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The Montebello

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Dosidicus gigas (Humboldt, or jumbo squid) is endemic to the California and Peru currents and their equatorial convergence. (See Figure 1A, p. 21.) Within this zone, the biomass of Dosidicus is immense. High abundance, an extremely flexible diet and high daily consumption rate combine to make the species an ecologically important predator.

Dosidicus gigas in hunting mode (photo Kim Fulton-Bennett/MBARI)

Monterey Bay witnessed Dosidicus in 2002, when a warm-water anomaly off southern Baja California was followed by a wave of mass strandings that swept northward from La Jolla to Mendocino. Local strandings were modest, but 2003 brought another wave and more media attention. Yet such events were not new: Monterey strandings were reported as early as 1912, and a similar northward wave occurred in 1934-1935, with the ravenous squid disturbing Monterey commercial and sport fishermen. In January 1936, Ed Ricketts purchased 400 pounds of Dosidicus caught by a purse seiner in southern Monterey Bay for Pacific Biological Laboratories. (See photo.)

Causes of these invasions and associated strandings are unknown. During strandings, squid typically swim actively onto the beach, suggesting some neurological defect. In 2003, I hypothesized intoxication by domoic acid, a toxin produced in harmful algal blooms that causes abnormal behavior and brain lesions in sea lions. Carl Elliger at Hopkins Marine Station and I have now analyzed stomach contents of beached Dosidicus from La Jolla and Monterey, and although the guts contained organisms known to harbor domoic acid (anchovies, sardines, pelagic red crabs), we detected no toxin.

Figure 1. Distribution and recent range extensions of Dosidicus gigas. A. Distribution of Dosidicus as given in a 1984 FAO report is shown as shaded. B. Detail of Pacific Northwest from panel A showing approximate areas and dates of recent northward range expansions

In reality, the number of squid stranded is probably a minute fraction of the invading horde, and factors behind the invasions may be key to understanding the strandings. Because Dosidicus is large (up to 40 kilograms) and locally abundant, an area must be highly productive to support a stable population. One such area may be the Monterey canyon system, where Dosidicus has been regularly seen during ROV operations by the Monterey Bay Aquarium Research Institute (MBARI) since 1998, according to MBARI scientists Bruce Robison and Louis Zeidberg. It now appears to be a year-round resident. Another area of permanent residence, at least since the 1970s, is the Guaymas Basin in the Sea of Cortez, where Dosidicus circulates seasonally between feeding grounds off Baja California Sur and Sonora. Why these particular areas were apparently successfully colonized at these particular times remains mysterious.

Edward F. Ricketts of Pacific Biological Laboratories in Monterey (1936) with an apparently preserved specimen of Dosidicus gigas (Photo by Ralph Buchsbaum, courtesy of John and Vicky Pearse)

Few areas may be rich enough to satisfy the appetite of this species, and ephemeral appearances and strandings of Humboldt squid elsewhere may reflect this. As depicted in Figure 1B, Dosidicus appeared in 2004 from Oregon to British Columbia following a warm-water anomaly off that coast (See www.thecephalopodpage.org/Dosidicusgigas.html.) In 2005, the range expanded further, past the Queen Charlotte Islands to Sitka, Alaska. How long Dosidicus remains in this northern area remains to be seen, but the reason it is there revolves around productivity. Temperature per se is not likely to be a critical factor, because (unpublished) electronic tagging studies with Mexican colleagues in the Sea of Cortez reveal that the squid tolerates large temperature swings as part of its daily vertical migrations.

Molecular genetic analysis by Carl Elliger and Zora Lebaric in my lab indicates that many Pacific Northwest Dosidicus are indistinguishable from specimens captured as far away as Chile. This suggests that Dosidicus is highly nomadic -- an amoeboid species that sends invading fingers into any area where productivity is high, regardless of the cause. If productivity persists, the squid remain and flourish. If the productivity burst is transient, the invading squid cannot be sustained. They must either depart or starve; perhaps some of these latter animals end up in strandings.

In order to understand the waxing and waning of Dosidicus on a global scale, we may paradoxically have to study individual animals. Electronic tagging of adults is being used to monitor long-distance migrations. Thus far, we have recorded migrations of up to 100 miles in three days, so sizeable migrations are possible. We are also locating spawning grounds by identifying hatchlings in plankton samples. One such area lies in the Sea of Cortez, but others remain undiscovered.

In 1945, Ed Ricketts wrote in unpublished notes:
"If you know the natural history,Éespecially the complete life history of the beasts chiefly involved, you can... understand just how and even why it occurs in a certain place at a given period..." (provided by K.A. Rodger, UC Davis). Old truths still have much to teach us.

William F. Gilly
Hopkins Marine Station of Stanford University