Tributary Streams Provide Migratory Fish with Access to Floodplain Habitats in a Regulated River: Evidence from Alligator Gar (Atractosteus spatula)

Abstract

Fishes that migrate within freshwater and exhibit periodic life history traits are broadly distributed and particularly sensitive to the effects of river regulation. However, persistence of migratory fishes in highly regulated rivers may be related to tributaries providing necessary spawning and early life stage habitats. To explore this, I studied the movement of Alligator gar, Atractosteus spatula, and hydrology, in a highly regulated North American river, the Brazos River. I hypothesized that: 1) mainstem flood pulses would be much more limited than tributaries due to historical river regulation and 2) fish movements into tributaries would be best predicted by higher flows and temperatures. My analysis revealed that flood pulses were drastically reduced on the mainstem, but not a tributary, and tributary occurrence was highest above mean temperatures (i.e., 25℃) and when flows exceeded a 3 pulse per season (i.e., 300 cms) frequency. These results provide a framework for advancing the conservation of migratory fishes in regulated rivers and further highlight the use of tributaries in buffering mainstem populations against the effects of river regulation.