2022 Wild Steelhead Coalition Scholarship
This year the WSC is honored to announce that Nick Chambers will be the recipient of a $5,000.00 scholarship. This scholarship is given on an annual basis to a graduate student focused on Wild Steelhead science. Nick’s work stood out this year, and we are pleased to support his project. Nick is a graduate student at the University of Washington School of Aquatic and Fishery Science. The research being funded is investigating how the dispersal of fry and distribution of redds interact to shape density dependence in the Skagit River Winter Steelhead.
Project Description:
Recovery efforts for Pacific salmonids generally seek to understand and reverse the factors leading to declining abundance, productivity, diversity, and distribution of populations. Juvenile density is often thought to be a strong factor regulating the productivity of salmonid populations. As density rises, the population growth rate will slow as the strength of competition increases until the population is at equilibrium with its environment. The effects of density are generally considered to influence three measurable factors: growth, survival, and dispersal and are broadly referred to as density dependence. The latest model for winter steelhead in the Skagit River found strong evidence of density dependence (Scheuerell et al. 2021). Although that model is based on the latest science, it relied solely on adult-to-adult data due to insufficient data on juveniles. Unfortunately, little is known about the strength and role of density dependence at different life stages of steelhead. For salmonids, density dependence is often thought to manifest as mortality at the fry stage but influence individual growth at the parr stage (Milner et al. 2003).
Although the majority of research on life stage-specific density dependence has focused on Atlantic Salmon and Brown Trout, some research on steelhead supports the idea that density dependent mortality occurs during the first year of life (Close and Anderson 1992, Sogard et al. 2009). While little is known about the effects of density at specific life stages of juvenile steelhead, it is clear the greatest period of mortality occurs at the fry stage. Thus, even small changes in the fry mortality rate could significantly alter the number of fish recruited to the parr stage. Steelhead fry appear to be relatively immobile during the first summer of life, and if high density of fry leads to mortality rather than dispersal this has important implications for population dynamics of steelhead. If redds are unevenly distributed (i.e., patchy) in a watershed, fry may be unable to disperse to unoccupied habitats leading to lower recruitment to the parr stage relative to a broad distribution of redds. This could lead to underestimates of habitat capacity and incorrect management targets by overestimating the amount of accessible habitat. Thus, it is important to understand more about the factors influencing mortality of fry and the role of density dependence in growth, dispersal and survival at individual life stages of steelhead.
To that end, I am attempting to answer the following questions about steelhead fry in the Upper Skagit River:
• What is the maximum dispersal distance of fry from single and clustered redds?
• Given their dispersal distance, how much habitat can fry access in the mainstem Skagit River
based on the spatial distribution of steelhead redds?
• Do density-dependent effects on fry growth, survival and dispersal change in relation to the
density/dispersal of redds?
• Can the spatial distribution of redds provide additional predictive power for estimating the
habitat capacity and escapement goals?
• What methods would be most effective at incorporating estimates of redd dispersal into
existing population dynamics models?
I will accomplish this in several ways. First, I will use observations of dispersal distance from isolated single and clustered redds to map density within dispersal kernels of fry. This information will allow me to generate dispersal contours explicitly for steelhead in the Skagit and quantitatively estimate the amount of habitat accessible to fry in the first summer of life. I will then evaluate growth and changes in density within dispersal kernels to determine if redd density influenced patterns of growth, survival or dispersal distance. Last, I will combine the dispersal contours with habitat measurements to evaluate the role of physical factors in patterns of fry growth, dispersal and survival.
Justification
Effectively managing ESA-listed and imperiled populations depends on knowledge about the factors regulating population size and growth rate and being able to determine when important bottlenecks occur in life. Most, if not all, steelhead populations in the Pacific Northwest experience their greatest period of decline prior to the collection of data that is being used to set fishing seasons, harvest rates and escapement goals. Observations of density dependent signals within these data sets is generally assumed to indicate that the habitat is fully seeded and increasing productivity of the population will require increasing the quality or quantity of habitat. While this assumption may be true in some cases, it is also possible that historical reductions in abundance have resulted in truncation of spawning distributions (e.g., Thurow et al. 2020), potentially leading to incorrect assumptions about factors regulating population size. In these instances, it may be necessary to increase escapement goals to test the capacity of the habitat and evaluate whether increased breeding distributions could in fact increase overall productivity.
Tremendous resources have been dedicated toward recovery of Pacific Salmonids in recent decades, yet examples of recovery are relatively rare. One potential reason is that recovery actions typically only seek to increase abundance and productivity as they are relatively easily measured with standard methods. Diversity and spatial structure are typically recognized as critical components of population health (McElhany 2000) yet are often difficult to quantify and incorporate into recovery and management plans. For species with a diverse array of life histories such as steelhead, abundance and productivity are functions of diversity and spatial structure and are not biologically separable. If my findings are consistent with research on Atlantic Salmon and Brown Trout, this research will provide additional methods for incorporating measures of spatial structure into biological targets such as escapement goals. The ability to link spatial structure with abundance and productivity in existing models would improve our ability to develop biologically sound escapement goals and ensure enough fish reach the spawning grounds to fully utilize the available habitat.
Lastly, this research is focused on improving our collective understanding of basic biological mechanisms which regulate steelhead populations and therefore has implications throughout their range. While the data I collect will be specific to steelhead from the Upper Skagit River, it is highly unlikely that steelhead in other watersheds are following dramatically different patterns. This research will not only improve our ability to manage Skagit River steelhead effectively but can be readily applied to other populations.