THE BEEAVIOUR AND PHYSIOLOGY OF HERRING AND OTHER CLUPEIDS 327
2. Survival value of shoaling
Ulrich (1951) made underwater observations on herring in the
Baltic and found that they formed up into shoals in response to stimulation from himself or the presence of fish. Schafer (1955) also observed
the disturbigg effect of predators on herring in aquaria. The pattern
of movement was related to the position of cod on approach of the
shoal, an indentation being caused in that part of the shoal nearest the
cod. Manteufel and Radakov (1960) found that only straggling herring
were taken by predators in an aquarium, tight shoals causing I' confusion ,' of the predators. Blaxter and Parrish (1958) reported an
extreme tightening of shoaling in Sprattus sprattus preyed on by Caranx,
but few of the sprats survived as a result. Allen (1920) observed a
" ball " of Sardinops meruka, 2 m in diameter, under attack from
diving birds. The birds caused indentation of the ball but apparently
were unable to extract fish from it. Phillips and Radovich (1952)
found that shoals of Sardi~wp8 and Engraulis were not overexcited by
attacks from carangids and sphyraenids and only stragglers were
taken. If the shoals became disorganized, they were then more prone to
attack. Breder (1959) reported seeing shoals of Sardinella attacked by
Caranx, without affecting the behaviour of the shoals. While most
evidence has been interpreted as shoaling preventing predators picking
out their prey, there is the possibility that large shoals might cause a
concentration of predators in a particular area, so that the overall
survival value of shoaling must remain somewhat uncertain. Shoals
might, of course, act as a frightening stimulus to predators, large,
tightly-packed shoals appearing as a single organism.
Shoaling may aid the fish in efwapo frorn movirig netfl, hot rwtain
t y p e s of fiRhing practice, for irrntrtncf: ptirnr: miflifig, rjftfrrmrj 0 1 1 f h
presence of shoals cJf remonabh size. Mantt:ufi:l and f l a h k o v ( I W ) )
reported that it WRH more difficult to catch tightly packed shoals of
herring in tho Baltic, though Galkov (1068) was of the opinion that the
mobility of the herring determined their susceptibility to capture,
shoaling perhaps playing a subsidiary rola. (See Section VI, V for
further discussion.)
Breder (1959) and Manteufel and Radakov (1960) also pointed out
the importance of transmission of stimuli by shoals. The passage of a
stimulus seemed to depend on the transmission of visual movements,
rather than of noise through a shoal, noises probably being absorbed
in many cases. While solitary fish might well react to noise, visual
stimuli would be more quickly passed through a shoal and would also
be more quickly received than a sound ono, as long as the water was
clear. It seeme rather unlikely that any clupeids produce an " alarm
2. Survival value of shoaling
Ulrich (1951) made underwater observations on herring in the
Baltic and found that they formed up into shoals in response to stimulation from himself or the presence of fish. Schafer (1955) also observed
the disturbigg effect of predators on herring in aquaria. The pattern
of movement was related to the position of cod on approach of the
shoal, an indentation being caused in that part of the shoal nearest the
cod. Manteufel and Radakov (1960) found that only straggling herring
were taken by predators in an aquarium, tight shoals causing I' confusion ,' of the predators. Blaxter and Parrish (1958) reported an
extreme tightening of shoaling in Sprattus sprattus preyed on by Caranx,
but few of the sprats survived as a result. Allen (1920) observed a
" ball " of Sardinops meruka, 2 m in diameter, under attack from
diving birds. The birds caused indentation of the ball but apparently
were unable to extract fish from it. Phillips and Radovich (1952)
found that shoals of Sardi~wp8 and Engraulis were not overexcited by
attacks from carangids and sphyraenids and only stragglers were
taken. If the shoals became disorganized, they were then more prone to
attack. Breder (1959) reported seeing shoals of Sardinella attacked by
Caranx, without affecting the behaviour of the shoals. While most
evidence has been interpreted as shoaling preventing predators picking
out their prey, there is the possibility that large shoals might cause a
concentration of predators in a particular area, so that the overall
survival value of shoaling must remain somewhat uncertain. Shoals
might, of course, act as a frightening stimulus to predators, large,
tightly-packed shoals appearing as a single organism.
Shoaling may aid the fish in efwapo frorn movirig netfl, hot rwtain
t y p e s of fiRhing practice, for irrntrtncf: ptirnr: miflifig, rjftfrrmrj 0 1 1 f h
presence of shoals cJf remonabh size. Mantt:ufi:l and f l a h k o v ( I W ) )
reported that it WRH more difficult to catch tightly packed shoals of
herring in tho Baltic, though Galkov (1068) was of the opinion that the
mobility of the herring determined their susceptibility to capture,
shoaling perhaps playing a subsidiary rola. (See Section VI, V for
further discussion.)
Breder (1959) and Manteufel and Radakov (1960) also pointed out
the importance of transmission of stimuli by shoals. The passage of a
stimulus seemed to depend on the transmission of visual movements,
rather than of noise through a shoal, noises probably being absorbed
in many cases. While solitary fish might well react to noise, visual
stimuli would be more quickly passed through a shoal and would also
be more quickly received than a sound ono, as long as the water was
clear. It seeme rather unlikely that any clupeids produce an " alarm