Degree-Days Outperform Other Methods in a Large Meta-Analysis to Predict Egg Hatch

Degree-days have fallen out of favour as a method for predicting when fish eggs will hatch. Common criticisms are that degree-days assume that development scales linearly with temperature, and that there is a wide range of degree-days over which eggs will hatch. In this study, I use published data from 64 freshwater and anadromous fishes to show that degree-days are usually as good as or better than other models at i) describing relationships between days to hatch and incubation temperature, and ii) predicting when eggs will hatch in the field. I also derive accurate degree-day models from life history traits such as minimum spawning temperature and optimum egg development temperature. Overall, these results show that degree-days have practical appeal, and that common criticisms may be unwarranted.