Precautionary rules for exotic trout aquaculture in fishless shallow lakes of Patagonia: minimizing impacts on the threatened hooded grebe (Podiceps gallardoi)

Abstract

ABSTRACT1. Conflicts between habitat use and conservation are inherent to the management of wetlands. A major challenge for their management is to preserve habitat while addressing the demands from multiple users. In southern Patagonia (Argentina), a growing aquaculture activity based on rainbow trout introductions in shallow lakes is generating concerns about the effects on the waterbird fauna, including some endemic species.2. Generalized linear models (GLM) were used to analyse data on the endemic hooded grebe (Podiceps gallardoi) collected over a diverse set of lakes to: (1) build presence-absence models as a function of environmental variables; (2) assess current and potential overlap with trout aquaculture; (3) explore the power of alternative lake assignment algorithms based on habitat variables to segregate critical habitat and aquaculture activities; and (4) explore the correlation between the probability of grebe presence and their abundance in given lakes.3. Hooded grebe presence is clearly correlated with macrophyte cover, lake area, and water conductivity. Medium size lakes, with a combination of emerging macrophytes, adjacent to open water areas had the highest probability of both hooded grebe presence and abundance.4. Different lake allocation scenarios are identified that could grant significant protection to hooded grebes without substantial losses for trout producers. The a priori probability to hold hooded grebe, assigned by the model based on lake characteristics, provides a tool that can be used by managing authorities to derive precautionary management rules to regulate aquaculture and to preserve primary hooded grebe habitat.

Dams versus habitat: predicting the effects of dams on habitat supply and juvenile rainbow trout along the Santa Cruz River, Patagonia

“…GAMs allow identification of the general shape of the response variable for each explanatory variable, whereas GLMs provide a more direct and robust technique to evaluate the goodness-of-fit and to interpret the results (Guisan & Zimmermann, 2000). To take advantage of the strength of each technique, we used a two-stage model fitting approach, similar to that used by Franklin (1998) and Lancelotti et al (2010) based on combining GAMs and GLMs, both assuming a scaled Poisson distribution with a log-link function. This model structure provides a good description of the error structure of discrete variables (i.e., number of fish) when there is variance overdispersion (variance larger than the mean).…”

Diet of the exotic Rainbow Trout in the critical habitat of the threatened Hooded Grebe

“…Therefore, amphipods could represent one of the primary prey for Hooded Grebes, especially in unvegetated lakes, where these organisms represent the only abundant large prey. Large unvegetated lakes were frequently used by non-breeding flocks of Hooded Grebes in periods previous to trout introductions (Fjeldsa, 1986), whereas the presence of this species was seldom observed after the trout introduction in these lake types (Lancelotti et al, 2010). This observed change in lake use could respond to a decrease in prey abundance as a direct effect of trout predation.…”

“…For instance, partially vegetated lakes are likely to be increasingly used as the preferred nonvegetated lakes are used up, which could increase the spatial overlap between trout and the Hooded Grebe (Lancelotti et al, 2010). Besides, two of the most important reproductive habitats for Hooded Grebes, the Islote lake (included in this study) in the Lake Strobel meseta, and Lake El Sello (71 • 20 W, 46 • 55 S) in the Lake Buenos Aires meseta, have been stocked with trout in recent years.…”

“…From October to March the Hooded grebe congregates in the basaltic mesetas to reproduce. Throughout the ample gradient of lake characteristics, Hooded grebes strongly prefer lakes with a combination of emerged macrophytes (dominated by the Myriophillum elatinoides) surrounded by open water areas (Fjeldsa, 1986;Lancelotti et al, 2010). The Myriophillum generate carpets over the water surface, where Hooded Grebes build their nests using the macrophytes as building material.…”

“…However, in several of the large vegetated lakes trout have also been stocked at the onset of the aquaculture activity. On the other hand, all small vegetated and turbid lakes remain fishless (Lancelotti et al, 2010). Because of habitat restrictions (e.g.…”