By Doug Obegi, Natural Resources Defense Council
In recent weeks, agribusinesses and water districts that support the Trump Administration’s efforts to gut protections for salmon and other endangered species in California’s Bay-Delta have ramped up their claims that “new” science shows that the Trump Administration is right to weaken protections for endangered species, which would significantly increase water diversions from this imperiled estuary. However, these water agencies have a vested interest in claiming that fish don’t need water: so that they can divert even more of this public resource for their own use.
Over the past decade, State and federal agencies have continued to publish peer reviewed scientific research that largely strengthens our understanding of how the volume, timing, temperature, and quality of water – and the operations of existing dams and water diversion facilities, including the state and federal water projects – adversely affect salmon and other fish and wildlife. Far from proving that fish don’t need water, this research shows all too clearly how California’s current levels of water diversions, and our existing dams and infrastructure, are driving salmon and other native fish and wildlife towards extinction.
Here’s a small sample of recent scientific publications regarding the effects of flows on fish in the Bay-Delta watershed. Please keep in mind that the summaries of these papers in the parentheses are my own interpretations, and readers can click on the links below to read the papers and abstracts:
- Michel, C.J., A.J. Ammann, S.T. Lindley, P.T. Sandstrom, E.D. Chapman, M.J. Thomas, G.P. Singer, A.P. Klimley, and R.B. MacFarlane 2015. Chinook salmon outmigration survival in wet and dry years in California’s Sacramento River. Can. J. Fish. Aquat. Sci. 72: 1749–1759. dx.doi.org/10.1139/cjfas-2014-0528. (survival of acoustically tagged juvenile salmon migrating down the Sacramento River and through the Delta was significantly lower in four low flow years (2.8-5.9%) than in one high flow year (15.9%)).
- Cyril J. Michel 2018. Decoupling outmigration from marine survival indicates outsized influence of streamflow on cohort success for California’s Chinook salmon populations. Canadian Journal of Fisheries and Aquatic Sciences, 2019, 76(8): 1398-1410, doi.org/10.1139/cjfas-2018-0140. (finding that survival of migrating salmon through the Bay-Delta watershed is the primary driver of smolt to adult ratios for hatchery salmon, with ocean conditions playing a critical role in years with abnormally poor marine conditions, and that the volume of streamflows during migratory periods accounts for over 35% of the variability in smolt to adult ratios for fall run, winter run, and late fall run hatchery salmon).
- Friedman, W. R., B. T. Martin, B. K. Wells, P. Warzybok, C. J. Michel, E. M. Danner, and S. T. Lindley 2019. Modeling composite effects of marine and freshwater processes on migratory species. Ecosphere 10(7):e02743. 10.1002/ecs2.2743. (publishing life cycle model for fall run Chinook salmon which finds that water temperatures during egg incubation, freshwater flow during juvenile outmigration, and predation in the early ocean life stage are the primary drivers of fall run Chinook salmon production).
- Henderson, M.J., I. S. Iglesias, C. J. Michel, A. J. Amman, and D. D. Huff 2018. Estimating spatial-temporal differences in Chinook salmon outmigration survival with habitat and predation related covariates. Canadian Journal of Fisheries and Aquatic Sciences, 2019, 76(9): 1549-1561, https://doi.org/10.1139/cjfas-2018-0212. (study based on five years of monitoring survival of acoustically tagged late fall run Chinook salmon in the Sacramento River found that the most important covariate affecting survival was flow).
- Perry, R. W., A. C. Pope, J. G. Romine, P. L. Brandes, J. R. Burau, A. R. Blake, A. J. Amman, and C. J. Michel 2018. Flow-mediated effects on travel time, routing, and survival of juvenile Chinook salmon in a spatially complex, tidally forced river delta. Canadian Journal of Fisheries and Aquatic Sciences, 2018, 75(11): 1886-1901, https://doi.org/10.1139/cjfas-2017-0310. (finding that survival of migrating salmon from the Sacramento River through the Delta decreases sharply, and more salmon are routed into the interior Delta where survival is low, when Delta inflows decline below 35,000 cfs, and that opening the Delta Cross Channel gates also reduces survival and increases routing into the interior Delta)
- Zeug, S., K. Sellheim, C. Watry, J. D. Wikert, and J. Merz 2014. Response of juvenile Chinook salmon to managed flow: lessons learned from a population at the southern extent of their range in North America. Fisheries Management and Ecology, 2014, 21(2), https://doi.org/10.1111/fme.12063. (based on 14 years of monitoring data on the Stanislaus River, survival of juvenile migrating salmon was positively related to winter/spring flow volume and variability and those variables explained approximately 2/3rds of the variation in juvenile salmon survival in those years)
- Cordoleani, F., J. Notch, A. S. McHuron, A. J. Amman, C. J. Michel 2017.Movement and Survival of Wild Chinook Salmon Smolts from Butte Creek During Their Out-Migration to the Ocean: Comparison of a Dry Year versus a Wet Year.Transactions of the American Fisheries Society 147:171–184, 2018, DOI: 10.1002/tafs.10008. (finding significantly lower survival of wild migrating spring run Chinook salmon from Butte Creek during lower flows in 2015 as compared to the higher flows in 2016)
- Nobriga, M.L. and J.A. Rosenfield 2016. Population Dynamics of an Estuarine Forage Fish: Disaggregating Forces Driving Long-Term Decline of Longfin Smelt in California’s San Francisco Estuary, Transactions of the American Fisheries Society, 145:1,44-58, DOI: 10.1080/00028487.2015.1100136 (publishing a life cycle model of longfin smelt which finds that the volume of Delta outflow during the winter and spring months is strongly related to longfin smelt recruitment and abundance in the following fall)
- Martin, B. T., A. Pike, S. N. John, N. Hamda, J. Roberts, S. T. Lindley, and E. M. Danner. Phenomenological vs. biophysical models of thermal stress in aquatic eggs. Ecology Letters 2016, 20(1), https://doi.org/10.1111/ele.12705. (finding that laboratory models of water temperatures underestimate adverse impacts on salmon, identifying critical temperatures where temperature-dependent mortality begins and confirming devastating temperature-dependent mortality of endangered winter-run Chinook salmon below Shasta Dam in 2014 and 2015)
- Kimmerer, W. J. and K. A. Rose 2018. Individual‐Based Modeling of Delta Smelt Population Dynamics in the Upper San Francisco Estuary III. Effects of Entrainment Mortality and Changes in Prey, Transactions of the American Fisheries Society, 147:1, 223-243, https://doi.org/10.1002/tafs.10015 (life cycle model of Delta Smelt, finding that entrainment and food limitation had similar adverse effects on the species’ abundance)
- Rose, K. A., W. J. Kimmerer, K. P. Edwards, and W. B. Bennett 2013. Individual-Based Modeling of Delta Smelt Population Dynamics in the Upper San Francisco Estuary: II. Alternative Baselines and Good versus Bad Years, Transactions of the American Fisheries Society, 142:1260–1272, https://doi.org/10.1080/00028487.2013.799519. (evaluation of different variables affecting Delta Smelt using a life cycle model, concluding that entrainment has population level effects on the species and strongly critiquing paper by Maunder and Deriso)
- Bever, A. J., M. L. MacWilliams, B. Herbold, L. R. Brown, and F. V. Feyrer 2016. Linking Hydrodynamic Complexity to Delta Smelt (Hypomesus transpacificus) Distribution in the San Francisco Estuary, USA, San Francisco Estuary and Watershed Science 14(1), http://dx.doi.org/10.15447/sfews.2016v14iss1art3(reinforcing prior studies, finding that overlap of low salinity, high turbidity, and relatively low velocity provides conditions necessary to support Delta Smelt, as in the fall of 2011 when the low salinity zone was located in Suisun Bay)
- Takata, L., T. R. Sommer, J. L. Conrad, and B. M. Schreier 2017. Rearing and migration of juvenile Chinook salmon (Oncorhynchus tshawytscha) in a large river floodplain, Environmental Biology of Fishes (2017) 100:1105-1120, DOI 10.1007/s10641-017-0631-0 (duration of flooding in the Yolo Bypass was positively related to salmon growth rates and size, but at least for the small sample sizes to date there was no evidence of higher survival to adulthood for salmon raised on the floodplain versus those that rear in the Sacramento River)
These are only a few of the studies published in peer reviewed journals by agency and independent scientists in recent years which show that the volume, timing, temperature and quality of flows is essential to survival and abundance of native fish and wildlife in the Bay-Delta watershed. These studies support the conclusion that current levels of water diversions and operations of existing dams and diversion facilities, including the State Water Project and Central Valley Project, are significantly harming salmon and other native fish species.
The Bay-Delta is one of the best studied estuaries in the world. Nearly every day, biologists and agency staff are out in the field monitoring fish and wildlife, hydrology, water quality, and other data in order to improve our understanding of how the Bay-Delta system operates. That ongoing research continues to support findings in the 2008 and 2009 biological opinions, such as the 2015 MAST report (finding that summer/fall outflows have population-level effects on Delta Smelt), or the 2016 Six-Year Acoustic Telemetry Steelhead Study (which concludes that “The survival estimates from the 2016 six-year study support the conceptual model” that higher Delta inflows, lower exports, and a lower I:E ratio results in higher survival of steelhead migrating from the San Joaquin River).
Beware Trumpian claims that “new” science shows that fish don’t need water, particularly such claims from those water districts and agribusinesses that would benefit from increased water diversions from the Delta.