Marine biologist Jennifer Anderson-Cruz sits on the dock of Nahant Marsh in west Davenport and listens . . . . . . . . . for frogs. She has been counting frogs at the marsh (by listening) for 10 years. She goes every other week during breeding season and records the number and type of frogs she heres. The device on the deck gives her humidity and temperature readings as well as time. She is trying to see since the marsh was cleaned out of lead if the frog population will or has recovered.