Stock assessment and virtual population analysis of River shad, Tenualosa ilisha (Bloch & Schneider, 1801) in the Shatt Al-Arab River, Iraq

Abstract

Historically, the river shad, Tenualosa ilisha fishery is the most significant marine fishery from the economic-socio point of view in Basrah province for a long time, but its contribution declined from 90.2% of total landings in 1965-1973 to 5.8% in 2020. The stock and virtual population analysis of the species in the Shatt Al-Arab River, Iraq was assessed using FiSAT II software. Samples were collected from two sites in the river from November 2015 to October 2016. A total of 462 individuals of T. ilisha ranging from 7.0 to 42.5 cm were collected. The length-weight relationship was derived, indicating a positive allometric growth for the species. L∞, K, and Ø were 59.1 cm, 0.27, and 2.975, respectively. Total (Z), natural (M) and fishing (F) mortalities were 1.94, 0.59, and 1.35, respectively. The exploitation rate (E) was 0.70. Length at first capture (Lc50) was found to be 24.4 cm. The recruitment pattern of T. ilisha was continuous throughout the year with two unequal prominent peaks. The relative yield per recruit analysis revealed that the current exploitation rate (E) of T. ilisha was higher than both E0.1 and Emax. Also, the 40 cm length group was more vulnerable to fishing according to VPA analysis, followed by the 34 cm and 26 cm length groups. For management purposes, it must be introduced an extensive T. ilisha management action plan by protecting brood species during the breeding season by imposing a ban on fishing in the Shatt Al-Arab River during the main spawning migration and conserving the small T. ilisha (Milat <23.0 cm) from catching.

Population Dynamics of the Common Carp (Cyprinus carpio L. 1758) Stock in Lake Arekit, Ethiopia: Implications for Management and Conservation

“…Te asymptotic length (L ∞ ) of C. carpio in the current study was higher than that of the species in some waters [25] but lower than that of the species in other waters [34][35][36][37][38] (Table 6). Diferent environmental circumstances, food availability, metabolic activity, reproductive activity, fsh size, survey technique, and fshing pressure are a few variables that may have an impact on how diferently the same species grows in different places [32,42]. A fsh's ability to grow is infuenced by three factors: its genetic makeup, the growth-restraining abiotic environment it encounters, and the biotic environment [43].…”

“…A fsh's ability to grow is infuenced by three factors: its genetic makeup, the growth-restraining abiotic environment it encounters, and the biotic environment [43]. Moreover, the development rates of related species can vary depending on habitat [32,44]. Fish lifespan has been linked to the Von Bertalanfy curvature parameter K [45] and longevity has been linked to mortality [46].…”