Assembling a fish fauna: insights for conservation

Authors: Christopher Hoagstrom

Year: 2024

Abstract

A native-fish assemblage represents species that passed through a series of faunal filters. The history of the filtering process for any given waterbody reveals critical events and processes that explain faunal ecology. For example, the middle Pecos River formed on the southern Great Plains and is populated by fishes adapted to this relatively harsh and inaccessible ecosystem. The initial river course developed via groundwater sapping as artesian springs created associated surface waters and ultimately established base streamflows. Spring waters were ion rich and prone to concentration in evaporative habitats. Surface outflow to the Edwards Plateau likely provided the first influx of fishes, which were spring associates. As the drainage grew, it captured adjacent watercourses, making plains streams tributary to the spring-dominated drainage and introducing plains-river fishes. Concurrently, intensification of the southwestern monsoon made late-summer thunderstorms part of the annual flow regime. By this time, the river systems likely included a mix of springfed tributaries and wetlands, evaporative wetlands, and alluvial channels and floodplains, each with native fishes. More recent glacial climates facilitated additional river captures that provided a direct connection to mountains, adding mountain gravels and snowmelt runoff to the river system and introducing more fishes that joined the assemblage. The invigorated river overflowed its closed basin into what became the lower Pecos River, allowing influx of big-river fishes. Next, industrial development added reservoirs and non-native fishes, while diminishing water sources and altering ecosystem properties. Modern compartmentalization of the drainage challenges ecological integrity by disarticulating ecosystem components, but ecological contributions of each component are poorly described and tenuously linked with native fishes. Maintaining a functioning ecosystem depends on the ability to understand the significance of each ecosystem component in order to preserve, reestablish, or recreate key ecosystem processes in a natural mix that provides for the full fish assemblage.