Water quality and stock assessment of Schizothorax niger (Alghad snowtrout) in Manasbal Lake, Kashmir Himalaya

Abstract

The current work was conducted to investigate fisheries dynamics, rate of growth, and mortality, along with demographic features of Schizothorax niger using length-frequency data collected monthly from Manasbal Lake from August 2020 and July 2022. The length data for estimation was categorized into 13 bins, and population parameters were explored utilizing various options in ELEFAN I, with the best fit (Rn = 0.282) calculated by means of the FiSAT-II application. TW = 1.94 TL^2.94, with a =  − 1.94, b = 2.94, and an attuned r² = 0.77 were derived for the weight and length association. The growing performance metric (ϕ) was calculated as 2.80. S. niger harvested stock in Manasbal Lake was prevalent in length categories of 20.5 to 25.4 and 25.5 to 30.4 cm. Different growth attributes were valued utilizing length frequency statistics as L_∞ = 46.05 cm, k = 0.30/year, and t₀ =  − 0.493 years. Over all mortality (Z), natural mortality (M), and fishing mortality (F) coefficients were evaluated as 1.43 year⁻¹, 0.56 year⁻¹, and 0.87 year⁻¹, respectively. The fish’s average length was assessed at the culmination of the 1st, 2nd, 3rd, 4th, 5th, and 6th year as 15.42 cm, 22.78 cm, 28.09 cm, 32.61 cm, 36.03 cm, and 38.53 cm, respectively. Recruitment patterns in S. niger from Manasbal Lake indicate a singular annual recruitment occurrence, exclusively observed during the month of June. The current value of the exploitation (fish harvest) ratio (E) was 0.61 by the size-transformed catch curvature method, found to be marginally lower than the maximum value (E_max) of 0.699 depicting that the species is on the brink of overexploitation, and caution is required to maintain sustainability. The seasonal analysis of water quality parameters revealed that except for pH and free carbon dioxide, the other parameters showed pronounced temporal variations. Total alkalinity values were reflective of hard water type of the lake, and dissolved oxygen and free carbon dioxide values were reported to be suitable for S. niger.