Staten Island’s eel population is in a cold plunge. The year’s icier-than-normal winter has put a partial freeze on the city’s American eel migration, with nearly half of the wriggly and nearly-invisible critters making their annual pilgrimage from the ocean into Richmond Creek this season. Just about 4,000 juvenile eels — referred to as “glass eels” at this point because they are almost see-through — have been collected at the estuary as part of the state’s annual eel count, which invites students to wade in the waters, count the fish by hand and learn about the lesser-known city slickers. The state’s annual eel count is under way at Richmond Creek on Staten Island — helped along by local schoolkids. stefano Giovannini for NY Post (From left) Donovan Lee, Jordy Minchala and Oginga Thompson visit the creek every week with 61 classmates to aid in the count.…