During late spring and summer a fish species enters our waters that always makes me think of the Los Angeles music group "Jack Mack and the Heart Attack." Of course I'm referring to the baitfish known as jack mackerel which are especially abundant in the Dive Park as I write this. No, I don't associate the fish with a heart attack- seeing them actually produces a calm sensation due to the beauty of their schools as they move. Well, occasionally I do think of the fact that larger predators including sharks do feast on them, and if the water is murky...

Jack mackerel form very large schools of tens of thousands of individuals or more. They are incredible to watch as the schools sinuously weave through the water along the outer edge of the kelp forest and in open water, or quickly scatter when a predator nears. Individual fish are very streamlined in shape with a bluish or greenish color on top and silvery undersides. A key feature in identifying them is the black spot on the upper gill cover.

These baitfish are known from the Gulf of Alaska to the tip of Baja and may be found more than 1,000 miles offshore. The younger ones frequent inshore waters and it is these fish that form the large schools that we see here in the nearshore waters. They are most common off southern and Baja California. Larger (about 2 ft.) and older (15-30 years) fish are more common either singly or in small groups farther offshore and often in deeper water to depths in excess of 1,000 ft. They are more common throughout the species' range.

This is a fast growing species with the young reaching about 8" in length after their first year when they become sexually mature. Spawning occurs through most of the year with the larger fish spawning first and the smaller, nearshore fish following later in the summer. Females release their eggs into the water column where they drift as plankton while developing into larvae. Although dependent on the water temperature, the eggs usually hatch in 3-5 days.

Jack mackerel are at the lower end of the mutual eating society (or food chain). They feed mainly on plankton including copepods and other crustaceans, juvenile squid and small fishes. Being low on the food chain, they have a wide range of predators. These include dolphins and porpoises, sea lions, black sea bass, blue and soupfin sharks, albacore and cormorants. In short, they get hit from all sides. That's what it's like being the "cattle of the sea." Someone has to provide the buffet for the rest of the ecosystem. After all, we can't all be herbivores!

Jack mackerel became an important commercial species in 1947 when the Pacific sardine industry collapsed (as predicted by my hero, "Doc" Ricketts on Cannery Row). The primary target is the large inshore schools of smaller fish. Interestingly, I see jack mackerel schools occasionally intermingle or swim alongside Pacific sardines in the Dive Park. Perhaps the sardines are grateful for the protection given them by jack mackerel.

Originally this species' common name was "horse mackerel," but commercial fishermen decided it wasn't an appealing name for food so it was officially changed to jack mackerel in 1948. There are other examples of fish with unpalatable names undergoing a taxonomic transformation in order to make them more sellable in markets. Eating jack mackerel can cause scombroid poisoning if the flesh is improperly stored. This is due to chemicals produced by bacteria in the flesh which can cause nausea, vomiting and diarrhea. Of course almost any food I cook could produce the same result!

© 2004 Dr. Bill Bushing. Watch the "Dive Dry with Dr. Bill" underwater videos on Catalina Cable TV channel 49, 10:00 AM and 5:00 PM weekdays.

Close up of jack mackerel showing black spot on gill cover;
schools of jack mackerel in Catalina's Dive Park

This document maintained by Dr. Bill Bushing.
Material © 2004 Star Thrower Educational Multimedia