The Devils Hole Pupfish, another canary in the global climate change coal mine ?

Authors: Stanley Hillyard, Frank Breukelen

Year: 2009 (xli)

Abstract

The Devils Hole pupfish, Cyprinodon diabolis, is only found in a single pool in western Nevada, one of the most restricted habitats for any known vertebrate species. The main pool has a stable temperature of 33-34° C but breeding occurs on a shallow ledge where temperatures fluctuate annually. In the summer, direct sunlight allows for food production but produces temperatures that may exceed 39° C on some parts of the ledge. The pool is shaded in the winter and cool air temperatures may lower water temperatures on the ledge to 28-30° C. However, food production is much reduced. Reproduction primarily occurs during a narrow window of time, approximately February- May, when cool temperatures prevail and primary production produces food and oxygen. The C. diabolis population has steadily declined from a maximum of over 500 in 1995 to as low as 38 in 2006 for reasons that remain speculative. Analysis of nutrient inputs to Devils Hole, has led to the hypothesis that population size is energy limited. We have quantified metabolic energy requirements of hybrid fish (Cyprinodon diabolis x C. nevadensis mionectes) in larval, juvenile and adult stages. When these numbers are extrapolated to population size the number of fish that can be supported by allochthonous and autochthonous production is near the minimal size measured in 2006. Our results strongly indicate that supplemental feeding is required for recovery of the population, at least until productivity can be restored to that of the mid 1990s. Our experiments also indicate that oxygen delivery is limited at temperatures routinely encountered in Devils Hole due to the combination of increased metabolic rate and low oxygen solubility. Therefore, these fish are sensitive indicators for the effects of increasing temperatures that might result from global climate change.