Niels Jepsen

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Surgical implantation has become a well-established method for attaching telemetry transmitters in studies of fish behaviour. However, a rather large number of reports of transmitter expulsion, fish mortality and adverse effects on fish physiology or behaviour, suggests that refinement and evaluation of the methods is needed, especially when tagging fish(More)
High mortality-rates of seaward migrating salmonid smolts when passing reservoirs and lakes have earlier been found in the Danish River Gudenå watershed. To reveal the causes of mortality of migrating smolts in Lake Tange, a 12 km long, shallow reservoir, 50 salmon smolts and 24 trout smolts were tagged with internal miniature radio-transmitters, and(More)
The fate of radio-tagged hatchery-reared salmon smolts (Salmo salar L.) was investigated in the tailrace of a hydropower station in the Danish River Gudenaa during 2 years. Seventeen and 27 smolts were tagged and released in late May 1996 and during April 1999, respectively. Out of the total of 44 smolts, only two were recorded to leave the river and enter(More)
The effects of disturbances from recreational activities on the swimming speed and habitat use of roach Rutilus rutilus, perch Perca fluviatilis and pike Esox lucius were explored. Disturbances were applied for 4 h as (1) boating in short intervals with a small outboard internal combustion engine or (2) boating in short intervals combined with angling with(More)
Adult roach (Rutilus rutilus) (13–25 cm) from two shallow lakes, one turbid and one with high water transparency, were tagged with surgically implanted miniature radio transmitters and their habitat use was monitored. Repeated tracking series over the course of the year provided information on seasonal changes in behaviour of roach in the two lakes. The(More)
Effects of artificial salmon lice infection and pharmaceutical salmon lice prophylaxis on survival and rate of progression of Atlantic salmon (n = 72) and brown trout post-smolts (n = 72) during their fjord migration, were studied by telemetry. The infected groups were artificially exposed to infective salmon lice larvae in the laboratory immediately before(More)
Between days 10 and 21 after inoculation of Lupinus angustifolius seedlings with Rhizobium NZP 2257, the average nodule fresh weight increased 3-fold and the number of bacteroids per nodule increased more than 10-fold.The viability of Rhizobium bacteroids, as judged by their ability to form colonies on yeast-extract agar, declined from about 10% on days 10(More)
A method has been developed for culturing detached nitrogen-fixing root nodules of lupin (Lupinus angustifolius L.) on a simple nutrient medium. Under the best conditions devised, the acetylene reduction activity of mature detached nodules was maintained at 10 to 25 nmoles of ethylene hr(-1) mg(-1) fresh weight for 3 days. Under the same culture conditions,(More)
An investigation has been made of the combined effects of low temperature and high light on the level of several photosynthetic products in the leaves of a group of plants differing widely in their tolerance to this stress. Starch levels in these plants after chilling are dependent on the time of day that temperatures are lowered and seem related to rates(More)
From September to November in 1995 a total of 49 mature sea trout were caught and radio tagged in the estuary (Randers fjord) or at the river mouth of the River Gudenå in Eastern Jutland. The tagged trout were between 2 and 6 yr old with total body length of 56–85 cm. Twenty-five of the tagged trout ascended the river. They were tracked every third day, for(More)