Current Research
Optimizing control of a freshwater invader in time and space
Manuscript under review
Co-authors: Sarah Converse, Matt Chmiel, Andy Stites, Julian Olden
The continued and growing impacts of invasive freshwater fishes has prompted many natural resource agencies to implement control programs with the goal of population suppression or eradication. Mechanical removal is the favored control method with respect to cost and reduced likelihood of collateral damage, yet its past success in achieving species management goals varies substantially. Control programs that optimally allocate removal effort across space and time offer promise for improving invasive species suppression or eradication, especially given the limited resources available to these programs. Here we leveraged two intensive fish eradication programs for green sunfish (Lepomis cyanellus) in intermittent streams of the Bill Williams River in Arizona, USA, to explore alternative management strategies involving variable allocation of removal effort in time and space and compare static versus dynamic decision rules to guide actions. We used Bayesian hierarchical modeling to estimate demographic parameters using existing removal data. We show strong evidence that both removal programs led to successful eradication, with 0.39 probability of eradication (i.e., <2 individuals remaining) in McGee Wash and East Ash Creek. Alternative management strategies were then simulated, revealing the importance of continued sampling after zero fish are captured and the increased efficiency of dynamic management. Simulated alternative management strategies revealed that population suppression could be achieved with fewer locations sampled via dynamic management based on catch rate, compared to randomly sampled locations. High removal frequency and program duration, including continued collections even after no fish were previously captured, contributed to eradication success.
Map of tributaries within Trout Creek, AZ watershed where the Arizona Game and Fish Department (AZGFD) conducted green sunfish removals. Removal sites are identified by points. Panel A is the watershed including all removal sites, panel B is East Ash Creek, and panel C is McGee Wash. Panel D is AZGFD staff using a seine net to remove fish (photo credit AZGFD), panel E is a net full of green sunfish (photo credit Julian Olden), panel F is one of the pools in McGee Wash (photo credit AZGFD), and panel G is a close up of a green sunfish caught in Burro Creek within the Bill Williams River Basin, AZ (photo credit Jessica Diallo).
Model estimated green sunfish population (line) and number removed (grey bars) over time in McGee Wash, Arizona. Insets show posterior probability distributions of the total population at the start (upper left) and end (lower right) of the removal program. Grey ribbon represents the 95% credible interval.
Fish invaders cause a lifetime of trophic change in native desert fishes
Manuscript in preparation
Invasive fishes modify the structure and function of riverine food webs through their presence and competitive and predatory interactions with native fishes. The degree of trophic plasticity of native fishes at different life stages in response to invaders is unknown. This research provides insight into life-long trends in dietary isotope values using fish eye lenses that grow incrementally and are comprised of metabolically inert, proteinaceous tissue. The findings demonstrate significant shifts in 13C/12C and 15N/14N throughout an individual’s lifetime that vary ontogenetically and differ for native species in native-only versus mixed native-invasive fish assemblages. Trophic level generally increases throughout ontogeny, with native fishes in mixed assemblages displaced to a lower trophic position compared to native-only. Native fish conservation should consider how invasive fishes impact native fishes at multiple life stages, with implications for individual growth and population persistence.
Jess using backpack electrofishing to capture fish in Burro Creek, Arizona during April, 2021 (top left). A roundtail chub (Gila robusta) (lower left) and desert sucker (Catostomus clarkii) (right)
Jess conducting fish eye lens dissection for stable isotope analysis (left). Partially dissected eye lens (top right). Stable isotope results for a single roundtail chub. Eye lens layers are plotted as individual points from the core (1) to the outer layer (8) (bottom right)
Otoliths from captured fish were used to age the fish and link eye lens layers to fish age and points in time. This is possible using species-specific relationships between fish length and eye lens diameter, fish length and otolith diameter, as well as individual fish measurements of growth (age vs. fish length).
Roundtail chub lapillar otoliths (top left), green sunfish sagittal otoliths (bottom left), roundtail chub polished lapillar otoliths (top and bottom right). Otolith width ~ 2mm
Leveraging PIT tag data to better understand northern pikeminnow movement in the Columbia River Basin
Collaborators at NOAA’s Northwest Fisheries Science Center: Beth Sanderson, Katie Barnas, and Jim Faulkner
Northern pikeminnow are native to the Columbia River, but their increased predation of juvenile salmonids due to habitat modification has led to long-term population control efforts. The Northern Pikeminnow Management Program (NPMP) is a targeted harvest program, comprised primarily of a sport reward fishery, that has been operating in the Columbia and Lower Snake Rivers since 1991. As a result of this sport reward fishery, over 5.5 million piscivorous (≥ 200mm FL) northern pikeminnow have been harvested for cash rewards. Each year data are collected to monitor and evaluate the program. Northern pikeminnow have been PIT tagged through the NPMP since 2003 to calculate the program’s exploitation rate, with the goal of reducing the population by 10-20%. The model used assumes closed populations separated by dams and leads to an estimated annual reduction in predation. After being tagged, most northern pikeminnow are never recaptured, but their movement is passively tracked by PIT tag antennas. We combined data from the Columbia Basin PIT Tag Information System (PTAGIS) database with NPMP tagging and harvest data. Initial results reveal that individuals traveled as far as 968 km. Nearly 13% of northern pikeminnow harvested through the NPMP were captured in different reservoirs (or river sections separated by dams) than where they were initially tagged. Understanding northern pikeminnow movement will inform the exploitation rate calculation as one of the key measures of NPMP success. As the NPMP evolves over time, information on northern pikeminnow movement may also inform future management strategies.