Mysterious gathering of giant sturgeon a boon for Bay Area anglers

These are bizarre but productive times for anglers who ply San Francisco Bay waters in the hope that a monstrous, prehistoric-looking white sturgeon will pick up their bait.

That’s because these typically elusive bottom-feeding behemoths, which have been known to measure nearly 20 feet long and weigh in excess of 1,500 pounds, have gathered en masse within San Pablo Bay, a vast tidal estuary north of the main bay.

The congregation has perplexed scientists, who are associating the phenomenon with above-normal rainfall and runoff, but are unable to state precisely why so many of these mysterious fish — the largest freshwater fish in North America — have gotten together in one location.

The Marin Independent Journal, quoting biologists, reports that in heavy rainfall years sturgeon typically travel much farther inland, beyond the Sacramento-San Joaquin River Delta into the Sacramento River, for a spawning season that occurs between December and June. That’s where scientists would have expected most large sturgeon to be now.

One biologist, Michael Thomas of the University of California at Davis, said it was possible that abundant rainfall triggered an early spawn and that “what we’re seeing is a large congregation of post-spawn fish in San Pablo Bay.”

Keith Fraser, a veteran angler and owner of San Rafael bait shop, believes all the rain “pushed” the sturgeon downriver.

Whatever the reason, fishermen venturing into San Pablo Bay are enjoying the best season for sturgeon in recent history.

Commenting to the Marin newspaper, fisherman Rico Petri said that 10 of the sturgeon he has caught and released recently measured longer than the 5.5-foot maximum size limit and one was 7.5 feet long. Reports of 8- or 9-foot-long sturgeon have been commonplace and a specimen landed and released in late March measured 12 feet.

(By state law, anglers can only keep sturgeon measuring between 46-66 inches, in order to protect the larger fish.)

White sturgeon, which can live to be 100 years old, inhabit estuary waters along the West Coast, mostly from Central California to the north. Fishing regulations are strict in the hope of enabling the species to recover from decades of relentless overfishing, degradation of habitat caused by the construction of dams, and agricultural runoff.

In California, the official state record is a 468-pounder landed near Benicia in Delta waters in 1983, 10 years before a maximum size limit was put in place. That’s also listed as an all-tackle world record by the International Game Fish Assn.

The Marin newspaper reports, however, that the unofficial state record might be a 1,500-pound, 16-foot sturgeon that was hauled from the Sacramento River in the 1880s by horses, after it had been enticed to bite on a rabbit placed on a meat hook.

— Photo: San Rafael angler Sean Daugherty displays 76-inch sturgeon caught and released recently just outside San Pablo Bay. Image is courtesy of Sean Daugherty