Food limitation may be linked to a record sea lion pup stranding in California. As large numbers of the creatures flood local animal rescue centers, researchers are looking at why this phenomenon is currently occurring.
Booming sea lion numbers combined with declines in the highest-calorie prey around the Channel Islands breeding rookeries have left nursing females struggling to support their pups. This, mostly likely, is the cause of the massive amount of strandings that are occurring.
In this latest effort, researchers analyzed changes in fish populations that sea lions hunt as prey. They examined changes in the abundance of four main prey species - sardines, anchovies, rockfish and market squid - from 2004 to 2014. In the end, the scientists found that high-calorie sardines and anchovies have declined since the mid-2000s in the areas around the Channel Islands where female sea lions forage. This, in turn, has forced them to prey on market squid and rockfish, which contain less fat and fewer calories.
"When you have hundreds of thousands of animals to feed and you have a fluctuating prey base that has trended downward, you are going to have starving animals," said Sam McClatchie, lead author of the new research. "Sardines and anchovies have both trended downward, and that compounds the problem for the sea lions."
The close correlation between the fish available and the weight of sea lion pups indicates that the type of fish available drastically impacts a mother's milk and, thus, how well sea lion pups are able to survive. This actually builds on other studies that showed pup weights decrease during El Niño events and when the female diet is predominantly squid and rockfish.
"The overall driver appears to be the natural fluctuations in fish populations," said McClatchie. "They do fluctuate up and down over time and, since 2004, they're doing it in phase."
The findings reveal that the amount of fish prey available and the type of fish prey available drastically impacts the survival of sea lion pups. This is especially important to keep in mind when viewing it through the lens of climate change.
