THE BEHAVIOUR AND PHYSIOLOGY OF HERRING AND OTHER CLWEIDS 291
Colton et al. (1961) found that larger herring larvae in the Gulf of Maine
were caught mainly a t night by a metre net ; the latter authors using a
Hardy high-speed plankton recorder also found the ratio of larva0
caught by this gear, compared with the metre net, increased with
increasing size of the larvae. Silliman estimated that Sardinops caerulea
larvae would have to swim a t about 5 cm/sec to escape a net towed a t
50 cmlsec.
Blaxter (1962), using herring larvae from 8-20 mm long in tanks,
tested their reaction to visual stimuli such aa moving obstacles, and
vibrations up to 10 c/sec, and measured their swimming speeds. He
found that they were remarkably unreactive to such stimuli under tank
conditions. The maximum swimming speed varied from about 3 cm/sec
for larvae 8 mm long to 30 cm/sec for larvae 20 mm long. There was a
tendency for an increase in maximum swimming speed a t the stage
when the caudal fin developed a t about 15 mm. Bishai (1960~) worked
on sustained swimming speed of herring larvae 6-8 mm long and found
that they could maintain 0.58-1.03 cm/sec for a t leaat 1 hr.
From these data it seems likely that clupeid larvae have the swimming ability to escape nets towed at low speeds of, say, up to 2 knots
(100 cmlsec) ; it is unlikely that they would escape from a high speed
sampler towed a t 6-6 knots (250-300 cmlsec). If the evidence put
forward in this review of the importance of sight in clupeids is accepted,
and sight is the most important means of detecting such nets, then even
nets hauled slowly will catch larger larvae a t night. .
N. Rmponse of larvae to light
Spooner (1933) studied the reaction of herring larvae to light using
convergent and parallel beams to separate intensity and direction
effects. Their photo-positive behaviour was in general more a reaction
to direotion, activity falling off at low light intensities. Woodhead and
Woodhead (1966) also found a drop in activity of herring larvae kept
in a dish with diffuse light from below-from 35% of the time active
at 4,000 lux to 20% at 20 lux. This photo-orthokinesis waa accompanied by phototaxis, the larvae swimming towards directional light.
In a, tall vessel the larvae were active in complete darkness. Below
100 lux most movement WES vertical ; at higher light intensities more
and more horizontal movement was observed aa if there were a dorsal
light reaction. It was suggested that this movement provided a mechanism for vertical migration. It is necessary to note also, however, that
herring larvae gradually develop more horizontal movement during
the yolk-m stage as part o f ' feeding behaviour. Soleim (1942) found
herring larvae more often in lighted parts of an aquarium. Buckmann
20
Colton et al. (1961) found that larger herring larvae in the Gulf of Maine
were caught mainly a t night by a metre net ; the latter authors using a
Hardy high-speed plankton recorder also found the ratio of larva0
caught by this gear, compared with the metre net, increased with
increasing size of the larvae. Silliman estimated that Sardinops caerulea
larvae would have to swim a t about 5 cm/sec to escape a net towed a t
50 cmlsec.
Blaxter (1962), using herring larvae from 8-20 mm long in tanks,
tested their reaction to visual stimuli such aa moving obstacles, and
vibrations up to 10 c/sec, and measured their swimming speeds. He
found that they were remarkably unreactive to such stimuli under tank
conditions. The maximum swimming speed varied from about 3 cm/sec
for larvae 8 mm long to 30 cm/sec for larvae 20 mm long. There was a
tendency for an increase in maximum swimming speed a t the stage
when the caudal fin developed a t about 15 mm. Bishai (1960~) worked
on sustained swimming speed of herring larvae 6-8 mm long and found
that they could maintain 0.58-1.03 cm/sec for a t leaat 1 hr.
From these data it seems likely that clupeid larvae have the swimming ability to escape nets towed at low speeds of, say, up to 2 knots
(100 cmlsec) ; it is unlikely that they would escape from a high speed
sampler towed a t 6-6 knots (250-300 cmlsec). If the evidence put
forward in this review of the importance of sight in clupeids is accepted,
and sight is the most important means of detecting such nets, then even
nets hauled slowly will catch larger larvae a t night. .
N. Rmponse of larvae to light
Spooner (1933) studied the reaction of herring larvae to light using
convergent and parallel beams to separate intensity and direction
effects. Their photo-positive behaviour was in general more a reaction
to direotion, activity falling off at low light intensities. Woodhead and
Woodhead (1966) also found a drop in activity of herring larvae kept
in a dish with diffuse light from below-from 35% of the time active
at 4,000 lux to 20% at 20 lux. This photo-orthokinesis waa accompanied by phototaxis, the larvae swimming towards directional light.
In a, tall vessel the larvae were active in complete darkness. Below
100 lux most movement WES vertical ; at higher light intensities more
and more horizontal movement was observed aa if there were a dorsal
light reaction. It was suggested that this movement provided a mechanism for vertical migration. It is necessary to note also, however, that
herring larvae gradually develop more horizontal movement during
the yolk-m stage as part o f ' feeding behaviour. Soleim (1942) found
herring larvae more often in lighted parts of an aquarium. Buckmann
20