Is the Megamouth Shark susceptible to mega-distortion? Investigating the effects of twenty-two years of fixation and preservation on a large specimen of Megachasma pelagios (Chondrichthyes: Megachasmidae)

Abstract

On 18 August 1988, the third reported Megamouth Shark (Megachasma pelagios Taylor, Compagno and Struhsaker, 1983) became stranded on a beach in Western Australia. The 5.15 m TL male shark (WAM P.29940–001) was preserved at the Western Australian Museum (WAM) and put on public display. Many deep water chondrichthyan species, including M. pelagios, possess soft and fl abby muscle tissue and a poorly calcifi ed skeleton. Such species are prone to distortion through dehydration due to the fi xation and preservation process. Such distortions may result in taxonomic and nomenclatural issues. The WAM Megamouth Shark was recently relocated, providing an opportunity to remeasure the specimen to allow a comparison with measurements taken of the specimen when it was fresh, and to assess the extent of change to these measurements after 22 years of preservation. We found that with the exception of the pelvic-fi n, that we hypothesise is the fl eshiest part of M. pelagios with the least skeletal support, the specimen has suffered little to no distortion over this time. However, there has been some degradation of teeth and denticles that is most likely due to the acidity of the formalin solution.