Whale shark (Rhincodon typus)

Whale shark
Rhincodon typus

TAXONOMY AND NAMING

Class : Chondrichthyes
Subclass : Elasmobranchii
Order : Orectolobiformes
Clade : Neoselachii
Family : Rhincodontidae
Genus/species : Rhincodon typus
Common names :
English : Whale shark
Spanish : Tiburón ballena
French : Requin baleine

ANATOMY AND MORPHOLOGY

Whale sharks are the largest of all fish, with a maximum total length (TL) of 18–20 m. Maturity is attained at 9–10 m TL in females (estimated to be reached at 30–40 years) and 7–9 m in males (estimated at 25 years). Longevity is currently unknown, as whale sharks appear to have determinate growth, but the species has been validated to attain at least 50 years old, and maximum age may exceed 100 years.

BEHAVIOUR AND LIFE HISTORY

Whale sharks reproductive cycle is likely to be biennial, at a minimum, and probably longer. While they have a large litter with 300 pups, their pups emerge free-swimming at a small ( 50–70 cm TL) size, and are assumed to face a high initial mortality rate. The whale shark is one of only three known filter-feeding shark species. It feeds on plankton, small squid or fish.

Each whale shark has a characteristic and unique white-spotted pattern on their dorsal surfaces. These create the opportunity for photo-identifying individual sharks and have enabled non-invasive population, movement, and growth studies on the species in the Caribbean region and elsewhere.

DISTRIBUTION, ABUNDANCE AND CONSERVATION STATUS

Whale sharks are distributed circum-tropically from approximately 30°N to 35°S, with seasonal penetration into temperate waters. The whale shark is primarily epipelagic and can be encountered in both coastal and oceanic environments, but they are capable of diving to bathypelagic depths (maximum documented 1,928 m). Whale sharks are divided into two different subpopulations – Atlantic and Indo-Pacific. Approximately 37% of the global population lives in the Atlantic and 63% lives in the Indo-Pacific. In the Wider Caribbean region, sightings are more common in the Meso-American Barrier Reef area (MABR) and, in the northern Gulf of Mexico.

The whale shark is highly mobile. Over their lifetimes, adult whale sharks move away from coastal areas and live, almost exclusively, in off-shelf oceanic habitats. They exhibit site fidelity to feeding and possibly to pupping and mating grounds. Their high mobility means that local abundance of whale sharks is usually related to the ephemeral presence of high prey densities.

THREATS

Whale sharks are often caught accidentally in large nets set for other species. Whale sharks are a common bycatch in tuna purse-seine fisheries. Surveys have indicated that whale shark fins come at a high prices, which could lead to increased targeting by fisheries and trade. Moreover, overfishing of spawning fish may have reduced the attraction for some locations for whale sharks, since they are known to feed on fish eggs.
Whale sharks are exposed to the threat of vessel strikes due to their frequent surface feeding behaviour. Entanglement, particularly in discarded or lost fishing gear, is also a likely source of significant mortality.

Whale shark tourism is growing in popularity. Six weeks of whale shark tourism in Belize was estimated to be worth US$3.7 million to the country. Tourism activities may increase the risk of vessel strikes, local disturbance from interference, crowding or provisioning.

ABUNDANCE AND CONSERVATION STATUS

Overall, the global whale shark population was inferred to have declined by ≥50% over the last three generations (75 years). Thus the IUCN defines the Whale shark’s global conservation status as ‘Endangered’ and its trend ‘decreasing’.

The Atlantic subpopulation was provisionally assessed as Vulnerable during that process, based on an inferred decline of ≥30% over the last three generations (75 years).

PROTECTION STATUS

SPAW Protocol : yes since 2017 _ Annex III

CITES : yes_ Annex II

CMS : yes

Memorandum of Understanding on the Conservation of Migratory Sharks (Sharks MoU) : yes since 2010 _ Annex I

Bibliography
Proposal for the uplisting of whale shark from Annex III to Annex II of the SPAW Protocol