Pathological findings in stranded harbor porpoises (Phocoena phocoena) with special focus on anthropogenic causes

Lonneke L. IJsseldijk*, Mardik F. Leopold, Lineke Begeman, Marja J.L. Kik, Lidewij Wiersma, Maria Morell, Elisa L. Bravo Rebolledo, Thierry Jauniaux, Hans Heesterbeek, Andrea Gröne

*Corresponding author for this work

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Humans impact natural systems at an unprecedented rate. The North Sea is one of the regions in the world with the highest levels of anthropogenic activity. Here, the harbor porpoise (Phocoena phocoena) is an abundant species and is often regarded as an ecosystem sentinel. A post-mortem surveillance program was established in the Netherlands aimed at increasing knowledge of the effects of human activities on harbor porpoises. In this study, we describe the pathological findings related to anthropogenic and natural causes of death categories in 612 harbor porpoises that stranded between 2008 and 2019, and assess their relations to age, sex, season, and location. The largest anthropogenic category was bycatch (17%), with mainly juveniles affected and peak periods in March and September–October. Other, infrequently diagnosed anthropogenic causes of death were trauma (4%), largely most likely due to ship collisions, and marine debris ingestion and entanglement (0.3%). The risk of dying from anthropogenic causes was highest for juveniles. Lesions compatible with noise-induced hearing loss were investigated in carcasses which were fresh enough to do so (n = 50), with lesions apparent in two porpoises. Non-direct human-induced threats included infectious diseases, which were by far the largest cause of death category (32%), and affected mainly adults. Also, gray seal (Halichoerus grypus) attacks were a frequently assigned cause of death category (24%). There were more acute predation cases in the earlier study years, while porpoises with lesions that suggested escape from gray seal attacks were diagnosed more recently, which could suggest that porpoises adapted to this threat. Our study contributes to understanding porpoise health in response to persisting, new, emerging, and cumulative threats. Building up such knowledge is crucial for conservation management of this protected species.

Original languageEnglish
Article number997388
Number of pages19
JournalFrontiers in Marine Science
Publication statusPublished - 11 Oct 2022

Bibliographical note

Funding Information:
Necropsies of harbor porpoises in the Netherlands are commissioned by the Ministry of Agriculture, Nature and Food Quality, and since 2016 embedded under the Legal Research Tasks Nature & Environment unit of Wageningen UR (project reference numbers 140000353, WOT-04-009-045).The ears were analyzed at the Technical University of Catalonia, Spain (UPC-Barcelona Tech) from 2008 to 2013, at the University of British Columbia (UBC), Canada from 2013 to 2017 and to the Institute for Neurosciences of Montpellier, France from 2017 to 2019 with appropriate CITES permits. The inner ear collection, preservation and analysis were funded by Rijkswaterstaat (WoZEP 2016), the Natural Sciences and Engineering Research Council (NSERC) of Canada Discovery and Accelerator grants RGPAS 446012-13 and RGPAN 312039-13, the Spanish Ministry of the Environment (grant number: 083/SDGTB/2007) and Marie Skłodowska-Curie Individual Post-doctoral Fellowship (grant number: 751284-H2020-MSCA-IF-2016).

Publisher Copyright:
Copyright © 2022 IJsseldijk, Leopold, Begeman, Kik, Wiersma, Morell, Bravo Rebolledo, Jauniaux, Heesterbeek and Gröne.


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