IN5TITUT SErEGkLiiI?~ DE RECHERCHES AGRICOLES 3rd...
IN5TITUT SErEGkLiiI?~ DE RECHERCHES AGRICOLES
3rd note : ME BIOLCGY OF THE ETHHALOM
IN THE Gt4d3IAN HATERS
W.J * XHEFFERS ( 1)
F, cw:w
(2)
(1) Fisheries biologist. Pro ject FAO WP GkW S2,&06
“Development of Inshore Fishery”, Fisheries Division,
Banjul, The Gambia.
(2) Océanographe biologiste de l’ORSTCW3, Centre de
Recherches Océanocqraphiques de Dakar-Thiaroye,Jénégal
CENTRE DE RECHERCHES ~E~~P~I~~~~
DE DAKAR-THIAROYE
DfXuE~~RIT XIENTIFI~~ No 5 9
AVRIL 1976
?:bStZWCt - Fh5sumcs
1. Introduction
2 l &lydroPogy
3. Fiaterial and msthods
4. Length - zeight relationskip
5. Vertebral countinys
6. Catch composition and migration
7. Reproduction
7.1
Sexratio
7.2 Length of first reproduction
7.3 Spawning period and ores
- Limonthly variation of the gonado-somatic index
- J%e gonad breeding cycle
- iJont&ly percentages of fema%es in matwrity stage V
- Ckcurence and abundance of planktonic %arvae
- Conclusion on the spawning period and area
2, Ccnclusions and comparaison vith the Ethmabosu-“fimbriata
population in Phe Saint Louis region.
References.
2
:.dat&t compositions bave $een analysed br t6’1e gowth and t6w mi~rration
of ePkmu~osa
l
<’ compasison is made between thé resadts of the present study and
t&e one. obtained f r o n t the ‘ikint Loui.23 rec-$.on.
bo composition des captures est ana.llysSe pour &Pudier la croisscnce et Ii
~k~r~ti0n des poissons.
In the sonegambian repion, landings by the canoe bisherioa, of
cthmalof3a - Ethmalosa fimbriata - are very important and represunt
yearly around 25,303 t o n s . fhe biggestpart of the catch is for
Cresh conwmption the rest is 5moked or dried.
TO ovaBwczte khis important coostal pelagic stock and to skwdy
i=ts bicblogy, landinqa and samples bave been anally~ed and planktaw
*:~rveys; effscted, in different centers in 52negali and Gambia. :orràE
of Phe mwlts have ahsady been published (.%hebffers Cp &. , 1972 ;
'~~@bm!kS, 19?%, 15z3, 1974) otherq -are in preparation.
3X.s article deals vith bio9ocjy and reproduction of Phe ethrrra,Bssa
from the gambian waters.
[,ydrologicaI.By the yaïnbian 5daters 9oLLow the same pattern ~3s ther
cenegaless waters und accordiny to tkmxignol and P,boussouun ( I%X)
three hydrological seaaons cari brz distinguished.
The coSd and saline water season “wpwel.lin~ waters” : December - 1.pri.l
The warm ad saline water acason “trapicfll waters” 0 E ky - Ikptember
moved by the “guinean waters”. (T :> 24°C
;
:,j <(“s:.. /QO ) coming fror2 the
5owPh. In idovember the coolin of tho c!cter kx3$.ns with ths wrrival
of the trade winds and the coostol upwel.%inc and in Gecsmber the
“cjwineun waters“ ure pwshed off-shore and to the South.
i Sumber of kertebrae
River Casamance
Weigh’
0
60(
40(
201
t F o r k Isngth ( c m )
2 0
3 0
FigP N*l
Length-weight relationship for Ethmalosa fimbriata from gambian waters.
River
Senegal
-4
/
P e t i t e C ô t e
q
c-
S i n e Saloum
The Gambia
e
Casamance
<
*
I
I
I
I
42.9
43,o
43.1
43,2 V e r t e b r a s
Fig. N*2
Average number of vertebrae and its confidence intervals ( ‘99% )
for different areas in the senegambian region.
TO stwdy ths ~rowth cmd t&e mic~ration o f Ethenaboea fimbrkt2, Bength
frequencies (p ercentc~es) bave been m a d e , ad monthly cgxwped, 0~ scmplaa
Fram olandinqs cAons the F*tlantic cocrst a n d t k e river.
For the :I,tlantic coastal area tho monthby Jlenc_:th frequencies are
prsçented i n -fig. 3 (Lnnexes XI, I I I ) . ? 59 diapams (except Aus, 72)
ht-me CI mode between 20 cm! 25 ml, ‘Imullhr modss at respectively -‘,
II-12 cmd 10 cm cre observed in J~nu2ry, ;!ugwcjt 4d .September, and
!>iger modes arsund 30 cm in 3cnuury, i larch and ;~!~y.
In Sanwary witk thE intrusion of the saline water the popuhotion
of sthmclosa with CI modal hength of 242 cm und an apz of orownd 2 ysars
( Meffsrs, 1973) moves river up to 200 km, they are fo%loved in :arch
ii; ths fish born the previou 9 year during the spriwg and sommer spavn-
inç period, with modrJ1 leï&ks of rcsp. ‘02-14 cm and 15-17 CRT. In .hI.y-
i’kJpst, with the fresh wc?ter QBov, *ho ethmalosa retwrns to *he 56x2
where moda.5. longths are Pound a$ C-9 cm cnd 1 I-12 cm, representin~;
PndividucLz barri that year. The biyyer fiches stoy i n Phe coaçtaI CXGC.
Tho recoolin~~ of the coastal waters in November-December, nnd t5e low
Pempereturs ~i.U, ,
ixxh êan be one of the reasonç for the bhe migration o
f
ths oth;nc;losa river wp wdaere H-te temperature of the ~la$er BS cPircy%
/2içher (JcheVfers, 197?). Mowever iaa spi.tc30f t h e csld water period, t’7e
vah~es of the condition factor X = i’olOQ/k for females, froc %,i-2 cm
sampllvd ehrw- thc3 atkantic toast
du n o t vcry, Phouyh P&~C year (i;:nncx ‘!1.)
cxx! t h e fox! situation does nst appear te, be the principcrl recson for kha
iioipution. The feeding area of the river is rather 1imited and the campe-
Pition for food k4tRi otker srsecies wiJ..l bti higher thon in tho sec. T&a velue:;
of 2< for individucbs from thB river may be for this reaçon .lower than the
ones from thc sec! (înnex VC) .
Ile most important reason for Phe mi0rution
v
up river seems to be thc
repxdwction in the spawning places of the river.
0
Sept 70A6
““;y
II
,,
,4ug 72
1
250
Ns?16
Nov 70
I, ,, “,/(=J-&
,,
Nov 73
,I
0
r
ev
0
Febr. 74
0
25*
0
25.
0
J*
25s
Nt750
0
25,
0
Fig. No3
Monthly length frequencies
(percentages) of Ethmalosa
fimbriata of the coastal area. 25
5
10
15
2 0
25
3 0
3 5 FL(cm)
TANKULAR
B A L I N G H O
K A N I K U N D A
I
N :61
I
2 5
I
N: 132
I
March 7 4
-5
25’
N:127
0
25.
0
25.
N:204
,, ,, ,I ,, ,, I ,p& (, ,,
N: 61
l ?,+A
July 7 4
0
1, -
10
15 20 25 30
-
10
15
20 25 30
-
10 15
20
25
30 F L ( c m
Fig. No4
Monthly length frequencies (percentage) of Ethmalosa fimbriata
--LII--
from different places along the river Ga.mbia.
3.
Fork
tength (cm)
14
16
18
20
Fig. No5
Percentages of grouped maturity stages ( stages IV ,V ,v1,vMII )
of females in different length classes.
û
I
t
c
2
25
1
0
S’o’N’D;J’F’M’A’M’J’J’A’S’
I
1 9 7 0
I
1971
‘Fig. No6
The bimonthly gonadosomatic index(G. S. 1. ) of ethmalosa
( females) from the coastal area of The Gambia.
The birnonthly percentages of females in maturity stage V.
1 - - - -
J
N
D 1974
VI VI-III
J 1974
F’ig. IF”?
Monthly pe reenta~e s of different maturity stage :I; cif
Ethrnalosa firnbriata frwm samples of Che coastal
area and the river Gazmbia .
Two types of variation cre possible, one connected with the heur,
the tidal current, and the lunar period of collecting, the other with
seasonal and geographical variations.
Influence of the hour, tidal current and the IMJCX period of co8Éectina.
O-““-rr-r-rrr--------------- m m w- e - - .a.-am
Collections of pbwkton in Wanjul have been done monthly in IV5
ut the time of new moon, For each night of collecting, the nwmber of
larvae of ethmalosa caught evory two haurs is analysed. Thc results
*uPe expressed in Table 2.
Table 2.0 kdumber of larvae of ethmalosu collected montbly (values are given
per 1000 cubic meter).
Pn anulysis of variante shows that there is no evidence, at the 95
percent of confidence level, for the catch to be dependent on the hour,
Then to see if there is a difference in density according to the
different stages of the moon, in Ane 1975, at a moment of intensive
reproduction, four nights of colhectiona +KW~ been done : at the new
mon (NJ, tDie first quarter (F(Z), th~1 fubl moon (F:!), and the East
quarter (b-i). The results
are expressed in Tubls 3. An wnalysis of thesc
observotions is very difficult due ta the influence on the catch, on
ono hard of the moon period the 1ight and the tidul current, und on the
other han3 the variation of the population itself during the month. 140
evident correlation seems to occur. However, it is probably safer to do
the swrveys os have been done, at the same stage of the moon.
Finally we have taken us a monthPy index of obundance, the totul
cetch of larvae per night divided by th@ total volume of the stroined
water .
Total
296
1292
I
Table 3.0 E:lumber sf larvae 0% etkmalosa csUected every twc hsurs
ut different stages of the moon, (vaLes are given per
1000 cubic meter : ? Fkoodstream ; JEbbstream)
3casonaB and geoqruphical distribution
The rssults are given for alB fish Barvae on a family level in Lnnex
X kV 13. Concsrning the ethmalosc they cxc presented in figures X,3 and 10.
Kt cun be pointed oukthat D
- in *Ianju8 the reproduction 8s ccsntinoua however with 11 minimum
in Deeembor,January cnd February (T4 23°C ; Ti > 35 >DO), und vi-87 perio-
dicaP peaks in i iarch, June-Jw%y ond Bêtober-November (fis. ?) . The
region of the estuary with mixing waters may be a good nursery C;rownd
for the species.
The spriny (2nd summer reproduction periods OCCVF bath in waters
with a high sulinity (S > 35 $0) and with c.101 increwsing water Pempera-
bure (20” to 2EoC)o The automn reproduction takes place after tho
flood of the river tdhen the salinity is Bow(S<25 $0) whiBe the
water temperature is high (X4. i; L 29’C). The llo\\r~ reproduction intensity
during spring ‘ly774 is probably due Po the low temperature in the previaus
months (Cnnex AI).
- I
n
Tankul.as the numbcr of ethma%osc Ilarvco was alwirc~ct lov,
anc.! with the arriva% of the fresh w0ter’Xl.y
- h.gJst, fhey disuppear
completely. The ethmabosa J.wrvwe wsre rsplaced by P!wwe of 7d.Brxw1~
af.zePiuai.
- In Galingho during the first aurveys in February the larvae
of ethmalosa were allready obundant. T&e wuter temperature was ci*
that time 2344°C and the saliinity of the surfacx wuter about 10 $0.
The yeak of abundance occures i n
;:a~, onemonth earlisr than in Lanjul,
in waters with temperature 00 about 2’Ii°C and suHiniPy about 20 $0 (fig. SS).
- In Kanikunda the collection hrns been dono: on$y from ;iuy to 4uBy
t’ t the maximum of saline watsr penetration. ICn June ti!e found the Aarvae
0
N & 0
J
\\
Q + 10
0
V
0
Y
u
il
1
*
8
bcnnchnce I n d e x
Abundance I n d e x
mo-
50
of e$hia9ssa mixed with the pe.llonwla. ht that time the salini$y tras
ab~ve 10 5.0. I n J :ay when $47e ùalinity wa8 lover snfy peQ.snwba larvae
were cawjht.
In tRe coaatall area, QemaEes i n
post-spawning stages first appear5
0nJ.y in Leptember which may indicate a partial q3atk.n~ of the femahs
before that time. The individuah around 12 cm which arrive a$ first
maturation, do no% participate in the spring spawniny period according
to tkeir gonada-somatic index cycle,
T%e reçults concerninq the ethmaBosa population in ahe YainR Louis
region (Scheffers g &. , 672 p Scheffers, 1973) are compared with the
ones of the present paper.
- The len@h-weight reBationship i s
very similar in spite of the differ-
ence in the sea water temperature.
- kjo significant difference exiats between the number of vertebree.
- 20th populations show thé same anadromous migration durins tke intrw-
sion of the seawater in the dry season,
- T&e sex ratio for bath population ia very chse PO 1.
- T&e minimal reproduction Een@h was 17 cm for the femalles and 15 cm
for the mabes, in ZkGnP Louis. F:QT the gambian area however the
minimal reproduction Pen@ 6or the Females was 13 cm.
- fhe spauniny begins in bot&7 areas, i n the r i v e r , and Ilonc~s until the
arriva1 of the QBood. In the estuary and in tke sec the spawning
continues the whoàie year round with a minimum dwrins the cold rneason
(December ta Febrwary) . C:eyond the two spawniny periods observed inSaint
Louis ; one in spring (“p~wsshe printaniére) and one in surnmer (0pou~s6e
estivale”) a thirdono MCE observed for the gambian area in aut~p~
- Spawning takes place in water with sahity between 3.!.-3’: ::;a.
- The temperature whick is -lower in Saint Louis durit-q the winter time
(Gecember SO February) influences the spawning. ,I;, temperature of
21n-23”C 8s necessary for the be$3ning of the first spawnik7~ period
in spring time.
- T&e construction OP dams in bath rivers wiU. influence the migration
anQ spawning pattern of ethmalosa and other sea fish spscie5. The
salini$y bosrndary wi1.l be changed and fixed. An intense ~tudy has
to be done especially before, and aPs0 after the construction of ths
dams J inorder to see the conequencies on the different fisIl populations8
of sea and freshwater species.
1 /
REFEREf*GES
I.n., 1974$i.- ~ttiydroI.o~ical and Popographical çtudies of %he Gambia river .
j ,(jkjRj!‘{ p. , l$I7$,- Tke EisQiery of Gambia - a comprekensive repor%. La+1 -
Rome.
i,OELV T. , ELS;JERT(311SPiL J., 1970.- Observations pr&hinaires sur 31a @Ch@
de E%hmalosa fimbria%a (Gowdich) d e s e a u x c&n&daises et XWI
aspec% biologique, Cons. Interna%. Explor. ;;elc. & e% :+OC.
-
-
Verb . , 159, pp lC&i?g.
RO~sE.%oL A. ,
Mydro~ogie marine cô%ike de ICI ~RBV-
~*~~~~~~~~~
i.1.
T l ,
1 $@v; . -
qw D âle dw cap Ver%. Public. prov. U.R.S.T.0.~ i., ikkiX.
.,CF:W-FERS !Y. J e , 1971 - No%e pr&liminaire sur quelquee aspec%s de la 5ia.!.a-
l
cio de Ethamlosa fimbriata (Gowdich) dans les eauz! siné?am-
biennes . Pro-j ec% i..NW~~~F 264~ 5EN C .R .Q. Uakar-ThiarOye (9) .
qyFFFg-R$
.,. -4 b -
b.j.4 ., 1973.- E%u$e de k%hmaL%oaa fimbriaka (Dowdich) dans la
r6gion sénégambienne. 2kme no%e : L a p ê c h e e% Ic S%OC~ des
efhmaloses dans Ile QBeuve Sén4ga.l. e% %a région de .iuint Lo~ir,.
Docr
I,e.
Provis.
Cen%. &SA~. Océanogr . ilakar-lhitaroye (4?) e
.3X;EFFEfC V.J., 197cl.- Plydrsl.ogical surface observations in iMcau (i’:%k~%$,c
coaç%) and in differenk places aPsn~ %he river éktmbia. Oc%ober
1972 - :hi 1975. ProjecP UHDP/FA~ U..I 72/006 Fisheries Division.
v-
Canjvk. Fisheries publication (12).
:;cgEFFEp
1972.- E%ude de E%hmal,ose fi.mbrj.a%a
4 i v
\\ .J l , fJ.MYdD
& l , afgxr<
e: , ,
(Gowdich) dans la r@ion çh4gambienne. 1 &re no%8 p, ConPribu-
Pion ,à aa connairsancs de la reprodwe%ian dans 9s fl~ve
SehQgall et Ba région de :Sain% huis. Lpoc e ;C. Provo Cen% ,F<ech,
Ochanogr. Dakar-Pkiaroye ($4).
- - - -
XHEFFERS Y
h”. J
., JI&x:; l!k, , 1976 a - h’Jydrologica1 surface observations in Sakau
o n the Sod~ern atkantic coas%, snd i n kmjwk o n the estuary o f
Phe river Gambia dwring 1975. ProjecP LhKV/FACI GA d 73006
Fiskeries. Division. GanjuJ.. disheries publ.icatG (í%).
-
-I_-
-------
nuaber
mean
number
me ;7n
number
me :3n
nimbe r
of
weight
of
weight
O f
weight
13 f
Fishes
------T
fiches
fishes
fishes
T--“
-
-
"---
;:
2
15
i
l524 19
33
19
2
35
52
33
:2
l
3:
30
31
$0
3
51
65
2
53
5
53
73
53
21
S6
63
$7
53
3
85
74
81
22
82
32
$2
24
110
51
103
75
106
77
125
212
127
2c9
126
186
14.5
316
144
266
170
221
163
326
197
125
138
214
220
47
211
64
242
13
241
16
267
2
281
5
302
2
327
1
284.
351
1
395
2
399 1
1
412
9
425
2
482
1
;g
s7
495
7
562
- m m " -
. - - - - . . . - - - .
-
- .--...e^"-
Year
-
:Ionth
I
--_Cm..--.-
1970
IX
1971
XI
i
1
II
III V
VII
1 2:
I.w-.-..--. .-.--
6
7
0.9
314
9
702
10
6.1
i
I l
3.1
12
0.3
cc 1
13
X3
14
1.5
15
5:’
: 2
11.1
16
2.1
3.8
17
0.1
1*4
0.4
0.1
0.3
1.4
0.6
18
005
13.5
Ce$
5.1
2.7
0.3
8.0
9.C
6*7
7.6
13
23.7
25.2
2369
9e2 27.9
31.6
20
27.1
33.6
34.0
IF.5
31.4 23.3 33.8
33.2
21
24.2
10.6
24.0
39.3
a.7 39.3 21.1
22
13.7
17.5
1.7
19.2
9.1
23
3.3
0.2
l*P
2.0
5.5
@*5
24
0.1
0.4
1.5
25
0‘1
0.1
0.2
PL
/
2U
0.3
27
28
0,6
90
0.9
;;
o.co
0.2
1.6
31
0.5
1.2
32
0.5 0.7
33
0.1
0.7
34
j
0.1
35
i
L
- .T-.--
1
70,cf
.--
7 .
__ 3. sixs
1000
242c
'475
326
2109
978
-,
750
Arme:s: III : é:on-thly length distx5butions (percentCages)
Of f?tiUïl~d.OSâ
from the ooastal area of The
Gmbia.
Konth
I
1972
VIII
5
6
0.9
1.8
;
9
::5"
10
12.5
II
28.6
12
29.5
13
17.0
14,
O,P
Î5
15
0.2
17
0:7
2.2
c*7
18
0.4
0.3
5.8
19
:::
2.2
1.1
2.5 11.7
:::
20
16 * ci v
17.1
~Ca.6
16.9
10.6 13.9
7*7
21
264
35.2
34.. 1
43.8
43.8 m.3
15.p
22
27.7
25.8
32.3
28.9
254 23.0
33.8
23
13.1
11.0
9.7
8, 6
7.9 16.3
26.8
24
3.5
LJ l
" 5
4.5
207
0.3
0.e 5.6
25
1.4
0.7
0,8
2 6
0.G
0.2
27
2c
z:
;
i'4
35
c h
L
Y
GI
Y
FQ
w
I
----w--L--
.
..-
----
-.
gnriex V p,. Dimonthly ccnditjon factor (X)
o f cthualosa 2uring 1370-1971
---LcI_-
----__--
.
PQV.
JCBl,
i’ arch
PaJ
July
sept.
,
qc
t
2.0 2,
2.0
1.9
2.0
2.1
1.3
2.1
I
19
1
2ao
: .p
2.0
2.c
2.1
2.0
!
20
1*9
2.0
2.0
2*0
2.0
2.0
2.0
1
21
1
1.9
2.0
2.P
2.0
2.0
2.0
2.0
i
22
l
1.9
1.9
2.0
2.0
1.3
A*9
2.0
I
*Liver Gambia (malcs and îwales)
1
_C.--
Ii
2
l
l
1.8
1.7
2.0
1.7
1.7
1.6
le6
1.7
1.7 1.8
t
21
1*7
1.9
1.7
1.7
1.8
22
1
1.8
1.9
1.7
1*7
1.7
9
i
1
23. Condition factor (K) for each cm class
of ethzalosa from thc river Gambia and
tho Coastal aroa
1 Lengti c l a s s t River Gambia 1 CoaaLal arca 1i
î
-----A
1
10
1.75
!
1.64
11
1.58
I
i
12
1.64
I&l
1.59
I
1.79
:34
1.57
5.84
15
1.6-1
1.69
16
1.74
~85
17
1.72
2.o3
18
1.77
2.01
19
1.73
11.97
20
1.72
1095
21
1.73
1.97
22
1.75
1694
23
1.64
1 .y
24
1.71
1 .88
25
1.74
1 .p1
26
1.51
2*02
27
1.90
1.92
28
1.78
1.8L$
29
1.83
1.9
3Q
1077
31
leso
--
-...
30. of Fishcs
377
/
--.-- --.-----....--
CO zls-k a1 arca
River G.mbia
po of fishes
!
/
1j
l
322
I
39.4
60.6
103
45.5
,
400
j
1$-+
.L2
115.3
37.0
290
26.9
12,l
6:.c
3P
‘?*Z
44.7
265
43.8
lC.1
3S.l
24;
!
4
L&,.
l
55.8
539
47*7
52~3
142
l
58.5
41.5
715
53*9
28.7
17.4
t
gnn3x VII : 1:aturity s t a g e s (y$ p3r lengtki
Glass o f ethmalosa (fez~ales) f r o m
Gambian waters dcrin;; -j?"O-197<,
GI?OLpZd
I
?i@ c of
ix
III
IV
V
vI*VI-III
IV,V,VI
fishos
VI-III
e-
.- 1 -cm
4
1
100 .o
32
i
1ZG.O
57
SS.6
.-0 . 4
/:7
‘s.
Y3.5
6.4
47
72,s
27.2
i
SI
32.3
2.0
2.9
2*9
!
102
1
1
15
15
46
i
Em:
~ 17
59.3
io.5
4.7
4.7
18
!
0.8
3:1
57.3
22.9
16.7
16.7
96
18
19
37*7
2:
36.2
2*3
2,3
40.8
130
10.7
71.5
4.8
4.8
53.3 272
20
5.2
17:2
61.7
11.5
77.6
3s.4
21
299
16.1
65.2
12.1
3::
Si.0
454
-
-
Eo. of
fis5he.F
-.-WV.-
223
345
1007
159
58
7
22.$
2"182
&lnex : VIII n : Limonthly gonade-soncikic index
(G.S,I.) of ethmalosa from Gambien
wztess in 1970-1971.
Nov.
-
-
.--
2.7
5.3
5.4
507
3.5
3.l
1.7
2.4.
3.7
3.9
3.0
2.3
-----
---
-w..--
1.8
3.2
2.2
1.8
1.1
1 .@!
1.5
1.6
.--
“,W a~-
B : Bimonthly G.S,I. per lcngth Glass
--.
c-
18
21
2 2
sept. 1970
2.3
2.1
2.8
Hov.
1.1
3.2
3.0
Jnn. 1971
143
5.0
6.0
TInrch
2”5
6.1
G.0
;: ‘ay
4.3
6.1
5.6
JdY
2*9
3.8
3.6
Sept.
A*9
3.5
3.0
1:arch 1971
3.3
5+2
1Fay
1.8
3.5
July
2*9
2*0
.--
gnnex 1;: : i&nthly matLliAty stages distribu-tions
(7;) O f fC%dL
-0 of ethalosa from 18 cm
Corwtnl nrea-*----y_
Stages
II
III
IU
u
VI
No. of Fishes
VI-III
I
-
-
-
sept. 1970
1
14
53
168
1
Nov.
10
27
60
4
272
î
Jan. 1971
14.2
I
4
9
62
25
rarch
4
8
65
22
190
i:ay
1
2
65
33
123
July
2
91
6
82
Se.l?L
6
24
61
Y
136
Kov. 1973
15
40
45
124
DCC.
16
35
39
10
3-l
JE& 1974
3
31
56
32
Feb.
1
2G
73
t
I
July
12
88
sagFt*
38
58
5
Hov.
10
42
41
7
DCC.
II
Go
25
1 Jan. 1975
37
63
i
River Gambia
stages
II
III
_ !
VI
U
VI
fio, of Fishcs
I @ch
1971
12
33
49
7
43
i-
7 . .
i Y
10
23
58
10
40
July
39
61
23
I
February 1974
II
87
2
54
1;arch
2
21
28
4?
47
I'-ay
23
20
47
47
23
fl
.jnncx :: A : Yonthly i;bund,7noc of fish lûrvae in 1974.
(values are expressed by thz total catch of
the night, itivi.ded by tho total volur.le o f
na-ter filter(A i n :GO o f cubi.c mvters)
J J
A
L:an*jul
Cliq~?i.dae Simalosa
I
123 1 26 18
Ilishn
I
&CdCS
Ijlxinidao
(J;;i-~,;gid:1e
011
(
Cyb .i id a e
Cww,~losr;idae
c
-
h
012
3x~pidilc
[
Ga'biidae
1
Iloni~hwqhidec
012
:‘iq:ilidae
1
fcmacasyidne
Sciaenidae
i
0'8
I
6 2
SO 1 e id ae
011
01
Sparidao
I
Syngnathidae
Tctraodont idae
Tankul Q.r
Clupcidao ?Ychmalosc?
Of5
2 10,4
Ilisha
011 !0,8
Pellonuln
011
l
&~Oc&3
Cyrw.:.lozsidae
UloFidne
Gobiidoe
0,4
i
TTc!,lirlz~ullphid,?e
: ryilidae
011
Sci :33rA:kte
S~rqn&kdtae
012
49
$1
)ll
)ll
011
7
j
i
i
Pcllonulr:
139
!:y no:; 10 :j :; i<: ae
96
Gabiidac
6
011
2
Scianidae
3yngnathidae
011
0'3
&ux!x ;C. B. j!onthly abunda.m~ of fish larvac in 4375.
(values are expressed by the total catch of tk
night, divided by thc total volui~z of wa-L:x fil-:emd
in 100 of c~M0 netcrs),
-.L
]LT
J
A
-
-
'987
$3,7
1545
1/,2
113
116
6 8 4.
9,P
OJ
O?l
023
0,4
093
58
091
os3
c,3 l,2
0,s
O,l
I
f49
?,l 10,Q
23,5
011
196
0,q. 0,g
011
036
62
7,3
2w
013
0 , 4.
031
011
* Unablc to se~~~x-&c thc y0u.ng lnrvac of Polyilc,zic!ae a,nd
Sciaenidac, WC havc .groupod the<i\\ under this rime.
-
-...
-.-.--_-
CG!%
OI f.j
,~-
.!
i
i i
--
03
2
C’J
0
3rd note : ME BIOLCGY OF THE ETHHALOM
IN THE Gt4d3IAN HATERS
W.J * XHEFFERS ( 1)
F, cw:w
(2)
(1) Fisheries biologist. Pro ject FAO WP GkW S2,&06
“Development of Inshore Fishery”, Fisheries Division,
Banjul, The Gambia.
(2) Océanographe biologiste de l’ORSTCW3, Centre de
Recherches Océanocqraphiques de Dakar-Thiaroye,Jénégal
CENTRE DE RECHERCHES ~E~~P~I~~~~
DE DAKAR-THIAROYE
DfXuE~~RIT XIENTIFI~~ No 5 9
AVRIL 1976
?:bStZWCt - Fh5sumcs
1. Introduction
2 l &lydroPogy
3. Fiaterial and msthods
4. Length - zeight relationskip
5. Vertebral countinys
6. Catch composition and migration
7. Reproduction
7.1
Sexratio
7.2 Length of first reproduction
7.3 Spawning period and ores
- Limonthly variation of the gonado-somatic index
- J%e gonad breeding cycle
- iJont&ly percentages of fema%es in matwrity stage V
- Ckcurence and abundance of planktonic %arvae
- Conclusion on the spawning period and area
2, Ccnclusions and comparaison vith the Ethmabosu-“fimbriata
population in Phe Saint Louis region.
References.
2
:.dat&t compositions bave $een analysed br t6’1e gowth and t6w mi~rration
of ePkmu~osa
l
<’ compasison is made between thé resadts of the present study and
t&e one. obtained f r o n t the ‘ikint Loui.23 rec-$.on.
bo composition des captures est ana.llysSe pour &Pudier la croisscnce et Ii
~k~r~ti0n des poissons.
In the sonegambian repion, landings by the canoe bisherioa, of
cthmalof3a - Ethmalosa fimbriata - are very important and represunt
yearly around 25,303 t o n s . fhe biggestpart of the catch is for
Cresh conwmption the rest is 5moked or dried.
TO ovaBwczte khis important coostal pelagic stock and to skwdy
i=ts bicblogy, landinqa and samples bave been anally~ed and planktaw
*:~rveys; effscted, in different centers in 52negali and Gambia. :orràE
of Phe mwlts have ahsady been published (.%hebffers Cp &. , 1972 ;
'~~@bm!kS, 19?%, 15z3, 1974) otherq -are in preparation.
3X.s article deals vith bio9ocjy and reproduction of Phe ethrrra,Bssa
from the gambian waters.
[,ydrologicaI.By the yaïnbian 5daters 9oLLow the same pattern ~3s ther
cenegaless waters und accordiny to tkmxignol and P,boussouun ( I%X)
three hydrological seaaons cari brz distinguished.
The coSd and saline water season “wpwel.lin~ waters” : December - 1.pri.l
The warm ad saline water acason “trapicfll waters” 0 E ky - Ikptember
moved by the “guinean waters”. (T :> 24°C
;
:,j <(“s:.. /QO ) coming fror2 the
5owPh. In idovember the coolin of tho c!cter kx3$.ns with ths wrrival
of the trade winds and the coostol upwel.%inc and in Gecsmber the
“cjwineun waters“ ure pwshed off-shore and to the South.
i Sumber of kertebrae
River Casamance
Weigh’
0
60(
40(
201
t F o r k Isngth ( c m )
2 0
3 0
FigP N*l
Length-weight relationship for Ethmalosa fimbriata from gambian waters.
River
Senegal
-4
/
P e t i t e C ô t e
q
c-
S i n e Saloum
The Gambia
e
Casamance
<
*
I
I
I
I
42.9
43,o
43.1
43,2 V e r t e b r a s
Fig. N*2
Average number of vertebrae and its confidence intervals ( ‘99% )
for different areas in the senegambian region.
TO stwdy ths ~rowth cmd t&e mic~ration o f Ethenaboea fimbrkt2, Bength
frequencies (p ercentc~es) bave been m a d e , ad monthly cgxwped, 0~ scmplaa
Fram olandinqs cAons the F*tlantic cocrst a n d t k e river.
For the :I,tlantic coastal area tho monthby Jlenc_:th frequencies are
prsçented i n -fig. 3 (Lnnexes XI, I I I ) . ? 59 diapams (except Aus, 72)
ht-me CI mode between 20 cm! 25 ml, ‘Imullhr modss at respectively -‘,
II-12 cmd 10 cm cre observed in J~nu2ry, ;!ugwcjt 4d .September, and
!>iger modes arsund 30 cm in 3cnuury, i larch and ;~!~y.
In Sanwary witk thE intrusion of the saline water the popuhotion
of sthmclosa with CI modal hength of 242 cm und an apz of orownd 2 ysars
( Meffsrs, 1973) moves river up to 200 km, they are fo%loved in :arch
ii; ths fish born the previou 9 year during the spriwg and sommer spavn-
inç period, with modrJ1 leï&ks of rcsp. ‘02-14 cm and 15-17 CRT. In .hI.y-
i’kJpst, with the fresh wc?ter QBov, *ho ethmalosa retwrns to *he 56x2
where moda.5. longths are Pound a$ C-9 cm cnd 1 I-12 cm, representin~;
PndividucLz barri that year. The biyyer fiches stoy i n Phe coaçtaI CXGC.
Tho recoolin~~ of the coastal waters in November-December, nnd t5e low
Pempereturs ~i.U, ,
ixxh êan be one of the reasonç for the bhe migration o
f
ths oth;nc;losa river wp wdaere H-te temperature of the ~la$er BS cPircy%
/2içher (JcheVfers, 197?). Mowever iaa spi.tc30f t h e csld water period, t’7e
vah~es of the condition factor X = i’olOQ/k for females, froc %,i-2 cm
sampllvd ehrw- thc3 atkantic toast
du n o t vcry, Phouyh P&~C year (i;:nncx ‘!1.)
cxx! t h e fox! situation does nst appear te, be the principcrl recson for kha
iioipution. The feeding area of the river is rather 1imited and the campe-
Pition for food k4tRi otker srsecies wiJ..l bti higher thon in tho sec. T&a velue:;
of 2< for individucbs from thB river may be for this reaçon .lower than the
ones from thc sec! (înnex VC) .
Ile most important reason for Phe mi0rution
v
up river seems to be thc
repxdwction in the spawning places of the river.
0
Sept 70A6
““;y
II
,,
,4ug 72
1
250
Ns?16
Nov 70
I, ,, “,/(=J-&
,,
Nov 73
,I
0
r
ev
0
Febr. 74
0
25*
0
25.
0
J*
25s
Nt750
0
25,
0
Fig. No3
Monthly length frequencies
(percentages) of Ethmalosa
fimbriata of the coastal area. 25
5
10
15
2 0
25
3 0
3 5 FL(cm)
TANKULAR
B A L I N G H O
K A N I K U N D A
I
N :61
I
2 5
I
N: 132
I
March 7 4
-5
25’
N:127
0
25.
0
25.
N:204
,, ,, ,I ,, ,, I ,p& (, ,,
N: 61
l ?,+A
July 7 4
0
1, -
10
15 20 25 30
-
10
15
20 25 30
-
10 15
20
25
30 F L ( c m
Fig. No4
Monthly length frequencies (percentage) of Ethmalosa fimbriata
--LII--
from different places along the river Ga.mbia.
3.
Fork
tength (cm)
14
16
18
20
Fig. No5
Percentages of grouped maturity stages ( stages IV ,V ,v1,vMII )
of females in different length classes.
û
I
t
c
2
25
1
0
S’o’N’D;J’F’M’A’M’J’J’A’S’
I
1 9 7 0
I
1971
‘Fig. No6
The bimonthly gonadosomatic index(G. S. 1. ) of ethmalosa
( females) from the coastal area of The Gambia.
The birnonthly percentages of females in maturity stage V.
1 - - - -
J
N
D 1974
VI VI-III
J 1974
F’ig. IF”?
Monthly pe reenta~e s of different maturity stage :I; cif
Ethrnalosa firnbriata frwm samples of Che coastal
area and the river Gazmbia .
Two types of variation cre possible, one connected with the heur,
the tidal current, and the lunar period of collecting, the other with
seasonal and geographical variations.
Influence of the hour, tidal current and the IMJCX period of co8Éectina.
O-““-rr-r-rrr--------------- m m w- e - - .a.-am
Collections of pbwkton in Wanjul have been done monthly in IV5
ut the time of new moon, For each night of collecting, the nwmber of
larvae of ethmalosa caught evory two haurs is analysed. Thc results
*uPe expressed in Table 2.
Table 2.0 kdumber of larvae of ethmalosu collected montbly (values are given
per 1000 cubic meter).
Pn anulysis of variante shows that there is no evidence, at the 95
percent of confidence level, for the catch to be dependent on the hour,
Then to see if there is a difference in density according to the
different stages of the moon, in Ane 1975, at a moment of intensive
reproduction, four nights of colhectiona +KW~ been done : at the new
mon (NJ, tDie first quarter (F(Z), th~1 fubl moon (F:!), and the East
quarter (b-i). The results
are expressed in Tubls 3. An wnalysis of thesc
observotions is very difficult due ta the influence on the catch, on
ono hard of the moon period the 1ight and the tidul current, und on the
other han3 the variation of the population itself during the month. 140
evident correlation seems to occur. However, it is probably safer to do
the swrveys os have been done, at the same stage of the moon.
Finally we have taken us a monthPy index of obundance, the totul
cetch of larvae per night divided by th@ total volume of the stroined
water .
Total
296
1292
I
Table 3.0 E:lumber sf larvae 0% etkmalosa csUected every twc hsurs
ut different stages of the moon, (vaLes are given per
1000 cubic meter : ? Fkoodstream ; JEbbstream)
3casonaB and geoqruphical distribution
The rssults are given for alB fish Barvae on a family level in Lnnex
X kV 13. Concsrning the ethmalosc they cxc presented in figures X,3 and 10.
Kt cun be pointed oukthat D
- in *Ianju8 the reproduction 8s ccsntinoua however with 11 minimum
in Deeembor,January cnd February (T4 23°C ; Ti > 35 >DO), und vi-87 perio-
dicaP peaks in i iarch, June-Jw%y ond Bêtober-November (fis. ?) . The
region of the estuary with mixing waters may be a good nursery C;rownd
for the species.
The spriny (2nd summer reproduction periods OCCVF bath in waters
with a high sulinity (S > 35 $0) and with c.101 increwsing water Pempera-
bure (20” to 2EoC)o The automn reproduction takes place after tho
flood of the river tdhen the salinity is Bow(S<25 $0) whiBe the
water temperature is high (X4. i; L 29’C). The llo\\r~ reproduction intensity
during spring ‘ly774 is probably due Po the low temperature in the previaus
months (Cnnex AI).
- I
n
Tankul.as the numbcr of ethma%osc Ilarvco was alwirc~ct lov,
anc.! with the arriva% of the fresh w0ter’Xl.y
- h.gJst, fhey disuppear
completely. The ethmabosa J.wrvwe wsre rsplaced by P!wwe of 7d.Brxw1~
af.zePiuai.
- In Galingho during the first aurveys in February the larvae
of ethmalosa were allready obundant. T&e wuter temperature was ci*
that time 2344°C and the saliinity of the surfacx wuter about 10 $0.
The yeak of abundance occures i n
;:a~, onemonth earlisr than in Lanjul,
in waters with temperature 00 about 2’Ii°C and suHiniPy about 20 $0 (fig. SS).
- In Kanikunda the collection hrns been dono: on$y from ;iuy to 4uBy
t’ t the maximum of saline watsr penetration. ICn June ti!e found the Aarvae
0
N & 0
J
\\
Q + 10
0
V
0
Y
u
il
1
*
8
bcnnchnce I n d e x
Abundance I n d e x
mo-
50
of e$hia9ssa mixed with the pe.llonwla. ht that time the salini$y tras
ab~ve 10 5.0. I n J :ay when $47e ùalinity wa8 lover snfy peQ.snwba larvae
were cawjht.
In tRe coaatall area, QemaEes i n
post-spawning stages first appear5
0nJ.y in Leptember which may indicate a partial q3atk.n~ of the femahs
before that time. The individuah around 12 cm which arrive a$ first
maturation, do no% participate in the spring spawniny period according
to tkeir gonada-somatic index cycle,
T%e reçults concerninq the ethmaBosa population in ahe YainR Louis
region (Scheffers g &. , 672 p Scheffers, 1973) are compared with the
ones of the present paper.
- The len@h-weight reBationship i s
very similar in spite of the differ-
ence in the sea water temperature.
- kjo significant difference exiats between the number of vertebree.
- 20th populations show thé same anadromous migration durins tke intrw-
sion of the seawater in the dry season,
- T&e sex ratio for bath population ia very chse PO 1.
- T&e minimal reproduction Een@h was 17 cm for the femalles and 15 cm
for the mabes, in ZkGnP Louis. F:QT the gambian area however the
minimal reproduction Pen@ 6or the Females was 13 cm.
- fhe spauniny begins in bot&7 areas, i n the r i v e r , and Ilonc~s until the
arriva1 of the QBood. In the estuary and in tke sec the spawning
continues the whoàie year round with a minimum dwrins the cold rneason
(December ta Febrwary) . C:eyond the two spawniny periods observed inSaint
Louis ; one in spring (“p~wsshe printaniére) and one in surnmer (0pou~s6e
estivale”) a thirdono MCE observed for the gambian area in aut~p~
- Spawning takes place in water with sahity between 3.!.-3’: ::;a.
- The temperature whick is -lower in Saint Louis durit-q the winter time
(Gecember SO February) influences the spawning. ,I;, temperature of
21n-23”C 8s necessary for the be$3ning of the first spawnik7~ period
in spring time.
- T&e construction OP dams in bath rivers wiU. influence the migration
anQ spawning pattern of ethmalosa and other sea fish spscie5. The
salini$y bosrndary wi1.l be changed and fixed. An intense ~tudy has
to be done especially before, and aPs0 after the construction of ths
dams J inorder to see the conequencies on the different fisIl populations8
of sea and freshwater species.
1 /
REFEREf*GES
I.n., 1974$i.- ~ttiydroI.o~ical and Popographical çtudies of %he Gambia river .
j ,(jkjRj!‘{ p. , l$I7$,- Tke EisQiery of Gambia - a comprekensive repor%. La+1 -
Rome.
i,OELV T. , ELS;JERT(311SPiL J., 1970.- Observations pr&hinaires sur 31a @Ch@
de E%hmalosa fimbria%a (Gowdich) d e s e a u x c&n&daises et XWI
aspec% biologique, Cons. Interna%. Explor. ;;elc. & e% :+OC.
-
-
Verb . , 159, pp lC&i?g.
RO~sE.%oL A. ,
Mydro~ogie marine cô%ike de ICI ~RBV-
~*~~~~~~~~~
i.1.
T l ,
1 $@v; . -
qw D âle dw cap Ver%. Public. prov. U.R.S.T.0.~ i., ikkiX.
.,CF:W-FERS !Y. J e , 1971 - No%e pr&liminaire sur quelquee aspec%s de la 5ia.!.a-
l
cio de Ethamlosa fimbriata (Gowdich) dans les eauz! siné?am-
biennes . Pro-j ec% i..NW~~~F 264~ 5EN C .R .Q. Uakar-ThiarOye (9) .
qyFFFg-R$
.,. -4 b -
b.j.4 ., 1973.- E%u$e de k%hmaL%oaa fimbriaka (Dowdich) dans la
r6gion sénégambienne. 2kme no%e : L a p ê c h e e% Ic S%OC~ des
efhmaloses dans Ile QBeuve Sén4ga.l. e% %a région de .iuint Lo~ir,.
Docr
I,e.
Provis.
Cen%. &SA~. Océanogr . ilakar-lhitaroye (4?) e
.3X;EFFEfC V.J., 197cl.- Plydrsl.ogical surface observations in iMcau (i’:%k~%$,c
coaç%) and in differenk places aPsn~ %he river éktmbia. Oc%ober
1972 - :hi 1975. ProjecP UHDP/FA~ U..I 72/006 Fisheries Division.
v-
Canjvk. Fisheries publication (12).
:;cgEFFEp
1972.- E%ude de E%hmal,ose fi.mbrj.a%a
4 i v
\\ .J l , fJ.MYdD
& l , afgxr<
e: , ,
(Gowdich) dans la r@ion çh4gambienne. 1 &re no%8 p, ConPribu-
Pion ,à aa connairsancs de la reprodwe%ian dans 9s fl~ve
SehQgall et Ba région de :Sain% huis. Lpoc e ;C. Provo Cen% ,F<ech,
Ochanogr. Dakar-Pkiaroye ($4).
- - - -
XHEFFERS Y
h”. J
., JI&x:; l!k, , 1976 a - h’Jydrologica1 surface observations in Sakau
o n the Sod~ern atkantic coas%, snd i n kmjwk o n the estuary o f
Phe river Gambia dwring 1975. ProjecP LhKV/FACI GA d 73006
Fiskeries. Division. GanjuJ.. disheries publ.icatG (í%).
-
-I_-
-------
nuaber
mean
number
me ;7n
number
me :3n
nimbe r
of
weight
of
weight
O f
weight
13 f
Fishes
------T
fiches
fishes
fishes
T--“
-
-
"---
;:
2
15
i
l524 19
33
19
2
35
52
33
:2
l
3:
30
31
$0
3
51
65
2
53
5
53
73
53
21
S6
63
$7
53
3
85
74
81
22
82
32
$2
24
110
51
103
75
106
77
125
212
127
2c9
126
186
14.5
316
144
266
170
221
163
326
197
125
138
214
220
47
211
64
242
13
241
16
267
2
281
5
302
2
327
1
284.
351
1
395
2
399 1
1
412
9
425
2
482
1
;g
s7
495
7
562
- m m " -
. - - - - . . . - - - .
-
- .--...e^"-
Year
-
:Ionth
I
--_Cm..--.-
1970
IX
1971
XI
i
1
II
III V
VII
1 2:
I.w-.-..--. .-.--
6
7
0.9
314
9
702
10
6.1
i
I l
3.1
12
0.3
cc 1
13
X3
14
1.5
15
5:’
: 2
11.1
16
2.1
3.8
17
0.1
1*4
0.4
0.1
0.3
1.4
0.6
18
005
13.5
Ce$
5.1
2.7
0.3
8.0
9.C
6*7
7.6
13
23.7
25.2
2369
9e2 27.9
31.6
20
27.1
33.6
34.0
IF.5
31.4 23.3 33.8
33.2
21
24.2
10.6
24.0
39.3
a.7 39.3 21.1
22
13.7
17.5
1.7
19.2
9.1
23
3.3
0.2
l*P
2.0
5.5
@*5
24
0.1
0.4
1.5
25
0‘1
0.1
0.2
PL
/
2U
0.3
27
28
0,6
90
0.9
;;
o.co
0.2
1.6
31
0.5
1.2
32
0.5 0.7
33
0.1
0.7
34
j
0.1
35
i
L
- .T-.--
1
70,cf
.--
7 .
__ 3. sixs
1000
242c
'475
326
2109
978
-,
750
Arme:s: III : é:on-thly length distx5butions (percentCages)
Of f?tiUïl~d.OSâ
from the ooastal area of The
Gmbia.
Konth
I
1972
VIII
5
6
0.9
1.8
;
9
::5"
10
12.5
II
28.6
12
29.5
13
17.0
14,
O,P
Î5
15
0.2
17
0:7
2.2
c*7
18
0.4
0.3
5.8
19
:::
2.2
1.1
2.5 11.7
:::
20
16 * ci v
17.1
~Ca.6
16.9
10.6 13.9
7*7
21
264
35.2
34.. 1
43.8
43.8 m.3
15.p
22
27.7
25.8
32.3
28.9
254 23.0
33.8
23
13.1
11.0
9.7
8, 6
7.9 16.3
26.8
24
3.5
LJ l
" 5
4.5
207
0.3
0.e 5.6
25
1.4
0.7
0,8
2 6
0.G
0.2
27
2c
z:
;
i'4
35
c h
L
Y
GI
Y
FQ
w
I
----w--L--
.
..-
----
-.
gnriex V p,. Dimonthly ccnditjon factor (X)
o f cthualosa 2uring 1370-1971
---LcI_-
----__--
.
PQV.
JCBl,
i’ arch
PaJ
July
sept.
,
qc
t
2.0 2,
2.0
1.9
2.0
2.1
1.3
2.1
I
19
1
2ao
: .p
2.0
2.c
2.1
2.0
!
20
1*9
2.0
2.0
2*0
2.0
2.0
2.0
1
21
1
1.9
2.0
2.P
2.0
2.0
2.0
2.0
i
22
l
1.9
1.9
2.0
2.0
1.3
A*9
2.0
I
*Liver Gambia (malcs and îwales)
1
_C.--
Ii
2
l
l
1.8
1.7
2.0
1.7
1.7
1.6
le6
1.7
1.7 1.8
t
21
1*7
1.9
1.7
1.7
1.8
22
1
1.8
1.9
1.7
1*7
1.7
9
i
1
23. Condition factor (K) for each cm class
of ethzalosa from thc river Gambia and
tho Coastal aroa
1 Lengti c l a s s t River Gambia 1 CoaaLal arca 1i
î
-----A
1
10
1.75
!
1.64
11
1.58
I
i
12
1.64
I&l
1.59
I
1.79
:34
1.57
5.84
15
1.6-1
1.69
16
1.74
~85
17
1.72
2.o3
18
1.77
2.01
19
1.73
11.97
20
1.72
1095
21
1.73
1.97
22
1.75
1694
23
1.64
1 .y
24
1.71
1 .88
25
1.74
1 .p1
26
1.51
2*02
27
1.90
1.92
28
1.78
1.8L$
29
1.83
1.9
3Q
1077
31
leso
--
-...
30. of Fishcs
377
/
--.-- --.-----....--
CO zls-k a1 arca
River G.mbia
po of fishes
!
/
1j
l
322
I
39.4
60.6
103
45.5
,
400
j
1$-+
.L2
115.3
37.0
290
26.9
12,l
6:.c
3P
‘?*Z
44.7
265
43.8
lC.1
3S.l
24;
!
4
L&,.
l
55.8
539
47*7
52~3
142
l
58.5
41.5
715
53*9
28.7
17.4
t
gnn3x VII : 1:aturity s t a g e s (y$ p3r lengtki
Glass o f ethmalosa (fez~ales) f r o m
Gambian waters dcrin;; -j?"O-197<,
GI?OLpZd
I
?i@ c of
ix
III
IV
V
vI*VI-III
IV,V,VI
fishos
VI-III
e-
.- 1 -cm
4
1
100 .o
32
i
1ZG.O
57
SS.6
.-0 . 4
/:7
‘s.
Y3.5
6.4
47
72,s
27.2
i
SI
32.3
2.0
2.9
2*9
!
102
1
1
15
15
46
i
Em:
~ 17
59.3
io.5
4.7
4.7
18
!
0.8
3:1
57.3
22.9
16.7
16.7
96
18
19
37*7
2:
36.2
2*3
2,3
40.8
130
10.7
71.5
4.8
4.8
53.3 272
20
5.2
17:2
61.7
11.5
77.6
3s.4
21
299
16.1
65.2
12.1
3::
Si.0
454
-
-
Eo. of
fis5he.F
-.-WV.-
223
345
1007
159
58
7
22.$
2"182
&lnex : VIII n : Limonthly gonade-soncikic index
(G.S,I.) of ethmalosa from Gambien
wztess in 1970-1971.
Nov.
-
-
.--
2.7
5.3
5.4
507
3.5
3.l
1.7
2.4.
3.7
3.9
3.0
2.3
-----
---
-w..--
1.8
3.2
2.2
1.8
1.1
1 .@!
1.5
1.6
.--
“,W a~-
B : Bimonthly G.S,I. per lcngth Glass
--.
c-
18
21
2 2
sept. 1970
2.3
2.1
2.8
Hov.
1.1
3.2
3.0
Jnn. 1971
143
5.0
6.0
TInrch
2”5
6.1
G.0
;: ‘ay
4.3
6.1
5.6
JdY
2*9
3.8
3.6
Sept.
A*9
3.5
3.0
1:arch 1971
3.3
5+2
1Fay
1.8
3.5
July
2*9
2*0
.--
gnnex 1;: : i&nthly matLliAty stages distribu-tions
(7;) O f fC%dL
-0 of ethalosa from 18 cm
Corwtnl nrea-*----y_
Stages
II
III
IU
u
VI
No. of Fishes
VI-III
I
-
-
-
sept. 1970
1
14
53
168
1
Nov.
10
27
60
4
272
î
Jan. 1971
14.2
I
4
9
62
25
rarch
4
8
65
22
190
i:ay
1
2
65
33
123
July
2
91
6
82
Se.l?L
6
24
61
Y
136
Kov. 1973
15
40
45
124
DCC.
16
35
39
10
3-l
JE& 1974
3
31
56
32
Feb.
1
2G
73
t
I
July
12
88
sagFt*
38
58
5
Hov.
10
42
41
7
DCC.
II
Go
25
1 Jan. 1975
37
63
i
River Gambia
stages
II
III
_ !
VI
U
VI
fio, of Fishcs
I @ch
1971
12
33
49
7
43
i-
7 . .
i Y
10
23
58
10
40
July
39
61
23
I
February 1974
II
87
2
54
1;arch
2
21
28
4?
47
I'-ay
23
20
47
47
23
fl
.jnncx :: A : Yonthly i;bund,7noc of fish lûrvae in 1974.
(values are expressed by thz total catch of
the night, itivi.ded by tho total volur.le o f
na-ter filter(A i n :GO o f cubi.c mvters)
J J
A
L:an*jul
Cliq~?i.dae Simalosa
I
123 1 26 18
Ilishn
I
&CdCS
Ijlxinidao
(J;;i-~,;gid:1e
011
(
Cyb .i id a e
Cww,~losr;idae
c
-
h
012
3x~pidilc
[
Ga'biidae
1
Iloni~hwqhidec
012
:‘iq:ilidae
1
fcmacasyidne
Sciaenidae
i
0'8
I
6 2
SO 1 e id ae
011
01
Sparidao
I
Syngnathidae
Tctraodont idae
Tankul Q.r
Clupcidao ?Ychmalosc?
Of5
2 10,4
Ilisha
011 !0,8
Pellonuln
011
l
&~Oc&3
Cyrw.:.lozsidae
UloFidne
Gobiidoe
0,4
i
TTc!,lirlz~ullphid,?e
: ryilidae
011
Sci :33rA:kte
S~rqn&kdtae
012
49
$1
)ll
)ll
011
7
j
i
i
Pcllonulr:
139
!:y no:; 10 :j :; i<: ae
96
Gabiidac
6
011
2
Scianidae
3yngnathidae
011
0'3
&ux!x ;C. B. j!onthly abunda.m~ of fish larvac in 4375.
(values are expressed by the total catch of tk
night, divided by thc total volui~z of wa-L:x fil-:emd
in 100 of c~M0 netcrs),
-.L
]LT
J
A
-
-
'987
$3,7
1545
1/,2
113
116
6 8 4.
9,P
OJ
O?l
023
0,4
093
58
091
os3
c,3 l,2
0,s
O,l
I
f49
?,l 10,Q
23,5
011
196
0,q. 0,g
011
036
62
7,3
2w
013
0 , 4.
031
011
* Unablc to se~~~x-&c thc y0u.ng lnrvac of Polyilc,zic!ae a,nd
Sciaenidac, WC havc .groupod the<i\\ under this rime.
-
-...
-.-.--_-
CG!%
OI f.j
,~-
.!
i
i i
--
03
2
C’J
0