Demographics and 2008 Run Timing of Adult Lost River (Deltistes luxatus) and Shortnose (Chasmistes brevirostris) Suckers in Upper Klamath Lake

Abstract

We used capture-recapture data to assess population dynamics of endangered Lost River suckers (Deltistes luxatus) and shortnose suckers (Chasmistes brevirostris) in Upper Klamath Lake, Oregon. The Cormack-Jolly-Seber method was used to estimate apparent survival probabilities, and a temporal symmetry model was used to estimate annual seniority probabilities. Information theoretic modeling was used to assess variation in parameter estimates due to time, gender, and species. In addition, length data were used to detect multiple year-class failures and events of high recruitment into adult spawning populations. Survival of adult Lost River and shortnose suckers varied substantially across years. Relatively high annual mortality was observed for the lakeshore-spawning Lost River sucker subpopulation in 2002 and for the river spawning subpopulation in 2001. Shortnose suckers experienced high mortality in 2001 and 2004. This indicates that high mortality events are not only species specific, but also are specific to subpopulations for Lost River suckers. Seniority probability estimates and length composition data indicate that recruitment of new individuals into adult sucker populations has been sparse. The overall fitness of Upper Klamath Lake sucker populations are of concern given the low observed survival in some years and the paucity of recent recruitment. During most years, estimates of survival probabilities were lower than seniority probabilities, indicating net losses in adult sucker population abundances. The evidence for decline was more marked for shortnose suckers than for Lost River suckers. Our data indicated that sucker survival for both species, but especially shortnose suckers, was sometimes low in years without any observed fish kills. This indicates that high mortality can occur over a protracted period, resulting in poor annual survival, but will not necessarily be observed in association with a fish kill. A better understanding of the factors influencing adult survival and recruitment into spawning populations is needed. Monitoring these vital parameters will provide a quantitative means to evaluate population status and assess the effectiveness of conservation and recovery efforts.

Status of Lost River Sucker and Shortnose Sucker

“…Recruitment to the spawning populations has been negligible for the past 10-12 years Cooperman 2002, Janney et al 2008). Length-frequency data suggest that the last significant recruitment to the adult population in Upper Klamath Lake occurred in the late-1990s from fish that were spawned earlier in that decade (Janney et al 2008). Consequently, spawning populations consist of a relatively homogenous size distribution strongly skewed toward large individuals, which is interpreted to mean that the age distribution is also relatively homogenous.…”

“…Spawning populations of Lake River sucker and shortnose sucker within Upper Klamath Lake are currently declining (Janney et al 2008). Between 1999 and 2008, approximately 25,000 Lost River sucker were captured and tagged during surveys of the spawning populations in Upper Klamath Lake.…”

“…Between 1999 and 2008, approximately 25,000 Lost River sucker were captured and tagged during surveys of the spawning populations in Upper Klamath Lake. Approximately 10,000 were associated with the river-spawning life history and the remainder with the springspawning life history (Janney et al 2009). Close to 14,000 shortnose sucker, which predominantly exhibit the river-spawning life history, were captured and tagged in Upper Klamath Lake between 1995 and 2008 (Janney et al 2009).…”

“…Approximately 10,000 were associated with the river-spawning life history and the remainder with the springspawning life history (Janney et al 2009). Close to 14,000 shortnose sucker, which predominantly exhibit the river-spawning life history, were captured and tagged in Upper Klamath Lake between 1995 and 2008 (Janney et al 2009). From these spawning populations, large numbers of larvae are hatched each year (Cooperman and , Cooperman et al 2010, Ellsworth et al 2010, and age-0 juveniles can be found until late summer, when they become very scarce (Bottcher and.…”

“…However, these ratios declined for both species during this period. Sex ratios of trammel-net captures of Lost River sucker associated with the eastern shoreline springs (1999)(2000)(2001)(2002)(2003)(2004)(2005)(2006)(2007)(2008) also steadily declined over time, from 4.72 males per female in 1999 to 0.91 in 2008, with a median ratio of 1.82 (data from Janney et al 2009). Males consistently exhibit higher mortality rates than females (Janney et al 2008), which can explain much of this declining trend in sex ratios, but the ultimate causes of this disparity in mortality rates is unknown.…”