by Erin E Tracy, Jon A. Walter, Karrigan Bork, Anna Steel, Francisco J Bellido-Leiva, Scott Colborne, Sarah Yarnell
Over 65 million years ago, as Tyrannosaurus rex roamed the great plains, green sturgeon (Acipenser medirostris) were already roaming the world’s waters. While these ancient fish survived the fall of dinosaurs, they are now in danger of extinction largely due to habitat degradation and losses from water management infrastructure and its operation (e.g., impairing flow, disrupting thermal regimes). While you would think the potential loss of a prehistoric giant (up to 8 feet long and hundreds of pounds) would capture the world’s attention, the imminent sturgeon extinction has unfortunately been under the public radar. Reasons for the lack of attention include their cryptic behavior (moving unseen through deep murky waters) and their late maturity (not reproducing until around 15 years old). These traits make it harder to notice and document population declines. To combat these challenges, we are working on a life cycle model that could shed some light on sturgeon ecology.
Though their cryptic nature makes them difficult to study, we know their life history and habitat requirements are different from another prominent anadromous California fish, the salmon. Because salmon are highly visible both in their natural habitat and on our dinner plates, much is known about their habitat needs and life history. Additionally, salmon conservation has received wide public attention and current water management decisions often center on salmonid protection. Yet differences between salmon and sturgeon, such as their life span, spawning periodicity, physiology, habitat use, and historic and cultural significance, result in different and sometimes conflicting management needs. Protecting salmon doesn’t necessarily protect sturgeon.
State and federal laws such as the Endangered Species Act (ESA) mandate sturgeon protection. The green sturgeon southern distinct population segment (sDPS), which spawns in California’s Central Valley, is listed as threatened under the ESA. Protections from this status include prohibitions on “take”[1] and a requirement that federal agencies “insure that any action authorized, funded, or carried out by such agency . . . is not likely to jeopardize the continued existence of any endangered species,” either directly, or through destruction or modification of the species’ habitat (16 U.S.C. § 1536(a)(2).) This second provision requires agencies to analyze impacts of water management actions that support the life-blood of California’s agriculture and economy. This includes operation of the Central Valley Project (CVP) and the State Water Project (SWP) and reconsideration of hydropower licenses across the state.
However, knowledge gaps about sturgeon movement and behavior, driven in part by the near impossibility of directly observing sturgeon over their decadal lifespans impede sound analysis. The 2018 biological opinions on the CVP and SWP operations noted that “there are significant data gaps to describe the ecology of this species in the action area” (BiOp at 112). Our limited knowledge of sturgeon is part of the reason conservation measures for water project operations generally target salmonids (BiOp at 796). We need a better understanding of the green sturgeon sDPS to ensure that it is adequately considered in environmental permitting decisions. Better information can lead to better management, fewer litigation risks for agencies, and, we hope, better outcomes for the sturgeon. Furthermore, using improved knowledge on life cycle model development and simulations of their movements and population dynamics can be essential to inform conservation and water management.
Some computational models of sturgeon behavior and movement are already in use, helping to understand the consequences of habitat and environmental change. Whether a model is useful for a specific problem is similar to the tale of Goldilocks and the Three Bears–except instead of preferences in chairs, porridge, and beds, it’s whether the model’s representation of space, time, and the sturgeon life cycle reflects the problem at hand. Some models depict what happens over hours to days in small areas; these are useful for local impacts of local changes in river habitat. Others depict what happens over many years across large areas; these are useful for assessing long-term population trajectories. An ideal model for testing how water management impacts sturgeon must exist between these scales, capable of resolving how sturgeon move among bay, delta, and river segments over short time scales, while maintaining a long-term perspective on population trends.
Our group proposes the development of an Individual Based Model (IBM) to provide evidence-based predictions of the impacts of multiple water use scenarios and alternatives on sDPS green sturgeon in the Central Valley. IBMs are a promising framework, as it represents discrete individuals from a population and their individual life cycles and experiences, establishing links describing their interactions with the environment (e.g., movement through the system, rearing and spawning habitat selection) based on the best available information. Importantly, these modeled interactions are more likely to maintain their predictive power in new scenarios, providing the ability to analyze potential impacts of alternative water management practices.
Sturgeon are an incredible fish. They are ancient prehistoric survivors that, with a little help from humans, may continue to inhabit our waterways. However, more information about their behavior and demographics is needed to ensure we better understand and manage these stately creatures effectively. Improved life cycle models will provide us with information to help ensure a future for these imperiled fish. We hope shining a light into the dark murky waters these fish call home will inspire more awe about our natural world and lead to decisions that better protect it.
[1] Take is a technical term that includes direct harm, harassment, or “significant habitat modification or degradation where it actually kills or injures wildlife by significantly impairing essential behavioral patterns, including breeding, feeding or sheltering.”(50 C.F.R. § 17.3 (2017).
Erin E. Tracy is a PhD Candidate in the Department of Wildlife, Fish & Conservation Biology working with the Rypel and Fangue labs at the University of California Davis, Jonathan A. Walter is a Senior Researcher at the Center for Watershed Sciences at UC Davis, Karrigan Börk is an Acting Professor of Law at the UC Davis School of Law and an Associate Director at the Center for Watershed Sciences, Anna Steel is a Project Scientist in the Ecophysiology Laboratory of Nann Fangue at the UC Davis. Francisco Bellido Leiva is a Postdoctoral Scholar with the Center for Watershed Sciences at UC Davis, Scott F. Colborne was a postdoctoral researcher at UC Davis and is currently a Research Specialist at the Quantitative Fisheries Center at Michigan State University, and Sarah Yarnell is a Senior Researcher at the Center for Watershed Sciences at UC Davis
Further Reading
Colborne, S.F., L.W. Sheppard, D.R. O’Donnell, D.C. Reuman, J.A. Walter, G.P. Singer, J.T. Kelly, M.J. Thomas, and A.L. Rypel. 2022. Intraspecific variation in migration timing of green sturgeon in the Sacramento River system. Ecosphere 13: e4139.
Heublein, J.C., J.T. Kelly, C.E. Crocker, A.P. Klimley, and S.T. Lindley. 2009. Migration of green sturgeon, Acipenser medirostris, in the Sacramento River. 84: 245-258.
Kelly, J.T., A.P. Klimley, and C.E. Crocker. 2007. Movements of green sturgeon, Acipenser medirostris, in the San Francisco Bay estuary, California. Environmental Biology of Fishes 79: 281-295.
Miller, E.A., G.P. Singer, M.L. Peterson, E.D. Chapman, M. Johnston, M.J. Thomas, R.D. Battleson, M. Gingras, and A.P. Klimley. 2020. Spatio-temporal distribution of Green Sturgeon (Acipenser medirostris) and White Sturgeon (A. transmontanus) in the San Francisco Estuary and Sacramento River, California. Environmental Biology of Fishes 103: 577-603.
Mora, E.A., R.D. Battleson, S.T. Lindley, M.J. Thomas, R. Bellmar, L.J. Zarri, and A.P. Klimley. 2018. Estimating the annual spawning run size and population size of the southern Distinct Population Segment of Green Sturgeon. Transactions of the American Fisheries Society 147: 195-203.
Moser, M.L.. J.A. Isreal, S.T. Lindley, D.L. Erickson, B.W. McCovey Jr., and A.P. Klimley. 2016. Biology and life history of Green Sturgeon (Acipenser medirostris Ayres, 1854): state of the science. Journal of Applied Ichthyology 32: 67-86.
Steel, A.E., M.J. Thomas, and A.P. Klimley. 2018. Reach specific use of spawning habitat by adult green sturgeon (Acipenser medirostris) under different operation schedules at Red Bluff Diversion Dam. Journal of Applied Ichthyology 35: 22-29.
Thomas, M.J., A.L. Rypel, G.P. Singer, A.P. Klimley, M.D. Pagel, E.D. Chapman, and N.A. Fangue. 2022. Movement patterns of juvenile green sturgeon (Acipenser medirostris) in the San Francisco Bay Estuary. Environmental Biology of Fishes 105: 1749–1763.
Related blog posts:
Colborne, L.S., L.W. Sheppard, D.R. O’Donnell, D.C. Reuman, J.A. Walter, G.P. Singer, J.T. Kelly, M.J. Thomas, and A.L. Rypel 2023. Green Sturgeon in California: Hidden Lives Revealed From Long-Term Tracking.
Moyle, P.B. and A.L. Rypel. 2023. Monster Fish: Lessons for Sturgeon Management in California.
Schreier, A., P.B. Moyle, N.J. Demetras, S. Baird, D. Cocherell, N.A. Fangue, K. Sellheim, J. Walter, M. Johnston, S. Colborne, L.S. Lewis, and A.L. Rypel. 2022. White sturgeon: is an ancient survivor facing extinction in California?
