Ecological roles of suckers (Catastomidae) in Southwestern streams.

There are approximately 5 species of suckers in the desert Southwest—but interestingly, they appear to come in species “sets”. In many cases, a stream/river will have 2 species of suckers, one which is an apparent omnivore, and the other a primary herbivore. In Aravaipa and Bonita Creeks, these 2 species generally coexist in similar microhabitats, but the herbivorous species (Pantosteus clarkii) tends to only be found in faster, cobbly riffles and pools, whereas the omnivorous species (Catostomus insignis) is more ubiquitous, and was present in nearly all areas over 30cm deep, regardless of substrate. These fish appear to exert strong control over the algal community, greatly reducing the presence of filamentous algae (as well as reducing ChlA and AFDM in general), and change the stoichiometry of the algae as well. In addition, these species appear to be able to survive over a very large temperature and elevational gradient—Aravaipa Creek is a Sonoran Desert stream (approx 2500ft elevation) with massive temperature swings during summer (18-32C between 6am and 2pm); these fish also live in cool streams in the White Mountains of AZ (aprox 8-10,000 ft).

I am currently working on an assessment of the importance of fish in Southwestern streams, by investigating the functional significance of two catostomid fish species, Catostomus insignis and Catostomus clarki, along an elevational gradient. In particular, I am measuring the effects of these species on critical stream processes including primary production and dynamics of benthic organic matter along a gradient from warm water, hydrologically unpredictable low desert streams to cool water, high mountain streams with predictable seasonal hydrology.

Movement and Habitat Use

Little is known about the movement of fish in southwestern streams, with the majority of studies concerned with rare and endangered fishes of the Colorado River (Razorback suckers, squawfish, and humpback chub), and the remaining studies recapturing so few fish that it is difficult to make generalizations about patterns of movement. Recent advances in tagging technology such as Visual Implant Elastomer (VIE) and Passive Integrated Transponder (PIT) telemetry, combined with intensive short term sampling, have enabled me to document movement and habitat use of Catostomus insignis and Catostomus clarki, in small streams along an elevational gradient in Arizona, as well as in the upper Gila River of New Mexico. In small streams, these species appear to move relatively short distances over the span of several weeks, with the majority of fish (85-185mm SL) remaining in the same or adjacent habitat. In the larger upper Gila River, there is a nearly even split between fish (120-400mm SL) that move and those that remain in the same habitat. In addition, fish that move regularly tend to move greater distances between detections.