Journal of the Marine Biological Association of India

Volume 48 Issue 2

Immediate effects of experimental otter trawling on the physico-chemical parameters of seawater off Mangalore

Zacharia, P.U., Anoop A.Krishnan, Raveendra N.Durgekar and P.K.Krishnakumar

Experimental otter trawling was carried out for 11 months (May 2001 -November 2002) off Mangalore coast to evaluate its immediate effect on physicochemical parameters of seawatej. Five stations (1-5) with increasing depths (]Om, 20m, 30m, 40 m and 50rn) were selected for the study using a systematic BACI (Before1 After and Controlllmpact) design. Trawling impact on the changes in salinity, temperature, dissolved oxygen, total suspended solids and nutrients (nitrite, nitrate, phosphate and silicate) were assessed. Temperature, salinity and pH were similar before and after trawling. The results indicate that TSS at surface and bottom waters increased immediately after trawling which was prominent at the shallow stations with significant difference (P < 0.05) at station 2. Changes in nutrient load by trawling were occasionally observed. Trawling had only a minor effect on transparency, dissolved oxygen and nutrients. Multivariate analysis (PCA) also revealed minor impact on the physicochernical parameters due to trawling


Bottom trawling, physico-chemical parameters, nutrients, Mangalore

Date : 30-12-2006