THE BEHAVIOUR AND PHYSIOLOQY OF IIERRI??Q AND OTHER CLUPEIDY 363
herring were both to be found at Stage V in September on the East
Anglian grounds, the winter spawners spending a further 2 to 3 months
in this stage before spawning in the English Channel. One can only
conclude that these fish are giving different responsea to the same
environmental stimuli, implying a genetical difference (Blaxter, 1958).
The control of the process of maturation may well be due to a number of essential factors interacting. An adequate food supply and a
certain temperature history prior to spawning seem to be important,
while the influence of day length is possible from studies on other fish,
though uncertain in herring.
The age of first spawning may well depend on a “ critical length ”
being reached before maturation commences, certain phases of maturation requiring a given level of fat before they proceed further. This
critical length may be a product of the genotype and vary between
M e r e n t races (for instance, Atlanto-Scandian herring first spawn at a
much greater length than many other races, and also have a greater
maximum length). Superimposed on this, a certain temperature history
might advance or retard maturation a little. Stimulation of the gonads
by the pituitary, at least in the later stages, would be timed by these
two factors as well as being possibly more basically timed by day
length.
Two apparently contradictory observations are relevant here.
One was the observation of herring workers at Lowestoft in the 1950’s
(e.g. Cushing and Burd, 1957) that the southern North Sea herring
seemed to have changed its age at first spawning from predominantly
4 years old to predominantly 3 years old, the significant points bcing
increased growth rate and a decrease in age of fimt 8j)awners of e&ly
one ?/ear. The implication here is firntly of it gfmtdhil tmfi!,roJ of ~ ~ ~ L W I I
ing time and of an inflexible reaction to the wivirorirnwit, rriich ~ l p rriigtit,
be expected from day length as a critical controlling fac:tr,r, othcrwinc
increased growth rate and maturation might have led to spawning weeks
or months earlier rather than one year. Set against this must be the
Norwegian observations by Devold (1961) t h a t the spawning time of the
Atlanto-Scandian herring is becoming progressively later each year off
tho Norwegian coast, the hypothesis of Piirrish (personal communication) that southcrn North Sea herring may Romotimes tend to Rpawn
progrcssivcly carlier each year aa thcy get older, and the general
observation that recruit spawners spawn libter than older fish.
7. Duration of maturity stages
Naumov (1956) recorded the number of months in the year when
the Murmansk herring could be found at any particular maturity stage.
herring were both to be found at Stage V in September on the East
Anglian grounds, the winter spawners spending a further 2 to 3 months
in this stage before spawning in the English Channel. One can only
conclude that these fish are giving different responsea to the same
environmental stimuli, implying a genetical difference (Blaxter, 1958).
The control of the process of maturation may well be due to a number of essential factors interacting. An adequate food supply and a
certain temperature history prior to spawning seem to be important,
while the influence of day length is possible from studies on other fish,
though uncertain in herring.
The age of first spawning may well depend on a “ critical length ”
being reached before maturation commences, certain phases of maturation requiring a given level of fat before they proceed further. This
critical length may be a product of the genotype and vary between
M e r e n t races (for instance, Atlanto-Scandian herring first spawn at a
much greater length than many other races, and also have a greater
maximum length). Superimposed on this, a certain temperature history
might advance or retard maturation a little. Stimulation of the gonads
by the pituitary, at least in the later stages, would be timed by these
two factors as well as being possibly more basically timed by day
length.
Two apparently contradictory observations are relevant here.
One was the observation of herring workers at Lowestoft in the 1950’s
(e.g. Cushing and Burd, 1957) that the southern North Sea herring
seemed to have changed its age at first spawning from predominantly
4 years old to predominantly 3 years old, the significant points bcing
increased growth rate and a decrease in age of fimt 8j)awners of e&ly
one ?/ear. The implication here is firntly of it gfmtdhil tmfi!,roJ of ~ ~ ~ L W I I
ing time and of an inflexible reaction to the wivirorirnwit, rriich ~ l p rriigtit,
be expected from day length as a critical controlling fac:tr,r, othcrwinc
increased growth rate and maturation might have led to spawning weeks
or months earlier rather than one year. Set against this must be the
Norwegian observations by Devold (1961) t h a t the spawning time of the
Atlanto-Scandian herring is becoming progressively later each year off
tho Norwegian coast, the hypothesis of Piirrish (personal communication) that southcrn North Sea herring may Romotimes tend to Rpawn
progrcssivcly carlier each year aa thcy get older, and the general
observation that recruit spawners spawn libter than older fish.
7. Duration of maturity stages
Naumov (1956) recorded the number of months in the year when
the Murmansk herring could be found at any particular maturity stage.