Fish Fauna Faces Anthropogenic Double Trouble: Erosion of Fish Diversity in Tropical Oxbow Lake of the Ganga River Basin in Eastern India

Abstract

Fish diversity in Oxbow lake is adversely impacted due to diverse anthropogenic activities like over-exploitation, indiscriminate use of fine meshed fishing gears, jute retting etc. To quantify the impact of such anthropogenic activities on fish diversity and aquatic health, a survey with seasonal analysis of diversity indices, relative frequencies and abundance status of native fish populations was conducted from April 2013 to March 2014 in a semi closed Oxbow lake in Nadia district in eastern India. The level of p<0.05 was accepted as statistical significance. Of the 33 native fish species recorded 33% belonging to 8 orders and 17 families fell under vulnerable or endangered categories. Native species like Amblypharyngodon mola, Chanda nama, Pethia ticto and Notopterus notopterus, Colisa fasciata, P. ticto, were the most dominant and frequent fishes. Shannon-Weiner diversity index was decreased by 41% by precipitating impact of monsoonal anthropogenic activities during post-monsoon. Low native fish diversity indices are pointers to poor ecosystem health status owing to intense adverse activities like jute retting, indiscriminate fishing aggravated by influx of turbid water from the river Ganga following episodic flood events during monsoon. Regulation and prevention of such anthropogenic activities are urgently warranted for sustainable conservation and management of the Oxbow lake.

Impact of Jute Retting on Physicochemical Profile of Chhariganga Oxbow Lake in Nadia District, West Bengal, India

“…The present discussion on the physic-chemical study indicate that the high values of parameters like pH, Secchi disc transparency, total hardness, total alkalinity, orthophosphate and low values of DO, BOD, COD, N/P ratio, GPP and NPP showed the present semi-closed oxbow lake water of poor to moderate quality and it may be classified as oligo-mesotrophic in nutrient status with high to moderate organic pollution due to jute retting. The poor health status assessed with the physicochemical properties does also corroborate with the findings of the studies on the same oxbow lake assessed with rotifer diversity indices (Ghosh and Biswas, 2014), zooplankton diversity indices (Ghosh and Biswas, 2015a), macrophytes diversity (Ghosh and Biswas, 2015d), phytoplankton diversity (Ghosh and Biswas, 2015e), fish diversity (Ghosh and Biswas, 2017a;2017c), fish productivity (Ghosh and Biswas, 2017b) during the same period of study on the same oxbow lake.…”

Catch per unit efforts and impacts of gears on fish abundance in an oxbow lake ecosystem in Eastern India

“…The findings of the current study regarding the CPUE of different fishing gears are also in full or partial agreement with the results of other similar studies (6,9-13). The oxbow lake in the present study is a moderately to poorly productive body of water the fish abundance of which is decreasing (2,3). Fishing nets were found to be the most harmful among all studied gears (1).…”

“…The overall catch per unit or gear effort (CPUE or CPGE), a measure of relative abundance (n or g/h and n or g/e), was calculated by dividing the total catch in number (n) or wet biomass (g) from gear (s) by total hours (h) or efforts (e) of operations of gear(s) used during those three seasons and the year. Average mean fish density (n/m 3 ) and standing biomass (g/m 3 ) was calculated by dividing the total number (n) or wet biomass (g) of fish encountered in an area (m 3 ) operated by gear (s) for each season. Statistical analyses determined the mean, standard deviation (SD), and degree of relationships with the help of MS Excel software.…”

“…It supports rich biodiversity and offers a livelihood and nutritional security, yet its conservation is less studied in India. Fish abundance in oxbow lakes is severely impacted by human activities like over-exploitation and the indiscriminate use of fine-meshed fishing gear, which always forces the development of systematic and appropriate planning for biodiversity conservation and management strategies (1)(2)(3). Among the different types of fishing gear studied (4,5), those like gill nets and seine nets exhibit highly destructive effects (6-9) on fish abundance.…”

“…The average daily catch per fisher has been reported as 1.43 kg with different fishing efforts (no of gear/day): push nets (6.75), gill nets (3), cast nets (8), lift nets (5.25), current nets (3.75), and hook (67) (11). Fishing durations (h/d) of gill nets (6)(7)(8)(9)(10)(11)(12), push nets (0.5-2), drag nets (2-4), lift nets (2-6), and hooks (2)(3)(4)(5) have also been reported with the highest density of fishers and catches in the monsoon season, and the lowest was reported in the pre-monsoon season (5,14). However, not enough information is available on the estimation and impact of CPUE of different fishing gear on the patterns of native fish species abundance in the oxbow lake of the Nadia district, India in particular.…”