Irrigation Districts Can’t See Past Killing Bass to Save Salmon

Many San Joaquin Valley irrigation districts can’t get past the refrain on the broken record that controlling striped bass and black bass will save salmon and steelhead. They’ll do anything to avoid releasing more water from reservoirs; in many cases, killing bass is held up as the miracle cure that will allow them to release even less.

In an April 9, 2016 article in the Modesto Bee,[1] striped bass are cast as the prime villain, joining a chorus led by several members of Congress who represent the San Joaquin Valley.  This is in part because striped bass have state and federal legal protections, and in part because photos of captured stripers disgorging baby salmon are particularly dramatic.

The article quotes Doug Demko, President of the Fishbio consulting firm, and unabashedly states that Mr. Demko’s firm “has worked with districts seeking a way around … increased flow demands.”  The article attributes to Mr. Demko the assertion that [his] 2012 study showed a 96 percent loss of juvenile salmon in the Tuolumne River downstream of Waterford to predation.

Review of the study shows that the estimate of loss is based on the recovery of a grand total of 46 juvenile salmon (21 in March and 23 in May) from the stomachs of smallmouth bass, largemouth bass and striped bass.  Most of the bass captured during the study had no salmon in them at all.[2]  At flows of 2100 cubic feet per second (cfs), the survival of juvenile salmon was almost three times higher that it was at flows of 400 cfs.[3]  In a poster describing the results of the study, Fishbio attributed to stripers a “potential” impact of only 14.7% of overall predation by bass in the Tuolumne.[4]  One should be careful about the “potential” however, because the poster also extrapolates the 46 juvenile salmon actually recovered to a “potential” predation impact of 42,000 in the river.  There are so many assumptions, including the assumption that salmon’s migration rates in the river are constant: they are not.

Water releases from reservoirs on the Merced, Tuolumne and Stanislaus rivers were originally part of the agreements that allowed the dams and infrastructure to be built and the associated water rights to be approved.  They have been extremely ineffective in the San Joaquin basin.  Dam releases are inadequate to maintain spawning, rearing, and migration habitat degraded by dams and water storage.  They are also inadequate to protect water quality and the aquatic habitats of the San Joaquin River, Delta, and Bay.

Required flow pulses from the San Joaquin River are limited in Decision 1641 to the April 15 to May 15 time period.  The limitation was also present during the Vernalis Adaptive Management Program (VAMP) that supplanted Decision 1641 with reduced flow requirements in the years 2000 through 2011.  Late timing of pulses tends to keep fish in San Joaquin tributaries late in the season, and then stimulates outmigration of salmon when water temperatures have warmed and both black bass and stripers are active.  While this may help the Merced River Fish Hatchery to release large juveniles, it promotes limited life-history diversity, putting all the fish eggs in one time-window basket.

In short, the changes wrought by the water projects have made it easier for some fish to eat other fish.  Lower streamflows, clearer and warmer water, and altered physical habitats favor striped bass, black basses, and native pikeminnow.  It doesn’t help that one of the protective benefits of VAMP – reducing exports at the Delta pumps during San Joaquin pulse flows – is no longer in place, and the Delta pumps gulp San Joaquin River salmon and steelhead as they gulp San Joaquin River water.

Changing fishing regulations that would increase harvest of bass from a few percent to just a few more percent is not going to solve the problem.  Spending millions to actively “control” the predators with such actions as bounties on pikeminnow, killing all Delta salvaged striped bass, largemouth bass, and sunfishes, or killing all largemouth caught and weighed-in at bass tournaments in the Delta will also not solve the problem.  Most of the predatory fish will still be out there, and fishermen who seek the two most popular sport fish in the state will be really angry.

So what should be done?  The water districts need to gripe less and do more:

  1. They should contribute more to better hatchery programs, as EBMUD has done on the Mokelumne River. The Merced River Fish Hatchery needs a complete rebuild and a refocus to include native strains of trout as well as salmon.
  2. They should invest more in better river habitat, including reduction of predator habitat. In 1996, this was the big answer that was going to allow salmon to thrive in the Tuolumne River under low flow conditions.  The investments were paltry and survival in the Tuolumne has trended sharply downward in the twenty years since.
  3. They should find ways to use less water. They should invest more in water conservation themselves and seek other sources of money to improve efficiency.  No one believes that they can come up with all the money that’s needed on their own.
  4. They should come to grips with the need to release more water more often on a more variable schedule.

Two other relatively aggressive solutions offer opportunities to improve survival of juvenile salmonids in the short term:

  • Fish agencies should barge hatchery and wild salmon and steelhead juveniles to the Bay to bypass the predators, at least in dry years when they are most at risk and wild fish are more easily captured.
  • Fish agencies should also actively capture predators in upstream migrant traps placed in lower Valley tributaries, at least in dry, low-flow years when predators do the most damage and they are they are more easily captured, and truck them to the Bay or Valley reservoirs and lakes.

For more on the predation problem see a previous post: .


[2] See 2012 Predation study, Table 5.3-2, p. 5-12.

[3] Id., Table 5.3-4, p. 5-15.

[4] See Poster, Predation of Juvenile Salmon in the Tuolumne River

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