Recently, I summarized survey information from the Bay-Delta on Sacramento splittail that depicted a potentially grim picture of the future of this special status species. In that post, I did not include trawl survey info from Suisun Marsh Fish Study collected annually by UC Davis (Figure 1), which indicates a core population of adult splittail still present in Suisun Marsh. Other core populations exist in San Pablo Bay (Petaluma and Napa Rivers). Peter Moyle and Teejay O’Rear (UC Davis, personal communications) believe the Marsh core population is sufficiently strong and resistant to extinction.
Looking at Figure 1, the Suisun Marsh population survived the 1987-1992 drought, building in numbers with strong recruitment (ages 0 and 1) in the wet years of 1995-2000. Recruitment declined during the 2007-2009 drought, but there was strong recruitment in the wetter 2010 and 2011 water years. Recruitment declined in the 2012-2014 drought years, but remains substantially higher than at the end of the 1987-1992 drought. Teejay O’Rear states the population has remained strong through 2015 and 2016, with some recruitment in the wetter 2016, and likely strong recruitment in the spring of 2017, presuming it stays wet.
Figure 1. Catch-per-unit-effort of Sacramento splittail in Suisun Marsh 1980-2014 by age group. (Source: Teejay O’Rear, UC Davis)
The prognosis for splittail was not good in 2015 after four years of drought and little recruitment since 2011. The below-normal water year in 2016, with its limited winter flooding, brought no apparent recovery in the Fall Midwater Trawl Index (Figure 1). Summer salvage (Figure 2) indicated that there was some production in 2016, although salvage was two orders of magnitude lower than the previous normal water year 2010 (Figure 3) and three orders of magnitude less than the previous wet water year 2011 (Figure 4).
If water year 2017 were to continue on its current trajectory and become a wet year with widespread flooding, conditions for splittail spawning and rearing this winter and spring would be optimal. A positive response in salvage, Fall Midwater Trawl Survey, and FWS Seine Survey would indicate some form of recovery in the population. However, a lack of response on the order of that which occurred in 2011 would be a signal that the population is in dire straits and at risk of recruitment failure and eventual extinction. In the absence of a 2011-magnitude response in the next wet year, the fisheries agencies should conduct a comprehensive review to evaluate whether to re-list splittail under the federal and state endangered species acts.
Figure 1. Splittail Fall Midwater Trawl Survey Index 1967-2016. (Data Source)
Figure 2. Splittail salvage in 2016. Export rate for federal and state pumping plants. (Source)
Figure 3. Splittail salvage in 2010. Export rate for federal and state pumping plants. (Source)
Figure 4. Splittail salvage in 2011. Export rate for federal and state pumping plants. (Source)
Since I last posted about splittail, there has been little sign of their recovery in the Bay-Delta. Flooding in the Sacramento Valley brought modest production in 2016, but a dry year in the San Joaquin Valley brought little there. Numbers observed in summer south Delta pumping plant salvage are now very low (chart), with little evidence of recovery of the population. The 2011 year class of 5 year olds, the last good wet-year year class, produced minimal offspring in the past three years. It is fair to say that the recovery potential for the species is improbable. The next several years will be the last for the 2011 year class, leaving the viability of the species in question. As I stated in the earlier post, splittail should not have been removed from the federal list of endangered species.
Salvage of Splittail at south Delta export facilities from April 2011 to July 2016.
Splittail, formerly listed as threatened under the federal Endangered Species Act (1994), were delisted in 2003 after nearly a decade of wet years that brought about apparent recovery. Dr. Moyle’s recent warnings about other Delta native fish after nearly a decade of drought surely apply to splittail. Once the most abundant fish in late spring and early summer salvage collections at the south Delta export facilities, splittail are now rarely collected. Once common in dry periods (1987-1992) and prone to abundance in wet periods (1993-2001), they are now rare in dry periods (2007-2009, 2012-2015). Because they live 5-8 years, they are able to spawn successfully in infrequent flood years, 2011 being a good example. The modest production from 2011 will be five years of age in 2016. One can only hope that 2016 will be a wet year.
I argued at a January 2001 CALFED workshop on splittail for retaining the listing of the species as threatened; however the consensus was “statistical power to detect real population trends in the past 30 years is low, thereby undermining confidence in any estimates of extinction risk based on abundance”. The 15 production years since the workshop have clearly added to the “statistical power”. I would argue for relisting splittail, if only for the reason they are now far less abundant then they were prior to the original listing, and to ensure something is done to protect them over the next several years so they indeed do not go extinct.