Strangers in a strange land; freshwater fish introductions, impacts, management and socio-ecological feedbacks in a small island nation – the case of Aotearoa New Zealand

Abstract

Invasive non-native species (INNS) are key drivers of global biodiversity loss. This is particularly evident in freshwater ecosystems, where the rates of both vertebrate biodiversity loss and biological invasion exceed those of marine and terrestrial systems. Aotearoa New Zealand (henceforth Aotearoa) like many other island nations, has a troubled history with NNS. However, it is also unique, as the main islands were the last major landmasses on Earth to remain uninhabited by humans. The endemic fauna had evolved in isolation from any anthropogenic influence or introduced NNS, until the mid-thirteenth century with the arrival of Māori, the first people to inhabit Aotearoa. Centuries later, following European colonisation, many non-native freshwater fish were deliberately introduced by acclimatisation societies. Currently, most of the native freshwater fish species of Aotearoa are at risk of extinction, despite almost 90% of these being found nowhere else on earth. Many of these species are highly valued by the indigenous people of Aotearoa, who have repeatedly highlighted biases towards NNS in freshwater fish management. With the rate of biological invasions increasing, it is timely to address interconnected issues concerning the history, impacts, management and current / future policy directions, including those involving biosecurity, for non-native freshwater fish in Aotearoa. We do this by applying a social-ecological systems (SES) lens, with a focus on causal-loop relationships and feedbacks to improve understanding of the dynamics of drivers, mechanisms and impacts of such invasions. We highlight the tensions that have resulted from managing some NNS as ‘pests’ threatening native biodiversity, while simultaneously promoting a tourism and recreational fishery resource for specific NNS. This has generated extremely polarized views on the ‘status’ of non-native freshwater fish species and given rise to contradictory and divergent goals for their management. We show how a disjointed and often incoherent policy landscape has contributed to legal ‘anomalies’ for NNS, including policy misalignments and gaps, hampering effective use of resources, while also entrenching contradictory management programmes for different stakeholders. Our study shows how these interconnected issues have been manifested in social-ecological feedback loops on core aspects of NNS policy and management, past and present. Consequently, there is a need for increased comprehension of the diverse array of potential impacts of NNS for different environments, stakeholders and Māori while developing coherent and practical management methods to reduce such impacts and improve social-ecological resilience. We conclude that adopting a SES approach will aid this endeavour.