Evening star., 1938-10-13
OF STARS,
MEN AND ATOMS
Notebook of Science Prosress
in Field, Laboratory
and Study.
BIZ THOMAS r. HENRY.

By THOMAS r. HENRY.
How salmon build, and defend their
nests is described in the annual report
of the Smithsonian Institution by Leon
ard p. Schultz. assistant curator Of fishes
of the United States National Museum.
1t Is essentially q labor of the female
of the species. he finds. with the male
standing guard and occasionally giving .
little help.
The completed nests are saucer-like
depressions In stream bottom, each
with small mound Of sand or gravel on
the downstream side. The depth ana
size Of a nest depend on the size of the
fish which constructs It, the shape OF her
body and the rate Of dow Of the water
over the spot.
A pair Of these fish-Dr. Schultz chose
the landlocked species Of salmon known
As reddish for his observation-disclosures
q time for building their nest when there
are no other fish around to moleSt them.
The female will turn over on her side
and vigorously mex her tail from four to
six times against the bottom, this motion
carrying her a foot or more upstream.
The tail of the ash during these move
ments comes in contact with the bottom
and vigorous hydraulic forces are set up
by the upward movement Of the tail.
which lift the gravel and sand OF the
bottom.
The material thus disturbed is carried
by the swift current downstream, the
smaller particles farthest and the larger
stones but q few inches before they
settle. If undisturbed, DR.. Schultz OBJ
served, female in twenty minutes may
complete as many as seventy separate
nest-building acts, with intervals Of from
four seconds to little more than q min
ute between them. From few hours to
a few days are required to build single
nest pit. The male usually stands by
idly.
A fish about foot long builds 4 nest
from two to four inches deep, DR.. Schultz
found, depending on the type Of stream
bottom. In moderately flowing water the
width of the nest is one to two times
the length of the owner, and the length
of the nest two or three times. The
mound Of sand and gravel at the lower
end of the nest lies from one to three
inches above the average level OF the
stream bottom and extends two or three
feet downstream below the depression.
In the case of large salmon. . single
nest may occupy several square yards.
The nests, DR.. Schultz found, are con-
tinuously changing, because after
female deposits q portion Of her eggs she
covers them with gravel, and as she pro-
gressively excavAtes one or more new
nests upstream some OF the excavated
material of the new location covers the
eggs in the older nests deeper and
deeper-a real engineering achievement.
Once the nest Is built both male and
female defend 1t against invading fishes
by rushing at them. Sometimes the
male defender in his rush at an invad-
ing fish catches his teeth in the abdo-
men of the foe, and before he can free
himself the two drift downstream some
distance. As soon as he 10 loose the de-
fender usually returns to his nest and
Immediately takes up his position above
and a little to one side of the female.
Her Job seems to be that Of defending
the upper portions Of the nest, the sector
where attack is least likely. The male
keeps guard in all directions. Very rarely
he is completely ousted by much larger
male. who then takes possession OF both
the nest and the female. apparently With
no resistance on her part.
Sometimes when an invading male
approaches he Is escorted away by the
male owner OF the nest. Inc OelcHQlilB
male may swim out to meet him, elevat.
ing one of his fins dehantly. II the In
truder does not retreat the defender will
swim slowly toward him. and when about
q foot or so away he will turn 50 that the
two fish are nearly parallel and they
then proceed slowly upstream, some
times as far as ten feet. before the in
vader either goes his own way or makes
q dash for the nest
In general, DR.. Schultz found, the male
occupies much of his time driving away
other males. The female drives away
either invading males or fish Of her own
sex. Should the invading male be sue
cessful in driving away the original
owner, he takes possession Of the nest.
Several males usually pair of with the
female owner Of the nest before she has
laid all her eggs.
DR.. Schultz reports careful observa-
tions Of the courtship activities of the
salmon. The male shows of before the
female and one Of his most frequent acts
to call attention to himself is nudging.
He swims gently up to the female and
pushes her In the side with his snout.
Urges Complete Isolation