Characterization of Pallid Sturgeon (Scaphirhynchus albus) Spawning Habitat in the Lower Missouri River

Acipenseriformes (sturgeons and paddlefish) globally have declined throughout their range due to river fragmentation, habitat loss, overfishing, and degradation of water quality. In North America, pallid sturgeon (Scaphirhynchus albus) populations have experienced poor to no recruitment, or substantial levels of hybridization with the closely related shovelnose sturgeon (S. platorynchus). The Lower Missouri River is the only portion of the species’ range where successful reproduction and recruitment of genetically pure pallid sturgeon have been documented. This paper documents spawning habitat and behavior on the Lower Missouri River, which comprises over 1,300 km of unfragmented river habitat. The objective of this study was to determine spawning locations and describe habitat characteristics and environmental conditions (depth, water velocity, substrate, discharge, temperature, and turbidity) on the Lower Missouri River. We measured habitat characteristics for spawning events of ten telemetry-tagged female pallid sturgeon from 2008–2013 that occurred in discrete reaches distributed over hundreds of kilometers. These results show pallid sturgeon select deep and fast areas in or near the navigation channel along outside revetted banks for spawning. These habitats are deeper and faster than nearby river habitats within the surrounding river reach. Spawning patches have a mean depth of 6.6 m and a mean depth-averaged water-column velocity of 1.4 m per second. Substrates in spawning patches consist of coarse bank revetment, gravel, sand, and bedrock. Results indicate habitat used by pallid sturgeon for spawning is more common and widespread in the present-day channelized Lower Missouri River relative to the sparse and disperse coarse substrates available prior to channelization. Understanding the spawning habitats currently utilized on the Lower Missouri River and if they are functioning properly is important for improving habitat remediation measures aimed at increasing reproductive success. Recovery efforts for pallid sturgeon on the Missouri River, if successful, can provide guidance to sturgeon recovery on other river systems; particularly large, regulated, and channelized rivers.     

Behavioural response of Kootenai white sturgeon (Acipenser transmontanus,Richardson, 1836) early life stages to gravel,pebble, and rubble substrates: guidelines for rearing substrate size

Guidelines for creating rearing substrate for sturgeon early life stages are needed for restoration programmes creating habitats for spawning and rearing of early life stages. To determine the effects of rock size on motile early life stages, experiments were conducted in artificial streams to observe the behaviour of free embryos and larvae of Kootenai River white sturgeon (Acipenser transmontanus) relative to rock size. Most (≥90%) of the free embryos in replicate test streams with 100% gravel, 100% pebble, or 100% rubble hid under rocks, with few moving downstream. There was no difference in downstream movement of free embryos among rock treatments, therefore all rock types provided cover habitat. Similarly, in rock mixture tests, with a variable percentage of pebble, small rubble, or large rubble in different tanks, even fewer free embryos moved downstream. With increasing age, larvae increasingly used the open bottom and velocity refuges downstream of or alongside rocks of any size while drift feeding. Downstream movement of larvae in both rock regime tests was affected by rock size, with significantly reduced movement relative to increasing abundance of large rock (rubble). However, in all rock mixtures, free embryos (and later, larvae when they stopped dispersing) preferred the smallest rock size available (pebble; P = 0.0001). This suggests a strong innate preference of both life stages for small substrate that is likely related to increased survival. A rock mixture of 10% gravel (16–32 mm diameter) and 30–40% pebble (diameter, 30–60 mm) should provide adequate rearing substrate for free embryos and early‐larvae. The remaining 50–60% should be mixed rubble and boulders for spawning and egg rearing.     

Post‐hatch dispersal of lake sturgeon (Acipenser fulvescens,Rafinesque, 1817) yolk‐sac larvae in relation to substrate in an artificial stream

Knowledge of the effects of environment and genotype on behavior during early ontogenetic stages of many fish species including lake sturgeon (Acipenser fulvescens) is generally lacking. Understanding these effects is particularly important at a time when human activities are fundamentally altering habitats and seasonal and diel physical and biotic stream features. Artificial stream channels were used in a controlled experiment to quantify lake sturgeon yolk‐sac larvae dispersal distance and stream substrate preference from different females (N = 2) whose eggs were incubated at different temperatures (10 and 18°C) that simulated stream conditions during early and late spawning and incubation periods in the Black River, Michigan. Data revealed that yolk‐sac larvae exhibited considerable variability in dispersal distance as a function of family (genotype), temperature experienced during previous (embryonic) ontogenetic stages, and environmental ‘grain’. Yolk‐sac larvae dispersal distance varied as a function of the juxtaposition of substrate to location of egg hatch. Lake sturgeon yolk‐sac larvae dispersed from mesh screens attached to bricks and settled exclusively in gravel substrate. Dispersal distance also varied as a function of family and egg incubation temperatures, reflecting differences in offspring body size and levels of endogenous yolk reserves (yolk sac area) at hatch. Expression of plasticity in dispersal behavior may be particularly important to individual survival and population levels of recruitment contingent upon the location, size, and degree of fragmentation of suitable (gravel) habitats between adult spawning and yolk‐sac larvae rearing areas.     

Keeping close to the river,shore and surface: the first marine migration of brown trout (Salmo trutta) and Arctic charr (Salvelinus alpinus) post-smolts

Acoustic telemetry was utilized to track 49 brown trout (Salmo trutta) and 37 Arctic charr (Salvelinus alpinus) first-time migrants of wild origin [post-smolts; mean L_F (fork length): 169 and 172 mm] in a large fjord in northern Norway. The S. trutta were registered at sea for more than twice the time of the S. alpinus (medians of 54 and 22 days, respectively). Both species were mostly detected near river mouths (>80% of detections) and almost exclusively spent their time (>95%) within the interior 18 km of the fjord. They were surface oriented, with most detections at <1 m depth and S. trutta deeper on average (median mean depths of 0.7 and 0.5 m, respectively). This study concludes that post-smolts of both species stay closer to the surface and to river mouths than larger veteran migrants. This study emphasizes the importance of river mouths and upper water layers for the survival of both species during their first marine migration.     

Resident spawning of Japanese smelt,Hypomesus nipponensis,along gravel shorelines in Lake Nojiri,Central Japan

In Lake Nojiri, the Japanese smelt, Hypomesus nipponensis McAllister, 1963, population has been thought to be maintained by artificial spawning, and stocking efforts as natural spawning in in-flowing streams is unlikely due to the lack of inflowing stream habitat. In this study, novel resident Japanese smelt spawning was observed along the lakeshore in shallow areas with clean gravel and flow. Spawning occurred at night during early March to mid-April and eggs, confirmed on gravel substrate, progressed to the eyed state in 5–6 weeks. Although natural spawning was observed, the ratio of eggs that progressed to the eyed stage was minimal, possibly due to thick algae cover in areas with low flow velocity. Therefore, resident Japanese smelt spawning along the lake shoreline is physically possible and potentially contributes to the overall population in Lake Nojiri, but in-lake spawning alone presumably is not a biologically viable method for population sustainability due to low survival rates and egg density at present. Environmental improvements such as construction of fish ladders to suitable in-flowing spawning habitat, introduction of clean gravel to shorelines, and water level management adjusted to the smelt spawning run would contribute to higher recruitment by natural smelt reproduction, and consequently enhance the smelt production in Lake Nojiri.

     

Environmental requirements of common riverine European salmonid fish species in fresh water with particular reference to physical and chemical aspects

This review attempts to assess, as quantitatively as possible, the habitat requirements in fresh water of three common and widespread European salmonid species. Namely: the trout (Salmo trutta L.), the salmon (S. salar L.) and the grayling (Thymallus thymallus L.). Requirements are considered for spawning, incubation and emergence, juveniles and smolts and for adults and spawning movements.     

Seasonal growth differences of larval Hyporhamphus picarti (Hemiramphidae) in the Sine Saloum estuary,Senegal

The African halfbeak Hyporhamphus picarti (Hemiramphidae) is one of the most abundant species within the ichthyoplankton community of the Sine Saloum estuary (Senegal). A year‐round occurrence of larvae suggests that the Sine Saloum is an important spawning habitat for this species. Annual fluctuations in water temperature, however, can have severe impacts on the survival probabilities of marine fish larvae. To determine whether temperature has an effect on the growth of H. picarti during its larval development, larval age at length and somatic growth rates were investigated for two contrasting spawning seasons in 2014: February (cold season, 20.8°C) and June (warm season, 26.4°C). In both months H. picarti larvae were sampled at the mouth of the Saloum River using neuston nets. Sagittal otoliths’ increments were counted to estimate the larva age at a given standard length (SL). The age of larvae ranged between 2 and 22 days, with SL of 3.86–21.68 mm, respectively. In order to describe larval age at length during the contrasting spawning seasons, two distinctive Gompertz functions were applied. Accordingly, specimens sampled in June (0.94 ± 0.17 mm per day) exhibited significantly higher somatic growth rates than those sampled in February (0.60 ± 0.06 mm per day). These findings suggest that water temperature is an important factor influencing larval growth in H. picarti. Information concerning the early life stages of H. picarti are scarce and the results of the present study may contribute to a better understanding of the species’ biology and ecology.     

Length‐weight relationship of two mudskippers (Gobiidae: Oxudercinae) Oxuderces dentatus (Eydoux & Souleyet, 1850) and Scartelaos histophorus (Valenciennes, 1837) from Dhamara estuary,Odhisa, India

Oxuderces dentatus and Scartelaos histophorus species were collected seasonally from the Dhamara estuary (Odhisa, India) using scoop nets, cast nets as well as by hand for a period of 1 year (January 2015–December 2015). Length–weight relationships were estimated. Total lengths (TL) for O. dentatus ranged from 42 to 80 mm, and from 58 to 122 mm for S. histophorus. Similarly, total weights of O. dentatus and S. histophorus ranged from 2.5–10.7 g to 7.7–26.5 g, respectively. The ‘b’ values estimated for O. dentatus (2.718) and S. histophorus (2.689) were below 3. The condition factors of O. dentatus and S. histophorus were minimum in summer and maximum post‐monsoon.     

Influence of habitat dynamics on the distribution and abundance of the federally threatened Santa Ana Sucker, <Emphasis Type="Italic">Catostomus santaanae</Emphasis>, in the Santa Ana River

Habitat degradation affects native stream fish populations worldwide. We examined the impact of fluctuation in environmental variables on the population dynamics of the federally threatened Santa Ana sucker, Catostomus santaanae, in the Santa Ana River, California through: 1) annual quantitative surveys of C. santaanae abundance and habitat at three 100-m sites between 2001 and 2008 and 2) annual surveys of habitat composition within a 30-km stretch of the Santa Ana River between 2006 and 2008. We used Akaike’s Information Criterion (AIC) to evaluate competing models that used environmental variables to explain variation in C. santaanae abundance among sites and years. The most plausible model identified a positive relationship between C. santaanae abundance and both the amount of coarse substrate (i.e., gravel and cobble) and rate of discharge among site-years. Surveys at the 30-km scale indicated that the prevalence of coarse substrate declined in a downstream direction in each year and that the total amount of this habitat type varied annually. Specifically, cobble/gravel habitat was mostly confined to the upstream 4 km, 9.6 km, and 5.1 km of the survey area in 2006, 2007, and 2008, respectively. Fine sediment comprised the bulk of downstream habitat every year. This large-scale flux in the distribution of coarse sediment likely has a large effect on the population dynamics of C. santaanae in the Santa Ana River. Our results underscore the need to maintain and enhance suitable C. santaanae habitat to ensure its long-term persistence in the Santa Ana River.     

Phylogeography,genetic structure,and conservation of the endangered Caspian brown trout, <Emphasis Type="Italic">Salmo trutta caspius</Emphasis> (Kessler, 1877), from Iran

The Caspian Sea, the largest inland closed water body in the world, has numerous endemic species. The Caspian brown trout (Salmo trutta caspius) is considered as endangered according to IUCN criteria. Information on phylogeography and genetic structure is crucial for appropriate management of genetic resources. In spite of the huge number of studies carried out in the Salmo trutta species complex across its distribution range, very few data are available on these issues for S. trutta within the Caspian Sea. Mitochondrial (mtDNA control region) and nuclear (major ribosomal DNA internal transcribed spacer 1, ITS-1, and ten microsatellite loci) molecular markers were used to study the phylogeography, genetic structure, and current captive breeding strategies for reinforcement of Caspian trout in North Iranian rivers. Our results confirmed the presence of Salmo trutta caspius in this region. Phylogenetic analysis demonstrated its membership to the brown trout Danubian (DA) lineage. Genetic diversity of Caspian brown trout in Iranian Rivers is comparable to the levels usually observed in sustainable anadromous European brown trout populations. Microsatellite data suggested two main clusters connected by gene flow among river basins likely by anadromous fish. No genetic differences were detected between the hatchery sample and the remaining wild populations. While the current hatchery program has not produced detectable genetic changes in the wild populations, conservation strategies prioritizing habitat improvement and recovering natural spawning areas for enhancing wild populations are emphasized.     

Spawning habitat selection and suitability for Japanese dace, Tribolodon hakonensis

We have investigated the effects of three current velocities and three substrate sizes (gravel to cobble) on the spawning behavior of Japanese dace, Tribolodon hakonensis, in spawning-induction and habitat-selection experiments. In the spawning-induction experiment under laboratory conditions the number of females induced to spawn was significantly fewer at low current velocity (ca. 5 cm s^–1) than at medium (ca. 30 cm s^–1) or high (ca. 50 cm s^–1) current velocity. Females spawned independently of substrate size in the experimental tank, and did not bury their eggs in the substrate bed. In the habitat-selection experiment under field conditions, females selected the substrate microhabitat and spawned more frequently at a site with medium substrate size (very coarse gravel; major axis ca. 40 mm) than at sites with small (fine gravel; ca. 8 mm) or large (cobble; ca. 70 mm) substrate size. We conclude that Japanese dace select spawning sites at least partly on the basis of current velocity and substrate size, which affects the survival rate of eggs.     

Size,relative abundance,and catch‐per‐unit‐effort of round goby,Neogobius melanostomus,in anthropogenically modified and natural habitats in the western basin of Lake Erie

To determine if anthropogenically modified habitats possess greater numbers of round goby and serve as dispersal vectors, we used angling to compare catch‐per‐unit of effort for 64 natural and modified habitat areas. In addition, a gravel natural habitat was seined to compare length frequency distribution with anthropogenically modified habitats. Natural habitats included gravel beaches and natural rubble and cliff wall, while modified habitats included artificial riprap, concrete sea wall, and metal sheet piling. No significant difference in relative abundance was observed in round goby preference among modified habitats (P = 0.52), but natural gravel habitats were significantly different from modified habitats that included artificial riprap (P = 0.002), concrete sea wall (P < 0.001), and metal sheet piling (P = 0.003). When habitat subcategories were compared using anova , the natural gravel beach habitat was significantly different from the three artificial substrates and from natural rubble and cliff wall substrates (P < 0.004). No round goby were caught from gravel beach habitats; thus, this habitat was removed from further analysis. A Student t‐test indicated no significant difference between habitats was found between the natural rubble and cliff wall habitat and the three other artificial habitats (concrete sea wall, P = 0.33; riprap, P = 0.53; metal sheet piling, P = 0.11). We further evaluated gravel beach habitats to determine the reason for the lack of goby capture. We seined gravel beach habitat and collected 328 individuals, with which we evaluated the length‐frequency distribution and calculated length–weight relationships by sex. Our results indicated that only 5.2% of the goby population was available for capture by angling on the gravel beach habitat. A t‐test comparing the demographic attributes between seining and angling indicated a significant difference between goby length (P < 0.001) and weight (P < 0.001). The regression slope indicated an ontogenetic habitat shift occurred near 62 mm standard length. Smaller round goby individuals were found in less structurally complex gravel beach habitat, while larger individuals were associated with complex habitat.     

Contributions to molecular systematics of water scavenger beetles (Hydrophilidae,Coleoptera)

Phylogenetic relationships within Hydrophilidae were examined by analyses of separate and combined nuclear and mitochondrial markers (28S rRNA, 18S rRNA, 16S rRNA, 12S rRNA, COI and COII genes). The preferred (Bayesian) tree topology suggests a sister group relationship between Spercheidae and Hydrophilidae, supporting the ‘hydrophilid lineage’; Epimetopidae are placed on the base of the ‘helophorid branch’, the monophyly of Sphaeridiinae is highly supported, nested deeply within Hydrophilidae closest to Enochrus, making Hydrophilinae and Acidocerini paraphyletic; Hydrobius appears as sister taxon to (Hydrochara + Hydrophilus) without a closer relationship to Acidocerini; the hydrophiloid–histeroid sister group relationship is confirmed. The topology of several taxa remains contradictory, and requires further investigations with a larger taxon sampling and additional molecular markers.     

Balancing competing life‐stage requirements in salmon habitat rehabilitation: between a rock and a hard place

Gravel augmentation is often applied to rivers and streams to rehabilitate salmonid spawning and incubation habitat. However, the effect of gravel size on salmon spawning utilization and embryo survival during incubation is not well understood. We conducted an experiment on a regulated and previously mined Northern California salmonid‐bearing stream in which different sized gravel (small, medium, and large) patches were placed into the stream's degraded spawning reach. We documented Oncorhynchus tshawytscha (Chinook salmon) spawning activity within the three gravel sizes for two seasons. In addition, we deployed Chinook salmon embryos into each gravel size patch and allowed them to incubate until estimated emergence time. Although all experimental gravel sizes were predicted to be within the spawning population's mobilization capabilities, model results indicated the probability of salmon building redds decreased as substrate size increased. Conversely, embryo survival increased as gravel size increased. A possible mechanism of disparate Chinook salmon embryo survival is provided by an observed decrease in embryo survival correlating with greater presence of embryo predators (leeches), which are associated with smaller gravel. Our results indicate a parent‐offspring conflict in optimal spawning gravel size for Chinook salmon, and suggest that an intermediate gravel size would maximize overall reproductive success across both spawning and incubation life stages.     

Phylogenetic relationships among North Atlantic redfish (genus Sebastes) as revealed by mitochondrial DNA sequence analyses

Species structure and phylogenetic relationships among the four currently recognised North Atlantic redfish species, Sebastes mentella (‘deep‐sea’ and ‘oceanic’ phenotype), S. marinus (including ‘giant’ phenotype), S. fasciatus and S. viviparus, were investigated by sequencing the complete mitochondrial NADH dehydrogenase subunit 3 (ND3) gene for 313 individuals (333 including outliers). Low levels of sequence divergence of 0.3–2.3% between the North Atlantic Sebastes haplotypes, low resolution in phylogenetic trees and a star‐like statistical parsimony network indicate a population bottleneck and/or founder event with a subsequent population expansion and a rapid speciation in North Atlantic Sebastes. Diagnostic mutations within the ND3 gene were recognised for some of the species. The results lead to the hypothesis that the ancestral haplotype lineage is now very rare or has suffered extinction and that the most basal lineage is found in S. viviparus. The results further indicate direct descendants in the S. fasciatus and S. marinus lineages from the S. mentella lineage, whereas the S. viviparus lineage originates from an earlier division. The observation of two haplotype lineages in S. marinus with a relatively high level of intraspecific genetic divergence, points towards a possible cryptic speciation.     

Spawning lake sturgeon (Acipenser fulvescens Rafinesque, 1817) and their habitat characteristics in Rainy River,Ontario and Minnesota

Lake Sturgeon (Acipenser fulvescens) spawning habitat in the Rainy River was studied in light of the ongoing review of the rules governing water levels upstream that affect discharge rates through the International Falls dam. The objectives of this study were to assess the current status of spawning Lake Sturgeon below the dam by: (i) evaluating weight–length relationships, condition, age and growth; (ii) identifying spawning locations and characterizing its physical attributes; and, (iii) evaluating the effects of water surface elevation on the availability of spawning habitat. Spawning was confirmed with use of egg mats, and targeted sampling of spawning individuals was completed using gillnets and electrofishing. Physical attributes of spawning locations, including temperature, depth and water velocity were collected at a range of water levels using an Acoustic Doppler Current Profiler and representative sediment sampling. Biological characteristics and timing of spawning events were consistent with those previously reported for Lake Sturgeon. However, a wider range of depths (0.3–10.5 m) and velocities (0.01–1.9 m³/s) than reported in most single site studies was found here, with the ranges encompassing what is reported in the literature as a whole. Lake Sturgeon were found to prefer coarse spawning substrates dominated by bedrock, boulder or cobble. The availability of preferred spawning habitat varied significantly with the changing water levels observed during the study and was eventually limited at higher water levels by river channel form. Because of the implications for dewatering of nest sites, keeping flows constant during spawning is critical to Rainy River Lake Sturgeon spawning success.     

Selection and preference of benthic habitat by small and large ammocoetes of the least brook lamprey (<Emphasis Type="Italic">Lampetra aepyptera</Emphasis>)

In this laboratory study, we quantified substrate selection by small (<50 mm) and large (100–150 mm) ammocoetes of the least brook lamprey (Lampetra aepyptera). In aquaria, ammocoetes were given a choice to burrow into six equally-available substrate types: small gravel (2.360–4.750 mm), coarse sand (0.500–1.400 mm), fine sand (0.125–0.500 mm), organic substrate (approximately 70% decomposing leaves/stems and organic sediment particles, and 30% silt and fine sand), an even mixture of silt, clay, and fine sand, and silt/clay (<0.063 mm). Fine sand was selected with a significantly higher probability than any other substrate. Fine sand habitat is limited in many streams, in part owing to geology, but also as a result of channelization and excessive silt/clay sedimentation, which is a conservation concern. Our results indicate that ammocoetes of least brook lampreys are habitat specialists that prefer fine sand habitat. Hence, availability of fine sand habitat may limit distributions and population sizes.     

Phylogeographic structure of brown trout Salmo trutta in Britain and Ireland: glacial refugia,postglacial colonization and origins of sympatric populations

The phylogeographical structure of brown trout Salmo trutta in Britain and Ireland was studied using polymerase chain reaction–restriction fragment length polymorphism (PCR–RFLP) analysis of four mitochondrial DNA segments (16S/ND1, ND5/6, COXIII/ND5 and ND5/12S). Analysis of 3636 individuals from 83 sites–morphotypes revealed a total of 25 haplotypes. These haplotypes were nested in seven two‐step clades. Although there was a clear geographical patterning to the occurrence of derived clades, admixture among ancestral clades was extensive throughout the studied area. A relevant feature of the data was that some populations contained mixtures of highly divergent clades. This type II phylogeographic pattern is uncommon in nature. Clade intermixing is likely to have taken place during earlier interglacials as well as since the Last Glacial Maximum. The anadromous life history of many S. trutta populations has probably also contributed to clade mixing. Based on the data presented here and published data, postglacial colonization of Britain and Ireland most likely involved S. trutta from at least five potential glacial refuges. Probable locations for such refugia were: south of England–western France, east of the Baltic Sea, western Ireland, Celtic Sea and North Sea. Ferox S. trutta, as defined by their longevity, late maturation and piscivory, exhibited a strong association with a particular clade indicating that they share a common ancestor. Current evidence indicates that the Lough Melvin gillaroo S. trutta and sonaghen S. trutta sympatric types diverged prior to colonization of Lough Melvin and, although limited gene flow has occurred since secondary contact, they have remained largely reproductively isolated due to inlet and outlet river spawning segregation. Gillaroo S. trutta may reflect descendents of a previously more widespread lineage that has declined due to habitat alterations particularly affecting outlet rivers. The mosaic‐like distribution of mtDNA lineages means that conservation prioritization in Britain and Ireland should be based on the biological characteristics of local populations rather than solely on evolutionary lineages.     

Lake sturgeon spawning on artificial habitat in the St Lawrence River

In 1996, lake sturgeon (Acipenser fulvescens) spawning was documented for the third consecutive year on an artificially placed gravel bed in the St Lawrence River. Two distinct spawning periods were observed in 1996. Spawning initially commenced on 17 June, when water temperature reached 15°C. A second spawning event was documented from 28 June to 1 July (16°C). Sturgeon egg densities were monitored in three transects on egg trays, on the gravel surface, and within interstitial spaces in the gravel. Counts of developing eggs in the gravel bed during both spawning periods were used to estimate a total of 275 000 eggs on the study area (0.075 ha). Average egg density was highest in the transect with the highest water velocities. Lake sturgeon fry were first observed in the gravel on 24 June (15.5°C), and first emergence from the gravel was documented on 28 June. Hatching following the second spawning event commenced on 3 July. Based on assessment of average embryo viability (61.6%) and egg‐to‐emergent fry survival (17.6%) an estimate of about 171 000 sturgeon eggs hatched, producing over 49 000 emergent fry. Current velocity, substrate particle size, depth of substrate, and maintenance of sediment‐free interstitial spaces are important considerations in planning future spawning habitat enhancement projects.     

Hook selectivity as a mitigating measure in the catches of the stingray Pteroplatytrygon violacea (Bonaparte, 1832) (Elasmobranchii,Dasyatidae)

Hook selectivity, sex ratio of catches and relative abundance (Catch Per Unit Effort – CPUE) were assessed for the pelagic stingray Pteroplatytrygon violacea (Bonaparte, 1872), caught by longline gear in the southwestern Atlantic Ocean over the continental slope and adjacent oceanic area. The catches were carried out at depths of 200–4000 m by research cruises in 2002 and 2003, from Cabo Frio (22°52′S) to Laguna (28°28′S); and by hook selectivity experiments from 2004 to 2008, from Itajaí (26°54′S) to Tramandaí (29°59′S). Hook selectivity experiments indicated higher catches of stingrays with ‘J’ hooks (9/0, 10° offset) commonly used by the pelagic longline fleet than with ‘circle’ hooks (18/0, 10° offset). ‘circle’ hooks reduce the longline by‐catches of this species. Most of the stingrays caught were males (6 : 1). One female aborted mid‐term embryos at the time of capture. CPUE was highest between spring and autumn and lowest during winter.