52 .
.
THE BIOLOGY OF FISHES
and other causes is'distressingly high. In the
longer rivers of the Pacic, where the distance travelled
'
.upstream may be anything up to 1000 miles, the
reaches a maximum.
Evermann hasÏfound that
“
in the
'
head— waters of the large streams, unqueStionably all die ;"
‘
'
'
in the small streams and near the sea, an unknown percentage
probably survive.” 1
..
From experiments
in Scotland and Norway the
,
Salmon Would appear to possess a homing instinct, and
Buckland thought that the organs of smell, which are very
strongly developed in the Salmon, have something to do
With this (Young). In one case noted by Buckland and
quoted by Day—, some twenty or thirty salmon ascending
from the sea Were captured and marked, then taken round
an island and set free in a lake not far distant from the
original Water, but separated by land. In the course of’the
saine season some of these marked salmon were retaken in
or near their Own pool ; to do Which they must have ‘traVelled
round the coast some forty miles, passing several streams
.
on the Way. Butwe cannottake this aS_-’a general rule. ;It
,
maybe that these particular Salmon have more intelligence _;
they-may have been trained by many generations of
tion and learnt to'make a ner discrimination of thewaters ;
bùt in other waters under less strenuouS conditions the
Salm0n is frequently at fault.’ Thus some-have been found
_
try—ing to_ enter the Thames ,« from ”which: pollution haslong
,
*
AndlnthePac1c,where
"
…
Countlessf lli‘01iS; tthngfrequently
'
crowd foi—ie; another
no access to the
Yeteventherethe sh diSplays a certain
-
amountofselectwe ÿpè'Wèr;
for
that the
‘SQCKÇÿê 'Ê'Q'rÏ RedSalmon
ascends a stream
'
thatÏ-has;notfiohe ormorelakes at: its head Waters, whilst;thC
È;o'g Salmon seem to” prefer the smaller
-c0astal
'ERegarding' the : Humpback, : Evermann
,
Thé
Order
parases, has
_
Tunnycame into the
'
to”g‘et -tid of their parasites by scratChihg
the rocks—_»Î_ ;_ j,_‘_.…;f