Population decline to record lows and renewed interest in captive propagation of the endangered Devils Hole pupfish Cyprinodon diabolis has highlighted information deficits in some aspects of the species’ reproductive ecology. We conducted a monitoring study from February to December 2010 to investigate environmental factors associated with spawning activity in Devils Hole pupfish in Devils Hole, Death Valley National Park, Nevada. A fixed underwater camera provided continuous monitoring of a portion of a shallow, submerged rock shelf used for spawning. Dissolved oxygen, temperature, and light intensity datalogging meters continuously recorded environmental data from a fixed point on the shelf, and we conducted once or twice monthly algal/cyanobacterial surveys to measure percent cover of key species across the shelf. Water level and precipitation data provided by the National Park Service recorded earthquake and storm-induced flash- flood disturbances. Visual surveys conducted at the water surface from January to December 2010 provided additional information on spatial preferences in spawning. Zero-inflated Poisson regression showed greatest spawning activity was associated with the following conditions: dissolved oxygen 2.6–4.8 mg/L, total daily light intensity 133,250–400,300 lux, mean percent cover filamentous algae/cyanobacteria 24–60% and especially 24–27%, and presence of earthquake disturbance in the form of seiches. Among significant interaction effects, more spawning occurred at approximately 2.6 mg/L dissolved oxygen when diel dissolved oxygen variation was low (approximately 0.3–1.6 mg/L); at lower to mid-range monthly mean percent cover filamentous algae/cyanobacteria (approximately 24–32%) when total daily light intensity was lower to mid- range (110,000–330,000 lux); and post-earthquake when diel dissolved oxygen variation was low (0.6–1.3 mg/L). Increases in spawning activity occurred after earthquakes on 27 February and 21 October 2010; however, an earthquake during the peak spawning period (4 April 2010) was not associated with increased spawning activity. There was significant spatial variation in spawning, with most spawning activity occurring over the northeast area of the shelf. Our study provides new information on spawning in Devils Hole pupfish in Devils Hole, Nevada, including: temporal and spatial patterns, associated environmental factors, and effects of mechanical disturbance. Dissolved oxygen, diel dissolved oxygen variation, total daily light energy, percent cover filamentous algae/cyanobacteria, earthquake disturbance, and location on the shelf are the strongest predictors of spawning behavior in Devils Hole pupfish within Devils Hole. These factors in spawning might be utilized in adaptive management of the wild population, captive propagation to produce reserve populations, and efforts aimed at the recovery of the species. This work was provided in a thesis and a report to the USFWS. This work was published December, 2015 in the North American Journal of Fisheries Management.
