Category Archives: Sturgeon

Sturgeon are being Decimated by Water Management in Spring 2016

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Green and White sturgeon spawn in the Sacramento River in spring, usually in April and May. Green sturgeon spawn predominantly above Red Bluff (RM 243) to near Redding (RM 264); they also spawn below Red Bluff, downstream to Hamilton City (RM 200) (see Figure 1). White sturgeon spawn primarily below Hamilton City in the lower river above and below Wilkins Slough (RM 125, downstream of area shown on map). Like other endangered fish in the Central Valley, sturgeon too were hurt during the recent four years of drought 1 by low flows and high water temperatures.

Figure 1. Map of the upper Sacramento River Basin (Princeton Ferry to Keswick Dam)

Figure 1. Map of the upper Sacramento River Basin (Princeton Ferry to Keswick Dam)

But this year is supposed to be different. Water Year 2016 is a wetter year (designated “Below Normal” for Sacramento Valley), and Shasta Reservoir is nearly full. Reclamation’s Central Valley Project should be able to meet the criteria set forth in the Basin Plan, Water Right Order 90-05, and the salmon and green sturgeon Biological Opinion that are designed to maintain habitat for salmon and sturgeon in the Sacramento River. Those criteria have a common element of maintaining Red Bluff (RM 243) spring-summer water temperature below a daily average of 56°F. The Basin Plan extends the criteria downstream to Hamilton City (RM 200) and adds a 68°F criterion from there downstream to Sacramento (RM 60) to protect salmon, sturgeon, and other fish. The criteria have been in place for decades, and are based on extensive science. Salmon spawning requires daily average water temperatures below 56°F. Water temperatures above 68°F are lethal to juvenile sturgeon.2 Governing requirements in each of the documents cited above allow the applicable criteria to be applied further upstream in drier years when Shasta storage and cold-water pool resources are less than adequate.

This year, the responsible agencies have apparently decided that the cold-water pool volume is inadequate despite the fact that Shasta is virtually full. The agencies have set the Control Point at Redding, with a 58°F daily average limit. By allowing the Red Bluff 56°F objective to be substantially weakened, the National Marine Fisheries Service (NMFS), the federal agency responsible for salmon and sturgeon, is thus accepting great risk not only to Winter Run salmon (decimated over the past two years), but also to green and white sturgeon.

To save the Shasta cold-water pool, Reclamation has been releasing a minimum amount of water from Shasta and is taking the water primarily from the upper warm surface layers of the reservoir.3 This has resulted in water temperatures in the lower river at Red Bluff in excess of 56°F (Figure 2). It has also resulted in water temperatures below Red Bluff (Figure 3) that exceed 65°F, the upper thermal optima for sturgeon embryo development, and even 68°F, the lethal level for newly hatched sturgeon juveniles.4 The warm water in the lower river is also a consequence of unusually low seasonal flows in the lower Sacramento River in spring 2016 (Figures 4 and 5).

May and June are precisely the months of concern for the sturgeon. Sturgeon begin spawning when water temperatures start to exceed 55°F, which generally occurs in April. Green sturgeon young spawned above Red Bluff pass downstream through Red Bluff in May and June (Figure 6). Those passing Red Bluff and those spawned between Red Bluff and Hamilton City likely encountered their upper thermal optima of 65°F during May and early June. White sturgeon spawned in the lower river were subjected to lethal water temperature during much of May 2016. Lethal water temperatures predominated in May 2014 and 2015 (Figure 7), Critically Dry years, as well as in Below Normal 2016 (Figures 3 and 7). River flows at Wilkins Slough were also very low in these same years (Figure 5). In contrast, higher flows and lower water temperature were maintained in spring of years 2008-2013, which included four drought years.

The overall risk is greatest to White sturgeon, which spawn in the lower river where water temperatures are highest. That high risk is the result of unusually low seasonal river flows from a seemingly overzealous need by Reclamation to conserve Shasta storage this year. This effect is compounded by the fact that, of the 7000 cfs being releases from Shasta, only 3000 cfs is reaching the lower river. The rest is diverted by Reclamation’s north of Delta contractors, who received 100% of their allocations this year.

The sturgeon deserve 100% of their needs as well. That would require colder water and higher releases from Shasta to get flows at Wilkins Slough into the range of 5000-7000 cfs that was achieved in drought years 2008, 2009, 2012, and 2013 (Figure 5). That would amount to 4000-8000 acre-feet per day (0.1-0.2%/day) of a nearly full Shasta Reservoir (currently with 4,200,000 acre-feet of stored water). Such releases will be required in any event to meet export demands from the Delta in June.

For more detail on the issue see the following:

  1. http://www.waterboards.ca.gov/waterrights/water_issues/programs/drought/sacramento_river/
  2. http://www.norcalwater.org/wp-content/uploads/2011/12/swrcb_summary_apr_2014.pdf
Figure 2. Water temperature of Sacramento River at Red Bluff (RM 243) in May and early June 2016. Target for salmon and other fish is 56°F (red line).

Figure 2. Water temperature of Sacramento River at Red Bluff (RM 243) in May and early June 2016. Target for salmon and other fish is 56°F (red line).

Figure 3. Water temperature of Sacramento River at Wilkins Slough (RM 125) in May and early June 2016. Target for sturgeon and other fish is 68°F (red line).

Figure 3. Water temperature of Sacramento River at Wilkins Slough (RM 125) in May and early June 2016. Target for sturgeon and other fish is 68°F (red line).

Figure 4. Daily average Sacramento River flow at Wilkins Slough (RM 125) in May 2016.

Figure 4. Daily average Sacramento River flow at Wilkins Slough (RM 125) in May 2016.

Figure 5. Sacramento River flow at Wilkins Slough (RM 125) 2008-2016. Circles denote unusually low flows 2014-2016.

Figure 5. Sacramento River flow at Wilkins Slough (RM 125) 2008-2016. Circles denote unusually low flows 2014-2016.

Figure 6. Capture patterns of young Green sturgeon in USFWS traps at Red Bluff 2003-2012.

Figure 6. Capture patterns of young Green sturgeon in USFWS traps at Red Bluff 2003-2012.

Figure 7. Water temperature in the Sacramento River at Wilkins Slough 2008-2016. The Basin Plan objective and the lethal water temperature for young sturgeon of 68°F is depicted with red line.

Figure 7. Water temperature in the Sacramento River at Wilkins Slough 2008-2016. The Basin Plan objective and the lethal water temperature for young sturgeon of 68°F is depicted with red line.

Fremont Weir Overflows Again – Prepare for Salmon and Sturgeon Rescues

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fish rescuesIt is one of those wet springs when the Sacramento River has spilled over the Fremont Weir at the upstream (north) entrance to the Yolo Bypass near Verona. In a January post I summarized the need to fix salmon and sturgeon passage at the weir. In early April 2011 adult sturgeon and salmon were rescued at Tisdale and Fremont weirs1 under nearly the same circumstances that have developed since mid-March this year. In the coming weeks, many adult sturgeon and Winter Run salmon attracted by the high Bypass flows will again show up and become stranded at the Fremont Weir as the weir ceases to overflow. River levels are expected to drop as much as eight feet in the coming week. As the Bypass slowly drains in the coming days more and more salmon and sturgeon will migrate up the Bypass via Cache Slough near Rio Vista. Many will become stranded in the upper Bypass as far up as the Fremont Weir concrete apron, where rescues occurred in the past.

map of flowsOthers will make their way to the west side of the upper Bypass to outlet of the Knights Landing Ridge Cut (KLRC), and migrate up into the Colusa Basin via the Colusa Basin Drain where they will be lost. In spring 2013, many Winter Run salmon were found stranded in the Colusa Basin under similar circumstances. The peak migration of Winter Run and sturgeon is in March and April. So I expect many salmon have or will be headed up the Ridge Cut, which is flowing 500-600 cfs.2 The CDFW trap is removed from the Ridge Cut outlet at such high flows.

Fixes for both problems are in the works, as they are required in the Central Valley Salmon Biological Opinion for operating the state and federal water projects. Reclamation District 108 is working on the outlet solution for the KLRC. DWR, DFW, and others are working on Fremont Weir passage. 3

In the meantime, trapping and rescues are the only measures to save fish again this year. These efforts should start soon. Note similar problems occur at the Moulton, Colusa, and Tisdale weirs (see map and last photo).

Above Photo: Fremont Weir on March 13, 2016. Overflow to Yolo Bypass was 30,000-40,000 cfs. Overflow peaked at 65,000 cfs two days later, as river stage rose to 36 ft, two feet above that in photo. For video of overflow event and Bypass flooding see http://youtu.be/9hrn2bSgg8A .

Above Photo: Fremont Weir on March 13, 2016. Overflow to Yolo Bypass was 30,000-40,000 cfs. Overflow peaked at 65,000 cfs two days later, as river stage rose to 36 ft, two feet above that in photo. For video of overflow event and Bypass flooding see http://youtu.be/9hrn2bSgg8A .

Above Photo: Fremont Weir on March 20, 2016 when overflow temporarily ceased at river stage dropped to 33.5 ft. Insert: 2011 rescue photo.

Above Photo: Fremont Weir on March 20, 2016 when overflow temporarily ceased at river stage dropped to 33.5 ft. Insert: 2011 rescue photo.

Above photo: Moulton Weir in January 1997.

Above photo: Moulton Weir in January 1997.

Sturgeon Science Symposium Puts Onus on Sport Fishing

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Life History of Southern DPS Green Sturgeon

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

  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.

Fremont Weir Fish Passage Update

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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.

 

Photo of Fremont Weir Fish Ladder

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 on wier

Photo above looking South from top of weir toward target pond

Photo of fish ladder

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

  1. http://calsport.org/fisheriesblog/?p=497; http://calsport.org/fisheriesblog/?p=421 ↩
  2. Thomas, M. J., and others. 2013.  Stranding of Spawning Run Green Sturgeon in the Sacramento River: Post-Rescue Movements and Potential Population-Level Effects.  North American Journal of Fisheries Management 33:287–297.  ISSN: 0275-5947 print / 1548-8675 online. DOI: 10.1080/02755947.2012.75820. ↩

Sturgeon and the Drought

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The State Water Board’s weakening of the water temperature standards in the Sacramento River below Shasta at the request of Reclamation and concurrence by NMFS this late spring and early summer has likely led to excessive take during this spawning season of listed Green Sturgeon, increasing their risk of their extinction. Lower flows and higher temperatures in the Sacramento River’s Green Sturgeon spawning reach from Anderson (RM 280) to Hamilton City (RM 200) has likely resulted in a substantial mortality of eggs and larval Green Sturgeon, as well as White Sturgeon, during and following their May-June spawning season.

Water temperatures below Red Bluff (RM 240) exceeded the upper thermal optimum for Green Sturgeon embryos (17-18°C, 62-65°F1) from late spring to early summer 2015 (Figure 1), but rarely in 2012, the first year of the present drought (Figure 2), when standards were not weakened. Water temperatures exceeded 62°F nearly to Anderson at times this summer (Balls Ferry and Jelly’s Ferry). Approximately half the spawning reach has been severely degraded by warm water from weakened standards (Figure 3). Lower flows and higher water temperatures have likely led to earlier spawning and more concentrated spawning in the upper end of the spawning reach. The river below Hamilton City, where eggs and fry drift and many young rear, is degraded with high water temperature even above 100% lethal levels (23°C, 73°°F) at Wilkins Slough (RM 120) (Figure 4). In 2012, when standards were not weakened, conditions at Wilkins Slough were much better and near optimum (Figure 5). However, even in 2012 (the first year of the present drought cycle) Green Sturgeon tended to spawn further upstream in the spawning reach than in previous years2 because of lower river flows and/or higher water temperatures.

What applies to Green Sturgeon also applies to the non-listed White Sturgeon, whose spawning and rearing requirements, timing, and locations are similar to those of the Green Sturgeon3. Concerns for the White Sturgeon are ever increasing4. The risks extend to adult White Sturgeon, which have undergone a die-off in the Columbia River under similar circumstances5.

Figure 1

Figure 1. Water temperatures at Red Bluff on Sacramento River late spring and early summer 2015. (Source: CDEC)

figure 2

Figure 2. Water temperatures at Red Bluff on Sacramento River late spring and early summer 2012. (Source: CDEC)

Figure 3

Figure 3. Green Sturgeon spawning reach in the Sacramento River (green highlight). Reach degraded by high water temperature in 2015 (red highlight).

Figure 4

Figure 4. Water temperatures at Wilkins Slough (RM 120) on Sacramento River late spring and early summer 2015. (Source: USGS)

Figure 5

Figure 5. Water temperatures at Wilkins Slough (RM 120) on Sacramento River late spring and early summer 2012. (Source: USGS)

  1. “Water temperature for spawning and egg incubation is near optimal (15oC/ 59oF)) from RBDD upriver during the spawning season. Below RBDD, water quality, in terms of water temperature, gradually degrades and eventually exceeds the thermal tolerance level for egg incubation, when egg hatching success decreases and malformations in embryos increase above 17 oC/62 oF, at Hamilton City”. (NMFS OCAP Biological Opinion p276) ↩
  2. William R. Poytress, Joshua J. Gruber, Joel P. Van Eenennaam & Mark Gard (2015) Spatial and Temporal Distribution of Spawning Events and Habitat Characteristics of Sacramento River Green Sturgeon, Transactions of the American Fisheries Society, 144:6, 1129-1142, DOI: 10.1080/00028487.2015.1069213 ↩
  3. White Sturgeon generally spawn lower in the river than Green Sturgeon. ↩
  4. http://www.scout.com/outdoors/fish-sniffer/story/1563429-ca-dfw-considers-slashing-sturgeon-fishing
    https://cdfgnews.wordpress.com/2015/08/11/responsible-angling-practices-help-conserve-sturgeon-populations/
    ↩
  5. http://www.cbbulletin.com/434540.aspx ↩