Gas bubbles in seals, dolphins, and porpoises entangled and drowned at depth in gillnets.

Gas bubbles were found in 15 of 23 gillnet-drowned bycaught harp (Pagophilus groenlandicus), harbor (Phoca vitulina) and gray (Halichoerus grypus) seals, common (Delphinus delphis) and white-sided (Lagenorhyncus acutus) dolphins, and harbor porpoises (Phocaena phocaena) but in only 1 of 41 stranded marine mammals. Cases with minimal scavenging and bloating were chilled as practical and necropsied within 24 to 72 hours of collection. Bubbles were commonly visible grossly and histologically in bycaught cases. Affected tissues included lung, liver, heart, brain, skeletal muscle, gonad, lymph nodes, blood, intestine, pancreas, spleen, and eye. Computed tomography performed on 4 animals also identified gas bubbles in various tissues. Mean +/- SD net lead line depths (m) were 92 +/- 44 and ascent rates (ms(-1)) 0.3 +/- 0.2 for affected animals and 76 +/- 33 and 0.2 +/- 0.1, respectively, for unaffected animals. The relatively good carcass condition of these cases, comparable to 2 stranded cases that showed no gas formation on computed tomography (even after 3 days of refrigeration in one case), along with the histologic absence of bacteria and autolytic changes, indicate that peri- or postmortem phase change of supersaturated blood and tissues is most likely. Studies have suggested that under some circumstances, diving mammals are routinely supersaturated and that these mammals presumably manage gas exchange and decompression anatomically and behaviorally. This study provides a unique illustration of such supersaturated tissues. We suggest that greater attention be paid to the radiology and pathology of bycatch mortality as a possible model to better understand gas bubble disease in marine mammals.

Marine vertebrate zoonoses: an overview of the DAO special issue.

The role of marine birds, mammals, turtles and fish as vectors of infectious agents of potential risk to humans can be examined from a variety of perspectives. The studies in this DAO Special include a broad survey of multiple agents and species, a sequencing study of Giardia intestinalis haplotypes known to be pathogenic to humans, an assessment of risks to humans working with marine mammals, a source tracking study using E. coli ribotypes, studies of regional Salmonella and Brucella epizootiology, a serology survey and a case report of a herpes simplex infection in a dolphin. Additionally, a recently published study (Venn-Watson et al. 2008; Dis Aquat Org 79:87-93) classifying pure cultures of bacteria from a captive dolphin colony also pertains to this theme. These studies raise the following questions: whether the presence of zoonotic agents in marine vertebrates represents a risk to other marine vertebrates, humans, or both; what are the routes by which these marine vertebrate zoonotic infections are acquired and circulated in the marine ecosystem; to what degree are such agents subclinical versus causes of overt disease in marine vertebrates; what are the subsets of the human population most likely to be affected by such infections; and which human health preventive measures would seem reasonable?