Jackson, TN – A west Tennessee state biologist says a once-popular sport is on the decline. Frog gigging season on state-run lands runs through the end of June. Wildlife biologist Rob Colvin says the number of bullfrogs has declined, and hunting them has become more difficult. Colvin says scientists are studying the frog's disappearance. Some theorize fertilizer runoff from farms is killing the animals. Colvin says currently bullfrogs haven't declined enough to go on the threatened species watch list. Residents can still get a small game hunting license for frogs. The bag limit is 20 per night.