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Harbor porpoise strandings & USS Shoup SONAR (preliminary report)

NOAA Fisheries / National Marine Fisheries Service / Northwest Region

9th February 2004

Summary of the Preliminary Report on the investigation of harbor porpoise stranded in Washington around May 2003 coinciding with mid-range sonar exercises by the USS Shoup.

During the period of May 2, 2003, to June 2, 2003, the National Marine Fisheries Service (NOAA Fisheries) Northwest Marine Mammal Stranding Network received reports of 14 stranded harbor porpoise in Washington, an abnormally high number when compared to the average stranding rate of 6 per year recorded over the past decade. The reports coincided with the use of mid-range sonar by the naval vessel USS SHOUP transiting Haro Strait on 5 May 2003, and observations by researchers and the public who reported altered behaviour of marine mammals in the area. Eleven of the 14 porpoise were collected for examination.

NOAA Fisheries assembled a multi disciplinary team of biologists, veterinarians, veterinary pathologists, research scientists and a neuroanatomist who conducted extensive classical forensic necropsy examinations from 22 July through 24 July, followed by laboratory diagnostic and histological analyses and complemented by high resolution computerized tomography scans. Samples were taken for a variety of analyses, including disease screening, parasitology, chemical contaminant and lipid analyses, aging studies, prey identification and domoic acid analysis.

The Preliminary Report presents a summary of past porpoise stranding reports, information on the discovery and collection of porpoise during the May-to-June timeframe, gross and microscopic findings from the necropsy examinations, analysis of the high resolution image data, and discussion on the possible causes of mortality.

More than 70 percent of the specimens were in moderate to advanced states of decomposition, which made interpretation of the cause of death difficult. The cause of death was determined for 5 of the 11 porpoises examined by the multi disciplinary team. Of these five animals, two were found to have suffered blunt force trauma, while illness was implicated in the remaining three cases. No cause of death could be determined for the remaining six animals. The examinations did not reveal definitive signs of acoustic trauma in any of the porpoises examined. The possibility of acoustic trauma as a contributory factor in the mortality of any of the porpoises examined could not be ruled out. The multi-disciplinary team noted that lesions consistent with acoustic trauma can be difficult to interpret or obscured, especially in animals in advanced post-mortem decomposition.

Full Report (PDF file 3.4MB)

Full Report without Tables & Appendices (PDF 2.3MB)

Tables & Appendices (PDF 1.0MB)

News Release (PDF 73KB)

The preliminary report is available for scientific review and comments for 30 days. This review is to obtain scientific comments on the panel’s pathology and trauma findings and analyses.

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