Did Trucks Prompt the Salmon Resurgence?

Biological data suggest that a program to truck salmon around the delta is behind the current salmon comeback.

As many as 92 percent of non-trucked, hatchery salmon die in the delta. Credits: Wikimedia Commons

The ocean salmon fishing season is set to open on April 2 and fishery managers estimate that coastal waters currently boast more salmon than at any time in the past five years. Indeed, it appears that the severe drop in the Chinook salmon population in recent seasons has reversed. But the question is why? Is it more rain and snow in the Sierra, resulting in more freshwater in the Sacramento-San Joaquin River Delta? Or, is it more food for salmon in the Pacific Ocean?

Actually, some scientific data indicate that the salmon resurgence is artificial and has nothing to do with the health of the delta or the ocean. In fact, data from a program that tags young salmon and recaptures them suggest that an elaborate system that trucks salmon from Central Valley fish hatcheries and deposits them into San Pablo Bay is primarily responsible for the salmon recovery. Some experts believe that without this artificial life-support system, the salmon in the Sacramento River might all but vanish. That’s because the trucking system enables fish to bypass the delta and avoid the deadly pumps that send water to the San Joaquin Valley and Southern California.

Biologists with the California Department of Fish and Game and the US Fish and Wildlife Service found that tagged salmon, or smolts, born in hatcheries, loaded into tanks, and transported to release sites near the Carquinez Strait are several times more likely to appear as adults in catch surveys than those that are left to travel unassisted downstream, through the delta, and out to sea. Experts suspect that non-trucked salmon are dying in the delta, where pumping facilities create hazards for small fish, either killing them directly or drawing them into sloughs and backwaters, where predators await.

Information collected by the National Marine Fisheries Service has shown that as many as 92 percent of young, non-trucked salmon die in the delta. “Getting the fish around the delta is critical,” explained Roger Thomas, captain of the Salty Lady, a party fishing boat in Sausalito, and a board member of the Golden Gate Salmon Association. “Until we improve the health of the (river’s) ecosystem, we’ll have to keep trucking the fish.”

The revelations about salmon survival rates come from a joint effort by state and federal fishery managers to tag a portion of the 30 million fish they produce annually in Central Valley hatcheries and observe their rates of survival into adulthood. To make the young fish identifiable as adults, hatchery managers clip the salmon’s fleshy dorsal lobe, called the adipose fin, from 25 percent of smolts prior to release. The same fish are fitted with nearly-microscopic “coded wire tags” imprinted with numeric data. Last year, 121 of these fin-clipped salmon — caught as adults — were reported by sport fishermen on boats out of Sausalito. Fish and Game biologists who removed and analyzed the coded wire tags from the 121 fish found that 81 — or 66 percent — had been trucked around the delta and released into San Pablo Bay.

In addition, coded wire tags turned over by commercial ocean fishermen that same summer showed that fish born in 2008 at the Coleman National Fish Hatchery on the Sacramento River and trucked to San Pablo Bay were seven times more likely to reach adulthood than fish from the same hatchery that were released into the river. Wild salmon must also navigate their way to the sea unassisted and presumably face the same threats as the non-trucked hatchery fish in the delta region.

Fishery data also suggest that the recent collapse of the salmon fishery may have been due in part to a suspension of the salmon-trucking system in 2005 and 2006, an interruption caused by state budget constraints. Adult salmon populations crashed in the following years. The program has resumed in force, and salmon numbers appear to be climbing. Biologists estimate that 1.1 million adult fish are currently off the California coast — about three times the estimated ocean population of last spring.

However, some experts blame other factors for the salmon collapse and recovery. Two panels of government biologists appointed by the Pacific Fishery Management Council, or P-Council, proposed in a recent report that the salmon collapse over the past few years was due to food shortages in the Pacific Ocean in 2005 and 2006 caused by a lack of upwelling of nutrient-packed waters from the ocean floor.

Still, other experts, including a coauthor of the report, Chuck Tracy, a P-Council salmon staff officer, believes excessive water diversions from the delta played a major role in the collapse of the fall-run salmon population. The run hit rock bottom in the fall of 2009, when 39,000 spawning adults returned to the Sacramento River — down from 800,000 in 2002. In an interview, Tracy said high delta pumping levels in the spring of 2007 combined with half or less the rainfall of normal years to create “a ratio of pumping to water in the river that was much higher than usual.”

The conflicting data and opinions have left some fishery experts unsure as to the impact of the trucking program. For example, Melodie Palmer-Zwahlen, a biologist with Fish and Game’s Ocean Salmon Project who is currently analyzing data from the coded wire tags collected last summer by Bay Area ocean sport fishermen, remains undecided as to what is driving the rise and fall of salmon numbers. “Is something happening to these salmon in the river,” she asked, “or is something happening at sea?”

But Dick Pool, president of the Concord-based fish conservation group Water4Fish, feels certain that the key problems dwell in the delta. “The ocean conditions did zap a lot of the fish in 2005 and 2006, but since then we’ve had excellent ocean conditions, but the fall run collapsed into a disaster zone,” said Pool. He believes the delta environment remains as devastated as ever and that the salmon population could easily crash again. “Without that trucking program,” he said, “we might have no ocean fishery.”