(MNN) – With Minnesota’s fishing opener on the horizon, experts are raising concerns about the mild winter’s impact on some fish species. Dr. Gretchen Hansen with the U of M College of Agriculture and Natural Resource Sciences says some species like walleye or yellow perch need a certain period of cold temperatures for their eggs to develop as fully; a short winter could hinder their eggs from developing fully. Hansen says these impacts have already been observed in places like Lake Erie, but studies are still “ongoing” in Minnesota.