The population dynamics and the fishery of Penaeid prawns in tudor creek, Mombasa with Special emphasis on penaeus monodon, fabricius 1798

Abstract

A population of penaeid prawns was studied with emphasis on recruitment, growth of juveniles and emigration of the sub-adults. Five sampling stations in Tudor Creek, Kenya were monitored for surface water temperature, salinity and pH as well as larval and post larval penaeid densities. Temperature and salinity varied least in the creek mouth (23.5-30.0 degree C) and (32-35ppt), and most in the inner creek (22.5-32.0 degree C and 10.0-35.5ppt). The pH values varied little (7.5-8.4) with lowest values up the creek. Results showed that larvae which spawned offshore arrived in the creek at the late mysis and early postlarval stages with the water currents. Larval incidence in the samples decreased up the creek. Spring tide night samples had the highest incidence followed by the spring tide day samples and neap tide night samples. Peak larval counts were encountered at 20.30 hour during the two 24 hour cycles studied. Setting penaeid postlarvae and juveniles favoured specific bottom types. However, all the common penaeid species of Penaeus indicus, P. monodon and P. semisulcatus were most abundant in the stations with soft silty mud bottom type with mud-mangrove banks and dense vegetation cover. The three species recruited intensely into the creek in distinct cohorts between August and March. Peak recruitment for P. indicus was in January, P. monodon in November and P.semisulcatus in December. The size ranges of the carapace length for the three species were as follows: 1.5-21.5mm. (P. indicus), 1.5-29.5mm (P. monodon) and 1.5-21.5mm (P. semisulcatus). In the castnet fishery of the Tudor Creek, P. indicus formed 46.3% of the catch, P. monodon 42.9% and P. semisulcatus 4%. Estimated growth curves and other population parameters on annual basis were performed for P. monodon females and males. This study concluded that Tudor Creek is a nursery ground for penaeids especially P. monodon.