Potential Barriers to Aquatic Habitats
It is obvious that fish need water to live, but what is less obvious is why some waters support fish communities while others do not. Additionally, why do some species only persist in specific aquatic environments whereas other species seem to thrive anywhere? The short answer is that aquatic habitat is complex. The quantity and quality of water is important, but so is the range in temperature, the substrate of the stream bed, the availability of cover in the water column, and the changes in water flow through the habitat. Fish require specific habitat to spawn, forage and shelter. For some species these different habitats are in close proximity, but for others it is necessary to migrate long distances to access these specific habitats.
Blue Sucker are a big-river obligate species that occur throughout the Red River below Lake Texoma. For most of the year, Blue Sucker occupy the mainstem of the Red River, but in springtime when warming temperatures coincide with large flow pulses, individuals will migrate from just below Denison Dam or beyond the Arkansas border to spawn in the Blue, Muddy Boggy, and Kiamichi rivers. Unlike the Red River, these tributaries have steep-gradient riffles with large, cobble and boulder substrate, or in other words, the required spawning habitat for Blue Sucker. Investigation of the age structure of the population indicated that early spring flow pulses in Muddy Boggy and stable summer flows in the Red River produced the strongest year classes in the Blue Sucker population below Denison Dam. However, the population in the Kiamichi River, below Hugo Dam, appeared to be shrinking each year. When considering this evidence in the context of dam operation, it appeared that the free-flowing Muddy Boggy River supported the population below Denison Dam, but dam operations in the Kiamichi River likely lured Blue Suckers to spawn, only to leave the nests stranded in dry rocks when the dam gates were closed. One final point on the effects of dams on Blue Suckers is that Blue Sucker were not found upstream of either dam. Blue Sucker have historically occurred in the Arkansas River as well, but they may now be extirpated due to the high degree of fragmentation throughout the river.
Dams that create large reservoirs negatively affect several big-river obligate fishes including Alligator Gar, Eel, Paddlefish and Sturgeon, but road crossings also have the potential to negatively affect stream fishes in smaller wadeable streams. These road crossings not only create physical barriers but also change the flow regime and alter habitat. When the stream flow is constricted through culverts or concrete structures, the water velocity can exceed the swimming capability of native fishes, effectively creating a barrier. Further, when flow is restricted, the road crossing can have a damming effect creating a small impoundment that is much different from the natural stream environment. By retaining water, these stream crossings have an effect like a flood control dam that suppresses small flow pulses and amplifies large flows. The results are fragmented streams, altered habitat, and interrupted spawning cues.
OCC and the Oklahoma Wildlife Department have taken the lead in partnering with the Southeastern Aquatic Resources Partnership to inventory and work toward replacing problematic road crossings. Members of other state agencies, nonprofit organizations, and universities are pitching in to assist with surveying and contributing to the inventory of road crossings across the state.
Author: Joseph Dyer, Monitoring & Assessment Specialist