An attempt has been made to evolve a suitable mesh size for the commercially significant size group of S. guttatus. To obtain maximum sustainable yield taking biological factors also into consideration, 52 mm mesh bar nets are suggested for exploiting the fishery on both the East coasts of India

Dawson, P.

Mathai, T.J.

Rao, J.S.

Sreekrishna, Y.

Sulochanan, P.

Aquatic Commons

ESH SEL SPOTTE 
sco E S GUTTt~TUS 
SEE 
sc El 
Y. SREEKRISHNA, J. SITARAMA RAO AND PERCY DAWSON 
Central Institute of Fisheries Technology Sub-station, Kakinado, Andhra Pradesh 
& 
T .. JOSEPH MATHAI AND P. SULOOHANAN 
Central Institute of Fisheries Technology (Croft & Gear Division), Cochin~S 
An attempt has been made to evolve a suitable mesh size 
for the commercially significant size group of S. guttatus. To obtain 
maximum sustainable yield taking biological factors also in to con-
sideration, 52 mm mes1-J ~?r nets are suggested for exploiting the 
fishery on both the East c-oasts of India. 
INTRODUCTION 
Buchanan - Wollaston (1927); Hogson 
(1927); Havinga and Deelder (1948); Nom-
ura (1961) and Burd (1963) have stressed 
the importance of selecting the minimum 
mesh size in gill nets and trawls from the 
standpoint of conservation of population· 
Joseph and Sebastian (1964), on the other 
hand, emphasised the need for the selection 
of suitable mesh size to increase the out put 
of gill nets. Holt (1957) analysed the gill 
net data on the assumption that for two 
giil nets the meshes of which differ slightly 
in size, the shape of their selection curves 
is the same and the mean selection length 
is proportional to the mesh size. This 
method has been successfully made use of 
by Olsen (1959) and Olsen et al (1961) 
for herring and halibut; Peterson (1964) 
for pacific Salmon and Koura and Shahun 
(1969) for Nile perch. Baranov (l948)sh-
owed that the mesh size is proportional 
to the modal length of fish caught in it. 
VoL IX No. 2 1972 
Based on studies conducted at Kakinada 
the East Coast and Cochin in the Vlfest 
Coast the correct mesh size of the gear 
required for the capture of commercially 
important size group of spotted seer (S. 
guttatus) has been evolved using Baranov's 
formula. The results are dealt with in 
this communication. 
MATERIAL AND METHODS 
Based on a survey of the existing seer 
gill nets on both the East and West coasts 
of India, three different mesh sizes viz. 
50 mm, 60 mm and 70 mm mesh bar were 
selected for the studies. The experimental 
gear consisted of two fleets, one consisting 
of fifteen nets, five nets in each mesh 
size and the other consisting of nine nets, 
three nets in each size. Webbings were 
hung at a hanging coefficient of 0.5 ho-
rizontally, effecting the corresponding 
vertical coefficient of 0.86. In the absence 
of separate selvedge meshes, the upper 
133 
Sreelhistlna et. al: Mesf1 Selectivity to·r spotted Seer, Scomtieromorus 9uitatus ('Bloc!Z & Scftneider) 
and lower edge meshes were doubled and 
reeved through the corresponding head and 
foot ropes. 
The investigations were carried out 
during 1966-68 seasons. The nets were 
operated as surface drift nets from two 9.15 
m. (30') mechanised vessels. The depth of 
fishing ranged from 10-60 metres. The 
arrangement of the nets in each days op-
eration was statistically designed. The 
buoyancy of head rope and weight of foot 
rope were kept constant throughout. the 
TABLE I : QUANTITY OF DIFFERENT SPECIES 
period of experimentation. A total of 82 
fishing operations were conducted and the 
necessary morphometric data collected. 
. The predominant size groups of S. gutt-
atus from the commercial seer fishery have 
also been recorded regularly from seer 
}anding centres at both the east and west 
coasts. 
RESULTS 
The catch of three species of seer 
caught in the experimental gear is given 
in Table -I in both number and weight. 
OF SEERS CAUGHT IN THE EXPERIMENTAL GEAR 
SL Mesh size S. Guttatus S. Commersoni S. Lineolatus Total 
No. bar len- No. Wt. No. No. Wt. in No. Wt. gthmm m ll1 m 
kg kg kg kg 
A 50 185 193.54 39 110.80 16 30.10 240 334.44 
B 60 60 79.05 35 114.35 15 26.50 110 219.90 
c 70 20 21.72 25 
The data have been analysed statisti-
cally by using analysis of variance technique, 
after converting the catch figures into their 
89.05 45 46.92 
corresponding logarithmic values. The 
results of analysis are given in Table - IL 
TABLE II: ANALYSIS OF VARIANCE TABLE FOR CATCH OF S. GUTTATUS 
Source of variation S. S. 
Total 
Between 
Error 
19.0085 
nets 5.6106 
13.3979 
*':' Indicates significance at 1% level 
Critical difference for nets 0.1036 
D. F. M.S. F. 
170 
2 2.8053 35.20** 
168 0.0797 
The mean logarithmic catches of the 3 nets 
50 mm mesh bar 0.5334 
60 mm mesh bar 0.2579 
70 mm mesh bar 0.0945 
The percentage length frequeney dis-
tribution of the three species of seer compu-
ted from the data recorded at both the 
134 
landing centres and those caught in the 
experimental gear are given in Table IlL 
f'JSHERY TECHNOLOGY 
Sreelhisl'tna et. al: Mesfi Selectivity fo1· spotiiiid Seer, ScomtJeromorus Guttatus ('Blocf, & Sdineider) 
TABLE III: PERCENTAGE LENGTH FREQUENCY DISTRIBUTION OF DIFFERENT SPECIES OF 
SEER IN COMMERCIAL AND EXPERIMENTAL CATCH 
Size- group 
mm 
S. Guttatus 
250- 300 
300-350 
350-400 
400-450 
450-500 
500-550 
550- 600 
600- 650 
650-700 
700-750 
750- 800 
800- 850 
850-900 
900- 950 
950- 1000 
1000- 1050 
1050- 1100 
1100- 1150 
1150- 1200 
1200- 1250 
1250- 1300 
A 
0.08 
0.99 
2.40 
12.83 
25.98 
18.59 
20.93 
15.46 
1.52 
0.32 
0.26 
0.13 
0.23 
0.10 
0.08 
0.10 
A: Commercial catch 
B 
11.32 
17.36 
24.15 
20.75 
18.49 
4.90 
1.88 
0.37 
0.75 
B : Catch in experimental nets. 
Table - IV 1s formulated from the 
commercial catch data, showing predomi-
VoL IX No 2 1972 
S. Commersoni 
A 
2.12 
2.74 
0.25 
1.25 
1.37 
4.24 
6.73 
9.60 
11.70 
8.84 
17.56 
12.58 
9.58 
3.60 
3.48 
2.12 
1.50 
0.75 
B 
2.04 
2.04 
5.10 
5.10 
9.19 
13.26 
10.20 
17.36 
10.20 
13.26 
10.20 
1.02 
1.02 
S. Lineolatus 
A 
1.19 
0.53 
2.28 
3.08 
9.20 
U.06 
7.73 
14.00 
ll8.40 
22AO 
3.87 
3.33 
0.80 
B 
9.68 
16.13 
35.48 
25.81 
9.68 
3.22 
nant size group, their percentage representa= 
tion and central values. 
135 
SreefZrisfma et. al: M esf1 8electioity for spotted Seer, 8com($eromorus Gutta ius (13LocfZ & 8d'tneideY) 
TABLE IV: PREDOMINANT SIZE- GROUPS PERCENTAGE COMPOSITION AND THE 
CENTRAL VALUES OF DIFFERENT SPECIES OF· SEER 
Name of species Predominant 
size- group 
mm 
S. Guttatus 400- 650 
S. Commersoni 650- 1000 
S. Lineolatus 600:- 900 
The number and percentage of S. 
guttatus caught in 1A 1 and 'B' nets are 
Percentage Central values 
representation 
mm 
93.79 525 
71.25 825 
84.79 750 
shown in Table - V, while mesh selectivity 
curves are presented in Figure- 1. 
TABLE V: PERCENTAGE OF S. GUTTATUS IN THE NETS OF A AND B 
Length 
mm 
380 
430 
480 
530 
580 
630 
680 
730 
780 
830 
880 
DISCUSSION 
Fig. 1 
Nos. 
5 
22 
43 
45 
38 
23 
5 
3 
1 
A- Nets 
A- O.CU i:M!~t-1 
11 -eo w:a ta£Btl 
% 
2.70 
11.89 
23.24 
24.33 
20.54 
12.43 
2.70 
1.62 
0.54 
As evident from Table - I, 1 A 1 nets 
(50 mm bar) are found effective for 
136 
B- Nets 
Nos. % 
2 3.33 
9 15.00 
14 23.33 
17 28.33 
11 18.33 
4 6.67 
I 1.67 
I 1.67 
1 1.67 
S. guttatus whereas 1C' nets (70 mm bar) 
have shown restricted efficacy for S. 
commersoni. The selectivity of S. guttatus 
in 1 A' nets is well marked and accounted 
to 3 and 9 times to those of 'B' and 1C1 
nets respectively. The results from the 
analysis of variance technique (Table -II) 
show that the variation between the nets 
is significant at 1% level. With a view 
to separate significant net effects, critical 
difference was evaluated. The results su-
pport . the superiority of 1 N nets over 'B' 
and 'C' nets. when drift nets of different 
FISHERY TECHNOLOGY. 
Sreeihisfma et. al: Mesfl Seleciioit!J fo1· spotted Seer, Scomoeromoi'ttS 9uttaitts ('Bloc!?- & Sct!neider) 
mesh sizes are employed in juxtaposition 
and the catches are repeated the percentage 
represent<'.tion of the different length group3 
reflect the representation of the different 
groups in the stock of a popub.tion (von 
Brandt, 1955; S. Dutt, 1965). The per-
centage representation of seers given under 
the commercial catch in Table - HI may 
be considered as the population in the 
broader sense since they were landed by 
gill nets of varying mesh sizes and in 
conformity with the normal frequency 
distribution. The percentage length freq~ 
uency of seers in the experimental gear is 
also exhibiting the same general trend of 
commercial catch except for so lineolatus. 
it is very likely that this may b(; due to 
the restricted availability of this species. 
Selectivity of Experimental Nets 
From Figo 1, it is evident that the 
mesh-selectivity curves are in conformity 
with normal frequency distribution shifting 
mode length with increase of mesh size. As 
seen in Table -IV, the length groups of 
525 mm, 825 mm and 755 mm represent 
the central values of the predominant size 
groups of S. guttatus, S. commersoni and 
S. lineolatus respectively. Baranov C(l948) 
showed that mesh size is proportional to 
the modal length of fish caught ii1 it and 
established the relationship between them 
by the formula. 
a k 1 
Where 'k' IS a constant 
'a' mesh bar in mm. 
and '1' the modal length in mm. 
constant 'k' can be calculated empirically 
by two methods after experimenting with 
more than one probable mesh bar. 
(1) Length-measurement method 
2 (a 1 a 2 ) 
k 1 0 (a 1 +a2 ) 
Vvhere a 1 and a~ are the two mesh bars 
and 1 0 the length of fish in mm caught 
in equal proportions by both the nets. 
VoL IX No 2 1972 
Substituting the values from Table-V and 
Fig. 1, 
2 (50x60) 
k OJOl 
540 (50-!--60) 
(2) Modal length method 
. J!ere the calculation is based by sub-
stJtutmg values of modal lengths obtained 
in both the 50 mm and 60 mm bar nets. 
k 50 
- 530 
60 
- 0.094 
580 - 0.103 
530 mm and 580 mm represent the 
modal lengths recorded in 50 mm and 
60 mm bar nets respectively. Taking the 
arithmetic mean of the three values 
' 
k 0.101 + 0.094 + 0.103 = 0.099 
= 3 
By substituting the value of 'k' in 
general formula the appropriate mesh size 
for any length group of S. guttatus is cal-
culated. Relationship between mesh size 
and mean selection length of fish represen-
ting both the experimental and calculated 
values is whown in Fig. 2. 
~HT.2, R2LATlON:-:H1f> G~T"'E"i!/1 ru:;:~ ::r;z:;: C. t:ZAM m::L€.CTI0!1 Lt::rr.;TM _r:i'Tl'-1 C.Po:tlZ.:~fn?.( 
AiiO C!.ll::tr_:..TEO VALUES 
Fig. 2 
The latter value was obtained by sub-
stituting the 'k' value for the three expe-
rimental mesh sizes. The reason for the 
137 
Sreelhisftna et. al: Mesft Selectivity for spotted Seer, Scom6eromorus 9uttatus (13Iocft & Scftneider) 
slight difference between the two values 
may be assigned to the unequal represen-
tation of different length-groups in the 
population. It follows, therefore the sui-
table mesh aize for the centrally represe-
nted length group of 525 mm and the most 
predominent commercial size group 480 mm 
of S. guttatus are 51.98 mm (525 x 0.099) 
and 47.50 mm (400 x 0.099) respectively. 
From the studies of Krishna Moorthy (1958) 
on the Biology of S. guttatus it is evident 
that 525 mm length group of S. guttatus 
would have spawned at least once. 
ACKNOWLEDGEMENT 
The authors are greateful to Dr. V. K. 
Pillai, Director, for going through the 
paper critically and for offering valuable 
suggestions, to Shri G. K. Kurian, Senior 
Fishery Scientist -cum -Head of Division 
(Craft & Gear) for guidance and the valua-
ble suggestions in carrying out this experi-
ment and bringing out this paper in the 
present form and to Shri H. Krishna Iyer 
for the statistical anilysis of the data. 
REFERENCES 
Alvin, E. Peterson 1964 U. S. Fish and 
Wild lzfe service Fish. Bull. 2 : pp 
381-390. 
13S 
Barnov, F. I. 1948 Pischepromizdat, Mos-
cow: 435 U.S.S.R. P, 
Buchanan- Wollaston, H. J. 1927 Journ. 
du. cons. 11 (I): pp 343..:.55. 
Burd, A. C. 1963 Ibid. 14 (1): pp 91-120. 
Dutt, S. 1965 Fish. Techno! 2 (2): pp 
249-50. 
Havinga, B. & Deelder, C. L. 1948 Rapp. 
Cons. Explor. Mer. 125 (11): pp 249-50 
Hogson, W. C. 1927 Ibid 2 (l): pp 356-60. 
*Holt, S. J. 1957 Joint. Sir. Meet. ICNAE 
ICES & FAO Pap. No. 515, Lisbon. 
Joseph K. M. & Sebastian, A. V. 1964 
Fish. Techno!. 1 (2): 180-82. 
Krishna Moorthy, B. 1958 Ind. J. Fish. 
5 (2): 270-81. 
Koura, R. & Shahun, A. A. 1969 Stud. 
Rev. Gen. Fish. Coun. Medit. 39: 1-12 
Nomura, M. 1961 Bull. of· Tokai. Reg. 
Fish. Res. Lab. 30: pp 50-56. 
Olsen, S. 1959 J. Fish. Res. Bd. Can. 
16 : PP. 339. 
Olsen, S. and Jemalsen, J. T. 1961 ICES. 
Compenhative Fishing Committee 
No. 18. 
Von Brant, A. 1955 Joun. du. Cons. 
21 (1) : 8-16. 
FISHERY TECHNOLOGY 


Mesh selectivity for spotted seer, Scomberomorus guttatus (Bloch & Schneider)

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Mesh selectivity for spotted seer, Scomberomorus guttatus (Bloch & Schneider)

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