NINA-rapport 646: Laks i framtidens klima (pdf)

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NINA-rapport 646: Laks i framtidens klima (pdf)

NINA Rapport 646

Abstract

Finstad, A.G., Hedger, R., Jonsson, B., Kvambekk, Å.S, Ekker, R., Forseth, T., Ugedal, O.,

Sundt-Hansen, L. & Diserud, O. 2010 Atlantic salmon in future climates: Rewiew of current

knowlegde and scenarios with focus on water discharge and temperature – NINA Report 646.

99 pp.

Here, we give future temperature and discharge scenarios for model salmon rivers located in

Southern, Western and Northern Norway based on downscaled climate data from two different

global circulation models and two different emission scenarios. The temperature and discharge

scenarios are then used as a basis for modeling the effects of possible future climate changes

on freshwater production of Atlantic salmon. The report also includes a review study of present

knowledge of the response of Atlantic salmon to climate variables, with special emphasis on

discharge and temperature in freshwater.

Temperature and discharge scenarios: The water temperature simulations are based on

previous discharge scenarios from the Nordic CES-project for the control period 1961-1990

and for 2071-2100. Climate data are from HadAM3H (Hadley Center) and ECHAM4 (Max

Planck Institute), downscaled to 55 km 2 quadrants using the HIRAM model (Norwegian Metrological

Institute). Emission scenarios used are A2 and B2. A real river (Nausta, located at the

Norwegian west-coast) is used as a standardized river profile, and discharges from Gjerstad

(Southern watershed) and Karpelv (Northern watershed) are scaled so that the median discharge

in the control period is equal for the three watersheds. The rivers thus retain their

charcteristics in terms of annual discharge pattern. Water temperatures is modeled using the

one-dimensional model RICE, and boundary conditions in the upper part of the watershed are

determined as a delayed function of water temperature. Two different scenarios (high or negligible)

for groundwater inflow are also simulated.

In rivers with negligible groundwater input, water temperatures rise by 3 to 4°C during the

summer period compared to the control period in all rivers and all climate scenarios. The winter

period is reduced by two months in the Northern Norway, but continues to be stable with permanent

ice-cover under future climate scenarios. In southern Norway the winter period is reduced

by one and a half months, and becomes less stable with variable ice-cover and and inrease

in water temperature by 1 to 1.5°C compared to the control period. In western Norway,

ice-cover disappears almost completely and winters became one month shorter. In rivers with

modeled high groundwater input, summer temperatures increase on average by 2 to 4°C, with

winter temperatures remaining similar to those of rivers with negligible groundwater input.

Current knowledge, salmon and climate: There has been a rapid increase in the amount of

literature covering climate change and ecological responses. The effect of temperature and

discharge on salmonid fishes is well covered, partly due to a bulk of studies covering effects of

hydropower regulation. Short term variation in climate affects behavior, physiology and lifehistory

as revealed by changes in e.g. spawning time, egg development time, swim-up time,

growth, size and age of maturation. Climate also affects Atlantic salmon more indirectly

through effects on competing fish species, predators, pathogens, and water quality. Such indirect

climate effects are also expected to affect population size and species distribution.

Discharge and temperature are among the most important abiotic variables affecting the

freshwater phase of Atlantic salmon. Temperature affects the physiology of the fish directly.

This is an important rationale for why climate directly influences the development time, growth

and life-history traits. Temperature also affects the behavior of the fish through temperature

scaling of movement capability and scope for migration. Changes in discharge may also have

a comparable effect, but discharge also affects salmon density and thus density-dependent

mortality through changes in usable area.

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