Vidal, Nicolas; Trochine, Carolina; Amsinck, S. L.; Barmuta, L.A.; Christoffersen, K. S.; Ventura, Marc ; Buchaca, Teresa ; Landkildehus, Frank; Hardie, Scott A.; Meerhoff, Mariana; Jeppesen, Erik. Inland Waters : DOI: 10.1080/20442041.2020.1724047 (2020) DIGITAL CSIC
Non-native ﬁsh invasions threaten native fauna and ecosystem functioning, not least in isolated island lakes. In Tasmania, where the native ﬁsh are mostly galaxiids, 9 non-native freshwater ﬁsh species have been introduced over the past 150 years, with uncertain ecological outcomes. We evaluated the eﬀects of non-native predatory ﬁshes (NNPF) and various environmental and biological variables on the trophic niche of native ﬁsh (galaxiids) and potential cascading eﬀects. We analysed Layman’s food web metrics based on both stable isotope (δ15N and δ13C) values and ﬁsh stomach contents in 14 shallow Tasmanian lakes along a NNPF abundance gradient. The food web metrics calculated were (1) range of δ13C (CR) and δ15N (NR) centroid distance (CD) and (2) standard ellipse area. Our results showed that NNPF relative abundance in the ﬁsh catch per unit eﬀort was negatively related to the galaxiids’ trophic niche metrics (e.g., CRG, NR G, and CDG), trophic position, and the pelagic contribution to the diet. Moreover, the proportion of galaxiids in the diet of NNPF was higher in turbid lakes. The zooplankton standard ellipse area was negatively correlated with the pelagic contribution to the NNPF diet, and NNPF relative abundance was positively correlated with the maximum body size of calanoid copepods. While our results suggest a negative eﬀect of NNPF on the trophic niche of galaxiids, the cascading eﬀect on phytoplankton biomass was weak. Non-native predatory ﬁsh aﬀect native ﬁsh prey, and the outcome of these interactions should be considered for conservation purposes, particularly for island lakes, such as those in Tasmania.