Understanding causes of morbidity and mortality in Southern Hemisphere small Odontoceti: a scoping review

Marine mammals serve as sentinels for environmental health, offering insights into ecosystem health. Enhancing management and conservation strategies for these species requires a comprehensive understanding of factors contributing to their morbidity and mortality. 

This review aims to identify reported causes of morbidity and mortality in small Odontoceti within the Southern Hemisphere. 

A scoping review of literature was conducted, searching Scopus, PubMed, and Web of Science, with additional screening of citations for articles not captured in the search. 

The review encompassed 198 articles, with a total sample size of 25567 deceased small Odontoceti across 20 genera. A major challenge emerged, with the cause of death undetermined or unspecified in 39% of cases. Known entanglements accounted for 47% of total mortalities. Mass strandings (11%) and infectious disease (1.1%) were also reported. The study identified 14 primary infectious pathogens in 276 animals, spanning viral (CeMV = 214, H5N1 = 1), bacterial (Brucella sp. = 15, Erysipelothrix sp. = 1, Streptococcus iniae = 1, Enterobacter kobei = 1), parasitic (Toxoplasma gondii = 15, Halocercus sp. = 17, Clistobothrium grimaldii = 1, Stenurus globicephalae = 1, Giardia sp. = 1), and fungal (Aspergillus sp. = 2, Paracoccidioides brasiliensis = 5, Cryptococcus sp. = 1) origins. 

Anthropogenic-induced mortality emerges as a significant threat to small Odontoceti of the Southern Hemisphere, underscoring the urgent need for enhanced conservation and management strategies. Increased surveillance of infectious pathogens is imperative, aiming to deepen our understanding of pathogen distribution, prevalence, and impact on Odontoceti health.