The Legacy from Decades of Deliberate Introduction
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Hydrobiologia https://doi.org/10.1007/s10750-018-3597-9 ADVANCES IN CICHLID RESEARCH III Widespread colonisation of Tanzanian catchments by introduced Oreochromis tilapia fishes: the legacy from decades of deliberate introduction Asilatu Shechonge . Benjamin P. Ngatunga . Stephanie J. Bradbeer . Julia J. Day . Jennifer J. Freer . Antonia G. P. Ford . Jonathan Kihedu . Tabitha Richmond . Semvua Mzighani . Alan M. Smith . Emmanuel A. Sweke . Rashid Tamatamah . Alexandra M. Tyers . George F. Turner . Martin J. Genner Received: 18 December 2017 / Revised: 9 March 2018 / Accepted: 16 March 2018 Ó The Author(s) 2018 Abstract From the 1950s onwards, programmes to locations, including 14 taxa restricted to their native promote aquaculture and improve capture fisheries in range and three species that have established popula- East Africa have relied heavily on the promise held by tions beyond their native range. Of these three species, introduced species. In Tanzania these introductions the only exotic species found was blue-spotted tilapia have been poorly documented. Here we report the (Oreochromis leucostictus), while Nile tilapia (Ore- findings of surveys of inland water bodies across ochromis niloticus) and Singida tilapia (Oreochromis Tanzania between 2011 and 2017 that clarify distri- esculentus), which are both naturally found within the butions of tilapiine cichlids of the genus Oreochromis. country of Tanzania, have been translocated beyond We identified Oreochromis from 123 sampling their native range. Using our records, we developed models of suitable habitat for the introduced species based on recent (1960–1990) and projected (2050, Guest editors: S. Koblmu¨ller, R. C. Albertson, M. J. Genner, 2070) East African climate. These models indi- K. M. Sefc & T. Takahashi / Advances in Cichlid Research III: Behavior, Ecology and Evolutionary Biology cated that presence of suitable habitat for these introduced species will persist and potentially expand Electronic supplementary material The online version of across the region. The clarification of distributions this article (https://doi.org/10.1007/s10750-018-3597-9) con- provided here can help inform the monitoring and tains supplementary material, which is available to authorized users. A. Shechonge Á B. P. Ngatunga Á R. Tamatamah J. J. Day Department of Aquatic Sciences and Fisheries, University Department of Genetics, Evolution and Environment, of Dar es Salaam, P.O. Box 35064, Dar es Salaam, University College London, Darwin Building, Gower Tanzania Street, London WC1E 6BT, UK A. Shechonge Á J. Kihedu Á S. Mzighani Á A. G. P. Ford Á A. M. Tyers Á G. F. Turner E. A. Sweke Á R. Tamatamah School of Biological Sciences, Bangor University, Tanzania Fisheries Research Institute (TAFIRI), Bangor, Gwynedd LL57 2UW, UK P.O. Box 9750, Dar es Salaam, Tanzania A. G. P. Ford S. J. Bradbeer Á J. J. Freer Á T. Richmond Á Department of Life Sciences, Centre for Research in M. J. Genner (&) Ecology, Whitelands College, University of Roehampton, School of Biological Sciences, University of Bristol, Life Holybourne Avenue, London SW15 4JD, UK Sciences Building, 24 Tyndall Avenue, Bristol BS8 1TQ, UK e-mail: [email protected] 123 Hydrobiologia management of biodiversity, and inform policy related eight major freshwater ecoregions (Abell et al., 2008). to the future role of introduced species in fisheries and Although much of this species richness is restricted to aquaculture. the Great Lakes of Malawi, Tanganyika and Victoria (Darwall et al., 2005), over 300 described species have Keywords Cichlid Á Invasive species Á Aquaculture Á been recorded from other water bodies (Eccles, 1992). Capture fisheries Á Tilapia Á Oreochromis Tilapiine cichlids of the genus Oreochromis are typically abundant in lakes and slow flowing rivers across the country. In the most recent field guide (Eccles, 1992), 23 Oreochromis species were listed, Introduction and 21 of these still considered valid Oreochromis species [Eschmeyer (2017); Fig. 1)]. Several of these In Africa, inland aquaculture is a rapidly growing food species are significant species of inland capture sector (FAO, 2016), but one of the major conse- fisheries (Bwathondi & Mwamsojo, 1993), particu- quences of expansion of aquaculture can be the larly the introduced Nile tilapia Oreochromis niloticus associated spread of cultured species into non-native (L.) in Lake Victoria. However, although the intro- ecosystems (Naylor et al., 2001), which has led to duction has been successful in terms of fisheries detrimental effects for many local habitats (Ehrenfeld, production, it may have precipitated loss of native 2010; Gichua et al., 2014). Among the most widely tilapiine cichlid species from much of their former cultured groups of freshwater fish species are tilapiine range (Ogutu-Ohwayo, 1990; Witte et al., 1991). cichlids. They have been introduced to over 140 Since the 1990s, landings from capture fisheries in countries, and established feral populations in at least Tanzania have remained stable at approximately 114 of these (Deines et al., 2016). The spread to 350,000 tonnes (FAO, 2017). Aquaculture is now natural habitats from culture facilities has been both seen as the potential solution to meeting the increased unintentional, with individuals escaping from aqua- demand for fish that will accompany a growing human culture facilities (Canonico et al., 2005), and deliber- population (Tanzania Government, 2010). Nile tilapia ate, with tilapia being released into natural water is a favoured species for aquaculture expansion in bodies to improve capture fisheries (Canonico et al., Africa due to its growth performance, suitability for 2005; Genner et al., 2013). Spread of tilapia species aquaculture, marketability and stable market prices. into non-native habitats has resulted in negative The species has also been subject to genetic improve- ecological effects on native species and their habitats ment techniques which could improve yield (e.g. through competition and habitat alteration (Canonico Ponzoni et al., 2011). However, the species can be et al., 2005). It has also resulted in the loss of unique invasive, and has had detrimental effects on native population genetic structure through hybridisation species at multiple locations in Africa (D’Amato et al., (D’Amato et al., 2007). Where studies have been 2007; Zengeya et al., 2013), and elsewhere in its undertaken, the ecological impacts on native species introduced range (Canonico et al., 2005). Thus, from are generally perceived to be negative, but ecosystem the perspective of balancing conservation with services provided have been perceived to be positive expanding aquaculture, one possibility is that future where they make large contributions to economic initiatives could be based on large-bodied native income (Deines et al., 2016). Thus, when tilapia species, with aquaculture species zoned according to introductions are being considered, benefits need to be which species are native to specific catchments (Lind evaluated in light of potential ecological and economic et al., 2012). Such large-bodied species could include, costs. for example, Oreochromis urolepis (Norman 1922), Tanzania has a rich freshwater fish fauna over 630 Oreochromis shiranus Boulenger 1897 and Ore- described fish species (Darwall et al., 2005) spanning ochromis jipe (Lowe 1955) (Table 1). One limitation of this approach, however, has been the limited information available on the current distributions of A. M. Smith Evolutionary and Environmental Genomics Group, both the native species or introduced species in School of Environmental Sciences, University of Hull, Tanzania (Lind et al., 2012). Hull HU5 7RX, UK 123 Hydrobiologia (a) (b) Victoria Manyara Eyasi Pangani Tanganyika Pemba / Malagarasi Wami Zanzibar Ruvu Rukwa Ruaha / Rufiji 250km Malawi / Nyasa Ruvuma O. niloticus (c) (d) O. leucostictus O. esculentus 0 10,000 Altitude (m) Fig. 1 a Major watersheds of Tanzania, and b–d the distribution of species introduced beyond their native ranges (O. niloticus, O. esculentus and O. leucostictus). See Supplementary Information 1 for sampling locations and coordinates Here we contribute information on the present of the Malagarasi catchment that was not known to be distributions of Oreochromis species across Tanzania, naturally occupied by the species. We combine these based on fieldwork conducted between 2011 and 2017 data with projections to predict suitable habitat for the across all major catchments in the country. We report translocated and exotic species, in current conditions these as either native (naturally found in catchment), and those projected under future climate regimes. translocated (species is naturally from Tanzania, but These data build on earlier work on tilapia distribu- introduced into the catchment) or exotic (naturally tions (Trewavas, 1983; Eccles, 1992), and help clarify found only outside Tanzania, but introduced into the current distributions. Collectively our results Tanzania and the catchment), following the definitions demonstrate an unexpectedly wide distribution of in Copp et al. (2005). We also highlight a case where introduced species in Tanzania, and highlight the translocations of Nile tilapia have taken place to part scope for their further range expansion. 123 Hydrobiologia Table 1 Oreochromis species in Tanzania considered in this study, focussing on those sampled between 2011 and 2017 Speciesa Common Maximum IUCN status Native range Exotic/translocated name standard in Tanzania length (cm)b Species samples