While the ecology and evolution of partial migratory systems (defined broadly to include skip spawning) have been well studied, we are only beginning to under- stand how partial migratory populations are responding to ongoing environmen- tal change. Environmental change can lead to differences in the fitness of residents and migrants, which could eventually lead to changes in the frequency of the strategies in the overall population. Here, we address questions concerning the life history of the endangered Gila cypha (humpback chub) in the regulated Colorado River and the unregulated tributary and primary spawning area, the Little Colorado River. We develop eight multistate models for the population based on three movement hypotheses, in which states are defined in terms of fish size classes and river locations. We fit these models to mark–recapture data col- lected in 2009–2012. We compare survival and growth estimates between the Col- orado River and Little Colorado River and calculate abundances for all size classes. The best model supports the hypotheses that larger adults spawn more frequently than smaller adults, that there are residents in the spawning grounds, and that juveniles move out of the Little Colorado River in large numbers during the monsoon season (July–September). Monthly survival rates for G. cypha in the Colorado River are higher than in the Little Colorado River in all size classes; however, growth is slower. While the hypothetical life histories of life-long resi- dents in the Little Colorado River and partial migrants spending most of its time in the Colorado River are very different, they lead to roughly similar fitness expectations when we used expected number of spawns as a proxy. However, more research is needed because our study period covers a period of years when conditions in the Colorado River for G. cypha are likely to have been better than has been typical over the last few decades.
ABSTRACT: The Colorado River below Glen Canyon Dam, Arizona, is part of an adaptive management programme which optimizes dam operations to improve various resources in the downstream ecosystem within Grand Canyon. Understanding how populations of federally endangered humpback chub Gila cypha respond to these dam operations is a high priority. Here, we test hypotheses concerning temporal variation in juvenile humpback chub apparent survival rates and abundance by comparing estimates between hydropeaking and steady discharge regimes over a 3-year period (July 2009–July 2012). The most supported model ignored flow type (steady vs hydropeaking) and estimated a declining trend in daily apparent survival rate across years (99.90%, 99.79% and 99.67% for 2009, 2010 and 2011, respectively). Corresponding abundance of juvenile humpback chub increased temporally; open population model estimates ranged from 615 to 2802 individuals/km, and closed model estimates ranged from 94 to 1515 individuals/km. These changes in apparent survival and abundance may reflect broader trends, or simply represent inter-annual variation. Important findings include (i) juvenile humpback chub are currently surviving and recruiting in the mainstem Colorado River with increasing abundance; (ii) apparent survival does not benefit from steady fall discharges from Glen Canyon Dam; and (iii) direct assessment of demographic parameters for juvenile endangered fish are possible and can rapidly inform management actions in regulated rivers.
ABSTRACT: Recovery of imperiled fishes can be achieved through suppression of invasives, but outcomes may vary with environmental conditions. We studied the response of imperiled desert fishes to an invasive brown (Salmo trutta) and rainbow trout (Oncorhynchus mykiss) suppression program in a Colorado River tributary, with natural flow and longitudinal variation in thermal characteristics. We investigated trends in fish populations related to suppression and tested hypotheses about the impacts of salmonid densities, hydrologic variation, and spatial–thermal gradients on the distribution and abundance of native fish species using zero-inflated generalized linear mixed effects models. Between 2012 and 2018, salmonids declined 89%, and native fishes increased dramatically (∼480%) once trout suppression surpassed ∼60%. Temperature and trout density were consistently retained in the top models predicting the abundance and distribution of native fishes. The greatest increases occurred in warmer reaches and in years with spring flooding. Surprisingly, given the evolution of native fishes in disturbance-prone systems, intense, monsoon-driven flooding limited native fish recruitment. Applied concertedly, invasive species suppression and efforts to mimic natural flow and thermal regimes may allow rapid and widespread native fish recovery.
Between 1999 and 2005, drought in the western United States led to a >44 m fall in the level of Lake Powell (Arizona-Utah), the nation's second-largest reservoir. River discharges to the reservoir were halved, yet the rivers still incised the tops of deltas left exposed along the rim of the reservoir by the lake-level fall. Erosion of the deltas enriched the rivers in sediment such that upon entering the reservoir they discharged plunging subaqueous gravity flows, one of which was imaged acoustically. Repeat bathymetric surveys of the reservoir show that the gravity flows overtopped rockfalls and formed small subaqueous fans, locally raising sediment accumulation rates 10–100-fold. The timing of deep-basin deposition differed regionally across the reservoir with respect to lake-level change. Total mass of sediment transferred from the lake perimeter to its bottom equates to ~22 yr of river input.
The summer after my Junior year, I studied abroad in Denmark and was given the opportunity to create my own research topic. My interest in Sustainability has always revolved around food, so I started thinking about ways that I could incorporate this interest with the geographical backdrop of Århus, Denmark. Food is a medium for so many uniquely human creations: celebrations, art, connection, and taste. Food is also a big driver of climate change, as the meat and agriculture industries account for more than half of all greenhouse gas emissions. However, I wanted to research more than food. I wanted to incorporate balance; a balance of local and global food systems, a balance of individual and community relationships, and a balance of science and art. I wanted to show how food is a driving force in achieving global sustainability and resilience.
After much contemplation, I began researching the connections between local food and community wellbeing in the city. I interviewed farm-to-table chefs, local farmers, farmer’s market vendors, street food vendors, and consumers on their relationships with food. The topic itself was flexible and open-ended enough so that each interviewee could relate it to their lives in a unique way. I loved the research so much that I decided to continue interviewing stakeholders in the Phoenix metropolitan area. Through the continuation of my research in Arizona, I was able to include a comparative element that offered a better perspective on the matter. I found that the history of the country itself has a significant influence on people’s mindsets and actions surrounding food and the environment. The common theme I heard from all interviewees, however, was their confidence in the power of food to unite people to one another and to the natural world.
I chose to create this illustrated book because my research experience was a whole and inseparable experience; it could never be fully expressed in words. I wanted my project to be an intellectual and visual map of my journey, inspiring the reader to go on a journey of their own. Therefore, I partnered with an undergraduate art student at Arizona State University, Sofia Reyes, to help create my vision. I shared my experiences, photos, and stories with her so that she could create the beautiful watercolor paintings that make the book so visually appealing and accessible to all demographics. The images act as a way of engaging all of our human senses, initiating a stronger connection to the material presented.
Creating this project was my favorite experience as an undergraduate, and I feel fortunate to be able to tell the stories of those intimately tied to the local food system. I am in the process of entering my book in various competitions including Writer’s Digest, Reader’s Favorites, The Food Sustainability Media Award, and The Indie Book Awards. I am also going on to publish the book through a small publishing company.