Monster Seminar JAM - Seasonal dynamics in coastal fish abundance - hydroacoustic studies in a coastal bay in the Baltic Sea
Dr. Sture O. Hansson, Department of Systems Ecology & Center for Limnology, Stockholm University & University of Wisconsin - Michigan
Regular hydroacoustic surveys in May-November 2000 and May-September 2001 provided data to identify, measure, and compare seasonal pelagic fish population dynamics in a coastal area of the northwestern Baltic Sea. For each of the surveys, a dense system of transects allowed us to assess the fish biomass with high precision. The variation in echointegration, expressed as the width of the 95% confidence interval for the sA value, was <30% of the mean in 90% of the surveys, and <18% in 50%. Through the hydroacoustic data we could follow intra annual dynamics in fish biomass, densities and size composition, which showed similar trends in both years. Spring and early summer fish densities were low and were followed by a dramatic increase in late summer (numbers increased on average 20¿, biomass 11¿), caused mainly by the recruitment of yoy herring to the acoustically assessable fish population. In autumn, the densities decreased slowly. Our study shows that hydroacoustic technique is valuable in order to quantify and analyse the biology and dynamics of pelagic fish to obtain, for example, early assessments of year-class strength.
Date and Time:
May 6, 2004,
11:00 am - 12:30 pm