Assessment of Growth, Reproduction and Longline Soaking Time of the Spangled Emperor, Lethrinus nebulosus, in the Red Sea, Egypt

This investigation explored the growth patterns and reproductive strategies of Lethrinus nebulosus, identifying key spawning aggregation zones within the Red Sea. Additionally, it evaluated catch per unit effort (CPUE) using longline techniques through various fieldwork strategies. The CPUE of longline fishing was influenced by both soaking time and fishing season. Collected specimens ranged in total length from 14.3 to 71.3cm. The length-weight relationship indicated an almost isometric growth pattern, with the body shape parameter (b) = 2.95. L. nebulosus exhibiting a long lifespan, with a maximum age of 18 years, identified through transverse sections of sagittal otoliths. The growth parameters derived from the von Bertalanffy model were L∞ = 73.0cm, K = 0.12 year⁻¹, and t₀ = -0.32. Spawning likely occurs in spring, with aggregations recorded from mid-April to mid-May in specific locations. Six spawning aggregation sites were identified and documented. The observed sex ratio of 1:1.15 did not show a statistically significant deviation from the hypothesized 1:1 ratio (χ², P > 0.05). Males reached sexual maturity (Lm) before females, with lengths of 33 and 36cm, respectively. The length at first capture (Lc = 29cm) was much lower than the length at first maturation, raising concerns about overexploitation. It is proposed that management interventions be implemented to prevent the capture of immature fish, thereby protecting the stock and ensuring its long-term sustainability.