The project was based at KMFRI headquarters in Mombasa, with Tudor Creek (a fully saline area of mangroves, mud and open water) as the study area. Sampling mainly involved the use of plankton nets and fine-meshed beach seines, in all months from February to November, 1985. Sampling frequencies of hours, days and weeks were also employed in order to cover the diel, circatidal, semilunar and lunar cycles. From the samples, prawn post-larvae, fish eggs and larvae, and juvenile fish and prawns were sorted, identified as far as possible, and counted in order to provide data on their occurrence, distribution and abundance. Records of temperature, and some other abiotic parameters, were also maintained.
The fish and prawn fauna of Tudor Creek, is described from the results of the seine-net sampling and is found to include 6 species of panaeid prawn and 135 species (49 families) of teleost fish; additional families were recorded only as larval stages in the plankton. Many of the fish occurred as juveniles, but very few of these were species commercially exploited on nearby reefs and trawling grounds. Differences have been found between the creek mouth and inner creek in terms of both planktonic and juvenile stages, and are associated with a gradient of decreasing depth and dissolved oxygen concentration, and increasing temperature and turbidity from the mouth inwards. One of the most conspicuous trends has been the decrease in fish egg density and diversitty along this gradient, which suggests that while the creek can be regarded as a fish and prawn nursery area, it is not an important spawning ground, at least for pelagic spawners. The existence of the gradient also results in tide-related changes in egg-density which are probably best explained in relation to the tidal incursion of egg-rich coastal water into the creek rather than tidal spawning cycles of adult fish. The latter have not been discounted, however, and may emerge from further analysis of data from individual taxa. No clear indication of general systematic seasonal changes in either the planktonic or juvenile stages were found, but the lowest catch-rates of some species of juveniles occurred during the early part of the SE Monsoon (April - July). Again further analysis of data from individual taxa of both planktonic and juvenile stages, and of the size-frequency data collected, may reveal clearer evidence of seasonal periodicity. The results are discussed in relation to the literature available on similar ecosystems in other tropical area, and in relation to the major problems encountered in carryng out the work. It is concluded that much has still to be learned about the role of mangrove creeks as nursery area, and also that this role is important in the context of future fisheries management and environmental monitoring. With this application in mind, it is recommended that future work should concentrate on the post-settlement juvenile stages rather than on the planktonic stages, and an argument is presented to support this view.
