A quantitative life history of humpback chub that spawn in the Little Colorado River: variation in movement, growth and survival

Authors: Charles Yackulic, Michael D. Yard, Josh Korman, David R. Van Haverbeke

Year: 2013 (xlv)

Abstract

A number of studies have addressed important aspects of the life history of the population of humpback chub, Gila cypha, living in and around the Little Colorado River. However, the tendency to study the Little Colorado River or Colorado River portions of the population independently has hindered a synthetic view. Here we address basic life history questions and quantify variation in vital rates between the two rivers, albeit over the relatively short period of 2009-2012. We fit multistate mark-recapture models in which states are defined in terms of both size class and location (i.e., Colorado River versus Little Colorado River). We use these models to address four questions: 1) What is the rate of skip spawning in humpback chub that migrate from the Colorado River to the Little Colorado River to spawn and does this rate change as fish grow?; 2) Are there humpback chub that reside in the Little Colorado River year round?; 3) How much movement is there between the Little Colorado River and the Colorado River prior to adulthood?; and 4) How do survival and growth of different size classes vary between the Colorado River and the Little Colorado River and what is the fitness of migrants relative to residents? We find that larger adult humpback chub (>250 mm) are more likely to migrate into the Little Colorado River during the spawning season than smaller adult humpback chub (200-250 mm). We also find evidence in support of the hypothesis that there are adult residents in the Little Colorado River. Humpback chub less than 200 mm move infrequently between rivers with the exception of a large outmigration of year-zero fish from the Little Colorado River, coincident with the summer monsoon season. Humpback chub in the Colorado River have both higher monthly survival and lower growth than the same size classes in the Little Colorado River and over the short study period, the fitness of both life history strategies appear to be fairly similar.