Executive Summary

Survival of juvenile endangered Lost River and shortnose suckers is thought to limit recruitment into the adult populations and ultimately limit the recovery of these species in Upper Klamath Lake, Oregon. Although many hypotheses exist about the sources of mortality, the contribution of each speculated source of mortality has not been examined. To examine causes of mortality, validate estimated age to maturity, and examine movement patterns for juvenile suckers in Upper Klamath Lake, passive integrated transponder (PIT) tags and remote tag detection systems were used. Age-1 suckers were opportunistically tagged in 2009 and 2010 during another study on juvenile sucker distribution. After the distribution study concluded in 2010, USGS redirected sampling efforts to target age-1 suckers for tagging. Tags were redetected using an existing infrastructure of remote PIT tag readers and tag scanning surveys at American white pelican (Pelecanus erythrorhynchos), double-crested cormorant (Phalacrocorax auritus), and Forster’s tern (Sterna forsteri) breeding and loafing areas. Individual fish histories are used to describe the distance, direction, and timing of juvenile sucker movement. Sucker PIT tag detections in the Sprague and Williamson Rivers in mid-summer and in autumn indicate tagged juvenile suckers use these tributaries outside of the known spring spawning season. PIT tags detected in bird habitats indicate predation by birds was a cause of mortality.

First posted March 19, 2013