Temporal variation, population and growth parameters of swordfish (Xiphias gladius Linnaeus, 1758) in the nearshore waters of Kenya

Abstract

Swordfish (Xiphias gladius) is a pelagic species found in the tropical waters. The species is an important fishery. The scientific knowledge, stock structure and distribution of the fishery in Kenya is limited. The objective of this study was to investigate the temporal variation in catch rates and growth parameters for swordfish. Data was collected between August 2015 and December 2016 from five sites. The Length-Frequency data and gear selectivity were analyzed using FISAT (ELEFAN) and von-Bertalanffy. Catch rates were also determined. Virtual Population Analysis using FISAT II performed to estimate survivors and mortalities. Size ranged between 68 cm and 234cm Lower Jaw Fork Length (LJFL). The growth parameters were as follows; L͚ = 208 cm; K = 0.28/ year; t0 = 0.18; and φ = 4.08. Mortality rates were; Z = 1.13/ Year; M = 0.44/Year; F = 0.69/Year; E = 0.61/Year. Over 91% were below sexual maturity (L50). Fishing mortality rate (F) of 0.69/Year is higher than the optimal (0.5/Year). A comprehensive study to establish the stock structure and maturity status of this fishery is recommended to avoid localized depletion.