A decline in California’s anchovy and sardine levels is likely responsible for a growing population of malnourished or starving sea lion pups, whose pregnant or nursing mothers are not able to find the fish that promote growth in their babies.
The loss of higher trophic-level species, such as sea lions, from the ecosystem, is dangerous “as their removal can have dramatic consequences on entire food webs,” according to the National Oceanic and Atmospheric Administration. Though sea lions are sometimes simplistically viewed as competitors to fisheries because their prey includes commercially viable species like salmon, rockfish, herring, and squid, the decline of sea lions actually highlights the plights of overfishing and water pollution by humans. Healthy sea lion populations, conversely, are a sign of sustainable fishing practices.
According to a new report published by the NOAA, California’s sardine and anchovy biomasses have decreased substantially in the last decade, while less healthful options like squid and rockfish have been abundantly available.
Sardines and anchovies contain more calories and have a higher fat content than squid and rockfish, which makes them critical to the healthy growth and development of sea lion pups. In observing the sea lion population of the San Miguel rookery, researchers found that the weight of sea lion pups fell when sardines and anchovies levels were low and squid and rockfish levels were high.
Over the next several years, generations of baby sea lions are expected to malnourished and have high rates of early mortality as the levels of their preferred foods drop and become more difficult to forage.