Abstract
The geographical characteristics of Chile may provide excellent habitat for the establishment of diadromous fish species. The objective of this study was to document migratory life histories of native galaxiids and introduced salmonids from a wide latitudinal range in Chilean Patagonia (39-48°S). Otolith microchemistry data were analysed using a recursive partitioning approach, with the main goal of testing the hypothesis of diadromy for several populations of galaxiids and salmonids. Based on annular analysis of Sr:Ca ratios, a diadromous life history was detected for populations of native Aplochiton taeniatus, A. marinus, and Galaxias maculatus. Residency in freshwater was suggested for populations of A. zebra and confirmed for G. platei. Among introduced salmonids, populations of Oncorhynchus tshawytscha and O. kisutch exhibited anadromous migratory patterns consistent with their life history in the native range, whereas the populations of O. mykiss examined appeared restricted to freshwater areas. Salmo trutta exhibited variable habitat use consistent with the establishment of more than one type of life cycle. Multivariate classification and regression trees (CART) were used to assess changes in ratios of all elements assayed (Sr, Mg, Mn, Ba, Ca) across chronological sequences of otoliths. Changes in Sr had highest relative influence in species that dwell prevalently in saltwater and brackish habitats, whereas changes in Mg and Mn appeared to discriminate fishes that moved exclusively between freshwater environments. Some species (e.g., O. tshawytscha) showed equally strong variation in all elements assayed suggesting that time spent between fresh headwaters and the sea jointly influenced otolith microchemistry. As accelerated growth in hydropower capacity further disrupts migratory routes of native and introduced fishes alike, special concern in conservation assessments should be given to diadromous species and populations with dire conservation status or economic importance.