The northeastern Pacific gray whales (Escherichtius robustus) migrate annually from summer foraging regions in Arctic and subarctic waters to winter calving and breeding grounds in temperature or subtropical southern regions. Between 1980 and 2005, there have been sporadic grey whale strandings along Washington State and British Columbia coasts and in 1999 and 2000 an unusual mortality event was designated within the Northeastern Pacific.
In contrast to previous stranding episodes which comprised both adult and juvenile animals, between 18 April and 25 July, 2005, 10 juvenile gray whales stranded along the outer and inner coasts of Washington State. The cohort comprised 5 males, 2 females and 3 whales of undetermined gender. Total lengths ranged from 660-1230 cm. Comprehensive necropsies were conducted on 5 whales and more cursory examinations completed on 2 individuals. Three additional whales were sampled for genetics and contaminant work-ups, but not evaluated due to autolysis. Five of the necropsied whales were severely emaciated and 1 whale presented in good body condition. There were 3 individual cases of presumptive net entanglement, blunt force trauma, and attempted killer whale predation. Two whales, recovered moribund or fresh dead, were lodged between pier pilings.
Histopathology of harvested tissue disclosed splenic and hepatic hemosiderosis within virtually all the examined animals; the accumulation of iron was attributed to generalized emaciation, although a maladaptation type syndrome, peracute sepsis, and other disease entities could not be entirely discounted. Within multiple animals, there was variable multisystemic edema fluid suggestive of hypoproteinemia and an unusual proliferative dermatitis with superficial ballooning degeneration and intracytoplasmic inclusions suggestive of parapoxvirus infection was detected in select individuals. Samples were forwarded to an outside reference lab and initial screening with known parapoxvirus primers was negative.
Routine aerobic culture of harvested tissues yielded either no bacteria or polymicrobial isolates. Polymerase chain reaction of pooled tissues was consistently negative for Brucella spp and dolphin morbillivirus. Efforts to quantify contaminant loads and domoic acid exposure are underway.
Post mortem examination of these animals provides valuable insights into potential human interactions, fisheries entanglements, pathogen recruitment and dissemination, contaminant loads, and the natural history of this species.