Seasonal age distributions and maturity stage in a naturalized rainbow trout (Oncorhynchus mykiss Walbaum) population in southern Chile reveal an ad-fluvial life history

¹ Escuela de Graduados, Facultad de Ciencias Forestales, Universidad Austral de Chile, Casilla #567 Valdivia, Chile
² Current address: Department of Geosciences, Oregon State University, 3200 SW Jefferson Way, Corvallis, OR 97331, USA
³ Darwin Initiative, Laboratorio de Genética, Acuicultura y Biodiversidad, Universidad de Los Lagos, Avenida Fuschlocher 1305, Osorno, Chile
⁴ Inland Water Resources and Aquaculture Service (FIRI), Fisheries Department, FAO of United Nations, Via delle Terme di Caracalla, 00100 Rome, Italy

^* Corresponding author: Ivan.Arismendi@oregonstate.edu

Received: 21 April 2010
Accepted: 4 January 2011

Abstract

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.