SEASONAL AND DAILY CYCLES IN SOUND PRODUCTION ASSOCIATED WITH SPAWNING IN THE WEAKFISH, CYNOSCION REGALIS

Hydrophone recordings were made to document the daily and seasonal cycles of weakfish, Cynoscion regalis (Sciaenidae), sound production in the Delaware Bay. Recordings were made at three stations perpendicular to the shore and rated qualitatively on a scale of 0-4. 'Drumming' (sonic muscles, males only) and 'chattering' (pharyngeal stridulation, both sexes) were tallied separately. Weakfish were collected from the field throughout the spring and summer to monitor the reproductive status of the population. A clear seasonal trend was noted in both drumming and chattering activities. Drumming activity rose abruptly in mid-May to maximal levels, which were maintained through late June, then dropped off in July and ceased in August. Chattering activity began abruptly in late June, then rose through July and remained high in August. Seasonal drumming activity was more intense at the inshore station. On a daily scale, drumming activity was at its lowest level during the early to mid-morning, then increased to maximal levels in the early evening and remained high until the following morning. There was no daily trend in chattering activity. Daily drumming activity was also most intense at the inshore station. Male and female reproductive readiness, determined by gonadosomatic indices, sperm motility and plasma androgen levels, peaked within the period of maximal seasonal drumming activity.