TUESDAY, 13 JULY 2021
With a tongue that can weigh as much as an elephant and songs louder than a jet engine, the blue whale has long captured people’s hearts the world over. It is tempting to think the accolade of largest creature on our planet might have kept these giants safe from commercial whaling, but while some saw their remarkable size as something to be marvelled at, others saw it as a possibility for profit. In the first half of the 20th century, more than 340,000 blue whales were killed for their meat and blubber, pushing them to the brink of extinction.This sad story was repeated across many of the 89 species of whales, dolphins, and porpoises, collectively known as cetaceans. The true death toll of commercial whaling remains unknown, but recent estimates indicate close to 3 million cetaceans were killed between 1900 and 1999. This may be the largest animal cull in our history in terms of total biomass.
The cessation of commercial whaling by most countries, following a global moratorium in 1986, allowed some populations to begin to recover. However, the slow reproduction rate of many whale species left them vulnerable to extinction. The threat of whaling has been replaced by numerous other human hazards. The sheer number of vessels on our seas and oceans dramatically increases the likelihood of fatal ship strikes. Smaller cetaceans risk becoming bycatch in fishing nets, while larger whales face entanglement in fishing ropes and equipment, which can lead to death through drowning, infection, or starvation.
An ever-increasing threat to cetaceans is man-made noise pollution. Sources are varied, and their impacts on cetaceans can be acute — such as seismic exploration for oil and gas — or cumulative — including constant noise from ships. Cetaceans are known for their songs, calls, and clicks, and use hearing as their dominant sense. Baleen whales, such as blue whales and humpbacks, tend to use low frequency sounds for long distance communication. Toothed whales, including sperm whales and beaked whales, use higher frequency echolocation to navigate, essentially allowing them to ‘see’. Interruptions to these vital communication and navigation mechanisms are likely to have huge negative impacts on how cetaceans search for food and mates, as well as how they identify and avoid obstacles in the water. Mid-range sonar frequencies used in military operations have even been implicated in fatal stranding events of beaked whales.
In order to safeguard cetaceans and encourage recovery of their populations, human impact in cetacean habitats must be lessened. Given the number of different species, each with a unique set of characteristics, such as diet, migration behaviour, and range, a greater understanding of each species is required in order to identify their distribution and inform beneficial policies which facilitate population recovery.
Sadly though, the elusive nature of whales can make them particularly difficult to study. Only a small proportion of their lives is spent at the surface of the water where they can be seen, so marine scientists are increasingly turning to innovative technology to gain an insight into the world of cetaceans.
A study published in Nature Scientific Reports used satellite tracking to investigate the distribution of a population of blue whales off Chilean Patagonia, confirming this area as an important feeding ground. By combining satellite tracking data of an individual blue whale with daily vessel trafficking information, researchers produced a striking animation that illustrated the struggle of one blue whale to avoid the many ships crossing the area in a week, which amounted to almost 1,000 vessels. ‘What the blue whale graphic illustrated so well was ... the constant physical obstruction. The cumulative impact is worrying at both an acoustic and a physical level,’ says Emma Clarke, a marine biologist who studied at Dalhousie University in Halifax, Canada.
Satellite tracking provides a snapshot of the movements of individual whales, as opposed to methods such as passive acoustic recordings, which allow for constant monitoring of an area. Acoustic recording can also circumvent the difficulty of finding and tagging smaller, more elusive whales.
Clarke, whose research with Fisheries and Oceans Canada involved monitoring beaked whales using acoustic recordings, explains, ‘There are more and more hydrophones recording in the ocean, so if you can draw on that data and start to identify ... where species are being heard at what times, you can start to get spatial and temporal resolution of their distribution.’ For toothed whales, which rely on echolocation, ‘acoustic recording can come in really handy and allow you to identify particular species, because those clicks have species-specific characteristics’.
A huge benefit of passive recording is that it can pick up changes in species distribution over years, but analysing this data manually is no mean feat. As Clarke describes, ‘To find clicks, you are searching at the scale of milliseconds and then you have to look at that for a minute and then for a day and these underwater recorders are often out there for a year, so it is a huge amount of data to process’. The development of machine learning tools that can identify cetacean vocalisations has vastly increased the amount of data which can be processed, in some cases allowing for near real-time detection.
The wealth of knowledge provided by these kinds of data can be used to identify areas in which enforced regulations could lessen our impact on endangered cetaceans. These areas can be designated as ‘Marine Protected Areas’ (MPAs) and range from marine national parks to special areas of conservation. There are currently 600 MPAs for the protection of cetacean habitats, each with a different set of rules depending on the location and the reason for the MPA. However, only a small proportion have tight restrictions such as total bans on commercial fishing.
As well as MPAs, it is still possible to reduce the impact of human activity by rerouting busy shipping lanes, banning seismic exploration in cetacean habitats, establishing temporary fishery closures, and enforcing vessel speed limits. For example, mandatory season-long speed limits of 10 knots along the U.S. eastern seaboard led to an 86% reduction in lethal ship collision risks for North Atlantic Right whales.
Yet, with fewer than 100 breeding females of this species left, many conservationists are calling for tougher restrictions. A report by Fisheries and Oceans Canada showed that vessels often speed up before reaching a speed restricted area in anticipation of the reduced speed, raising the risk of fatality from a collision to 100% just outside the zone. This example alone illustrates the complexity of safeguarding cetaceans while still accommodating a level of human activity, which is unlikely to be drastically reduced in the near future.
As our understanding of cetacean habitats evolves, it is essential that governments, industry, commerce, and the military work with marine scientists to put in place and adhere to regulations that are flexible, under constant review, and based on area-specific cetacean presence and behaviours. As Clarke puts it, ‘To lose them before we even get to know them feels [like] a huge tragedy, especially knowing that we caused this in the first place and there are very tangible actions that we can take to help lessen our impacts’
Hazel Walker is a fourth year PhD in Immunology at Fitzwilliam College. Artwork by Eva Pillai.
