Three different types of otter boards varying in shape were tried to find out their relative catch efficiency. They were operated with two types of nets. The results indicated that the curved otter boards gave more catch per unit effort with all the combinations of nets and riggings tried

Narayanappa, G.

Aquatic Commons

THE RELATIVE CATCH EF_ _CIENCY "-)F 
DIFFEx't ENT SHAPED OTTE- , 	 A,RD!' 
BOTTOM TRAWLSN 
G. NARAYANAPPA 
Central Institute of Fisheries Technology Sub-Station, Kakinada-2 
Three different types of otter boards varying in shape were 
tried to find out their relative catch efficiency. They were operated 
with two types of nets. The results indicated that the curved otter 
boards gave more catch per unit effort with all the combinations of 
nets and riggings tried. 
INTRODUCTION 
That any modification or alteration to 
the fishing equipment has to be aimed to 
obtain maximum catches needs no parti-
cular emphasis. This is all the more so in 
otter trawling wherein a great deal of 
changes have been effected to the size and 
shape of the otter boards for the increased 
efficiency of the gear. Poliakov (1962), 
based on his experiments conducted on the 
East Coast, recommends the use of an 
oval single slitted doors. This type of 
boards are in frequent use in the Kakinada 
area, as against the conventional flat 
rectangular boards used at other centres. 
In order to evaluate the relative efficiency 
of the different otter boards under identi-
cal fishing conditions and in terms of 
catch, comparative experiments were 
undertaken with three different shaped 
otter boards at Kakinada Centre and the 
findings of these experiments are incorpo-
rated in this paper. 
MATERIALS AND METHODS 
Three types of otter boards in flat 
rectangular, horizontal curved and oval 
(Hydrofoil in cross section with single slit) 
shapes, were used for the study. The 
specifications and design details of each of 
the boards are similar to those used by 
Mukundan et at. (1967). Since two types 
of two seam trawls and two rigging are 
popular in this region, these otter boards 
were experimented with each combination 
to evaluate their comparative efficiency 
under all combinations. The nets used 
were 12.9 m. (42.5') two seam trawl (Satya-
narayana and Nair, 1962) and 11.89 m 
(39') two seam trawl, the design details of 
which are given in Fig. I. 
The two types of riggings include the 
use of double legs of 7.3 m (24') between 
the otter board and the net and 15 in 
single sweep wire in addition to 7.3 m 
(24') legs, which is a similar method as 
adopted by Poliakov (1962), 
15 
A small trawler 'Fish Tech. No. l' 
(9.13 m (30') 0. A. L. with 36 H. P. 
Engine) was used for experimental fishing. 
Operations were conducted off Kakinada 
during the fishing season of 1964-65, at 
depths ranging between 10 to 25 m (mostly 
at 10 to 18m), and where the bottom is 
muddy. oth the nets were towed at an 
approximate speed of 2 knots. 
With each of the four combination i. e. 
12.90 m (42.5') net with 7.3 m (24') 
double legs, 'B' 12.90 m (42.5') net with 
double legs of 7.3 m (24') and single sweep 
of 15 m wire, 'C' 11.89 m (39') net with 
7.3 m (24') double legs and 'D . 11.89 m 
(39') net with 7.3 m (24') legs and 15 m. 
single sweep wire, the three otter boards 
were successively operated in rotation, 
thus keeping the net and rigging constant, 
the varying factor being the otter boards. 
For each haul, the horizontal spread bet- 
ween otter boards, the warp tension on 
board, and the catch details were recorded. 
The methods suggested by Deshpande 
(1960) and Satyanarayana and Nair (1965) 
for calculation of spread and estimation 
of warp tension respectively were adopted. 
The shooting and hauling operations 
of the gear were done by the conventional 
method from the stern of the boat using 
winch and rollers. Sweep wires were 
hauled up by the winch side drums after 
completely hauling the warps and locking 
 
the otter doors to the stern posts. 
RESULTS 
The details of the average catch rate 
in each combination of the net and rigging 
as well as the combined results with the 
three types of otter boards are given in 
Table I. 
The corresponding average horizontal 
spread (in terms of distance between otter 
boards) and warp tension are given in 
Table III while the percentage frequency  
of the highest catch per unit effort in 
each combination with three boards are 
tabulated in Table II. 
DISCUSSION 
Relative Catch Efficiency 
Table I clearly indicates that the 
total catch per one trawling hour is more 
with curved otter boards for all combina-
tions of gear except in 'D', where the 
catch rate with oval otter board is slightly 
more by only 0.8% which can he 
taken as non-significant. This increased 
catch with curved doors may be due to 
increased area swept during trawling. The 
combined results of all the operations, 
irrespective of gear and rigging also show 
an increase in catch with curved otter 
boards by about 39.5% and 36.0% resp-
ectively over the flat and oval otter boards. 
The efficiency of the latter two boards 
in terms of catch per unit effort was more 
or less equal. 
Better prawn catch, both in terms of 
quality and quantity, was seen for all 
combinations of gear operated with curved 
otter boards than with other boards. This 
fact is due to increase in horizontal 
spread and coincides with the observations 
of Kuriyan et al. (1962), that for in-
creasing the prawn catch, horizontal spread 
of the net should be more, so as to cover 
more area laterally instead of vertically. 
In terms of fish catch also, the same trend 
i. e., increase in catch, was noticed under 
all experimental combinations with curved 
otter boards except in 'D' where oval otter 
boards gave comparatively better catch. 
It is evident from Table II that the 
percentage of frequency of the highest 
catch per unit effort is always more in the 
case of observations made with curved 
otter board proving its efficiency over the 
others. The highest percentage of catch 
rate at 50% confirms the efficiency of the 
curved otter board over that of oval otter 
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board in 'D' combination where the 
average catch rate with the latter is more. 
Horizontal Opening 
From table III it would be seen that 
the lateral spread between the otter boards 
in all combinations of experiments was 
always more with curved otter boards than 
the other two and is 15% and 21.7% more 
with double leg and single sweep systems 
respectively. This increase may be due to 
the increased shearing force or force of 
efficiency which arises according to Crewe 
(1964) from its forward surface being at 
smaller angle to the direction of motion 
than in the case of flat otter boards, thus 
allowing the water to flow round it more 
smoothly. 
The horizontal spread, obtained in 
the case of the other two types of otter 
boards is found to be practically same in 
all combinations and is not in confirm-
ation with the observations of Treschev 
(1964) that the oval shaped slotted otter 
boards have 15% greater spreading force 
than comparable rectangular otter boards. 
This difference may arise from the fact 
that there is some difference in areas and 
surface ratio between them. 
Warp resistance 
Taking into consideration that the 
fishing gear, rigging and conditions same, 
the difference in warp resistance is attri-
buted to the different otter boards used. 
As can be seen from the Table III, the 
oval otter boards gave less tension in all 
combinations, where as curved otter boards 
gave more .resistance followed by flat otter 
board (Mukundan et a/., 1967). 
SUMMARY 
Three different types of otter boards 
varying in shape were tried to find out 
their relative catch efficiency. They were 
operated with two types of nets. The  
results indicated that the curved otter 
boards gave more catch per unit effort 
with all the combinations of net and rigging 
tried. The efficiency or the flat rectangular 
and oval otter doors was more or less equal. 
With curved otter boards the net gained 
more horizontal spread when compared 
with the other two types of otter boards 
with which the lateral spread of the net 
was more or less equal. Oval otter boards 
gave less warp resistance, while the curved 
otter boards gave more tension followed 
by flat rectangular otter boards. 
ACKNOWLEDGMENT 
The author thanks Dr. A. N. Bose, 
Dircctor, Mr. G. K. Kuriyan, Senior 
Research Officer, and Mr. A.V.V. Satyana-
rayana, Research Officer, Central Institute 
of Fisheries Technology, for their valuable 
suggestions for preparing this paper. His 
thanks are also due to Mr. K. A. Sada-
nandan, Research Officer, Central Institute 
of Fisheries Technology, for his guidance 
during the execution of the work. 
REFERENCES 
Crewe, P. R. 1954. "Modern Fishing Gear 
of the World", Fishing news (Books) 
Ltd., London. pp. 165-180. 
Deshpande, S. D. 1960. Ind. J. Fish VII, 
2, 458. 
Kuriyan, G. K, Deshpande, S. D & George, 
N. A. 1962. Ind. Fish. Bull. IX, 4, 31. 
Mukundan M., Satyanarayana, A. V. V., 
& Krishna Iyer, H. 1967. Fish. 
Technol., 4, 2, 53. 
Poliakov, M. P. 1962. F. A. 0/E. P. T. A. 
No. 1573. 
Satyanarayana, A. V. V. & Nair, R. S. 
1962. Ind. Fish. Bull. fft, 4, 4. 
Satyanarayana, A. V. V. and Nair R. S. 
1965. Res. Ind, X, 8, 229. 
Treschev, A. I. 1964. "Modern Fishing 
Gear of the World" Fishing News 
(Books) Ltd., London. pp. 206-208. 
20 


On the relative catch efficiency of different shaped otter boards in bottom trawling

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On the relative catch efficiency of different shaped otter boards in bottom trawling

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