THE BEHAVIOUR AND PHYSIOLOGY OF HERRING AND OTHER CLUPEIDS 346
water of 5°C or less at the surface. Temperature may elao affect movement downwards. Biryukov (1968), also in the North Sea, found that
herring would not move downwards by day through thermoclines which
were too steep (for instance, 3 deg. C in about 10 m). They then
remained by day at the depth of the thermocline, moving upwards to
the surface at night. Solovyev (1959) found in the East Iceland Current
that herring would not move down into colder water, and Devold
observed that these herring would not move into cold water when feeding in the summer. Brawn (1960b) found a complex relationship between the daytime depth of immature herring shoals in Passamaquoddy
Bay and the water temperature (measured at 30 m). At temperatures
below about 7°C there was an inverse relation between the median
depth of the shoals and temperature, the herring tending to go deeper
when the water was colder. Above about 7°C the herring did not stay
higher by day. This could not be explained by a simple temperatureactivity hypothesis, the herring sinking lower in cold water due to
inactivity, because at night they rose to the surface layers, regardless
of the temperature. ZusBer (1958a) reported that Atlantic and Baltic
herring and the Caspian sprat Clupeonella did not swim below water of a
certain temperature, and Lovetskaya (1956) that Clupeonella showed
greater vertical movements at higher temperatures.
Aquarium observations (Kamshylov and Gerasimov, 1960) showed
that young Murman herring would not swim from water at 4-2°C to
water of 1.8"C in a tank, while Shelford and Powers (1915), using
Clupeu pallasii, found they reacted to temperature differences of 04°C.
4. Feeding
Girsa (1961) related the vertical migration of marine organinmR in
general to the change in availability of their food. Richardmn (1 952)
and Ryzhenko (1961) reported vertical migration in herring which were
not feeding. However, Ryzhenko also described herring which may
have been following luminescent patches of plankton. It wemH unlikely from both sea and aquarium observations (see Section VI, B)
that clupeids feed by night and it is probable that feeding is at it8 peak
at dusk and dawn. Why less foeding seems to be found by day is not
certain.
ti. Other factors
Aquarium observations on herring one year old (Biickmann et al.,
1953) suggested that they might bo prwented from vertical migration
by sharp salinity gradients, and Kamshylov and Gerasimov (1980)
reported that young Murman herring in aquaria would not swim
water of 5°C or less at the surface. Temperature may elao affect movement downwards. Biryukov (1968), also in the North Sea, found that
herring would not move downwards by day through thermoclines which
were too steep (for instance, 3 deg. C in about 10 m). They then
remained by day at the depth of the thermocline, moving upwards to
the surface at night. Solovyev (1959) found in the East Iceland Current
that herring would not move down into colder water, and Devold
observed that these herring would not move into cold water when feeding in the summer. Brawn (1960b) found a complex relationship between the daytime depth of immature herring shoals in Passamaquoddy
Bay and the water temperature (measured at 30 m). At temperatures
below about 7°C there was an inverse relation between the median
depth of the shoals and temperature, the herring tending to go deeper
when the water was colder. Above about 7°C the herring did not stay
higher by day. This could not be explained by a simple temperatureactivity hypothesis, the herring sinking lower in cold water due to
inactivity, because at night they rose to the surface layers, regardless
of the temperature. ZusBer (1958a) reported that Atlantic and Baltic
herring and the Caspian sprat Clupeonella did not swim below water of a
certain temperature, and Lovetskaya (1956) that Clupeonella showed
greater vertical movements at higher temperatures.
Aquarium observations (Kamshylov and Gerasimov, 1960) showed
that young Murman herring would not swim from water at 4-2°C to
water of 1.8"C in a tank, while Shelford and Powers (1915), using
Clupeu pallasii, found they reacted to temperature differences of 04°C.
4. Feeding
Girsa (1961) related the vertical migration of marine organinmR in
general to the change in availability of their food. Richardmn (1 952)
and Ryzhenko (1961) reported vertical migration in herring which were
not feeding. However, Ryzhenko also described herring which may
have been following luminescent patches of plankton. It wemH unlikely from both sea and aquarium observations (see Section VI, B)
that clupeids feed by night and it is probable that feeding is at it8 peak
at dusk and dawn. Why less foeding seems to be found by day is not
certain.
ti. Other factors
Aquarium observations on herring one year old (Biickmann et al.,
1953) suggested that they might bo prwented from vertical migration
by sharp salinity gradients, and Kamshylov and Gerasimov (1980)
reported that young Murman herring in aquaria would not swim