Fish: It's What's for Dinner

Sea lions are predators of oppotunity, and their diets consist of an array of fish and cephalopods.  Northern anchovy, Pacific sardine, Pacific whiting, Pacific mackerel, jack mackerel, shortbelly rockfish, and market squid are the main prey of California sea lions residing in the Pacific of Southern California. They also consume many other species but in smaller amounts. Predatory habits are affected by a variety of factors that influence the prevelance of certain fish species. Seasonal changes contribute to what California sea lions eat, as market squid for example are more heavely consumed in the fall and winter months for they are more prevalent at these times. California sea lions have also be found to hunt steelhead salmon during the salmon rush. They wait by the mouth of Lake Washington (and various other locations along the Pacific Coast) and consume large amounts of these salmon. This has become a debated issue as salmon populations lose more and more numbers.

A California sea lion has a nice salmon meal off the coast of the Pacific Northwest near the Columbia River. Recently there has been much debate among environmentalists about the toll sea lions are taking on endangered salmon populations, and in an attempt to protect the salmon 37 sea lions have even been euthanized in the last four years.   Read more here.

While sea lions are a prominant predator, there is still a "bigger fish in the sea," as well as "a bigger mammal in the sea." And while the most threatening predator to sea lions is far and away humans, sea lions must still watch their backs for great white sharks and killer whales. Their best defense against such predators is to swim quickly towards the shore and get onto land where they cannot be reached (though killer whales have been known to make their way onto sandbars and beaches to capture sea lions). Over the course of history humans have hunted sea lions for many purposes such as food, oil from the blubber, and bones to make tools and weapons. It is only recently, as sea lions numbers have been greatly reduced, that they are beginning to be protected, and in many nations killing sea lions is illegal.

An orca whale comes to the shore to prey on a sea lion.

The tables are turned as a sea lion attacks a shark in the Galapagos.

Sea lions are industrious, and opportunistic predators and will eat almost any kind of fish (as seen above). They eat when food is available, and travel to areas where food is more prevalent at certain times of the year. They are also quite adept at escaping their few predators. The predatory patterns of these animals are vast and somewhat unpredictable, and thus there is much potential for future research.

http://www.seaworld.org/animal-info/info-books/killer-whale/diet.htm
http://forums.highdefdigest.com/water-cooler/101072-sea-lions-killed-eating-too-many-salmon.html
http://www.seaworld.org/animal-info/info-books/california-sea-lion/diet.htm
http://swfsc.noaa.gov/textblock.aspx?Division=PRD&ParentMenuId=148&id=1252