Age, growth and reproductive biology of threatened westslope cutthroat trout Oncorhynchus clarkii lewisi inhabiting small mountain streams.

Age, growth and reproductive characteristics of six westslope cutthroat trout Oncorhynchus clarkii lewisi populations were studied in the south-western Rocky Mountains in Alberta, Canada. Sagittal otoliths were collected from 605 fish ranging in size from 36 to 250 mm (fork length). The maximum detected age (13 years for females and 12 for males) was higher than has been reported previously in published literature; but no significant differences in age distributions between males and females were found. Length growth rates, estimated using the von Bertalanffy growth function, showed that males and females had similar growth rates. Sex ratios varied between 0.3 to 2.0 females per male. Age and size at 50% maturity were greater for females than males (4.9 years and 139 mm v. 3.7 years and 125 mm). Mature females were yearly spawners with highly variable fecundities (mean ± S.D. = 223 ± 94) and their ovaries contained both developed and undeveloped eggs. Across all populations, mean instantaneous mortality rate (Z) was estimated as 0.555, annual survival rates for 0-1 year-old fish were 3.2 and 57.4% for older fish. An altitudinal distribution gradient was observed, with older fish occupying upper stream reaches. This study provides a comprehensive evaluation of biological characteristics and structure of O. c. lewisi populations inhabiting small, mountain streams and should provide useful basic information for management policies of this threatened species in eastern drainage of the Canadian Rocky Mountains.

Integrating ontogenetic shift, growth and mortality to determine a species' ecological role from isotopic signatures.

Understanding species linkages and energy transfer is a basic goal underlying any attempt at ecosystem analysis. Although the first food-web studies were based on gut contents of captured specimens, the assessment of stable isotopes, mainly δ13C and δ15N, has become a standard methodology for wide-range analyses in the last 30 years. Stable isotopes provide information on the trophic level of species, food-web length, and origin of organic matter ingested by consumers. In this study, we analyzed the ontogenetic variability of δ13C and δ15N obtained from samples of three Neotropical fish species: silver sardine (Lycengraulis grossidens, n=46), white lambari (Cyanocharax alburnus, n= 26), and the red-tail lambari (Astyanax fasciatus, n=23) in Pinguela Lagoon, southern Brazil. We developed a new metric, called the Weighted Isotopic Signature (φ 15N or φ 13C, ‰), that incorporates ontogenetic variability, body growth, and natural mortality into a single number.