monolayers of primary cultures of shark rectal gland (SRG) epithelial cells were used to analyze the signal transduction pathway by which C-type natriuretic peptide (CNP) stimulates chloride secretion. CNP binds to natriuretic receptors in the basolateral membrane, elevates cellular cGMP, and opens cystic fibrosis transmembrane conductance regulator (CFTR) chloride channels in the apical membrane. CNP-provoked chloride secretion was completely inhibitable by the nonspecific protein kinase inhibitor staurosporine and the PKA inhibitor H89 but insensitive to H8, an inhibitor of type I and II isoforms of cGMP-dependent protein kinase (cGKI and cGKII). CNP-induced secretion could not be mimicked by nonhydrolyzable cGMP analogs added alone or in combination with the protein kinase C activator phorbolester, arguing against a role for cGK or for cGMP-induced PKC signaling. We failed to detect a dogfish ortholog of cGKII by molecular cloning and affinity chromatography. However, inhibitors of the cGMP-inhibitable isoform of phosphodiesterase (PDE3) including milrinone, amrinone, and cilostamide but not inhibitors of other PDE isoenzymes mimicked the effect of CNP on chloride secretion in perfused glands and monolayers. CNP raised cGMP and cAMP levels in the SRG epithelial cells. This rise in cAMP as well as the CNP and amrinone-provoked chloride secretion, but not the rise in cGMP, was almost completely blocked by the Gαi-coupled adenylyl cyclase inhibitor somatostatin, arguing against a role for cGMP cross-activation of PKA in CNP action. These data provide molecular, functional, and pharmacological evidence for a CNP/cGMP/PDE3/cAMP/PKA signaling cascade coupled to CFTR in the SRG.

Assessing reproductive status in elasmobranch fishes using steroid hormones extracted from skeletal muscle tissue.

Elasmobranch fishes (sharks, skates, and rays) are particularly susceptible to anthropogenic threats, making a thorough understanding of their life history characteristics essential for proper management. Historically, elasmobranch reproductive data have been collected by lethal sampling, an approach that is problematic for threatened and endangered species. However, recent studies have demonstrated that non-lethal approaches can be as effective as lethal ones for assessment of the reproductive status of an animal. For example, plasma has been used to examine concentrations of steroid hormones. Additionally, skeletal muscle tissue, which can be obtained non-lethally and with minimal stress, can also be used to quantify concentrations of steroid hormones. Skeletal muscle progesterone, testosterone, and estradiol concentrations were determined to be statistically significant indicators of reproductive status in the oviparous Leucoraja erinacea, the yolk-dependent viviparous Squalus acanthias, and the yolk-sac placental viviparous Rhizoprionodon terraenovae. The results of the present study demonstrate that steroid hormones present in non-lethally harvested skeletal muscle tissue can be used as reliable indicators of reproductive status in elasmobranchs.

Species biology of elasmobranch by-catch in bottom-trawl fishery on the northern Patagonian shelf, Argentina

AB Aquatic Biology Contact the journal Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections AB 19:239-251 (2013) - DOI: https://doi.org/10.3354/ab00535 Species biology of elasmobranch by-catch in bottom-trawl fishery on the northern Patagonian shelf, Argentina A. C. Crespi-Abril*, S. N. Pedraza, N. A. García, E. A. Crespo Centro Nacional Patagónico (CONICET), Boulevard Brown s/n, Puerto Madryn, Chubut 9120, Argentina *Email: crespi@cenpat.edu.ar ABSTRACT: The present study analyzes the species composition of elasmobranch by-catch of bottom trawlers that targeted common hake Merluccius hubbsi on the northern and central Patagonian shelf during 2001, 2002 and 2003. Six surveys were conducted, and a total of 20 species of elasmobranchs were observed. Zearaja chilensis and Squalus acanthias were present in all surveys. The mean values of relative abundance ranged between 9.12 and 151 ind. km-2 for Z. chilensis and between 8.24 and 298 ind. km-2 for S. acanthias. Bathyraja brachyurops, B. macloviana, B. magellanica, Discopyge sp. and Psammobatis lentiginosa were registered only in 1 survey, and their relative abundance did not exceed 15 ind. km-2. There were no patterns detected between the mean size of the individuals and the depth of capture for any of the captured species. Length-to-weight relationships were estimated for 14 species, and size-at-maturity was estimated for 8 species. KEY WORDS: By-catch · Size-at-maturity · Elasmobranchs · Length-to-weight relationships Full text in pdf format PreviousNextCite this article as: Crespi-Abril AC, Pedraza SN, García NA, Crespo EA (2013) Species biology of elasmobranch by-catch in bottom-trawl fishery on the northern Patagonian shelf, Argentina. Aquat Biol 19:239-251. https://doi.org/10.3354/ab00535 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in AB Vol. 19, No. 3. Online publication date: October 24, 2013 Print ISSN: 1864-7782; Online ISSN: 1864-7790 Copyright © 2013 Inter-Research.

Transcriptome responses in the rectal gland of fed and fasted spiny dogfish shark (Squalus acanthias) determined by suppression subtractive hybridization

Prior studies of the elasmobranch rectal gland have demonstrated that feeding induces profound and rapid up regulation of the gland's ability to secrete concentrated NaCl solutions and the metabolic capacity to support this highly ATP consuming process. We undertook the current study to attempt to determine the degree to which up regulation of mRNA transcription was involved in the gland's activation. cDNA libraries were created from mRNA isolated from rectal glands of fasted (7days post-feeding) and fed (6h and 22h post-feeding) spiny dogfish sharks (Squalus acanthias), and the libraries were subjected to suppression subtractive hybridization (SSH) analysis. Quantitative real time PCR (qPCR) was also used to ascertain the mRNA expression of several genes revealed by the SSH analysis. In total the treatments changed the abundance of 170 transcripts, with 103 up regulated by feeding, and 67 up regulated by fasting. While many of the changes took place in ‘expected’ Gene Ontology (GO) categories (e.g., metabolism, transport, structural proteins, DNA and RNA turnover, etc.), KEGG analysis revealed a number of categories which identify oxidative stress as a topic of interest for the gland. GO analysis also revealed that branched chain essential amino acids (e.g., valine, leucine, isoleucine) are potential metabolic fuels for the rectal gland. In addition, up regulation of transcripts for many genes in the anticipated GO categories did not agree (i.e., fasting down regulated in feeding treatments) with previously observed increases in their respective proteins/enzyme activities. These results suggest an ‘anticipatory’ storage of selected mRNAs which presumably supports the rapid translation of proteins upon feeding activation of the gland.

From gelatinous to muscle food chain: rock cod Patagonotothen ramsayi recycles coelenterate and tunicate resources on the Patagonian Shelf

Stomach contents of 4808 fishes of 20 species caught in the eastern part of the Patagonian Shelf between 1999 and 2012 were analysed to assess dietary contributions of gelatinous plankton resources. Gelatinous plankton occurred in diets of seven species with two species, Patagonotothen ramsayi and Squalus acanthias, having >10% ctenophores in their diet. Consumption of gelatinous plankton was important in P. ramsayi and was strikingly seasonal, with maximum occurrence (up to 46% of non-empty stomachs) in late summer to autumn. Ctenophores were most abundant in P. ramsayi of 25-34 cm total length, L(T) whereas salps were more frequent in larger >35 cm L(T) individuals. In winter to spring, occurrence of gelatinous plankton in diets was minimal, reflecting their overall seasonal abundance in the ocean. The recent increase in abundance of P. ramsayi has enabled the species to recycle a significant proportion of the ecosystem production from gelatinous dead end to the main muscular food chain via seasonal reliance on ctenophores, jellyfish and tunicates. This additional influx of production that has been diverted from the gelatinous food chain favours the increase in abundance of several piscivorous top predators and affects the trophic web structure of the Patagonian Shelf ecosystem.

Modeling of the spatial distribution of Pacific spiny dogfish (Squalus suckleyi) in the Gulf of Alaska using generalized additive and generalized linear models

The Pacific spiny dogfish (Squalus suckleyi) is a common bycatch species in the Gulf of Alaska. Their spatial distribution is poorly understood, as most catch is discarded at sea. We analyzed spiny dogfish spatial distribution from fishery-dependent and -independent observations of longline gear between 1996 and 2008 using generalized additive and generalized linear models. Poisson, negative binomial, and quasi-Poisson error structures were investigated; the quasi-Poisson generalized additive model fit best. Models showed that spiny dogfish catches were concentrated east of Kodiak Island in waters ≤100 m deep. Results facilitate design of future spiny dogfish assessment surveys and identification of areas in which to focus at-sea observations for fishing mortality estimation, and provide the basis for first-ever designation of spiny dogfish essential fish habitat, despite US legal requirements for essential fish habitat designations since 1996. Identified areas of high bycatch may expedite spatial management by indicating areas in which directed spiny dogfish fisheries could be focused or, conversely, areas in which heightened conservation and catch accounting efforts would be most effective to prevent overfishing of this long-lived, late-maturing species.

Evaluating the Efficiency of Flushed Stomach-tube Lavage for Collecting Stomach Contents from Dogfish Sharks

Concern over the use of lethal techniques to collect basic biological data from sharks has necessitated the development of nonlethal methods of data collection. We evaluated the nonlethal method of removing stomach contents using acrylic tubes. Stomach contents of Spiny Dogfish (Squalus acanthias) captured with bottom trawls and longlines were collected using acrylic tubes flushed with seawater. The largest tube used during the trawl survey was 30 mm in diameter, while a larger tube (37 mm in diameter) was used during longline sampling due to catches of larger dogfish. The average ef- ficiency of stomach content removal was 79.5% overall, and improved to 93% with the addition of the larger tube. Selection of a tube with a diameter 10-20 mm less than mouth width can be reasonably expected to recover over 90% of stomach contents. Stomach- tube lavage is a useful and efficient method for nonlethal sampling of stomach contents from Spiny Dogfish, and perhaps other small sharks.

Differences in Microthrix Form Between Stomach and Spiral Intestine Stages of the Cestode,Trilocularia: Interspecific Variation or Development?

Tetraphyllidean cestodes of the genus Trilocularia have been reported from Squalus acanthias throughout this shark's global distribution, occupying both the stomach and spiral intestine. This study investigated whether variation seen in microthrix form among specimens within this host species is indicative of interspecific variation or is attributable to developmental transformation of a single cestode species. Sequence data for the 2 nuclear genes 28S rDNA (D1-D3) and ITS1, and the mitochondrial gene 16S rDNA, were generated for 22 specimens of Trilocularia; 3 from the stomach and 19 from the spiral intestine, including individuals exhibiting each of the 3 spinithrix forms found. Sequence data for 22 specimens were identical for the 2 nuclear genes. Some variation was seen in the mitochondrial gene but maximum likelihood analysis revealed no pattern with either site or microthrix type, suggesting microthrix variation may be developmental. To explore the developmental hypothesis further, a total of 118 juvenile worms from the stomach and 124 from the spiral intestine were collected from S. acanthias off the coast of Rhode Island and examined with either scanning electron microscopy (SEM) or light microscopy. SEM revealed differences in microthrix form between worms from the 2 sites. Of the stomach and spiral intestine worms examined, respectively, 98% versus 30% were scolopate, 2% versus 47% were aristate gladiate, and 0% versus 15% were lingulate in microthrix form. In addition, 3 of the 77 specimens from the spiral intestine examined with SEM exhibited mixtures of spinitriches. ANOVAs showed significant differences in the morphometrics of stomach worms, when compared to spiral intestine worms, as well as significat differences in the scolex width:below scolex width ratio of worms with scolopate spinitriches when compared to those with aristate gladiate or lingulate spinitriches. In combination, these data suggest that microthrix form may change over the course of development, indicating that caution should be exercised when interpreting microthrix patterns in the context of species designations.

Incorporating density dependence in pup production in a stock assessment of NE Atlantic spurdog Squalus acanthias

Abstract De Oliveira, J. A. A., Ellis, J. R., and Dobby, H. 2013. Incorporating density dependence in pup production in a stock assessment of NE Atlantic spurdog Squalus acanthias. – ICES Journal of Marine Science, 70: . An age- and sex-structured stock assessment model for Northeast Atlantic spurdog Squalus acanthias is presented that includes length-based processes, such as maturation, pup production, growth, and gear selectivity, with a length-at-age relationship to convert length to age. It relates pup production functionally to numbers of pregnant females, allowing for density-dependent effects. The model was fitted to a combined Scottish groundfish survey biomass index, to proportion-by-length category data from both trawl surveys and commercial catch sampling from target and non-target fisheries, and to fecundity data. The model was run from 1905 to better reflect virgin conditions and to allow early fecundity data to be fitted in order to estimate the extent of density dependence in pup production. The model estimated 2010 population levels to be about 23% relative to 1955 and 19% relative to 1905. Results confirm that the stock is depleted, but not to the extent estimated in a previous assessment. Current estimates of depletion would support an IUCN listing of “Endangered”, but not “Critically Endangered”. Model projections showed that a TAC of 1422 t (the last non-zero TAC) would allow future population growth.

Recent advances in artificial production of glass eels for conservation of anguillid eel populations

AbstractRemarkable progress in techniques for maturation of adults and rearing of larvae has been achieved for the Japanese eel Anguilla japonica over the past 50 years, but recent efforts have not yet succeeded in the mass production of glass eels. This article reviews recent advances in techniques for artificial production of A. japonica glass eels. Successful new protocols for obtaining viable eggs and larvae of A. japonica are largely resulting from using artificially feminised eels instead of wild silver eels. The feminisation technique by administration of 17β‐estradiol to glass eels not only provides an opportunity for using females as experimental broodstock throughout the year, but also accelerates their oocyte development or even increases the competence of females to respond to salmon pituitary extract. Induced spontaneous spawning with paired eels can improve the success rate for obtaining good‐quality eggs compared with the traditional stripping‐insemination method. As a result of the accumulation of field data on natural environmental conditions, such as an optimum temperature, where eel eggs and larvae were collected, the survival and growth rate of captive eel leptocephali have been much improved under these conditions. However, 50% diluted sea water (17.5 psu) that is far from the natural condition can result in better growth and survival performance in A. japonica leptocephali, possibly because it reduces the energy necessary for osmoregulation. Starvation can be a cue for triggering the onset of metamorphosis in A. japonica leptocephali, reducing the prolonged duration of the larval stage in captivity. To reach the mass production of glass eels at a commercial level, further improvement in quality of an artificial larval diet not containing eggs of the endangered shark Squalus acanthias is needed. The control of deformities in captive leptocephali and glass eels is also an important task. New techniques reducing the excessive use of exogenous hormones with parent eels should also be developed, to avoid public perception of an unhealthy product. If these techniques are completely established, we can exchange artificially produced glass eels with some part of the wild glass eels that are heavily exploited and provided to the eel aquaculture industry, and this can help to reduce the impact of eel consumption, which will contribute to the conservation of eel species worldwide.

Anatomy and muscle activity of the dorsal fins in bamboo sharks and spiny dogfish during turning maneuvers

Stability and procured instability characterize two opposing types of swimming, steady and maneuvering, respectively. Fins can be used to manipulate flow to adjust stability during swimming maneuvers either actively using muscle control or passively by structural control. The function of the dorsal fins during turning maneuvering in two shark species with different swimming modes is investigated here using musculoskeletal anatomy and muscle function. White-spotted bamboo sharks are a benthic species that inhabits complex reef habitats and thus have high requirements for maneuverability. Spiny dogfish occupy a variety of coastal and continental shelf habitats and spend relatively more time cruising in open water. These species differ in dorsal fin morphology and fin position along the body. Bamboo sharks have a larger second dorsal fin area and proportionally more muscle insertion into both dorsal fins. The basal and radial pterygiophores are plate-like structures in spiny dogfish and are nearly indistinguishable from one another. In contrast, bamboo sharks lack basal pterygiophores, while the radial pterygiophores form two rows of elongated rectangular elements that articulate with one another. The dorsal fin muscles are composed of a large muscle mass that extends over the ceratotrichia overlying the radials in spiny dogfish. However, in bamboo sharks, the muscle mass is divided into multiple distinct muscles that insert onto the ceratotrichia. During turning maneuvers, the dorsal fin muscles are active in both species with no differences in onset between fin sides. Spiny dogfish have longer burst durations on the outer fin side, which is consistent with opposing resistance to the medium. In bamboo sharks, bilateral activation of the dorsal in muscles could also be stiffening the fin throughout the turn. Thus, dogfish sharks passively stiffen the dorsal fin structurally and functionally, while bamboo sharks have more flexible dorsal fins, which result from a steady swimming trade off.

Using a multi-parameter approach to reassess maturity of spiny dogfish, Squalus acanthias, following increased fishing pressure in the Western North Atlantic

Age at size was linked to sexual maturity in 147 male and 249 female spiny dogfish, Squalus acanthias, from the Gulf of Maine using three criteria: (1) gross reproductive morphology, (2) histology and (3) steroid hormone concentrations. Collected specimens ranged from 25cm to 102cm stretch total length, and 0 to 24 years old. Maturity ogives for males, based on data gathered for clasper length, circulating testosterone concentrations and proportion of tissue with mature spermatocysts within the testes, predicted that 50% maturity occurred at a total length of 63.1mm and 7.5 years of age. For females, maturity ogives, based on data gathered for embryo presence, ovary mass, shell gland mass, follicle size and circulating estradiol concentrations, predicted that 50% maturity occurred at a total length of 76.9cm and 9.1 years of age. These maturity parameters for females decreased by over 7cm and 3 years from those previously reported two decades ago for S. acanthias in the Western North Atlantic. While the causes for the decrease in maturity parameters could not be determined, as this was beyond the scope of the current study, these changes occurred over a period of increased fishing pressure.

Biotic and abiotic factors influencing forage fish and pelagic nekton community in the Columbia River plume (USA) throughout the upwelling season 1999–2009

Abstract Litz, M. N. C., Emmett, R. L., Bentley, P. J., Claiborne, A. M., and Barceló, C. Biotic and abiotic factors influencing forage fish and pelagic nekton community in the Columbia River plume (USA) throughout the upwelling season 1999–2009. – ICES Journal of Marine Science, 71: . Large river plumes modify coastal environments and can impact production across multiple trophic levels. From 1999 to 2009, the assemblages of forage fish, predator fish, and other pelagic nekton were monitored in coastal waters associated with the Columbia River plume. Surveys were conducted at night to target vertically migrating species, and community structure evaluated to better understand ecological interactions. Distinct inshore and offshore communities were identified during spring and summer that were correlated with ocean temperature, salinity, plume volume, and upwelling intensity. Resident euryhaline forage fish species, such as smelts, anchovy, herring, market squid, juvenile salmon, and spiny dogfish, showed a high affinity for inshore habitat and the lower salinity plume during spring. Highly migratory species, such as sardine, piscivorous hake, sharks, and mackerels, were associated with warmer, saltier waters offshore, during strong upwelling periods in summer. Overall, our study of pelagic nekton revealed that temporal dynamics in abundance and community composition were associated with seasonal abiotic phenomenon, but not interannual, large-scale oceanographic processes. Forage fish assemblages differed seasonally and spatially from the assemblages of major piscivorous predators. This finding suggests a potential role of the plume as refuge for forage fish from predation by piscivorous fish in the northern California Current.

Atypical Antigen Recognition Mode of a Shark Immunoglobulin New Antigen Receptor (IgNAR) Variable Domain Characterized by Humanization and Structural Analysis

The immunoglobulin new antigen receptors (IgNARs) are a class of Ig-like molecules of the shark immune system that exist as heavy chain-only homodimers and bind antigens by their single domain variable regions (V-NARs). Following shark immunization and/or in vitro selection, V-NARs can be generated as soluble, stable, and specific high affinity monomeric binding proteins of ∼12 kDa. We have previously isolated a V-NAR from an immunized spiny dogfish shark, named E06, that binds specifically and with high affinity to human, mouse, and rat serum albumins. Humanization of E06 was carried out by converting over 60% of non-complementarity-determining region residues to those of a human germ line Vκ1 sequence, DPK9. The resulting huE06 molecules have largely retained the specificity and affinity of antigen binding of the parental V-NAR. Crystal structures of the shark E06 and its humanized variant (huE06 v1.1) in complex with human serum albumin (HSA) were determined at 3- and 2.3-Å resolution, respectively. The huE06 v1.1 molecule retained all but one amino acid residues involved in the binding site for HSA. Structural analysis of these V-NARs has revealed an unusual variable domain-antigen interaction. E06 interacts with HSA in an atypical mode that utilizes extensive framework contacts in addition to complementarity-determining regions that has not been seen previously in V-NARs. On the basis of the structure, the roles of various elements of the molecule are described with respect to antigen binding and V-NAR stability. This information broadens the general understanding of antigen recognition and provides a framework for further design and humanization of shark IgNARs.

Discarding and fishing mortality trends in the U.S. west coast groundfish demersal trawl fishery

Quantifying discarded catch is needed to guide effective fishery management and recognize the unintended impacts of fishing; ultimately to promote a more sustainable fishery. To understand fishing mortality prior to the establishment of an IFQ management system, we provide estimates of discarded and total catch (sum of discard and landings) in the U.S. west coast groundfish demersal trawl fishery from 2002 to 2009. West Coast Groundfish Observer Program (WCGOP) data were expanded to fleet-level discard estimates using a ratio estimator. Total estimated discard in the fishery declined by 52% across the study period. On average, 29% of the annual groundfish catch was discarded at-sea. A high proportion of catch was discarded during 2002, but subsequently overall discard decreased even though fishing effort (landings and trawl tow hours) increased in the fishery from 2004 to 2009. The largest components of discard (by weight) were Pacific hake (Merluccius productus), arrowtooth flounder (Atheresthes stomias), skates (Rajidae sp.) and spiny dogfish (Squalus acanthias). In 2009 relative to 2002, the discarded fraction of catch for rebuilding species, which constrain the fishery, had increased by 39%. In contrast, the discarded fraction of catch for target species had decreased by 24%. In addition, much of the fishing effort shifted to deeper waters. Our results represent a baseline for future comparisons as the fishery shifted from trip limit management to an Individual Fishing Quota (IFQ) program in 2011.

Spine-based ageing methods in the spiny dogfish shark, Squalus suckleyi: How they measure up

The second dorsal spine has historically been used for age determination in the spiny dogfish shark. The dorsal spines are located on the external surface of the body and are subjected to natural wear and breakage. Two methods have been developed to account for the worn portion of the spine and extrapolate the lost annuli. We compared the performance of these methods using a large data collection assembled from multiple sources, and evaluated their utility for stock assessment and management of the spiny dogfish shark Squalus suckleyi in the Northeast Pacific Ocean. Our results showed that the two methods produced very different age estimates for older fish with worn spines. Both methods raised significant questions about some aspects of the age estimates produced, and further exploration of techniques to account for worn spine annuli is needed. It is therefore important to develop alternative methods for shark age determination, including those using stained vertebrae.

A dynamic model describing ecosystem-level changes in the Strait of Georgia from 1960 to 2010

We developed an ecosystem model of the Strait of Georgia which emulates biomass and mortality changes between 1960 and 2009 to study ecosystem mechanisms governing dynamics in fished species and marine mammals. The model uses hindcast annual variation in bottom-up production, fisheries catches and predator-prey dynamics to simulate observed changes in fish, mammal and bird populations in the Strait of Georgia. This model emulates the timing and magnitude of historic changes in biomass and mortality of Coho and Chinook salmon as well as other major species like Pacific herring, orcas, harbour seals, lingcod, spiny dogfish and marine birds. Simulated production trends indicate the Strait of Georgia had relatively high production from the mid-1970s to late 1980s and entered a lower production regime in the early 1990s that has persisted to 2009. The simulations also indicate that the mean trophic level of vertebrates declined over the period 1990 to 2009. This model provides a tool to evaluate potential ecosystem changes in the Strait of Georgia.

A step forward in development of fish protein hydrolysate-based diets for larvae of Japanese eel Anguilla japonica

Eggs of spiny dogfish Squalus acanthias are an indispensable and effective component of the compound diets currently used for larvae of the Japanese eel Anguilla japonica. However, this fish species, a natural resource, is becoming more scarce, suggesting that suitable diets should be developed using more sustainable components. In the search for appropriate diets without shark eggs, we have designed test diets in which shark eggs were replaced with general feed materials, such as fish protein hydrolysate (FPH), with the notable improvement that the FPH had been pre-digested with integral enzymes from frozen krill. Feeding trials were conducted to assess the effects of the test diets on survival and growth of Japanese eel larvae at early developmental stages. Larvae fed on the test diets were found to be able to survive up to 65 days after hatching, the maximum total length and body depth were 14.1 and 1.5 mm, respectively. Although larvae fed on the test diets still exhibited a low survival rate and poor growth, the FPH-based diets had a nutritional value that promoted substantial larval growth based on the significant difference between the initial and final body sizes. Our results suggest that the development of FPH-based diets not based on shark eggs but rather on general feed ingredients is promising but that there is much room for improvement.

The international trade and fishery management of spiny dogfish: A social network approach

The management of the spiny dogfish (Squalus acanthias) is a matter of international concern, as this species was a candidate for inclusion in lists for trade regulation. The major demand for its meat is from the European Union (EU) market, with the US and Canada as its two major contributors. The US has yet to support a spiny dogfish listing, although the US Atlantic stock is under a fishery management plan (FMP) that proved to be successful in providing a certified sustainable fishery. We employed a cumulative sum technique to compare trade data for frozen spiny dogfish export from US and Canada to the EU in relation to the FMP adoption. We also constructed a social network to visualize changes in the European trade scenario for spiny dogfish after adoption of the FMP and to predict future trade flow potentially affecting the conservation status of regional dogfish stocks in relation to recent management measures introduced in Europe. The social network analysis revealed that the exclusion of spiny dogfish from trade regulation lists eventually will affect the conservation status of dogfish stocks in Africa, Asia, South America, and the Mediterranean and Black Seas. Our results suggest that the species listing would provide an economic benefit for the US Northwest Atlantic fishery, and will eventually foster the conservation status of other regional stocks worldwide and the search for a more sustainable global exploitation of spiny dogfish.