Difference between revisions of "Smallmouth Bass Page"

PAGE, Ariz. —On July 1, 2022, juvenile smallmouth bass were found in the Colorado River below the Glen Canyon Dam. Smallmouth bass are a predatory non-native fish that have adversely impacted native and federally protected fish in the upper basin of the Colorado River over the last 20 years. The National Park Service (NPS) is working closely with partners and stakeholders to coordinate rapid response actions to address this finding in accordance with previously approved management plans.

Lower lake levels at Lake Powell and rising temperatures in the Colorado River have increased concerns that non-native, warm-water predators, including smallmouth bass, could pass through the dam and begin reproducing. If these warm-water predators establish populations below the dam, it is likely they would negatively impact native fish communities in Glen Canyon National Recreation Area and in Grand Canyon National Park.

The NPS encourages anglers to report any observations or catches of smallmouth bass below the dam. If caught, please remove the fish, put on ice and contact staff at Glen Canyon National Recreation Area or Grand Canyon National Park with a description of the location where found. Report findings to: Jeff Arnold, Glen Canyon National Recreation Area, e-mail us or Brian Healy, Grand Canyon National Park, e-mail us. [2]

• Nonnative Invasive Aquatic Species

• Evaluate effects of flow spikes to disrupt reproduction of smallmouth bass in the Green River downstream of Flaming Gorge Dam

2022

• 'Worst fears confirmed' in biologists' fight to save ancient Colorado River fish
• Flow spike to reduce smallmouth bass reproductive success, Green River, 2021
• Near-Term Threat of Smallmouth Bass Establishment below Glen Canyon Dam
• Fish modelling to support management decisions

Description: Smallmouth bass are a non­native fish that was introduced into Arizona in 1921 (AGFD 2005). They are native to the upper Mississippi River basin. [3] These bass are most often bronze to brownish in color, with dark vertical bars on the sides. In contrast to the largemouth bass, the upper jaw does not extend beyond the rear margin of the eye. The eye is reddish in color and there is a shallow notch in the dorsal fin. The soft dorsal fin has 13 to 15 rays. Length can vary between 12 and 22 inches, and smallmouth bass can weigh between 8 ounces and 7 pounds. [4]

Location and Habitat: Within its native range the smallmouth bass seems most abundant in pools of streams that consist of a substantial proportion of riffle habitat, clean, rocky, hard bottoms, and gradients of 0.5 to about 5.0 m per km. In large rivers and lakes, smallmouth bass tend to congregate over hard, stony bottoms, where currents are present (Minckley 1973). At the present time, smallmouth bass occur in the mainstream of the Colorado River, in the Verde River system, and throughout the Salt River Basin below about 2,200 meters in elevation (Minckley 1973). [5]

Temperature:

Turbidity and Dissolved Oxygen:

Salinity:

Reproduction: Spawning occurs from March though May in Arizona, when water temperatures reach 15C to 18C. Males fan an oval depression in sand or gravel through violent, lateral movements of the body and caudal fin. Individual nests usually contain about 2,000 fertilized ova; eggs hatch in 3 to 5 days at typical water temperatures; the young remain in the interstices of gravel for about a week. The fry then rise as a school, and are herded about and defended vigorously by the male until 30 to 40 mm in total length (Minckley 1973). [6]

Food: Foods of young smallmouth bass consist mostly of tiny crustaceans. As they grow, they shift over to insects, then to other fishes, and finally to a mixed diet of crayfish and other fishes. [7]

Risk: In Arizona, smallmouth bass reportedly are responsible for eliminating or reducing some populations of native fishes. [8]