An aerial method of assessing spawning activity of Atlantic salmon, Salmo salar L., and brown trout, Salmo trutta L., in Norwegian streams

Abstract

A method using light aircraft to observe spawning activity of Atlantic salmon and brown trout in some Norwegian streams was tested between the years 1981 and 83. From the air, spawning redds of these species appear as light, oval spots in the river bottom. The method was successfully applied to most of thc rivers studied, and information about numbers of redds, distribution of redds and spawning times was obtained. However, it has several limitations. the most important bcing that it proved to be unsuccessful in a deep river with high water turbidity. Also, during periods with high precipitation and high water level, thc method cannot be used. Several quantitative and qualitative aspects of the results obtained by this technique arc discussed.

Spawning Microhabitat Selection by Brown Trout in the Linthkanal, a Mid-Sized River

“…Unfortunately, the number of excavated redds er R spawning females seems to be variable. Although Crisp (1989) reported t at one completed redd er female is the rule and Heggberget (1986) showed that at least 88% -97% of o g served salmon redds contained eggs (i.e. were completed redds), a rule may not be true for the size of the spawning population at least one redd, be hi her than the value which neverthe ess provides important insight into a threatened population).…”

Twenty years of hydropower regulation in the River Alta: long-term changes in abundance of juvenile and adult Atlantic salmon

“…Shortly after the spawning season, spawning redds of Atlantic salmon were counted along the river from a helicopter (described by Heggberget et al, 1986a) in the period 1996-2005, except in 1998. The validity of redd counts as an index of the number of spawning females depends on at least two assumptions (Dunham et al, 2001): that counts are representative of actual redd numbers (i.e.…”

Migratory behaviour of wild and farmed Atlantic salmon (Salmo salar) during spawning

“…Salmon redds in the river were located four times (17, 21, 24 and 31 October) by helicopter as described in Heggberget et al (1986~). Spawning areas were defined as those parts of the river where redds were found.…”