Using sound to map fish spawning: Determining the seasonality and location of spawning for weakfish and red drum (Family Sciaenidae) within Pamlico Sound, NC

Abstract

Fish produce species-specific sounds during courtship, during aggressive encounters with other fish of the same species, and as a response to threats from predators. Particular sounds are species-specific and have been recorded from fish during spawning in captivity. Such acoustical data may be used to identify and locate fish that are reproductive in the sea. In this paper, nocturnal sound production and planktonic egg production are correlated for weakfish (Cynoscion regalis) and red drum (Sciaenops ocellatus) (Family Sciaenidae), two species for which there are concerns over declining stocks. Recordings of underwater sounds and ichthyoplankton net tows were made after sunset at ten sites in Pamlico Sound, NC. Sites were relocated with a differentially corrected Global Positioning System receiver on a biweekly basis from May through October 1997. Based on laboratory studies, weakfish ‘‘purring’’ sounds and red drum ‘‘knocking’’ sounds only occur during spawning. ‘‘Purring’’ was recorded along with sciaenid eggs at stations near Ocracoke and Hatteras Inlets during May through July. ‘‘Knocking’’ was recorded in September and October at sites away from the inlets, also occurring with sciaenid eggs in one case. Mapping of sciaenid spawning areas may be possible using acoustical data alone, but may overestimate egg production.