Quantcast
Environmental News for a Healthier Planet and Life

Scientists Find Answer to Why Thousands of Sea Lion Pups Are Starving

Animals

Scientists finally have an explanation for why so many starving sea lions have been stranded along Southern California's coast in recent years. Their mothers are not getting enough nutritious food.


Last year, more than 3,000 sea lions were found stranded on Southern California beaches, a number higher than the previous five years combined. As of last week, there have been at least 375 sea lion strandings in 2016. Photo credit: NOAA Fisheries West Coast/Flickr

High-fat, high-calorie fish species—namely sardines and anchovies—that female sea lions prefer to feed on have become less abundant where the sea lions commonly hunt near the Channel Islands, National Oceanic and Atmospheric Administration (NOAA) researchers reported Tuesday in the journal Royal Society Open Science.

Instead, female sea lions have had to settle for less nourishing food sources, such as rockfish and market squid. According to the scientists, 81 percent of the change in sea lion pup weights between 2004 and 2013 could be attributed to the decline in sardines and anchovies.

California Sea Lion Pup and Yearling Strandings for California, Jan-May 2004-2015. For the 5 month period of January – May 2015, California sea lion strandings were over 10 times the average stranding level for the same 5 month period, during 2004 – 2012. Credit: NOAA

And while the researchers knew that anchovies and sardines become scarce in El Niño years, they wondered whether the effects were limited to only El Niño years.

The Los Angeles Times reported:

To find out, they needed to know where pregnant and nursing sea lions liked to hunt. They estimated a likely foraging range based on the movements of six female sea lions from San Miguel Island that were tagged by researchers in the 1990s. The data from those tags showed they liked to hunt off the California coast between Big Sur and Malibu.

Next they had to figure out what kinds of fish were available in those waters. For more than 30 years, researchers from NOAA's Southwest Fisheries Science Center have been taking a census of young rockfish and other fish species in central California. Data for the area they needed was available from 2004 to 2014.

Finally, they looked up the average weight of 14-week-old sea lion pups from San Miguel Island for each year between 2004 and 2011. During that period, the average weight ranged from 14.8 kilograms to 20.9 kg for female pups and from 17.5 kg to 23.6 kg for male pups.

The pattern they found was clear: When sardines and anchovies were abundant and rockfish and squid were scarce, sea lion pups weighed more. Conversely, when rockfish and squid were plentiful and sardines and anchovies were not, sea lion pups weighed less.

The scientists said they couldn't study “composition or quantity of mothers' milk," and therefore, couldn't make a direct link between the types of fish in the sea and the nutritional value of their milk. However, they said their results "offer compelling evidence" that the sea lion pups are starving because their mothers can't produce adequate amounts of milk.

"Our results refocus the debate on the causes of sea lion pup weight loss from episodic stresses associated with El Niño years to a longer-term trend of declining forage quality in the waters around the California Channel Island rookeries," the scientists concluded.

And the trend is likely to continue. "We expect repeated years with malnourished and starving sea lion pups," they said.

Last year, more than 3,000 sea lions were found stranded on Southern California beaches, a number higher than the previous five years combined. As of last week, there have been at least 375 sea lion strandings in 2016. That's above the average of 160 for the first two months of a typical year, according to NOAA data.

Marine conservation groups, such as Oceana, criticized NOAA for not recognizing the role overfishing has played in causing the sea lion crisis.

EcoWatch Daily Newsletter

Deserted view of NH24 near Akshardham Temple on day nine of the 21-day nationwide lockdown to curb the spread of coronavirus on April 2, 2020 in New Delhi, India. Raj K Raj / Hindustan Times via Getty Images

India is home to 21 of the world's 30 most polluted cities, but recently air pollution levels have started to drop dramatically as the second-most populated nation endures the second week of a 21-day lockdown amidst coronavirus fears, according to The Weather Channel.

Read More Show Less
A Unicef social mobilizer uses a speaker as she carries out public health awareness to prevent the spread and detect the symptoms of the COVID-19 coronavirus by UNICEF at Mangateen IDP camp in Juba, South Sudan on April 2. ALEX MCBRIDE / AFP / Getty Images

By Eddie Ndopu

  • South Africa is ground zero for the coronavirus pandemic in Africa.
  • Its townships are typical of high-density neighbourhoods across the continent where self-isolation will be extremely challenging.
  • The failure to eradicate extreme poverty is a threat beyond the countries in question.
Read More Show Less
Sponsored
The outside of the Food and Drug Administration headquarters in White Oak, Md. on Nov. 9, 2015. Al Drago / CQ Roll Call

The U.S. Food and Drug Administration has approved the use of two malarial drugs to treat and prevent COVID-19, the respiratory infection caused by the SARS-CoV-2 coronavirus, despite only anecdotal evidence that either is proven effective in treating or slowing the progression of the disease in seriously ill patients.

Read More Show Less
Some speculate that the dissemination of the Antarctic beeches or Nothofagus moorei (seen above in Australia) dates to the time when Antarctica, Australia and South America were connected. Auscape / Universal Images Group / Getty Images

A team of scientists drilled into the ground near the South Pole to discover forest and fossils from the Cretaceous nearly 90 million years ago, which is the time when dinosaurs roamed the Earth, as the BBC reported.

Read More Show Less
The recovery of elephant seals is one of the "signs of hope" that scientists say show the oceans can recover swiftly if we let them. NOAA / CC BY 2.0

The challenges facing the world's oceans are well known: plastic pollution could crowd out fish by 2050, and the climate crisis could wipe out coral reefs by 2100.

Read More Show Less