Assessment of age-0 Colorado pikeminnow survival in backwater habitats in the middle Green River

Authors: Joseph A. Skorupski

Year: 2012 (xliv)

Abstract

Sampling of age-0 Colorado pikeminnow (Ptychocheilus lucius) has been conducted annually since the mid-1980s to assess the abundance and distribution of young fish. Since 1994, these surveys have shown a drastic reduction in the abundance of age-0 Colorado pikeminnow in the alluvial section of the Green River between Split Mountain and Desolation Canyon. However, studies monitoring the abundance of larval Colorado pikeminnow drifting from the Yampa Canyon spawning site during the same time, suggest that larval fish production has not decreased from previous levels when age-0 Colorado pikeminnow were more abundant in this reach. Several possibilities exist for why age-0 Colorado pikeminnow are not being caught as frequently as they once were, such as an increase in nonnative fishes. To address the possible influence nonnative fishes may have on age-0 pikeminnow, a blocking study was established in 12 separate backwater habitats. Backwaters include three treatments, all of which were initially depleted of nonnatives before the arrival of Colorado pikeminnow: (1) four control backwaters that will not be blocked after initial depletion; (2) four backwaters blocked by 1/4 inch mesh nets; and (3) four backwaters that are blocked by a 1/2 inch mesh nets. In general, blocked backwaters had a greater abundance of native fishes, with high growth rates. The blocking study will enhance our knowledge of ways to increase the survival of age-0 Colorado pikeminnow and other native species that utilize backwater habitats.