Cause of Death Analysis of Necropsied CI Belugas
Causes of death for most stranded CI belugas remain largely unknown. Post-mortem exams are hampered by the lack of road access and extensive hazardous tidal flats in Cook Inlet. In addition, the remote nature of much of Cook Inlet’s coastline preclude the timely reporting of carcasses suitable for necropsy and make responding with a necropsy team logistically difficult. Additional carcasses may go unexamined because animals may sink after dying or be surrounded by winter ice and swept out of the Inlet prior to detection. From 1998 to 2013, only 38 carcasses out of 164 observed dead stranded belugas were subjected to some degree of post-mortem examination or necropsy (Burek-Huntington et al. 2015). Necropsied belugas were concentrated close to Anchorage and along the road system. Burek-Huntington et al. (2015) reviewed the causes of morbidity and mortality determined from these examinations. A more detailed discussion of the necropsy analyses from 1989–2009 is provided in Appendix H – Cause of Death Analysis.
Of the 38 CI beluga carcasses examined from 1998 to 2013, a primary cause of death was not identified in 29% of the cases, primarily because most carcasses were in an advanced state of decomposition (Burek-Huntington et al. 2015). Identification and reporting of strandings, both live and dead, as well as the subsequent responses, need to be accelerated and enhanced in order to obtain the quality information necessary to understand the causes of morbidity and mortality in CI belugas. Nevertheless, it is often difficult to determine a cause of death even when carcasses are examined promptly under laboratory conditions. Conditions identified as a primary cause of death in CI belugas included previous mass or single live stranding (24%), trauma (18%), perinatal mortality (13%), malnutrition (8%), and disease (8%). Factors considered contributory to mortality (i.e., findings not assigned as a primary cause of death) included disease, aspiration of glacial silt and/or stomach content, malnutrition, and trauma. It has been noted that the number of documented mortalities of CI belugas seems to be equivalent to that of belugas in the St. Lawrence Estuary in Canada (P. Béland, St. Lawrence National Institute of Ecotoxicology, unpub. data), which has a much larger estimated population size of about 889 individuals (COSEWIC 2014).