Quantcast

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

Farms with just one or a handful of different crops encourage fewer species of pollinating and pest-controlling insects to linger, ultimately winnowing away crop yields, according to a new study.

Up to half of the detrimental impacts of the "landscape simplification" that monocropping entails come as a result of a diminished mix of ecosystem service-providing insects, a team of scientists reported Oct. 16 in the journal Science Advances.

Monocrop palm oil plantation Honduras.

SHARE Foundation / Flickr / CC BY-NC 2.0​

"Our study shows that biodiversity is essential to ensure the provision of ecosystem services and to maintain a high and stable agricultural production," Matteo Dainese, the study's lead author and a biologist at Eurac Research in Bolzano, Italy, said in a statement.

It stands to reason that, with declines in the sheer numbers of insects that ferry pollen from plant to plant and keep crop-eating pests under control, these services will wane as well. But until now, it hasn't been clear how monocultures affect the number and mix of these species or how crop yields might change as a result.

Aiming to solve these questions, Dainese and his colleagues pulled together data from 89 studies cutting across a variety of landscapes, from the tropics of Asia and Africa to the higher latitudes of northern Europe. They tabulated the number of pollinating and pest-controlling insects at these sites — both the absolute number of individuals and the number of species — along with an assessment of the ecosystem services the insects provided.

In almost all of the studies they looked at, the team found that a more diverse pool of these species translated into more pollination and greater pest control. They also showed that simplified landscapes supported fewer species of service-providing insects, which ultimately led to lower crop yields.

The researchers also looked at a third measure of the makeup of insect populations — what they called "evenness." In natural ecosystems, a handful of dominant species with many more individuals typically live alongside a higher number of rarer species. The team found as landscapes became less diverse, dominant species numbers dwindled and rare species gained ground. This resulting, more equitable mix led to less pollination (though it didn't end up affecting pest control).

"Our study provides strong empirical support for the potential benefits of new pathways to sustainable agriculture that aim to reconcile the protection of biodiversity and the production of food for increasing human populations," Ingolf Steffan-Dewenter, one of the study's authors and an animal ecologist at the University of Würzburg in Germany, said in the statement.

The scientists figure that the richness of pollinator species explains around a third of the harmful impacts of less diverse landscapes, while the richness of pest-controlling species accounts for about half of the same measure. In their view, the results of their research point to the need to protect biodiversity on and around crops in an uncertain future.

"Under future conditions with ongoing global change and more frequent extreme climate events, the value of farmland biodiversity ensuring resilience against environmental disturbances will become even more important," Steffan-Dewenter said.

Reposted with permission from our media associate Mongabay.

View of an Ivorian cleared forest at the edge of the 35.000 hectares Peko Mont National Park on Oct. 8, 2016. The Mont Péko National Park is located in the west of Ivory Coast where the forest officers fight with illegal immigrants to protect an exceptional flora and fauna, espacially dwarf elephants. SIA KAMBOU / AFP / Getty Images

Ivory Coast's rainforests have been decimated by cocoa production and what is left is put in peril by a new law that will remove legal protections for thousands of square miles of forests, according to The Guardian.

Read More Show Less
Sponsored
The Apusiaajik Glacier, as seen from Kulusuk village in East Greenland. Like most glaciers in Greenland, it's retreating rapidly, changing the local landscape year by year. Photo credit: Karin Kirk

By Karin Kirk

Greenland had quite the summer. It rose from peaceful obscurity to global headliner as ice melted so swiftly and massively that many were left grasping for adjectives. Then, Greenland's profile was further boosted, albeit not to its delight, when President Trump expressed interest in buying it, only to be summarily dismissed by the Danish prime minister.

During that time I happened to be in East Greenland, both as an observer of the stark effects of climate change and as a witness to local dialogue about presidential real estate aspirations, polar bear migrations and Greenland's sudden emergence as a trending topic.

Read More Show Less

Heavy metals that may damage a developing brain are present in 95 percent of baby foods on the market. Cirou Frederic / PhotoAlto Agency RF Collections / Getty Images

Heavy metals that may damage a developing brain are present in 95 percent of baby foods on the market, according to new research from the advocacy organization Healthy Babies Bright Futures (HBBF), which bills itself as an alliance of scientists, nonprofit organizations and donors trying to reduce exposures to neurotoxic chemicals during the first three years of development.

Read More Show Less
Chicago skyline on July 22 as high winds continue to push the waters of Lake Michigan over the top of the pedestrian and bike trail along the lakefront in Chicago. Raymond Boyd / Michael Ochs Archives / Getty Images

By Daniel Macfarlane

Every fall, I take my environmental studies class camping at Sleeping Bear Dunes National Lakeshore on Lake Michigan. Some years the beach extends more than three meters to the water. This year, in many spots, there was no beach at all.

Read More Show Less
Sponsored
Insects like bees, butterflies and even certain species of beetle and ant incidentally pollinate our crops when they collect protein-rich pollen and sugary nectar. Rolf Dietrich Brecher / CC BY 2.0

By Kerstin Palme

Creepy-crawlies are among the oldest life forms on this planet. Before dinosaurs ever walked the earth, insects were certainly already there. Some estimates date their origins to 400 million years ago. They're also extremely successful. Of the 7 to 8 million species documented on Earth, around three quarters are likely bugs.

But several insect species could disappear for good in the next few decades and that would have serious consequences for humans.

Read More Show Less
Swedish automaker Volvo unveils its first electric vehicle the XC40 Recgarge EV, during an event in Los Angeles on Oct. 16. Frederic J. BROWN / AFP / Getty Images

Volvo introduced its first-ever all-electric vehicle this week, kicking off an ambitious plan to slash emissions and phase out solely gas-powered vehicles starting this year.

Read More Show Less
Cars are queued in Turin, Italy in August. Particulate matter levels were the highest in Italy, Poland and the Balkans countries. Nicolò Campo / LightRocket / Getty Images

Air pollution in Europe led to more than 400,000 early deaths in 2016, according to the most recent air quality report published by the European Environment Agency (EEA).

The report, released Wednesday, found that almost every European who lives in a city is exposed to unhealthy air, Reuters reported.

Read More Show Less