Growth, mortality, and fishing rates of the vulnerable horse mackerel Trachurus trachurus (Teleostei: Carangidae) in the Canary Current Large Marine Ecosystem North (Morocco): variation among stock-units

Hayat EM and Mohammed Z

Published on: 2023-01-26

Abstract

Growth is biological activity that connects many processes and influences the life history traits of fishes. Among these, natural mortality and fecundity can be directly related to growth. Such information on growth and age is of great importance in fisheries evaluation. In this study, we investigated population parameters of the Atlantic horse mackerel Trachurus trachurus using body length-age obtained in specimens from three fishing areas in the Canary Current Large Marine Ecosystem (Larache, Safi and Dakhla) in July-September 2018. The age was estimated from otolith readings and the Von Bertalanffy growth parameters were calculated using the Beverton and Holt’s method. Longevity and natural mortality rates were derived from the growth parameters. For inter-population comparisons, the growth constant rate longevity was body-size corrected based on interspecific an auximetric relation determined from published data on T. trachurus. The size-corrected growth constant rate (k/L∞b) in this study, are higher in Safi area (0.077) than in the Dakhla (0.045) and Larache (0.036). The corresponding size-corrected longevities (t0.99/ L∞b) were similar in Larache and Dakhla (8.4 years), and lower in Safi (5.1 years). The instantaneous rates of total mortality (Z), natural mortality (M) and fishing mortality (F) were estimated and accordingly the exploitation ratio (E) was determined. (Z, yr-1) rate was 0.85 for Larache and Safi and 1.06 for Dakhla.  (M, yr-1) was lower (0.22) for Safi, intermediate for Dakhla (0.35) and higher for Larache (0.42). (F, yr-1) were higher in 0.71 and 0.63, respectively for Dakhla and Safi and lower in Larache (0.43). Stocks revealed to be overexploited (E > 0.5) in Safi and Dakhla (E=0.74 and 0.66, respectively) whereas Larache stock is rather its optimal rate of exploitation (E=0.50). The obtained results indicate the existence of differences in the growth patterns among the three studied T. trachurus stock-units off the Moroccan Atlantic waters.