Is this the end of the line for the giant hump-backed mahseer?
Despite a general increase in fish numbers over a 12 year study period, more detailed analysis of the data collected by the Galibore Fishing Camp tells another story. Published in the international journal ‘Endangered Species Research’, this latest publication has catapulted the River Cauvery’s hump-backed mahseer and the Mahseer Trust into the international news.
A. Pinder, R. Raghavan and R. Britton (2015) The legendary hump-backed mahseer Tor sp. of India’s River Cauvery: an endemic fish swimming towards extinction? Endangered Species Research 28, 11-17
The Western Ghats region of India is an area of exceptional freshwater biodiversity and endemism. Mahseer of the genus Tor are considered prized sport fishes of great cultural significance; nevertheless, they are threatened as a result of increasing anthropogenic stressors. In the River Cauvery, the mahseer community comprises a ‘blue-finned’ and an orange-finned, ‘hump-backed’ fish. Whilst it is not yet known whether these are distinct species or 2 different
phenotypes, evidence suggests that the hump-backed phenotype is endemic to the river, whereas the blue-finned phenotype was introduced in the 1980s. Angler-catch data from a managed fishery on the River Cauvery, gathered between 1998 and 2012 and comprising 23 620 h of fishing effort, revealed that captured individuals ranged in size from 0.45 to 46.8 kg, with the blue-finned phenotype comprising 95% of all captured fish and the remainder being hump-backed. The catch per unit effort (CPUE) of the blue-finned phenotype significantly increased over the study period, while the mean weight of individual fish significantly declined. By contrast, the CPUE of the hump-backed phenotype declined significantly over the period, with individual mean weights significantly increasing. These data suggest a recent recruitment collapse in the hump-backed phenotype resulting in an ageing population that may be headed towards extinction. The introduced blue-finned phenotype, however, continues to recruit strongly, suggesting that the mahseer community of the River Cauvery has undergone considerable shifts in the last 30 yr.
Photo courtesy John Bailey
This paper is available ‘open access’ and free to download at http://www.int-res.com/articles/esr2015/28/n028p011.pdf