The impact of non-native rainbow trout within Afro-montane streams in eastern Zimbabwe

Abstract

Non-native trout species have been associated with many negative effects in receiving ecosystems. The first aim of this study was to determine the impact of non-native rainbow trout Oncorhynchus mykiss on distribution and abundance of native mountain catfish Amphilius uranoscopus within Afro-montane streams in Nyanga Mountains, eastern Zimbabwe. The second aim was to compare macroinvertebrate community responses to the presence of the trout and the catfish. We examined trout impact on catfish's habitat associations, whereas macro-invertebrate composition was compared using open fish and fish exclosure experiments in habitats with and without trout. Trout influenced both the distribution and abundance of the catfish that occupied shallow reaches possibly to avoid predation from trout that occurred in the deeper habitats. Within trout invaded reaches, most macro-invertebrate taxa were more abundant in exclosure than open treatments. By contrast, within trout-free reaches, most macro-invertebrates either did not differ between treatments or were generally more abundant in open than exclosure treatments. This suggests that the macro-invertebrate communities responded differently within invaded and non-invaded reaches. By influencing distribution and abundance of native biota, non-native rainbow trout may have wider ecological effects, such as influencing trophic interrelationships within invaded habitats.

Non-native rainbow trout change the structure of benthic communities in headwater streams of the Cape Floristic Region, South Africa

“…Rivers-Moore et al (2013) found differences in invertebrate assemblage composition between sites above and below waterfalls that act as dispersal barriers to rainbow and brown (Salmo trutta Linnaeus, 1758) trout in headwater streams in KwaZulu-Natal (South Africa), but could not attribute the observed differences to the presence of trout. On the other hand, Kadye et al, (2013) found that rainbow trout tended to deplete benthic invertebrate abundance more strongly than did the benthic-feeding native mountain catfish Amphilius uranoscopus (Pfeffer, 1889) in headwater streams in the Nyanga Mountains (Zimbabwe). These results contrast with the relatively weak suppression of benthic invertebrates by trout observed in our study but are in line with the view that introduced trout generally elevate predation pressure on benthic invertebrates (Simon & Townsend, 2003;Townsend, 2003).…”

Evidence of hidden diversity and taxonomic conflicts in five stream fishes from the Eastern Zimbabwe Highlands freshwater ecoregion

“…The present study uncovers a classic example where underestimation of taxonomic diversity and poor understanding of the spatial distribution of species has misdirected conservation efforts, to the extent that the EZH freshwater ecoregion is currently not listed among the priority freshwater Key Biodiversity Areas within the Eastern Afromontane Biodiversity Hotspot (see CEPF 2012). This is however unfortunate because the highly sensitive Afromontane streams and rivers in this region have been severely transformed and are experiencing ongoing human impacts, including illegal mining activities, deforestation, increased sedimentation, uncontrolled burning and introduction of non-native invasive piscivorous species (Kadye and Magadza 2008; Kadye et al 2013). For example, the rocky streams which drain the Chimanimani Mountains used to have intact indigenous riparian vegetation, had clear water and perennial flow, but surveys in 2013 revealed that human encroachment, increased agricultural activities and the associated loss of riparian vegetation has transformed these streams into sluggish flowing, and highly turbid and heavily silted habitats.…”

Rainbow Trout in Europe: Introduction, Naturalization, and Impacts

“…One of the most studied interactions is with the Galaxiidae fish of the Southern Hemisphere on which the trout was shown to have a negative impact, mostly through predation but also through competition and habitat alteration across their entire range, especially in Australasia (Lintermans, 2000;Cambray, 2003;McDowall, 2003McDowall, , 2006Young et al, 2010;Juncos et al, 2013). Negative influences on other fish species have been recorded elsewhere: rainbow trout influence the distribution and abundance of the mountain catfish (Amphilius uranoscopus) in eastern Zimbabwe (Kadye et al, 2013), and have a negative effect on ten of the 50 fish species listed in the South African Red Data book (Skelton, 1987); evidence indicates they present a significant threat to some nongalaxiid endemic fish in Patagonia (Macchi et al, 1999;Ortubay, 2000;Pascual et al, 2002;Macchi et al, 2007), while in Chile they have a negative affect on the Chilean Silverside (Basilichthys australis), which is a weak competitor (Pardo et al, 2009); there is also evidence emerging of their destructive nature in tropical regions, as naturalization in the Dominican Republic has most probably led to localized extinctions of the endemic Poecilia dominicensis (Sartorio, 2003), while in Sri Lanka they have played a role in the extinction of at least some endemic fish (Pethiyagoda, 1994;Senanayake and Moyle, 1982). Furthermore, rainbow trout have been shown to have a negative effect on the Little Colorado spinedace (Lepidomeda vittata) from Arizona (Rinne and Alexander, 1994), on the yellow perch (Perca flavescens) from the Great Lakes (Galbraith, 1967;Crawford, 2001) and on some other non-salmonid fish in the United States (Krueger and May, 1991).…”

“…In other words, as long as a population is continuously stocked it cannot be considered as properly selfsustaining, even if reproduction and fry are regularly confirmed, as this does not guarantee that the population will persist once the stocking ceases. In general, naturalized populations have been recorded in many parts of North America, especially the Great Lakes region, the Rocky Mountains and the Appalachians (Crawford, 2001;Fausch et al, 2001;Fausch, 2007a); in Patagonia and other temperate parts of South America and also in some highland regions of more tropical areas (MacCrimmon, 1971;Sartorio, 2003;Riva Rossi et al, 2004;Valiente et al, 2007); New Zealand and Australia (Crowl et al, 1992;Arthington and Bl€ uhdorn, 1995); Hokkaido, Japan (Kitano, 2004;Nomoto et al, 2010); some highland parts of the Indian subcontinent, including Sri Lanka (Gopalakrishnan et al, 1999;Jinadasa et al, 2005); the Levant basin (Goren and Galil, 2005); parts of South Africa and Zimbabwe and over parts of East Africa including Kenya and Ethiopia, and also on La R eunion Island (MacCrimmon, 1971;Ngugi, 1999;Cambray, 2003;Berrebi, 2006;Kadye et al, 2013).…”