|Abstract or Summary
- Upper Klamath Lake in southern Oregon has two species of lacustrine suckers,
Lost River sucker Deltistes luxatus and shortnose sucker Chasmistes brevirostris that
were historically abundant. Results of surveys performed in the mid-1980's indicated that populations of both species were declining and ageing with apparent recruitment failure in most years since 1970. In 1988 both species were listed as endangered species and high priority has been placed on investigating recruitment of Upper Klamath Lake
suckers. Lapilli are the preferred otolith for ageing suckers. Lapilli form predictably on the day of hatch, have the most conservative morphology of the three otoliths, and deposit
easily discernable increments that begin on the day of hatch and proceed daily, and grow
in a predictable relationship with somatic growth. Ages estimated by otolith analysis and
resulting hatch dates of young-of-the-year Lost River sucker and shortnose sucker were
consistent annually and consistent with reported spawning period for suckers from Upper
Otolith increment analysis is necessarily lethal, whereas scale circuli analysis is not lethal. My findings suggest that scale circuli count is an inefficient estimator of daily Daily age estimates for
age in young-of-the-year Lost River sucker and shortnose sucker. any given circuli count varied by approximately 51 days in Lost River sucker and 30 days Additionally, my results do not accurately predict the size or age at
in shortnose sucker.
which scales are formed, thereby invalidating an assumption of age and growth models.
Consequently, scale circuli analysis cannot be used to produce accurate estimates of age or growth for young-of-the-year Lost River sucker and shortnose sucker. Lost River sucker and shortnose sucker achieve a relatively large size by the autumn of their first year, consistent with other members of Catostomidae. Interspecific
difference in growth rates was evident in each year with Lost River sucker exhibiting
faster growth than shortnose sucker in each year. Abundance of young-of-the-year suckers does not appear to be strongly correlated to somatic growth rate, though hatch date and environmental parameters are highly correlated with abundance. In both Lost River sucker and shortnose sucker, in years with the highest abundance (1991 and 1993), the mean hatch dates of surviving fish were later
than in years with the lowest abundance. Also, young-of-the-year Lost River sucker and shortnose sucker experienced wide environmental fluctuations in Upper Klamath Lake as seasonal limnological and climatic variation create a dynamic habitat for young suckers. Water temperature, precipitation, air temperature, and minimum lake elevation are all strongly correlated to abundance of young-of-the-year suckers.