Galeorhinus Research Articles

Having confidence in productivity susceptibility analyses: A method for underpinning scientific advice on skate stocks?

National and European shark conservation plans aim to manage elasmobranch stocks sustainably. However uncertainties and deficiencies with available data hamper traditional, quantitative assessment methods of stock status to inform those plans, and thus effective management. The International Council for the Exploration of the Sea (ICES) Expert Groups have explored a range of data deficient assessment methods that may be used to support management advice, including Productivity Susceptibility Analysis (PSA). This method was applied to the demersal elasmobranch fauna (21 species) of the Celtic Sea to explore how such approaches could inform the management of skates (Rajidae). This species complex is an important catch component for demersal trawl and gillnet fisheries and is currently managed under a mixed species total allowable catch (TAC). PSAs were conducted on both of these fisheries, by four experts from three countries to introduce independence, and to quantify the range in perceptions of each stock. Confidence scoring of attributes was incorporated and probability distributions generated to model uncertainty in the expert responses to susceptibility attributes. Results showed that three shark species (tope, Galeorhinus galeus; angel shark, Squatina squatina and spurdog, Squalus acanthias) were the most vulnerable species in both fisheries (a consequence of their life history strategy and large size), followed by two skates (otter trawl) and three skates (gillnet). All of these species have some form of restrictive management and, apart from tope, are either currently listed as prohibited species or have a zero TAC in the area. Blonde ray, Raja brachyura was ranked as the next most vulnerable member of the commercially exploited skate complex. This adaptation of the PSA approach enabled skate species of higher and lower risk to be ranked and thus inform where management efforts should be focussed, whilst giving a novel consideration to uncertainty through canvassing expert opinion.

A trans-ecosystem fishery: Environmental effects on the small-scale gillnet fishery along the Río de la Plata boundary

To improve the understanding of the environmental processes affecting small-scale gillnet fisheries along neighboring waters of estuaries, we analyzed the main climatic forcing and the environmental conditions, the fishery landing spatial and temporal variation, including the relative importance of site, distance to coast, temperature and salinity in the structuring of landed species profile. Data were collected monthly in two sites along the adjacent south coast of the Río de la Plata between October 2009 and September 2010. The gillnet fishery was dominated by four species (Cynoscion guatucupa, Micropogonias furnieri, Mustelus schmitti and Parona signata) from a total of 38 species landed, which accounted for 98.6% of total landings. The fishing effort and landings by the fishery were largely conditioned by the availability of fish species in the fishing grounds resulting from the combination of the species reproductive behavior and the predominant environmental conditions. The highest abundances for some species occurred before (M. furnieri, C. guatucupa, P. signata) or during the reproductive period (M. schmitti, Squatina guggenheim), while in other species it was associated with favorable environmental conditions during cold months (Squalus acanthias, Callorhinchus callorhynchus, Galeorhinus galeus) or warm months (Trichiurus lepturus). The predominant seasonal environmental conditions along the coast were mainly determined by the location of Río de la Plata boundary, whose spatial extent was forced by the wind patterns and freshwater discharge. The strong environmental dependence means that the small-scale fishery is in fact a seasonal trans-ecosystem fishery. This attribute, together that shared the resources with the industrial fishery and the overlap of the fishery ground with essential habitat of sharks, make this kind of small-scale gillnet fishery particularly relevant to be included in the development of a coastal ecosystem-based management approach.

Patterns of extirpation. II. The role of connectivity in the decline and recovery of elasmobranch populations in the German Bight as inferred from survey data

ESR Endangered Species Research Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials ESR 25:209-223 (2014) - DOI: https://doi.org/10.3354/esr00583 Patterns of extirpation. II. The role of connectivity in the decline and recovery of elasmobranch populations in the German Bight as inferred from survey data Heino O. Fock*, Wolfgang Nikolaus Probst, Matthias Schaber Thünen-Institute of Sea Fisheries, Palmaille 9, 22767 Hamburg, Germany *Corresponding author: heino.fock@ti.bund.de ABSTRACT: Abundance trends and distribution patterns from 1902 to 1932 for 7 elasmobranch species in the German Bight (eastern central North Sea) were analyzed and compared to survey trends for 1991 to 2009. Abundances of thornback ray Raja clavata, common skate Dipturus batis, smoothhound Mustelus spp., tope shark Galeorhinus galeus, and spiny dogfish Squalus acanthias declined and common skate was extirpated, while abundances of starry ray Amblyraja radiata and lesser spotted dogfish Scyliorhinus canicula increased. A meta-population approach was developed to analyze connectivity in terms of the surrogate parameter Ĉ representing donor population Nj, separation distance Di,j, and migration range parameter α. As populations declined, connectivity between sub-populations was lost before resident populations finally collapsed. The loss of connectivity was caused by both a loss of sub-populations and a subsequent increase in the distance separating the remaining sub-populations. For lesser spotted dogfish, an increase in the donor population fostered the establishment of a local sub-population after 2000. For starry rays, an apparent increase in Nj due to a concentration of the donor population near the study area increased connectivity with the local sub-population. The interpretation of local abundances in terms of meta-population dynamics demonstrates the importance of seasonally resolved survey information for conservation planning. KEY WORDS: Meta-population models · North Sea · Fish diversity · Historic time series Full text in pdf format Supplementary material PreviousNextCite this article as: Fock HO, Probst WN, Schaber M (2014) Patterns of extirpation. II. The role of connectivity in the decline and recovery of elasmobranch populations in the German Bight as inferred from survey data. Endang Species Res 25:209-223. https://doi.org/10.3354/esr00583 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in ESR Vol. 25, No. 3. Online publication date: October 17, 2014 Print ISSN: 1863-5407; Online ISSN: 1613-4796 Copyright © 2014 Inter-Research.

Evidence for multiple paternity in the school shark Galeorhinus galeus found in New Zealand waters.

This study assessed the levels of relatedness of Galeorhinus galeus of progeny arrays using six microsatellite DNA markers. A parentage analysis from five families (mother and litter) from the North Island of New Zealand suggested the occurrence of genetic polyandry in G. galeus with two of the five litters showing multiple sires involved in the progeny arrays. This finding may be consistent with the reproductive characteristics of G. galeus, in which females can potentially store sperm for long periods of time after the mating season.

Big catch, little sharks: Insight into Peruvian small‐scale longline fisheries

Shark take, driven by vast demand for meat and fins, is increasing. We set out to gain insights into the impact of small-scale longline fisheries in Peru. Onboard observers were used to document catch from 145 longline fishing trips (1668 fishing days) originating from Ilo, southern Peru. Fishing effort is divided into two seasons: targeting dolphinfish (Coryphaena hippurus; December to February) and sharks (March to November). A total of 16,610 sharks were observed caught, with 11,166 identified to species level. Of these, 70.6% were blue sharks (Prionace glauca), 28.4% short-fin mako sharks (Isurus oxyrinchus), and 1% were other species (including thresher (Alopias vulpinus), hammerhead (Sphyrna zygaena), porbeagle (Lamnus nasus), and other Carcharhinidae species (Carcharhinus brachyurus, Carcharhinus falciformis, Galeorhinus galeus). Mean ± SD catch per unit effort of 33.6 ± 10.9 sharks per 1000 hooks was calculated for the shark season and 1.9 ± 3.1 sharks per 1000 hooks were caught in the dolphinfish season. An average of 83.7% of sharks caught (74.7% blue sharks; 93.3% mako sharks) were deemed sexually immature and under the legal minimum landing size, which for species exhibiting k-selected life history traits can result in susceptibility to over exploitation. As these growing fisheries operate along the entire Peruvian coast and may catch millions of sharks per annum, we conclude that their continued expansion, along with ineffective legislative approaches resulting in removal of immature individuals, has the potential to threaten the sustainability of the fishery, its target species, and ecosystem. There is a need for additional monitoring and research to inform novel management strategies for sharks while maintaining fisher livelihoods.

Trophic ecology and bioindicator potential of the North Atlantic tope shark

Sharks are top marine predators vital in maintaining ecosystem health and food web structure. In order to assess tope shark (Galeorhinus galeus) trophic ecology, stable isotope ratios and trace metal concentrations in muscle tissue were determined, according to size and gender, for 124 individuals caught within the Mid-Atlantic region. Data was complemented and analysed according to previous stomach content information and compared with studies performed in the North East Atlantic. Our results revealed that tope sharks fed at a low trophic level and within a more pelagic-based food web when compared with other North Atlantic regions. MixSIR application reflected its piscivorous diet and study area topography, oligotrophic waters and volcanic nature, suggesting the occurrence of a Mid-Atlantic tope shark population. Considering a non-anthropogenic volcanic source for observed metal contents, the results reflect bioaccumulation and suggest biomagnification processes for As and Hg. These metals exceeded legislated maximum limits for some countries with a maximum of 28.98±1.26 and 0.57±0.01mgkg−1 wet weight, respectively, increasing significantly with size for both males and females. Conversely, Cr, Rb and Zn were relatively stable while Cd and Pb were not detected. Hg and Se were strongly correlated, suggesting a Se toxicity mitigation role. Given the tope shark travel capacity and the results obtained, the species may be used as a Mid-Atlantic bioindicator of environmental quality.

Identification of putative allergens from school shark, a cartilaginous food fish

Background Fish is counted among the major allergenic foods causing mild to severe IgE-mediated reactions. Parvalbumin (PV), a highly stable muscle protein, has been described as the fish panallergen in different fishes. School shark (Galeorhinus galeus), a cartilaginous fish called ‘petite roussette’, is a popular food fish in the French cuisine. In this study, we aimed at identifying putative allergens from school shark.

Diving behaviour of the critically endangered tope shark Galeorhinus galeus in the Natural Reserve of Bahia San Blas, northern Patagonia

BackgroundTope sharks (Galeorhinus galeus) aggregate in large numbers during spring and summer in closed gulfs and bays in northern Patagonia; these locations are considered the main nursery areas for the species. However, little is known about the spatial ecology or diel behaviour of this critically endangered species. The aim was to evaluate the short-term diving behaviour and habitat preferences of tope sharks using electronic tagging.FindingsFive female tope sharks, four adult and one sub-adult, were tagged with pop-up satellite archival tags in the Natural Reserve of Bahía San Blas, northern Patagonia, during spring 2011 and 2012. High-resolution archived data were collected for 40 days, including 29 days for two recovered tags. Sharks travelled up to 51.2 km after release. Archived data indicated that female tope sharks preferred to remain within 24.5 m of the surface and that there were no diel changes in preference. Individuals spent most of the time within 10 m of the surface during the day (80%) and at night (83%), and were primarily in water between 17°C and 19°C (day, 75%; night, 70%). Moreover, tope sharks exhibited vertical oscillatory movement (‘yo-yo diving’). Maximum vertical speeds and dive depths were recorded at night. Ascents from depth had a greater speed than descents, overall.ConclusionsFemale tope sharks were found in shallow coastal areas during November at Bahía San Blas, near the surface at relatively restricted depths and temperatures. Longer tracking periods will be important for describing the species’ migratory movements across the south-west Atlantic.

Chondrichthyan occurrence and abundance trends in False Bay, South Africa, spanning a century of catch and survey records

Commercial fishing in False Bay, South Africa, began in the 1600s. Today chondrichthyans are regularly taken in fisheries throughout the bay. Using a combination of catch, survey and life history data, the occurrence and long-term changes in populations of chondrichthyans in False Bay are described. Analyses of time series data from five fishing methods between 1897 and 2011 provided trends in relative abundance. Of the 37 species found in False Bay, 25 showed no significant trends for any fishing method. Of the 12 species and two genera with catch trends, four showed a common trend across methods, two increasing (Mustelus mustelus and Carcharhinus brachyurus) and two decreasing (Galeorhinus galeus and Raja spp.), while another two species (Triakis megalopterus and Isurus oxyrinchus) showed highly significant declines in one method only. A productivity index was used in conjunction with information on species distribution, catch frequency and trends in abundance to assess the vulnerability of False Bay chondrichthyans. Among the various habitats and depth strata, the surf-zone has been most impacted by exploitation, whereas the conservation of deep-water, soft-sediment species has benefited from the ban on trawling in False Bay implemented in 1928. Continued monitoring using catch data from beach-seine, recreational shore-angling and the commercial linefishery is recommended, along with improved species identification.

Chondrichthyan Occurrence and Abundance Trends in False Bay, South Africa, Spanning a Century of Catch and Survey Records

Commercial fishing in False Bay, South Africa, began in the 1600s. Today chondrichthyans are regularly taken in fisheries throughout the bay. Using a combination of catch, survey and life history data, the occurrence and long-term changes in populations of chondrichthyans in False Bay are described. Analyses of time series data from five fishing methods between 1897 and 2011 provided trends in relative abundance. Of the 37 species found in False Bay, 25 showed no significant trends for any fishing method. Of the 12 species and two genera with catch trends, four showed a common trend across methods, two increasing (Mustelus mustelus and Carcharhinus brachyurus) and two decreasing (Galeorhinus galeus and Raja spp.), while another two species (Triakis megalopterus and Isurus oxyrinchus) showed highly significant declines in one method only. A productivity index was used in conjunction with information on species distribution, catch frequency and trends in abundance to assess the vulnerability of False Bay chondrichthyans. Among the various habitats and depth strata, the surf-zone has been most impacted by exploitation, whereas the conservation of deep-water, soft-sediment species has benefited from the ban on trawling in False Bay implemented in 1928. Continued monitoring using catch data from beach-seine, recreational shore-angling and the commercial linefishery is recommended, along with improved species identification.

The artisanal elasmobranch fishery of the Pacific coast of Baja California Sur, Mexico, management implications

Artisanal fisheries in Mexico account for approximately 40% of the total national catch. In 2009, Baja California Sur (BCS) had the second largest catch of elasmobranchs on the Mexican Pacific coast. This paper characterizes and describes the artisanal elasmobranch fishery of Pacific coast of BCS from 2000 to 2010. Sixty artisanal camps were documented, of which 45 targeted elasmobranchs, using primarily gillnets and longlines. We identified 52 elasmobranch species. Gillnetting accounted for 73.5% of the fishing effort and most frequently captured Rhinobatos productus, Mustelus henlei and Myliobatis californica . Longline fishing accounted for 26.5% of effort, most frequently capturing Prionace glauca and Isurus oxyrinchus . The prevalence of juveniles of several species (e.g., Cephaloscyllium ventriosum, Galeorhinus galeus, Isurus oxyrinchus , and Myliobatis californica ) within landings suggests that fishing effort may be opportunistically directed at breeding or nursery areas. Despite the dominance of species with wide distributions, we observed a significant biogeographic pattern in the abundance of some species relative to Bahia Magdalena. Results of the present study will be useful to detect changes in the structure of commercially exploited elasmobranch populations, and to provide useful indications for management purposes.

Pup numbers of the Australian sea lion (Neophoca cinerea) at The Pages Islands, South Australia, over two decades

The Australian sea lion is an Australian endemic, restricted to South Australia and Western Australia, with 86% of the population in South Australia. It was listed under the Commonwealth Environment Protection and Biodiversity Conservation Act as Vulnerable in February 2005, and the International Union for the Conservation of Nature has listed it as Endangered. Sea lions are taken as bycatch in the gill-net fishery for school shark and gummy shark, and the risk of extinction of breeding colonies is high even from low levels of bycatch. We assessed trends in pup population size at The Pages Islands, a large breeding colony in South Australia. Pup abundance was estimated by direct counting of live and dead pups; the maximum count in each breeding season was used for trend analysis. The average of direct counts of pups in 14 breeding seasons between 1989–90 and 2009–10 was 473 (s.d. = 58.4). There was no trend in pup numbers, contrasting with two other large colonies: Seal Bay, Kangaroo Island (decreasing), and Dangerous Reef (increasing since 2000). The Australian Sea Lion Management Strategy of the Australian Fisheries Management Authority aims to reduce sea lion bycatch in the shark fishery; a key item is a fishery closure around each breeding colony in South Australia. Implementation of the closure around The Pages should lower the risk of bycatch of its sea lions with foraging areas that previously overlapped with the fishery and should allow the colony’s population size to increase.

Effects of species biology on the historical demography of sharks and their implications for likely consequences of contemporary climate change

Climate variation is an important factor shaping the demographic histories of many marine species, though impacts likely differ depending on species life history, habitat preferences and ecology. Investigating how species responded to historic climate fluctuations may provide critical insights into a species’ response to current climate change. Despite their ecological diversity, shark species share many similar life history characteristics and may be especially vulnerable to anthropogenic and climate impacts. We compared patterns of genetic variability, mismatch distributions and demographic reconstructions from coalescence approaches among temperate and tropical shark species with differing ecological characteristics, to investigate the effect of the past glaciation cycles on population abundance. Genetic diversity at two mitochondrial DNA regions (ND2 and control region) was assayed in four North Pacific species, Pacific spiny dogfish, Pacific sleeper sharks, salmon shark, and bluntnose sixgill shark. In addition, control region sequences acquired from GenBank for five shark species [tope shark (California/Australia), white shark (California), blacktip shark (eastern and western Gulf of Mexico), lemon shark (Bahamas), and whale shark] were analyzed. General patterns in genetic diversity, mismatch analyses and Bayesian skyline plots supported our hypothesis that species biology affected the impact of climate variation on demographic history. Consequently, our results suggest that effects of contemporary climate change on sharks may be to some degree predictable from species biology, distribution, habitat and the impact of past climate events.

High Post-Capture Survival for Sharks, Rays and Chimaeras Discarded in the Main Shark Fishery of Australia?

Most sharks, rays and chimaeras (chondrichthyans) taken in commercial fisheries are discarded (i.e. returned to the ocean either dead or alive). Quantifying the post-capture survival (PCS) of discarded species is therefore essential for the improved management and conservation of this group. For all chondrichthyans taken in the main shark fishery of Australia, we quantified the immediate PCS of individuals reaching the deck of commercial shark gillnet fishing vessels and applied a risk-based method to semi-quantitatively determine delayed and total PCS. Estimates of immediate, delayed and total PCS were consistent, being very high for the most commonly discarded species (Port Jackson shark, Australian swellshark, and spikey dogfish) and low for the most important commercial species (gummy and school sharks). Increasing gillnet soak time or water temperature significantly decreased PCS. Chondrichthyans with bottom-dwelling habits had the highest PCS whereas those with pelagic habits had the lowest PCS. The risk-based approach can be easily implemented as a standard practice of on-board observing programs, providing a convenient first-step assessment of the PCS of all species taken in commercial fisheries.

Bycatch of sharks (Elasmobranchii) in the Patagonian red shrimp Pleoticus muelleri (Bate, 1888) fishery

The double–beam trawl fishery for the Patagonian red shrimp (Pleoticus muelleri) is the main crustacean fishery of the Southwestern Atlantic Ocean. The shark bycatch in 723 tows of this fishery was surveyed from April 2003 to October 2003. Six species of sharks were recorded: Squalus acanthias (n=321); Squalus mitsukurii (n=1); Squatina sp. (n=1); Schroederichthys bivius (n=327); Galeorhinus galeus (n=4) and Mustelus schmitti (n=13). Length-frequency structure, sex composition, spatial distribution and estimation of density and bycatch per unit of effort are given for the main species. The bycatch of sharks in this fishery was estimated in ~61 mt/ year, equivalent to 0.15% of the shrimp total capture in 2003. S. acanthias contributed with 30.5 mt (50.15%) whilst S. bivius contributed with 22.6 mt (37.2%). Whereas the abundance for S. acanthias in Patagonian waters increased by three fold between 1997 and 2001, the abundance of S. bivius in the same period have decreased in the same amount. In addition, losses of important reproductive sites in southern Patagonia for S. bivius were detected. These issues together with the results presented herein add the Patagonian red shrimp fishery to the potential threats S. bivius is exposed to.

Influence of mercury bioaccessibility on exposure assessment associated with consumption of cooked predatory fish in Spain

Predatory fish tend to accumulate high levels of mercury (Hg). Food safety assessment of these fish has been carried out on the raw product. However, the evaluation of the risk from Hg concentrations in raw fish might be modified if cooking and bioaccessibility (the contaminant fraction that solubilises from its matrix during gastrointestinal digestion and becomes available for intestinal absorption) were taken into account. Data on Hg bioaccessibility in raw predatory fish sold in Spain are scarce and no research on Hg bioaccessibility in cooked fish is available. The aim of the present study was to evaluate Hg bioaccessibility in various kinds of cooked predatory fish sold in Spain to estimate their health risk. Both Hg and bioaccessible Hg concentrations were analysed in raw and cooked fish (swordfish, tope shark, bonito and tuna). There were no changes in Hg concentrations during cooking. However, Hg bioaccessibility decreased significantly after cooking (42 ± 26% in raw fish and 26 ± 16% in cooked fish), thus reducing in swordfish and tope shark the Hg concentration to which the human organism would be exposed. In future, cooking and bioaccessibility should be considered in risk assessment of Hg concentrations in predatory fish.

Characterization of 13 microsatellite loci for the tope shark, Galeorhinus galeus, discovered with next-generation sequencing and their utility for eastern Pacific smooth-hound sharks (Mustelus)

The tope shark, Galeorhinus galeus, is a commercially important member of the Triakidae that has been exploited globally for the past 80 years. Here we describe 13 microsatellite loci for G. galeus discovered by next-generation sequencing (Roche 454 pyrosequencing) and their utility for eastern Pacific smooth-hound sharks (Mustelus). These loci were polymorphic (3–12 alleles) with observed heterozygosity between 0.11 and 0.86 and expected heterozygosity between 0.24 and 0.87. Several loci (7 of 13) amplified consistently for Mustelus californicus and M. henlei. These loci are the first to be characterized explicitly for G. galeus and should be useful in the investigation of population structure of this vulnerable elasmobranch.

First record of a dicephalic specimen of tope Galeorhinus galeus (Elasmobranchii: Triakidae)

The first case of dicephalia in tope Galeorhinus galeus analysed in developing foetuses removed from a pregnant female caught off the Mar del Plata coastal waters, Argentine Sea, is reported here.

Evaluation and use of a portable field kit for measuring whole-blood lactate in sharks

Measurement of lactate is becoming a common procedure in assessing the physiological effects of capture stress in sharks, although the necessity to measure the concentrations in the laboratory limits the ability for field assessments. Portable lactate analysers offer an alternative, but await validation against laboratory assays for sharks. The present study assessed the reliability of a portable Lactate Pro analyser for measuring whole-blood lactate in the school shark, Galeorhinus galeus, in the field. Laboratory determination of whole-blood and plasma lactate obtained by spectrophotometry was highly correlated with field determinations. Because shark lactate concentration can exceed the upper detection limit of the portable analysers, which were designed for mammalian use, a method for dealing with values greater than the maximum detection limit was evaluated. Whole-blood diluted by 50% with acidified saline solution, tap water and distilled water gave measured values of 55, 56 and 52%, respectively, of the original values, allowing accurate estimation of concentrations exceeding the upper detection limit of the analyser. These findings indicated that the Lactate Pro can be used to rapidly and reliably measure lactate for sharks in the field.

Origin of resources and trophic pathways in a large SW Atlantic estuary: An evaluation using stable isotopes

The Río de la Plata (34° 36′ S, 55° 58′ W; Argentina and Uruguay) estuary, one of the most important South American estuarine environments, is characterized by weak seasonal freshwater discharge, low tidal amplitude (<1 m), a wide and permanent connection to the sea, and a salt-wedge regime. Using stable isotope analysis, we explored the relative importance of the different sources of primary production in the food web. Our results show that phytoplankton and macrodetritus from terrestrial salt and freshwater marshes both contribute to the food web of the Río de la Plata estuary. On the basis of the sampled species, we identified four trophic levels. The clam Mactra isabelleana, the calanoid copepod Acartia tonsa, and the opossum shrimp Neomysis americana are the primary consumers. The rays Atlantoraja castelnaui and Squatina guggenheim and the shark Galeorhinus galeus are the top predators. The Río de la Plata food web shows an important input of nutrients derived from phytoplankton. Rays, sharks, and predatory gastropods reveal an important contribution of C4 plants (likely Spartina spp.). However, production derived from C3 plants is also important for some species. The fishes Brazilian menhaden, Brevoortia aurea; the stripped weakfish Cynoscion guatucupa; and the whitemouth croaker, Micropogonias furnieri, showed differences in their isotopic signatures as juveniles and adults, indicating different food sources, and they were therefore treated as different components of the food web. Our data suggest that detritus from salt and freshwater marshes is reaching the Río de la Plata estuary and can be an important allocthonous source of energy to this environment.