Investigation of a Stranded Minke Whale (Balaenoptera acutorostra) in the Chesapeake Bay
IAAAM 2000
Cindy Driscoll1, DVM; Nancy Santiago2, DVM; Ana Baya3, PhD; Susan Knowles1; Brenda Kibler1
1Maryland Department of Natural Resources, Oxford, MD, USA; 2Armed Forces Institute of Pathology, Washington, DC, USA; 3Maryland Department of Agriculture, College Park, MD, USA

Abstract

Introduction

Marine mammal strandings occur in all coastal areas of the United States. Dead cetaceans, once found on the beach, are often too decomposed to retrieve valuable diagnostic information. While life history data is collected on most carcasses regardless of condition, without in depth diagnostics the cause of the stranding often remains undetermined. Freshly dead baleen whales present a rare opportunity for in depth investigation into the cause of death. Late in the afternoon of 10 June 1999 the Maryland Marine Mammal Stranding Network received a call concerning a floating, dead whale that had been seen thrashing prior to its death in the Chesapeake Bay at the mouth of the Chester River, Queen Anne's County, MD. The whale was towed to shore at dusk on 10 June 1999. As the animal was hoisted from the water by a crane several gallons of blood ran from the oral cavity. The carcass was placed on a flatbed truck, and covered with tarp to prevent predation overnight. The examination proceeded at 0600 hr the following morning.

Results

Gross External Examination

The whale was a freshly dead, sub adult minke whale (B. acutorostra) 418 cm in length, weighing 698.5 kg, and in good body condition. It was relatively fresh (2+ on the Smithsonian decomposition scale) and intact. A complete set of morphometrics was recorded and photos were taken. No signs of ante-mortem human interaction were apparent. Numerous circular, raised lesions, ranging in size from 1-8 cm, were evident on the dorsal body surfaces. Two abrasions from the towing procedure were noted on the right lateral surface.

Gross Internal Examination

The examination began with DNA skin sampling and microbiologic sampling of the skin and blow hole. This was followed by removal of the blubber layer, pectoral and dorsal fins. Blubber thicknesses measured 3.3 cm dorsally, 3.0 cm mid laterally, and 2.8 cm ventrally. Blubber and muscle contained no signs of trauma. No fractures were found. The ribs were removed and trachea/lungs examined. A 45-cm croaker was lodged head first in the trachea extending down into the right bronchus occluding the airway. The right lung had evidence of patchy areas of hemorrhage (40% of right lung). Two abscesses 4 cm in diameter were found in each lobe of the lungs. A blind-ended pouch ventral to the trachea contained the skull of a large fish. Heart and vessels appeared normal. The gastrointestinal tract was dissected beginning with the tongue and proceeding caudally. Fish scales and various parts were found in the esophagus. Three croakers with a slurry of fish parts were found in the stomachs weighing a total of 7.2 kg. The intestines contained light brown fluid and were not remarkable. The reproductive tract was not remarkable. The kidneys were deep red in color and not remarkable. The bladder was empty. Organ systems were sampled for histology and microbiology.

Histologic and Microbiologic Results

Proteus vulgaris was isolated from the lung, bladder, spleen, trachea, lymph node, blowhole, and skin lesions. Vibrio vulnificus was isolated from additional skin lesions. Histologically, fibrinous, necrotizing, subacute, multifocally extensive, severe, bronchopneumonia with abscess formation was the prominent finding in the lungs. Skin lesions were characterized as suppurative, granulomatous dermatitis with multifocal fungal hyphae consistent with Zygomycetes. Other organ systems were not remarkable histologically.

Discussion

A complete post mortem examination of stranded animals is critical to determining the cause of death. The gross post mortem examination initially indicated a possible asphyxiation as the cause of the animal's demise. However, upon further diagnostic testing and analyses of histologic and microbiologic results, bacterial bronchopneumonia was most likely the primary contributing factor that led to this animal's death. Bacterial infection leading to debilitation and inability to feed properly may have caused the whale to become weakened and asphyxiate while feeding. Without the basic diagnostics conducted on this animal a complete and appropriate diagnosis would not have been possible.

Speaker Information
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Cindy P. Driscoll, DVM
Maryland Department of Natural Resources
Cooperative Oxford Laboratory
Oxford, MD, USA


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