Understanding the Role of Wetlandsin the Salmon Lifecycle

Salmon & Wetlands

Many people enjoy wetlands as placesof beauty. These are places we can go toenjoy the experience of walking throughnature, watching birds and otheranimals, as well as the bountiful plantlife. As more people move into thecities, wetlands and other undevelopedareas become more valuable as placeswhere we can experience and learnabout the natural world.

Text © 2000 Wetnet of Audubon WashingtonGraphic Design and Illustration © 2000 Fusion Studios

Salmonids lay their eggs in gravel bedscalled redds. This gravel must be smallenough to be moved by the female increating her nest, but large enough toprovide sediment-free cavities for theeggs and fry to develop. Fine sedi-ments and silt, which can come fromclearcuts and developments, may coatthe eggs, depriving them of oxygen.Wetlands slow water before it getsinto the stream, so these sedi-ments can settle in the wetland,not the gravel beds. Wetlands alsohelp to reduce peak flows instreams - these sudden high flowscan sweep away all or part of theredds.

The Salmon Lifecycle:UNDERSTANDING THE ROLE OF WETLANDS

The eggs hatch into fry with yolk sacs thatprovide food for the first few weeks of theirlives. When the yolk sacs are used up, the fryfeed on insects. These insects may drop intothe stream from overhanging trees, or may livein streams and wetlands. The trees on thestream banks also shade the stream and keep

the stream cool enough for the fry.Wetlands help to keep the water coolby releasing cool ground water intothe stream flow.

Different species of salmon and trout spenddifferent amounts of time in their streams beforemigrating to the ocean where they will grow intoadults. Coho may live in streams for up to twoyears; chinook spend more time in streams thansockeye, chum or pink. Freshwater wetlands areused by small cutthroat trout, steelheadtrout and coho salmon for winterrearing. By living in a wetland ratherthan the fast moving river channel, thesefish spend less energy fighting thecurrent, have more energy for feedingand so can grow much faster than fishthat stay in the main channel. Duringfloods, young fish take refuge in wet-lands. Without wetlands and beaverponds, many young fish can be sweptto their deaths by floods.

All anadromous fish head downstreamto the ocean. Now called smolts, theyneed to move quickly because theirphysiology is changing so that they cansurvive in saltwater. This migration istimed to match the spring runoff, whichhelps to rush the smolts to the ocean.Dams and reservoirs disorient the smoltsand slow them down. The smolts stayfor a while in estuaries, to acclima-tize to saltwater, and use estuarinewetlands for food and shelter. Thetime spent in the estuary varies withspecies, but chinook smolts rearextensively in estuarine wetlands beforeentering the salt ocean.

Some salmonid species spend several years in the ocean and can grow to large sizesbefore returning to their home stream for spawning; varieties adapted to small tributariesdo not grow very large. How the salmon and trout find their way back to the place wherethey hatched is still unknown, although smell is thought to play a part.

Once back in the streams,adult salmonids move quicklyupstream to spawn as theirbodies begin to deteriorate.Blockages such as dams,culverts and low water levelsslow their movement up-stream. Wetlands helpmaintain in-stream flows byholding water from wetterseasons and releasing itduring the dry summermonths.

Once safely upstream, the salmonidsmust find gravel beds for spawning, afterwhich their life comes to an end. Theircarcasses provide food for aquatic insectswhich will themselves become food forthe next generation of fry to emergefrom the gravel. Trapped in wetlands,these carcasses also act as a fertilizer forthe wetland, stream and forest. In deaththe salmon benefit not only futuregenerations of salmon, but also thewetlands, streams and forest that in turnsustain them and us.

Text © 2000 Wetnet of Audubon WashingtonGraphic Design and Illustration © 2000 Fusion Studios

Glossary of TermsANADROMOUS FISH: fish that hatch infreshwater, migrate to the ocean as young, thenreturn to freshwater to spawn. This complex lifecycle allows them to exploit different parts of theenvironment at different points of their life cycle,reducing competition for resources betweenyoung and old. But it adds physiological complica-tions not experienced by other animals, as therequirements for living in freshwater are quitedifferent from those for saltwater. Salmon andsome trout species are anadromous.

ESTUARINE WETLANDS: – wetlands in estuaries– where rivers meet the ocean. The water inestuaries is brackish— it is a mixture of saltwaterfrom the ocean and freshwater from the river.

FRESHWATER WETLANDS: wetlands that aredominated by fresh water.

FRY: young salmon that have used up the yolksupply from their egg.

INSTREAM FLOW: the level of water in astream or river. Fish need a minimum level ofwater to live in.

PEAK FLOWS: the highest level of floodwaterin a river or stream.

REDDS: gravel beds where salmon and troutlay their eggs.

SALMONIDS: a family of fish that includessalmon, trout, grayling and whitefish.

SMOLT: juvenile salmon moving to the ocean.

WETLANDS: places that have water at or justbelow the surface of the soil.

The creation of this brochure was made possiblethrough WaterWorks, the King County WaterQuality Block Grant awarded by the KingCounty Department of Natural Resources.