The fur seal is a marine mammal that only lives in the Southern Ocean. Credit: Llus Cardona.
The climate crisis is limiting the availability of krill, a small crustacean that is vital in the marine food chain. This involves a decrease in the food abundance for female seals in the summer and a decrease in their reproductive success. The leopard seal's prey has increased due to a lower number of penguins. The impact of the climate crisis on the fur seal in winter has been ignored.
The experts Llus Cardona, Manel, published an article in the journal Scientific Reports about the distribution of this marine mammal in the winter in the icefield of the South Pole.
How does the fur seal adapt to global change?
During the first half of the 19th century, the fur industry exploited theAntarctic fur seal. The populations of these pinnipeds have been declining since 2003 after a notable recovery.
The predator feeds on fish and crustaceans. Most of the colonies are close to the polar front, but the South Shetland Islands are the only place in the world where the species is found. The study provides answers to many doubts about the importance of environmental factors that regulate the distribution of this population in winter.
During the summer season of the year in the Southern Shetland Islands, the team conducted their research in the Gabriel de Castilla research station. The study focused on juvenile and sub-adult males since they represent more than 80% of the seals that remain in the water during the winter.
Females leave the Southern Shetland Islands during the winter to go to warmer areas near Southern Georgia islands and the South American continent. Men remain in the Antarctic continent.
The study states that juvenile and sub-adult individuals are predominating the male populations. The male population is skewed towards younger individuals due to the late sexual maturity and high mortality in adults caused by the cost of defending a breeding area. Female adults are the most abundant because they reach sexual maturity when they are three years old.
Males spend most of the winter time in the ocean, without going to the mainland, and they preferentially select areas of less than 1000 meters deep, located about 200 kilometers from the ice borders and with high levels of chlorophyll and a surface temperature below 2o C.
The main prey of these otariids are the krill. The fur seals move north during winter due to the seasonal dynamics of ice. As winter progresses, males dive deeper into the water to eat, sometimes up to 180 meters deep, according to Cardona.
We know how this marine mammal is distributed in the winter in the Antarctica thanks to satellite tracking. Credit: Llus Cardona.
The males and females fight for food.
The sexual dimorphism of the species could be related to the different habitats occupied by males and females during the austral winter. The males are bulkier than the females. The difference between thermoregulatory skills and diving performance when adapting to a new extreme environment is a major determinant of their diving performance.
"An increased body mass allows adult males to dive deeper when searching for food, because they have more capacity to store oxygen," says Cardona.
The South Georgia islands have shown the greatest amount of krill in the summer over the last two decades. Fur seals increase their fish intake when the food source decreases. The population of the fur seal in the Kerguelen Islands is less abundant than the one in the Antarctic.
Climate change and polar fauna are changing.
The climate crisis is changing the environment. Changes in the distribution, abundance and ecology of many species in polar latitudes are necessary for surviving the global change.
Fur seal males and females are exposed to the environmental changes that affect the Antarctica during the austral summer. Females are also affected by the changes in those areas at latitude 40-50o in subantarctic latitudes.
The climate crisis can cause a higher level of leopard seal attacks on pups. The colonies of the fur seal should move south across the peninsula to adapt to the external changes, but this is an extremely slow process.
In the future, we will need to manage properly the fishing activities in these areas, and this will require to consider not only the female consumption during summer but also the consumption associated with males of all ages during the four seasons of the year."
The distribution of juvenile and sub-adult male fur seals along the western Antarctic Peninsula was reported in the Scientific Reports. There is a DOI titled: 10.1038/s41598-021-01700-w.
Scientific reports are in the journal.
The climate crisis affects the Antarctic fur seal.
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