Research Areas

My research goals can be summarized as ‘advancing solutions for society’s most pressing issues for stream fish conservation’.

Understanding and mitigating threats to imperiled populations:

1. Characterizing genetic integrity of small, fragmented fish populations.

   Declining populations at the edge of their range are often relegated to small isolated habitats, which can have important demographic and genetic consequences. I recently investigated this topic by studying brook trout populations at the edge of their southeastern range that have a history of hatchery stocking to inform future translocation and reintroduction efforts. I found that these populations had among the lowest genetic diversity and highest amounts of differentiation recorded across their native range (Pregler et al. 2018). These data were then incorporated into a range-wide assessment where we found similar patterns for the southeastern distribution relative to their northern populations (Kazyak et al. accepted, in revision). Many small isolated populations like the brook trout I studied are likely candidates for genetic rescue, that is, artificial gene flow to increase genetic diversity, reduce negative impacts of isolation and inbreeding, and increase population size, which brings me to the next major topic of my program.

2. Using genetic rescue to mitigate extinction risk in imperiled species.

Genetic rescue has emerged as an important tool to stave off extinction and improve fitness of declining populations. While there are high profile cases of genetic rescue in action (e.g., Florida panthers, Pimm et al. 2006), there has been reluctance by managers to apply this tool due to concerns about outbreeding depression (Frankham 2015). There is an urgent need to understand when artificial gene flow does and does not lead to genetic rescue. I recently explored this topic as part of my postdoctoral research at UC Berkeley and NOAA-Fisheries. In particular, working with a team of conservation geneticists, hatchery staff, and population biologists, I evaluated the success of a genetic rescue intervention focused on a population of endangered Central California Coast Coho Salmon ESU using ~17 years of genetic and demographic data pre- and post-outcrossing with salmon from a nearby watershed. We found that outcrossing decreased relatedness among adults, and their hybrid progeny had higher fitness in both captive and field settings relative to non-hybrids (Pregler et al. submitted). This study highlights that genetic rescue can be a useful tool in the conservation of imperiled salmonids.

In the future, I aim to conduct further research on the risks of inbreeding vs outbreeding depression to understand the conditions when genetic rescue should be used as a tool to rescue declining, inbred stream fishes.

Evaluating population level changes following management interventions:

1. How well can we detect changes in population trends over time?

   The ability to accurately monitor the status and trends of populations is a key goal and challenge of managers working to manage aquatic biodiversity at broad spatial scales in a changing environment. But our ability to detect such population trends is challenging. A major goal of my program is to use methods from population biology to detect changes in population dynamics through time. This is critically important for evaluating the impact of various management interventions (e.g., genetic rescue), but also to detect changes in response to shifting environmental conditions. As one example, using a long-term dataset for brook trout across their southeastern range, I conducted simulations using state-space models to evaluate our power to detect trends. While it is challenging to detect low level declines (e.g. 1%), I found that - in this system - long-term monitoring of existing sites is more important than increasing the number of sites (Pregler et al. 2019), presumably because of the synchrony in dynamics across sites. Through this effort, I also successfully advocated for collaboration across state-agency boundaries to facilitate monitoring efforts.

   I’m interested in developing a combined genetic-demographic approach to evaluate the success of captive breeding programs, which I discuss next.

2. Evaluating success of captive breeding programs.

   Severely declining populations are often candidates for management actions such as propagation through captive breeding to ensure their persistence.  While captive breeding programs have been long established, evaluating the success of their efforts remains a challenge, primarily because the small population size hampers robust statistical analysis. Additionally, implementing a captive breeding program requires many logistical decisions such as where the broodstock originates, which life stages to release, and where and how many sites are stocked with captive-born animals. A captive broodstock program for Ccoho salmon was initiated in the Russian River in California following a severe population bottleneck in 2003.  Since the inception of the program nearly 20 years ago, managers have been fine-tuning their protocols to maximize juvenile survival to ensure higher adult coho salmon returns.  Building on our previous genetic rescue research in this system, we aim to evaluate the effectiveness of various rearing and release strategies using long-term demographic data (e.g. mark-recapture, productivity, & count data) using an integrated population model.

   Along these same lines I recently wrote a grant that was funded to evaluate the progress of the San Joaquin River Restoration Program’s spring-run Chinook salmon reintroduction initiative.  Spring-run Chinook salmon were reintroduced to the San Joaquin River in 2014 after being extirpated since the 1940s following construction of the Friant Dam.  We will be testing whether current conservation strategies have minimized the genetic risks of captive-breeding.  We will then test if there are genetic and phenotypic traits of captive-bred fish that influence reproductive success in the San Joaquin River restoration area.  Our results will provide insights into whether the current genetic protocols, and restoration habitats are meeting the life history needs of spring-run Chinook salmon.

   Building on my previous research, I anticipate the potential for numerous opportunities for collaboration with other captive-breeding stakeholders to evaluate success of existing captive breeding efforts and to help guide development of new ones.

Environmental drivers of fish population ecology:

More generally, I am interested in exploring the impact of a suite of human-induced environmental changes, including shifts away from historical baselines for temperature and precipitation, on stream fish populations. In the western United States, extreme drought and mega-fires are becoming the norm. I am currently exploring this topic through a collaboration focused on understanding the impacts of the 2014 drought on the ability of upriver migrating adult salmon to access breeding areas, Our preliminary results suggest flow-phenology mismatches for salmonid species in California - in brief, when drought leads to delayed rains, delayed high flows can result in upstream migrating salmonids being unable to access breeding habitat. Exploring consequences of shifting climates on dynamics and distributions of stream fishes will continue to be a major research theme in the future.

A full list of publications can be found here.