Pathological findings in bycaught harbour porpoises (Phocoena phocoena) from the coast of Northern Norway

Kathrine A Ryeng,Jan Lakemeyer,Peter Wohlsein,Ursula Siebert,Marco Roller

doi:10.1007/s00300-021-02970-w

Abstract

Due to little prior knowledge, the present study aims to investigate the health status of bycaught harbour porpoises from the northernmost Arctic Norwegian coastline. Gross, histopathological and parasitological investigations were conducted on 61 harbour porpoises (Phocoena phocoena phocoena) accidentally captured in fishing gear from February to April 2017 along the coast of Northern Norway. Most animals displayed a good nutritional status, none were emaciated. Pulmonary nematodiasis (Pseudalius inflexus, Halocercus invaginatus and Torynurus convolutus) was found in 77% and associated with severe bronchopneumonia in 33% of the animals. The majority (92%) had parasites in the stomach and intestine (Anisakis simplex sensu stricto (s. s.), Pholeter gastrophilus, Diphyllobothrium stemmacephalum, Hysterothylacium aduncum and Pseudoterranova decipiens s. s.). The prevalence of gastric nematodiasis was 69%. In the 1st stomach compartment A. simplex s. s. was found in 30% of the animals, causing severe chronic ulcerative gastritis in 23%. Campula oblonga infected the liver and pancreas of 90% and 10% of the animals, respectively, causing severe cholangitis/pericholangitis/hepatitis in 67% and moderate pancreatitis in 10% of the animals. Mesenteric and pulmonary lymphadenitis was detected in 82% and 7% of the animals, respectively. In conclusion, the major pathological findings in the investigated Arctic porpoises were parasitoses in multiple organs with associated severe lesions, particularly in the lung, liver and stomach. The animals were generally well nourished and most showed freshly ingested prey in their stomachs. The present study indicates that the harbour porpoises were able to tolerate the detected parasitic burden and associated lesions without significant health problems.

Highlights

Marine mammals may be used as sentinel organisms to evaluate the health of marine ecosystems
Most of the bycaught harbour porpoises (HP) were from age group 2 (36%)
The present study reports for the second time the pathological findings in HPs bycaught in gill net fisheries along the Norwegian coast, and focuses on the northernmost part of the coastline, between Senja in the south and the Varanger Fjord in the northeast

Summary

Introduction

Marine mammals may be used as sentinel organisms to evaluate the health of marine ecosystems. The harbour porpoise (Phocoena phocoena) is one of the smallest cetacean species and common in shallow coastal waters of the Northern hemisphere (Benke et al 1998). Phocoena is continuously distributed in the European. The population size of harbour porpoises in Norwegian waters is estimated to be > 180,000 animals (Moan et al 2020). The single greatest threat to harbour porpoises is bottom-set large-mesh gillnets operated by the Norwegian small-vessel fleet. Most porpoises are taken in gillnets intended to catch Atlantic cod (Gadus morhua), monkfish (Lophius piscatorius), and to some extent, saithe (Pollachius virens) (Moan et al 2020). Several studies on the health status of harbour porpoises in European waters have been reported

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