Use of radiography to determine age class and assist with the post‐mortem diagnostics of a Bryde's whale ( Balaenoptera brydei )

Abstract

Vessel collisions are considered an important source of mortality for some cetacean species, and this is likely for the New Zealand Bryde's whale ( Balaenoptera brydei ), a species currently classified as “nationally critical”. Nevertheless, the occurrence and frequency of vessel strikes involving whales in New Zealand waters is yet to be systematically evaluated. Herein, we document the use of radiography as a diagnostic tool to examine the pectoral nippers of a Bryde's whale carcass recovered from Hauraki Gulf, New Zealand. To determine age class, radiographs were used to assess the degree of epiphysial fusion in the pectoral flippers. Additionally, evidence of bone damage and repair was examined in an attempt to clarify cause of mortality. Radiographs were definitive for age‐class determination, revealing the specimen to be a juvenile, as evidenced by open physes, incompletely ossified epiphyses, and incompletely ossified cuboidal bones of the carpus. The degree of epiphyseal development of the distal radial and ulnar secondary ossification centres suggests a late stage two or early stage three degree of development. Radiographs were less definitive in clarifying cause of mortality. Bilateral distal antebrachial fractures were observed on both the left and right pectoral flippers. The fractures evident in the distal right antebrachium of the left flipper were considered atypical of acute blunt trauma. The fracture fragment ends were not sharp edged as expected, but instead exhibited the appearance of remodelled and/or pulverised fracture fragment ends. Regardless of cause, the degree of bone remodelling and callus formation is evidence that the whale likely survived any initial trauma, thus suggesting mortality was not immediate. However, the absence of appropriate histopathology sampling and a systematic necropsy prevent confirmation of this hypothesis.

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