Demographics and exploitation of two Near Threatened freshwater eels, Anguilla bengalensis and Anguilla bicolor, in small‐scale subsistence fisheries and implications for conservation

Abstract

Tropical freshwater eels (Anguilla bengalensis and Anguilla bicolor) contribute a major share of the world's wild‐caught eel production, having become the next major target owing to the declines in availability of both Anguilla japonica and Anguilla anguilla, species that have traditionally contributed to eel aquaculture and trade. Although both A. bengalensis and A. bicolor are assessed as Near Threatened on the International Union for Conservation of Nature Red List, these assessments are primarily based on anecdotal information and local knowledge on population declines. Demographics and exploitation levels of A. bengalensis and A. bicolor were determined from small coastal river systems, and their adjoining aquascapes in the Western Ghats hotspot of southern peninsular India, and the value of these data for future conservation planning discussed. The computed estimates of annual catch data for freshwater eels from the study region are between 0.17 (A. bicolor) to 0.30 t (A. bengalensis). Virtual population analysis of exploitation showed a drastic decline (in number) in the length groups >45 cm for both species, suggesting that they were less likely to attain their asymptotic length in the region. Current exploitation rates of A. bengalensis are unsustainable, and those for A. bicolor are almost close to reaching this level. Exploitation of all life stages from yellow eels to adults (29–171 cm) is likely to cause recruitment failure and significant mortality of spawning individuals of both species. An integrative conservation approach, including raising awareness (leading to voluntary restrictions), fishing closures in reservoirs, village‐level quotas, and regular monitoring of populations, will ensure a sustainable future for the freshwater eel species in the Western Ghats hotspot, and elsewhere in the tropics where these species are exploited.

Slippery customers for conservation: Distribution and decline of anguillid eels in South Africa

“…in Mayotte (Valade, Hoarau & Bonnefoy, 2018). A similar pattern was also found for A. bicolor in India (Shanmughan et al, 2022). In contrast, both A. mossambica and A. bengalensis are found far inland and at the highest altitudes.…”

“…With this in mind, local stakeholders should formulate precautionary fisheries regulations for the relevant species. Recommendations from the Global South include, for example, the closure of fishing reservoirs, village‐level quotas and the monitoring of populations (Shanmughan et al, 2022). In Réunion, where there is a strong eel fishery tradition (Hanzen et al, 2019), all life stages are allowed to be harvested.…”

Ontogenetic habitat shift of Anguilla marmorata and A. japonica in the rivers of southern Japan: Implications for habitat use evaluation and conservation

“…Some species have extremely high economic value globally, while others are exploited locally (Kuroki, Righton & Walker, 2014), making them one of the most important fisheries and aquaculture species worldwide. However, the populations of some species have been declining sharply (Jellyman, 2022; Shanmughan et al, 2022). These declines are believed to be a consequence of various factors, including changes in oceanic conditions (Miller et al, 2009; Westerberg et al, 2018), overfishing (Tsukamoto, Aoyama & Miller, 2009) and anthropogenic pollution (Bourillon et al, 2022).…”