Tag Archives: seal

Skinny seals and hungry cod point to trouble in the Baltic Sea

Not all is well in the Baltic Sea, new research suggests — the local food networks are in trouble.

Baltic sea sky.

Image credits Michal Jarmoluk.

The top predators of the area, gray seals and cod, are losing weight, the study reports. This development is linked to the worsening health of the cornerstones of the Baltic’s local food networks: bottom-living crustaceans, isopods, and amphipods.

Sinking food stocks

“It is important that you understand how the food web works when managing a fishery. It is not enough to manage how the fish and fisheries are changing. The availability and quality of food is at least as important,” explains Lena Bergström, researcher at the Department of Aquatic Resources at the Swedish Agricultural University and the study’s corresponding author.

The study, a collaboration between several universities, looked at the health and abundance of key species over the last two decades in the Bothnian Sea and the Baltic Proper. Seal, cod, herring, sprat, isopods, amphipods, and zooplankton all made the object of this study, as they are important players at different levels of the local food webs. These networks are very complex, the team writes, and the same species can be both prey and predator — for example, herrings eat zooplankton and bottom fauna while being hunted by cod and seals in turn.

The authors show that there is a link between the health of cod and seals, the top predators in this ecosystem, and that of bottom-dwelling species, which are the lowest rung on the ladder. Seals are indirectly linked to these bottom-feeders, as they dine on herrings (who in turn dine on the bottom-dwelling species). The worsening health of both cod and seals, the authors explain, is tied to climate change and eutrophication. Eutrophication is an excess of nutrients in a body of water, frequently due to run-off from land, which causes a dense growth of bacteria and algae.

“Oxygen levels in Baltic Sea have reduced since the 1990s, in big part due to eutrophication, creating vast oxygen-free areas. This leads to less living space for the bottom-living prey animals,” says Agnes Karlsson, lead author and researcher at the Department of Ecology, Environment, and Plant Sciences (DEEP) at Stockholm University.

“This has, among other things, led to the fact that the isopods have become fewer and smaller, making them a poorer food choice for cod.”

The team explains that, while the mean weight and fat content of herring in the Bothnian Sea have recently been on the uptick — made possible by an increase in the quantity of bottom-living amphipods — this isn’t an improvement; it’s a recovery. These crustaceans were almost wiped out by a period of extremely heavy rains in the early 2000s which changed the quality of local waters.

“The upturn is relative, because the amphipod in the Bothnian Sea collapsed in the early 2000s and what we now see are signs of a recovery,” Karlsson adds.

“With climate change it is likely that we will see similar extreme events more frequently in the future,” Bergström adds. “If activities that lead to eutrophication are not reduced, oxygen shortage in the Baltic Sea will likely continue, leading to further reductions in the numbers of bottom-living animals. This can have far reaching effects for the economy, with reference to the fish species that are important commercially. To manage a fishery, we must also manage the environment and the food web.”

The paper “Linking consumer physiological status to food-web structure and prey food value in the Baltic Sea” has been published in the journal Ambio.

Penguin and seal poop create biodiversity hotspots in Antarctica

The desolate landscapes of the Antarctic receive an unexpected boom from penguins and seals, whose feces fertilize large areas, providing nutrients that help an entire ecosystem.

Image via Max Pixel.

The cold lands of Antarctica are inhospitable, but not completely barren. A small group of plants and animals brave the cold and the ice and manage to form sustainable ecosystems. As in all ecosystems, plants are the ones that bring new energy into the mix — they absorb solar energy through photosynthesis and transform it into nutrients. But plants also need to draw some nutrients from the soil.

This is where poop comes in to save the day.

“What we see is that the poo produced by seals and penguins partly evaporates as ammonia,” says Stef Bokhorst, a researcher in the Department of Ecological Sciences at Vrije Universiteit Amsterdam. “Then, the ammonia gets picked up by the wind and is blown inland, and this makes its way into the soil and provides the nitrogen that primary producers need in order to survive in this landscape.”

The process isn’t limited to the area of the colony. In fact, Bokhorst and colleagues found that the benefits of this poop spread to an area up to 240 times the size of the colony, enabling the development of thriving communities of moss and lichens, which in turn support impressive biodiversity consisting of invertebrates. The numbers of springtails and mites, for instance, far exceeds what is typically found in more temperate areas.

“You can find millions of them per square meter here, but in grasslands in the US or Europe, there are only about 50,000 to 100,000 per square meter,” says Bokhorst, adding that identifying these small species was so painstakingly laborious that he’d much rather prefer trekking through the cold temperatures of the Arctic. “It took months and months of sitting in the lab counting and IDing them under a microscope,” he says, adding that the system is still too unproductive to support mammals such as mice or rats.

Ultimately, this bio-cycle of nutrient enrichment is not surprising, but what was surprising was how far it spread, and the fact that it had nothing to do with how cold an area was. The good news is that since penguin and seal colonies can be monitored with relative ease, this information can then be used to infer the enrichment area, offering a secondary monitorization. The bad news, however, is that climate change and human activity are already taking a toll on this existing biodiversity.

The vibrant communities that researchers discovered flourish, in part, because they have no natural predators. But the introduction of invasive species might affect the delicate balance of the ecosystem. Limiting our impact on Antarctica is crucial for the conservation of these communities.

The study “Nitrogen inputs by marine vertebrates drive abundance and richness in Antarctic terrestrial ecosystems”  has been published in Current BiologyDOI: 10.1016/j.cub.2019.04.038.

Seal hitches a ride on the back of a whale

Australian photographer Robyn Malcolm has captured a mind blowing picture: a seal hitching a ride on the back of a humpback whale off the coast of New South Wales, Australia.

“I was surprised to find photos of the cheeky seal in amongst the other shots as I didn’t notice him at the time,” Malcolm told Lucy Cormack over at The Sydney Morning Herald. “I don’t think he stayed there for long.”

Humpbacks are baleen whales, they have no teeth, and use their baleen filter system to sift small fish and plankton and krill from the water. They can consume enormous quantities of food, up to 1,400 kg every day, which is likely why the seal was around.

Whale expert Geoff Ross from New South Wales National Parks and Wildlife Service said:

“Humpbacks force fish into very tight bait balls, that means everyone can dart through the inside or the middle – anything that makes it easier to catch fish, seals will be involved.”

To my honest surprise, he explained that this behavior is not unheard of.

“The only other time was a seal trying to get away from a killer whale,” said Ross. “The seal hopped on the back of the pectoral fins of a humpback whale.”

Right now, humpback whales are making their way down the Australian coast en masse as they head to Antarctica for the summer, resting and feeding as they go.

seals pup bond

Oxytocin seals bond between mother and child

Seals from colonies on the North Atlantic island of North Rona that had higher levels of the hormone oxytocin in their blood stay closer to pups. This suggests that the hormone, often called the love hormone because of its role in love and in female reproductive biological functions, is paramount to forming mother-child bond.

seals pup bond

Image: Pixabay

Lead author  Dr Kelly Robinson of University of St. Andrews says oxytocin may predict maternal relationships in both humans and seals. “The link between oxytocin and maternal behaviour not only has important consequences for pup survival in grey seals, but helps us understand why some individuals, including humans, are better mothers than others,” Robinson said.

Oxytocin is a hormone that is made in the brain, in the hypothalamus. It is transported to, and secreted by, the pituitary gland, which is located at the base of the brain. It’s sometimes known as the “cuddle hormone” or the “love hormone,” because it is released when people snuggle up or bond socially.  A 2007 study published in the journal Psychological Science found that the higher a mom’s oxytocin levels in the first trimester of pregnancy, the more likely she was to engage in bonding behaviors such as singing to or bathing her baby.

“Mother-pup separation often results in starvation and is the largest cause of pup death in grey seals. Preventing separations between mothers and pups within a busy breeding colony is crucial for infant survival,” Robinson said.

“The link between oxytocin and maternal behaviour not only has important consequences for pup survival in grey seals, but helps us understand why some individuals, including humans, are better mothers than others,” she added.

Robinson’s team found that the distance between mothers and their pups ranged from 0 to 30 meters, and those mother seals that kept closest to their offspring had the most oxytocin in their blood. The less oxytocin, the larger the distance between mother and pup.

In 2011, a study on mice showed that oxytocin injections tamed even the most irresponsible mothers, mewling pup in their mouths.

“Some grey seal mothers are much better at raising pups than others, even when allowing for differences in the mother’s age and size and, as a result, some pups on a breeding colony die while others thrive. Studying the role of oxytocin, a hormone that regulates maternal behaviour, offers some insights into why such differences in individual behaviour occur,” Robinson said in a statement.

“Oxytocin has been linked to optimal maternal behaviour in humans and many captive animal species, but this is the first time such a link has been shown in completely wild animals in their natural habitat.”

Reference: Kelly J. Robinson et al. Maternal Oxytocin Is Linked to Close Mother-Infant Proximity in Grey Seals (Halichoerus grypus), PLOS ONE (2015). DOI: 10.1371/journal.pone.0144577.

Moulting elephant seal

Seals and bacteria are leaching mercury even in unpolluted waters

Researchers detected unusually high levels of toxic metals, including the dangerous neurotoxin methylmercury, in a pristine coastal area and a saltwater tidal extension. This was surprising given there were no nearby industrial sites or other runoff pollution sites. They found that the toxic substances were leached by two unexpected sources: moulting elephant seals and bacteria.

Moulting elephant seal

Photo by Frank Balthis

Typically, there are two major sources of mercury pollution in the water: either the substance is dumped directly in the water along with other chemicals by industrial processes, or the airborne mercury  – again sourced from industrial processes, only his time released as flu gas or other types of emissions – gets absorbed by the ocean.

All humans are exposed to some level of mercury. Most people are exposed to low levels of mercury, often through chronic exposure (continuous or intermittent long term contact). The inhalation of mercury vapour can produce harmful effects on the nervous, digestive and immune systems, lungs and kidneys, and may be fatal. The inorganic salts of mercury are corrosive to the skin, eyes and gastrointestinal tract, and may induce kidney toxicity if ingested. Particularly dangerous is a mercury compound called methylmercury which is neurotoxic and particularly damaging to foetuses and pregnant women.

It all starts with the elemental mercury. Like mentioned earlier, it eventually ends up in the water or soil where it’s absorbed by bacteria. The bacteria then converts the mercury into the organic form, methylmercury, through metabolic processes.  Methylmercury then bioaccumulates (bioaccumulation occurs when an organism contains higher concentrations of the substance than do the surroundings) and biomagnifies in the whole ecosystem. The bacteria might be eaten by small fish which in turn get eaten by larger predators and so on until the top animals in the food chain should see the highest concentration of methylmercury. This is why you may have heard warnings issued by the FDA or other government bodies suggesting to stay away from fish and seafood sourced from certain ‘hot spots’.

California’s Año Nuevo State Reserve coast, however, has eight times more methylmercury than any other site on the West Coast. This has perplexed researchers for a while, until they noticed an interesting pattern: the methylmercury levels were relatively the same all year long apart from a peak which coincided with the elephant seal moulting season – when the animals shed their skin. Jennifer Cossaboon of San Diego State University in California analyzed the methylmercury levels in both the water and the elephant seals’ skin. The correlation was staggering seeing how the skin contained high levels of mercury. These seals typically live half the year in open water, and another half on the coast where they barely eat anything at all. While in open waters, the seals consumed contaminated fish whose mercury accumulated in their fur.

To get an idea of how high this mercury contamination was, Cossaboon and colleagues calculated that the amount of mercury compounds leached through the fur of seals n the US and Mexico is about the same as that produced by the nearby San Francisco bay does. That’s a huge amount considering there are scores of industrial process and coal-fired plants that leach mercury into estuaries which eventually wash-up in the San Francisco bay. Fortunately, the Año Nuevo area is a marine reserve so there’s no immediate danger to public health as fishing is prohibited. It’s still startling to hear the findings, though. “I just can’t get over how high the concentrations of methylmercury in the water are,” says Amina Schartup of Harvard University. “It’s incredible. I’ve never seen anything like that.”

Schartup was part of a team of researchers who studied mercury leach off in another area – Canada’s Lake Melville, a river-fed fjord that meets the ocean. The surrounding area is far away from any source of major pollution, yet they found alarming levels of methylmercury in the waters. The likely culprit is, again, floating bacteria which process the mercury washed into the lake from the soil. This process is well known in the ocean, but never seen in an estuary. The problem is that local authorities are planning damming the river. This would cause more mercury to wash downstream to the fish that local Inuit communities depend on. It would also double methylmercury in the lake. “We’re opening the methylmercury era,” Schartup says. “We’re going to uncover more and more things that we didn’t realise were out there.”

“I think it’s important when trying to understand the global mercury cycle, that we’re really looking at the whole picture,” Cossaboon says. “It’s really interesting to see how wildlife can be exacerbating the cycle.”

It’s official – The Monk Seal is extinct


The Caribbean Monk seal (or West Indian seal) has been announced extinct on Friday. This comes as a shock (at least for me – and many others), as this is the first seal species announced extinct due to human activities; now, it will only be seen in drawings.After five years of futile efforts in which not even a single sighting has been reported, the U.S. declared extinct, and also declared that no other seal species has been extinct because of us. This probably (and sadly) opens the way for more such species to become extinct – unless something changes.

The Caribbean Monk Seal was a relatively small seal (6-9 feet) with rolls of fat around its neck and brown pelage that faded to a yellow-white color on the stomach. The last recorded sighting occurred in 1952.

Perhaps what’s even more important here is the lesson that must be learned. Humans left the population unsustainable due to overhunting. To how many other species have we done this? This will (and already is) ultimately affect us! Take just 10 seconds and think about that.