Earlier investigations with 13.69 m (45') four seam shrimp trawl indicated the optimum depth of belly to be 70 meshes. Present communication details further experiments on similar lines with a bigger shrimp trawl of size 17.07 m (56') without overhang. The results obtained have not only given corroborating evidence in support of the earlier findings but also helped in arriving at a relationship that for a given stretched width of belly ‘L’ the stretched depth of belly could be either 2L/5 or 40% of ‘L’ with an allowance of ± 2 meshes

Jegadeesan, G.

Mhalathkar, H.N.

Aquatic Commons

El E STU IES s p 
H. N. MHALATHKAR'te AND G. JEGADEESAN** 
Central Institute of Fisheries Technology, Craft & Gear Wing, Cochin-5 
Earlier investigations with 13.69 m ( 45') four seam shrimp 
trawl indicated the optimum depth of belly to be 70 meshes. 
Present communication details further experiments on similar lines 
with a bigger shrimp trawl of size 17.07 m (56') without over-
hang. The resu]ts obtained have not only given corroborating 
evidence in support of the earlier findings but also helped in 
arriving at a relationship that for a given stretched width of belly 
'L' the stretched depth of beUy could be either 2L/5 or 40% of 
•L' with an allowance of ± 2 meshes. 
INTRODUCTION 
In the two earlier papers_ Mhalathkar 
and Iyer (1966) and Mha]athkar and 
Jegadeesan (1970) have shown that the 
depth of belly in a 13.69 m (45') shrimp 
trawl could be reduced. As the next 
step, experiments were conducted with a 
17.07 m (56') four seam trawl, not only 
to determine the possibility of reducing 
the depth of beUy when fishing for 
shrimps but also to evolve a possible 
mathematical equation to determine the 
maximum depth of belly in shrimp trawls. 
The investigations were carried out at 
Cochin during the fishing season in the 
year 1967-68. 
MATERIALS AND METHODS 
A 17.07 m (56') four 
trawl of non-over-hang 
seam cotton 
type, (Fig 1) 
with 140 meshes in its belly depth was 
chosen as the control net 'A', to suit 
the capacity of the trawler, Fishtech H. 
Two other experimental nets 'B' and 'C' 
were also simultaneously fabricatedp 
which were identical to net •A• except 
for the number of meshes in the belly 
depth. Following similar pattern as in 
the earlier experiments (Mhalathkar and 
Jegadeesan, foe cit) the depth of beHy 
in net 'B' was 102 meshes while that 
of net •c' was 80 meshes. In the net 
'B' the number of meshes reduced in 
the depth of the belly was proportionai 
to the number of meshes reduced in the 
net •E' (13.69 m four seam trawl) men-
tioned by Mhalathkar and Jegadeesan 
foe cit), which is almost 2/5 or 40% of 
the 5tretched width of the belly along 
the bosum. The dimensions of the bellies 
*Present address: 
** 
,, 
C. I F. T. Sub-Station, Veraval (Gujarat) 
C. I. F. T. Unit, Panaji (Goa). 
167 FISHERY TECHNOLOGY 
the bosum. The dimensions of the beHies 
in nets 'B' and 'C' are shown in doHed 
Jines in Fig 1. 
AH the three nets, 'A', 'B', and 'C' 
were operated in rotation during each 
day of operation. To the best possible 
extent, aU the fishing conditions namely, 
fishing ground, fishing depth, length of 
warp released, towing direction, towing 
duration, towing speed, buoyancy on 
head rope, weight of sinkers on foot 
rope and the size of otter boards were 
kept constant 
RESULTS AND DISCUSSION 
17·07m FOUR SEAM 
~ MESHES 
T 
7-62C'I'fte 
~ 
2o/al3 S·OSCmn 
SHRIMP TRAWL; 
1 25M ' 
~ 60M 3·9~l'Tl 
l 
/; 130M 
70M 
In aU 27 fishing trips were made and 
27 hauls per net were taken on a com-
parative basis. Data regarding towing 
duration, percentage horizontal opening, 
tension on warps (resistance) and catches 
collectively and individually were gathered 
and are tabulated in Table I. 
F\G.t. DIFFERENT STAC~ES OF BELLIES AND SIDE V!EDGES. 
Nets 
'A' 
(140 meshes in 
depth) 
'B' 
( 102 meshes in 
depth) 
'C' 
(80 meshes in 
depth) 
No. of 
hauls 
27 
" 
Table I Details of operation: 
Towing 
duration 
in mins.* 
44 
, 
%Horizontal 
openiBg* 
58.30 
58.85 
58.04 
Tension 
on warps 
kcr * b 
389.00 
379.66 
384.14 
Prawn 
10.63 
1J.55 
8.48 
Catch in kg.* 
Fish 
14.00 
19.00 
13.96 
* Average of 27 operations for each net. 
Tab!e II Analysis of variance: 
Horizontal opening: Source of variation S.S. D.F. M.S. F. 
Total 
Between nets 
Between days 
Error 
** 
8855.73 
9.23 
869L83 
154.67 
80 
2 
26 
52 
4.615 
334.30 
2.97 
1.56 
112.56** 
s. s. 
170100.00 
1476.22 
153456.00 
1567.68 
Tension in warps: 
D. F. M.S. 
80 
2 738.11 
26 5902.15 
52 291.69 
ss 
MS-
Indicates significance at 
Sum of Squares. 
Mean Square. 
1% leveL 
DF 
F 
Degree of Freedom 
Variance Ratio. 
VoL VIII No. 2 1971 
Total 
24.63 
32.55 
22.44 
F. 
2.53 
20.23** 
168 
The nets were randomised over the 
fishing days throughout the experiment. 
Data coHected for horizontal opening, 
tension on warps, prawn catch., fish catch 
and total catch were analysed using 
analysis of variance technique. For tensiorn 
and horizontal opening the data were 
used as such. but for prawns, fish and 
total catch the figures were converted 
into their corresponding log values. The 
analysis of variance tables prepared are 
shown in Tables H and HI. 
In the horizontal opening and the 
tension on warps, there was no significant 
difference among the nets 'A', 'B' and 
'C', at 5% level (Table H). But the 
diflferernce was significant (P < .01) in the 
catching rate of the three nets with regard 
to prawn and total landings (Table III). 
The logarithmatic figures of the prawn 
landings of the three nets 'A', 'B' and 
'C' were respectively 21.2827, 24.1254 and 
20.1071. This clearly indicates that the 
net 'B' was catching significantly more 
of prawns when compared to the other 
two nets. The cat~h. of prawns of net 
'C' was relatively less amongst the three 
nets. Likewise the logarith.mati.c values 
for the total landings, namely 34.7295 
for net 'A', 38.0682 for net 'B' and 
33.9046 for net 'C', also showed super· 
iority in the catching rate of the net 'B'. 
The difference in the rate of fish catch 
was significant at 5% level as shown io 
Table IU and here also the catching rate 
of the net 'B' was superior to those of 
nets 'A' and 'C'. In aUthe above cases, 
the between day variations were significant 
< .01), which. could be due to the 
highly fluctuating conditions of the sea 
during the investigation. 
Earlier investigations of Mh.alath.kar 
and Iyer (Joe cit) and Mh.alath.kar and 
Jagadeesh.an (foe cit), had proved the 
possibilities of reducing the depth of the 
belly for a 13.69 m (45') four seam 
169 
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FISHERY TECHNOLOGY 
shrimp trawL Based on the earlier find-
ings and from the present studies, it has 
been quite possible to arrive at a mathe= 
maticali equation viz; D = 2 L/5, where 
'L' denotes the stretched width of the 
beUy either in inches or em and 'D' 
denotes stretched depth of belly with 12 
meshes for any marginal adjustments 
while either hand-braiding or tailoring 
the webbing. 
Further, reduction of the belly depth 
resulted finaHy in the economy of the 
twine utilized, with least effect on the 
catching efficiency as well as the mechani= 
cal characteristics of the net. The reduc-
tion in the twine utilized was as significant 
as 47.9% and 27J% in the case of 
13.69 m (Mha1athkar, eta!, loc cit) and 
17.07 m four seam coHon trawls respect-
ively. This reduction also resulted in 
considerable reduction of the number of 
meshes in the beHy region particularly 
and this accounted to about 46.16% 
and 27.76% respectively in the case of 
the above referred 13.69 m and 17.07 m 
trawls. This adds to the saving of fabrica-
tion charges, as trawl nets are mostly 
hand-braided in India till the present day. 
VoL VIII No. 2 1971 
Thus there is bound to be a definite 
reduction in the initial cost of fabrication 
of the gear on the whole. 
ACKNOWLlEDGlEMlENT 
The authors are grateful to Dr. A. N. 
Bose, former Director, Central Institute 
of Fishei'ies Technology, Ernakulam for 
his valuable encouragement during the 
course of work and to Dr. V. K. PiUai 
present Director for according kind 
permission to publish. this work. They 
are highly indebted to Shri G.K. Kuriyan, 
Fishery Scientist (Craft & Gear) for his 
most valuable support and for having 
gone through the manuscript critically. 
They are also thankful to Shri H. Krishna 
Iyer, Assistant Fishery Scientist (Statistics) 
for his help in the statistical analysis 
of the data. They also thank the crew 
of Fish Tech II from which the opera~ 
tions were carried out. 
RlEFERlENCJES 
Mhalathkar, H. N. and Iyer H. Krishna, 
1966. I. P. F. C. Occasional paper 
67/6. 
Mhalathkar, H. N. and Jagadeeshan G, 
1970. Fish. Techno/. 9 (2), 177. 
170 


Belly depth studies for shrimp trawls - Part III

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Belly depth studies for shrimp trawls - Part III

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