The biology and ecology of anadromous brown trout (Salmo trutta) at sea is poorly understood. This study provided information on spatial and temporal distribution of sea trout in the ocean. The behaviour of 115 individuals (veteran migrants, 270–700 mm) was tracked by using acoustic telemetry in a fjord system during April–September in 2012–2013. Overall, fish spent 68% of their marine residence time close to river mouths (<4 km). Most fish registrations (75%) were in nearshore habitats, but pelagic areas were also used. The maximum migration distance of tagged fish was categorized as short (<4 km from river mouth, 40% of fish), medium (4 – ∼13 km, 18% of fish), or long (>∼13 km, 42% of fish). Long-distance migrants had poorer body condition in spring prior to migration, used pelagic areas more often, and returned earlier to fresh water than short- and medium-distance migrants. Marine residence time was 7–183 days and was positively correlated to body length and smolt age, but negatively correlated to the date of sea entry.

Amphibian populations are declining at an alarming pace in many parts of the world. Consequently, as part of the strategy for establishing a 360 km 2 conservation and reference area for amphibians in central Norway, 341 lentic water bodies were surveyed to investigate and briefly describe their hydrography and the occurrence of the newts Triturus vulgaris (L.) and T. cristatus (Laurenti) in the area. In particular we investigated the factors that could explain the presence of the respective newt species, including biotic and abiotic factors. The multiple logistic regression analyses suggested that the presence of T. cristatus was best explained by altitude and ion concentration, both in a nonlinear fashion, whereas fish had a negative effect on T. cristatus, which was never found coexisting with fish. The presence of T. vulgaris was best explained by altitude (linear relationship) and ion concentration (convex relationship), besides the occurrence of T. cristatus. Triturus vulgaris was occasionally found to occur at low densities in ponds having fish. For both species the probability of presence was higher when the opposite newt species was present. pH influenced both species in a convex nonlinear fashion with highest probability of presence around pH 6.5. This area is valuable for conservation, monitoring and reference for marginal amphibian populations. Any decline in their abundance would be discovered relatively quickly, and likely causes could be inferred. It can also serve as a reference area for future comparative studies of amphibians elsewhere.

No abstract

No abstract

The early migration and habitat use of brown trout Salmo trutta post-smolts tagged with acoustic transmitters (n = 50) were investigated in a fjord system in central Norway from 30 April to 26 November 2014. The main aims were to investigate return rate, marine residence time and spatial use of the fjord system. Median seaward migration and return to fresh water dates were 22 May and 4 July, respectively. Of the 40 seaward migrating smolts, 26 returned to fresh water, giving a minimum return rate to fresh water of 65%. Entrance to the fjord from the river occurred mainly at night (80% of the S. trutta), however, no such diurnal pattern was observed during the return migration. Mean marine residence time was 38 days, but with large individual variation (22-99 days). The innermost parts of the study area were more utilized than the outer part of the fjord system during the sea residency, and with more use of the near shore habitat than the open, pelagic areas. Many post-smolts also utilized the outer part of the fjord system, however, and 94% of the post-smolts were recorded at least 14 km from the home river mouth. Marine survival and distribution in the fjord were size dependent with the largest individuals utilizing outer fjord areas and having higher return rates to fresh water. As far as is known, this is the first published study on temporal and spatial behaviour in the marine environment of first-time S. trutta migrants during the full course of their first trip to sea.