Swimming capabilities and in situ measurement of muscle activity from adult Atlantic salmon (Salmo salar) at two seasonal temperatures were measured using radio transmitted electromyogram (EMG) signals. Forced sustained levels of activity and critical swimming speeds were determined and correlated to radio transmitted EMG signals using a modified Blazka swim speed chamber. There were no differences in swimming performance levels between tagged and untagged individuals. At 18 °C, sustained activity and critical swimming speeds were approximately 70% and 20% higher than at 12 °C, respectively. No differences in burst activity were observed at these temperatures. EMGs recorded from salmon during ascent of an artificial flume at cold temperatures revealed that overall muscle activity is greater than that observed for critical swimming speeds. This implies that white muscle may be recruited at this temperature. However, in contrast, most activity at 18 °C is below that observed during critical swimming speed. Moreover, salmon required almost twice as long to traverse the flume at 18 °C than at 12 °C. Together, our data demonstrates that salmon may recruit white muscle fibres and incur an oxygen debt at colder temperature as a strategy for ascending velocity obstructions at a quicker rate.

Atlantic salmon juveniles were subjected to a precocious (day 104 after first feeding) photoperiodic (P) and thermic (T) control. After rearing the fry at 16 °C, constant (16 hours of light and 8 hours of darkness, 16 °C) (C) and shortened simulated natural S photoperiod and temperature regimes were used in a factorial experimental design until transfer to seawater. The growth obtained with constant (C) regimes was better than with S regimes. In all cases, we observed very early (day 141, mid-June) a clear segregation of the population into two different subpopulations. Among the conditions, all the differences between the upper and lower modes were growth-dependent. We observed different developmental trends of the gill (Na+-K+)-ATPase activity: the S regime gave a very progressive increase of the enzymatic activity, while we had a rapid decrease after a first phase of increase with a constant photoperiod. The absolute levels of the gill (Na+-K+)-ATPase activity were slightly lower than those observed in one year-old smolts. However, they are quite similar to those of upper-mode fish that have a good salinity tolerance. After transfer to seawater, fish subjected to shortened simulated temperature and photoperiod had the lowest mortality and osmotic disturbance (after 48 hours and 3 weeks). Although the freshwater phase generally lasts more than 15–17 months for this species in a natural environment, we concluded that it is possible to obtain a good salinity tolerance after 7–8 months, with shortened simulated natural photoperiod and temperature regimes, in spite of the absence of a real smoltification; these regimes, however, must be applied during the "dynamic" presmolting phase when the growth is intense.

The final phase of spawning migration of eight adult male Atlantic salmon, Sulnio solar L., was analysed by radio-tracking in relation to sea age and size in a spawning tributary of the Kiver Sélune. Four grilse and four multi sea-winter fish, one of which as a previous spawner, were radio-tagged and released. Their fork length ranged from 602 to 882 mm. The daily movement in the first two days alier release and the furthest upstream distance recorded from the trap during the study period were independent of fish length. Maximum amplitude of movement observed over the entire study period was inversely correlated with length. Daily movement decreased in all males during the spawning period and was negatively correlated with the size of fish. Surviving males remained in the vicinity of the spawning grounds after spawning. It was concluded that the length of male seemed to influence its behaviour in the last phase of the spawning migration, enabling a much more successful participation of the larger males in spawning.

The general characteristics of the main salmon (Salmo salar L.) stocks in the Massif armoricain (Brittany and Lower Normandy), in the Loire-Allier and in the Adour-Gaves-Nive have been summarized. Due to the poor quality of the previous fishing statistics, there is no clear picture of the historical evolution of the salmon stock. However, a dramatic decrease in the endemic range of Atlantic salmon in France can be shown since the mid-18th century and more particularly during the last 50 years. The lack of precise informations describing the size of the catches and the levels of exploitation at sea and in the estuaries make it impossible to estimate the impact that exploitation has led on the evolution of salmon stocks. The mean age of salmon in freshwater ranges from 1 to 1.5 years. The Loire-Allier basin is characterized by a relatively high proportion of large salmon (3 fish) in the rod catches. Fish native to Brittany and Lower-Normandy (Massif armoricain) have lover growth rates than those from the Loire-Allier and Adour-Gaves-Nice Basins. A greater proportion of the early grilse stocks (migration May-July) are males than compared with fish running later. The sex ratio of the multi-sea-winter salmon is biased towards females.

The use of an image analysis microsystem with a specially developed software enabled scale image processing, outline extraction and computation of features which are not available in the conventional approach of scale analysis. Those parameters (shape factors, moment invariants and elliptic Fourier coefficients) were introduced into a discriminant analysis process to test their usefulness in stock identification. The method was applied to European stocks originating from Norway (Etne river) and France (Elorn river). The low misclassification rate obtained indicates that this approach is particularly promising.