The Effects of Red Swamp Crayfish, Procambarus clarkii, on Experimental Populations of the Amargosa Pupfish, Cyprinodon nevadensis amargosae.

Authors: Bailey Gillis, Brandon Paulson, Craig Stockwell

Year: 2018

Abstract

Invasive crayfish species threaten the persistence of numerous desert fishes, but how crayfish density influences native fish persistence is not well understood. One hypothesis predicts that negative impacts increase with higher crayfish densities (Rogowski & Stockwell 2006; Biol. Invasions 8:79-87), while an alternative hypothesis predicts that impacts decrease with higher crayfish densities, presumably due to interference competition (Taylor & Thomas 2013; Freshwater Sci.32:1309-1317). To test these hypotheses we established experimental populations of Amargosa Pupfish, Cyprinodon nevadensis amargosae, and Red Swamp Crayfish, Procambarus clarkii, that included allopatric pupfish (control); pupfish + low-density crayfish; pupfish + high-density crayfish and pupfish + high-density tethered crayfish. The latter two treatments were compared to evaluate if conspecific interactions among crayfish affected impacts on pupfish. We found significant effects of crayfish on pupfish adult survival (X2 = 11.8; P < 0.01). Adult survival did not differ between the control (97 ± 8.0%) and low-crayfish treatments (84 + 13%; P > 0.05). Adult survival was significantly lower for the high-density crayfish treatment (69 ± 14%; P < 0.02) compared to the control. However, adult survival did not differ between the low-crayfish and high-crayfish treatments (P > 0.05), nor between the high-crayfish and high-density tethered treatments (P > 0.05). Crayfish had significant effects on juvenile productivity (X2 = 15.8; P < 0.002). Juvenile productivity did not differ between the control (705 ± 92 juveniles / tank) and low-crayfish treatment (704 ± 167; P > 0.05), while both of these treatments had higher juvenile productivity than the high-crayfish treatment (271 ± 107%; P < 0.006 and P < 0.006, respectively). When comparing the two high-density crayfish treatments, tethering resulted in significantly higher juvenile productivity (494 + 156; P < 0.03). Our results show density-dependent effects of crayfish on experimental pupfish populations. Limiting conspecific interactions among crayfish did not affect adult survival, but increased juvenile production. Our results suggest that short-term solutions to crayfish invasion may be simply to reduce crayfish densities.