Fish resources of Dhofar khawrs (coastal lagoons) in the Sultanate of Oman

Abstract

Abstract A fish resource monitoring programme was undertaken during 1992–1993 in nine Dhofar khawrs (coastal lagoons) of Oman. The khawrs contained a large number of fish comprising mostly milkfish, Chanos chanos (Forsskal), and mullet, Mugil cephalus L. A wide range of species were recorded (47) with Khawr Sawli supporting the highest number (26). Most fish use khawrs as nursery grounds and migrate to the sea for breeding. Mullets matured in winter, milkfish in early spring and the other species in spring‐summer except the sleeper, Ophiocara porocephala (Valenciennes), which breeds all year round. Three species of invertebrates with commercial value were collected: Indian white shrimp, Penaeus indicus H. Milne Edwards, Mud crab, Scylla serrata (Forskal), and swimming crab, Portunus pelagicus (L.). Khawr water temperature followed a seasonal cycle and surface temperatures were higher than the deeper waters. Heavy rains in early spring caused extensive flooding and opening of khawrs to the sea. This had little effect on water salinity in some khawrs (Rawri and Mughsayl), while others displayed marked elevation in salinity (Taqah, Sawli and Jnawf) or reduced salinity by 50% (Qurm al‐Kabir). Sedimentation and organic decomposition added during flooding produced drastic reduction in dissolved oxygen. Khawrs were again connected to the sea during monsoon (June–September) as water levels increased. Intrusion of sea water increased salinity and continued for several months in shallow khawrs (Jnawf); however, freshwater seepage reduced salinity in most khawrs. Massive fish mortality following heavy rains was the most significant seasonal occurrence. Extensive fish losses also occurred when water levels dropped after opening khawrs to the sea, and left many fish stranded in shallow areas. Other environmental perturbations existed in most khawrs (e.g. pollution and overgrazing). However, these khawrs have potential for small‐scale fisheries and different types of aquaculture. Management problems are identified and options for solutions suggested.