Efficacy of Mechanical Removal of Nonnative Fish from Closed Systems. an Update on Bonita and Aravaipa Creeks.

Authors: Heidi Blasius, Jeff Conn

Year: 2018

Abstract

Bonita and Aravaipa Creeks are located within southeastern Arizona and are unique in that they still support intact native fish assemblages and exceptional riparian and aquatic values. Past native fish recovery actions, including construction of fish barriers that prevent or hinder future upstream incursions of nonnative fishes from downstream sources, have benefitted both creeks. However, both native fisheries are still threatened by the presence of nonnative predatory and competitive fish species. To reduce the threat of nonnative fishes in both systems, the BLM, Safford Field Office, collaborated with federal, state, private, and non-governmental partners to begin mechanical removal of Green Sunfish in 2009 at Bonita Creek and 2010 at Horse Camp Canyon, Aravaipa Creek. Green Sunfish were targeted due to their highly piscivorous nature and their ability to thrive in these two systems. In Bonita Creek, nonnative fishes were removed from a 1.9 mile reach dominated by beaver dam pools and glides. Beaver dams effectively reduce the movement of Green Sunfish within the removal area. In Horse Camp Canyon, nonnative fishes were removed from a 0.5 mile reach that is characterized by boulder-strewn bedrock pools and slots. Boulders and other natural features restrict movement of fish into the removal reach of Horse Camp Canyon except during seasonal flood events when a surface connection exists to Aravaipa Creek. Baited Gee metal minnow traps, collapsible Promar traps, and hoop nets were the primary removal methods used at both creeks. Occasionally seines, dip nets, and backpack electrofishers were used to augment and assess efforts. Total effort using Gee metal minnow traps, collapsible Promar traps, hoop nets, and custom and crab traps was 46,677 overnight net sets from 2009-2017, which resulted in the removal of 22,709 Green Sunfish from Bonita Creek. In 2018, 1,146 overnight net sets at Bonita Creek resulted in zero Green Sunfish captured. No Green Sunfish have been seen or captured from Bonita Creek since October 2017. A total of 3,910 Green Sunfish were removed from Horse Camp Canyon from 2010-2015, and 2018. The majority (n=2,675) were captured with Gee metal minnow traps and Promar collapsible nets. Seining, dip netting, and backpack electrofishing captured 1,235 Green Sunfish. No Green Sunfish have been seen or captured since October 2015. Results to date, suggest Green Sunfish have been eliminated from both systems above their barriers.