Occurrence Of Sharks Research Articles

Occurrences of large sharks in the open waters of the southeastern Mediterranean Sea

Analysing large pelagic fisheries data from the open waters of the southeastern Mediterranean Sea during 1998 to 2005, we identified no more than 10 species of large sharks, although most updated literature cites more than twice this number in the region. We identified a statistically significant decline in species richness, with the probability of shark occurrence reducing to its lowest level in the most recent years. Blue shark was the predominant species, comprising approximately 70% of all large sharks encountered. A Milk shark was observed for the first time in the region. Based on their capture location, a series of maps depicting the spatial distribution of large sharks is provided. It seems as if currently the continuity of the presence of some species in the region may be questionable or that some species may have become too rare to be detected in the course of a conventional monitoring survey.

Segregation and foraging ecology of whale sharks, Rhincodon typus, in the southwestern Gulf of California

Sharks segregate by sex and size, but few studies have attempted to explain such behaviors. To address this, we examined aggregations and the foraging ecology of whale sharks in Bahia de La Paz (BLP) with aerial and ship surveys and direct observation. Zooplankton abundance and composition, and hydrographic conditions were analyzed in relation to whale shark occurrence to explore underlying factors causing segregations. We observed large aggregations of juveniles ( 9 m TL) offshore, composed of 84 % females. Juvenile sharks were associated to turbid shallow waters in BLP, where they performed stationary and dynamic suction feeding on dense copepod swarms. Adults occurred in oceanic waters and fed by ram-filtering on diffuse patches of euphausiids, with no association to oceanographic conditions. Such segregation may be advantageous to juvenile R. typus utilizing shallow coastal waters to find abundant preferred prey needed for their fast growth rates. Our studies suggest that the main driving forces of whale shark segregation by sex and size in BLP may be diet preference for juveniles and habitat preference for adult sharks.

Reef sharks and inshore habitats: patterns of occurrence and implications for vulnerability

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 460:115-125 (2012) - DOI: https://doi.org/10.3354/meps09722 Reef sharks and inshore habitats: patterns of occurrence and implications for vulnerability Andrew Chin1,*, Andrew Tobin1, Colin Simpfendorfer1, Michelle Heupel1,2 1Fishing and Fisheries Research Centre, School of Earth and Environmental Sciences, James Cook University, Townsville, Queensland 4811, Australia 2Australian Institute of Marine Science, Townsville, Queensland 4810, Australia *Email: andrew.chin@jcu.edu.au ABSTRACT: Reef sharks play important roles in tropical reef environments, but population declines have occurred in various locations including the Great Barrier Reef (GBR). While many reef shark studies focus on coral reefs, some reef sharks have been found across a range of inshore and coastal habitats. This study analyses fisheries observer data across large spatial scales (19314 km2) to investigate the occurrence of reef sharks amongst a mosaic of inshore habitats in the GBR lagoon. Six reef shark species were recorded, but comprised a relatively small proportion (1.8% by number) of the elasmobranch catch. The blacktip reef shark dominated the catch of reef sharks (60.2% by number), with lemon sharks, zebra sharks, grey carpet sharks, whitetip reef sharks and grey reef sharks less frequently encountered. Reef sharks occur in several habitat types, and logistic regression models suggest that they are most likely to occur in reef habitats and shallow shore habitats. The presence of a reef within 2 km increased the encounter probability in all habitat types. While the use of these different habitats by reef sharks is not well understood, these habitat use patterns affect the exposure of these species to risks, including some risk factors not considered previously, and could also lead to cumulative impacts. These habitats may also perform important ecological functions in sustaining reef shark populations. Habitat use patterns should be considered in risk assessments and management and have important implications for method selection and survey design in field studies of reef sharks and other mobile reef species. KEY WORDS: Habitat use · Vulnerability · Cumulative impact · Reef shark · Great Barrier Reef · Coastal habitat Full text in pdf format Supplementary material PreviousNextCite this article as: Chin A, Tobin A, Simpfendorfer C, Heupel M (2012) Reef sharks and inshore habitats: patterns of occurrence and implications for vulnerability. Mar Ecol Prog Ser 460:115-125. https://doi.org/10.3354/meps09722 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 460. Online publication date: July 24, 2012 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2012 Inter-Research.

Effects of Turtle Excluder Devices (TEDs) on the Bycatch of Three Small Coastal Sharks in the Gulf of Mexico Penaeid Shrimp Fishery

Abstract The stock of blacknose sharks Carcharhinus acronotus in the U.S. South Atlantic and the Gulf of Mexico is overfished, and according to the 2007 stock assessment conducted by the National Marine Fisheries Service overfishing continues to occur. Penaeid shrimp trawl bycatch rates in the Gulf of Mexico were modeled for this species as well as for the Atlantic sharpnose shark Rhizoprionodon terraenovae and bonnethead shark Sphyrna tiburo using a combination of research trawl and observer data. Research trawls have never used turtle excluder devices (TEDs), which are expected to exclude larger specimens of blacknose sharks. Most of the observer data that contain blacknose shark occurrences were collected during the pre-TED era when the two data sets tracked one another. Minimum observer data were available for the post-TED period (1990–present). As a consequence, the pre-TED (1972–1989) relationship between observer and research trawl catch per unit effort (CPUE) is driving the observer CPUE estimates...

Validating the occurrence of Caribbean reef sharks, Carcharhinus perezi (Poey), (Chondrichthyes: Carcharhiniformes) in the northern Gulf of Mexico, with a key for sharks of the family Carcharhinidae inhabiting the region

Among the sharks inhabiting the continental shelf waters of the western North Atlantic Ocean, those within the genus Carcharhinus are the most speciose (Castro 2011). Authoritative sources agree on the presence of twelve species of carcharhinids in the northern Gulf of Mexico; however, they disagree on the presence of a thirteenth species, C. perezi (Poey), in the region (Compagno 1984, Compagno 2002, McEachran & Fechhelm 1998, Castro 2011). While the range of C. perezi is well-documented to extend from the southeastern coast of Florida and the Bahamas to Brazil (Castro 2011), published records of C. perezi occurring in the northern Gulf of Mexico are limited to two sources. In their description of Eulamia springeri, a junior synonym of C. perezi, Bigelow & Schroeder (1944) place the species in the northern Gulf of Mexico based on “a somewhat shrivelled skin with head” from a specimen collected off the west coast of Florida that was reported by the authors to be “probably of this species.” Later, Springer (1960) reported the capture of a single specimen off the Mississippi River Delta in 1947; however, no detail of the capture was provided other than it being listed within a table summarizing shark species collected during exploratory fishing operations.

Occurrence and biological characteristics of broadnose sevengill sharks (Notorynchus cepedianus) in Pacific Northwest coastal estuaries

The broadnose sevengill shark (Notorynchus cepedianus) is a high-order marine predator distributed worldwide in shallow coastal waters of temperate seas. Recent reports have suggested it may be a prevalent component of Pacific Northwest coastal estuarine communities, although biological characteristics of the shark population remain undocumented despite growing interest in recreational harvest of the species. Longline sampling was conducted in Willapa Bay and Grays Harbor, Washington, USA seasonally during 2003–2006 to collect sevengill shark size, maturity, and sex ratio data, and establish some baseline catch rate information. Sevengill sharks were collected on 65% of longline sets and catches were composed of subadult and mature individuals (122–283 cm TL) of both sexes. Most male sevengill sharks were large sexually mature adults, based on external clasper calcification levels, whereas most comparably sized females were considered subadults, based on literature-based size-at–maturity estimates. Neonates and young sharks <120 cm were not collected, nor have they been reported in other historic estuary sampling efforts. Sex ratios were skewed toward males in Willapa Bay and suggest some degree of sexual segregation for the species, as has been shown for populations elsewhere. We suggest sevengill sharks are a largely ignored but potentially important predator in Pacific Northwest estuaries. This study therefore provides some of the first, basic information for guiding management decisions associated with a late-maturing, slow-growing shark species in these coastal habitats.

Records of Great White Sharks (Carcharodon carcharias) in New Caledonian Waters

The occurrence of great white sharks (Carcharodon carcharias) in New Caledonia is documented from 30 observation events (sightings or captures or forensic examination of wounds) made between 1943 and 2009, involving 34 individual sharks. Nine of the observation events concerned animals caught on lines set for deep-sea fishes, five were encounters with scuba divers or snorkelers, and one was a fatal attack on a surfer; two other observations included great white sharks feeding on whale carcasses; two were from pop-up archival transmitting tag records that monitored individuals tagged in the Chatham Islands, New Zealand; one was a forensic identification from wounds sustained by another large shark; and seven were fortuitous sightings from boats. Nearly all observations were of solitary sharks. Observation events were concentrated in the southern lagoon of New Caledonia or along its barrier reef. They occurred from July to March, with most records in September and November, coinciding with a peak of occurrence of large cetaceans.

Environmental influences on the occurrence of coastal sharks in estuarine waters

Long-term fisheries independent gill net surveys conducted in Texas estuaries from 1975 to 2006 were used to develop spatially explicit estuarine habitat use models for 3 coastal shark species: bull shark Carcharhinus leucas, blacktip shark C. limbatus, and bonnethead shark Sphyrna tiburo. Relationships between environmental predictors and shark distribution were investigated using boosted regression trees (BRT). Bull shark was the most abundant species (n = 5800), followed by blacktip (n = 2094), and bonnethead sharks (n = 1793). Environmental conditions influenced dis- tribution patterns of all species and relationships were nonlinear, multivariate, and interactive. Results showed very good model performance and suggested shark distribution is most closely linked to salinity, temperature, and proximity to tidal inlets. By interpolating the BRT models, maps of the probability of capture were produced using ordinary kriging. Results showed that the central region along the Texas coast contains the most important estuarine shark habitat. This area was character- ized by warm temperatures, moderate salinities, and abundant tidal inlets. Bull sharks also extended into low salinity estuaries, while blacktip and bonnethead sharks were restricted to areas near tidal passes with moderate salinities. Juvenile sharks were frequently captured, suggesting the Texas coast may constitute important nursery areas for all 3 species. The development of these spatially explicit models allows for prioritization and conservation of areas in a region that has great potential for human disturbance and climate change impacts. These results provide new insight into the habi- tat requirements of coastal sharks in the northwestern Gulf of Mexico and practical information for managing this resource.

Sightings of whale sharks ( Rhincodon typus) off Angola and Nigeria

Knowledge of the whale shark, Rhincodon typus, in the south-east Atlantic off the coast of West Africa is limited to several bycatch and stranding records. Ten at-sea sightings of whale sharks from Angola (N = 9) and Nigeria (N = 1) are presented, consisting of nine sightings from offshore platforms and a single record from a helicopter. Eight of the records were from oceanic waters exceeding 1000 m, while single records originated from shelf-edge and continental shelf waters. The records support a year-round occurrence of whale sharks in offshore West African waters, although the majority (N = 8) of sightings occurred during the spring and summer months between September and January. Most sightings (N = 8) were of whale sharks estimated to be in the 5–7 m length-range. These records represent the first verified at-sea sightings in the West Africa region providing novel information on behaviour and distribution, and also confirm Nigeria as a range state for the whale shark.

Environmental effects on blue shark (Prionace glauca) and oilfish (Ruvettus pretiosus) distribution based on fishery-dependent data from the eastern Mediterranean Sea

Blue sharks (Prionace glauca) and oilfish (Ruvettus pretiosus) are frequently caught incidentally in the swordfish surface drifting longline fishery of the eastern Mediterranean Sea. An information theoretic generalized additive model approach, modelling separately: (1) the probability of making a catch; and (2) the positive catch rates, suggested the presence of intra-annual variations in their abundance and revealed interesting associations with some environmental features. Blue sharks were more frequently encountered during late summer in cool water masses. However, the likelihood of making a larger catch peaked in warmer waters through late spring in the vicinity of land. Occurrences of blue sharks were more frequent to the south-west (Ionian Sea), while positive catch rates were higher in the eastern-most regions (Levantine). Oilfish occurrences, as well as catch rates, were always above average to the east. Intra-annual variation was analogous to that of blue sharks. The species showed a preference for cooler water bodies and its distribution was strongly dictated by the lunar cycle. Annual time series showed a decreasing trend of blue sharks abundance. Catch rates for both species depended on fishing gear configuration. Deeper settings (&gt;20 m), more resilient lines and use of fish attractant light-sticks increased the probability of capturing a fish.

Size distributions and sex ratios of sharks caught by Oman's artisanal fishery

Oman's fishery resources are exploited by artisanal and industrial fisheries, but the former accounts for almost 90% of landings. Within the artisanal fishery, sharks have traditionally been harvested for their flesh, but the development of a valuable export market for shark fin has led to increased utilisation of this resource, and anecdotal information suggests that shark abundance has decreased in recent years. Whereas management of the shark fishery is desirable, the biological and socio-economical data on which to base any management plan are lacking. The present study was undertaken to collect size frequency and sex ratio information from the shark species most commonly encountered in the artisanal landings, namely Carcharhinus falciformis, C. limbatus, C. macloti, C. sorrah, lago omanensis, Loxodon macrorhinus, Rhizoprionodon acutus and Sphyrna lewini. The occurrence of large female sharks in the landings, combined with a high proportion of juveniles of certain species, suggests that species-specific size restrictions should be considered in any management plan for Oman's shark fishery.

Modeling environmental, spatial, temporal, and operational effects on blue shark by-catches in the Mediterranean long-line fishery

A study was conducted from 1998 to 2001 on blue shark (Prionace glauca) by-catch of the Italian and Greek surface-drifting swordfish long-line fisheries in the Mediterranean Sea. The focus was on examining whether catches are related to some environmental, spatial, temporal or operational parameters and to what extent, applying generalized linear model (GLM) approaches. Analyses indicated that most appropriate for the dataset was the Delta-lognormal model, which is a binomial error distribution for the probability of a non-zero catch and lognormal error for positive catch rates. Spatial and temporal factors were the most influential regarding blue shark distribution and abundance, with a considerable interaction between them; the modeled environmental factors were of minor importance. Spatial distribution revealed a strong longitudinal gradient whereby blue shark occurrences increased in an east to west direction, whereas catches by latitude were higher in southern- and northern-most regions. Blue sharks were more frequently encountered in autumn and in distant open waters; however, the likelihood of making a larger catch peaked in late spring–early summer and in the vicinity of land. Catch rates differed significantly depending on the fishing gear configuration. Deeper settings (>20 m), more resilient lines and use of fish attractants increased the probability of P. glauca capture.

Occurrence, Diet and Growth of Juvenile Blacktip Sharks,Carcharhinus limbatus, from Los Roques Archipelago National Park, Venezuela

Abstract. Distribution, occurrence, diet and growth of juvenile blacktip sharks, Carcharhinus limbatus, were examined based on specimens caught between 1995 and 2002 by the artisanal shark fishery from Los Roques Archipelago. Fishery monitoring revealed that C. limbatus was the species most frequently caught, accounting for 48.5% of the shark catch. Capture of neonate and juvenile sharks was concentrated in the central lagoon of the archipelago, indicating that this area corresponds to a nursery area for the species. Birth season was approximately from mid June to the end of August. Average length at birth was 63.5 cm TL, based on neonates with an open umbilical scar. The smallest mature male and female sharks measured 152 and 161 cm TL, respectively. Diet was composed of teleost fishes, with the most important prey being Eucinostomus argenteus (13.3 %IRI), Opisthonema oglinum (6.9 %IRI) and Gerres cinereus (5.5 %IRI). Monthly length frequencies revealed that juveniles remain within the nursery area for 1...

The influence of seasonality, tide and time of activities on the behavior of Sotalia guianensis (Van Bénéden) (Cetacea, Delphinidae) in Pernambuco, Brazil

Data on Sotalia guianensis Van Bénéden, 1864 occurrence on the beaches of Pernambuco (Northeastern Brazil) is restricted to information on stranding and on printed material from local newspapers; actual observations of such animals have not been published. This study intends to determine the use of habitat, behavioral activities and assess the relationships between environmental factors and the recorded behavior. Observations were conducted on open sea coastal areas, on the beaches of Olinda and Piedade, as well as in sheltered areas, in the ports of Recife and Suape. Monitoring was carried out every month in each area, during two consecutive days, from September 2004 to August 2005. Results corroborate that this species prefers to occupy more protected environments, the port of Recife being the main concentration area for such species. Piedade is just an exploratory area, possibly due to shark occurrence. Olinda is only occasionally used. Concentration areas seem to be used for feeding, and incidence of caudal exhibition suggests that most of the estuarine dolphin prey items are demersal. Environmental conditions (seasonality, tide and time) did not show to be significant when related to the estuarine dolphin behavior.

Occurrence of whale sharks ( Rhincodon typus) in Madagascar

Whale sharks are known to occur in Malagasy waters although very little research has been completed to further document the species. In order to increase the current national knowledge of the species, it is planned to conduct whale shark surveys in Madagascar. An initial investigation based on interviews of local fishers and dive operators was completed to establish the logistical baseline for such surveys. It was found that whale sharks are present around the majority of the Madagascar coastline but most known sightings have occurred along the north-western coast. In Nosy Be, it appears whale sharks occur all year round, particularly during planktonic blooms. Plans for further assessment involving a combination of boat based observations, photo identification, and acoustic and satellite tagging are described.

Occurrence of whale shark ( Rhincodon typus) in the Indian Ocean: A case for regional conservation

From the first whale shark ( Rhincodon typus) described in 1828 from the Indian Ocean, the region continues to be one of the most important areas for whale shark sightings. However, the species has been the subject of several targeted fisheries and thus sustained massive, rapid declines in population numbers. The known range of occurrence and targeted fisheries for whale sharks in the Indian Ocean are discussed, along with stated national conservation measures in the range states. The results of a preliminary survey of 16 regional cooperative partners from 11 of the Indian Ocean range states are presented for whale shark occurrence, monitoring, perceived threats and realized conservation measures. These data are already proving valuable by facilitating cooperation between organisations regionally. The current international conservation framework is briefly described and suggestions made as to possible linked regional conservation initiatives, such as under the auspices of the Convention on Migratory Species.

Reproduction and seasonal occurrence of the copper shark, Carcharhinus brachyurus, from north Patagonia, Argentina

Abstract The copper shark, Carcharhinus brachyurus, is the only member of its genus with a preferred habitat in temperate waters, and it usually gives birth in the cooler extremes of its range. Maturation patterns, reproductive condition, monthly sex ratios, and seasonal occurrence of copper sharks were analysed, mostly from Anegada Bay (Argentina), a presumed nursery area for the species. Males mature between 200 and 220 cm total length (LT), with a 50% size at maturity (L50) of 216.18 cm LT. Females mature between 215 and 223 cm LT (with an L50 of 222.16 cm LT). Maturity off Argentina is at a slightly smaller size than off South Africa and Australia. There is no sexual dimorphism in size at maturity. Only two pregnant females, each carrying 16 advanced embryos, were caught. The hepatosomatic index (IH) of adult males showed significant monthly changes, related possibly to an increase in the gonadosomatic index (IG). IH and IG of adult females showed no significant trend throughout the fishing season. The IH of adult females was significantly correlated with maximum diameter of ovarian follicles. Small translucent ovarian follicles in two gravid females indicated that ovarian and gestation cycles run sequentially, with maturation of oocytes subsequent to parturition. Neither newborns nor significant numbers of females bearing term embryos were recorded, and there was no evidence of a copper shark primary nursery area in Anegada Bay. However, most copper sharks in Anegada Bay were large juveniles and sub-adults. The species is found off Argentina from October to late March, but they do not move southwards to Anegada Bay until December, and they leave the bay again by April. These movements appear to be related more to water temperature rather than to migration of potential prey. Monthly variation in sex ratios is associated mainly with fluctuations in the sex ratios of juveniles.

Reproductive biology of the school shark, Galeorhinus galeus, off Argentina: support for a single south western Atlantic population with synchronized migratory movements

synopsis We sampled school sharks, Galeorhinus galeus, in Anegada Bay, Argentina, to investigate reproductive ecology. Males dominated the catches in October and April, while females were more abundant than males from November to March. Males were estimated to mature at a smaller size (108-119 cm total length) than females (mean 125 mm total length). Differences between fecundity and fertility were not dependent on mother size. The largest embryos were found in late October and November, coinciding with ovulation. This indicates that gestation lasts about 12 months. Embryonic growth was best described by a Gompertz model. Four groups of females were recognized: (1) juveniles up to 129 cm TL, with translucent-to-white ovarian follicles; (2) mature, non-pregnant, pre-ovulatory females with yellow ovarian follicles and low gonadosomatic index (GSI); (3) mature non-pregnant ovulating females with large yellow ovarian follicles, high GSI; and (4) pregnant females carrying near term embryos, with minute ovarian follicles. These observations support a 3-year female reproductive cycle. The patterns of occurrence, reproductive condition, and embryonic growth of school sharks in northern Argentina are complementary to those from southern Brazil, supporting the hypothesis that there is a single large population of school sharks in the south western Atlantic.

The Occurrence of White Sharks, Carcharodon carcharias, Around the Balearic Islands (Western Mediterranean Sea)

The regular presence of the white shark, Carcharodon carcharias, off the Balearic Islands (western Mediterranean) is shown from 27 captures carried out with trap nets between the 1920s and 1970s and from eight attacks on cetaceans and marine turtles from the 1990s to the present. The geographic distribution, seasonality and population structure of the species in the area are analysed and discussed in relation to environmental conditions and to the proposed distribution of this species in the Mediterranean Sea.

Occurrence of Carcharias taurus in nursery areas of the Eastern and Western Cape, South Africa

This study was initiated to investigate the occurrence, size and stage of sexual maturity of ragged tooth sharks (Carcharias taurus) in their putative nursery areas. Information on size and seasonality of catches was obtained from the National Marine Linefish System revealed that juvenile and immature individuals occur in the Eastern Cape throughout the year and make up ~80% of the line-fishing catches. Their occurrence west of Storms River along the south coast of the Western Cape is more common in summer. Individuals large enough to be sexually mature are found in the Eastern Cape almost throughout the year. This suggests that the Eastern Cape is both the both primary and secondary nursery area for this shark. The smallest individuals (&lt;9 kg) occur mainly from September to December. Eastern Cape samples comprised 95 males ranging between 84 cm (4.5 kg) and 262 cm total length (120 kg) and 166 females of 985 cm (5.5 kg) to 288 cm (163 kg). Size at maturity conformed to previous studies and one pregnant female was recorded in October. Catches were from the intertidal zone to 100 m. Underwater observations showed the sharks to prefer high-relief reefs with caves and gullies by day.