Immediate fish community responses to changes in habitat quality and resource availability following ash flows from the Whitewater-Baldy Complex Fire in southwestern New Mexico

Authors: James E. Whitney, Keith B. Gido, David L. Propst

Year: 2012 (xliv)

Abstract

Little is known about the effects of forest fires and subsequent ash flows on fish communities, owing to the general lack of pre-fire data. Even less well-understood are the impacts of historically-unprecedented forest fires, which are predicted to increase as a result of climate change and fuel load accumulation from fire suppression. The Whitewater-Baldy Complex Fire burned 120,534 hectares in the headwaters of the Gila River Basin in southwestern New Mexico during May 16^th-July14^th 2012, with a subsequent series of ash flows occurring between July 4^th and September 14^th 2012. The objective of this research was to examine the immediate effects of these ash flows on fish communities via their impacts on habitat quality and resource availability. Fish density and richness were measured at 9 ash flow sites and 4 non-ash flow sites during June, August, and October 2012. We quantified percent silt to assess changes in habitat quality and chlorophyll a concentration to evaluate resource availability change. Linear regression was used to examine relationships between changes in habitat or resources and fish community attributes. Between June and August, percent silt at ash flow sites increased an average of 119% (+/-69% SE), whereas percent silt decreased by 56% (+/-27% SE) at non-ash flow sites. During this same time period, chlorophyll a concentration decreased an average of 77% (+/-7% SE) at ash flow sites while only decreasing 14% (+/-14%) at non-ash flow sites. Fish density and richness exhibited decreases at ash flow sites, declining 17% (+/-19%) and 6% (+/-13%), respectively. Conversely, fish density and richness increased on average at non-ash flow sites by 29% (+/-51%) and 7% (+/-26%), respectively. Changes in fish density and richness were generally not explained by changes in habitat and resources however, with the only statistically-significant relationship exhibited between chlorophyll a change and fish density change (F=5.58; p=0.04; R²=0.32). Investigation into other impacts of ash flows on fishes, such as alteration of water quality, coupled with long-term monitoring will be required to elucidate the overall impact of this catastrophic forest fire on the Gila River fish community.