Marine Creature: Spinner Dolphin (Stenella longirostris)Kindly compiled by Maddalena Fumagalli from the Hurghada Environmental Protection & Conservation Association (HEPCA)
Spinner dolphin are pantropical, occurring in all tropical and subtropical waters around the world between 30-40°N and 20-30°S.
The scientific name Stenella longirostris (and most of the common names in various languages) refers to the relatively long beak (rostrum) which, together with the coloration pattern, helps differentiate the species from other similar Stenella. Its English common name (“spinner dolphin”) comes from their ability to perform a highly acrobatic aerial behavior called “spin”: in acceleration, the animal jumps out of the water and start turning around its longitudinal axis up to 14 times before it splashes back on the surface. The reasons for this behaviour are unknown, hypothesis include a possible function in intra-group communication (echolocation or social facilitation), play and parasites’ dislodgement.
Spinner dolphins belonging to coastal ecotype show a clear daily cycle: since feeding occurs at night in the open sea and therefore entails an important energetic efforts, at sunrise the animals look for sheltered bays and lagoons where they can spend morning and early afternoon hours resting. Before sunset, the cycle starts again with the pod alert and awake leaving the quiet waters and heading offshore for another night to spend foraging.
Sexual dimorphism is appreciable in adult animals, with females usually carrying a falcate dorsal fin, opposite to the males that have a very triangular one, in some cases even bending forward or sideways; females also show a smooth and slender silhouette, whereas males are more robust and present a very obvious hump in the genital area.
While resting in shallow lagoons, they actually represent a key element in the balance of the reef ecosystem as their feces and regular regurgitations constitute a resource for reef fish (surgeonfish and fusilier fish, among others). They do vomit but this is not a sign of sickness: this is a very natural behavior to prevent sharp and chitinous indigestible material to proceed further in the digestive system and possibly injure their internal organs. Regurgitation content includes, for example, fish vertebras and otholits as well as squids’ beaks.
Spinner dolphins are polygynous and mating is promiscuous. Females attain sexual maturity when 4-7 years old, pregnancy lasts approximately 11 months: newborns are about 80cm in length and nursing lasts 1-2 years. Calving interval is 3 years. Males are sexually mature when they are 7-10 years old. Breeding is seasonal, with one or two annual reproductive peaks. In Egypt, the presence of newborns shows a peak in summer months (June to August).
Feeding & Hunting
For the coastal form, feeding occurs at night in the open sea on small squids and fish belonging to the so called mesopelagic boundary community, whose vertical and horizontal nocturnal migration (the so called Deep Scattering Layer) brings preys in waters more easily accessible by spinner dolphins. Groups are likely to join offshore once left the resting areas in order to feed cooperatively. In the dark, hunting relies completely on the echolocation system. The pelagic form lacks a clear daily pattern, it is often associated with pantropical spotted dolphins (Stenella attenuata) and preys on small mesopelagic fish and squids, diving to 600+ m.
Main direct threats for the species includefisheries bycatch (purse seines, trawling and drift nets) and tourism-related activities (dolphin watching and swimming-with operations).
Conservation Status & International Protection
The species is listed in Appendix II of CITES and included in the Appendix II of the Convention on the Conservation of Migratory Species of Wild Animals (CMS). They are covered by the Marine Mammal Protection Act in American waters. Impacted by the ETP tuna purse-seine fishery, regulations to protect the species have been adopted both nationally and internationally (IATTC).
Local and regional policies for responsible dolphin watching and swimming-with activities have also been promoted in several locations, as well as protected areas established (Sha’ab Samadai, in the Egyptian Red Sea, for example).
The IUCN Red List classify the species as “Data deficient”: the conservation status of each subspecies and regional population still need to be assessed.
Spinner dolphins are playful and curious animals we have the great luck to observe and possibly meet in inshore waters. However, it has to be stressed that the good time for interactions most often corresponds to a crucial phase of their daily cycle: swimmers and watchers should always keep this in mind, be aware of local regulations and claim the respect of codes of conduct issued by local agencies and organisations, as well as promote protected areas. Effective conservation comes with knowledge so get informed, learn and share (more info can be gained from Samadai case study). HEPCA suggested code of conduct for the Egyptian Red Sea . Moreover, community-based monitoring and outreach programmes often seek the involvement of visitors and tourists through the report of sightings and images possibly useful for photo-identification purposes. In Egyptian Red Sea, please refer to HEPCA and its MEGAbase programme.
Best places in the world to see these creatures:
Scientist Profile: Maddalena Fumagalli
Funding bodies: Italian Cooperation in Egypt, Rufford Small Grant for Conservation (Samadai Project), eco-volunteering (RSDP)
Among a series of mounting environmental threats negatively affecting the Egyptian Red Sea region, it soon became apparent that the diving community had to form into a visible association to represent the industry and prioritize environmental conservation. In 1992, a meeting between twelve members representing the diving community inaugurated HEPCA’s inception as an Egyptian NGO whose mandate was the protection of the Egyptian Red Sea. Main areas of intervention include conservation of marine habitats through mooring installation, lobby against unsustainable coastal development and fisheries, scientific research on coastal habitats and key species; solid waste management and recycle; community development and capacity building.
A Cetacean Research Unit was established in 2010 and is currently carrying out the first extensive research programmes ever endeavoured in the waters of the Southern Egyptian Red Sea. Projects include the Red Sea Dolphin Project (RSDP), Samadai Project and the community-based MEGAbase programme.
Importance of work
Spinner dolphins represent an attraction in the area of Marsa Alam where they are known to regularly visit two coastal reefs, namely Samadai and Satayah. Despite the fact that HEPCA research, as well as previous efforts, are disclosing much about the local populations, still little is known about the possible short and long-term consequences that human impacts (mostly unregulated) interesting the species on a daily basis had and are leading to. In 2004, the establishment of Samadai as a protected area with a management plan has been a milestone achievement whose value is emerging from the data collected so far but still awaits to be properly promoted within the community. Concerns over the health of the population visiting the second site (Satayah Reef), where no regulations are in place yet, have been raised and the site is currently under investigation. All efforts aim at exhaustively describing the local situation in order to contribute to the knowledge of the species at large and, on a regional scale, promote best practices and plans for its protection.
Volunteer /Paid Work Opportunities
The Samadai Project accepts volunteers and trainees from Egyptian Universities willing to engage in cetacean research.
The Red Sea Dolphin Project (RSDP) recruits field assistants to join seasonal surveys carried out in summer and winter months. Requirements include but are not limited to: previous experience in marine mammals research, preferred in boat-based surveys; easygoing, patient, adaptable and sociable people as interns are expected to work and live as part of a team and share small spaces with researchers, crew and eco-volunteers for long time; proficiency in English, good written and oral communication skills; proficiency in swimming and snorkelling; basic computer literacy. For more info, contact email@example.com.
Websites: www.hepca.com / http://redseadolphinproject.wordpress.com http://www.ruffordsmallgrants.org