Published: February 23, 2018

By Mark Seth Lender

A group of sea lions sunbathe on their favorite rock. (Photo: Mark Seth Lender)

Living on Earth's explorer-in-residence Mark Seth Lender writes on the impact of a changing climate and warming seas on California sea lions.

The sea lions of this story live in an inaccessible cove below the Pacific Coast Highway. The last time I was there, more inaccessible than ever. The road had washed out in four places, the result of major floods. It took eight months to make repairs. The floods themselves are climate-driven, part of the chaos of our time. One would like to think the end product – inaccessibility - creates greater not lesser security for these sea lions: It doesn’t.

As of 2018, the California sea lion population is burgeoning – now at or near carrying capacity. It is a huge change from only a decade earlier when they were starving all up and down the California coast. When the Pacific warms, it drives the fish sea lions eat (sardines in particular) deeper in the water column. Adult sea lions are capable of deep dives and females in particular are known to make descents of up to 400 meters. But deep dives are costly in both energy and time and there is a limit on how long even the strongest and most experienced among them can hold their breath. Juvenile sea lions are not strong enough nor do they have the lungs to dive anywhere near as deep as the adults. Another compensating strategy is to travel out from shore to where the water is cooler and the fish school at more shallow depth. But again, this is beyond the capacity of the juveniles.

In between El Niños, the water is cooler and sea lions thrive. But overall, year on year, the oceans of the world are heating up.

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