Intraspecific Response of Sonora Suckers to Consecutive Wildfire Disturbances

Authors: Crosby Hedden, Skyler Hedden, Keith Gido, James Whitney

Year: 2018

Abstract

With the increasing size, frequency and intensity of wildfires across the American Southwest, assessment of wildfire effects on native fish populations is needed to better identify critical steps in recovery following these disturbances. Two large, contiguous wildfires in consecutive years (2011 and 2012) burned >100 km2 in the upper Gila River basin, New Mexico. Our objective was to quantify how occupancy and growth of juvenile and adult Sonora Suckers, Catostomus insignis, were influenced by these large fires to help develop a timetable of recovery for this species. Fish populations were sampled in June and October at five sites throughout the basin before fires (June 2008-June 2011), during the influence of fires (October 2011-June 2013), and post fires (October 2013-October 2015) to assess the response of juvenile and adult Sonora Suckers. Growth rates were measured for age-0 fish using length frequency analysis between June and October sampling events while growth for larger juveniles (>100mm) was based on recaptures of PIT tagged fish. Juvenile frequency of occurrence was high (>0.8) throughout the basin during all years in June but varied in October samples where occurrences before the fires were high (1.0), declined during years immediately following wildfire (0.4) and recovered in post fire years (0.73). Frequency of occurrence for adult fish was high (>0.6) during all years in October but varied in June samples where occurrences before and during the years of wildfire occurrence remained relatively high (>0.8) but were absent (0.0) in years following wildfires. Average body size of age-0 fish in June was smaller at upstream sites (mean = 31.2 and 36.7 mm) compared to the most downstream site (mean = 51.6 mm) (p-value=0.003 and 0.011), but juvenile body sizes did not differ among sites in October samples (p-value=0.885). Growth for adult fish differed among years with the highest growth occurring immediately following fires, lowest during pre-fire years, and highly variable growth post-fire years. Understanding the differing responses of multiple age-classes to disturbance events can aid managers to develop better management and conservation strategies.