ResourcesIdentification of Important Habitats in Coastal New HampshireChapter 5. Atlantic SalmonAtlantic salmon, Salmo salar, historically were a premier recreational
and food fish species in New England. Over harvest, degradation of water
quality and obstruction of streams has caused a drastic decline, which
has been only partly corrected by stocking of young fish and construction
of some fishways. Following is a description of life stages, and the information
for mapping existing salmon habitat in the study area. Danie et al. (1984) provides the following summary of salmon life history.
Atlantic salmon ascend freshwater streams to spawn on gravel substrate
from mid-October to mid-November. In Maine, eggs incubate for 175 to 195
days depending on water temperature, and hatch in April or early May.
After hatching, the 15 mm long yolk-sac larvae (alevins), remain buried
in the gravel depressions for up to 6 weeks while absorbing the yolk-sac
for nourishment. The resulting 25 mm long fry begin foraging for themselves
and emerge, usually at night, from the gravel depressions. Larger freshwater
juveniles (parr) will remain in riffle sections of streams until they
are 125-150 mm in length, which may take from 2 to 3 years. Failure to
attain this length by spring or early summer of the year, will prevent
parr from transforming into smolts (seaward migrating juveniles). After
attaining this critical length, parr undergo smoltification which includes
physical and physiological changes adaptive to a migration to a marine
environment. The parr marks disappear and the skin develops a silvery
pigmentation from deposition of guanine in the skin, the tail lengthens
and becomes more deeply forked, and schooling behavior develops. Increases
in water temperature and water level trigger downstream migration of smolts.
Smolts from the western Atlantic migrate, within 3 m of the surface of
the ocean, to feeding areas in the Davis Strait between Labrador and Greenland.
Atlantic salmon will return to natal rivers to spawn after 1 (grilse)
or 2 (bright salmon) years at sea. Salmon accumulate in estuaries, bays,
and river mouths, before ascending streams. Upstream migration of salmon
coincides with increases in water flow. Adult salmon do not feed while
in freshwater. Atlantic salmon do not consistently die after spawning,
and many spent fish (kelts) survive the winter in freshwater and begin
to feed again. Mortality is high when kelts enter saltwater. Those kelts
that survive and migrate to feeding grounds in the Davis Strait, may become
repeat spawners. Mapping of Habitat Because obstructions on tributary streams prevent upstream migration
of Atlantic salmon in the study area, we did not specifically map spawning
habitat. Salmon fry are stocked in tributaries of the Cocheco and Lamprey
Rivers where habitat is suitable for juvenile salmon. The goal of these
stocking efforts is to provide angling opportunity downstream, from returning
adult fishes. Our mapping of juvenile habitats was based on NHF&G
stream surveys; we selected polygons from NWI digital maps which corresponded
to areas delimited by Douglas Grout (NHF&G). These areas were scored
10 (0 - 10 scale) since they are known to satisfy environmental requirements
of juvenile salmon (Figure of Atlantic Salmon Juvenile
Habitat). |
