No abstract

Habitat use and habitat selection by young Atlantic salmon and brown trout were investigated by direct underwater observation. We sampled during winter and summer water temperatures (low: 3 -7°C; high: 9 -12°C) coinciding with low and high waterflows (12-20 and 60-80 m 3 s − 1 ), and during day and night in winter, and on six selected stations in the river. Observations of 396 salmon and 120 trout indicated a distinct seasonal pattern in behaviours and habitat selection. Feeding was the dominant behaviour at high water temperatures during summer. In winter, there was a diurnal pattern in behaviour; both species sheltered in interstitial spaces in the substrate during daylight, but during night held positions on or close to the substrate in slower flowing stream areas. Coarse substrate providing cover was therefore an important habitat factor during daylight at low water temperatures, while slow-flowing water was important during night. Although spatial niche overlap was considerable both in summer and winter, salmon and trout segregated with respect to meso-and microhabitat selection, and relatively more at low temperatures. Both species changed their use of mesohabitats towards more slow-flowing glide/flat habitats in winter. Irrespective of season, trout preferred in general more slow-flowing water than salmon did, but the difference was more pronounced in winter. Salmon used a wider range of water depths and in particular water velocities, than did trout. Both species were less tolerant of high water velocities at low water temperatures. The seasonal and diurnal pattern in habitat selection reported have important implications for habitat research and habitat-hydraulic modelling. Copyright

Radio transmitters were implanted in wild brown trout, Salmo trutta L., in the River Ma˚na at low summer water flows (n = 18), higher flow in summer (n = 20), and variable, peaking flows in autumn (n = 20), and tracked two to four times day and night for 4-5 weeks. Individuals were caught and released in a 4-km uniformly channelised section, and in a 4-km natural diverse river section. Substantial individual variation in home range and total movement (924-85 818 m 2 and 295-7014 m) suggested flexibility to adapt to local environmental conditions. Fish were stationary most of the time (median movement 0 m), but some individuals undertook few and apparently sporadic longer movements, sometimes involving shifts in home range. No consistent diurnal pattern in movements was found. Trout in the uniform habitat section appeared to have larger home ranges and moved more than trout in the natural section. Differences were, however, not statistically significant in most comparisons, due to large individual variation. Similarly, larger home ranges and movements between trials related to higher flow were found, but differences were generally not significant. No consistent effects of sudden, extreme peaking flows on area use or movements by the brown trout were observed. K E Y W O R D S : brown trout, habitat, movement, stream, telemetry, water flow.

T h e seaso n al m o rta lity o f b la c k gro u se Tetrao tetrix w as studie d in so u th eastern N o rw ay (6 0°2 6'N , 10°54'E ), in a stu dy are a d o m in ated b y up to 80% N o rw ay sp ruce Picea abies. M o d e m fore stry w ith cle ar-cu ttin g s has been p ractised , an d 50% o f th e fo rest w as y o u n g e r th an 30 years. F o u rteen m ales and seven fem ale s w ere cap tu red o n a le k in spring 1991 and eq u ip p ed w ith rad io tran sm itte rs. D u rin g th e fo llo w in g 12 m onth s, 72% o f th e bird s w ere killed, m ostly by p red ato rs. N o birds d ie d fro m cap tu re th ro u g h July. In au tu m n , p re d a tio n w as h ig her, w ith fo u r b la c k g ro u se b ein g killed. M o rta lity w as h ig h est du rin g w inter, w ith 58% o f the bird s dying. T h e g o sh aw k Accipiter gentilis w as th e m o st im p o rta n t p re d a to r du rin g w inter. H ig h p red atio n by go sh aw k s in w in ter 1991-92 m ay have b e e n th e re su lt o f b la c k gro u se b ein g m ore v u ln erab le to p re d atio n b ecau se lim ited sn ow fall p reclu d ed snow ro o stin g , or o f an in vasion by gosh aw ks. T h erefo re, snow ro o stin g m ay b e an im p o rta n t an tip red ato r b eh av io u r in b la c k grouse . T h e effe ct o f in creased ad u lt m o rta lity is d iscu ssed in rela tio n to ch ic k p ro d u c tion.

The last of 12 brown trout Salmo trutta stocked in a small pond in south-east Norway in 1979 were caught in July 2011. These fish represent a curiosity regarding longevity and growth pattern, and ageing from otoliths was consistent with the known life history of this specimen. Despite almost total stagnation in growth since the age of 16 years, the testes were fully developed.