Deadly acute Decompression Sickness in Risso’s dolphins

Abstract

Diving air-breathing vertebrates have long been considered protected against decompression sickness (DCS) through anatomical, physiological, and behavioural adaptations. However, an acute systemic gas and fat embolic syndrome similar to DCS in human divers was described in beaked whales that stranded in temporal and spatial association with military exercises involving high-powered sonar. More recently, DCS has been diagnosed in bycaught sea turtles. Both cases were linked to human activities. Two Risso’s dolphin (Grampus griseus) out of 493 necropsied cetaceans stranded in the Canary Islands in a 16-year period (2000–2015), had a severe acute decompression sickness supported by pathological findings and gas analysis. Deadly systemic, inflammatory, infectious, or neoplastic diseases, ship collision, military sonar, fisheries interaction or other type of lethal inducing associated trauma were ruled out. Struggling with a squid during hunting is discussed as the most likely cause of DCS.

Diving Behavior and Fine-Scale Kinematics of Free-Ranging Risso's Dolphins Foraging in Shallow and Deep-Water Habitats

“…The records of higherVO 2 in the bottom phase of deep dives is consistent with the registered increase in body roll and stroke rate and suggest a greater effort involved in the pursuit of deep-water prey items. These results support the notion of shift in prey type with increasing foraging depth and could be related to the observed escalation of prey length as (Fernández et al, 2017). Such squid, including species from genera Todarodes, have strong locomotor abilities (O'dor and Webber, 1991) and present high energy density per unit of wet weight (3-4.5 kJ g −1 wet weight , constituting a potential high-quality target for Risso's dolphins during deep dives.…”

Retrospective Study of Traumatic Intra-Interspecific Interactions in Stranded Cetaceans, Canary Islands

“…In Stephens et al (72), the "goosebeak" larynx of the dolphin was displaced, compressed ventrally, and obstructed with a remaining tentacle. In our cases 17 and 20, no larynx dislocation was present, but struggling with the squid may have resulted in severe alterations in the diving profile and physiologically induced formation of gas emboli (44).…”

“…Finally, two Risso's dolphins (cases 17 and 20) presented fatal interaction with large squids and died from decompression sickness (44). The dolphins presented evidence or struggling/fighting with the squid.…”

“…Severe changes were observed also in the longissimus dorsi, with multifocal polyphasic myocyte degeneration and necrosis: segmental myonecrosis associated with the stress stranding syndrome, atrophy due to emaciation, and myositis due to the shark bites (7). The other cases were two Risso's dolphins (cases 17 and 20) with decompression sickness (44). The first animal (case 17) was an immature male with good body condition that presented multifocal lacerations consistent with a live stranding as well as social intra-interspecific interaction marks.…”

Pathologic findings and causes of death of stranded cetaceans in the Canary Islands (2006-2012)

“…Fatal gas embolism was diagnosed in two animals (animal no.147 and 163) [ 27 , 28 ]. A thalamic high-grade astrocytoma (glioblastoma multiforme) was diagnosed in an adult male Atlantic spotted dolphin (animal no.…”