ILL 13tonzass
refee sppp. and Peisos
pctriurkevifr*hi. somr epip~ltigic i i l d upper meNopelegic shrimps occur in
vad swttrnis in rest!rictcd waters. Thus thcir distribution is usually
uneven both vertically aiid horizontally. ('hpability of certain micronektonic animals to avoid nets by visiial perception during daytime is
pronounced at shallow depths, 118 confirmed by Pearcy and Laura
(1966) and 13rinton ( 1 967). I havc often found that the biomass and
species composition of snmples varied wit11 the sampling time and
position, PVOH if thc! Ramp gear and sampling technique were used. In
certain waters t,Iw most ctbtindant spwics changed in each sampling.
These phcnomeritt suggest that ( 1 ) tho mobility of the shrimps varies
considerably among the species, (3) the shrimps are often patchily
distributed and (3) the position, zone and density of the swarms are
changing incessantly.
UnlesR the distributional and biological features of the individual
species are known, an accurate estimate of the true abundance of the
shrimps is difficult. Tho real density of Sergestes siinilis and Sergia
Zuccns in the swarms is believed to be more than 20 inds./mg, but
estimation by net haul has never exceeded 3 inds./m3 (Omori et al.,
1972). Thus our sampling only gives an average underestimated
density of the shrimp in the fairly large amount of water where the
net, was t o w d Natirrully, the biomass data determined with such
surnpliiqp iiro qiiite insrrficicnts to evnluntt. the role of each species in
the seit.
Table IT sliow.~ the itpproxi t n d o biomtiss (dry weight) of pelagic
shrimps nbove 1 000 ni depth in various parts of the oceans. These
values w c w drrivetl by re-eulculation of the data from available
referenccs, but nny errors or wrong interpretations are mine. The
re-calaulatione have been rnadc by rising the foliowing convertion
factor ol)taincvl with several Npeciea of the genera Sergeste~, Sergia and
Acnnthephgm: 1 g dry weight = 9.2 g wet weight = 6.7 ml displacement volnme (Omori, unpublished).
The depth of' bhe maximum concentration of the shrimp biomass,
as noted in Section IV, vctrics according to the locality, but a8 far
tts the water column shallower than 1000 m is concerned, the geographical vciriation of the average biomass in a wide area i s not very
great. The biomass is large in inshore waters and localities over the
continental slope. ' It decreases with increasing distance from the
coast. Thc concentfration of shrimps is particularly great in water
where the bottom slopes steeply away close to shore. Usually, the
As seen in S~qoslas .uindis, Sergin lucms,
refee sppp. and Peisos
pctriurkevifr*hi. somr epip~ltigic i i l d upper meNopelegic shrimps occur in
vad swttrnis in rest!rictcd waters. Thus thcir distribution is usually
uneven both vertically aiid horizontally. ('hpability of certain micronektonic animals to avoid nets by visiial perception during daytime is
pronounced at shallow depths, 118 confirmed by Pearcy and Laura
(1966) and 13rinton ( 1 967). I havc often found that the biomass and
species composition of snmples varied wit11 the sampling time and
position, PVOH if thc! Ramp gear and sampling technique were used. In
certain waters t,Iw most ctbtindant spwics changed in each sampling.
These phcnomeritt suggest that ( 1 ) tho mobility of the shrimps varies
considerably among the species, (3) the shrimps are often patchily
distributed and (3) the position, zone and density of the swarms are
changing incessantly.
UnlesR the distributional and biological features of the individual
species are known, an accurate estimate of the true abundance of the
shrimps is difficult. Tho real density of Sergestes siinilis and Sergia
Zuccns in the swarms is believed to be more than 20 inds./mg, but
estimation by net haul has never exceeded 3 inds./m3 (Omori et al.,
1972). Thus our sampling only gives an average underestimated
density of the shrimp in the fairly large amount of water where the
net, was t o w d Natirrully, the biomass data determined with such
surnpliiqp iiro qiiite insrrficicnts to evnluntt. the role of each species in
the seit.
Table IT sliow.~ the itpproxi t n d o biomtiss (dry weight) of pelagic
shrimps nbove 1 000 ni depth in various parts of the oceans. These
values w c w drrivetl by re-eulculation of the data from available
referenccs, but nny errors or wrong interpretations are mine. The
re-calaulatione have been rnadc by rising the foliowing convertion
factor ol)taincvl with several Npeciea of the genera Sergeste~, Sergia and
Acnnthephgm: 1 g dry weight = 9.2 g wet weight = 6.7 ml displacement volnme (Omori, unpublished).
The depth of' bhe maximum concentration of the shrimp biomass,
as noted in Section IV, vctrics according to the locality, but a8 far
tts the water column shallower than 1000 m is concerned, the geographical vciriation of the average biomass in a wide area i s not very
great. The biomass is large in inshore waters and localities over the
continental slope. ' It decreases with increasing distance from the
coast. Thc concentfration of shrimps is particularly great in water
where the bottom slopes steeply away close to shore. Usually, the
As seen in S~qoslas .uindis, Sergin lucms,