AimEstuaries support multiple human needs and are currently witnessing rapid and unplanned developments thus posing threats to associated large marine fauna such as Indo-pacific humpback dolphins Sousa chinensis. In our study, we assess the influence of varying levels of anthropogenic and environmental factors on behaviour of dolphins using a major (M), minor (m) and Intermediate (I) estuarine port as reflected in their space use and time activity budgets.
MethodsThis study was conducted in 3 estuaries, Kochi, Munambam and Ashtamudi during 2012-13 using a grid-based approach. Shore based scan sampling was used to assess dolphin presence, behavior, vessel traffic and fishing intensity for 432 hrs (n=2597). Dolphin locations were plotted in GIS using reticle method. Ecological parameters such as water quality, depth, prey availability and distribution were assessed using quantitative techniques and interview surveys.
ResultsDolphins occurred at levels higher than expected in I, lower in M and as expected in m. A higher number of non-fishing motororised vessels used M. Predominant activity in all 3 estuaries was foraging (M: 56%, I: 58%, m: 77%). Dolphins in M spent more time travelling (29%) as compared to m and I and displayed no milling. Milling was highest in I suggesting this area is suitable for resting and feeding. Ecological and anthropogenic determinants of dolphin use are being analysed.
ConservationResults show that dolphins seem to be behaviorally responding to changes in their habitat on a spatio-temporal scale by varying their activity budgets and space use in order to continue to persist and survive in these estuaries (high resource areas). Reduced access, however, to such high resource areas and decreased usage of the same by dolphins can threaten their survival and have serious conservation implications.