Decompression like sickness in Risso´s dolphins

Abstract

Although marine mammals appear to have developed adaptations to avoid most mechanical and physio!ogical effects related to thís type of diving disease (Kooyrnan, 1989), gas bubble-like !esions have been found in mass strandings of beaked whales lfami!y Ziphíidae) associated in time and space with naval exerdses (Fernandez et al., 2005). Severa! hypotheses have been proposed as a cause-effect re!ationshíp between MFA sonar use and these stranding events (Cox et al., 2006}. One of them is the alteratlon of beaked wha!es' divlng behaviour in response to MFA sonar exposure in such a manner that behavioural or physiological mechanisms employed far protecting against the formation of nitrogen gas (N2) bubbles are overridden (Fernández et al., 2005; Cox et al., 2006). According to this proposal, bubble evolutíon occurs as a resu!t of severe alteralions in dive behaviour (e.g. extremely rapid surfacíng or remainíng at the surface and possibly vigorously swimming). Risso's do!phins inhabit deep oceanic and continental slope waters, general!y 400-1,000 m deep, mostly occurring seaward of the continental s!ope. Risso· s dolphins have not been reported in atypícal mass strandings iinked to naval exerdses, but "gas bubb!e" !esions have been found in single stranded Risso·s dolphins in UK and now in the Canary lslands. A description of these cases with the corresponding pathological findíngs will be presented in this communication as weH as most !ikely línked cause/s.