West African bycaught dolphins provide insights for new method for health assessment
Winners of the 2016 WDC Bharathi Viswanathan Award, Marie-Francoise Van Bressem and colleagues, studied photographs of dolphins bycaught in fishing gear from three Ghanaian ports, to develop an opportunistic, non-invasive research tool to examine epidemiological aspects of the general health of free-ranging and by-caught cetaceans. Read more about this novel research here and if you are interested in applying for the 2017 Award please submit your application by mid-day (GMT) April 24th 2017.
An initial visual assessment of general health of small cetaceans from West Africa
by Marie-Francoise Van Bressem, Joseph Debrah, and Koen Van Waerebeek
Several species of small cetaceans, including the common bottlenose dolphin (Tursiops truncatus), common dolphin (Delphinus sp.), Clymene dolphin (Stenella clymene), pantropical spotted dolphin (Stenella attenuata), spinner dolphin (Stenella longirostris), melon-headed whale (Peponocephala electra), short-finned pilot whale (Globicephala macrorhynchus), rough-toothed dolphin (Steno bredanensis), Atlantic humpback dolphin (Sousa teuszii) and harbour porpoise (Phocoena phocoena) are suffering significant mortalities in fisheries off Mauritania, Senegal, Ghana, Nigeria and Cameroon. However, very little is known of the other factors that could negatively affect their survival and reproductive fitness, including diseases and traumata. In this context we have so far examined images of 148 delphinids, belonging to 13 species landed at three Ghanaian ports between 1998 and 2016, and photos of a number of free-ranging short-beaked common dolphins off Northwest Africa and short-finned pilot whales off La Gomera, Canaries, for the presence of traumas, deformations, skin disorders and commensal phoronts .
Generally, in comparison to other ocean provinces, it was striking how few skin disorders and other macroscopically visible health conditions affected West African small cetaceans.
Ghanaian fishing ports (Axim, Dixcove, Apam from W to E) where the dolphins examined in this study were landed.
Pale skin patches of unknown aetiology, highly prevalent in Peale’s dolphin (Lagenorhynchus australis) in polluted waters from Chilean Patagonia[1], affected the dorsal fin of a single free-ranging common dolphin and a pilot whale, so prevalence here was low.
Pale skin patch, partly ulcerated, in a short-beaked common dolphin free-ranging off Northwest Africa.
Cookie-cutter shark (Isistius sp.) bites were observed in 10 species of by-caught odontocetes with prevalence levels varying between 12 % in pantropical spotted dolphins and 61% in rough-toothed dolphins. Interestingly, these data increase the documented species distribution range of Isistius spp. into the waters of the northern Gulf of Guinea.
Cookie-cutter shark bite scars in a melon-headed whale.
Miscellaneous other scars were seen in nine individuals landed in Ghana and, in four cases, were regarded as caused by fisheries interactions, including a large star-shaped scar in a Clymene dolphin, possibly resulting from a dislodged hand-held harpoon. Very similar scars have been seen also in Peruvian dolphins where harpooning is also commonplace. Evidently anthropogenic traumatic injuries, mainly from fisheries, may have an impact on the health, survival and welfare of West African dolphins.
An adult rough-toothed dolphin landed in Ghana had several skin nodules, some possibly ulcerated, on its back and dorsal fin, and a pantropical spotted dolphin in poor body condition,showed a medium-sized noduleon its right flank. Known aetiologies of skin nodules and granulomas in cetaceans include fungi (Trychophyton sp., Fusarium sp. and Paracoccidioides brasiliensis), bacteria (Streptococcus iniae and Pseudomonas spp.), papillomaviruses and macro-parasites (Anisakis spp.). Dozens of herpesvirus-like black skin lesions were observed on the body of a common bottlenose dolphin, butaetiology could not be examined. Also, poxviral tattoo skin lesions could not be positively identified in any species. Deformities, severe emaciation, commensalphoronts or ectoparasites were not detected in any of the species.
The present study further highlights the usefulness of good photographs of individual dolphins as an opportunistic, non-invasive research tool to examine epidemiological aspects of the general health of free-ranging and by-caught cetaceans. It provides a preliminary insight into the prevalence of a variety of cutaneous disorders, shark bites and other traumatic injuries affecting west African cetaceans and can help steer future, dedicated, research. In general, this technique may improve documentation of both natural and anthropogenic threats faced by cetaceans and may help to better understand their conservation status.
[1] Sanino GP, Van Bressem M-F, Van Waerebeek K, Pozo N (2014) Skin disorders of coastal dolphins at Añihue Reserve, Chilean Patagonia: a matter of concern. Bol Museo Nat Hist Nat, Chile 63: 127-158.
