Historic and recent age structure and growth of endangered Lost River and shortnose suckers in Upper Klamath Lake, Oregon

Abstract

Seventy-four lapilli from Lost River suckers captured in Upper Klamath Lake in 1970 during a snag fishery on spawning adults and 192 lapilli from adults sacrificed from 2001–2006 were examined to determine age and growth parameters; lapilli from 165 shortnose suckers sacrificed from Upper Klamath Lake from 2001–2006 were also examined. Relative marginal distance analyses indicated that growth marks were annuli and formed in December–January. Lost River suckers from the historic collection were aged to 57 years, while Lost River and shortnose suckers from the recent collection were aged to 40 years and 24 years, respectively. Larger and older Lost River suckers were represented in the historic collection compared to the recent collection. Uncoupling of otolith length and fish length in Lost River suckers as well as a large spread in the predicted age- at-size for shortnose suckers precluded the ability to back-calculate size-at-age. Likelihood ratio tests indicated the growth model parameters were significantly different at both the sex and collection level. Growth in body length for both species appeared determinate in that growth was rapid until maturity, and then slowed over several years until growth in length was nearly nonexistent; a 650–700 mm Lost River sucker could be between 14 and 57 years old, while a 460 mm shortnose sucker could range from 12–24 years old. In contrast, while growth in body length slowed for both species, body mass continued to increase. This growth strategy, which is also found in other western lake suckers, may allow for more energy to be utilized for reproduction and help populations persist in spite of years of limited recruitment or recruitment failure.