Proximate and Residual Effects of Exposure to Simulated Drought on Prairie Stream Fishes
Edie Marsh-Matthews and William J. Matthews
Abstract.—Using artificial stream mesocosms, we conducted two experiments in consecutive summers to examine proximate and residual effects of simulated drought on survivorship, body size, condition, and reproduction of fishes common in southern Oklahoma streams. In summer 2000, we examined proximate effects on central stonerollers Campostoma anomalum, bigeye shiners Notropis boops, black-stripe topminnow Fundulus notatus, longear sunfish Lepomis megalotis, and orange-throat darters Etheostoma spectabile exposed to either continuous flow or to simulated drought for 40 d. Survivorship did not differ between treatments for central stonerollers, bigeye shiners, or orangethroat darters, but was lower in the drought treatment for both blackstripe topminnow and longear sunfish. Body size of survivors in the drought treatment tended to be smaller for central stonerollers. Condition of bigeye shiner and central stoneroller individuals was lower in the drought treatment, and bigeye shiner females exposed to drought were less likely to have mature eggs. In summer 2001, we simulated drought for 35 d and examined residual effects on central stonerollers, bigeye shiners, and orangethroat darters approximately 6 months later. Survivorship assayed in spring 2002 was marginally lower for orangethroat darters. Body size of central stonerollers in the drought treatment was smaller, consistent with proximate effects of drought on body size. Bigeye shiners did not differ between treatments in either body size or condition, indicating no residual effect of drought on fat stores despite much lower condition immediately following drought in summer 2000. For orangethroat darters, individuals exposed to drought tended to be larger and in better condition and to have more mature gonads than individuals in the flow treatment after the recovery period. The results of our two experiments demonstrate that drought affects survival, growth, body condition, and reproduction in different ways for different species, and proximate effects do not necessarily predict residual effects on fishes that survive drought.