Preliminary Investigations on the Ichthyodiversity of Kilifi Creek, Kenya

Western IndianPRELIMINARY Ocean J. Mar. INVESTIGATIONS Sci. Vol. 4, No. ON 1, pp.THE 11–20,ICHTHYODIVERSITY 2005 OF KILIFI CREEK 11 © 2005 WIOMSA Preliminary investigations on the Ichthyodiversity of Kilifi Creek, Kenya Dalmas Oyugi IUCN-EARO, P.O. Box 68200 Nairobi, Kenya Key words: ichthyodiveristy, hill’s indices, Kilifi creek Abstract—In order to determine fish spatial variation, the Kilifi Creek was divided into three sampling zones: entrance, middle zone, and Creek end. Sampling was by both gill and cast nets. Hill’s diversity indices were used as a measure of spatial diversity variance. A total of 95 species from 45 families were recorded. Gerres filamentosus, Pomadasys multimaculatum, Leiognathus equula, and Terapon theraps occurred commonly. Highest species richness (No = 68) and diversity (N1 = 31.09) was recorded at the entrance and Creek middle respectively. Most of the species overlap with the highest overlap index (L = 2.52) recorded between Cynoglossus gilchristi and Scombroides lysan. The creek’s ichthyodiversity show considerable variability, with the high richness at the entrance attributed to the presence of open water visitor species. The high number of species compares well to records from Gazi Bay and Mida Creek with some species not found further south. INTRODUCTION Oyugi, 2002), two specimens found at Kilwa, Tanzania (Benno pers comm.) and 21 specimens Like many other tropical systems, the from Tanga region (Verheij pers comm). Previously ichthyodiversity of eastern Africa is remarkably this species was reported from Grand Comore high, almost comparable to the archipelagos of Island, south of Madagascar, the Mozambique South East Asia. It is one of the top three global Channel and in Indonesia. diversity hotspots (McAllister et al., 1994, from Ichthyodiversity in the Western Indian Ocean Gell and Whittington, 2002). To a large extent, (WIO) can significantly vary between habitats. this is due to heterogeneous and productive Gell and Whittington (2002) report that systems of mangroves, seagrass beds, coral reefs, ichthyodiversity in Quirimba (northern sand and mudflats besides the open pelagic Mozambique) varies significantly among pure systems, which occur in the region (Harling, 1980; seagrass beds to coral reefs and mangroves allies. Valentine and Heck, 1999; Gell and Whittington, De Troch et al. (1996) report three distinct 2002). McClanahan (1997) remarks that 85 % of communities, river fed creek, upstream and the bay fish catches in East Africa comes from the inshore proper, in Gazi Bay (about 70 Kms south of Kilifi habitats. Creek). Bock (1972; 1975) reports on several That new discoveries are still being made in differences in species distribution and densities the icthyofauna of the region is shown by the between shallow lagoons and creeks in Kenya. recent report of a coelocanth Latimeria chalumnae Smith and Heemstra (1986) show how the reefs in (Smith, 1939) off the Kenyan coast at Malindi only East Africa share common fish species despite their 50 km north of the Kilifi study site (De Vos and geomorphological differences (i.e. from fringing reefs to rock islands - atolls). E-mail: [email protected] 12 DALMAS OYUGI Ever-increasing human pressure leads to hotel to the east and a Yacht club to the west and habitat degradation: pollution, overfishing, c) the Creek end, later named Kibokoni, is nonselective harvesting of mangroves, besides characterized by narrower mangrove creeks and climate change critically threatens the general shallow waters and extends to the northwest, diversity of marine and coastal fauna and flora. where small streams such as Rare River enter. At There is an urgent need to determine the current low tides most of this zone becomes exposed ichthyodiversity of the region for comparison with making boat sampling almost impossible. Each historical data in order to develop conservation of the zones were further subdivided into 3 strategies. While such work has been done in Gazi subsections (Fig. 1). Bay (De Troch et al., 1996; Wakwabi, 1999) and in Mida Creek (Mwatha and Olembo, 1998) little Sampling methods is known of Kilifi Creek. A small motor vessel was used to access the three MATERIALS AND METHODS zones, but for fish sampling a small dugout canoe locally known as Dau was used to set out and haul nets. Sampling was carried out during the south- Sampling Sites east monsoon. Gillnets, castnets and handnets were used in sampling. Gillnets measured 20 m long Kilifi Creek is about 50 km north of Mombasa, with mesh size ranging from 5-10 cm. were set Kenya’s main coastal city. During high tide, the along the edge of the Creek, and across the Creek Creek extends 15 km inland with a depth ranging in the middle region. Handnets were used to sample from 0 m at the Creek end to 15 m at the mouth, cryptic species such as gobies and blennids in during the lowest low water. For sampling, the isolated intertidal pools at low tide. Nine samples Creek was divided into three zones: a) the were taken at each sampling site during the day at entrance, later named Kitsoka, which is high tide. Identification and nomenclature follows characterized by heavy waves from the open sea, Smith and Heemstra (1986) and Van Der Elst b) the middle zone, later named Musimuni, has a (1993). Fig. 1. A map of Kilifi Creek showing sampling stations PRELIMINARY INVESTIGATIONS ON THE ICHTHYODIVERSITY OF KILIFI CREEK 13 Fish diversity Terapon theraps (Cuvier, 1829) are widely distributed and commonly found in all the three Hill’s diversity indices (1973): No, N1, N2 and N∞ zones of the Creek. estimated site diversity as follows; Kitsoka had the highest species richness (No) No: diversity as the average number of of 68 followed by Musimuni 29 and Kibokoni 18. species per habitat. The same trend was followed by species diversity N : diversity as the exponent of Shannon 1 (N1), where Kitsoka had 31.09, Musimuni 19.39 Wiener diversity index given as; and Kibokoni 9.07. However, Musimuni had the N = exp (-∑ p (ln p )) (i) 1 i i highest species evenness (N2) and dominance (N∞) pi = ni / N of 14.29 and 7.36 respectively followed by Kitsoka where: pi: is the proportional abundance of ith 11.44 and 3.71, and Kibokoni 5.43 and 2.9 (Fig. species, 2). Figures 3 and 4 show positive correlation ni: number of individuals of ith species, between species evenness and dominance, and N: total number of individuals between species richness and diversity N2: species evenness index as a reciprocal respectively. of Simpson’s dominance Index; Most of the fish species overlap in the three 2 N2 = 1/∑ pi (ii) broader zones of the Creek with the highest overlap N+∞: species dominance index based on index (L) occurring between ripple fin tongue the reciprocal of the proportional Cynoglossus gilchristi (Ogilby, 1910) and double abundance of the commonest species; spotted queenfish Scombroides lysan (2.42); N+∞ = 1 / proportional abundance of the frogtail goby Oxyurichthys papuensis commonest species (iii). (Valensciennes, 1837) and toothed soapy Gazza minuta (Bloch, 1797) (2.19) and thornfish Terapon Habitat overlap jarbua (Forskål, 1775) and O. papuensis (2.06). On the other hand, the weakest overlap was To establish how different species share different recorded between yellowbanded goatfish Upeneus habitats, a parameter referred to as habitat overlap vittatus (Forskål, 1775) and C. gilchristi (0.11), S. index (L) was calculated as; lysan and U. vittatus (0.15), and O. papuensis and giant kingfish Caranx ignobilis (0.19) (Table 2). L = (A/XY) Σ(xiyi/ai) DISCUSSION Where: xi = number of species 1 in the habitat i yi = number of species 2 in the habitat i Fish diversity in the Western Indian Ocean is ai = availability of habitat i relatively high and generally both species richness A = the sum of habitat availabilities and diversity are higher than in temperate and X = total population of species 1 subtropical bays, and estuaries, where as few as Y = total population of species 2 (Hulbert, six species may contribute 70 % of the total catch 1978, from Abrams, 1980) (Quinn, 1980, Little et al., 1988). The preliminary assessment of Kilifi Creek shows this where the RESULTS most abundant eight families contributed only 66 % of the total catch. A total of 95 species belonging to 45 families were Fish communities are also different from one recorded from 306 specimens sampled from the habitat to another as shown by Gell and Creek. The total list of species and their zonal Whittington (2002) from the Quirimba distribution in the Creek is given in Table 1. Archipelago in northern Mozambique. This is also Threadfin pursemouth Gerres filamentosus Cuvier, seen in Kilifi Creek. The entrance to the Creek has 1829, cock grunter Pomadasys multimaculatum a higher species richness than the landward (Playfair,1866), Slimy Leiognathus equula stations, due to the presence of numerous oceanic (Forskål 1775), and straight-lined thorn fish fish. This was also observed by McClanahan and 14 DALMAS OYUGI 80 70 68 60 50 40 31.09 29 Diversity Index 30 19.39 20 18 11.44 14.29 10 7.36 9.07 3.71 5.43 2.8 0 Kitsoka Musimuni Kibokoni Sampling Zones No N1 N2 Ninf Fig. 2. Hill’s diversity Indices of Ichthyofauna in Kilifi Creek 8 7 6 y = 0.4585x - 0.1386 2 5 R = 0.7383 4 Ninf 3 2 1 0 468 10 12 14 16 N2 Fig. 3. Relationship between species evenness (N2) and dominance (Ninf) in Kilifi Creek PRELIMINARY INVESTIGATIONS ON THE ICHTHYODIVERSITY OF KILIFI CREEK 15 35 30 y = 0.4034x + 4.3869 2 R = 0.9255 25 20 N1 15 10 5 0 0 1020304050607080 No Fig. 4. Relationship between species richness (No) and diversity (N1) in Kilifi Creek Mangi (2000), who also noted that species mozambiquensis was not found yet was recorded evenness at local level (α diversity) in Kenya, from Kilifi Creek.

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