A review of the biology, fisheries and conservation of the whale shark Rhincodon typus

Although the whale shark Rhincodon typus is the largest extant fish, it was not described until 1828 and by 1986 there were only 320 records of this species. Since then, growth in tourism and marine recreation globally has lead to a significant increase in the number of sightings and several areas with annual occurrences have been identified, spurring a surge of research on the species. Simultaneously, there was a great expansion in targeted R. typus fisheries to supply the Asian restaurant trade, as well as a largely un-quantified by-catch of the species in purse-seine tuna fisheries. Currently R. typus is listed by the IUCN as vulnerable, due mainly to the effects of targeted fishing in two areas. Photo-identification has shown that R. typus form seasonal size and sex segregated feeding aggregations and that a large proportion of fish in these aggregations are philopatric in the broadest sense, tending to return to, or remain near, a particular site. Somewhat conversely, satellite tracking studies have shown that fish from these aggregations can migrate at ocean-basin scales and genetic studies have, to date, found little graphic differentiation globally. Conservation approaches are now informed by observational and environmental studies that have provided insight into the feeding habits of the species and its preferred habitats. Notwithstanding these advances, there remain notable gaps in the knowledge of this species particularly with respect to the life history of neonates and adults who are not found in the feeding aggregations.     

Patterns in composition, abundance and scarring of whale sharks Rhincodon typus near Holbox Island, Mexico

Photo-identification and conventional tagging were used to estimate population size and structure of the whale shark Rhincodon typus near Holbox Island, Mexico. From 2005 to 2008, photographs of spot patterns behind the last gill slit and in a lateral view on the left side of each animal were used to identify individuals. Additionally, 578 R. typus were tagged using conventional marker tags. Of these and the 350 R. typus that were identified from 1184 photographs, 65% were male; 27%, female and 8%, indeterminate sex. Photographed R. typus ranged in size from 2·5 to 9·5 m total length. Size was bimodal with a large peak at 6 m and a smaller peak at 7 m. Photo-identification showed that there was considerable loss of marker tags. Few of these remained on the animals for more than a year, so that interannual re-sights using tagging could not be used in population modelling. Forty six interannual re-sightings were found in the photographic library; the interval between these re-sightings was typically 1 year. It was estimated that the R. typus aggregation near Holbox Island ranged from 521 to 809 individuals, based on mark-recapture models. From 13 to 33% of R. typus photographed had scars that were attributable to boat strikes. This study provides a baseline for assessing the status of R. typus near Holbox Island. This information is useful to understand drivers of local population size and distribution and potential concerns about increasing effects of tourism on R. typus in this area and for designing better management programmes for R. typus conservation.     

Fisheries, management and conservation of the whale shark Rhincodon typus in Taiwan

The Taiwanese government introduced a catch-and-report system for the whale shark Rhincodon typus in 2001, and in the following year limited the total allowable catch (TAC) to 80 individuals. This limit was reduced over the following years, reaching a low of 30 individuals in 2007. In November 2007, a comprehensive ban on R. typus fishing came into effect and protection measures were adopted for the species. This study measured and recorded the total length (L(T) ), body mass and sex of 810 R. typus, using fisheries and other released data for the period 1995-2008. The mean L(T) of individuals caught from June to October was smaller than that for individuals caught from November to May. Mean annual catches in set nets were higher in south-western Taiwan than in other regions of Taiwan. The sex ratio showed that males were caught more frequently than females in Taiwanese waters, indicating sex segregation. For the first time, the stock structure, conservation and management regulation of R. typus in the north-west Pacific Ocean have been reviewed. The results provide a useful resource for future assessment of the possible development of R. typus ecotourism in Taiwan.     

New insights into whale shark <Emphasis Type="Italic">Rhincodon typus</Emphasis> diet in Brazil: an observation of ram filter-feeding on crab larvae and analysis of stomach contents from the first stranding in Bahia state

We describe the first record of a whale shark, Rhincodon typus, feeding in Brazilian coastal waters, and the first stranding record in the state of Bahia, Northeast Brazil. In April 2008, an individual of R. typus was observed surface feeding on Dromiidae crab larvae in the continental shelf off the coast of Bahia, near a gas platform. Other fishes were observed foraging in association with the whale shark. We also document the first stranding of R. typus on the coast of Bahia in October 2013. Biometric data confirmed that the stranded whale shark was a juvenile. Stomach content analysis revealed the ingestion of Geryonidae crab larvae. Plastic debris were also found in the gastric lumen of the stranded juvenile whale shark, and we speculate that it could have been a contributing factor to the stranding, and subsequent death of the whale shark. Crab larvae were observed in both of our records and likely to consist as relevant prey items for R. typus in Brazilian continental shelf. Our study provided a contribution on the diet and feeding behaviour of whale sharks in tropical oligotrophic waters and highlights the risks of marine pollution for the species conservation.     

First record of a whale shark Rhincodon typus in continental Europe

A whale shark Rhincodon typus was found in a set-net in southern Portugal in October 2011. This was the first record for continental Europe and represents an increase of the species' known range. Upwelling events and increase in sea-surface temperatures are possible reasons for this occurrence.     

DNA‐based species identification of krill consumed by whale sharks

DNA was purified from whale shark Rhincodon typus faecal material that contained DNA derived from their prey. A DNA‐based krill identification method was used to determine the exact krill species upon which the whale shark was feeding, where morphological analysis had failed to make an identification.     

A rare occurrence of a whale shark (Rhincodon typus) in a contaminated estuary in the Southwest Atlantic Ocean

Environmental Biology of Fishes - An individual whale shark (Rhincodon typus) was recorded on January 15, 2020, during the marine megafauna drone-monitoring. The animal was filmed for approximately...     

Genetic profiling reveals illegal international trade in fins of the great white shark, <Emphasis Type="Italic">Carcharodon carcharias</Emphasis>

Great white sharks are protected by national legislation in several countries, making this species the most widely protected elasmobranch in the world. Although the market demand for shark fins in general has continued to grow, the value and extent of utilization of white shark fins in trade has been controversial. We combine law enforcement with genetic profiling to demonstrate that illegal trade in fins of this species is occurring in the contemporary international market. Furthermore, we document the presence of fins from very young white sharks in the trade, suggesting a multiple-use market (food to trophies) exists for fins of this species. The presence of small fins in the trade contradicts the view that white shark fins have market value only as large display trophies, and not as food. Our findings indicate that effective conservation of protected shark species will require international management regimes that include monitoring of the shark fishery and trade on a species-specific basis.     

Deep-diving behaviour of a whale shark Rhincodon typus during long-distance movement in the western Indian Ocean

A whale shark Rhincodon typus satellite tagged off the coast of Mozambique showed a highly directional movement across the Mozambique Channel and around the southern tip of Madagascar, a minimum distance of 1200 km in 87 days. Dives to depths well into the mesopelagic and bathypelagic zones (1286 m maximum depth) were recorded in a bathymetrically non-constraining habitat. The water temperature range recorded during the fish's movement was 3·4–29·9° C.     

Isolation and characterization of microsatellite loci in the whale shark (Rhincodon typus)

In preparation for a study on population structure of the whale shark (Rhincodon typus), nine species-specific polymorphic microsatellite DNA markers were developed. An initial screening of 50 individuals from Holbox Island, Mexico found all nine loci to be polymorphic, with two to 17 alleles observed per locus. Observed and expected heterozygosity per locus ranged from 0.200 to 0.826 and from 0.213 to 0.857, respectively. Neither statistically significant deviations from Hardy-Weinberg expectations nor statistically significant linkage disequilibrium between loci were observed. These microsatellite loci appear suitable for examining population structure, kinship assessment and other applications.     

Global estimates of shark catches using trade records from commercial markets

Despite growing concerns about overexploitation of sharks, lack of accurate, species-specific harvest data often hampers quantitative stock assessment. In such cases, trade studies can provide insights into exploitation unavailable from traditional monitoring. We applied Bayesian statistical methods to trade data in combination with genetic identification to estimate by species, the annual number of globally traded shark fins, the most commercially valuable product from a group of species often unrecorded in harvest statistics. Our results provide the first fishery-independent estimate of the scale of shark catches worldwide and indicate that shark biomass in the fin trade is three to four times higher than shark catch figures reported in the only global data base. Comparison of our estimates to approximated stock assessment reference points for one of the most commonly traded species, blue shark, suggests that current trade volumes in numbers of sharks are close to or possibly exceeding the maximum sustainable yield levels.     

DNA barcoding of traded shark fins,meat and mobulid gill plates in Singapore uncovers numerous threatened species

The shark and ray (Elasmobranchii) trade is a commercially valuable industry that has negative consequences for wild populations. An estimated 100 million sharks are caught each year to supply the demand for cultural cuisines, traditions and practices, including shark fin soup and Traditional Chinese Medicine. Despite the establishment of frameworks and regulations by international trade and conservation bodies as well as national legislations, elasmobranch populations continue to decline. While their conservation becomes an ever more pressing concern, a major obstacle that hampers regulation is the mislabelling and/or misidentification of dried products or carcasses that have had fins removed. Here we use DNA barcoding to identify the species of origin for a variety of shark and ray products readily available to consumers in Singapore, a major importer of these goods. We amplified a fragment of the cytochrome c oxidase subunit I gene from shark fin, cartilage and meat, as well as ray gill plates and meat for DNA sequencing. Our analysis of 207 DNA barcodes yielded 28 positively identified elasmobranch species, eight of which are listed under Appendix II of the Convention on International Trade in Endangered Species of Wild Fauna and Flora, and 12 are listed as Endangered or Vulnerable by the International Union for the Conservation of Nature. This information will be useful to regulatory bodies in controlling trade and establishing new or revisiting previous conservation status listings.     

广东贺江水域野生鲮鱼体表寄生虫典型海弯水虱的种群动态

近年来,广东贺江暴发了由等足类寄生虫引起的严重的鱼类外寄生虫病,给当地网箱养殖和野生鱼类资源造成了严重危害.根据虫体的口器、触角、腹肢等形态学特征将其鉴定为等足目(Isopoda)、扇肢亚目(Flabellifera)、纺锤水虱科(Aegid ae)、海弯水虱属(Alitropus)的典型海弯水虱(Alitropus typus).为了弄清典型海弯水虱对贺江内野生鱼类资源的危害及其种群季节动态变化规律,作者从2006年5月份到2 007年4月份,用刺网定时定点捕获野生鲮鱼(Cirrhina molitorella),检查典型海弯水虱的寄生状况.结果发现:典型海弯水虱对鲮鱼的感染率、感染强度和平均密度均从20 06年5月份开始上升,至7月份达到高峰,然后逐渐下降,于次年的2月份达到最低点,从3月份开始有所回升.典型海弯水虱种群在不同月份及不同体长鲮鱼中均为聚集性分布,且聚集强度随着平均密度的增加而增加.典型海弯水虱种群在鲮鱼中的感染参数与水温呈显著的正相关,而与宿主的体长无明显的相关性.周年种群结构动态变化分析表明: 典型海弯水虱 1年只繁殖1次,繁殖受水温的影响,6、7月份是其繁殖高峰期 [动物学报 5 4(3):407-415,2008].     

Knowledge and Practices of Expert Fishermen of South Bahia,Brazil, Regarding the International Shark Fin Market

Little is known about the impacts of the international shark fin trade in emerging economies. This study describes and discusses the knowledge and practices of artisanal fishers in Bahia state, Brazil, concerning the global fin trade. All participants confirmed that fin trade is conducted locally, and 44 (67.7%) admitted to having sold fins. Shark fins reach high prices. Most fishers claim that the number of sharks captured is increasing, and 24.6% (n = 16) claim that this is the reason behind the drop in shark populations. The participants vehemently oppose finning and declare that vessels from other regions catch shark for finning in the area. Fishers believe that surveillance and heavy fines are an effective way to curb finning. Further studies should investigate the sociocultural, economic, and ecological impacts of the sale of fins by artisanal fishers.     

Feeding habits of the whale shark (<Emphasis Type="Italic">Rhincodon typus</Emphasis>) inferred by fatty acid profiles in the northern Mexican Caribbean

Whale shark (Rhincodon typus, Smith, 1828) is an endangered species with anthropogenic pressures due to increasing demand of encounter tourism activities. Research efforts to identify management and conservation strategies for this species are needed. The Northern Mexican Caribbean is one of the most important feeding aggregation sites of whale sharks worldwide. In this study, Mexican Caribbean whale shark feeding habits are assessed by means of fatty acid (FA) signature analysis, a biochemical non-destructive technique widely applied in trophic ecology studies. Sub-dermal tissue biopsies of 68 whale sharks and samples of their potential prey (zooplankton) were collected during 2010 and 2011 in two areas with high R. typus abundance. Zooplankton samples (n?=?17) were divided in two categories: mixed zooplankton (several groups of zooplankton) and fish eggs (> 95% of sample components were fish eggs). FA profiles of whale shark tissue sampled between years showed significant variability; while there was no intraspecific differences in FA signature related to sex, size and location. FA profiles of whale sharks and their potential prey were dominated by saturated fatty acids (SFA). R. typus FA signature was significantly different from that of mixed zooplankton; on the other hand, whale shark and fish egg FA profiles formed groups with overlapping values and registered high levels of oleic acid. PUFA average ω3/ ω6 ratio on whale shark FA profiles for both years was below 1. Arachidonic acid (ARA) percentage was higher in whale shark biopsies (13.2% in 2010, 6.8% in 2011) compared to values observed in fish eggs (2.0%) and mixed zooplankton (1.4%). Similarity between FA profiles of whale sharks and fish eggs, low levels of bacterial FA found in R. typus biopsies, as well as whale shark feeding behavior observations in the study area, suggest that R. typus is feeding mainly on surface zooplankton in Mexican Caribbean; however, elevated ARA percentages in whale shark samples may indicate that this species has complementary feeding sources, such as demersal zooplankton, which has been reported in other aggregation sites. Results obtained contribute to the knowledge of the whale shark trophic ecology in the area, but are inconclusive. Further studies are recommended to evaluate whale shark FA profiles from different tissues (muscle or blood); also, broader information is needed about zooplankton FA signature in the study area.     

Localization of microfilaments and a tubulin-like protein in crustacean (Rhynchocinetes typus) spermatozoon

Sperm from the decapod crustacean Rhynchocinetes typus undergo dramatic shape changes as they pass from the vas deferens to seawater and interact with the oocyte envelopes. Using FITC-phalloidin and antitubulin antibodies, we were able to localize microfilaments and a tubulin-like protein in R. typus spermatozoon. Microfilaments and the tubulin-like protein were associated with the sperm rays and spines, but were absent at the spike and at its base. Folded and unfolded spermatozoa display similar fluorescence patterns. SDS-PAGE of whole spermatozoa and electrotransfer to nitrocellulose confirmed the presence of actin and two proteins at 97 kd and 120 kd that bind to tubulin antibodies (tubulin-like proteins). These results demonstrate the presence of actin, but not tubulin, and localize microfilaments in these sperm. It is proposed that this cytoskeletal component is active in sperm during crustacean fertilization.     

Characterization of the pelagic shark‐fin trade in north‐central Chile by genetic identification and trader surveys

Shark fins have become a highly valued commodity with the major Asian fin‐trade centres supplied from global sources, including Chile. With growing concerns about the resilience of shark populations to heavy fishing pressure, there is a need for better information on shark landings to aid management efforts. In the widespread absence of shark landing records especially by species, monitoring the fin trade has been proposed as a way to assess species exploitation levels. Here, the first species assessment of the Chilean shark‐fin trade was provided. The goals of this study were to (1) determine the species composition and relative species proportion of sharks utilized in the fin trade, (2) determine the relationship between fin trader market names and species and (3) assess trader accuracy in identifying shark fin species based on fin photographs. Fins were analysed from two different fin drying facilities (n = 654) (secaderos) and two fin‐storage warehouses (n = 251). In contrast to official government landing records that only document four species in the landings, molecular species identification of the fins demonstrated that at least 10 pelagic shark species are present in the north‐central Chilean shark fin trade: Alopias superciliosus, Alopias vulpinus, Carcharhinus obscurus, Galeorhinus galeus, Isurus oxyrinchus, Isurus paucus, Lamna nasus, Prionace glauca, Sphyrna lewini, Sphyrna zygaena. The species composition of the fins from the secaderos was P. glauca (83·9%), I. oxyrinchus (13·6%), L. nasus (1·7%) and A. superciliosus (0·2%). There was generally good agreement between market names and single shark species for the trade categories ‘Azulejo’, ‘Tiburon’, ‘Tintorera’, ‘Cola de zorro’ and ‘Martillo’. In contrast, the market category ‘Carcharhinus’ consisted of a mixture of at least five species. The molecular results also identified two species (S. lewini and I. paucus) not previously recorded in Chilean waters. The fin identification survey given to nine regional traders demonstrated that they were highly accurate in recognizing pictures of fins from P. glauca and I. oxyrinchus. The overall strong concordance between market categories and fins from single species and the trader accuracy in survey fin identification suggests that monitoring the Chilean fin trade by market names will provide a reasonably accurate picture of the volume of sharks landed by species.     

The Species and Origin of Shark Fins in Taiwan’s Fishing Ports,Markets, and Customs Detention: A DNA Barcoding Analysis

The increasing consumption of shark products, along with the shark’s fishing vulnerabilities, has led to the decrease in certain shark populations. In this study we used a DNA barcoding method to identify the species of shark landings at fishing ports, shark fin products in retail stores, and shark fins detained by Taiwan customs. In total we identified 23, 24, and 14 species from 231 fishing landings, 316 fin products, and 113 detained shark fins, respectively. All the three sample sources were dominated by Prionace glauca, which accounted for more than 30% of the collected samples. Over 60% of the species identified in the fin products also appeared in the port landings, suggesting the domestic-dominance of shark fin products in Taiwan. However, international trade also contributes a certain proportion of the fin product markets, as four species identified from the shark fin products are not found in Taiwan’s waters, and some domestic-available species were also found in the customs-detained sample. In addition to the species identification, we also found geographical differentiation in the cox1 gene of the common thresher sharks (Alopias vulpinus), the pelagic thresher shark (A. pelagicus), the smooth hammerhead shark (Sphyrna zygaena), and the scalloped hammerhead shark (S. lewini). This result might allow fishing authorities to more effectively trace the origins as well as enforce the management and conservation of these sharks.     

Elasmobranchs in southern Indonesian fisheries: the fisheries, the status of the stocks and management options

The biology of elasmobranchs makes them very vulnerable to fishing pressure and there is increasing international concern over their exploitation. In northern Australia the stocks of some species may be shared with those in southern Indonesia. Indonesia has the highest landings of elasmobranchs worldwide (>100,000 t p.a.) and millions of Indonesian artisanal fishers rely heavily on elasmobranchs taken in target fisheries. They are also taken by industrial trawlers and as bycatch in pelagic tuna fisheries. This paper, resulting from a collaborative project between Australia and Indonesia, summarises the elasmobranch fisheries; the characteristics of the fisheries are outlined, the status of the stocks are assessed, and management options described and discussed. The project focussed on representative markets and fish landing sites in southern Indonesia from 2001 to 2005. Data were from market surveys, the records of the Indonesian Directorate General of Capture Fisheries, and from research cruises. Data from the ongoing tuna monitoring programme showed that shark bycatch from the tuna fleets forms about 11% of shark landings in Indonesia. Yield per recruit and related analyses were used to integrate biological information to indicate the productivity of each species to allow for management policy options and constraints. Research cruise data show that catch rates of elasmobranchs in the Java Sea declined by at least one order of magnitude between 1976 and 1997. The results indicate strongly that many of the shark and ray species in Indonesia are overfished and that the most effective management strategy may need to involve capacity control, such as licencing, gear restrictions and catch limits, together with controls on the fin trade.     

Performance of iSharkFin in the identification of wet dorsal fins from priority shark species

The past decade has seen a considerable rise in international concern regarding the conservation status of sharks and rays. The demand for highly prized shark commodities continues to fuel the international trade and gives fisheries incentive to use these resources, which have a low intrinsic capability to recover. Recognising the urgency for regulation, many countries voted to include more shark and ray species in the Appendices of the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES). However, the identification of fins in fisheries landings before they enter international trade is a major limitation for CITES compliance. This study reports the current performance of the iSharkFin system, a machine learning technology which aims to allow users to identify the species of a wet shark dorsal fin from its image. Photographs of 1147 wet dorsal fins from 39 shark species, collected in 12 countries, were used to train the algorithm over a four-year period. As new cohorts of images were used to test the performance of the learning algorithm, the accuracy of species assignments of known specimens was variable but did increase, reaching 85.3% and 59.1% at genus and species level respectively. The accuracy in predicting CITES-listed sharks versus unlisted sharks was 94.0% based on the 39 species currently represented in the baseline. Our results suggest that if supplied with high data inputs for specific fisheries assemblages and accompanied by user training, iSharkFin has promise for site-specific development as a rapid field identification tool in fisheries monitoring, and as a screening tool alongside traditional field morphology to detect potential CITES specimens for fisheries compliance and enforcement.