Differential effect of temperature on larval Razorback Sucker and Flannelmouth Sucker growth - could temperature be limiting larval Razorback Sucker recruitment?

Authors: Stephani Clark Barkalow, Platania L., P. Steven, Jennifer Kennedy, Gilbert L., I. Eliza

Year: 2016 (xlviii)

Abstract

Razorback Suckers spawn and produce larvae in both the San Juan River and the Colorado River in Grand Canyon but there is little evidence larvae recruit to juveniles in either system. Predation by non-native fishes has long been cited as a major barrier to recruitment, though both systems have a relatively low non-native obligate piscivorous fish burden. Thus other factors must limit Razorback Sucker larvae recruitment. In both of these systems Flannelmouth Suckers are abundant. Flannelmouth Suckers spawn at a similar time as Razorback Suckers and recruitment of larvae to juveniles is consistently documented. One hypothesis as to the differential recruitment success is that there is a differential effect of water temperature on growth. In 2011, larvae were collected from the San Juan River once a week between 22 April and 29 July. Species, age (days), and growth rate of a subset of larvae was determined by counting daily growth rings in otoliths and calculating accumulated standard length from date of hatch to dat e of capture. We first applied a simple linear regression to these data to determine how much variation in growth rate could be accounted for by temperature (measured as mean growing degrees days, accumulated between hatch and capture). Water temperature explained little variation in growth rates (R2M= = 0.009 and 0.088 for Flannelmouth Suckers and Razorback Suckers, respectively). We then used an analysis of variance modeling approach. A three-way interaction between species, age, and water temperature was significant (P = 0.002) for predicting standard length of fishes. Although the specific characteristics of this interaction are still under investigation, the result indicates that within the same thermal environment, growth of Razorback Suckers differed from that of Flannelmouth Suckers. Understanding the interaction between temperature and growth of Razorback Suckers in habitats where Flannelmouth Sucker larvae successfully recruit to juveniles is imperative for assessing recruitmen t limitations of Razorback Suckers and will provide for cross basin comparisons.