Rainbow trout effects on zooplankton in the reproductive area of the critically endangered hooded grebe

Abstract

ABSTRACT1. Aquaculture in arid Patagonia is potentially affecting the hooded grebe (Podiceps gallardoi), a critically endangered endemic waterbird. Exotic rainbow trout (Oncorhynchus mykiss) were stocked from 1994 in naturally fishless lakes, the primary reproductive habitat of this grebe.2. Trout and grebes are visual predators, whose diets overlap. Consequently, trout could reduce the abundance of prey of the hooded grebe.3. This study compared the size distribution and abundance of the pelagic zooplankton fraction preyed upon by trout in four fishless lakes and three lakes stocked with trout, including vegetated and unvegetated lakes.4. The mean size of Daphnia spp. was 45% and 35% larger in fishless lakes than in stocked lakes, for unvegetated and vegetated lakes, respectively. Boeckella spp. were larger in fishless than in stocked vegetated lakes.5. Fishless and stocked lakes had highly contrasting biomasses of large pelagic crustaceans. Amphipods were absent from the water column of all stocked lakes analysed, and were abundant in fishless lakes. Parabroteas sarsi was absent from the two large unvegetated lakes, stocked with trout.6. These shifts in the abundance and size spectrum of the zooplankton may reflect competition between trout and hooded grebe, affecting the survival of the latter species.7. The current conservation status of this rare aquatic bird demands the application of management tools to reduce the detrimental effects of aquaculture on their primary reproductive habitat.

Aquatic macroinvertebrates from littoral vegetated lakes in arid Patagonia: The influence of fish introduction on community structure

“…The results indicate that the introduction of non‐native fish (in this case, rainbow trout) in the lakes of the Strobel Plateau affected the structure of pleustonic macroinvertebrate assemblages, and this change in community structure would be expected to have cascading effects across these aquatic ecosystems and the adjacent terrestrial ecosystems. The effect of stocking fish was also observed in the pelagic crustacean community in other lakes in the same plateau, affecting species dominance and size structure (Lancelotti, Marinone & Roesler, 2017). Changes in microcrustaceans can have effects on the composition of phytoplankton and the diversity of rotifers, demonstrating the cascade effect that these non‐native fish can cause (Izaguirre & Saad, 2014; Porcel et al, 2020).…”

“…The lakes of the Strobel Plateau are characterized by the absence of native fish (Fjeldsa, 1986; Lancelotti, 2009; Lancelotti, Bandieri & Pascual, 2015). Since 1994, however, the non‐native rainbow trout ( O. mykiss ) has been introduced into 39 lakes for aquaculture and sport fishing, providing an exceptional opportunity to investigate the trophic role of rainbow trout and its effects on the trophic webs of these lakes (Lancelotti, Bandieri & Pascual, 2017). For the present study, 10 shallow lakes were selected (Figure 1).…”

“…In particular, the introduction of exotic predatory fish into aquatic environments naturally devoid of these organisms can produce profound alterations in the structure of the original communities and in the configuration of their biotic assemblages (Reissig et al, 2006). Studies on predation of native fauna by introduced fish have frequently shown important ecosystem changes, such as the disappearance of amphibian and reptile populations, and changes in the species composition and body sizes in zooplankton assemblages and benthic macroinvertebrates (Attayde & Hansson, 2001; Knapp, Matthews & Sarnelle, 2001; Khan, Wilson & Khan, 2003; Lancelotti, Marinone & Roesler, 2017).…”

“…(coot) populations have been observed in a Patagonian lake with introduced fish (Ortubay et al, 2006). Overall, the consequence of fish introductions has caused ecological alterations in these aquatic ecosystems (Izaguirre et al, 2018), including a loss of biodiversity (Ortubay et al, 2006) and changes in planktonic communities (Reissig et al, 2006; Lancelotti, Marinone & Roesler, 2017; Izaguirre et al, 2018). Moreover, the introduction of rainbow trout was proposed specifically as one of the main reasons for the declining hooded grebe population in lakes of the Patagonian plateau, either through competition for food or through the depredation of chicks (Roesler et al, 2012).…”

Climate variability and trends in the reproductive habitat of the critically endangered hooded grebe

“…The introduction of rainbow trout (Oncorhynchus mykiss) in lakes of the plateaus, the predation by alien American mink (Neovison vison), the consumption of eggs and chicks by a growing population of kelp gull (Larus dominicanus)favoured by the proliferation of garbage dumpsand the occurrence of extremely dry periods have all been proposed as major threats for this species (Lancelotti, Marinone, & Roesler, 2017;Roesler, Imberti, Casañas, Mahler, & Reboreda, 2012;Roesler, Imberti, Casañas, & Volpe, 2012;Fasola & Roesler, 2018).…”