|Scientific Name:||Rhincodon typus Smith, 1828|
|Taxonomic Source(s):||Penrith, M. J. 1972. Earliest description and name for the Whale Shark. Copeia 1972(2): 362.|
|Red List Category & Criteria:||Endangered A2bd+4bd ver 3.1|
|Assessor(s):||Pierce, S.J. & Norman, B.|
|Reviewer(s):||Dulvy, N.K., Simpfendorfer, C. & Kyne, P.M.|
The Whale Shark (Rhincodon typus), the world’s largest living fish, is a cosmopolitan tropical and warm temperate species. Genetic results indicate that two major subpopulations exist, in the Atlantic Ocean and Indo-Pacific, respectively.
Pronounced size- and sex-based segregation is present in most of the species’ known coastal feeding areas, with coastal sites typically dominated by juvenile male sharks. The largest known aggregation sites for Whale Sharks host hundreds or low thousands of individuals, based on counts and model estimates. Although individual sharks are highly mobile, many show a degree of site fidelity.
Directed fisheries and significant bycatch fisheries have targeted areas where high densities of Whale Sharks occur, leading to rapid reductions in catch per unit effort (CPUE) measures. Some bias toward juvenile Whale Shark-dominated aggregations are present in trend data; in the absence of information on other life-stages, these trends are inferred to be representative of population-level declines. While a number of commercial fisheries for the species closed during the 1990–2000s, Whale Shark products remain valuable and the species is still commonly caught in some countries. Serious injury and inferred mortality through vessel strike is a threat to several globally significant aggregations, as is bycatch in net fisheries, and the risk of ship strike. In the absence of conservation action, declines is likely to continue into the future.
Based on count data, modelled population estimates and habitat availability, 75% of the global Whale Shark population is inferred to occur in the Indo-Pacific, and 25% in the Atlantic. A variety of datasets present declines of 40-92%, inferring an overall decline of 63% in the Indo-Pacific over the last 75 years (three generations), resulting in a subpopulation assessment of Endangered A2bd+4bd. In the Atlantic, the overall population decline is considered to be lower at ≥30%, resulting in a subpopulation assessment of Vulnerable A2b+4b. Given the bulk of the global population occurs in the Indo-Pacific, the overall global decline is inferred to be ≥50%. Globally, the Whale Shark is therefore assessed as Endangered A2bd+4bd.
|Previously published Red List assessments:|
|Range Description:||The Whale Shark has a circumtropical distribution through all tropical and warm temperate seas, apart from the Mediterranean (Rowat and Brooks 2012). Their core distribution is between approximately 30°N and 35°S, with occasional seasonal penetration to the north and south (Colman 1997, Rowat and Brooks 2012, Sequeira et al. 2014). The northernmost records are from 44°N in the Bay of Fundy, Canada (Turnbull and Randell 2006) and the Sea of Okhotsk off Japan (Tomita et al. 2014), with the southernmost from 37°S in Victoria, Australia (Wolfson 1986). Whale Shark distribution is likely to be temperature limited, as they are rarely sighted in surface temperatures of less than 21°C (Iwasaki 1970, Colman 1997, Duffy 2002, Afonso et al. 2014, Tomita et al. 2014).|
Areas where 500 or more individuals have been documented through either counts or model estimates include the Arabian Gulf and Gulf of Oman (Robinson et al. in review), Ningaloo Reef in Western Australia (Meekan et al. 2006, Norman et al. submitted), Darwin Island in the Galapagos (Acuña-Marrero et al. 2014), Quintana Roo in Mexico (de la Parra Venegas et al. 2011, Ramírez-Macías et al. 2012), Inhambane province in Mozambique (Norman et al. submitted), the Philippines (Schleimer et al. 2015), and around Mahe in the Seychelles (Rowat et al. 2009, 2011; Brooks et al. 2010). Evidence from fisheries catches indicates that the Gujarat coast of India (Akhilesh et al. 2012), Taiwan (Hsu et al. 2012) and southern China (Li et al. 2012) also had large numbers of Whale Sharks in the vicinity, at least prior to the initiation of targeted fisheries in those countries, with estimated catches of up to 1,000 individuals per year (Li et al. 2012).
In the Indian Ocean, data from the tuna purse-seine fleet has identified the Mozambique Channel as having a high density of Whale Shark-associated sets (Sequeira et al. 2012). In the Atlantic and Pacific Oceans, Whale Shark sightings were correlated with effort (Harley et al. 2013, Sequeira et al. 2014). Modelled habitat suitability was highest in the eastern Atlantic in the area off Gabon and surrounding countries (Sequeira et al. 2014), while the Bismark and Solomon Seas have relatively frequent Whale Shark sightings within the Western and Central Pacific (Harley et al. 2013).
Native:American Samoa; Angola; Anguilla; Antigua and Barbuda; Argentina; Aruba; Australia; Bahamas; Bahrain; Bangladesh; Barbados; Belize; Benin; Brazil; Brunei Darussalam; Cambodia; Cameroon; Cape Verde; Cayman Islands; Chile; China; Colombia; Congo; Congo, The Democratic Republic of the; Cook Islands; Costa Rica; Côte d'Ivoire; Cuba; Curaçao; Djibouti; Dominica; Ecuador; Egypt; El Salvador; Equatorial Guinea; Eritrea; Ethiopia; Fiji; French Guiana; French Polynesia; Gabon; Gambia; Ghana; Grenada; Guadeloupe; Guatemala; Guinea; Guinea-Bissau; Guyana; Haiti; Honduras; India; Indonesia; Iran, Islamic Republic of; Iraq; Israel; Jamaica; Japan; Jordan; Kenya; Kiribati; Liberia; Madagascar; Malaysia; Maldives; Marshall Islands; Martinique; Mauritania; Mexico; Micronesia, Federated States of ; Montserrat; Morocco; Mozambique; Myanmar; Namibia; Nauru; New Caledonia; Nicaragua; Nigeria; Niue; Oman; Pakistan; Panama; Papua New Guinea; Peru; Philippines; Pitcairn; Portugal; Puerto Rico; Qatar; Saint Helena, Ascension and Tristan da Cunha; Saint Kitts and Nevis; Saint Lucia; Saint Martin (French part); Saint Vincent and the Grenadines; Samoa; Sao Tomé and Principe; Saudi Arabia; Senegal; Sierra Leone; Sint Maarten (Dutch part); Solomon Islands; Somalia; South Africa; Sudan; Suriname; Taiwan, Province of China; Tanzania, United Republic of; Thailand; Togo; Tokelau; Tonga; Turks and Caicos Islands; Tuvalu; United Arab Emirates; United States; Uruguay; Vanuatu; Venezuela, Bolivarian Republic of; Viet Nam; Virgin Islands, British; Virgin Islands, U.S.; Wallis and Futuna; Western Sahara; Yemen
Vagrant:Canada; New Zealand
|FAO Marine Fishing Areas:|
Atlantic – southeast; Atlantic – western central; Atlantic – eastern central; Atlantic – southwest; Indian Ocean – western; Indian Ocean – eastern; Pacific – northwest; Pacific – western central; Pacific – southwest; Pacific – eastern central; Pacific – southeast
|Range Map:||Click here to open the map viewer and explore range.|
|Population:||Based on counts, modelled population estimates and habitat availability, it is inferred that approximately 75% of the global Whale Shark population occurs in the Indo-Pacific, and 25% in the Atlantic. In the Indo-Pacific, a population reduction of 63% is inferred over the last three generations (75 years), and in the Atlantic a population reduction of more than 30% is inferred (see the discussion for each subpopulation below). Combining data from both regions, it is likely that the global Whale Shark population has declined by >50% over the last 75 years.|
Available datasets for Whale Sharks, in particular those from coastal sites, are typically dominated by juvenile male sharks. Acknowledging this, we make the assumption that trend data in the visible fraction of the population (i.e. mainly juveniles) is representative of the adult population.
Global population size
Whale Sharks are individually identifiable based on their characteristic spot patterns (Taylor 1994, Arzoumanian et al. 2005, Marshall and Pierce 2012). A global database of Whale Shark sightings, comprising submitted photographs from both researchers and the public, is hosted online at Wildbook for Whale Sharks (www.whaleshark.org) (Wild Me 2016, Norman et al. submitted). As of February 2016, there were 7,011 individual sharks on this database, identified from images submitted between 1964 and 2016. However, 70% of sexed individuals (n = 3,420) were male, with the majority of these likely to be immature based on length estimates (Norman and Stevens 2007, Ramírez-Macías et al. 2012, Rohner et al. 2015). This dataset is assumed to not fully represent female, small juvenile or adult sharks (Norman et al. submitted). Therefore, the total represents a minimum number of sharks alive over this period.
Two global-scale genetic studies on Whale Sharks have estimated genetic effective population size – the number of breeding adults – albeit based on small sample sizes of 70 (Castro et al. 2007) and 68 sharks (Schmidt et al. 2009), respectively. Castro et al. (2007) used mitochondrial DNA to estimate current genetic effective population size to be 119,000–238,000 sharks. Schmidt et al. (2009) estimated genetic effective population size to be 103,572, with a standard error of 27,401–179,794, based on microsatellite analysis. However, lack of knowledge on species-specific mutation rates mean these estimates should not be used for management purposes (J. Schmidt pers. comm., T. Vignaud and S. Planes pers. comm).
Global population structure
While global connectivity of Whale Shark subpopulations has been postulated (Sequeira et al. 2013b), a large global genetic study using both mitochondrial DNA and microsatellite analysis has demonstrated that the Whale Shark subpopulations in the Atlantic and Indo-Pacific are functionally separate (Vignaud et al. 2014). Large-scale photo-identification studies in the Indian Ocean (Brooks et al. 2010) and western Atlantic (Hueter et al. 2013), along with Wildbook online database results (Norman et al. submitted), have shown limited connectivity exists between non-contiguous countries. Based on these results, here we have considered two separate subpopulations in this assessment.
Atlantic subpopulation trend
A decline of ≥30% in the Atlantic subpopulation is inferred over the last three generations (75 years) based on data from tuna fleet observers off a likely centre of abundance for this subpopulation. Between 1980 and 2010 there was a decline in sightings per unit effort (SPUE) off western Africa, with SPUE peaking in 1995 and declining thereafter (Sequeira et al. 2014; Table 1 in the supplementary material). In absolute terms, sightings decreased from about 500 during the 1990s to around 150 during the 2000s. Peak-month sightings also declined by approximately 50% over this time (Sequeira et al. 2014).
At Gladden Spit in Belize, Whale Shark sightings declined from a mean of 4 to 6 sharks per day between 1998 and 2001 to less than 2 per day in 2003 (Graham and Roberts 2007), with reports from diving guides indicating that numbers have remained low until 2016 (R. Graham, pers. comm.).
In the Azores, there was a significant increase in sightings in 2008 and afterwards compared to the decade before (Afonso et al. 2014; Table 1 in the supplementary material). This was strongly correlated with the location of the 22°C isotherm, indicating that this increasing sighting trend is due to environmental conditions (Afonso et al. 2014).
Atlantic subpopulation size
Regional counts of identified sharks or modelled abundance estimates are available from many of the larger known aggregation or feeding areas. Ramírez-Macías et al. (2012) photo-identified 350 individual Whale Sharks from Holbox Island in Mexico between 2005 and 2008, and estimated that 521–809 sharks participate in this aggregation. Aerial surveys from this area and the adjacent Caribbean coast have counted up to 420 sharks in a single aerial survey (de la Parra Venegas et al. 2011). The largest-known aggregation as of February 2016 occurs seasonally off the Yucatan cost of Mexico, with over 1,100 identified sharks (Norman et al. submitted). Satellite-tagged sharks from this aggregation have been tracked to the northern Gulf of Mexico (Hueter et al. 2013), where aggregations of up to 100 sharks have been reported (Hoffmayer et al. 2005), south to Belize where 106 individual sharks were identified between 1998 and 2003 (Graham and Roberts 2007), and off the island of Utila, Honduras, where 95 sharks were identified between 1999 and 2011 (Fox et al. 2013). One shark, tagged in 2007, was tracked swimming across the equator to the South Atlantic Ocean, near the Mid-Atlantic Ridge (Hueter et al. 2013). The end point of this track was 543 km southeast from the Saint Peter and Saint Paul Archipelago, where 54 Whale Shark sightings were recorded between 2000 and 2005 (Hazin et al. 2008). This individual was subsequently photo-identified back off the Yucatan coast in 2011 and 2012 (Hueter et al. 2013).
Aside from St Helena Island (A. Dove, pers. comm.), there have been few photographic records from elsewhere in the Atlantic (Wild Me 2016). There were, however, 2,297 records of Whale Sharks from the logbooks of tuna purse-seine vessels between 1980 and 2010, mostly from the eastern Atlantic (Sequeira et al. 2014) and particularly off the coast of Gabon (Capietto et al. 2014). An additional 1,449 sightings were recorded from the Azores archipelago between 1998 and 2013 (Afonso et al. 2014).
Indo-Pacific subpopulation trend
A decline of >50% (likely around 63%) in the Indo-Pacific Whale Shark subpopulation is inferred over the last three generations (75 years) based on relevant indices of abundance from Mozambique, the broader Western Indian Ocean, the Philippines, Taiwan, Thailand and the Western and Central Pacific, and actual levels of exploitation in mainland China, the Maldives, India, the Philippines and Taiwan.
A commercial fishery for Whale Shark existed in Taiwan until 2007 (Hsu et al. 2012). Information provided by fishers operating from Hongchun harbour in southern Taiwan indicated that 50–60 sharks were caught each season in the mid-1980s, declining to less than 10 per year in each of 1994 and 1995 (Chen and Phipps 2002; Table 1 in the supplementary material). Although definitive catch trends are not available, there was a significant (58%) decrease in the estimated annual catch in 1997 of 272 sharks (Chen and Phipps 2002) to a reported catch of 113 sharks over 15 months in 2001–2002 (Chen and Phipps 2002; Table 1 in the supplementary material). A decline in the mean total length of landed sharks was noted between 2002 and 2007 (Hsu et al. 2012; Table 1 in the supplementary material). A decline in the mean size of landed sharks was also noted in southern Chinese waters, from 8.27 m prior to 2004 to 6.3 m in 2008–2011 (Li et al. 2012; Table 1 in the supplementary material).
Data from observers aboard the tuna purse-seine fleet in the Western and Central Pacific noted 1,073 Whale Shark sightings, with most from the Bismark and Solomon Seas (Harley et al. 2013). The occurrence of Whale Shark in free school sets decreased by approximately 50% between 2003 (1%) and 2012 (0.5%), potentially representing a fall in abundance (Harley et al. 2013; Table 1 in the supplementary material), although a weak linear increase in occurrence probability was modelled by Sequeira et al. (2014) between 2000 and 2010 (Table 1 in the supplementary material). However, model performance for this latter dataset was poor (Sequeira et al. 2014).
The influence of environmental variability on sightings of Whale Shark can complicate the interpretation of trend data, particularly with the shortage of long-term datasets. A decline in Whale Shark sightings along the eastern coast of South Africa between 1993 and 1998 (Gifford 2001) was included in the proposal for listing the sharks on Appendix II of the Convention on International Trade in Endangered Species (CITES 2002). However, with the benefit of hindsight, the substantial variability in sighting data from this area over summer months (Cliff et al. 2007) and seasonal changes in their oceanic distribution (Sequeira et al. 2012), makes it unclear whether these earlier data are indicative of a true subpopulation decline. North of this area, in the northern Mozambique Channel and broader western Indian Ocean, a slight increase in Whale Shark sightings was noted between 1991 and 2000 based on tuna purse-seine vessel data, then a decrease from 2000 to 2007 (Sequeira et al. 2013a; Table 1 in the supplementary material). In absolute terms, 600 sightings were reported from the 1990s decreasing to ~200 across 2000–2007 (Sequeira et al. 2014). Peak monthly sightings decreased by around 50% over the study period (Sequeira et al. 2014). In Inhambane, Mozambique, in the southern Mozambique Channel, sightings declined 79% between 2005 and 2011 (Rohner et al. 2013; Table 1 in the supplementary material). This decreased rate of sightings has persisted to at least January 2016 (S. Pierce, unpubl. data). Sharks routinely move between South Africa and southern Mozambique (Rohner et al. 2015, Norman et al. submitted), but there is limited or no connectivity between these and other known coastal feeding areas to the north in Djibouti, Seychelles and Tanzania (Brooks et al. 2010, Norman et al. submitted). Prior to the species being protected in the Maldives in 1995, catches of Whale Shark declined from around 30 each year from one of the significant fishing locations up until the early 1980s to a catch of 20 or less Whale Sharks from the entire archipelago by 1993 (Anderson and Ahmed 1993; Table 1 in the supplementary material).
Two hundred and fifty-three Whale Shark sightings were recorded by a local dive charter company in the Andaman Sea, Thailand, between 1991 and 2001 (Theberge and Dearden 2006). Sightings per unit effort showed a significant decline over this period, with an overall decrease from 1.58 Whale Sharks per trip in 1992–1993 to 0.13 sharks per trip in 2000–2001 (Theberge and Dearden 2006; Table 1 in the supplementary material). A low absolute number of sightings persisted until at least the 2002–2003 season, although effort data were not recorded (Theberge and Dearden 2006). Following the conclusion of data collection for that study, shark sightings have likely increased in frequency according to reports from dive operators. However, sharks are perceived to be smaller than those sighted in the 1990s (P. Dearden, pers. comm).
Bradshaw et al. (2008) analysed tourism sightings at Ningaloo Reef, Australia, between 1995 and 2004, corrected for search effort and environmental fluctuation, and identified a 40% decline in sighting rate and a decline in mean shark length of 1.6 m over this time period (Table 1 in the supplementary material), although seasonal shifts in peak abundance to outside observation months may also have contributed to this observed decline (Mau and Wilson 2007, Holmberg et al. 2009). Analysis of individual sighting data from 1995 to 2006 identified behavioural heterogeneity in the sharks at Ningaloo, with the majority showing some site fidelity in that they were sighted in multiple seasons (Holmberg et al. 2008). This (majority) subset of the study population was increasing over the course of this work (Holmberg et al. 2008). Follow-up analyses on a slightly longer dataset (1995 to 2008) confirmed this result, with smaller individuals contributing in larger numbers to recruitment, thereby potentially explaining the observed decline in mean size (Holmberg et al. 2009; Table 1 in the supplementary material). However, a genetic study on Ningaloo sharks indicated declining genetic diversity over five consecutive years for mtDNA (2007–2012) and two (2010–2012) for microsatellites (Vignaud et al. 2014; Table 1 in the supplementary material).
Whale Sharks were fished in the Philippines prior to protection in 1998, with Whale Shark catch per unit effort (i.e., per boat) declining from 4.44 to 1.7 in Pamilacan and 10 to 3.8 in Guiwanon between two surveys conducted in 1993 and 1997 (Alava et al. 2002; Table 1 in the supplementary material).
Indo-Pacific subpopulation size
Six hundred and seventy sharks were photo-identified in southern Mozambique between 2003 and 2014 (Norman et al. submitted). Off Mafia Island in Tanzania, 131 sharks were photo-identified between 2006 and 2014 (Norman et al. submitted). Off Djibouti, 297 individuals were photo-identified between 2003 and 2010 (Rowat et al. 2011), while 443 individuals were photo-identified off Mahe in the Seychelles between 2001 and 2009 (Rowat et al. 2011). A subset of the Seychelles dataset, comprising records from 2004 to 2009, was modelled to produce an abundance estimate of 469 to 557 sharks from that area (Brooks et al. 2010). Comparisons of identities collected from the Seychelles, Djibouti, Tanzania and Mozambique, comprising a total of 1,069 individual sharks sighted up to 2009, found no matches between these countries (Brooks et al. 2010). Norman et al. (submitted) updated these figures and found three international matches (all between Mozambique and Tanzania) from 1,098 individuals. A significant aggregation of juvenile Whale Sharks also occurs in the Red Sea off the Saudi Arabian coast, with 122 individuals identified to 2013 (J. Cochran, pers. comm). Aggregations of up to 100 sharks have been noted off the Qatar coast (Robinson et al. 2013). One hundred and six sharks have been identified around South Ari Atoll in the Maldives (Riley et al. 2010, Davies et al. 2012), with a modelled abundance estimate of around 74 to 104 sharks (Davies et al. 2012). There were 1,184 Whale Shark sightings in the Indian Ocean recorded by tuna purse-seine vessel logbooks between 1991 and 2007, with almost all of these from the Western Indian Ocean (Sequeira et al. 2013a).
Eighty-two sightings were recorded off Christmas Island, Australia, between 1996 and 2008 (Hobbs et al. 2009). Whale shark photo-identifications range back to the early 1990s off Ningaloo Reef in Western Australia (Meekan et al. 2006; Holmberg et al. 2008, 2009). Three hundred and eighty-six sharks were identified here between 1995 and 2008 (Holmberg et al. 2009), with over 1,000 sharks identified by 2015 (Norman et al. submitted). Although two satellite-tagged sharks were tracked moving from Ningaloo Reef to the vicinity of Christmas Island (Sleeman et al. 2010), no exchange of photo-identified sharks has been documented to date (Wild Me 2016). One photo-identified Whale Shark was, however, recorded from both Ningaloo Reef and Borneo (B. Norman, unpubl. data).
Whale Shark abundance at Ningaloo Reef, Australia has been modelled by two studies. Meekan et al. (2006) estimated super-population size to be 319 to 436 sharks between 1992 and 2004. Holmberg et al. (2009) estimated annual abundance to vary between 86 and 143 sharks in the years 2004 to 2007, when length was used as a covariate. Whale Shark abundance in this area is correlated with the Southern Oscillation Index and several other oceanographic variables, which potentially relate to the strength of ocean currents and local productivity (Wilson et al. 2001, Sleeman et al. 2010).
Over 820 individual sharks have now been photo-identified from the Philippines (Schleimer et al. 2015), with large aggregations recorded from around Donsol (Quiros 2007), Oslob on Cebu Island (Araujo et al. 2014, Schleimer et al. 2015), and Pintuyan on Southern Leyte (Schleimer et al. 2015). Excluding the Philippines, 326 sharks have been photo-identified from Southeast Asia (here including Cambodia , Indonesia , Malaysia , Myanmar , Taiwan  and both coasts of Thailand ) and added to the global database by February 2016 (Wild Me 2016).
In the Eastern Pacific, Whale Sharks are seasonally present in small numbers around Darwin and Wolf islands in the north of the Galapagos Archipelago (Hearn et al. 2013). Acuña-Marrero et al. (2014) identified 82 individuals here from 2011–2013 and estimated an annual study population size of 695±166 individuals for the Galapagos Islands. Males and immature females are rarely observed at this location, so this estimate refers predominantly to large, apparently pregnant females (Acuña-Marrero et al. 2014). Two hundred and fifty-one individual sharks were photo-identified in the Gulf of California, Mexico, between 2003 and 2009: 129 from Bahía de Los Ángeles, 125 from Bahía de La Paz and smaller numbers from other sites (Ramírez-Macías et al. 2012). Modelled abundance estimates from this dataset were 54 in 2008 and 94 sharks in 2009 from Bahía de Los Ángeles, and between 19 and 62 through 2005–2009 at Bahía de La Paz (Ramírez-Macías et al. 2012). Outside of these areas (Galapagos Islands and Mexico), few photo-identified sharks have been added to the global database from the Eastern Pacific (Wild Me 2016). Twenty-five whale sharks were reported from tuna purse-seine vessel observers in 2014 (Clarke 2015).
|Current Population Trend:||Decreasing|
|Habitat and Ecology:||Whale Sharks are found in both coastal and oceanic habitats (Rowat and Brooks 2012). Oceanic sightings are strongly correlated with temperature in the Indian and Atlantic oceans (Sequeira et al. 2014), with most occurring between 26.5° and 30°C in the Indian Ocean (Sequeira et al. 2012). Depth was an important predictor in the Atlantic and Pacific Oceans, but was not significant in the Indian Ocean (Sequeira et al. 2014). Whale Sharks are highly mobile, with mean daily movement rates of 24–28 km based on tethered geopositioning tags (Hueter et al. 2013). Cyclical or longer-term climate shifts affect Whale Shark occurrence and abundance (Sleeman et al. 2010, Sequeira et al. 2012), which needs to be considered when discussing local abundance trends.|
Whale Sharks spend the majority of time in the epipelagic zone, but dive to at least 1,928 m in depth (Tyminsky et al. 2015). The driver of these deep dives is unclear, but may be related to foraging behaviour, especially when crossing oceanic waters with comparatively low surface productivity (Sleeman et al. 2010, Brunnschweiler and Sims 2011, Tyminsky et al. 2015) and/or assist with energy conservation when moving between prey zones (Gleiss et al. 2011) or navigating (Tyminsky et al. 2015). Initial results from fatty acid dietary studies suggest that meso- and bathypelagic prey may be an important component of Whale Shark diet (Rohner et al. 2013), and dive data from pop-up archival tags provide some evidence for mesopelagic foraging behaviour (Tyminsky et al. 2015).
Most Whale Shark sightings occur at a small number of known coastal feeding areas for the species, where the sharks aggregate on the surface to exploit seasonal productivity such as fish spawning events or zooplankton blooms (Rowat and Brooks 2012). A degree of inter-annual site fidelity has been documented in many locations (Cagua et al. 2015, Norman et al. submitted). Sexual- and size-based segregation is typical in these locations, with a bias towards juvenile males from 4–8 m length (Rohner et al. 2015, Norman et al. submitted). This pronounced segregation indicates that ontogenetic and sex-specific habitat or dietary shifts are present in the species. In the Gulf of California, juvenile sharks, comprising 60% males, were found in shallower waters exploiting abundant prey. Larger sharks, composed of 84% females, occurred in oceanic waters where they fed on diffuse patches of euphasiids (Ketchum et al. 2012). An initial stable isotope study of Indian Whale Sharks showed a positive relationship between size and δ13C and δ15N, suggesting that larger sharks feed on prey items of a larger size and higher trophic level (Borrell et al. 2011). Females had lower values of δ13C and δ15N than males (Borrell et al. 2011) suggesting that they have a different, more pelagic diet, while individuals of <4 m total length (TL) also showed a lower δ13C than larger individuals suggesting a transition from pelagic to more coastal foraging habitats.
The largest recorded Whale Shark, approximately 20 m TL (Chen et al. 1997) and 42 t in mass (Hsu et al. 2014), have been reported from Taiwan. An individual extrapolated to be 18.8 m TL was caught in India (Borrell et al. 2011). Norman and Stevens (2007) found that 50% of males were mature, based on clasper morphology, at a visually estimated TL of 8.1 m in Western Australia, while 50% maturity was estimated to occur at 9.2 m TL using laser photogrammetry in Mozambique (Rohner et al. 2015). In the Gulf of Mexico, Ramírez-Macías et al. (2012) visually estimated 50% male maturity to occur at around 7 m TL. Given the genetic differentiation between the Indo-Pacific and Atlantic Oceans (Vignaud et al. 2014), this may represent a subpopulation-level difference in the size of maturation. Size at maturity in female sharks is approximately 9 m TL, based on visual (Acuña-Marrero et al. 2014, Ramírez-Macías et al. 2012) and laser photogrammetric estimates (Acuña-Marrero et al. 2014) from the Eastern Pacific, and a 9.6 m TL individual recorded from Taiwan (Hsu et al. 2014). All of seven stranded female specimens from 4.8 to 8.7 m TL in South Africa were immature (Beckley et al. 1997). The only confirmed pregnant female examined, from Taiwan, was 10.6 m TL (Joung et al. 1996).
Whale Shark reproductive ecology is poorly known. Pregnant female sharks are seasonally found in the Eastern Pacific, particularly off Darwin Island in the Galapagos Archipelago (Acuña-Marrero et al. 2014) and the Gulf of California (Eckert and Stewart 2001, Ramírez-Macías et al. 2012), but rarely sighted outside this region. An exception is St Helena Island in the mid-Atlantic, where pregnant female sharks are routinely observed on a seasonal basis (A. Dove, pers. comm). The single pregnant female that has been physically examined, from Taiwan, had 304 pups in various stages of development, the largest litter size reported from any shark species (Joung et al. 1996, Schmidt et al. 2010). This discovery established that Whale Sharks are aplacental viviparous. Paternity analysis on a subset of the offspring established that a single male might have sired the entire litter, suggesting that the species has the capacity to store sperm (Schmidt et al. 2010). The largest size class of embryos, 58–64 cm TL, appeared close to fully developed (Joung et al. 1996). The smallest free-swimming neonate found in the wild, from the Philippines, was 46 cm TL (Aca and Schmidt 2011). Size at birth is therefore presumed to be around this range (Aca and Schmidt 2011). Reproductive periodicity is unknown: resightings rarely occur in the areas where pregnant sharks are observed (Norman et al. submitted).
Age and growth data on Whale Shark are sparse. Stranded sharks in South Africa (Wintner 2000) and fishery catches in Taiwan (Hsu et al. 2014), respectively, have been assessed. Both studies were limited by small sample sizes of predominantly juvenile sharks. Hsu et al. (2014) concluded that growth band deposition is likely to be biannual and, based on this, estimated that male sharks begin maturing at ~17 years and females at 19–22 years in the Indo-Pacific. However, these estimates have some important caveats: biannual band deposition has been demonstrated in very few other shark species, and other orectolobiform species have been shown to have aperiodic band pair formation (Huveneers et al. 2013). Validation through wild growth studies is important to confirm these results. Initial results from laser photogrammetric studies indicate that growth increments over periods of 1–3 years are too small to be accurately measured, but the technique may have value over longer time-frames (Rohner et al. 2015). Generation length is estimated as 25 years.
|Generation Length (years):||25|
|Movement patterns:||Full Migrant|
|Use and Trade:||
Whale Sharks are subject to large- and small-scale bycatch in fisheries, with some national and international trade in products. They are also a focal species for marine tourism industries.
The only known targeted fishery for Whale Sharks to have existed in the Atlantic Ocean was located in Santa Cruz, Cuba, where 8–9 sharks were caught each year until the fishery was banned in 1991 (Graham 2007). Aside from Venezuela, where Whale Sharks were occasionally harpooned by fishers (Romero et al. 2000), there are few other records of utilization or trade of individuals from this subpopulation.
Prior to 1985, there was little demand for Whale Shark meat in Taiwan, with specimens of several tonnes weight selling at between US$200–300 (Chen and Phipps 2002). No dedicated fishery was present, though Whale Sharks were caught as bycatch in set-net fisheries (Chen et al. 1997). A meat fishery developed during the 1990s, with annual catches estimated to be 272 individuals in 1996 from set-net and harpoon catches (Chen et al. 1997). Total catches were likely to be higher (Chen et al. 1997). Whale Shark became the most expensive shark meat available in Taiwan by 1997, reaching prices of US$13.93/kg (Chen et al. 1997). A small 2 t Whale Shark could fetch US$14,000, with a larger 10 t shark selling for around US$70,000 in 1997 (Chen et al. 1997). Catches declined after this peak, potentially due to local stock depletion, to 80–100 sharks through the country each year after 1997 (Hsu et al. 2012). However, the annual volume of Whale Shark meat traded more than doubled between 1998 and 2000, to 60 t in 2000 (Chen and Phipps 2002). Market surveys in 2001 indicated that catch was under-reported in official statistics, and that significant quantities of meat were likely being imported through unofficial channels (Chen and Phipps 2002). Following the introduction of specific export codes for Whale Shark meat in 2001, 2 tonnes of exports (to Spain, valued at US$1.15/kg) and no imports were recorded over the following year (Chen and Phipps 2002). A total of 693 sharks were caught in Taiwan between 2001 and 2008 (Hsu et al. 2012). Total allowable catch quotas steadily reduced through to zero sharks from 2001 to 2007 (Hsu et al. 2012). A small international trade in live Whale Shark was also noted in Taiwan (Chen and Phipps 2002), and is also present in mainland China (Li et al. 2012).
Prior to the protection of Whale Shark in India (2001) and the Philippines (1998), Whale Shark meat was exported from those countries to Taiwan (Chen and Phipps 2002). From 1990 to 1997, 624–627 Whale Shark were caught from four of the primary fishing sites in the Philippines (Alava et al. 2002). Whale Shark meat from mainland China was also thought to be illegally exported to the Taiwanese market (Chen and Phipps 2002). While Whale Shark is not presently targeted off mainland China, there is a large bycatch, estimated to be more than 1,000 individuals per annum (Li et al. 2012). Whale Shark is considered a high value catch in this fishery, so they may be actively targeted in the future (Li et al. 2012). Although the species is technically protected, catches are unmonitored and enforcement is minimal (Li et al. 2012). A reduction in the mean size of landings has been reported, from 8.27 m prior to 2004 to 5.5 m from 2004–2007 and 6.3 m from 2008–2011 (Li et al. 2012). It is unclear whether this apparent decrease in mean catch length reflects a decrease in landings of large sharks.
In the 1990s, Whale Shark fins were regarded as low value due to poor quality and the difficulty of preparation (Chen and Phipps 2002). Demand for fins within trade was minimal, although they were sometimes sold as display or trophy fins for shark-fin soup restaurants (Chen and Phipps 2002). More recent surveys have reported that Whale Shark fins are now demanding high prices, which is likely to result in increased targeting (Li et al. 2012). Whale Shark fins are sporadically seen in Hong Kong markets (G. Curtis, pers. comm.), indicating that international trade in Whale Shark fins is still likely to be occurring. The source of these fins is unknown. A live shark was seen with a recently removed first dorsal fin in the Maldives (Riley et al. 2009). Whale Shark were also opportunistically finned in Indonesia in the 2000s (White and Cavanagh 2007).
The Whale Shark fishery in India was reviewed by Akhilesh et al. (2013). A traditional small-scale seasonal harpoon fishery in India took Whale Shark for their liver oil, which was used to waterproof boats. In the mid 1990s, fishery effort increased along the Gujarat coast to meet demand for oil, meat and fins from countries in Europe and Southeast Asia. From 1990 until 2001, when Whale Shark became legally protected in territorial waters, there was a targeted commercial fishery in Gujarat. Between 1889 and 1998, 1,974 sharks were recorded as landed through India. Some bycatch still occurs following the closure of this fishery, with 79 landings from 2001 to 2011 (Akhilesh et al. 2013).
A small opportunistic fishery is active in Oman (D. Robinson, pers. comm). Small-scale harpoon and entanglement fisheries for Whale Sharks have taken place in several other countries such as Iran and Pakistan (Rowat and Brooks 2012). Recent landings in these areas are unknown. Fishers in the Maldives used to take 20–30 individuals per year for their oil, but reported declining catches during the 1980s to early 1990s (Anderson and Ahmed 1993), and the fishery was banned in 1995. Occasional hunting may have continued following protection (Riley et al. 2009).
Tourism industries based on viewing Whale Shark have now developed in several countries or locations, including Australia, Belize, Cuba, Djibouti, Ecuador, Honduras, Indonesia, the Maldives, Mexico, Mozambique, Oman, Panama, the Philippines, St Helena, Saudi Arabia, the Seychelles, Tanzania and Thailand. These range in size between a maximum of 24 tourists at a time in Cuba (Graham 2007), to over 250 licensed tour operators off Quintana Roo in Mexico (Ziegler et al. 2012). Direct expenditure for Whale Shark-focused tourism at South Ari Atoll in the Maldives was estimated at US$9.4 million in 2013 (Cagua et al. 2014), while payments for tours alone off Quintana Roo in Mexico were estimated to be US$7 million in 2013 (R. de la Parra Venegas, pers. comm). In Western Australia, whale shark tourists spent an estimated AU$6 million in the Ningaloo region in 2006 (Catlin and Jones 2010). Tourist numbers have since doubled, from approximately 10,000 to 20,000 per year, so expenditure will also have substantially increased (B. Norman, unpubl. data). Graham (2007) projected that, globally, Whale Shark tourism was likely to be worth over US$42 million annually. Rapid increases in the numbers of tour participants in some key locations, such as in Mexico (R. de la Parra Venegas, pers. comm.), Australia (D. Robb, pers. comm.) and the Philippines (Araujo et al. 2014) indicate that the industry is growing fast in economic importance.
Major contemporary threats to Whale Sharks include fisheries catches, bycatch in nets, and vessel strikes. Other threats affect Whale Shark on local or regional scales.
Whale Sharks are presently fished in several locations. In southern China, large-scale commercial take of Whale Sharks appears to be increasing (Li et al. 2012). Although Whale Sharks are not necessarily targeted, they are routinely captured and retained when sighted (Li et al. 2012). A small-scale opportunistic fishery for Whale Sharks is also present in Oman (D. Robinson, pers. comm).
Whale Sharks have previously been targeted in large-scale fisheries from India, the Philippines and Taiwan, with hundreds of sharks caught annually in each country until species-level protections were implemented (Rowat and Brooks 2012). A smaller directed fishery occurred in the Maldives until Whale Sharks were protected in 1995 (Anderson and Ahmed 1993). Broader-scale subpopulation reduction caused by these fisheries was raised as a possible driver of declining sightings in Thailand (Theberge and Dearden 2006) and Western Australia (Bradshaw et al. 2008). Occasional directed catch or bycatch of Whale Sharks has been documented from many of their range states, particularly where large-mesh gillnets are in common use (Rowat and Brooks 2012).
Tuna are often associated with Whale Sharks, and tuna purse-seine fisheries often use Whale Sharks as an indicator of tuna presence, even setting nets around the sharks (Capietto et al. 2014). Direct mortality in purse-seine fisheries appears to generally be low, recorded as 0.91% (one of 107) and 2.56% (one of 38) of sharks where fate was reported by observers in the Atlantic and Indian Oceans, respectively (Capietto et al. 2014). However, estimated mortality rates in the Western Central Pacific purse-seine fishery were higher: 12% for 2007–2009 and 5% in 2010. This extrapolated to a total mortality of 56 sharks in 2009 and 19 in 2010 (Harley et al. 2013). Observer reports on release condition from this region from 2010–2014 were generally consistent, with 50–60% of encircled sharks released alive, 5–10% dying and 30–40% of status unknown (Clarke 2015). Assuming a poor outcome for the latter category, potential mortalities in 2014 range from a minimum of 11 to 42, with a higher number possible depending on longer-term survival of the sharks released alive (Clarke 2015). Available data on the number of Whale Sharks caught are likely to underestimate total catch (Clarke 2015). The longer-term survivorship of Whale Sharks released from nets has not been examined at this stage. Common release practices, such as being lifted or towed by the caudal peduncle, are likely to cause stress, injury and possibly death to the sharks.
Shipping lanes, where they are placed close to Whale Shark feeding areas, can create a serious risk of vessel strikes. Whale Sharks routinely feed at the surface (Motta et al. 2010, Gleiss et al. 2013), and propeller injuries are commonly recorded during monitoring programs (Rowat et al. 2006, Speed et al. 2008, Fox et al. 2013). While mortality events are seldom reported in the contemporary scientific literature, they were often noted from slower-moving vessels in the past (Gudger 1941). It is likely that fast-moving, large ships do not register or report impacts, and as Whale Sharks will typically sink upon death, these are unlikely to be documented (Speed et al. 2008). Areas where Whale Sharks appear to be at particular risk include the Mesoamerican reef countries in the Western Caribbean (Graham 2007, R. de la Parra-Venegas pers. comm.) and Gulf states (D. Robinson pers. comm.), where a high frequency of serious propeller injuries are observed during monitoring.
Inappropriate tourism may be an indirect threat to Whale Shark in some circumstances (for example from interference, crowding or provisioning). Marine pollution events occurring in Whale Shark hotspots, such as the Deepwater Horizon oil spill in the Gulf of Mexico in 2010 (Hoffmayer et al. 2005, McKinney et al. 2012), may result in mortality or displacement from preferred habitats. These more local threats, as well as potential future concerns such as climate change impacts (Sequiera et al. 2014), should be closely monitored.
The Whale Shark has been listed in a number of international conventions and agreements. The species is included in Annex I (Highly Migratory Species) of the United Nations Convention on the Law of the Sea (UNCLOS), which provides a framework for the conservation and management of fisheries, and other uses of the seas. To date, no management initiatives enacted through UNCLOS have included the Whale Shark. Under the aegis of this convention, the United Nations Agreement on Straddling and Highly Migratory Fish Stocks was introduced in 1995, which has potential for direct actions to be taken in relation to species such as Whale Shark, although none have yet been proposed (Rowat and Brooks 2012). Also in 1995, the FAO finalized a Code of Conduct for Responsible Fisheries, and then in 1998 the International Plan of Action for Conservation and Management of Sharks (Rowat and Brooks 2012). Davidson et al. (2015) noted that only 22 National Plans Of Action had been published at that time, limiting the effectiveness of this initiative.
The Whale Shark was listed on Appendix II of the Bonn Convention for the Conservation of Migratory Species of Wild Animals (CMS) in 1999. This identifies it as a migratory species whose unfavourable conservation status would benefit from the implementation of international cooperative agreements. The CMS has provided a forum for the development of more direct conservation approaches with the adoption, in 2010, of a Memorandum of Understanding on the migratory shark species listed on this agreement, including Whale Shark. There were 40 signatories to this memorandum as of February 2016, which aims to improve scientific knowledge, ensure fisheries sustainability, protect critical habitats, movement corridors and life stages of sharks, while increasing public participation and national, regional and international cooperation towards these objectives. Whale Shark routinely move across political boundaries (summarised in Rowat and Brooks 2012), emphasising the importance of this unified approach.
Whale Shark was listed on Appendix II of the Convention on International Trade in Endangered Species (CITES) in 2002. This requires fishing states to demonstrate that any exports were derived from a sustainably managed population, enabling exports and imports to be monitored through a permit system. Continued presence of Whale Shark fins in Hong Kong markets, a major international transit point, despite no records in the CITES Wildlife Trade Database (http://trade.cites.org) suggests that illegal trade is occurring outside the CITES permit system. No Whale Shark fisheries have been certified as sustainable under CITES Appendix II regulations. Identifying the source of these fins, and enforcing CITES regulations, should be a key goal for managers.
National- or territory-level management measures for Whale Shark, via shark fishing bans or specific species protection, are in place in American Samoa, Australia, Bahamas, Belize, Cambodia, Chagos Archipelago (UK), China, Congo-Brazzaville, Cook Islands, Costa Rica, Djibouti, Dominican Republic, Ecuador, Egypt, El Salvador, French Polynesia, Guatemala, Guadeloupe, Guyana, Honduras, Indonesia, India, Kuwait, Maldives, Malaysia, Marshall Islands, Mexico, Myanmar, New Caledonia, New Zealand, Nicaragua, Palau, Panama, Philippines, Qatar, Reunion, Saudi Arabia, Seychelles, South Africa, St Helena Island (UK), Taiwan, Thailand, Tokelau, United Arab Emirates and USA. Species-level legislative protection is an important conservation goal in countries where Whale Shark are still caught, either as a target or bycatch, including China, Mozambique, Oman, Pakistan and Tanzania.
While many of the larger commercial fisheries for Whale Sharks have now ceased, primarily due to rapid catch reductions, fishery and trade management is still required. The active fishery in Chinese waters is almost certainly unsustainable (Li et al. 2012). This national fishery is likely to be the largest single direct threat to Whale Shark recovery in the Indo-Pacific. Enforcement of existing laws for Whale Shark protection, and education and awareness programmes for fishers, will be an important component of management there.
Key habitats for Whale Sharks, in the form of coastal feeding locations or movement corridors, are protected in Australia (Ningaloo Reef), Belize (Gladden Spit), Costa Rica (Cocos Island), Ecuador (Galapagos Islands), Mexico (Yum-Balam Biosphere Reserve), Panama (Coiba Island) and the UK (St Helena Island). Site protection is necessary in some areas where high densities of Whale Sharks are present, as anthropogenic pressures on these sites could have disproportionate impact on subpopulation declines. Important aggregation areas for Whale Sharks in Mexico (de la Parra Venegas et al. 2011), Mozambique (Haskell et al. 2015) and Qatar (Robinson et al. 2013) are examples. Where Whale Sharks are routinely feeding on the surface, such as off Quintana Roo in Mexico (Motta et al. 2010, de la Parra Venegas et al. 2011), these areas should also be managed to reduce vessel strikes in nearby shipping lanes. This could entail either seasonal ‘go-slow zones’, or moving these routes to avoid the shark aggregations. Protection of the specific biological phenomena that influence Whale Shark presence at many aggregation sites, such as fish spawning events (Heyman et al. 2001, de la Parra Venegas et al. 2011, Robinson et al. 2013), would also help to safeguard these habitats.
Regional Fisheries Management Organisations (RFMOs) have banned the intentional setting of purse-seine nets around Whale Shark in the Eastern Pacific, Western Central Pacific (WCP) and Indian Oceans, though not yet in the Atlantic Ocean (Capietto et al. 2014). However, a large proportion of entangled Whale Sharks (73% in WCP; SPC-OFP 2012) were not sighted prior to nets being deployed. Therefore, fisher education and regulation on safe release practices should be a key management goal. The Inter-American Tropical Tuna Commission and Indian Ocean Tuna Commission require that best practices for safe release of Whale Sharks be followed when they are accidentally encircled (Capietto et al. 2014), and similar guidelines were endorsed by Western and Central Pacific Fisheries Commission members in 2015. All RFMOs should prohibit the deliberate setting of nets around Whale Sharks, and require that Whale Sharks be safely released when they are caught accidentally (i.e., using updated recommendations following Poisson et al. (2014) and the summary of guidelines by Clarke 2015). Fisher education and training initiatives would be useful to facilitate implementation.
Whale Shark tourism is managed through legislation in Australia, Belize, Ecuador, Mexico and St Helena Island (UK). At the time of writing, whale shark tourism was not legal in Qatar, where whale shark aggregations occur in a restricted oil field (Robinson et al. 2013). Voluntary codes of conduct exist in many other tourism locations. As tourism can increase the risk of boat strikes, due to the close proximity of boats and sharks, enforcing minimum approach distances for vessels can help to reduce shark stress (Pierce et al. 2010) and reduce the probability of boat strike. Similarly, enforcing general codes of practice for tourism industries will help to ensure their sustainability.
In some areas, such as China, India, Mozambique, Taiwan and Tanzania, the close proximity of whale shark feeding areas or movement corridors with net fisheries leads to regular incidental bycatch. Restrictions on mesh size, net length and fishing locations can help to avoid whale shark catch. Training in safe release, or provision of bycatch reduction technologies (deliberate weak points in nets or other ways to avoid entanglement) could help to reduce the likelihood of shark injury or mortality when interactions occur.
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|Citation:||Pierce, S.J. & Norman, B. 2016. Rhincodon typus. The IUCN Red List of Threatened Species 2016: e.T19488A2365291.Downloaded on 18 July 2018.|
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