Beached bachelors: An extensive study on the largest recorded sperm whale Physeter macrocephalus mortality event in the North Sea

Abstract

Between the 8th January and the 25th February 2016, the largest sperm whale Physeter macrocephalus mortality event ever recorded in the North Sea occurred with 30 sperm whales stranding in five countries within six weeks. All sperm whales were immature males. Groups were stratified by size, with the smaller animals stranding in the Netherlands, and the largest in England. The majority (n = 27) of the stranded animals were necropsied and/or sampled, allowing for an international and comprehensive investigation into this mortality event. The animals were in fair to good nutritional condition and, aside from the pathologies caused by stranding, did not exhibit significant evidence of disease or trauma. Infectious agents were found, including various parasite species, several bacterial and fungal pathogens and a novel alphaherpesvirus. In nine of the sperm whales a variety of marine litter was found. However, none of these findings were considered to have been the primary cause of the stranding event. Potential anthropogenic and environmental factors that may have caused the sperm whales to enter the North Sea were assessed. Once sperm whales enter the North Sea and head south, the water becomes progressively shallower (<40 m), making this region a global hotspot for sperm whale strandings. We conclude that the reasons for sperm whales to enter the southern North Sea are the result of complex interactions of extrinsic environmental factors. As such, these large mortality events seldom have a single ultimate cause and it is only through multidisciplinary, collaborative approaches that potentially multifactorial large-scale stranding events can be effectively investigated.

Trace element analysis reveals bioaccumulation in the squid Gonatus fabricii from polar regions of the Atlantic Ocean

“…Sperm whales alone are estimated to consume 1.5 million tonnes of G. fabricii annually in the northern Atlantic (Bjørke, 2001). Squid prey that was estimated from cephalopod beaks in stomach contents of sperm whales that stranded along the coasts of the North Atlantic consisted of up to 99% of G. fabricii (Bjørke and Gjøsaeter, 2004;Ijsseldijk et al, 2018;Martin and Clarke, 1986;Santos et al, 1999;). Narwhales, Monodon monoceros, observed in West Greenland waters during autumn almost exclusively fed on G. fabricii (Laidre and Heide-Jørgensen, 2005).…”

Bacteriological and histopathological findings in cetaceans that stranded in the Philippines from 2017 to 2018

“…Acoustic trauma was suggested as the cause of some previously reported cetacean stranding events in the Philippines, possibly due to blast fishing activities near the stranding sites [23,48]. In addition, the stranding event itself can induce trauma and stress myopathy on the animal, causing congestion, hemorrhage, and skeletal and cardiac muscle degeneration such as in the case of Zenker's necrosis [15,[49][50]. These lesions were observed in 86% of tissues.…”

Where are Solar storm-induced whale strandings more likely to occur?

“…weather, waves, current, military exercises, excessive underwater noise, parasites, diseases, poisons, plastic in the stomach, etc.) (Unger et al, 2016;IJsseldijk et al, 2018;Nielen, 2018). IJsseldijk et al (2018) and Nielen (2018) suggested that geomagnetic misinterpretations triggered by Solar storms could have influenced the animals' migration, either exclusively or in connection with other causes.…”

“…(Unger et al, 2016;IJsseldijk et al, 2018;Nielen, 2018). IJsseldijk et al (2018) and Nielen (2018) suggested that geomagnetic misinterpretations triggered by Solar storms could have influenced the animals' migration, either exclusively or in connection with other causes. Vanselow et al (2018) examined the possible reasons for the effects of such geomagnetic disturbances, leaving Solar storms as a possible causal explanation for the North Sea strandings in early 2016.…”

“…This phenomenon includes sperm whale ( Physeter macrocephalus ) beachings on North Sea coasts (Smeenk, 1997; Vanselow and Ricklefs, 2005; IJsseldijk et al ., 2018). There has been much discussion of the possible causes of recent sperm whale strandings around the North Sea at the beginning of 2016, when 29 animals beached within 4 weeks (Unger et al ., 2016; IJsseldijk et al ., 2018; Nielen, 2018; Vanselow et al ., 2018). However, despite intensive research, experts have struggled to determine the reason for this stranding episode (e.g.…”