Research from the National Oceanic and Atmospheric Association, National Marine Fisheries Service (NOAA Fisheries) suggests that food limitation, especially for nursing mothers, may be linked to record sea lion strandings in California. Their research is part of an ongoing effort to discover the cause of the decade-long unusual mortality event (UME) among California sea lion populations.
A UME is defined under the Marine Mammal Protection Act as “A stranding that is unexpected; involves a significant die-off of any marine mammal population; and demands immediate response.” (MMPA)
According to a study done by the NOAA National Marine Fisheries Service, there were a total of 6,000-recorded strandings of sea lion pups and yearlings along California beaches from 2015-2016. Not only are the animals coming into NOAA Stranding Network rehabilitation facilities for care dehydrated, malnourished, and emaciated, but the young sea lions also appear to be experiencing stunted growth in the early stages of their development. Scientists state that these events are likely the result of nursing mothers and newly weaned pups inability to locate and consume enough prey.
Research from the NOAA National Marine Fisheries Service now suggests a correlation between the elevated strandings and the overall conditions of the animals coming into care as the result of the decline in availability of nutrient rich foods, such as sardines. Pacific sardines have a higher calorie content than other prey such as market squid and rockfish. Without them, the California sea lion population has essentially been placed on a low calorie diet.
The NOAA National Marine Fisheries Service stated in their 2016 Sardine Assessment that the Pacific sardine population, after reaching its recent year peak in 2007, has plummeted an estimated 90% as of 2016. It’s estimated that the Pacific sardine population has dropped from around 1,037,000 metric tons in 2007, to about 86,586-metric tons in 2017. According to NOAA, this is well below the 150,000-ton threshold required for sustainable commercial fishing. Oceana states that in order to keep the current ecosystem in check, the sardine population would need to increase to around 640,000-metric tons.
Yet, what is the cause of this fish famine and who is to blame?
Overfishing is believed to be a likely culprit. In an effort to aid the recovery of the Pacific sardine population, the Pacific Fishery Management Council voted in 2016 to ban sardine fishing extending from Mexico to the Canadian border for the second year in a row. Although fishing isn’t the only problem at hand.
The dwindling Pacific sardine population is also believed to be associated with ever changing environmental conditions. A combination of abnormal climatic patterns such as changes in current and upwelling patterns have developed an unusually warm mass of water off of the west coast of North America, which University of Washington climatologist, Nick Bond, has dubbed “the blob.” As of now, “the blob” continues to linger, causing temperature sensitive fish, such as sardines, to go in search of cooler waters. As a result, sardine-spawning grounds have shifted further offshore, out of the sea lions’ feeding range, forcing them to travel vast distances for food and to find other means of nourishment.
The unusual mortality event among California sea lions is indicative of a much larger problem. Sea lions are considered to be a sentinel species, which means they’re used to evaluate the overall health of the aquatic ecosystem they call home—and things aren’t looking good.
So it’s important that we, as a global community, respond to such warning signs. If we strive to meet proper fishing and environmental regulations, we can help to ensure an abundant ecosystem and a healthy food supply for everyone that enjoys and depends on all the sea provides.
The National Oceanic and Atmospheric Administration’s National Marine Fisheries Service states that if you, or anyone you know encounters a sick or injured sea lion on the beach:
-Do not touch the animal.
-Do not allow pets to approach the animal.
-And to please observe the animal from a distance that’s both safe for you and the animal.
In addition, they encourage you to report sick or dead marine mammals to your local Stranding Network rehabilitation facility. You can learn more as well as find your local rehabilitation facility here.