FAO of United Nations

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FAO of United Nations

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Arismendi I.,Austral University of Chile | Arismendi I.,Oregon State University | Penaluna B.,Oregon State University | Soto D.,FAO of United Nations
Lake and Reservoir Management | Year: 2011

In South America, salmonids have been widely introduced to lakes, yet there are still many oligotrophic lakes without current abundance estimates. Catch per unit effort is a good estimator of fish abundance, but its correct implementation requires an expensive and long-term effort. Thus, there is a need to develop a rapid assessment to estimate the relative abundance of salmonids. Under well-delimited circumstances, condition indices may be a good technique to estimate fish population relative abundances. We sampled adult salmonids with gillnets from 6 oligotrophic lakes in southern Chile during the Austral summer. Our data show that as rainbow trout condition indices decrease, the abundance of salmonids increases both temporally and spatially. Because all 6 lakes are limited by food, the most likely reason for the change in the rainbow trout condition indices is change in salmonid abundance. The strong inverse relationship between condition indices of rainbow trout and the relative abundance of salmonids suggests that our model can be a useful tool for the estimation of relative fish abundance in lakes. This study provides a model that can be used to improve lake and fishery management decisions for introduced salmonids in southern South America. © 2011 by the North American Lake Management Society.

Arismendi I.,Austral University of Chile | Gonzalez J.,University of Concepción | Soto D.,FAO of United Nations | Penaluna B.,Oregon State University
Austral Ecology | Year: 2012

Trophic relations among introduced species may induce highly variable and complex effects in communities and ecosystems. However, studies that identify the potential impacts for invaded systems and illuminate mechanisms of coexistence with native species are scarce. Here, we examined trophic relations between two introduced fishes in streams of NW Patagonia, rainbow trout (Oncorhynchus mykiss) and brown trout (Salmo trutta). These species originate from different regions of the Northern Hemisphere but they now coexist as invading species over the world. We used gastric contents and stable isotopes analysis to compare the diets of two size-classes of these two invaders in three localities of southern Chile. Both species displayed similar ontogenic diet shifts with smaller trout consuming mostly invertebrates and larger trout being more piscivorous and epibenthic feeders. However, piscivory was more prevalent in brown trout than in rainbow trout and highest at the site with the greatest density of native fishes suggesting that the availability of native fishes as trout prey may limit the occurrence of trout piscivory. We found an elevated dietary overlap between the two trout species at larger sizes while at smaller size a higher intraspecific dietary overlap occurred suggesting a potential interference competition among the two fish invaders especially at larger sizes. Our results highlight that the impacts of invading species on non-native fishes are context specific (i.e. species and ontogenic stages) and thus, difficult to generalize. © 2011 The Authors. Journal compilation © 2011 Ecological Society of Australia.

Arismendi I.,Austral University of Chile | Arismendi I.,Oregon State University | Sanzana J.,University of Los Lagos | Soto D.,FAO of United Nations
Annales de Limnologie | Year: 2011

Rainbow trout is one of the most popular introduced game species around the world. Similar patterns of use for lake and inlet streams have been described for both native and introduced populations. However, for many introduced rainbow trout populations, there is a lack of information about how and when those habitats have been used. Here, we hypothesized that the majority of adult and sexually mature individuals inhabit inlet streams during the reproductive period most likely to spawn whereas juvenile trout occupy these same streams as nursery areas most of the year before emigrating to the lake. We studied rainbow trout age distribution and sexual maturity in a lake and its main inlet streams in southern Chile. We found that stream-dwelling individuals inhabited inlet streams up to age 2 + whereas lake-dwelling trout were older (most of them from ages 4 + to 6 +). During the reproductive period (May to September) older and sexually mature individuals were in both habitats probably indicating movement to upstream locations to spawn. Rainbow trout of the same ages were larger in the lake than in streams, which may imply better growth in the lenthic environment. Our study offers further evidence of the highly adaptable nature of rainbow trout. Future regulations should consider rainbow trout populations in lakes and streams separately because trout life histories suggest that both environments are important to different ontogenic stages. This study provides key information that may be useful in the management of ad-fluvial populations of rainbow trout in Patagonia. © EDP Sciences, 2011.

Arismendi I.,Oregon State University | Soto D.,FAO of United Nations
Knowledge and Management of Aquatic Ecosystems | Year: 2012

Using stable isotope analyses of N and C we present preliminary evidence of marine-derived nutrients from introduced Chinook salmon (Oncorhynchus tshawytscha Walbaum) in stream food webs of Laguna Los Patos, NW Patagonia. Similar to values reported within Chinook salmon's native distributional range periphyton and aquatic insects are the trophic levels that show the greatest enrichment of δ15N (5-6‰). Since there is a rapid expansion of Chinook salmon in South America future effort is needed to elucidate the mechanisms and consequences of nutrients subsidies from salmon carcasses in those invaded ecosystems. © 2012 ONEMA.

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