On May 5, 2003, the USS Shoup conducted a swept channel exercise which included deployment of active, mid range tactical sonar (system AN/SQS-53C). At the time of deployment, agitated and avoidance behavior were exhibited by a pod of southern resident killer whales (Orcinus orca) and a Minke whale (Balaenoptera acutorostrata) within the vicinity of the USS Shoup and sonar was detected by submerged hydrophones and was audible to humans above the water surface. Between 2 May and 2 June, 2003, 14 stranded harbor porpoises (Phocoena phocoena) were reported by the Northwest Marine Mammal Stranding Network and 11 intact carcasses recovered.
Comprehensive necropsies were conducted on ten animals. In addition to morphometric and computerized tomography (CT) scans, representative tissues were harvested and evaluated by histopathology, microbiology, molecular studies (polymerase chain reaction for morbillivirus, Brucella spp and Mycoplasma spp) and heavy metal analysis. Additional samples were also screened for chemical contaminants, domoic acid and fatty acid composition. CT scans were conducted on 7 carcasses and 1 decapitated head. In 5 of 8 samples, skulls were intact with no significant lesions. In 2 cases, scans were consistent with grossly noted physical trauma and retrobulbar parasitism and characterized by peribulbar and intracochlear hemorrhage. In all the animals, the middle ear spaces featured intact round and oval windows, and ossicles. Despite advanced post mortem decomposition, Salmonella septicemia, fibrinous peritonitis and occipital fractures were noted in 3 animals. In all 10 animals and 1 detached head, there was diffuse dark red black discoloration of the internal aspect of the calverium and superficial aspect of the brain. Although this appearance was attributed to autolysis, acute hemorrhage and hematoma formation also invested the cervical spinal cord and basioccipital region of the hindbrains of 5 of 11 animals. This hemorrhage was attributed to trauma incurred as agonal to terminal thrashing. Pooled tissues from each animal were negative for Brucella spp (universal primers), and morbillivirus and only 1 animal was positive for Mycoplasma spp. Variable, pure and mixed bacterial growth was recovered from all the animals with Salmonella Newport Group C2 isolated from 1 porpoise, Escherichia coli from 5 other animals and Staphylococcus spp from 4 porpoises. Inoculation of pooled tissue extracts on Vero cell lines was uniformly negative for cytopathic effect after 1 week. Percent blubber lipid composition ranged from 44-83% and reflected the overall nutritional profile of the animals. Blubber, liver and kidney concentrations of persistent organic pollutants were comparable to previously reported values. In 6 of 10 animals, there were no gastric ingesta. Stomach content analysis of 4 animals disclosed squid beaks and otoliths from Pacific whiting or Pollock, herring, sand dab, an unspeciated sculpin and market squid. There were no unusual prey remains and chemical analysis of the ingesta was negative for domoic acid.
Deployment of military sonar has been associated with abrupt mass strandings of multiple marine mammal species in the Bahamas, Canary Islands and possibly in Greece and Ireland. In this case series, there was no evidence of cochlear fenestral disruption, fresh intracochlear lesions, ossicular subluxation, nor were there visceral (hepatic or renal) microcavitations as previously reported with acoustic trauma or decompression-like processes. Trauma and infectious disease resulted in the loss of 5 of the 10 porpoises and a cause of death could not be determined in the remaining 5 animals. Based on the extent of autolysis and nature of the post mortem findings, there was insufficient evidence to confirm or discount the possibility that the porpoises strandings were related to acoustic trauma; however, the animals recovered in the northern Pacific Ocean did not feature any of the lesions as described in beaked whales stranded in the Bahamas and Canary Islands.