Freezing and thawing of pinniped carcasses results in artefacts that resemble traumatic lesions.

The objective of this study was to assess whether the freezing and thawing of pinniped carcasses prior to post-mortem examination could create artefacts that resembled lesions caused by trauma. Necropsy findings in New Zealand fur seals (Arctocephalus forsteri), captured incidental to commercial fishing, and either chilled (n=5) or frozen (n=5), were compared. Changes in frozen, but not in chilled, carcasses included: pseudo-bruising of subcutis; the accumulation of thick dark red fluid (resembling haemorrhage) in the thoracic cavity, pericardial sac and abdominal cavity; apparent subcapsular renal haemorrhage; pseudo-contusions of the brain; apparent haemorrhage from the nares; and blood-staining of the anterior ocular chamber. The processes of freezing and thawing were strongly associated with subcutaneous pseudo-bruises, the presence of thick, dark red abdominal fluid and renal subcapsular 'haemorrhage' (P=0.004). These artefacts probably develop due to a combination of autolysis and 'freeze-thaw' effects including lysis of cell membranes, fluid shifts into the extracellular space, and disruption of blood vessel walls. The results of the study demonstrate that artefacts resembling traumatic lesions are created during freezing and thawing of pinniped bodies. Such changes must be taken into consideration at post-mortem examination of previously frozen carcasses.