Population ecology and seasonal demography of the endangered grotto sculpin ( Cottus specus )

Subterranean fishes are understudied worldwide and often at risk before their populations are discovered and described. The nature of karst systems limits the applicability of ecological paradigms and hinders our ability to identify and preserve endemic fauna. Aquatic karst taxa in particular are subject to environmental threats that increase in severity over time. Once a population or species is recognised as distinct, it is imperative we gain understanding of its biology to inform effective resource management and mitigate risk factors. The grotto sculpin ( C ottus specus ) is endemic to P erry C ounty, M issouri, U . S . caves and was formally described and listed as endangered under the U . S . Endangered S pecies A ct in 2013. We used mark–recapture methods to quantify population densities and estimate population sizes in two caves and two corresponding spring branches. Size structure varied among habitats and seasons. Spring branches were dominated by juveniles year‐round with peak young‐of‐year ( YOY ) densities in M ay. Adult densities in both macrohabitats decreased in winter, possibly due to recruitment or seasonal stress, and were lower at spring branches compared to caves and declined further during late winter which may be indicative of cave spawning. YOY were captured variably underground with peak densities in summer. The ecology of grotto sculpin appears to be more complex than has been reported previously for subterranean fishes. Variable patterns of demography requiring multiple contiguous habitats are unique for cave species and support the recently substantiated suggestion that subterranean systems are not as simple or disconnected as once thought.