The Problem – Sturgeon are Declining

A day-long symposium on March 3, 2015, Sturgeon in the Sacramento–San Joaquin
Watershed: New Insights to Support Conservation and Management,¹ put the onus on sport fishermen to save Central Valley sturgeon. Contributors suggested that to maintain a healthy population of white sturgeon, mortality of adult females has to be eliminated, sport fishing harvest of adults should be halted, and sport fishing should be confined to no more than catch-and-release, with no fishing during the spawning season.

The stated reason for such constraints is that there is a 15- to 20-year period until first spawning, and that thereafter sturgeon often spawn only once every five years. “[I]t is essential not to lose the enormous re-population potential of each spawning female.”

The contributors also noted that strong year classes of sturgeon only occur in wet years when young survival is high. The 2006 year class was the last year class to contribute strongly to the adult population. Essentially what they are saying is that survival of young is so poor and intermittent that recruitment into the adult population is too low to allow any sport fishing harvest.

Of note, there was no mention whether the number of adults spawners has been or is now a limiting factor in the number of recruits produced in the very wet years. Such a state would indeed be a great concern. If the number of eggs laid in very wet years with the present adult population was insufficient to saturate the existing spawning and rearing habitat with young, then the population would be on an accelerated path to extinction. However, if the number of eggs laid is sufficient to saturate the habitat and recruitment (survival of young) is only a function of habitat conditions, then the reason for poor recruitment is not over-fishing but poor or degraded habitat. The intermediate condition where both factors are important is possible if not likely. How the fishery should be managed would also be different in the three conditions.

Also important are any changes in the trajectory of the habitat conditions. If habitat is being gradually degraded by man’s direct effects or climate change, that too can drive the population downward by reducing the production capacity of habitat or increasing the natural mortality of sturgeon. Sport fishing harvest has to be sensitive to such changes, if only to being falsely blamed for any decline or accepting a need to change even to the point of mitigating for the other effects.

Approach to Recovery

Based on the symposium and its summary paper it appears that the onus has been put on sport fishing as the cause as well as the solution to declining sturgeon populations. There was little mention about the effect of habitat conditions (other than the historical imposition of dams). There was mention of stranding and rescue of sturgeon in the Valley bypasses. “An individual-based model indicated that in the absence of rescue, the current population of green sturgeon in the river would have declined by 33% over 50 years (Thomas et al. 2013).” This anecdote was offered more as evidence that harvest should be curtailed as opposed to being a major factor in the decline that should be fixed. The fact is that large numbers of adult sturgeon get “lost” or become stranded or die in the Yolo and Sutter bypasses and in the Colusa Basin Drain each year, especially in wet years when their eggs are most needed.

There was discussion of juvenile survival. “[L]ittle is known of the swimming capacities of larval sturgeons, though the risk of larval sturgeon entrainment is likely influenced by both the ontogeny of swimming capacity and the interactions of sturgeon with water diversions.
Green sturgeon were also much more likely to become impinged upon screens (than White Sturgeon). “Of the more than 3,300 water diversions located in the Sacramento–San Joaquin watershed, the majority (ca. 98%) are estimated to be unscreened. The number of green sturgeon entrained and killed by unscreened water diversions is unknown….. Therefore, efforts to increase the number of migrating green sturgeon that successfully reach estuarine and marine environments should focus on juvenile life history stages, and take into account the behavioral and physiological changes that accompany such a migration… Substantial recruitment depends on extremely high Delta outflows during winter and spring. The mechanisms underlying this relationship are the subject of on-going investigations, but are likely some combination of adult attraction to upstream spawning grounds, suitability of spawning substrate, and survival of age–0 fish during the migration downstream to the estuary.” (Emphasis added)

Symposium Conclusions and Recommendation

There were three primary conclusions and associated recommendations from the symposium.

1. Maintain a healthy population of white sturgeon by eliminating mortality of adult females. Sportfishing harvest of adults should be halted, or fishing at least confined to catch-and-release outside of the spawning season. Having survived the 15- to 20-year period until first spawning, and subsequently only spawning every 5 years, it is essential not to lose the enormous re-population potential of each spawning female. Loss of a single spawning female that will produce several hundred thousand eggs each time she spawns. Comment: There was no mention of reducing the stranding of sturgeon in the flood bypasses (Yolo and Sutter) despite stating the important contribution of 24 rescued in a limited effort in a 2010 overflow event. Hundreds, perhaps thousands, of adult sturgeon stray into the bypasses each year.² Many are lost or unable to find suitable spawning habitat. That compares to the several hundred harvested each year by sport fishermen (see figure below) under strict harvest regulations, out of an adult population of 25,000-50,000.³
   

   Source: http://www.dfg.ca.gov/delta/data/sturgeon/bibliography.asp

2. Protect and restore critical key habitat in order to conserve and reestablish to conserve and reestablish sturgeon populations. Gravel beds are critical for successful spawning and egg survival. Deep holes are critical as energetic refuges for sturgeon holding in the river.Comment: No mention was made that many of these key spawning habitats are degraded in dry years by low flows and high water temperatures in the late spring spawning season. Demersal adhesive eggs and hatched young are subject to lethal water temperatures (>65oF) in dry years.⁴ Low flows also contribute to starvation, predation, and reduced downstream transport.
3. Take a holistic approach to life history and habitat research and monitoring. This should include a robust program of conventional mark–recapture to determine population size, population year–class composition, and mortality rate—in addition to advanced telemetry and habitat mapping methods. This approach should also include continuous monitoring of dissolved oxygen, the most critical environmental factor for oxyphilic sturgeons: they are broadly tolerant of wide ranges in temperature, salinity, and flow that are all much less critical factors for their population success. Comment: Water temperature, flow, entrainment, and predation are the key factors of poor recruitment (survival) in non-wet years. These factors are far more important for sturgeon in the long run than the harvest of several hundred adult sturgeon each year from a population of 25-50 thousand adults.

Source: http://www.dfg.ca.gov/delta/data/sturgeon/bibliography.asp

The Fremont Weir fish passage improvements at the upper end of the Yolo Bypass (see previous posts for details¹) are mandated in the National Marine Fisheries Service’s Central Valley Project and State Water Project joint biological opinion (2009 OCAP BO). The OCAP BO that allows limited take of endangered salmon, steelhead, and sturgeon for the wide array of water projects’ features (i.e. dams and water diversions), provided various improvements are made.

So far, as of the beginning of 2016 there have been no improvements or fixes at Fremont Weir, just more planning and discussion. Meanwhile, CDFW rescued hundreds of stranded salmon in the upper Bypass this fall. There has been no rescue of sturgeon since the Fremont Weir and Tisdale Weir rescue efforts in April 2011, when 24 endangered Green Sturgeon were rescued and radio tagged (21 eventually returned to the Pacific Ocean after migrating to spawning grounds in the upper Sacramento River²). Because of the drought, there have been no river flood flows over Fremont Weir into the Bypass since the April 2011 event. (Overflow of the Tisdale Weir into the Sutter Bypass did occur in Dec 2012 and Jan 2013.). However, salmon and sturgeon continue to be attracted to the Bypass by flows from local sources and to become stranded at the upper end of the Bypass.

“Fixes” under consideration for Fremont Weir include changes that would allow the Sacramento River to flood parts of the bypass at lower flows. The amount of water that might be diverted to the Yolo Bypass from the Sacramento River through prospective changes to the weir ranges from several hundred cfs to 6000 cfs. The larger end of the range of flows would be designed to provide for Bypass rearing of young salmon that would pass along with the water from the river to the Bypass. There is little doubt that young salmon do well in the over 40 miles of floodway habitats of the Bypass. The Delta also benefits from flow through the Bypass because of enhanced biological productivity.

It will take years to plan and implement such large sized enhancements in the Bypass. But an immediate solution to the adult salmon and sturgeon passage problem at Fremont Weir is not that complicated or contingent on other actions. OCAP BO Action 1.7– a Fremont Weir Ladder Project (reproduced below, with a deadline that is 5 years past) – should be implemented now

OCAP 

Action I.7. Reduce Migratory Delays and Loss of Salmon, Steelhead, and Sturgeon at Fremont Weir and Other Structures in the Yolo Bypass

Objective: Reduce migratory delays and loss of adult and juvenile winter-run, spring-run, CV steelhead and Southern DPS of green sturgeon at Fremont Weir and other structures in the Yolo Bypass.

Description of Action: By December 31, 2011, as part of the plan described in Action I.6.1, Reclamation and/or DWR shall submit a plan to NMFS to provide for high quality, reliable migratory passage for Sacramento Basin adult and juvenile anadromous fishes through the Yolo Bypass. By June 30, 2012, Reclamation and/or DWR shall obtain NMFS concurrence and, to the maximum extent of their authorities, and in cooperation with other agencies and funding sources, begin implementation of the plan, including any physical modifications. By September 30, 2009, Reclamation shall request in writing that the Corps take necessary steps to alter Fremont Weir and/or any other facilities or operations requirements of the Sacramento River Flood Control Project or Yolo Bypass facility in order to provide fish passage and shall offer to enter into a Memorandum of Understanding, interagency agreement, or other similar mechanism, to provide technical assistance and funding for the necessary work. By June 30, 2010, Reclamation shall provide a written report to NMFS on the status of its efforts to complete this action, in cooperation with the Corps, including milestones and timelines to complete passage improvements.

Rationale: The Yolo Bypass and Fremont Weir has been a documented source of migratory delay to, and loss of, adult winter-run, spring-run, CV steelhead and Southern DPS of green sturgeon. The existing fish passage structure is inadequate to allow normal passage at most operational levels of the Sacramento River. The project agencies must work with the Corps, which owns and operates Fremont Weir, to achieve improvements for fish. Other structures within the Yolo Bypass, such as the toe drain, Lisbon Weir, and irrigation dams in the northern end of the Tule Canal, also can impede migration of adult anadromous fish.

Additionally, stranding of juvenile salmonids and sturgeon has been reported in the Yolo Bypass in scoured areas behind the weir and in other areas. This action offsets unavoidable project effects on adult migration and minimizes the direct losses from flood management activities associated with operations.

Fremont Weir Fish Ladder (Looking North towards flooded Sacramento River)

Fremont Weir Ladder Project

Fremont Weir Fish Ladder Replacement. “The existing Fremont Weir Denil fish ladder will be removed and replaced with new salmonid passage facilities designed to allow for the effective passage of adult salmonids and sturgeon from the Yolo Bypass past the Fremont Weir and into the Sacramento River when the river overtops the weir. Specific design criteria of the ladder have not yet been determined. This facility will incorporate monitoring technologies to allow for collection of information to evaluate its efficacy at passing adult fishes.” From Draft BDCP CM 2 Yolo Bypass Fishery Enhancement, October 5, 2010.

The 2010 proposal cited above would have been insufficient, because any prospective fish passage improvement would have been limited to conditions when the weir would overtop (river elevation 33.5’). Present planning efforts are looking at options that provide flows and passage at river elevations from 14’ to 22’. The deeper the project goes, the more often passage can be provided. Elevation 14’ is likely the limit: otherwise water could flow in reverse (from the Bypass through the weir to the river). A 14’ elevation would allow passage in most dry years when such action is most needed. But even in a wet year overflow like 2011, a 14’ elevation would relieve Bypass stranding potential by increasing the passage window by 20%, and by offering better through-opening conditions for passage.

Options:

1. Dig and line channel to river from existing 30-ft ele down to 14/15-ft ele.
2. Rebuild existing 4-ft-wide, 4-ft-deep ladder from existing 33-ft top ele and 28-30 ft ele bottom, to 8-20 ft wide, 8-15 ft deep slot or open box-culvert weir.
3. Dig and line 10-ft-wide channel from weir apron down into Bypass to large pond about 50 yards distance. Bottom of channel should be about 14-ft ele through weir apron (it is presently at 28-ft ele). Bypass pond and Tule Canal downstream of weir (top center in photo below) is about 15-20-ft surface ele, thus channel to pond may have to incorporate step-pools. Channel enhancements may also be required between pond and Tule Canal.
4. The pond should be filled so fish do not become stranded

Photo above looking South from top of weir toward target pond

Ladder in center of photo. Bypass and apron to the left; River to the right (100 Yds).