The constraints of fisheries management in Punjab (Pakistan).

Abstract

Acute and chronic toxicity tests for malathion, diazinon, and sherpa and for Cu, Hg, Pb, Zn, Ni, and Fe were conducted. Mortalities and LC50-96 hr values for Barilius vagra and Cyprinus carpio exposed to pesticides were variable. Long-term exposure to pesticides modified morphology and behaviour. The LC50-96 hr values for Cu, Hg, Pb, Zn, Ni, and Fe were low for small fish. Selected metal residues were significantly greater in whole juvenile carp following exposure to sublethal concentrations. Water samples from selected industrial drainages and receiving streams showed abnormal pH and oxygen levels. Selected metals (Fe, Pb, Zn, Cd, Cu, Ni, Hg) were higher in all effluents. Static bioassays of the undiluted industrial effluents from three sites caused 100% mortality in carp during the first 24 hrs and some mortality when effluents were diluted by 50%. A mesh size vulnerability model using the girth retention function for the Mangla Lake Fishery was developed. The impact of variable mesh size on fish harvest was evaluated. Probability of encountering the net was proportional to the distance travelled by fish, and a corrected size distribution improved the use of the model. Harvest of a surplus of large fish could be achieved by: (1) increasing the number of commercial nets in the 65-105 mm mesh size and (2) using a broader range of mesh sizes. Controlling fishing intensity and mesh size regulation over time would provide feedback for subsequent management decisions. Dynamic changes in the population, permissible harvest, number of fingerlings stocked and maintenance of year classes would allow the development of a better management model. Three supplementary feeds from inexpensive ingredients were developed and their relative ability to increase the growth of three indigenous carp (Catla catla, Labeo rohita, and Cirrhinus mrigala) and two exotic carp (Cyprinus carpio and Hypophthalmichthys molitrix) were compared. The growth of indigenous carp was low on all three feeds. All species of fish grew best on feed three. Information is needed on the ecological niches and nutrient requirements of the native carps.