Killer whales are a diverse species that ranges through all oceans of the earth while living in locally distinct and adapted populations. Over the last decades, the number of strandings has not only increased but also shown interesting changes in location as we have covered in this incident.
Though this species is so widely distributed, its causes of death have not been widely studied. Raverty and colleagues (2020) now published the results of one of the first studies that analyzed the trends across orca necropsy reports. The main observation was the prevalence of human impact on deaths in all age classes.
For the study, 53 pathology reports on stranded killer whales from the Eastern Pacific Ocean and Hawaii, plus an additional 35 animals were analyzed. For 42%, findings of significant importance for population health could be found. In calves, malformations and infections were most prevalent. Sub-adults, on the other hand, predominantly succumbed to trauma, malnutrition, and diseases, while adults mostly died of infections, emaciation, and blunt force trauma. Killer whales who died of trauma were generally in a better bodily condition prior to death (Figure 1). Importantly, deaths linked to humans could be found across all age groups.
The authors stress that the human impact cannot only be blamed on indirect causes such as prey depletion, global warming and toxic water. It also heavily includes direct causes like ship strikes (as portrayed through trauma signs) and ingested fish hooks. SeaDoc Society Director Joe Gaydos points out that the fact “that humans are directly killing killer whales across all age classes is significant; it says we can do a better job."
The study establishes a baseline for the understanding of health and causes of mortality in stranded killer whales and argues for more comparable measurements. With the knowledge about human impacts, they hope to improve recovery strategies for the endangered species across the globe.
The study can be found here: https://doi.org/10.1371/journal.pone.0242505
Raverty S, St. Leger J, Noren DP, Burek Huntington K, Rotstein DS, Gulland FMD, et al. (2020) Pathology findings and correlation with body condition index in stranded killer whales (Orcinus orca) in the northeastern Pacific and Hawaii from 2004 to 2013. PLoS ONE 15(12): e0242505.
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