A Modeling Framework to Quantify the Influence of Hydrology on the Abundance of a Migratory Indian Shad, the Hilsa Tenualosa ilisha

Abstract

It is envisaged that the influence of river hydrology on the commercial catch of anadromous species in river–estuary systems is very pronounced. We delineate a general framework to quantify the effect of changing river hydrology on the catch of a very unique anadromous species, the Hilsa Tenualosa ilisha, a shad species that is distributed across the Indo-Pacific region. The Narmada River–estuary system was studied as a representative for the region. Two synthesized factors—migratory habitat availability (factor 1) and migratory habitat quality potential (factor 2)—were derived from five hydrological variables to explain 96% of the variability in the hydrological regime of the Narmada River–estuary system. Based on the proposed autoregressive integrated moving average with explanatory variables (ARIMAX) modeling framework, we found that both factors had significant positive effects. Model-based forecasts of Hilsa catch revealed a decreasing trend in the future if a similar hydrological regime prevails. In a simulated future scenario, a 15% increase in Hilsa catch was predicted to occur in response to a 2% increase in factor 1, considering the last 5 years’ average catch as a benchmark. Some management strategies focused on controlling the hydrological regime are suggested to enhance Hilsa fisheries.