Gastric evacuation rates in male Clearnose Skate (Leucoraja eglanteria) in the laboratory

Evacuation rates were determined for Clearnose Skate (Leucoraja eglanteria), an important predator in the mid-Atlantic United States shelf ecosystem. Male Skates (570–730 mm total length) were fed Sand Lance Ammodytes sp. and allowed to digest from 2–48 hr at two different temperatures. At selected times, fish were removed from tanks, sedated with tricaine methanesulfonate, and subjected to gastric lavage. This procedure was successful at removing the food from the stomachs without injury to the fish. Evacuation rates for the two temperature treatments were fit best by exponential models. The evacuation rates, per hour, were faster at 20°C than at 15°C, resulting in empty stomachs by 24 hr at 20°C, and 48 hr at 15°C. Evacuation rates at these temperatures were estimated as 0.102 and 0.059 proportion stomach contents per hour at 20 o C and 15°C. These evacuation rates and their temperature dependence are similar to that of other species of elasmobranchs and some teleosts. Evacuation rates are often combined with stomach content data to estimate consumption. The results of this study indicate that evacuation rates by some skates may be up to five times higher than currently used in multi-species and ecosystem models of the Northeast U.S. Shelf. The implication is that consumption may also be higher, highlighting the need for more research to increase the accuracy in evacuation rates estimates.