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Spatial and temporal variation in production of juvenile Atlantic salmon: the importance of small streams as rearing habitats

Goal: To understand the variation in individual migration and production of Atlantic salmon parr on different spatial and temporal scales with the use of electronic PIT tags.

Objectives:

To measure the individual migration into and out of and within small streams in the Tana river system in order to quantify the importance of small streams as nursery habitats on the production of smolts.

To estimate survival of the age classes of salmon parr found in the streams and the main river in relation to their choice of migratory strategy.

To compare growth, energy content and food consumption of parr with resident and transient life history strategies in small streams and the main river to quantify the costs and benefits of migrating.

To study the competitive impact from brown trout on salmon parr.

Results from previous studies on Atlantic salmon parr in the Tana River system show that they are migrating from the main stem river and into small-sized streams during the spring and summer. This migration is probably caused by favorable environmental conditions in the small streams compared with the large main river, with food being more abundant in the streams. However, little is known about the exact nature and benefits of this migration, as well as the extent and importance of this on the total production of salmon within a watercourse. Earlier studies show that the parr migration to small streams is extensive throughout the summer, indicating that the total number of parr visiting the streams might be considerable. By use of passive integrated transponder (PIT) tags, this project aims to quantify the importance of these streams as rearing habitats for the production of salmon smolts by studying the extent of migration and the life history parameters of salmon parr both on individual and population levels. Fish will be captured and individually PIT-tagged in traps and by electrofishing. Automatically PIT-registration stations will be established at the stream outlets to record up- and downstream migrating fish, and all tagged fish within the streams and main river will be tracked with a portable reader and recaptured with electrofishing.

This approach will generate new knowledge important to the management of salmon river systems and contribute to a better understanding of the value of small streams as a nursery habitat for juvenile salmonids. The abundance of the small streams is easy to underestimate and overlook, and at the same time the streams are vulnerable to anthropogenic disturbance. The Tana river system is still relatively undisturbed, so knowledge from this system has important value for managers planning habitat restoration projects.

For further information, contact Ben Letcher

Project partners:

Norwegian College of Fishery Science, University of Tromsø, Norway
Freshwater Biological Association, United Kingdom
Oulu Game and Fisheries Research, Finnish Game and Fisheries Research Institute, Finland
Norwegian Institute for Nature Research, Trondheim, Norway