Domestication is rife with episodes of interbreeding between cultured and wild populations, potentially challenging adaptive variation in the wild. In Atlantic salmon, Salmo salar, the number of domesticated individuals far exceeds wild individuals, and escape events occur regularly, yet evidence of the magnitude and geographic scale of interbreeding resulting from individual escape events is lacking. We screened juvenile Atlantic salmon using 95 single nucleotide polymorphisms following a single, large aquaculture escape in the Northwest Atlantic and report the landscape-scale detection of hybrid and feral salmon (27.1%, 17/18 rivers). Hybrids were reproductively viable, and observed at higher frequency in smaller wild populations. Repeated annual sampling of this cohort revealed decreases in the presence of hybrid and feral offspring over time. These results link previous observations of escaped salmon in rivers with reports of population genetic change, and demonstrate the potential negative consequences of escapes from net-pen aquaculture on wild populations.

Laser ablation sampling - inductively coupled plasma - mass spectrometry (LAS-ICP-MS) was an effective technique for the comparison of relative Sr concentrations in the opaque growth zones (annuli) in the fin rays of white sturgeon (Acipenser transmontanus). Three of 29 Fraser River white sturgeon (10.3% of the sample) showed significantly higher Sr fin ray concentrations in at least one annulus compared with the remainder of the fin ray, and this was interpreted as evidence of marine migrations. Eleven other individual fish had significantly higher mean Sr concentrations in their first 15 annuli compared with annuli 16-30 but lower than the concentrations of the three putative diadromous fish, and this was interpreted as evidence of time spent in the estuary. Eight Fraser River fish greater than 15 years old showed no significant increase in fin ray Sr concentations in the first 15 annuli, and Sr concentrations remained below 350 ppm throughout their lives. These individuals were considered likely to have spent most of their lives in a freshwater environment. Based on the evidence in this study, it is probable that the majority of white sturgeon in the lower Fraser River are not diadromous, but many spend extended periods of time in the Fraser River estuary as juveniles.

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Evidence mounts for the influence of climate variability on temporal trends in the phenology of many organisms including various species of fish. Accordingly, we examined variation in adult Atlantic salmon Salmo salar run timing in thirteen Newfoundland and Labrador rivers where returns were monitored at fishways or fishcounting fences. Run timing varied significantly among rivers with the median date of return differing by up to 5 weeks. Duration of runs was generally short with most adults returning over a period of three to 5 weeks. A mixed model analysis incorporating a first-order autoregressive error structure was used to generalise changes in run timing among all monitored rivers. Results indicated that the median date of return has advanced by almost 12 days over a 35-year interval from 1978 to 2012, while several individual rivers have advanced by almost 21 days. The influence of climate on median timing was evident when the simultaneous effects of both climate and salmon abundance were controlled. We found earlier runs associated with overall warmer climate conditions on the Newfoundland and Labrador Shelf. Results contrast with those from the north-east Atlantic where Atlantic salmon are returning later in some rivers coincident with warming climate conditions.

Incremental growth layers occur in the hard structures of many types of organisms (tree xylem, mollusc shells, vertebrate teeth, otoliths, scales, etc.). Microprobes have previously shown that these layers contain archival information about an organism's chemical environment. However, trace elements, including metals, are generally undetectable with these instruments. A relatively new technique, laser ablation – inductively coupled plasma – mass spectrometry (LA-ICP-MS) promises multielement analytical capability with extremely low detection limits (conservatively, <1 ppm), combined with very fine spatial resolution (down to 30–100 μm beam diameter). Fish otoliths and vertebrate tooth cement and dentin offer the greatest potential for retrieving element archival information, because they are not subject to resorption, and reflect the organism's exposure to or accumulation of trace elements from the ambient environment. Other structures are less promising, because they exhibit element mobility between growth layers (tree rings), or are subject to metabolic turnover and resorption (scales, bones, shells). While the LA-ICP-MS technique is novel in the biological sciences, the few studies available indicate that reproducible, year-by-year data on metal accumulation or exposure will probably be retrievable from many types of incremental structures. The main problem currently is the lack of solid standard reference materials which match the physicochemical properties of hard biological tissues.Key words: laser ablation, mass spectrometry, trace metals, environmental pollution, calcified tissues.