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Lower Colorado River Multi-Species Conservation Program Balancing Resource Use and Conservation

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Fisheries

      Information Article

After twilight has faded, underwater fishing lights go into the water and soon little flecks of light glisten just under the surface. The razorback sucker larvae are positively phototactic – instinctively drawn to light and quickly surround it. Nets are dipped into the water and larvae about 10-12 mm (just under ½ inch) in length are captured. Photo by ReclamationRecently captured larvae in an aquarium at Willow Beach National Fish Hatchery for grow-out, until they reach a length where they can be transferred to a larger tank - Photo by ReclamationWith her net in hand and underwater light dangling just below the water's surface, Biological Science Technician Trish Delrose stands near the side of her boat to collect larval razorbacks at Lake Mohave - Photo by Reclamation
  After twilight has faded, underwater fishing lights go into the water and soon little flecks of light glisten just under the surface. The razorback sucker larvae are positively phototactic – instinctively drawn to light and quickly surround it. Nets are dipped into the water and larvae about 10-12 mm (just under ½ inch) in length are captured - Photo by Reclamation   Recently captured larvae in an aquarium at Willow Beach National Fish Hatchery for grow-out, until they reach a length where they can be transferred to a larger tank - Photo by Reclamation   With her net in hand and underwater light dangling just below the water's surface, Biological Science Technician Trish Delrose stands near the side of her boat to collect larval razorbacks at Lake Mohave - Photo by Reclamation  

Goal Exceeded in Annual Lake Mohave larval Razorback Sucker Collection
By Steve Leon, Reclamation Public Affairs, Information supplied by Jim Stolberg, a general biologist in the LCR MSCP

Since 1994, more than 758,000 razorback sucker larvae have been collected from Lake Mohave.

What started out as pioneering work initiated by a small group of fisheries biologists known as the Native Fish Work Group (NFWG) has now become the cornerstone of the Lower Colorado River Multi-Species Conservation Program’s (LCR MSCP) Fish Augmentation Plan.

The end of April marked another successful year for the Lake Mohave Razorback Sucker Larval Collection Program.

For 2011, the LCR MSCP’s goal was to capture 25,000 razorback suckers for captive rearing. As of April 29, 2011 a total of 25,018 larvae had been collected from various spawning sites on Lake Mohave.

When the NFWG was founded in late 1989/early 1990 by Reclamation’s Tom Burke, Gordon Mueller of the U.S. Geological Survey, Mike Burrell from the Nevada Department of Wildlife, and Paul Marsh from Arizona State University, they sought to rebuild the adult stock of razorback suckers in Lake Mohave with the intention that these fish be used as brood fish for razorback recovery.  Their goal was to develop a population of 50,000 adult razorback suckers in Lake Mohave.

In 1994 it was determined that the capture of wild razorback larvae from the lake, and the subsequent rearing of these larvae in captivity prior to releasing them back into the reservoir, offered the best chance to successfully meet program goals.  The NFWG has continued this effort.

In achieving annual goals, crews take great care to recognize not only the quantity of larvae collected, but also the genetic quality of these fish.

The Fish Augmentation Plan has a target goal to produce a total of 660,000 razorback suckers and 620,000 bonytail for repatriation into the lower Colorado River over a 50-year period.

Additionally, the NFWG has grown to become a multi-agency partnership that includes the Arizona Game and Fish Department, Arizona State University, Marsh & Associates, Nevada Department of Wildlife, National Park Service, Southern Nevada Water Authority, and U.S. Fish and Wildlife Service, as well as Reclamation.

As part of this plan, the LCR MSCP needs to secure adequate numbers of young razorbacks for “grow-out.”  Lake Mohave’s adult razorback population, largely made up of fish repatriated by the program over the last 12 years, represents one of the most genetically diverse groups for this species in existence and is currently providing sufficient numbers of larvae for augmentation efforts.

Wild-born larval razorback suckers are collected from spawning sites on Lake Mohave between January and April of each year.  A large portion of this work is accomplished by the LCR MSCP Fisheries Group, which includes Jeff Anderson, Bonnie Contreras, Trish Delrose, Jeff Lantow, Andi Montony, Jon Nelson, Jim Stolberg, Randy Thomas, Nathan Lenon, Eric Loomis, Jenny Smith, and Ty Wolters, as well as other LCR MSCP staff, members of the NFWG, and Reclamation’s Dive Team.

Spawning sites on Lake Mohave are widespread, and larvae are routinely found in an area covering 30 river miles.

Crews travel to spawning sites each afternoon by boat, set out underwater fishing lights to attract larvae (Image 1 above), and collect them one at a time using aquaria dip nets (Image 2). Larvae are placed in five gallon buckets as they are collected, and then transported by boat or truck to Willow Beach National Fish Hatchery for captive rearing.  Larvae remain in the care of hatchery personnel (Image 3) for up to four years before reaching adult size and being repatriated to the lower Colorado River.

Because adult razorback suckers will move on and off spawning sites throughout the spawning season, and separate groups of adults will move onto spawning beds at different times, larval collections from each area have been spread out over several months to ensure they represent the genetic diversity found in the adult population.

Updated November 26, 2012