Mexico's Sea of Cortez as "Fish Trap" Logo
Mexico's Sea of Cortez as "Fish Trap"


Photo of Jim Mori with a Monterey Spanish Mackerel caught in the Sea of Cortez, Mexico.

"TRAPPED" IN MEXICO'S SEA OF CORTEZ--Jim Mori with a "trapped" Monterey Spanish Mackerel (Scomberomorus concolor) caught at San Lucas Cove, on the Sea of Cortez just south of Santa Rosalia, Baja California Sur, Mexico. This area is the southern limit for other "trapped" species, such as spotted bay bass, which are not usually caught south of about Punta Chivato. Other "trapped" species in the northern Sea of Cortez include white seabass, sheephead, grunion, ocean whitefish, and others.


By Gene Kira, April 7, 2003, as published in Western Outdoor News:

One of the most oft-quoted anecdotes about Mexico's Sea of Cortez--the semi-enclosed sea between Baja California and the Mexican mainland--is that it's the "world's greatest fish trap."

But nowhere have I been able to discover who coined those brilliant words, or find out exactly what "the world's greatest fish trap" actually means.

Of course, we think we know what it's supposed to mean: the cul-de-sac shape of the Sea of Cortez causes fish to get stuck there as they wander around in the otherwise open Pacific.

This idea was described by Jerry Klink in his 1974 Mexico sportfishing book The Mighty Cortez Fish Trap: "Migratory fish, working north along the coastal water of South America and the Mexican mainland are led into the Sea; here they find abundant food and remain to roam its shores."

But old Jerry also admitted that his book's catchy title might have stretched things a wee bit: "This is partly true...most of the population spawn, live, and die within its confines."

And Jerry never claimed to have invented the phrase anyway, saying that the Cortez had already "been called the largest fish trap in the world," presumably by someone other than himself.

Even Mexico sportfishing writer Ray Cannon in his 1966 classic book, The Sea of Cortez, made it clear that he didn't come up with what he considered a questionable idea: "Some writers have called the Cortez the world's greatest fish trap, and claimed that the fish lost and piled into it. Logic suggests that in a few million years the fish would have learned better." Cannon went on to state that it is the Cortez' rich food supply, not its enclosed shape, that causes it to have so many fish.

But regardless of who invented "Cortez fish trap," last week's historic albacore catch at East Cape, Baja California Sur, Mexico suggests an interesting alternative use for the phrase.

What if the water of the southern Sea of Cortez were to cool off temporarily? Is it conceivable that the albacore presently at East Cape might then make their way up to the cool Midriff Area and establish themselves there?

If that happened, and subsequently the water south of the Midriff returned to normal temperatures, we would then have a "trapped" albacore population in the central Cortez. These fish might live happily in the cool Midriff, but they would not be able to escape because of the warm water barrier south of them.

This would not be a unique situation. There are plenty of other "trapped" species in the northern Cortez. These are the same fish as found in similar latitudes of the Pacific Ocean, but the two populations are kept separated by the warm water barrier of the lower Cortez.

An impromptu list of these "trapped" fishes provided by San Lucas Cove angler Jim Mori includes: white seabass, yellowfin and spotfin croaker, halibut, grunion, spotted bay bass, corbina, ocean whitefish, sheephead, and the rare gulf or Monterey sierra (Scomberomorus concolor).

All of these species are found in the Pacific, of course. They are also found in the northern Sea of Cortez, but not in its south end. They are "trapped," and the cut-off line is centered around Santa Rosalia.

The fascinating question is, "How did these fish become trapped?" One anecdotal explanation is that when Baja split off from the mainland, millions of years ago, there was a "water bridge" connecting the Cortez and Pacific at the north end, and these cool-water fish came in that way.

However, a much easier explanation would be that during particularly cool periods, such as the last Ice Age ending about 11,000 years ago, the fish simply swam up the Cortez.

All that would be necessary for this to happen would be a water temperature drop of perhaps half-a-dozen degrees. No big deal for an Ice Age, or even a La Niña (opposite of an El Niño). Albacore at Bahia de los Angeles? Why not?

(Related Mexico articles and reports may be found at's main Mexico information page. See weekly fishing news, photos, and reports from the major sportfishing vacation areas of Mexico including the Mexico area in "Mexico Fishing News.")