348
J. H. S. BLAXTER AND F. a. T. HOLLIDAY
about 4 days after full moon and a second lower peak one day after new
moon.
Tester (1938b) analysed the catches of Clupea pallasii off Vancouver
Island from 1933-1937 and found the lowest catches at new and full
moon, which he thought was due to a reduction in the influx of herring
into the channel during the spring tides. Clark (1956) reported that
Californian sardine fishermen tied up during the full-moon period
because they caught so few fish. Normally the fish were found by the
phosphorescence they created and this was best observed before
moonrise or after it set.
It is clear that a lunar influence on catch may reflect the behaviour
of fish, or that of the fishermen. The following might be the causes of a
lunar influetice on fish behaviour, with a resultant effect on the catch :
(a) ‘I’lic light of thc mooti mighl. cuuso a change in tho activity lovul
of fish, particularly in shr~llow water, for instance in the southern
North Sea. It might change the extent of vertical migration
(particularly in deep water) or horizontal migration. These
effects might vary with the physiological state of the fish, e.g.
whether they were near spawning or not.
(b) The light of the moon (probably 0.5 lux or less) might raise the
level of illumination near the surface sufficiently to allow the
fish to see the nets (see Section VI, V), or to change the pattern
of shoaling.
( c ) The tidal effect associated with the moon’s phases might also
have a variable influence on the excitability of the fish, or on
their horizontal or vertical migration, or o n their shoaling
bchaviour.
(d) Tho light or tidal sffcct of 1.110 rnooti might affcot predator-prey
rolationships.
‘l’htw cliffwent factors, comhirit:il with tho pofisihlo (!ffcct o f woutthcr
and of moon 1)haso on fiHhitig pracl,icci, mako R caii~al unnlysir, of thiR
typo of data vory tiifEcult. I’omihly lunar cffccta may have been
smootlied out since tho war hy chatigcn in tho Icngth o f buoy ropes u ~ e d
on the ncts, by the us0 of ccIio-Houti(lcw, or by change^ in fishing
grounds.
U . Attraction to artificial lights
Published accounts of the attraction or repulsion of clUpC!idR to
1. Occurrence
artificial lights are shown in Table X.
J. H. S. BLAXTER AND F. a. T. HOLLIDAY
about 4 days after full moon and a second lower peak one day after new
moon.
Tester (1938b) analysed the catches of Clupea pallasii off Vancouver
Island from 1933-1937 and found the lowest catches at new and full
moon, which he thought was due to a reduction in the influx of herring
into the channel during the spring tides. Clark (1956) reported that
Californian sardine fishermen tied up during the full-moon period
because they caught so few fish. Normally the fish were found by the
phosphorescence they created and this was best observed before
moonrise or after it set.
It is clear that a lunar influence on catch may reflect the behaviour
of fish, or that of the fishermen. The following might be the causes of a
lunar influetice on fish behaviour, with a resultant effect on the catch :
(a) ‘I’lic light of thc mooti mighl. cuuso a change in tho activity lovul
of fish, particularly in shr~llow water, for instance in the southern
North Sea. It might change the extent of vertical migration
(particularly in deep water) or horizontal migration. These
effects might vary with the physiological state of the fish, e.g.
whether they were near spawning or not.
(b) The light of the moon (probably 0.5 lux or less) might raise the
level of illumination near the surface sufficiently to allow the
fish to see the nets (see Section VI, V), or to change the pattern
of shoaling.
( c ) The tidal effect associated with the moon’s phases might also
have a variable influence on the excitability of the fish, or on
their horizontal or vertical migration, or o n their shoaling
bchaviour.
(d) Tho light or tidal sffcct of 1.110 rnooti might affcot predator-prey
rolationships.
‘l’htw cliffwent factors, comhirit:il with tho pofisihlo (!ffcct o f woutthcr
and of moon 1)haso on fiHhitig pracl,icci, mako R caii~al unnlysir, of thiR
typo of data vory tiifEcult. I’omihly lunar cffccta may have been
smootlied out since tho war hy chatigcn in tho Icngth o f buoy ropes u ~ e d
on the ncts, by the us0 of ccIio-Houti(lcw, or by change^ in fishing
grounds.
U . Attraction to artificial lights
Published accounts of the attraction or repulsion of clUpC!idR to
1. Occurrence
artificial lights are shown in Table X.