328
J. H. 9. BLAXTER AND F. 0 . T. HOLLIDAY
substance ” (see Section VI, L) but this would be more effective in a
shoaling species. Just how well chemical stimulation would pass through
a shoal is not clear, but it would almost oertainly be slower than a
visual one.
Another possible advantage of shoaling might be in the deteotion of
gradients of hydrographical conditions, or of food, suoh that the part
of a shoal in favourable conditions might linger, the other side moving
faster and so wheeling round towards the more favourable conditions
(see Section VI, R).
Shaw (1962) has recently suggested that shoaling may be the most
efficient way to move through the water, turbulence being used in a
reciprocal way to reduce drag in neighbouring fish.
One is the
possibility of attracting predators to large concentrations of their
prey, the other is the limiting effect on food supply. MacGregor (1969),
for instance, found an inverse correlation between adult population
size and average length and condition factor of Sardirwps cuerzkz,
suggesting that there was less food available and poorer growth where
the population denaity was high.
3. Structure of s b a b
This is not well known in clupeids though Schlifer (1966) obeerved
that small herring were near the top in herring shoals of mixed size.
This type of size delimitation is discussed by Breder (1959). Phillips
and Radovich (1952) found mixed shoals of Surdinups ccleruleu and
Engraulis mordas, and in European waters it is common to find mixed
shoals of small herring and Spattus eprattus. It seems that clupeid
shoals may be mixed both in age and species.
An interesting observation was that of Wood et al. (1955) who found
no change in the shoaling behaviour of tagged herring, or of their
untagged neighbours, in aquaria.
4. Size and shape of shack
Off the
Norwegian coast they might be miles wide, though the more usual size
in the North Sea was probably “ that of a house ”. Jakobsson (1961)
found that some fishable shoals of herring in Icelandic waters contaiaed
60-200 tons of fish. Tibbo and Brawn (1960) estimated the density of
a shoal off the East American coast as about 2 kg/ms, and that one
shoal contained 22,000 metric tons. From a submarine, Radakov and
Solovyev (1959) estimated the length of some herring shoale in the
northern Atlantic to be 1500 m long. While shoals are probably in many
cases amorphous, Bolster (1968) found from echo ameye in the
The disadvantages of shoaling seem to be twofold.
The size of herring shoals is discussed by Balls (1951).
J. H. 9. BLAXTER AND F. 0 . T. HOLLIDAY
substance ” (see Section VI, L) but this would be more effective in a
shoaling species. Just how well chemical stimulation would pass through
a shoal is not clear, but it would almost oertainly be slower than a
visual one.
Another possible advantage of shoaling might be in the deteotion of
gradients of hydrographical conditions, or of food, suoh that the part
of a shoal in favourable conditions might linger, the other side moving
faster and so wheeling round towards the more favourable conditions
(see Section VI, R).
Shaw (1962) has recently suggested that shoaling may be the most
efficient way to move through the water, turbulence being used in a
reciprocal way to reduce drag in neighbouring fish.
One is the
possibility of attracting predators to large concentrations of their
prey, the other is the limiting effect on food supply. MacGregor (1969),
for instance, found an inverse correlation between adult population
size and average length and condition factor of Sardirwps cuerzkz,
suggesting that there was less food available and poorer growth where
the population denaity was high.
3. Structure of s b a b
This is not well known in clupeids though Schlifer (1966) obeerved
that small herring were near the top in herring shoals of mixed size.
This type of size delimitation is discussed by Breder (1959). Phillips
and Radovich (1952) found mixed shoals of Surdinups ccleruleu and
Engraulis mordas, and in European waters it is common to find mixed
shoals of small herring and Spattus eprattus. It seems that clupeid
shoals may be mixed both in age and species.
An interesting observation was that of Wood et al. (1955) who found
no change in the shoaling behaviour of tagged herring, or of their
untagged neighbours, in aquaria.
4. Size and shape of shack
Off the
Norwegian coast they might be miles wide, though the more usual size
in the North Sea was probably “ that of a house ”. Jakobsson (1961)
found that some fishable shoals of herring in Icelandic waters contaiaed
60-200 tons of fish. Tibbo and Brawn (1960) estimated the density of
a shoal off the East American coast as about 2 kg/ms, and that one
shoal contained 22,000 metric tons. From a submarine, Radakov and
Solovyev (1959) estimated the length of some herring shoale in the
northern Atlantic to be 1500 m long. While shoals are probably in many
cases amorphous, Bolster (1968) found from echo ameye in the
The disadvantages of shoaling seem to be twofold.
The size of herring shoals is discussed by Balls (1951).