Daytime intra-estuary movements and harmful algal bloom avoidance by Mugil cephalus (family mugilidae)

Abstract The estuarine movement patterns of Mugil cephalus (Mugilidae) in response to a Harmful algal blooms (HABs) was investigated in the eutrophied Sundays Estuary on the warm temperate coast of South Africa. The movements of six tagged M. cephalus (31–35 cm FL) were manually tracked using a Vemco VR100 acoustic receiver over 27 days during the typical summer bloom period. Fish were released above, within and below the mesohaline zone where Heterosigma akashiwo bloom maxima are known to occur. Physico-chemical variables and chlorophyll-a biomass were collected at each fish location and at four bloom monitoring sites, which locations were based on surface water salinity of 18, 10, 8 and 5. Mugil cephalus mostly occupied the upper mesohaline to lower oligohaline zones moving with the tidal ebb and flow. Phytoplankton biomass peaked at sites with a salinity of 10 and 8, with tagged fish only briefly (