50 Years of Cetacean Strandings Reveal a Concerning Rise in Chilean Patagonia

By collecting cetacean stranding data from the last 50 years in the Chilean coast, we found that strandings have been increasingly reporting at a higher rate during the last 10 years, particularly at the Patagonia, the southernmost part of Chile.

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Worldwide, cetaceans regularly strand around the coast. Such information can provide an accurate picture of what species are found in waters and show local and seasonal distribution.


Coauthors Dr. Mario Alvarado-Rybak (left) and Dr. Frederick Toro (right) preparing to perform a necropsy on a stranded Orca (Orcinus orca) past June in 2019. Both veterinarians have extensive field work performing dozens of necropsies to assess the causes of deaths.

Strandings that undergo post-mortem examination provide us with valuable information on causes of death, disease, contaminants, reproductive patterns, diet and also useful pointers to the general health of the populations living in the seas around our coasts. In this new study, Dr. Fernando Mardones, UC Davis epidemiologist and assistant professor at the School of Veterinary Medicine at the Pontifical Catholic University (PUC), and director of epi3lab at PUC, created a multidisciplinary team to establish a Cetacean Strandings Investigation Program based on the collection, analysis and report data for all cetacean strandings along the extensive Chilean coast (> 5,000 km). Senior authors, Dr. Mario Alvarado-Rybak (epi3lab postdoc) and Dr. Fred Toro (Director of Panthalassa NGO) are specialized veterinarians that have been working from years in determining the causes of death in stranded cetaceans, including by-catch and physical trauma.

Co-author Dr. Fred Toro performing a necropsy of a stranded pilot whale (Globicephala spp.) that was suspected to be killed by a ship strike. Ship strikes are massively under-reported as crews of large ships might not know they have hit a whale.

In this study, we used time series analysis and spatiotemporal methods from a novel data on cetacean strandings from last 50 years from the Chilean coast. Here, we identified a total of 389 CS events affecting eight cetacean families, 21 genera, and 35 species, which represent more than 85% of the reported species richness for the country. We also used spatio-temporal techniques to identify if strandings were aggregated in space and time during the study period. Such analyses determined a large number of hotspots reported in the southernmost part of the country, namely, Chilean Patagonia. Unfortunately, most causes of death from strandings are undetermined that limits our study to associate those events with any particular, however, our work provides key indicators (frequency, size, duration, and extension of strandings, among others) that can be of use for a number of initiatives that would promote conservation plans for cetacean and other marine animals.

Unfortunately, the COVID pandemic has delayed the launching of a monitoring program based on citizen science that is coordinated for a dozen of veterinary and marine biologists students at the PUC. In this initiative, anyone can report any spot of a stranded cetacean on the shoreline in Chile. The reporting person should take a photograph that will allow us to determine species and the level of decomposition (which affects whether to perform a post-mortem examination). It is also useful to estimate the animal's size (meters) and provide exact location and date. The information will be gathered from social network and media that will be collected by students at the UC. The information from the initiative would allow us to undertake surveillance on the incidence of disease in stranded cetaceans to identify any new threats to their conservation status. We will also be able to maintain a national cetacean tissue archive at the Pontifical Catholic University (PUC).

Postdoc at epi3lab Dr. Mario Alvarado-Rybak (left with yellow gloves) leading and teaching students to perform a necropsy and samples collection.


Fernando Mardones

Assistant Professor, Pontifical Catholic University of Chile