How does the climate crisis affect the Antarctic fur seal?
Climate change and polar fauna: changes in the horizon

Date:
December 2, 2021
Source:
University of Barcelona
Summary:
The climate crisis is limiting the availability of krill --
small crustaceans that are vital in the marine food chain --
during summer in some areas of the Antarctica. This involves a
decrease in the food abundance for female Antarctic fur seals in
summer and a decrease in their reproductive success. Moreover,
the predation of pups by the leopard seal has also increased due
to a lower abundance of penguins, the main prey of this voracious
Antarctic predator. However, the impact of the climate crisis on
the Antarctic fur seal in winter has been ignored to date, when the
cold, wind and ice make it harder to study the Antarctic ecosystems.



FULL STORY ==========================================================================
The climate crisis is limiting the availability of krill -- small
crustaceans that are vital in the marine food chain -- during summer
in some areas of the Antarctica. This involves a decrease in the food
abundance for female Antarctic fur seals in summer and a decrease in
their reproductive success. Moreover, the predation of pups by the
leopard seal has also increased due to a lower abundance of penguins,
the main prey of this voracious Antarctic predator.

However, the impact of the climate crisis on the Antarctic fur seal in
winter has been ignored to date, when the cold, wind and ice make it
harder to study the Antarctic ecosystems.


========================================================================== Thanks to satellite tracking, we know how this marine mammal is
distributed over the winter months in the Antarctica, as well as its relationship with krill and the Antarctic icefield during this period, according to an article published in the journal Scientific Reports by
the experts Llui's Cardona, Manel Gazo, David March, Massimiliano Drago
and Diego Rita, from the Faculty of Biology and the Biodiversity Research Institute of the University of Barcelona (IRBio), and Mariluz Parga,
from the SUBMON association.

How does the Antarctic fur seal adapt to global change? The Antarctic
fur seal (Arctocephalus gazelle) -- a marine mammal that only lives in
the Southern Ocean -- was intensively exploited by the fur industry
during the first half of the 19th century. After a notable recovery,
the populations of these pinnipeds are now regressing since 2003.

This predator feeds mainly from krill -- the Antarctic crustacean Euphasia superba -- and fish. Most of their breeding colonies are close to the
Antarctic Polar Front but the South Shetland Islands -- surrounded by
the polar icefield in winter -- host the most southern population of the species and the only Antarctic one. Now, the study provides answers to
many doubts about the importance of environmental factors that regulate
the distribution of this population in winter and their link to the ice
cycle and krill.

The team conducted the research during the austral summer season of 2019
in the Antarctic research station Gabriel de Castilla, in Deception Island within the archipelago of the Southern Shetland Islands. In the study,
the scientific monitoring via satellite tracking focused on juvenile
and sub-adult males since they represent more than the 80% of the seals
that remain in Antarctic waters during winter, while females leave the Antarctica during this period.



==========================================================================
This occurs because during winter, when the breeding season is over,
females leave the Southern Shetland Islands and move to warmer areas,
near Southern Georgia islands and the South American continent. However,
males remain in the Antarctic continent.

Juvenile and sub-adult individuals are those predominating the male populations, as stated in the study. In this species, the relatively
late sexual maturity -- after seven years -- and high mortality in adults caused by the cost of defending a breeding area makes male adults to live
few years and therefore the male population is skewed towards younger individuals. Female individuals reach sexual maturity when aged three
and they undergo a lower adult mortality, so female adults are the most abundant ones.

"Males spend most of the winter time in the Antarctic Ocean, without going
to the main land, and they preferentially select areas of less than 1000
meters deep, located about 200 kilometres from the ice borders and with
high levels of chlorophyll and a surface temperature below 2-oC," notes
Llui's Cardona, lecturer at the Department of Evolutionary Biology,
Ecology and Environmental Sciences and IRBio. " This coincides with
the favourite habitat of the Antarctic krill, the main prey of these
otariids. Due to the seasonal dynamics of ice, the krill-friendly
habitat moves north during winter and so do the fur seals. As winter progresses, krill migrate deeper into the water and males dive deeper
to eat, sometimes up to 180 meters deep," continues Cardona, director
of the Antarctic research project Flexseal within the study.

Males and females: an unequal fight for food These different habitats
occupied by males and females during the austral winter could be related
to the sexual dimorphism of the species: adult females can reach 20-50 kg
and adult males 140 kg. Juvenile and sub-adult males are even bulkier than females. This difference is a major determinant of their thermoregulatory skills and diving performance when adapting a new extreme environment
and feed successfully.



==========================================================================
"An increased body mass involves more capacity to store oxygen, which
allows adult males to dive deeper when searching for food," notes Cardona.

The most important reproductive population of the Antarctic fur seal
is in the South Georgia islands, the area that has shown the greatest
abundance of krill in the summer during the last two decades. "When
this food source decreases, fur seals increase their fish intake but
the reproductive success decreases.

Therefore, the species can survive without krill but the population of
the Antarctic fur seal is less abundant, like in the Kerguelen Islands,"
says the expert.

Climate change and polar fauna: changes in the horizon The climate crisis
is altering the ecosystems of the Antarctic peninsula and the Southern
Ocean. Surviving the global change successfully involves changes in the distribution, abundance and ecology of many species in polar latitudes.

In the context of global change, fur seal males and females are exposed
to the environmental changes that affect the Antarctica during the
austral summer.

However, unlike males, females are also affected by the changes in those
areas at latitude 40-50-o in subantarctic latitudes.

In some colonies, the climate crisis causes a higher predation of pups
by the leopard seal. "To adapt to the external changes, the colonies of
the Antarctic fur seal should move south across the Antarctic peninsula,
but this is an extremely slow process," notes Cardona.

Regarding the conservation of the Antarctic fur seal, "in the future,
we will need to manage properly the krill 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," concludes the researcher.

========================================================================== Story Source: Materials provided by University_of_Barcelona. Note:
Content may be edited for style and length.


========================================================================== Related Multimedia:
* Images_of_the_Antarctic_fur_seal ========================================================================== Journal Reference:
1. David March, Massimiliano Drago, Manel Gazo, Mariluz Parga,
Diego Rita,
Luis Cardona. Winter distribution of juvenile and sub-adult male
Antarctic fur seals (Arctocephalus gazella) along the western
Antarctic Peninsula. Scientific Reports, 2021; 11 (1) DOI:
10.1038/s41598-021- 01700-w ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/12/211202113448.htm

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