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In 2007, we find gizzard shad have occupied all of Lake Powell. It really only took 3 years for the migration of shad to reach from the upper San Juan to the dam all the way to the headwaters of the Colorado River. In netting samples during November 2006, gizzard shad accounted for almost as much fish flesh as striped bass. The largest shad caught to date came from Wahweap bay. The huge shad was 19.25 inches long and weighed 2.8 pounds. Gizzard shad grew to larger size than normal in the fertile waters found during 20003-2006. While threadfin numbers crashed in 2006 in response to heavy predation from massive numbers of adult game fish, gizzard shad adults continued to become more numerous. There are no natural predators for big gizzard shad. They just get big and eat algae and detritus off the bottom. Large numbers of adults are needed to provide the new crop of shad each spring that all game fish depend on for growth and survival. With threadfin presently low in numbers, the progeny of gizzard shad will provide needed food fish during the critical spring months. There may not be enough shad to go around in 2007 but the presence of gizzard shad will provide at least some food to keep the fisheries on track for the near term. Gizzard Shad- Background Information One single adult gizzard shad was collected from Lake Powell in 2000 near the San Juan inflow. While the origin of the new species in Powell is unknown it has been reported by US Fish and Wildlife Service that gizzard shad were accidentally introduced into Morgan Lake near Shiprock, NM with a shipment of largemouth bass in 1998. The bass came from Inks Dam National Fish Hatchery in south-central Texas in the Rio Colorado drainage where gizzard shad are abundant in the surface water used at the hatchery. Subsequent loads of bass transported to Morgan Lake from the hatchery were found to have as many as 9 different species besides largemouth bass (fish species included Guadalupe bass, logperch, gizzard shad, white bass, bluegill, and dollar sunfish). These shipments were refused but gizzard shad were already firmly established in Morgan Lake. Logistics prevent shad from being chemically removed from Morgan Lake which is an important sport fishery on the Navajo Reservation. The 1200 acre lake provides water to the APS power plant near Shiprock. Lowering the lake would require the power plant to be shut down for an extended period. Poisoning fish without lowering the lake would block intakes with dead fish and effectively shut down the power plant, as well. No gizzard shad were found in Lake Powell during 2001. The San Juan inflow (pictured here) was the site of gizzard shad access to Lake Powell. During routine fish sampling in August 2002 on Lake Powell's upper San Juan arm six gizzard shad were collected. Shad averaged 4 inches and were suspected to be naturally reproduced within the lake. Gill nets set from the mouth of the San Juan (Jacks Arch) to Neskahi Canyon in July 2003 collected 78 adult gizzard shad. Downlake movement of the new species is confirmed as they are present and commonly found in the entire San Juan arm.

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