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Risle Salmon production
I see no reason why we cannot increase the salmon entering the Risle from
the Seine at Pont Audumer. Canadian and American researches are far ahead of
the EU in natural in stream food production. Restoring Nutrients to Salmonid
Ecosystems (www.gpafs.org/confnutr) reported elevated fish production in
waterbodies with increased nutrient inputs from salmon carcasses or other
nutrient sources. These increases in productivity are the result of direct
feeding by fishes on carcasses and deposited eggs, as well as increased
productivity of other food sources such as macroinvertebrates. The influx of
ocean derived nutrients from these returning salmon can also stimulate
primary production and, subsequently, macroinvertebrate production. (Also
see the Pacific Northwest Research Stationís Research Findings 32 on "Food
for fish, food for thought: Managing the invisible components of streams,"
March 2001.) Others (Bilby et al. 1996, Bilby et al. 1998) have found that
these nutrients stimulate other components of riparian ecosytems, thereby
also stimulating in-stream production through allochthonous inputs.
Studies supported by NCASI and others have determined that the availability
of food can be an important parameter influencing preferred water quality
conditions. Trout have been shown to have maximum growth and survival
between 12 and 16 degrees C when fed at full satiation, but require cooler
water for optimal growth when fed at lower food levels. This relationship
between optimal temperature and food supply is not new, with work on sockeye
done in the early 1950ís (Brett, 1952). However while temperature regimes,
particularly with recent thermisters designs, are relatively straightforward
to describe, measures of food supply are not. Increased fish productivity is
often observed with riparian forest disturbance, despite degradation of
water quality or habitat characteristics, increased food availability and
fish production overwhelming other negative impacts (Bisson, et al. 1988).
In light of these challenges, are there objective metrics, which can be used
in the field to quantify the availability of food to fish?
Bilby, Robert E.; Fransen, Brian R., and Bisson, Peter A. Incorporation of
nitrogen and carbon from spawning coho salmon into the trophic system of
small streams: Evidence from stable isotypes. Canadian Journal of Fisheries
and Aquatic Sciences. 1996; 53(2):164-173.
Bilby, Robert E.; Fransen, Brian R.; Bisson, Peter A., and Walter, Jason K.
Response of juvenile coho salmon and steelhead to the addition of salmon
carcasses to two streams in southwestern Washington, U.S.A. Canadian Journal
of Fisheries and Aquatic Sciences. 1998; 55:1909-1918.
Bisson, Peter A.; Nielsen, Jennifer L., and Ward, James W. Summer production
of coho salmon stocked in Mount St. Helens streams from three to six years
post-eruption. Proceedings of the Western Association of Fish and Wildlife
Agencies and the Western Division American Fisheries Society. 1988;
Brett, John R. Temperature tolerance in young pacific salmon, Genus
Oncorhynchus. Journal of the Fisheries Research Board of Canada. 1952;
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