Effectiveness of sailkite has been evaluated in two trawl designs, namely, a 25m high opening trawl and a 32m large mesh demersal trawl, rigged with sailkite through full scale comparative field trials. A 25m high opening trawl showed significant increase in total catch by 54.4% ribbon fish (Trichiurus spp.) alone by 138.3% with a reduction in miscellaneous catch, comprising mostly small sciaenids and juvenile fish, by 13.2% while 32m large mesh demersal trawl showed an improvement in total catch by 9%, ribbon fish by 17.2% and miscellaneous catch by 7.7%. The difference in fishing performance between the two gear arrangements has been attributed to changed net mouth configuration because of higher head line lift and also the possible herding effect on the fish in the vicinity of trawl mouth, due to addition of sailkite

Boopendranath, M.R.

Krishna Rao, K.

Kunjipalu, K.K.

Subramonia Pillai, N.

Aquatic Commons

Effect of Sailkite I Umpir r vring 	 Jyyll Gear Performs ce 
M. R. BOOPENDRANATH, N. SUBRAMONIA PILLAT and K. K. KUNJIPALU* 
Veraval Research Centre of Central Institute Fisheries Technology, Veraval - 362 265 
and 
K. KRISHNA RAO 
Central Institute of Fisheries Technology, Cochin - 682 029 
Effectiveness of sailkite has been evaluated in two trawl designs, namely, a 25 m 
high opening trawl and a 32 m large mesh demersal trawl, rigged with sailkite through 
full scale comparative field trials. A 25 m high opening trawl showed significant incre-
ase in total catch by 54.4% ribbon fish (Trichiurus spp.) alone by 138.3% with a redu-
ction in miscellaneous catch, comprising mostly small sciaenids and juvenile fish, by 
13.2% while 32 m large mesh demersal trawl showed an improvement in total catch 
by 9% , ribbon fish by 17.2% and miscellaneous catch by 7.7%. The difference in 
fishing performance between the two gear arrangements has been attributed to 
changed net mouth configuration because of higher head line lift and also the 
possible herding effect on the fish in the vicinity of trawl mouth, due to addition of 
sailkite. 
Sailkite is a canvas sheering device atta-
ched to the net just behind the head rope, to 
lift the net during trawling. Benyami (1979 
a,b,c) by his flume tank studies on model 
nets and Garner (1977) through actual 
field trials have shown that sailkite can 
feasibly be used to improve the fishing 
height of trawls. Hi Soo Han et al. (1981) 
mentioned that canvas sheering device could 
fully open the mouth of a stow net and 
improve the catch per unit effort by 38.9%. 
Following reports of tank studies on sail-
kite, fishermen in New Zealand has been 
reportedly using this technique in commercial 
fishing operations. It has been tested using 
a high opening trawl by FAO Masterfisher-
man Capt. Lyzwa, in Burma, who used a net 
sonde to observe fishing height and reported 
both increase in vertical opening and enhan-
ced catches (Dr. Benyami, M., personal 
communication). South China Sea Fishe-
ries Institute has recently developed a head 
line lifting device known as flexible hydro-
foil float made of canvas and introduced 
into commercial fishing fleet with success 
(Anon 1984). 
*Present address : Central Institute of Fisheries 
Technology, Cochin-682 029 
In the present study, effectiveness of sail-
kite technique in improving the performance 
of two different trawl designs of proven effi-
ciency, developed at Veraval Research 
Centre of the Institute, has been evaluated 
using full scale comparative field trials. 
Materials and Methods 
A 25 m high opening trawl with eight 
panels and a 2 seam 32 m large mesh demer-
sal trawl described by Kunjipalu et al. (1979, 
1984) respectively, were used for the 
experiments, retaining the same rigging 
features and full complement of floats. 
Flat rectangular otter boards of wood and 
steel construction and size 1524X 762 mm, 
weighing 100 kg each, described by Kuriyan 
et al. (1964), were used for the operations. 
Fishing trials were conducted from the 
research vessel, Fishtech No. 8 of 15.2 m 
LOA, fitted with a 165 hp engine, during 
1982-84 at a depth range of 30-45 m, 
during day time. The two types of gear 
arrangements, namely, with and without sail-
kite, were operated alternately, maintaining 
the same depth, duration, direction of tow 
and engine revolutions, during each of the 
paired comparative hauls. Horizontal spread 
between the boards was estimated using the 
Vol. 23, 1985 
Off Veraval 20° 23'-34' and 
69° 44'-51' and 70° 15'-21' E. 
46 	 46 
66 h 05 min 
	 66 h 05 rain 
2.5 knots at 1250/1300 r.p.m. 
15.14 	 16.13 
657.11 	 650.72 
6440.5 	 4170.5 
1. Fishing ground 
2. Number of hauls 
3. Towing time 
4. Towing speed 
5. Average 
horizontal spread 
between otter 
boards (m) 
6. Mean warp 
tension (kg) 
7. Total catch (kg) 
20°. 34'-51' N. Lat 
Long. within 30 to 50 m depth 
32 	 32 
47 h 30 min 
	 47 h 30 min 
engine output 
18.66 18.91 
654.75 651.5 
2106.8 1933.4 
HDPE Rope 6mm 0 
I5cm 
46 M. R. BOOPENDRANATH, N. S. PILLAI, K. K. KUNJIPALU AND K. K. RAO 
Table 1. Details of comparative fishing operations 
Particulars 	 25 m high opening trawl 
with 	 without 	 32 m large mesh demersal trawl 
sailkite 	 sailkite 	 with sailkite 	 without sailkite 
method suggested by Benyami (1959) and 
Deshpande (1960) and tension on the warps 
was measured by a mechanical tension meter 
described by Satyanarayana & Nair (1965). 
Operational details are presented in Table 1. 
Sailkite was prepared from a rectangular 
piece of thick canvas, of 2.7 X 1.35 m size 
and natural white in colour. The outer 
edge was shaped to follow the catenary of 
the head line approximately and provided 
with aluminium eyelets for tying tightly 
along the head rope in the centre of the 
square (Fig. 1.). 
Results and Discussion 
(a) 25 in high opening trawl 
Details of catch rates and catch composi-
tion is presented in Table 2a and the results 
of statistical analysis using Student t test, 
for total catch and component groups 
in Table 3a. 
Introduction of sailkite in the rigging has 
improved the efficiency of the gear by 54.4%, 
in terms of total catch, which was found to 
be significant at the probability of 0.01. 
Highly significant improvement by 138.3% 
was observed in the case of ribbon fish 
(Trichiurus spp.) coupled with a reduction 
in the miscellaneous catch by 13.2%. Reduc-
tion in miscellaneous catch was brought 
Fig. 1. Construction and method of attachment 
of sailkite to the trawl. 
about by the reduced catch of bottom 
living sciaenids and juvenile fish. 
Horizontal opening between otter boards 
decreased by 6.5% and tension on the warps 
increased by 0.98%, with the addition of 
sailkite, which were significant at 0.05 pro-
bability level. 
FISHERY TECHNOLOGY 
SAILKITE IN IMPROVING TRAWL GEAR PERFORMANCE 	 47 
Table 2. Catch details and composition of 
catch 
a) 25 m high opening trawl 
Variety of 
fishes 
With 	 sailkite 
Catch Percen-
in 	 tage 
kg/h 
Without 
Catch 
in 
kg/h 
sail- 
kite 
Peree- 
ntage 
Ribbon fish 66.25 68.0 27.80 44.0 
Eel 2.68 2.8 1.64 2.6 
Lacatarius sp 1.28 1.3 0.83 1.3 
Squid 0.61 0.6 0.39 0.6 
Other fishes 26.64 27.3 32.47 51.5 
Total 97.46 100.0 63.13 100.0 
b) 32 m large mesh demersal trawl 
Ribbon fi,}11 6.19 14.0 5.28 13.0 
Lactarius sp. 6.20 14.0 4.05 10.0 
Squid 3.18 7.2 2.03 5.0 
Other fishes 28.78 64.8 29.34 72.0 
Total 44.35 100.0 40.70 100.0 
Table 3. Results of statistical analysis of 
total catch and catch components 
using Student t test 
a) 25 m high opening trawl 
Variety of 
fish 
	
Mean values 	 Diffe- 
	
(kg/h) 	 rence 
Calcu-
lated 
With 
sail- 
kite 
with- 
out sail-
kite 
't' 
Ribborn fish 66.25 27.80 	 38.45 2.93** 
Miscellaneous 
catch 31.21 35.33 	 -4.12 1.63 
Total 97.46 63.13 	 34.33 2.77** 
Degrees of freedom, n-1 : 45 
b) 32 m large mesh demersal trawl 
Ribbon fish 6.19 5.28 0.91 0.37 
Miscellaneous 
catch 38.16 35.42 2.74 0.67 
Total 44.35 40.70 3.65 0 75 
Degrees of freedom, n-1 : 31 
** Significant at the probability of 0.01  
(b) 32 m large mesh demersal trawl 
Catch details and composition of catch is 
presented in Table 2b and results of statis-
tical analysis in Table 3 b. 
Improvement in the total catch by 9% 
ribbon fish by 17.2% and miscellaneous 
catch by 7.7% was noted with kite but the. 
differences were not significant statistically. 
Ribbon fish lan dings were low because of 
poor availability in the fishing ground, 
during the period of field trials. Improve-
ment is contributed by Lactarius sp. and 
squid. 
Horizontal opening between otter boards 
and warp tension did not show any signi-
ficant difference statistically. Efficiency of 
25 m high opening trawl, a proven design 
especially for ribbon fish (Kunjipalu et al. 
1984), can be significantly improved further, 
by the addition of sailkite in the rigging, 
both in terms of total catch and catch of off 
bottom fishes like ribbon fish. In 32 m 
large mesh trawl, the effect of sailkite was 
less pronounced which could be attributed 
to the changed aspect assumed by the square 
of this two-panelled net during operation, 
compared to the eight-panelled high open-
ing trawl. Further observations using sail-
kites of larger area are required to confirm 
its effectiveness in the case of 32 m large 
mesh demersal trawl. 
Improvement in the catch in both the 
trawls, could be attributed to higher vertical 
opening and the improved herding effect on 
the fish in the vicinity of trawl mouth due 
to attachment of kite. The latter however 
requires confirmation through direct obser-
vational methods. Blaxter & Parrish (1964) 
have discussed the herding effect by the peri-
pheral parts of the trawl mouth under visual 
conditions and trawling speeds of less than 
three knots, as is the case here. 
The changes in the net mouth configura-
tion with reduced horizontal opening conse-
quent to higher vertical lift generated by the 
sailkite; with possibly lessened ground con-
tact would have contributed to reduced 
catch of sciaenids and juveniles fishes found 
close to the bottom. Dickson (1959) has 
reported that a common line of escape from 
the path of the net is below ground rope, 
Vol. 23, 1986 
48 M. R. BOOPENDRANATH, N. S. PILLAI, K. K. KUNJIPALU AND K. K. RAO 
when ground contact is inadequate. Effecti-
veness of a sa lkite and related canvas 
sheering devices depends on the design and 
construction of the gear especially the aspect 
assumed by square of the trawl, during 
operation, relative to water flow. A sail-
kite is ineffective in trawls with squares 
which are horizontal in action and also 
where there is excess webbing in the square 
(Benyani, 1979 a, b). In other case, use of 
sailkite is indicated either as an additions or 
substitution to the conventional head line 
lifting devices. The advantages of sailkite 
are that it is inexpensive, simple to fabri-
cate, install and handle. It can be wound 
into a net drum without any detrimental 
effects. Sailkite can be used at any depth 
and stowage is easy as it can be folded and 
kept. 
The authors are thankful to Shri M. R. Nair, 
Director, Central Institute of Fisheries Technology, 
Cochin for his permission to publish this paper, to 
Shri P. A. Panicker, Scientist-in-Charge (Gear Divi-
sion) for his keen interest in the study and to Shri 
K. K. Solanki, Scientist-in-Charge, Veraval Research 
Centre, for providing the facilities. They are also 
thankful to Shri M. S. Fernando, Skipper and his 
crew and technical assistants, Shri J. B. Paradva and 
Shri K, U. Dholia, for their co-operation during the 
investigations. The first author is grateful to Dr. 
M.Ben Yami, Fisheries Industries Division, FAO, 
for providing information on his pioneering tank 
studies on sailkite and also available details of its 
use in commercial fishing. 
References 
Anon (1984) Fishg. News Int. 23, 23 
Ben-Yami, M. (1959) in Modern Fishing 
Gear of the World (Kristjonsson, H. Ed.) 
vol. 1, p. 213, Fishing News (Books) 
Ltd., London 
Benyami, M. (1979a) Australian Fisheries 
38, 24 
Ben-Yami, M. (1979b) Second Note on 
Model tests of a Sailkite, Fisheries 
Industries Division, FAO 
Ben-Yami, M; (1979c) Fishg, News Inst. 18, 26 
Blaxter, J.H.S. & Parrish, B.B. (1964) in 
Modern Fishing Gear of the World, 2, 
p. 529, Fishing News (Books) Ltd., 
London 
Deshpande, S.D. (1960) Indian J. Fish. 7, 458 
Dickson, W. (1959) in Modern Fishing Gear 
of the World p. 166, Fishing News 
(Books) Ltd., London 
Hi Soo Han, Byong Moo Kang, Tae Hyun, 
JO, Bong Chae KIM & Jee Won Chang 
(1981) Bull. Fish. Res. Dev. Agency 27, 
119 
Garner John (1977) in Modern Deep Sea 
Trawling Gear 2nd end. p. 73, Fishing 
News Books Ltd., England 
Kunjipalu, K.K., Kuttappan, A.C. & George 
Mathai, P. (1979) Fish, Technol. 16, 19 
Kunjipalu, K.K., Boopendranath, M.R., 
Gopalakrishnan, K. & Kuttappan, A.C. 
(1984) Fish. Technol. 21, 86 
Kuriyan, G.K., Satyanarayana, A.V.V. & 
Nair, R.S. (1964) Proc. Indo. Pacif: 
Fish. Coun. 11, 204 
Satyanarayana, A.V.V. & Nair, R.S. (1965) 
Res. Ind. 10, 229 
FISHERY TECHNOLOGY 


Effect of sailkite in improving trawl gear performance

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Effect of sailkite in improving trawl gear performance

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