Nursery Habitat and Hatch Dates of Large River Fishes of the Lower Red River Catchment

Abstract

Many freshwater fishes in North America are of conservation concern. Both fine-and coarse-scale physicochemical conditions affect the quantity and quality of nursery habitat and can influence the hatches and growth of juvenile fishes thereby affecting successful recruitment. My research objectives were to describe nursery habitats for an assemblage of large river fishes, and determine factors related to hatch dates and growth of age-0 fishes of the lower Red River catchment. I used an occupancy model framework to determine how hierarchical factors related to occupancy of juveniles in 38 different species. I found large river nursery habitats were generally defined by reaches with off-channel slackwater habitat, having deep pools but shallow thalweg depths, located further away from dams, and with low percentages of limestone lithology. Species within the same genera often exhibited variable relationships with river slope, amount of large woody debris, channel shape, discharge, and position of reaches within the stream network. I also used a hurdle model framework and linear regression to analyze the hatch success and growth of three Centrarchidae species: Spotted Bass Micropterus punctulatus, Orangespotted Sunfish Lepomis humilis, and Longear Sunfish Lepomis megalotis. Successful hatch probability of all three species was positively related to increasing discharge conditions, whereas hatch frequency was influenced by a variety of species-specific conditions. Successful reproduction in Orangespotted Sunfish and Longear Sunfish was observed much earlier (February) and at lower temperatures than previously documented for the species. I also documented spatial differences in Spotted Bass hatch success during wet versus dry years. Additionally, hatches of all three species varied by stream, with the most consistent and protracted hatches occurring in the unregulated Muddy Boggy Creek. Growth of the three species was positively associated with warmer water temperatures. My results indicate important species-specific relationships that shape nursery habitats use and successful hatching. If the goal is to improve recruitment by fishes, consideration of the important species-specific differences would be beneficial if improvements are made to nursery habitats in the catchment. Moreover, careful consideration of dam operations will help maintain proper phenology and juvenile growth in certain parts of the river network.