for many decades, scientists at the marine biological association (mba) in plymouth and the centre for environment, fisheries and aquaculture science (cefas), formerly the directorate of fisheries research, at lowestoft have undertaken considerable research into the ecology and life histories of elasmobranch fish around the british isles.

elasmobranch fish are susceptible to over-exploitation by commercial and recreational fisheries and an increasing focus of conservation initiatives. the lack of accurate species-specific landings data in many european fisheries and the paucity of biological data have restricted the types of stock assessment that can be undertaken. hence, other methods of determining the overall status of elasmobranch fish are required. for demersal elasmobranchs around the british isles, the most widely available biological data describe life histories and abundance from fishery-independent surveys. here, we examine the length-distribution of demersal elasmobranchs caught during groundfish surveys, to determine which life history stages are sampled effectively. for these stages, we report trends in abundance and relate the trends to knowledge of the species' biology and fisheries, and to the decline criteria that are used to assess species' status by nature conservation agencies. the analyses show that many large demersal elasmobranchs have been severely depleted in uk waters but that groundfish surveys still provide a good source of data for monitoring changes in status of the more abundant species. for rare and highly depleted species, groundfish surveys often provide good retrospective descriptions of declines, but the surveys have limited power to detect recent changes in status.

published data on the diversity, life history, ecology, and status of freshwater and euryhaline elasmobranchs was reviewed in the context of anthropogenic threats and principles of conservation biology. at least 171 species of elasmobranch, representing 68 genera and 34 families, are recorded from fresh or estuarine waters. of these, over half are marginal in estuaries, less than one-tenth are euryhaline, and one-fifth are obligate in fresh water. obligate freshwater elasmobranchs are dominated by myliobatoid stingrays, of which two-thirds are potamotrygonids endemic to atlantic drainages of south america. freshwater and euryhaline elasmobranchs adhere to strongly k-selected life histories and feed at high trophic levels, similar to those of their marine relatives. however, freshwater and euryhaline elasmobranchs are also subject to habitat constraints, notably more limited volume and physicochemical variability than the ocean, that may render them more vulnerable than marine elasmobranchs to the effects of human activities. the greatest diversity and abundance of freshwater and euryhaline elasmobranchs occur in tropical countries with enormous and rapidly increasing human populations, notably south america, west africa, and south-east asia. knowledge of the biology, distribution, ecology, and status of freshwater and euryhaline elasmobranchs is frustrated by unresolved taxonomic problems, which are briefly summarized. to clarify selected issues in the conservation of freshwater and euryhaline elasmobranchs, special attention is given to sharks of the genus glyphis, pristids, and potamotrygonids. to foster live release when possible as well as prevent discard of specimens and loss of data, an illustrated key to differentiate carcharhinus from glyphis sharks is provided. obligate freshwater elasmobranchs with limited geographic ranges are deemed most vulnerable to extinction, but euryhaline elasmobranchs that require access to the sea to breed are also at significant risk. based on the foregoing data and principles of conservation biology, suggested action plans for the conservation of freshwater and euryhaline elasmobranchs and the conservation of freshwater habitats are provided.

the uk government's strategy for reducing greenhouse gas emissions to meet carbon mitigation obligations and the wider aims on sustainable development has provided the impetus for a rapid growth in activity associated with offshore renewable energy, particularly offshore wind farms. recently, consents for offshore renewable energy development (ored) were approved in three strategic areas—the outer thames estuary, the greater wash and the eastern irish sea. the scale of the planned developments means that each will have a large environmental footprint and multiple ored will have a cumulative effect on the environment. here we discuss current understanding of ored construction, operation and decommissioning with regard to the potential interaction with elasmobranchs because of the worrying status of elasmobranch populations within the uk coastal zone. based on the likely interactions between elasmobranchs and ored a framework is proposed which aims to promote cooperative initiatives between elasmobranch conservation management and the offshore renewables industry.

current concerns about the population levels of the basking shark (cetorhinus maximus) in the north-east atlantic have prompted a need to understand population distribution, habitat preference and centres of abundance. in this study, spatial distribution maps derived from satellite-tag geolocations, boat surveys and public sightings data were compared. the broad distribution patterns revealed by these different methods are similar, but there are considerable differences in density distributions. surface sightings data show high densities, or ‘hotspots’ in the hebridean sea, clyde sea, irish sea and close inshore around devon and cornwall. tag geolocations, in contrast, identified two areas where individuals spent considerable time outside the distributions indicated by surveys and public sightings: the celtic sea and western approaches of the english channel. the reason for this disparity and its implications for population estimates for the species are discussed.

amid concern about the status of skates and rays in welsh waters the present work set out to provide up-to-date information on the population biology of raja clavata in caernarfon bay. the von bertalanffy growth parameters were l∞=100.9 cm, k=0.18 y−1 and t0=−0.95 y for males; and l∞=117.6 cm, k=0.16 y−1 and t0=−0.7 y for females. male r. clavata reached 50% maturity at 58.8 cm and 3.9 y, which was smaller and younger than females (l50 and a50 were 70.5 cm and 5.3 y, respectively). although previously over-exploited, the present estimate of total mortality (z) was 0.48–0.49 y−1 which, in terms of replacement mortality (calculated as 0.7 y−1), suggests no immediate prospect of recruitment failure for r. clavata in caernarfon bay. the potential for the recovery of a depleted population is discussed in relation to the allee effect.

although depleted throughout the european continental shelf, the relatively high density of thornback rays raja clavata, in the thames estuary (uk) makes it an important stock centre and potential focus for species management. to describe spatial and temporal distribution, 197 thornback rays were tagged with electronic data storage tags (dsts) and released in the thames estuary in october 1999 and 2000, and 100 rays tagged with conventional tags in 2000. fifty-one per cent of dsts and 48% of conventional tags were returned. fishery-independent estimates of position (‘geolocations’) between the time of release and recapture using the tidal location method were possible using 75 individual data records of between 31 and 423 days. ninety-six per cent of rays were recaptured within the thames estuary. the rays were located in water of 20–35 m depth during the autumn and winter, then migrated into shallower water (<20 m depth) during the spring. fishery-independent analysis of distribution demonstrated that the rays were more widely distributed in the southern north sea during the autumn and winter. the range contracted in spring, when the fish moved into the inner thames estuary. no gross behaviour differences were observed between males and females. displacement and dispersion coefficients calculated from geolocation data demonstrated clear annual cycles, indicative of migration. these movements were not apparent from the mark–recapture data, a fishery-related effect. the extent of migration as determined from experiments with dsts was approximately three times greater than that suggested by conventional tagging data alone.

a shark tagging programme along the portuguese coast was initiated in 2001 in collaboration with the national marine fisheries service. from a total of 168 blue sharks (prionace glauca) tagged, 34 sharks were recaptured (20% return rate) providing important information on this species' movement patterns for the area. a total of 28 sharks travelled less than 1000 km while at liberty for time periods ranging from 22 to 1294 days. the remaining fish travelled long distances to north-west africa, central atlantic and the bay of biscay. only one shark made a transatlantic migration, being recaptured 3187 km from the tagging site. north–south movements seem to be related to seasonal sea-surface temperature variation in the north-east atlantic. seasonal segregation of different life stages also occurs.

specimens of the zipper sand skate psammobatis extenta were collected in the region of ubatuba off the northern coast of the state of são paulo, brazil, monthly for one year (january–december 2000), at 25- to 40-m isobaths. a total of 123 individuals were caught. the total length (tl) of females averaged 224.6 mm, and of males 217 mm. the overall sex ratio was 1:1. analysis of the length–weight relationship indicated the existence of positive allometry in females, and isometry in males. the length at onset of sexual maturity was determined for both sexes; females reached sexual maturity at smaller sizes than males (tl50=230.7 and tl50=237.7 mm respectively). females showed functional parity of both ovaries and uteri. females that were pregnant or were carrying vitellogenic oocytes were observed during nine of the 12 months of the survey, indicating a continuous reproductive cycle. psammobatis extenta was most abundant from january to april, and again from june to october. most individuals were collected at the 40-m isobath. both adults and neonates were collected in the study area. however, adolescent skates were scarce, which either indicates differential occupation of the area, or suggests that the shallow waters of the continental shelf are used as breeding grounds.

the presence of velvet belly, etmopterus spinax in angolan waters is confirmed by the capture and examination of 233 specimens caught between 2002 and 2004 on board the rv ‘dr. fridtjof nansen’. morphometric measurements are given.

between 1997 and 2003, there were 2088 natural predations by white sharks (carcharodon carcharias) on cape fur seals (arctocephalus pusillus pusillus) and 121 strikes on towed seal-shaped decoys were documented from observation vessels at seal island, south africa. white sharks at seal island appear to selectively target lone, incoming young of the year cape fur seals at or near the surface. most attacks lasted <1 min and consisted of a single breach, with predatory success rate decreasing rapidly with increasing duration and number of subsequent breaches. a white shark predatory ethogram, composed of four phases and 20 behavioural units, is presented, including four varieties of initial strike and 11 subsequent behaviour units not previously defined in the literature. behaviour units scored from 210 predatory attacks revealed that, for both successful and unsuccessful attacks, polaris breach was the most commonly employed initial strike, while surface lunge was the most frequent second event, closely followed by lateral snap. examination of video footage, still images, and tooth impressions in decoys indicated that white sharks at seal island bite prey obliquely using their anterolateral teeth via a sudden lateral snap of the jaws and not perpendicularly with their anterior teeth, as previously supposed. analysis of white shark upper tooth morphology and spacing suggest the reversed intermediate teeth of white sharks occur at the strongest part of the jaw and produce the largest wound. white shark predatory success at seal island is greatest (55%) within one hour of sunrise and decreases rapidly with increasing ambient light; the sharks cease active predation on seals when success rate drops to ±40%; this is the first evidence of cessation of foraging at unproductive times by any predatory fish. at seal island, white shark predatory success is significantly lower at locations where frequency of predation is highest, suggesting that white sharks may launch suboptimal strikes in areas of greatest intraspecific competition; this is the first evidence of social influence on predation in any elasmobranch. idiosyncratic predatory behaviours and elevated success rates of known individual white sharks at seal island suggest some degree of trial-and-error learning. a hypothetical decision tree is proposed that models predatory behaviour of white sharks attacking cape fur seals at the surface.

the tendency for marine fish to refuge in natural and artificial structures underwater is well documented, but the incidence of this behaviour among predatory sharks is not widely known. a sub-adult male nursehound scyliorhinus stellaris was tracked by intermittent acoustic telemetry over 168 days in a tidal sea lough. this individual, in-between undertaking nocturnal foraging excursions, refuged in at least five different narrow-entrance holes. refuge location was validated by underwater and surface observations during which time other nursehounds (sub-adult male and female), were also seen refuging, sometimes together. this indicates nursehound display philopatric behaviour centred on aggregation in ‘home’ refuges that, in this case, were labyrinthine rock systems.

video observation of oral gastric eversion in a free-living caribbean reef shark (carcharhinus perezi) shows voluntary gastric eversion followed by retraction not only occurs, but is extremely rapid (lasting ∼0.3 s). eversion may occur by stomach relaxation–oesophageal contraction coupled with increased abdominal pressures to enable prolapse, and retraction by a mechanism analogous to suction feeding. this behaviour provides a ‘cleansing’ function for removing indigestible food particles, parasites or mucus from the stomach lining. sharks, and possibly other animals with similar gut morphologies, may use this technique to help maintain a healthy alimentary tract.

discards represent a significant percentage of the total catches (up to 35%) in the north of spain trawl fishery. in the cantabrian sea (southern area of the bay of biscay), the estimated average total annual catch of small-spotted catshark (scyliorhinus canicula) is approximately 1500 tn, from which 80% is discarded. several experiments have been carried out in order to estimate the survival-rate of the small-spotted catshark caught by commercial trawlers in this area. the estimate of mean survival-rate from tagging surveys was 90% while from commercial trawlers it was 78%. several factors potentially influencing the survival-rate (sex, length, maximum depth fished, sorting time and trawl duration) were examined. no significant differences in survival-rates were found between males and females, and no strong relationships between survival-rate and depth fished, sorting time or trawl duration were evident. in commercial trawlers survival-rate was not dependent on the fish length.

a total of 67 discopyge tschudii was captured. individuals were sexed, measured and their stomach content analysed. siphon tips of the bivalve amiantis purpurata from each stomach were individually counted, weighed and their length and width measured. the size–frequency distribution of the local population of a. purpurata was surveyed for two years. siphons of a. purpurata were the main food item in 90% of individuals having stomach contents. the clam population was markedly bimodal, with 24 mm and 46 mm mean shell length for the younger and older size-classes, respectively. grazing by d. tschudii on a. purpurata varied with size and sex of the fish. small rays mainly ingested small siphons and large rays large siphons. nipped siphon tips were longer in male than in female rays.

the reproductive biology of the spiny dogfish, squalus acanthias, was investigated throughout a year, in the eastern mediterranean sea. one hundred and eighty specimens were sampled of which 119 were females and 61 males, ranging from 320 to 755 mm and from 350 to 820 mm total length (tl), respectively. the minimum size of mature females was 515 mm and 470 mm tl for mature males (smaller compared with sizes in other studies). gonadosomatic index (gsi) and hepatosomatic index (hsi) were higher during june and august in female dogfish, respectively; in males gsi had a peak in july and hsi showed its highest value in april. a total of 39 gravid females was identified with tl ranging between 570 and 755 mm. only 28 of them were bearing embryos; candled uteri were observed in the 11 other gravid animals. a positive relationship was recorded between maternal length and litter size. ovarian fecundity ranged between 1 and 6 (mean 2.1±1.1); uterine fecundity ranged from 1 to 6 (mean 3.3±1.2). the size of the pups varied from 72 to 220 mm tl and their weight ranged between 1.6–48.5 g (mean 11.7±8.6). the spiny dogfish was compared with fish from other study areas and was found to be smaller in size in the eastern mediterranean sea, reaching maturity at smaller sizes and obtaining lower fecundity than female fish in other areas.

etmopterus spinax and etmopterus pusillus are captured in large quantities in some deep-water fisheries along the portuguese coast and are always discarded. specimens were collected from february 2003 to may 2004 from deep-water fisheries and classified as mature or immature. maturity ogives were fitted and size at first maturity estimated for each sex of each species. both species are late maturing, with the maturity sizes varying between 75% and 87% of the maximum observed sizes, depending on species and sex. for both species, females tended to mature at and grow to larger sizes than males. the late maturation of these deep-water shark species makes these populations extremely vulnerable to increasing fishing mortality.

four captive specimens of sandbar shark carcharhinus plumbeus from the l'oceanogràfic aquarium (valencia, spain) were studied: one adult female (192 cm total length [tl]) reared for five months, her two new born pups (a female, 61 cm tl and a male, 60 cm tl), and one juvenile female, born in captivity, dead at nine months of age (90 cm tl). comparative measurements of length and diameter of vertebrae from three different regions of the vertebral column showed that vertebrae above the pelvic fins (nos. 59–63) are the biggest in this species. consequently, these vertebrae are preferred for age estimation given that growth marks are easier to identify. the only present mark in the vertebrae of the two neonate specimens was at the edge and was interpreted as the birth mark. a mark at a similar distance was present in the vertebrae of the juvenile and adult females.

adult female vertebrae analysis shows 23 marks without any variation in the banding pattern distribution during free-range growth and short period of captivity. the juvenile individual shows two clear growth marks developed after birth. the presence of these marks in a 9-month old individual suggests that the counting of all vertebral growth marks as annuli may result in the overestimation of age for this shark species.

one of 353 port jackson sharks, heterodontus portusjacksoni, caught off the southern coast of western australia, was a hermaphrodite. the female reproductive tract consisted of a large (functional) right ovary with three large yolked ova, a small non-functional left ovary and two well-developed uteri and oviducal glands. the male tract comprised two conspicuous but undeveloped testes, two vas deferens and two calcified claspers with grooves. this individual represents the first published example of hermaphroditism in the order heterodontiformes and is a rare example of an elasmobranch with a complete suite of both male and female reproductive structures.

the reproductive biology of 1045 female (9.5–67 cm (total length (tl)) and 1007 male (9.4–64.3 cm tl) blackmouth catsharks, galeus melastomus, was investigated. the sharks were caught off southern portugal by bottom crustacean trawlers at depths from 209 to 754 m. the sex ratio was 1:1, and this species is sexually dimorphic with males approaching maturity at smaller size than females. sexual segregation appears to be given for the stock within the study area. sexual maturity was reached at a total length above 49 cm in males and above 56 cm in females. mating and egg-deposition take place all year round, with two reproductive peaks of activity, in winter and summer. egg capsules are, on average, 54 mm long and 21 mm wide, with a maximum of 63×25 mm encountered. morphometric measurements of claspers, testes, ovaries, and oviducal glands were suitable for determining sexual maturity of blackmouth catshark.