Environmental monitoring methods in freshwater biology

Project Department: Uni Research Environment (group: LFI - freshwater biology) period: 01.09.07 - 31.12.18

About the project

LFI works to monitor and enhance salmonid populations through the collection of biological, chemical and physical data and mitigation and enhancement programs. Some methods and programs are detailed below.

Research and monitoring:

gytefisk_resampled_tellingCounting salmonid spawners: Atlantic salmon (Salmo salar) and seatrout (Salmo trutta)

During spawning season in late autumn, LFI biologists scuba dive down rivers and count fish in order to assess the population’s size and composition. In addition, LFI maps the distribution of spawning areas in each river. The resulting information provides a basis for population-specific management.

To the right: sea trout counted while spawning. Photography by Bjørn Barlaup, LFI.


_resampled_gytegrop_meinsbusundetAnalysis of spawning areas and redds

The quantity and quality of the salmonid spawning areas is important for recruitment. A number of physical and chemical factors, e.g. temperature, water chemistry, oxygen level, water flow, and gravel composition, will impact egg survival.

To the right: redd in LFI-planted spawning gravel, Bjornesfjorden. Photography by Bjørn Barlaup, LFI.



In order to sample live fish from rivers and streams we use an electric device with an output of 1500 volts directed into the water via cables and handheld probes. Fish entering the electric field lose consciousness long enough to be picked up with a net. This is a common method used to estimate density and age composition of juveniles in a defined area (often 100 m2) and is a standard method used to evaluate the status of fish populations.

To the right:  smolt of the typical size caught during electrofishing. Photography by Bjørn Barlaup, LFI.


_resampled_alderMulti-mesh net fishing

Multi-mesh nets are used to evaluate density, growth conditions and age composition of fish populations living in lakes, as well as to provide information about habitat preferences of a species (use of benthic vs. littoral vs. pelagic habitat). These specially designed nets are composed of 2.5 meter long segments with 12 different mesh sizes in order to capture fish of different sizes.

To the right: Age distribution of fish caught using a multi-mesh net.


resampled_smoltskrueSmolt monitoring

The smolt stage is critical in the life cycle of Atlantic salmon and seatrout. LFI captures smolts during their outmigration from the river in order to gain important information about timing of the smolt run, smolt quality and smolt production.

To the right: “fish traps” at Bolstad are used to capture migrating smolt. Photography by Gunnar B. Lehmann, LFI.


Mitigation and Enhancement Efforts:

resampled_Grusutlegg_i_DaleelvaGravel bed enhancement

Water diversions for hydroelectric development, canalisation and other human activities in the watershed may change patterns of water flow and sediment deposition in a river system. This can lead to loss or impairment of spawning areas, with negative consequences for stock recruitment. In order to mitigate for these effects, LFI creates and replenishes spawning areas through the addition of gravel. Results show that successful spawning is taking place in these enhanced gravel beds.  To the right:  spawning gravel placed in Daleelva, Vaksdal. Photography by Tore Wiers, LFI.



Eggplanting is an additional strategy used by LFI to enhance salmonid recruitment. One advantage of this technique is that resulting fry are more closely adapted to local natural conditions than hatchery-reared fish. The key to success in eggplanting is to provide conditions that promote egg survival. In order to do this it is essential to understand the spawning biology of the specific salmon stock, including factors such as appropriate gravel composition, egg burial depth, number of eggs per pocket and hydrological conditions.

To ensure good results it is important to adapt the method to the specific circumstances of a given river. The success of the eggplanting method must be assessed by monitoring egg survival and subsequent juvenile density.

To the right: Eggs are being deposited in gravel boxes under water. Photography by Tore Wiers, LFI.


_resampled_carlin_tinnholenUse of wild juveniles for cultivation

Since 2006, the Norwegian Directorate for Nature Management has recommended that hatchery programs for enhancement of lake populations use only local fish in cultivation. The purpose of this is to reduce the spread of invasive species and disease between rivers and regions, and to sustain the local populations. This means that fish used for stocking should preferably be from the same watershed where they are to be released.

 A method to generate “local” juvenile fish for stocking programs is to capture wild juveniles from high density streams or lakes within the watershed. LFI uses large fish traps, seine nets or electrofishing to capture fish for this purpose.

On picture: carlin tagged brown trout from Bjoreio, released in Tinnhølen. Photography by Gunnar B. Lehmann, LFI.


cp: 2019-12-04 11:15:44