Scientists discover why dozens of endangered elephants dropped dead, In 2020, 350 elephants mysteriously died in Botswana, with a further 35 dying in similar circumstances in Zimbabwe. Now scientists think they may have found the reason why by Phoebe Weston, 25 Oct 2023, The Guardian
In May and June 2020, the death of 350 elephants in Botswana’s Okavango delta baffled conservationists and sparked global speculation about what had caused it. Elephants of all ages and both sexes were affected, with many walking in circles before dying suddenly, collapsing on their faces. Two months later, 35 more elephants died in north-western Zimbabwe.
At the time, the deaths in Botswana were attributed to an unspecified cyanobacterial toxin, government officials said, and no further details were published.
But tests on the elephants that died in Zimbabwe have finally come back and shown the cause was a little-known bacterium called Pasteurella Bisgaard taxon 45, which resulted in septicaemia, or blood poisoning.
The bacterial infection has not previously been linked to elephant deaths, according to the paper published in the Nature Communications journal. Researchers believe it could have been the same one responsible for the deaths in neighbouring countries.
“This represents an important conservation concern for elephants in the largest remaining meta-population of this endangered species,” researchers wrote in the paper. It was written by an international team of researchers from the Victoria Falls Wildlife Trust, the University of Surrey, laboratories in South Africa and the UK government’s Animal and Plant Health Agency (APHA).
African savanna elephants are declining by 8% a year, primarily due to poaching, with 350,000 remaining in the wild. The paper suggests that infectious diseases should be added to the list of pressures they are facing.
Dr Arnoud van Vliet from the University of Surrey said the infection “adds to the growing list of disease-related threats to elephant conservation”. Elephants are highly sociable animals, and also were likely stressed due to the drought conditions at the time, which made such an outbreak more likely.
Pasteurella bacteria has previously been linked to the sudden death of about 200,000 saiga antelopes in Kazakhstan – an incident that researchers believe could shed light on what happened to the elephant herds. Scientists believe the Pasteurella bacteria generally lives harmlessly in the tonsils of some, if not all, of the antelopes. An unusual temperature increase to 37C, however, caused the bacteria to pass into the bloodstream, where it caused septicaemia.
Bisgaard taxon 45 has previously been found to exist in tigers and lions (found by testing a bite wound in a human) as well as chipmunks and psittacines, according to the paper.
Other things experts tested for included cyanide, which some people use to poison elephants, but there were no traces of any poisons in the carcasses or near the waterholes. Other theories included ingestion of toxins from algal blooms. Poaching was immediately ruled out because the carcasses still had tusks attached.
The lead investigator, Dr Chris Foggin, a wildlife veterinarian at the Victoria Falls Wildlife Trust, said investigating the mass deaths had been “challenging”.
“Identifying and then reaching the carcasses in time to obtain useful samples is one problem we often face. However, we also didn’t know what disease we may be dealing with,” he said.
“We initially suspected that it could be anthrax, which is known to occur in the area; or possibly some other disease that might pose a risk to human health. We therefore had to be cautious when undertaking the postmortem examinations on elephants which, in itself, is a difficult task with such a big animal, especially working in field conditions.”
Scientists were unable to visit the site in neighbouring Botswana and most official samples were collected from animals that had already started rotting. The paper says the findings of blood poisoning “may represent an ongoing phenomenon in this region”, with previous cases missed due to lack of testing.
Whales: Unusual deaths of hundreds of West Coast gray whales linked to lack of Arctic ice by Alex Baumhardt, Curry Coastal Pilot, Oct 21, 2023
The deaths of more than 700 West Coast gray whales since 2019 is likely the result of low food supplies caused by a lack of sea ice in the Arctic.
Declining Population
A team of researchers led by Joshua Stewart of Oregon State University found there have been three “unusual mortality events” in the last 36 years, where the delicate balance of ice in the Arctic shifts, leaving the whales without enough food or access to food. The team’s findings were published Oct. 13 in the journal Science.
Stewart, an assistant professor at Oregon State University’s Marine Mammal Institute, has studied West Coast gray whale populations recorded since the 1960s, as well as environmental data related to their habitats. The whales pass the Oregon Coast each year on their 12,000-mile summer migration from breeding grounds in Baja, Mexico to the Arctic to feed.
Stewart and his team identified three unusual mortality events, beginning in 1987, 1999 and 2019, and found each was tied to food availability issues caused by ice fluctuations. In some years, too much ice blocked the whales from accessing their traditional feeding grounds. In the current mortality event, the lack of robust ice means less algae is growing beneath ice sheets and falling to the sea floor. This has left the whales’ prey, small shrimp-like crustaceans called amphipods, in smaller numbers because of a lack of nutrients and the habitat they need. Warmer Arctic waters and faster currents have also brought the arrival of other creatures to compete for nutrients at the bottom of the food chain, further reducing the number of calorie-dense amphipods that whales need.
Between 2016 and 2023, the population of eastern North Pacific gray whales has declined by nearly half, from a high of 27,000 to about 14,500 today, according to the most recent data from the National Oceanic and Atmospheric Administration, or NOAA.
Stewart said climate change has played a role in driving recent sea ice loss, impacting the food chain and leading to malnutrition responsible for hundreds of whales washing up on the West Coast during the last four years. Each of the three die offs Stewart’s team has studied led to whale population declines of at least 25% in just a few years.
“We’re hoping that by diving a little deeper into the causes we can maybe better predict what the future of the gray whale population will look like, and then take some lessons from that for other large whale species and populations that are maybe increasingly impacted by climate change,” Stewart said.
West Coast gray whales have the longest migration of any mammal and are only found in the Pacific. They are among eight whale species in the Pacific. They were listed as endangered under the federal Endangered Species Act but recovered and came off the list in 1994.
Nevertheless, in 2019, 120 dead gray whales washed up on West Coast beaches. In the years that followed, about 600 whales washed ashore, appearing to be malnourished, according to scientists. Earlier this year, three gray whales washed up on Oregon beaches within two weeks, and in June, five washed up on shores in Washington. Most were malnourished. So far this year there have been 63 dead gray whales found on shores between the Baja and Alaska, according to NOAA data.
The current mortality event has gone on twice as long as the 1987 and 2019 events, Stewart said.
But there are signs it is coming to an end.
NOAA scientists in Baja found that gray whales in area lagoons are larger and healthier this year than in years prior. And for the first time in five years, the number of mothers with calves has increased.
Scientists have also counted fewer dead or stranded whales in Mexico and along the West Coast on their journey northward this year between February and May than in previous years.
“We need to stop human driven climate change, and even if we did stop that there’s some degree that’s probably baked into the system already, and will take quite a long time to reverse,” Stewart said. “That’s hard, right? I mean that’s pretty depressing. I don’t know what else to call it. It’s a hard pill to swallow, when you just see these impacts that may not be reversible.”
The collapse of eastern Bering Sea snow crab by Cody S. Szuwalski, Kerim Aydin, Erin J. Fedewa, Brian Garber-Yonts, and Michael A. Litzow, Oct 19, 2023, Science Vol 382, Issue 6668, pp. 306-310
DOI: 10.1126/science.adf6035
Editor’s summary
Marine heatwaves, a component of our impact on the Earth’s climate, can bring both expected and unexpected environmental change. Between 2018 and 2021, after a period of historically high crab abundance and a series of marine heatwaves, the population of snow crab in the Bering Sea declined by 10 billion. Szuwalksi et al. used survey data to model the potential drivers of the decline in this ecologically and commercially important species. They found that the temperature of the water was not above the species’ thermal limits, but it did increase their caloric needs considerably (see the Perspective by Kruse). This increase, in conjunction with a restriction in range, led to an unexpected mass starvation event. —Sacha Vignieri
Abstract
The snow crab is an iconic species in the Bering Sea that supports an economically important fishery and undergoes extensive monitoring and management. Since 2018, more than 10 billion snow crab have disappeared from the eastern Bering Sea, and the population collapsed to historical lows in 2021. We link this collapse to a marine heatwave in the eastern Bering Sea during 2018 and 2019. Calculated caloric requirements, reduced spatial distribution, and observed body conditions suggest that starvation played a role in the collapse. The mortality event appears to be one of the largest reported losses of motile marine macrofauna to marine heatwaves globally.
10 Billion Crabs In Alaska Slowly Starved To Death Due To Extreme Marine Heat Waves by Anna Louise, Oct 20, 2023, Nature World News
Billions of snow crabs have vanished from the waters near Alaska in recent years, and scientists believed that the warmer ocean temperatures likely starved them to death.
The finding comes just days after the Alaska Department of Fish and Game suspended the snow crab harvest season for the second year in a row, citing an excessive quantity of crabs missing from the Bering Sea’s generally chilly, hazardous waters.
Maritime Heat Waves
The study, released by National Oceanic and Atmospheric Administration scientists, discovered a substantial correlation between recent maritime heat waves in the eastern Bering Sea and the unexpected disappearance of snow crabs.
Scientists first noted a significant decrease in the quantity of snow crabs during a survey in 2021, which “found the fewest snow crabs on the eastern Bering shelf since the survey began in 1975,” according to the report.
Cody Szuwalski, lead author of the study and fishery biologist at NOAA, said they examined north of the Bering Sea, west toward Russian waters, and even deeper into the oceans and “ultimately concluded that the crabs did not move and that the mortality event was most likely a major driver.”
Warmer temperatures and higher population density were shown to be strongly associated with higher mortality rates among mature crabs. The cause of the mortality event is hungry crabs.
Snow crabs are cold-water animals that live mostly in places with water temperatures below 2 degrees Celsius, while they can function in seas as warm as 12 degrees Celsius.
Warmer ocean water is believed to have disrupted the crabs’ metabolism and raised their calorie requirements.
Researchers discovered that the amount of energy crabs need from food in 2018–the first year of a two-year maritime heat wave in the region–may have doubled compared to the previous year.
However, because the heat disrupted much of the Bering Sea’s food web, snow crabs had a difficult time hunting for food and couldn’t keep up with the caloric demand.
Read Also: Climate Change and Hypoxia: Blue Crabs More Resilient to Dead Zones Than Previously Thought
Climate Crisis Impacting Livelihood
Researchers said that the implications of fast rising ocean temperatures and more frequent heat waves in reaction to climate change are difficult to forecast, but the snow crab die-off is “a prime example of how quickly the outlook can change for a population.”
What’s occurring with Alaska’s crabs is proof that the climate problem is intensifying and affecting livelihoods, according to Szuwalski.
“This was kind of an unexpected, punctuated change in their populations,” he said. “But I think long term, the expectation is that the snow crab population will move north as the ice recedes and in the eastern Bering Sea, we probably won’t see as much of them anymore.”
The consequences of maritime heat waves are likely to be felt by creatures other than snow crabs.
Scientists often use historical data to predict and prepare for future developments.
However, the future increasingly features catastrophes that have never been recorded before, such as the snow crab population collapse, making them more difficult to prepare for.
Related Article: Popular Seafood Crabs Disappearing, Losing Sense of Smell: Climate Change Likely a Culprit [Study]