Studying of Trachurus trachurus (Linnaeus, 1758) Population Reproductive Dynamics in the Eastern Moroccan Mediterranean.

Horse mackerel (Trachurus trachurus, Linnaeus, 1758) is an epipelagic fish commonly found in Moroccan Mediterranean waters. This study was aimed at studying the ecology by monitoring gonadal development and reproductive indices of T. trachurus populations along the eastern Moroccan Mediterranean coast over a 12-month period. For that, a total of 390 specimens were sampled, with total lengths ranging from 7.8 to 33.8 cm and weights from 3.78 to 310.52 g. Several reproductive indices were analyzed. Monthly monitoring of the gonado-somatic index (GSI) identified two spawning periods for T. trachurus: the first in late winter-early spring (February-April), and the second in summer (July-September), confirming that this species is a fractional spawner fish. The hepato-somatic index (HSI) followed a similar trend to GSI, reflecting the energy allocation for reproduction. The size at first sexual maturity (L50) was estimated at 23.5 cm for females and 22.5 cm for males, representing critical metrics for fisheries management, as they help set regulatory guidelines, such as minimum landing sizes, and are also a prerequisite for estimating spawning stock biomass. The overall sex ratio showed a predominance in favor of males (62%) over females (38%). These results represent a valuable contribution to a better understanding of the biology of T. trachurus, and to the implementation of stock assessment to ensure the sustainability of catches.