Razorback sucker studies on Lake Mohave, AZ-NV

Status: Ongoing

In the years following the 1951 closure of Davis Dam on the lower Colorado River, the resident razorback sucker experienced a local population boom within newly created Lake Mohave.  Once the reservoir was filled, non-native fishes became established and most of the native fish fauna disappeared.  Although a substantial population of adult razorback sucker produced in the early 1950s survived, and successfully spawned and produced larvae in the reservoir, recruitment to adulthood was not observed.  The wild population that initially peaked at a hundred thousand or more individuals gradually declined to an estimated few dozen to a few hundred elderly fish in the early 21st century.  To augment the declining population, a stocking program was initiated in 1992 to capture wild produced larvae, rear young fish for up to three years in protective custody in lakeside backwaters and hatcheries, then PIT tag each individual prior to being repatriated back into the reservoir.  Nearly 150,000 thousand repatriates have been stocked into Lake Mohave, but the population estimated by mark-recapture methods is only approximately 1,500 fish.  The Lake Mohave population is valued both intrinsically and politically in that federal policy requires the preservation of the genetic variation of the population in the lake.  To date, this variation has been successfully maintained.

We are currently using acoustic telemetry, trammel nets, and remote PIT-scanners to monitor the repatriate population in Lake Mohave.  Data from monitoring have shown that large striped bass are hindering razorback sucker recovery efforts because they consume most individuals that are stocked.  Striped bass are relative newcomers to the reservoir, having been accidentally introduced in 1983.  A robust non-native trout stocking program has helped grow individual striped bass to record breaking size.  Because large striped bass are difficult to sample, we launched a campaign in early 2011 that rewards striped bass anglers who find native fish in the stomach of striped bass and who report their findings in an online forum.  You can view the web page here:  www.lakemohavestripers.com