Whales: threatened giants of the sea
Commercial whaling may have been stopped in all but a few countries and populations may be increasing, but whales are still at risk from several complicated and intertwined threats. Addressing them requires complex socio-ecological, political and economic cooperation. By
Whales may be safe from commercial whaling in most countries, but that doesn’t mean they are out of the woods. Dr Gwenith Penry, marine mammal biologist and research associate at the Institute for Coastal and Marine Research at Nelson Mandela University, told DM168 some “species have recovered pretty well, like humpback whales, and others haven’t – like blue whales”, explaining that the humpback whale population has increased since commercial whaling ended in South Africa.
“It depends … on the species. It’s like calling a lion and a leopard a cat – they have very different biologies and behaviours.”
South Africa supports the International Whaling Commission’s (IWC) moratorium on commercial whaling that was introduced in 1986, but according to the Department of International Relations and Cooperation, it has been a non-whaling nation since 1975.
“The population is increasing, which is why those groups are becoming more obvious and more apparent,” said Penry in reference to the “supergroup” whale pods seen along the West Coast recently.
The population of southern right whales, a migratory species also seen along our coastlines, has been increasing by about 7% a year. “A couple of decades ago, southern right whales were in a worse state than they are now, and the same with our humpback whales. So their conservation statuses have improved,” said Penry.
“But we’re seeing more drastic fluctuations in the numbers that come to our coastline, and current thinking is that this is related to reduced prey availability in their Southern Ocean feeding grounds.”
Humpback and southern rights aren’t classified as vulnerable, unlike the resident Bryde’s whale in which Penry specialises, but she said they were still of conservation concern because of a growing number of threats in our oceans.
“There are also massive ecosystem changes that are more noticeable on the West Coast, and that’s probably related to climate change and anthropogenic activities, which affect factors like productivity and current strength productivity, which is typically what is keeping those supergroups around.”
The WWF reported that six out of the 13 great whale species are classified as endangered or vulnerable.
Although commercial whaling has been banned by most countries (barring Japan, Iceland and Norway), whales still face many threats; they have just become more complicated and intertwined.
“Historically, commercial whaling was devastating, and some populations may never fully recover. Lengthy scientific and political processes were required before the mortarium was effected, but as a whole it was a single industry that could be identified and addressed,” explained Penry.
“Modern threats to whales are often more cryptic and intertwined, and addressing them requires complex socio-ecological, political, and economic cooperation.”
Penry said the conservation concerns SA whales were facing followed global trends: “increasing coastal development, increased shipping disturbance, more people living here, discarded fishing gear, plastic ingestion, pollutants, pollutant runoff from agricultural runoff”.
“I dissected a killer whale six years ago here that just had a stomach full of plastic.
So it’s our horrible lifestyles that are affecting them.”
Penry said that, globally, entanglement and ship strikes were the biggest threat to large whales, having population-level impacts. There is increased disturbance from shipping, both from noise and ship strikes.
“Those ‘supergroups’ on the West Coast [are at] a huge risk from ship strikes because they’re so close to shore and they feed and they are big dense groups.”
Entanglement was probably the biggest threat whales faced, she said, adding that there had been a rise in the past few years.
“It’s increased, one because fishing efforts have increased – more global demand, there’s more discarded or lost gear just floating around, because that happens.”
And second, “some populations are recovering, so the chances of an animal encountering it are higher”.
Mike Meyer, operations manager of the South African Whale Disentanglement Network, said there was a huge increase in whale entanglements in the years 2016 to 2020. In 2020 there were 38 reported entanglements, the most the group had ever had.
Meyer said “superpods”, which can consist of 300 to 400 animals, had faced more entanglement in recent years because of changes in wind affecting nutrient upwelling.
“We’ve had an increase in the southeasterly wind, carrying on right up to February, sometimes March, so what we get is this upwelling and nutrients coming to the surface, concentrating whales in the same area,” said Meyer. This coincides with the same area on the West Coast where the fishing industry is concentrated, which contributes to increased entanglements.
Penry explained that entanglement was killing some species at a rate that’s not replenishable – causing the population to decline.
“Fishery gear, both lost and that which is set, is just increasing and becoming more of a hazard,” explained Penry.
“But there’s a lot of work going on to improve gear. Some fisheries are on the whole quite open to changing gear or trying different gear types and mechanisms to reduce the amount of rope in the water column, which is an entanglement hazard.”
The South African Whale Disentanglement Network has made strides in this area, significantly decreasing entanglements in shark nets and octopus lines by changing mechanisms and gear.
Penry said these types of effort were a national imperative.
In October 2021, she accompanied the network to disentangle a young humpback whale (two years old) in Plettenburg Bay. The entanglement was so tight around its tail that it took three hours to release it.
But Meyer said the more important threat is global warming, as it influences food availability and movement.
“What has happened is that the animals are disappearing; they’re moving somewhere else, probably because there’s food somewhere else, and they’re not getting the food [here]. And as you know, the plankton in the Antarctic breeds mostly under the ice, and the ice is reducing. So things are changing, currents are changing, temperatures are changing, and food distribution is changing,” Meyer said.
Penry explained that changing temperatures and wind strengths had changed the current systems, reducing nutrient upwelling in the Southern Ocean.
Whales migrate to Antarctica to feed, but as Antarctica feels the effects of climate change more heavily, it’s having an effect on nutrient upwelling and thus the whole food chain.
“If that doesn’t happen, because of weakening currents, or temperatures are too high, the plankton blooms don’t happen ... then your whole food chain is affected,” said Penry.
The WWF explained: “Warming oceans and loss of sea ice in the Arctic and Antarctic can affect the habitats and food of whales. Large patches of tiny plants and animals that they feed on will likely move or change in abundance as climate change alters seawater temperature, winds, and ocean currents.
“It’s a much more cryptic ecosystem threat – to the ecosystem rather than to the individual whale,” said Penry. “So the environment is under attack by noise and pollution and rubbish, which then affects the health of the habitat that the whales rely on; their prey, their calving and resting areas, and their migration corridors.”
The WWF reported that whales were at the top of the ocean food chain and that they had an important role in the overall health of the marine environment.
“Whales play a significant role in capturing carbon from the atmosphere; each great whale sequesters an estimated 33 tonnes of CO₂ on average, thus playing their part in the fight against climate change.”
Penry agrees. “Whales play an important role in helping us to fight the climate crisis, both as carbon sinks – when a whale dies, it sinks to the bottom of the ocean, it takes a lot of the carbon down with it – but it also creates a really valuable nutrient source for organisms that don’t easily find food.
“In terms of their value to humans and fighting the climate crisis, they’re indicator species,” said Penry.
“They’re visible, they’re charismatic – people are watching them, studying them, they’re more accessible than some of the smaller, more cryptic species.
“Changes in whales’ distribution, their behaviours, their feeding strategies are visible to us,” Penry said. “And so they indicate changes in the environment to humans, which are then indicative of what’s happening in the ecosystem.”
In terms of their value to the ecosystem, they are vital in keeping the natural ecological balance of the food chain and help with nutrient cycling.
“There’s a recent study which recalculated the amount of prey that whales consume, and consumption was found to be three times higher than we originally estimated. Which is just showing that because there are [fewer] whales now there’s less nutrient cycling,” said Penry.
“It’s really important to ensure that numbers increase so that they eat more and then they defecate more nutrients into the system.”
I dissected a killer whale six years ago that had a stomach full of plastic. So it’s our horrible lifestyles that are affecting
them
Dr Gwenith Penry