Search

Many shark populations are in decline around the world, with severe ecological and economic consequences. Fisheries management and marine protected areas (MPAs) have both been heralded as solutions. However, the effectiveness of MPAs alone is questionable, particularly for globally threatened sharks and rays ('elasmobranchs'), with little known about how fisheries management and MPAs interact to conserve these species. Here we use a dedicated global survey of coral reef elasmobranchs to assess 66 fully protected areas embedded within a range of fisheries management regimes across 36 countries. We show that conservation benefits were primarily for reef-associated sharks, which were twice as abundant in fully protected areas compared with areas open to fishing. Conservation benefits were greatest in large protected areas that incorporate distinct reefs. However, the same benefits were not evident for rays or wide-ranging sharks that are both economically and ecologically important while also threatened with extinction. We show that conservation benefits from fully protected areas are close to doubled when embedded within areas of effective fisheries management, highlighting the importance of a mixed management approach of both effective fisheries management and well-designed fully protected areas to conserve tropical elasmobranch assemblages globally., (© 2024. Crown.)

A global survey of coral reefs reveals that overfishing is driving resident shark species toward extinction, causing diversity deficits in reef elasmobranch (shark and ray) assemblages. Our species-level analysis revealed global declines of 60 to 73% for five common resident reef shark species and that individual shark species were not detected at 34 to 47% of surveyed reefs. As reefs become more shark-depleted, rays begin to dominate assemblages. Shark-dominated assemblages persist in wealthy nations with strong governance and in highly protected areas, whereas poverty, weak governance, and a lack of shark management are associated with depauperate assemblages mainly composed of rays. Without action to address these diversity deficits, loss of ecological function and ecosystem services will increasingly affect human communities.

Decades of overexploitation have devastated shark populations, leaving considerable doubt as to their ecological status 1,2 . Yet much of what is known about sharks has been inferred from catch records in industrial fisheries, whereas far less information is available about sharks that live in coastal habitats 3 . Here we address this knowledge gap using data from more than 15,000 standardized baited remote underwater video stations that were deployed on 371 reefs in 58 nations to estimate the conservation status of reef sharks globally. Our results reveal the profound impact that fishing has had on reef shark populations: we observed no sharks on almost 20% of the surveyed reefs. Reef sharks were almost completely absent from reefs in several nations, and shark depletion was strongly related to socio-economic conditions such as the size and proximity of the nearest market, poor governance and the density of the human population. However, opportunities for the conservation of reef sharks remain: shark sanctuaries, closed areas, catch limits and an absence of gillnets and longlines were associated with a substantially higher relative abundance of reef sharks. These results reveal several policy pathways for the restoration and management of reef shark populations, from direct top-down management of fishing to indirect improvement of governance conditions. Reef shark populations will only have a high chance of recovery by engaging key socio-economic aspects of tropical fisheries.

Data on the occurrence of whale sharks, Rhincodon typus, in the Arabian Gulf and Gulf of Oman were collected by dedicated boat surveys and via a public-sightings scheme during the period from 2011 to 2014. A total of 422 individual whale sharks were photo-identified from the Arabian Gulf and the northern Gulf of Oman during that period. The majority of sharks (81%, n = 341) were encountered at the Al Shaheen area of Qatar, 90 km off the coast, with the Musandam region of Oman a secondary area of interest. At Al Shaheen, there were significantly more male sharks (n = 171) than females (n = 78; X2 = 17.52, P < 0.05). Mean estimated total length (TL) for sharks was 6.90 m ± 1.24 (median = 7 m; n = 296). Males (7.25 m ± 1.34; median = 8 m, n = 171) were larger than females (6.44 m ±1.09; median = 7 m, n = 78; Mann-Whitney U test, p < 0.01). Of the male sharks assessed for maturity 63% were mature (n = 81), with 50% attaining maturity by 7.29 m and 100% by 9.00 m. Two female sharks of >9 m individuals were visually assessed as pregnant. Connectivity among sharks sighted in Qatari, Omani and UAE waters was confirmed by individual spot pattern matches. A total of 13 identified sharks were re-sighted at locations other than that at which they were first sighted, including movements into and out of the Arabian Gulf through the Strait of Hormuz. Maximum likelihood techniques were used to model an estimated combined population for the Arabian Gulf and Gulf of Oman of 2837 sharks ± 1243.91 S.E. (95% C.I. 1720-6295). The Al Shaheen aggregation is thus the first site described as being dominated by mature males while the free-swimming pregnant females are the first reported from the Indian Ocean.

Whale sharks, Rhincodon typus, are known to aggregate to feed in a small number of locations in tropical and subtropical waters. Here we document a newly discovered major aggregation site for whale sharks within the Al Shaheen oil field, 90 km off the coast of Qatar in the Arabian Gulf. Whale sharks were observed between April and September, with peak numbers observed between May and August. Density estimates of up to 100 sharks within an area of 1 km(2) were recorded. Sharks ranged between four and eight metres' estimated total length (mean 6.92 ± 1.53 m). Most animals observed were actively feeding on surface zooplankton, consisting primarily of mackerel tuna, Euthynnus affinis, eggs.

The smoothnose wedgefish Rhynchobatus laevis, a shark-like ray classified as Critically Endangered by the International Union for Conservation of Nature, has received limited research attention. To address the knowledge gaps in its spatial behaviour, this study utilised satellite monitoring of a fortuitously captured female over a 51-day period in the Arabian Gulf. Based on the resulting movement track, the individual covered a minimum distance of 712 km, traversing the exclusive economic zones of three different countries. Its track began in the United Arab Emirates, from where it headed north, entering Iranian waters, where it spent most of its time, before continuing westward across the Gulf and eventually reaching Qatari waters. Novel insights into its behaviour revealed an observation of rapid ascents over the study period. Although both diurnal and nocturnal ascents were observed, they occurred predominantly during nocturnal periods. Contrary to the prevailing belief that wedgefish are bottom-associated, the study animal spent a considerable amount of time in the water column. The use of various depths in both nearshore and offshore waters highlights elevated susceptibility to multiple types of fishing gear. This underscores the need for an international cooperative approach to the management and conservation of shark-like rays in the Arabian Gulf. [ABSTRACT FROM AUTHOR]

Baited drumlines were employed to assess the relative abundance and demographics of sharks in three distinct but contiguous areas of the sublittoral environment of the eastern Caicos Bank, with a view to equipping policy-makers in the Turks and Caicos Islands with information pertinent to the conservation of local shark populations. Overall, the catch was dominated by nurse Ginglymostoma cirratum and Caribbean reef Carcharhinus perezi sharks, but tiger Galeocerdo cuvier, lemon Negaprion brevirostris, blacknose Carcharhinus acronotus and great hammerhead Sphyrna mokarran sharks were also captured. Size distributions were consistent with a combination of sexually mature and immature animals for most of these species. The results confirm that shallow sand flat, deep sand flat and coral reef environments are utilised by a variety of shark species and life stages, including the movement of individuals between these areas. Therefore, current marine protected areas in the Turks and Caicos Islands, which mostly centre on nearshore and coral reef environments, probably afford local shark populations only partial protection. [ABSTRACT FROM AUTHOR]

Species-specific biological data are commonly combined with fishery operational data to model exploited stocks and determine appropriate levels of exploitation. However, this approach to fishery management is predicated using the' to 'predicated on the ability of fishery data collectors to correctly identify exploited species. Sharks and other elasmobranch fishes (Elasmobranchii) can be particularly difficult to identify in the field, due to the close physical similarity to other species and/or a lack of taxonomic resolution in some lineages. This paper provides an overview of the difficulties surrounding the field identification of a number of elasmobranch species found in the Arabian/Persian Gulf, where they are heavily exploited and in urgent need of careful management. [ABSTRACT FROM AUTHOR]

The lemon shark is a large coastal species that is currently classified as Near Threatened by the International Union for the Conservation of Nature., As juveniles of the species utilize shallow, near shore habitat, they are particularly susceptible to anthropogenic impacts., The abundance, size characteristics, growth, condition factor and movement patterns of juvenile lemon sharks within the Bell Sound Nature Reserve were compared with those outside the Reserve., Sharks were more abundant within the Reserve, which also accommodated a greater proportion of smaller size classes., Although there was no difference in linear growth-rate between sharks inside and outside the Reserve, those outside exhibited higher condition factor values., It is suggested that these results are due mainly to habitat preference on the part of the sharks, with the predominantly shallower near shore waters of the Reserve offering a greater level of protection from predation., Regardless of the causative factor, the area occupied by the Bell Sound Nature Reserve appears to be highly important to the local juvenile lemon shark population., Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

An 829-bp fragment of the NADH dehydrogenase subunit 2 ( NADH2) gene was used to assess the taxonomic status of 1487 elasmobranch specimens, representing 52 putative species. Strong evidence was found for the existence of an undescribed E chinorhinus species and for cryptic speciation within R hynchobatus djiddensis. The results also provide strong molecular support for the existence of two previously reported, but undescribed, guitarfish species. Potential, but less conclusive, cryptic lineage diversification was also noted in C archarhinus leucas, L oxodon macrorhinus, I ago omanensis and G ymnura poecilura. A complex situation was found in the genus H imantura, with potentially three distinct lineages evident, one of which is probably an undescribed species, in the H . gerrardi complex. One dasyatid specimen could not be identified, but appears to be closely related to D asyatis ushiei, while H imantura leoparda and C archarhinus longimanus are reported from Oman for the first time. The results of the present study also reinforce previously reported geographical divisions within certain putative species, which has important implications for fishery management and conservation. © 2015 The Linnean Society of London [ABSTRACT FROM AUTHOR]

Sets of baited hooks decrease in fishing efficacy over time as catch accumulates and bait is lost, and this complicates the quantification of fishing effort for species abundance calculations. Although hook-timers facilitate a more accurate estimation of fishing time, they cannot provide taxonomic information in the case of escapees or bait loss, nor can they provide information on animals that approach the gear but do not physically engage with it. To overcome these limitations, the present study attached sport action cameras to baited drumlines during a catch-and-release survey of sharks in the shallow, coastal waters of the eastern Caicos Bank, Turks and Caicos Islands. Overall, the true fishing time was found to be appreciably less than the apparent fishing time and more sharks approached or interacted with the gear than were successfully captured by it. Furthermore, shark-gear interactions varied by species while the amount of bait loss differed between deployment areas. Taken together, these findings suggest that baited-hook surveys underestimate shark abundance and that the magnitude of this error varies by species and habitat type. • Bait loss results in a substantial reduction in the active fishing time of drumlines. • Baited hooks do not successfully capture all sharks that are attracted to the gear. • Shark interactions with baited drumlines vary by species. • Catch-per-unit-effort values for sharks derived from baited-hook surveys are negatively biased. [ABSTRACT FROM AUTHOR]

1. Anecdotal evidence suggests that sharks are being targeted in the United Arab Emirates artisanal fishery. However, little information is available on this fishery and baseline information is essential for understanding its impact on shark populations in the Arabian/Persian Gulf, and for managing sharks in this region. 2. The aim of this study was to investigate the artisanal shark fishery and gain an insight into the social, motivational and economic drivers behind it. Fishery characteristics were examined and the effect of fishing on local shark stocks assessed by interviewing Emirati fishermen across the country (n =126). 3. Sharks were found to be increasingly targeted owing to their high value in the global fin trade industry. The majority of fishermen (80%) confirmed that changes in species composition, abundance and sizes of sharks have been continuing for more than two decades, mainly because of overfishing, raising concerns about the sustainability of this fishery. 4. Results suggest that sharks are likely to be overexploited and that management measures will need to take into account the precautionary principle. There is an urgent need to formulate long-term and effective conservation and management plans to prevent further declines in a number of species. 5. Additional efforts should be directed to quantify the ecological implications of the observed changes and determine if these are aggravated by the life-history traits of the fished species. Such implications should be considered when assessing the sustainability of local fisheries. 6. The data gathered can now serve as a reference to managers, fisheries scientists and other stakeholders to prioritize future research as well as lay foundations for the development and implementation of national management plans for the protection and conservation of sharks. [ABSTRACT FROM AUTHOR]

The age, growth characteristics, maturity, and reproductive cycle of commercially caught spiny dogfish Squalus acanthias were investigated over a 12 month period. The specimens ranged in age from 4 to 30 years, with asymptotic lengths of 79 and 112 cm estimated for males and females, respectively. The lower age range reported here when compared with previous North Atlantic studies is attributed to fishing pressure. Fifty per cent maturity was estimated at 57.5 cm in males and 78.2 cm in females, and fecundity was positively correlated with female size. Although recently formed candles and full-term embryos were observed throughout the year, parturition occurred mainly from August to January. The minimum fecundity recorded was four (determined from developing ova/candled embryos), while the maximum was 16 (determined from embryo counts), and fecundity was found to increase by up to four between pregnancies. The overall sex ratio of embryos was 1:1, although this balance was rarely observed in any one female. The results presented here indicate that neither growth rate, size at maturity, nor fecundity have significantly changed due to fishing pressure. [ABSTRACT FROM AUTHOR]