Forest-Associated Fishes of the Conterminous United States

Freshwaters are important, interconnected, and imperiled. Aquatic ecosystems, including freshwater fishes, are closely tied to the terrestrial ecosystems they are embedded within, yet available spatially explicit datasets have been underutilized to determine associations between freshwater fishes and forested areas. Here, we determined the spatial co-occurrence between freshwater fish distributions and forests within 2129 watersheds of the conterminous United States. We identified 21% of freshwater fishes as associated with forested areas, and 2% as strictly present only in highly forested areas (75–100% forested). The northern coasts and southeast regions, both heavily forested, showed the largest numbers of forest-associated fishes in highly forested areas and fish species richness. Fish associated with low-forested areas occurred in the southwest and central plains. Imperiled fishes were relatively evenly distributed among percent forest categories, which was distinctly different from patterns for all fishes. The identification of forest-associated fishes provides insights regarding species-specific landscape contexts. Determining these large-scale patterns of freshwater biodiversity is necessary for conservation planning at regional levels, especially in highly impacted freshwater ecosystems.

Remarkable response of native fishes to invasive trout suppression varies with trout density, temperature, and annual hydrology

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.

Multispecies and Watershed Approaches to Freshwater Fish Conservation

<em>Abstract</em>—Introduction of invasive species, whether deliberate or inadvertent, poses a significant, human-mediated threat to biodiversity that has the potential to exacerbate other anthropogenic impacts and contribute to declines in fish biodiversity. In general, invasive species share life history traits that contribute to their success, such as prolific reproduction and the ability to thrive in highly disturbed habitats. These traits inherently pose difficulties in managing these species. Prevention is widely recognized as the most effective—and often only—management strategy. From a regulatory perspective, prevention often takes the form of a blacklist of prohibited species based on risk assessments, and both the list and associated regulations are developed with input from key stakeholder groups. In the case of prohibited tilapia in Texas, a long-standing regulatory exception allowing possession of Mozambique Tilapia <em>Oreochromis mossambicus </em>for pond stocking is believed to have resulted in frequent, unlawful escapes into public waters that may pose a threat to fish species of greatest conservation need and jeopardize the success of conservation initiatives. Spatial conservation prioritization is a method gaining popularity for identifying areas where conservation actions may have the greatest positive benefit, yet the “knowing-doing gap” between science and implementation is commonly recognized as a hurdle that must be overcome. There is a need to develop science to better inform regulatory approaches to prevention and management of invasive species. This is a unique, and successful, case study that demonstrates potential for development and implementation of systematic conservation planning approaches to conservation action that addresses this need. Spatial conservation assessment using Zonation software was a component of the planning framework that facilitated identification of science-based, regulatory zones that consider potential economic impacts to commercial stakeholders. Feedback from these stakeholders, decision makers, and those tasked with enforcement was obtained and incorporated into development of a realistic, balanced regulatory approach to mitigating impacts of invasive tilapia escape on imperiled fishes in Texas.