Tag Archives: marine mammals

The fish used for sushi has 283 times more parasites than in the 1970s

Nigiri, sashimi, maki, and many other types of sushi have grown popular over the years, now easy to find in restaurant menus and delivery apps. But the sushi boom came alongside growing concerns over the Anisakis, a parasitic worm that can be transmitted to humans who eat raw or undercooked seafood.

Credit Wikipedia Commons

A group of researchers at the University of Washington report on a 238-fold increase in parasite abundance since the 1970s. This could have consequences for the health of both humans and marine mammals.Other studies have looked at the abundance of the worm, but this is the first-time researchers look closer at its expansion over time.

“This study harnesses the power of many studies together to show a global picture of change over a nearly four-decade period,” said corresponding author Chelsea Wood.

Anasakis starts its life cycle in the intestines of marine mammals, is excreted into their feces and then infects fish, crustaceans, or krill. Eating the worms can lead to nausea, vomiting, and diarrhea, which ends when the worm dies a few days later. It’s not usually diagnosed, as people mistake it with food poisoning.

Most seafood processors and sushi chefs are trained at spotting the worm in the fish and taking it out before they reach the customers in stores and markets, Wood explained. The worms have up to 2 centimeters in length, similar to the size of a 5-cent nickel.

Wood and the group of researchers looked at past papers that had mentions of the Anisakis worms, as well as another worm called the “cod worm.” They focused on the studies that included estimates of the abundance of the worm at different points in time, finally discovering the 238-fold increase of the Anisakis.

While the risks of eating the worms are fairly low for humans, the study warned over the impact they could have on marine mammals like dolphins, whales, and seals.

“One of the important implications of this study is that now we know there is this massive, rising health risk to marine mammals,” Wood said. “It’s not often considered that parasites might be the reason that some marine mammal populations are failing to bounce back.”

The reason for the exponential increase of the Anisakis worms is not fully clear for the researchers, but they link it with climate change, growing nutrients from fertilizers and runoff, and an increase in marine mammal populations – all happening on the same period.

In the US, marine mammals are protected since 1972 by a protection act, which led to an increase in the population of many species. As the increase in the parasite’s population took place during the same period of time as the hike in marine mammals, Woods thinks the two are related.

“The increase in parasitic worms actually could be a good thing, a sign that the ecosystem is doing well. But, ironically, if one marine mammal population increases in response to the protection and its Anisakis parasites profit from that increase, it could put other, more vulnerable marine mammal populations at risk of increased infection,” Woods said.

The study was published in Global Change Biology.

Whales mourn, and grieve, and feel the loss of a loved one — just like you or me

A new study has found evidence of mourning behavior in more than six species of marine mammals. The animals have been seen clinging to the bodies of dead relatives or podmates, refusing to let go — a behavior similar to that of human grieving.

A mother orca with her dead newborn.
Image credits Robin W. Baird/Cascadia Research

The most likely explanation behind the animals’ observed behavior is grief, the researchers believe. Barbara King, emeritus professor of anthropology at William & Mary in Williamsburg, Virginia, and author of the book How Animals Grieve, defines animal grief as emotional distress coupled with a disruption of usual behavior.

“They are mourning,” says study co-author Melissa Reggente, a biologist at the University of Milano-Bicocca in Italy. “They are in pain and stressed. They know something is wrong.”

There is previous evidence of a growing number of species that seem to be stricken with grief at the loss of a family member. Elephants will even return over time to the resting place of a dead companion. All this lends weight to the argument that animals feel emotions. Throwing their hat into the controversy, Reggente and her colleagues gathered reports (most of them yet unpublished) of grieving behavior in seven whale species, from sperm whales to spinner dolphins. Their study found that all of these species have been reported to keep company with their dead around the globe. They’re not just isolated cases, either.

“We found it is very common, and [there is] a worldwide distribution of this behavior,” Reggente says.

And the animals seem to understand exactly what they’re doing. In one case, researchers on a boat in the Red Sea watched an Indo-Pacific bottlenose dolphin push the badly decayed corpse of a smaller dolphin through the water. When they lassoed the dead body and begun towing it towards land to bury it, the adult swam alongside the body, occasionally touching it. It escorted it until the water became dangerously shallow, and remained just offshore long after the carcass had been taken away. The relationship between the two dolphins isn’t clear, but Reggente believes they were either mother and child or close kin.

This behavior is even more striking when you consider just how costly it is for the animals. Keeping vigil over a dead companion means that the animals don’t feed and aren’t interacting with other whales, putting it at risk of starvation or social exclusion.

On other occasions, the scientists did have clues about the relationship between the mourner and the dead animals. One female killer whale, known as L72, was seen off San Juan Island in Washington carrying a dead new-born in her mouth. L72 showed signs of recently having given birth, and the researchers observing it reported that it was likely due to have another.

“She was trying to keep the [dead] calf up at the surface the entire time, balancing it on top of her head,” says study co-author Robin Baird of Cascadia Research Collective in Olympia, Washington, who witnessed the mother’s efforts.

A killer whale mother and her offspring may spend their whole lives together, he adds. When one dies Baird believes that “the animals go through a period where they’re experiencing the same kind of emotions you or I would when a loved one dies.”

The study also found reports of whales holding dead calves in their mouths, pushing them through the water or touching them with their fins. Grieving can also involve a whole community of whales — in one case, short-finned pilot whales in the North Atlantic Ocean created a circle around one adult and dead calf, seemingly protecting them.

Another case involving spinner dolphins took place in the Red Sea. Here, one adult pushed a young animal’s body toward a boat, and when the vessel’s crew lifted the carcass on board, the entire group of dolphins nearby circled the boat and swam off.

“We cannot explain why they did this,” Reggente says.

“Sure, sometimes we may be seeing curiosity or exploration or nurturing behavior that just can’t be ‘turned off,’” King said. “[But] it’s undeniable that we can also read something of the animals’ grief in the energy they expend to carry or otherwise keep dead infants afloat, to touch the body repeatedly, to swim in a social phalanx surrounding the primary affected individual.”

This behavior certainly has an element of curiosity or remanent nurturing instincts behind it, but they can’t, by themselves, explain what we’re seeing these animals do. They expend a whole lot of energy, either individually or as a group, in their rituals of carrying or keeping dead individuals afloat. The social interaction, centered on supporting the grieving individual, is also highly reminiscent of human society when confronted with the loss of its members.

We all know the pain and harrowing loneliness of losing a loved one, and it seems whales do too. The question now is how will we treat these animals, knowing they feel the same way as we do.

The full paper, titled “Nurturant behavior toward dead conspecifics in free-ranging mammals: new records for odontocetes and a general review” has been published online in the Journal of Mammalogy and can be read here.