Population structure of Himalayan mahseer, a large cyprinid fish in theregulated foothill section of the river Ganga

摘要

Studies were conducted to assess the population structure of Himalayan mahseer Tor putitora in the foothill section of the Ganga where the river has been extensively regulated through the construction of two bar;ages and an array of canals for hydropower generation, irrigation and recreation. The age composition of samples, measuring 14.3-98 cm in length varied from 1+ to 9+ and 1+ to 8+ during 1993-1994 and 1994-1995, respectively. The age classes 2 to 4+ accounted for 70-73% of fish, while age classes 5 to 9+ accounted for 27-30%. The 2+ class (33.1%) was largest in 1993-1994 while the 3+ class (32.3%) was largest in 1994-1995. Of all the age-classes, the percentage of 2+ males was high (40.6%) as compared with 2+ females (25%). No males were recorded in age groups beyond 5+. Approximately 95% of fish were immature. It is believed that this skewed age distribution is due to habitat modification resulting from impoundment and perhaps also overfishing.