366
J. H. S. BLAXTER AND F. 0 . T. HOLLIDAY
spawning of Chpea p&i.
The eggs were deposited in much the same
way as in Clwpea hare-,
but the males deposited the sperm directly
on top of the eggs. No pairing of the fish waa observed and again it
appeared a mass spawning. The madromous shads (Alosu sp.) spawn
in rivers, on fine gravel. There appears to be a form of nuptial behaviour
in these freshwater spawners (Medcof, 1957).
Less is known of the spawning of the clupeids that lay pelagic eggs.
Ahlstrom (1943) deduced that Sardinops cuerulea spawned in midwater between 2000 and 2400hr. This was confirmed by Cushing
(1960) in Sardina pdc?turdue.
4. Homing
Although the spawning grounds of herring, at least, remain much
the same from year to year, the extent to which herring spawn year
after year in the same place is not well known, and even less is known
about whether individual herring return to the grounds on which they
were spawned.
A study of meristic and other characters on different spawning
grounds in the southern North Sea led Zijlstra (1961) to the view that
homing might take place in herring, but only tagging of spawning fish,
to date largely unsuccessful, would c o n h this. However, Krefft
(personal communication) who tagged spawning herring in the Elbe
Estuary in April 1957, had a fish returned almost exactly 2 years later
from the Skagerak. There are also cases of sudden outbursts of
spawning in new places, e.g. of herring in the Texel area of the
southern North Sea in 1961.
The ability of recruit spawners to return to the grounds where they
themselves were spawned would dcmnnd a rc:rnarkrthlo f i d , of larval or
racial I‘ memory ”, greatly exceeding that of salmon id^. A t thin stage
one might aasume that if no change in spawning time took place between parents and offspring, the recruits would return, by reason of the
spatial and temporal dimension of their migration pattern, and possibly
by following older spawners, roughly to the area where they were
spawned. Once having achieved this, memory might play aomo part
80 that the recruits themselves the following year helped to l e d youngor
fish to the spawning grounds. At present it b not clear how different
spawning grounds might appear to fish due h thcir t~pograptry, typo
of bottom, fauna, chemical or hydrodynamic rmti~rc, IV, that w j t ;
spawning ground could be distinguished from another. W i t h ~ t
r r u m
evidence it would seem likely that any return would bo to tho approximate area of previous spawning.
Instances have been recorded, however, of spawning times and
J. H. S. BLAXTER AND F. 0 . T. HOLLIDAY
spawning of Chpea p&i.
The eggs were deposited in much the same
way as in Clwpea hare-,
but the males deposited the sperm directly
on top of the eggs. No pairing of the fish waa observed and again it
appeared a mass spawning. The madromous shads (Alosu sp.) spawn
in rivers, on fine gravel. There appears to be a form of nuptial behaviour
in these freshwater spawners (Medcof, 1957).
Less is known of the spawning of the clupeids that lay pelagic eggs.
Ahlstrom (1943) deduced that Sardinops cuerulea spawned in midwater between 2000 and 2400hr. This was confirmed by Cushing
(1960) in Sardina pdc?turdue.
4. Homing
Although the spawning grounds of herring, at least, remain much
the same from year to year, the extent to which herring spawn year
after year in the same place is not well known, and even less is known
about whether individual herring return to the grounds on which they
were spawned.
A study of meristic and other characters on different spawning
grounds in the southern North Sea led Zijlstra (1961) to the view that
homing might take place in herring, but only tagging of spawning fish,
to date largely unsuccessful, would c o n h this. However, Krefft
(personal communication) who tagged spawning herring in the Elbe
Estuary in April 1957, had a fish returned almost exactly 2 years later
from the Skagerak. There are also cases of sudden outbursts of
spawning in new places, e.g. of herring in the Texel area of the
southern North Sea in 1961.
The ability of recruit spawners to return to the grounds where they
themselves were spawned would dcmnnd a rc:rnarkrthlo f i d , of larval or
racial I‘ memory ”, greatly exceeding that of salmon id^. A t thin stage
one might aasume that if no change in spawning time took place between parents and offspring, the recruits would return, by reason of the
spatial and temporal dimension of their migration pattern, and possibly
by following older spawners, roughly to the area where they were
spawned. Once having achieved this, memory might play aomo part
80 that the recruits themselves the following year helped to l e d youngor
fish to the spawning grounds. At present it b not clear how different
spawning grounds might appear to fish due h thcir t~pograptry, typo
of bottom, fauna, chemical or hydrodynamic rmti~rc, IV, that w j t ;
spawning ground could be distinguished from another. W i t h ~ t
r r u m
evidence it would seem likely that any return would bo to tho approximate area of previous spawning.
Instances have been recorded, however, of spawning times and