But they also have reduced weight and water resistance of their lighter skull and very narrow jaw . This gives gharials the ability to catch rapidly moving fish . Although gharials have sacrificed the great mechanical strength of the robust skull and jaw that most crocodiles and alligators have , and in consequence can not prey on large creatures , the reduced weight and water resistance of their lighter skull and very narrow jaw gives gharials the ability to catch rapidly moving fish , using a side-to-side snapping motion .