Mammals · Dolphins

Spinner Dolphin

Stenella longirostris (Gray, 1828)

syn. Clymene alope, Clymene microps, Clymene stenorhynchus, Clymenia alope, Clymenia longirostris, Clymenia microps +15 more

129 - 240 cm77 Kg1-400 mCITES IILeast Concern

1313

The spinner dolphin (Stenella longirostris) is a small marine mammal found in tropical and subtropical oceanic waters worldwide. These dolphins are famous for their acrobatic aerial spins and belong to the family known as toothed whales. They inhabit pelagic regions with depths ranging from the surface to about 400 meters (1312 feet).

Adult spinner dolphins are slender creatures, measuring approximately 129 to 240 centimeters (4.2 to 7.9 feet) in length and weighing between 23 to 77 kilograms (51 to 170 pounds). Males can grow slightly larger than females, reaching up to 240 centimeters, while females usually reach up to 200 centimeters. Sexual maturity in females is achieved at lengths of 165-170 centimeters (5.4-5.6 feet) and between 160-180 centimeters (5.2-5.9 feet) in males.

These dolphins are known for their distinctive tripartite coloration: a dark gray back, lighter gray sides, and a pale or white underside. They have a characteristic dark stripe running from the eye to the flipper. Notably, geographic variations exist among these dolphins; some have smaller skulls or different dorsal cape colorations depending on their location.

Spinner dolphins' habitats span various warm waters, from coastal areas and islands to banks in the tropical Atlantic, 🌊 Indian Ocean, and 🌊 Pacific Ocean. In the eastern tropical Pacific, they are found offshore, with seasonal habitat changes noted.

The diet of spinner dolphins primarily consists of small fish, squid, and shrimp, which they often hunt at depths of 200–300 meters (650–980 feet). Hawaiian populations primarily feed at night, employing group hunting techniques. Predators such as sharks and possibly killer whales prey on these dolphins. They are also susceptible to parasitic infections.

During the day, spinner dolphins often rest in shallow bays near deeper waters, especially in Hawaii (🇺🇸 United States) and northern 🇧🇷 Brazil, engaging in synchronous group rest. When night falls, they venture out to forage. Their social structure is fluid, with groups forming and dissolving frequently. Notably, Hawaiian spinner dolphins show a strong preference for returning to specific bays.

Socially, spinner dolphins are known for their dynamic and complex behaviors. They exhibit promiscuous mating strategies, and strong bonds often form between mothers and their calves. They communicate via whistles, burst-pulse sounds, and echolocation. Female spinner dolphins experience a 10-month gestation period, nursing their calves for one to two years. The dolphins live for about 20 to 25 years, with reproductive maturity varying by sex and region.

Aside from their signature spins, spinner dolphins display a variety of acrobatic behaviors such as tail slaps and leaps. These are thought to play roles in communication or in dislodging parasites. Studies suggest that the underwater speed and angle contribute to the number of spins achieved in the air.

In summary, spinner dolphins are agile, adaptable, and highly social animals inhabiting global tropical oceans, with complex behaviors reflecting their interaction with the environment and each other.

Why it's threatened

Biological resource use

Intentional use: (subsistence/small scale) [harvest] · Unintentional effects: (subsistence/small scale) [harvest] · Unintentional effects: (large scale) [harvest]

Human intrusions & disturbance

Recreational activities

Over the period 1960 to 1972, it was estimated that more than 4 million dolphins were killed in the ETP yellowfin tuna purse-seine fishery (Wade et al. 2007). The main species killed were the Pantropical Spotted Dolphin (Stenella attenuata) and the Spinner Dolphin, both of which associate with tuna in that area. Fishermen use the dolphins to locate schools of tuna, and often purposely chase and encircle them in the nets; this maximizes the catch of tuna but can also result in entanglement and mortality of the dolphins (Gerrodette 2018). Mortality in the tuna fishery was estimated to have reduced the population of Eastern Spinners by 65% (Wade et al. 2007, Reilly et al. 2005). Since the Inter-American Tropical Tuna Commission (IATTC) implemented per-vessel mortality limits on the international fleet, the reported mortality of Eastern and White-bellied Spinners, combined, decreased dramatically to only a few hundred individuals (IATTC 2006). Despite this reduction in mortality, the eastern subspecies appears to be recovering slowly at best. Factors such as fishery-related stress, unobserved mortality due to calf separation and orphaning during fishing operations (Archer et al. 2001), mortality caused by small vessels that do not carry observers, and under-reporting of mortality have been suggested as possible reasons for the Eastern Spinner’s slow recovery (Gerrodette and Forcada 2005).

Throughout much of their range, Spinner Dolphins are taken as bycatch in purse-seine, gillnet, and trawl fisheries (Perrin et al. 1994, Donahue and Edwards 1996), often in high numbers. Spinner Dolphins are the most abundant dolphins in the Indian Ocean (Ballance and Pitman 1998) and are taken throughout that region in numbers that are largely unknown but may be substantial, especially as there is evidence that dolphins associate with tuna in this region (Anderson 2014). Annual bycatch levels of hundreds of Spinner Dolphins were reported in the few fisheries examined in India in the 1980s and early 1990s (Mohan 1994), and annual takes in the thousands were reported in Sri Lanka in the 1980s (Leatherwood and Reeves 1989). They were reported to be the most frequently bycaught cetaceans in the Union of the Comoros (Kiszka et al. 2008), and amongst the most commonly taken in Madagascar (Razafindrakoto et al. 2004), Mayotte, and other countries in the western Indian Ocean (Kiszka et al. 2008). Unknown numbers have been taken in the tuna purse-seine fishery in the eastern Atlantic (Donahue and Edwards 1996) and in small-scale gillnet fisheries in the western Atlantic (Siciliano 1994). They have been reported as bycatch in the Caribbean Sea (Vidal et al. 1994).

Dwarf Spinners are caught incidentally in shrimp trawls in the Gulf of Thailand (Perrin et al. 1999). Zerbini and Kotas (1998) reported on by-catches in Brazilian drift-net fisheries and Cockcroft (1990) on animals entangled in shark nets off KwaZulu-Natal, South Africa. There are likely to be undocumented interactions with fisheries off West Africa (Weir 2010, Jefferson et al. 1997).

In some areas, human use of bycaught cetaceans has led to directed hunting or deliberate gillnetting of Spinner Dolphins. For example, this has been reported in Sri Lanka (Leatherwood and Reeves 1989), the Philippines (Dolar 1994), and Indonesia (Kahn 2004). However. it is unclear whether, or how extensively, this activity continues in all of these places. Spinners may also be taken intentionally in West Africa (Van Waerebeek et al. 1999). Drive hunting of Spinner Dolphins takes place in Anakao, Madagascar (Cerchio et al. 2011) and in the Solomon Islands (Oremus et al. 2015).

The habit of resting in shallow coastal waters during the day leads to problems of disturbance by dolphin-watching boats and swimmers in many areas.

Threat classification from the IUCN Red List.