Pathology of grey seals Halichoerus grypus in southwest England including pups in early rehabilitation

Abstract

Few investigations have examined the pathology of grey seals Halichoerus grypus in southwest England, where it is the most abundant marine mammal. Here, primary pathological findings are presented from 107 post-mortem examinations of grey seals in southwest England between 2013 and 2020. Over three-quarters were pups in their first year of life; the origins of the carcasses reflected the known breeding season and breeding sites of grey seals in the region. Trauma was the most common primary pathological finding (n = 49), followed by infectious disease (n = 36). Traumatic findings included fisheries-related trauma (n = 15), other acute physical traumas (n = 15) and other chronic traumas (n = 19). Infectious disease findings included respiratory infections (n = 21) and gastrointestinal infections (n = 9). There was no difference in the primary pathological findings for seals found dead or that died or were euthanased on the day they were found compared to those dying in early rehabilitation, suggesting that it is appropriate to include findings from seals in early rehabilitation in studies of wild grey seal pathology. Seals that had not been frozen before post-mortem examination were nearly twice as likely to have a primary pathological finding of infectious disease or trauma than those that had been frozen, highlighting the need, wherever possible, to avoid freezing seals prior to post-mortem examination.

Hepatic Amyloidosis in a Chronically Entangled Grey Seal (Halichoerus grypus)

“…Why grey seals are the only species of phocid in which amyloidosis has been reported in the literature is unclear. Even in grey seals, a relatively small number of cases of amyloidosis have been reported, compared to the large number of inflammatory lesions reported in this species at least on British coasts (Baker et al, 1998;Barnett et al, 2021). A similar situation has been observed in humans, with less than 900 cases of AA amyloidosis in the whole of the United Kingdom over a period of more than 30 years despite the huge range of chronic inflammatory diseases that occur frequently in the general population (Ravichandran et al, 2020).…”

“…Grey seal entrapment in fishing gear in European waters is well documented (Baker et al, 1988;Vincent et al, 2005;Allen et al, 2012;Osinga et al, 2012;Cosgrove et al, 2016;Barnett et al, 2021). There are two recognised forms of entrapment in fishing gear: peracute underwater entrapment leading to near-immediate death and chronic entanglement.…”

Insights obtained from a multidecadal citizen science scheme: grey seal (Halichoerus grypus) strandings in Cornwall and Isles of Scilly (2000–2020)

“…Additionally, it suggests no major difference in drivers of mortality over time. In a study of 107 post-mortem examinations of grey seals in southwest England between 2013 and 2020, trauma was the most common primary pathological finding (45%) followed by infectious disease (34%; Barnett et al ., 2021). Fisheries-related trauma – bycatch and entanglement – was suspected to be the primary pathological condition in 14% of seals examined and rates of entanglement in marine debris as high as 5% have been observed elsewhere in live grey seals in Cornwall (Allen et al ., 2012).…”

“…Grey seals are one of the UK's most abundant marine mammals (Leeney et al ., 2010; Barnett et al ., 2021). Although they forage across wide ranges at sea, grey seals regularly return to land to rest, gathering in large aggregations during the breeding (September–December) and moulting (December–April) seasons (Hewer, 1974).…”