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

Wilbert T Kadye,Tendai Samukange,Lightone T Marufu,Albert Chakona

doi:10.1007/s10750-013-1624-4

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 macro-invertebrate 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.

Highlights

Invasion by non-native species is recognised as one of the major drivers of biodiversity loss globally (Pimentel, 2011)
Model comparisons showed that the trout model was significantly better than the model without trout
The hypothesis that in the absence of the rainbow trout O. mykiss, the native mountain catfish A. uranoscopus would utilise a wide range of habitats use was supported because individuals of the mountain catfish were collected from all the habitats sampled within trout-free reaches in this study

Summary

Introduction

Invasion by non-native species is recognised as one of the major drivers of biodiversity loss globally (Pimentel, 2011). Non-native trout species have become established within both previously fishless habitats as new functional groups and within habitats that already contain fish (Simon & Townsend, 2003; Strauss et al, 2006; Strayer, 2010) Their impacts on native fauna have been observed to range from subtle, such as influencing behaviour, distribution patterns and habitat use (Simon & Townsend, 2003; Penaluna et al, 2009), to local extirpation of local species (McIntosh, 2000; Bosch et al, 2006; Kadye & Magadza, 2008) and broad ecosystem impacts such as trophic cascades (Townsend & Crowl, 1991; Biggs et al, 2000; Nystrom et al, 2001). The risk of trout invasions, primarily through angler introductions, is high in many southern African rivers, but their impacts are less understood, and have rarely been assessed especially in tropical southern Africa (Kadye & Magadza, 2008)

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