The results of a major sperm whale investigation carried out by international marine experts – including the Scottish Marine Animal Stranding Scheme (SMASS) – have been published.
The international study into the strandings of 30 sperm whales (Physeter macrocephalus) in the southern North Sea in 2016, which can be read in the scientific journal PLOS ONE, concludes that the event most likely occurred due to a combination of several complex environmental factors, rather than any single factor.
The whales became stranded across five countries over a period of six weeks, after entering the southern North Sea where the water becomes progressively shallower – a known global hotspot for sperm whale strandings.
Teams of international scientists and experts from around Europe came together to investigate this event, including ZSL (Zoological Society of London), Utrecht University and University of Veterinary Medicine Hannover. Twenty-seven of the 30 sperm whales were examined during the investigation.
Dr Andrew Brownlow from SMASS, part of SRUC, described the post-mortem of a 30-tonne sperm whale in Angus back in March as one of his most challenging.
Speaking about the new report, he said: “These species range for thousands of miles through our seas, and investigating stranding events such as these enable us to learn about the health and ecology of these gigantic animals.
“This was one of the most detailed investigations into sperm whale mass strandings ever undertaken: logistically challenging, technically multidisciplinary and requiring close collaboration at an international scale. As a result, however, we were able to rule out many potential natural or human-induced causes and potentially shine a light into deeper issues of oceanic health.”
Lead Author Lonneke IJsseldijk, from the Faculty of Veterinary Medicine of Utrecht University, said: “We looked at the health status and nutritional condition of each animal. Several infections were found, including parasites and a new herpes virus, but all were deemed to be incidental findings in this large-scale stranding event. Being able to rule out disease as the primary cause of the event makes other causes more likely. So, we continued to investigate and look for different possible causes.
“We found no evidence of man-made trauma due to entanglement or ship-strike, nor was there evidence of significant levels of chemical pollution. In nine examined whales, marine debris (plastic) was also found, but had not caused obstructions of the gastrointestinal tract or starvation and were deemed to be of secondary importance. Marine earthquakes, harmful algal blooms and changes in sea surface temperature were also considered as possible drivers of the series of strandings but were ruled out.”
Part of SRUC and funded by Marine Scotland and Defra, SMASS has been investigating stranding events – including those involving whales, dolphins, porpoises, marine turtles and even sharks – since 1992.
During July, 59 strandings were reported to the team, with 20 cetaceans, 38 pinnipeds, and the skeletal remains of one basking shark. Eight of these animals went for necropsy; one harbour porpoise, two Sowerby’s beaked whales, three common seals, a grey seal and a Harp seal which was found on Balmedie beach in Aberdeen on the last day of the month.
To read SMASS’s full report for July, click here.