Status and trends of adult Lost River (Deltistes luxatus) and shortnose (Chasmistes brevirostris) sucker populations in Upper Klamath Lake, Oregon, 2017

Abstract

Survival estimate precision in early years of the study; however, are poor. Capture-recapture models and size composition data indicate that recruitment of new individuals into the SNS spawning population was trivial from 2001 to 2005. Models indicate that more than 10 percent of the population was new recruits in a number of more recent years. As a result, capture-recapture modeling suggests that the abundance of adult spawning SNS was relatively stable from 2006 to 2010. We are skeptical of the estimated recruitment in 2006 because of the known sampling issue. We also are skeptical of the estimated recruitment in other recent years because few small individuals that would indicate the presence of new recruits were captured in any of those years, and recapture probabilities in recruitment models were low. The best-case scenario for SNS, based on capture-recapture recruitment modeling, indicates that the abundance of males in the spawning population decreased by 78 percent and the abundance of females decreased by 77 percent from 2001 to 2015. Decreases in abundance for both sexes are likely greater than these estimates indicate. Despite relatively high survival in most years, we conclude that both species have experienced substantial decreases in the abundance of spawning adults because losses from mortality have not been balanced by recruitment of new individuals. Although capture-recapture data indicate substantial recruitment of new individuals into the spawning populations for SNS and river spawning LRS in some years, size data do not corroborate these estimates. As a result, the status of the endangered sucker populations in Upper Klamath Lake remains distressed, especially for SNS. Our monitoring program provides a robust platform for estimating vital population parameters, evaluating the status of the populations, and assessing the effectiveness of conservation and recovery efforts.

Colonial Waterbird Predation on Lost River and Shortnose Suckers in the Upper Klamath Basin

“…Juvenile suckers have been captured and PITtagged in Upper Klamath Lake since 2008 and in Clear Lake since 2010. A brief description of the USGS-led capture, tagging, and release methods are presented below (see Janney et al 2008;Hewitt et al 2010Hewitt et al , 2015 Hayes 2013 for detailed descriptions).…”

“…Results provide evidence of some size selectivity across sucker species and age-classes, whereby predation rates were highest on juvenile-sized suckers, followed by Shortnose Suckers, and lastly, the largest species, Lost River Suckers. These findings may be related to the foraging abilities of cormorants and pelicans, whereby smaller-sized suckers were more susceptible to bird predation than larger-sized suckers, particularly the largest Lost River Suckers, such as those from the shoreline spawning subpopulation (up to 800 mm FL: Hewitt et al 2015). The largest fish a double-crested cormorant can consume depends on the mass and shape of the fish, but is generally considered not to exceed about 450 mm FL (Hatch and Weseloh 1999).…”

“…Endangered Species Act (ESA). Numerous factors have been identified as limiting the recovery of sucker populations, including habitat loss, poor water quality, and a lack of juvenile recruitment into the spawning populations (Janney et al 2008;USFWS 2012;Hewitt et al 2015). The impacts of predatory birds on ESA-listed sucker populations, however, is currently unknown but may be significant based on the abundance and diversity of piscivorous waterbirds that reside in the Upper Klamath Basin, as well as the relative scarcity of suckers compared with the past.…”

“…Samples of Lost River and Shortnose suckers are tagged each year with PIT tags to gather information on their behavior and survival following release (Janney et al 2008;Hewitt and Hayes 2013;Burdick et al 2015;Hewitt et al 2015). The PIT tags allow specific information to be linked to individual fish, such as species, size, age-class (adult, juvenile), and release location.…”

“…In addition to physical captures, passive encounters of PITtagged suckers using remote underwater antennas were also used to provide information about sucker availability. Remote antenna systems at spawning areas in Upper Klamath Lake (see Hewitt et al 2015 for a full description of these systems) detected both 125-kHz tags (fish tagged before 2005) and 134-kHz tags (fish tagged during 2005 to 2014). At Clear Lake, remote antennas were used in Willow Creek (beginning in 2006; see Hewitt and Hayes 2013) and in a channel in a shallow strait between the two lobes of Clear Lake (beginning in 2014).…”