CM 1995 I K:50
ICES C.M. 1995
THE llSE OF STATOLITHS IN AGE DETERMINATION OF THE LONG FINI\"ED SQUID, LOLIGO VULGARIS (CEPHALOPODA: LOLIGINIDAE)
V. Betteneourt, M. L. Coelho, J. P. Andrade
UCTR..A,., Uruversidade do Algarve, Campus de Gambelas
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8000 Faro, Portugal
ABSTRACT
This paper presents some information on the ageing of L. l'Ulgaris, using the
increment countings on statoliths. The inerements ,were identified using a serniautomatie image analysis system and a light microseope. The results of this study
indicate that the dorsal mantle length is significantly correlated v:ith botl!, the statolith
length and the increment numbers. However there are differences in respeets to total
statolith length when eomparing male and female statolith growths.
The gwwth rate of the statolith deereases v..;th the growth. This result is related
v\'ith the o'nset ofthe sexl.lal maturation.
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Key words: Loligo vulgaris, ageing, statoliths, growtl!, South Portugal
Introductiorl
Thc long-finncd squid, Loligo l'ulgaris, is the most important loliginid species, in terms
of totallandings in southem Portugal.
Studies on the biology of this species (Natsukari & Komine, 1992; Coelho cl al., 1994;
Rocha, 1994) indicate that L. l'ulgaris is a species with a short life cycle, and both, the
variability of the growth rates and the extended spa\vning season contribute to a complex
structure of the populations.
Published information on the age determination of L. vulgaris is restricted to Natsukari
& Komine (I992) and Guerra & Rocha (I 994). These studies show that the analysis of the
increments ofthe statoliths can be used in the ageing ofthis species.
This paper provides complementaI)' information on the use of the statoliths in the age
determination of L. 17Ilgaris. The general morphology of the statolith is provided and the
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number of increments are related with statolith length, sex and maturity stages of the
individuals.
Materials and methods
A total of 419 long-finned squid was collected from commercial catches in OIMo
(southern Portugal) during March and May 1993 and from July to September 1993.
The distance between the antero-dorsal protuberance and the apex ofthe tail fm (DML)
\vas measured to the nearest 1 mm.
The maturity stages were accessed according to Ngoile (1987) for both sexes.
The statoliths were removed and measured the total statolith length with a binocular dissecting
microseope. After that, the. statoliths were grinded and polished on both sides, using a
commercial sand paper v/ith 30 mm and 1 mm grain, respectively.
A semi-automatic image analysis system and a light microscope have been used to
identify the growth increments in the right statolith, from the hatclüng ring to the end of the .
rostrum. According to Guerra cl al. (I 993), the statoliths that presented more than 20% with
white zones were rejected. A total of 161 statoliths has been used in the age readings. The
hypothesis ofthe daily deposition ofthe increments was assumed in this study.
The DML \vas related with the total statolith length (TSL) and with the increment
number (IN), for males and females, separately.,Thestatolith length (TSL) was related with the
increment numbers (IN), irrespectively of the sex or the stage of maturity. The growth index
(GI) of each statolith (GI=TSLIIN x 100) was related with the DML in the immature and in
the mature individuals, separately.
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The regressIon lines were fitted by the least squares method and compared by
covariance analysis and the F test (SokaI & Rohlf, 1981).
Hesults
The statoliths of L. mlgaris show prominent dorsal and lateral lobules, and a long and
finger-like rostrum. The wing is white and easily removed from the remaining statolith.
The statolith length ranged from 0.93 mm (DML=32 mm) to 2.24 m (DML=345 mm)
and [rom 1.16 mm (DML=IOI mm) to 2.16 mm (DML=386 mm), for females and males,
respectively.
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Figure 1 shows the relationship between the DML and the TSL. There is a significant
correlation between these two variables, Vv;th higher values of r2 (0.80) for the females. The
regression equations fitted are significantly different between males and females (F=14.78;
p<O.OOOI).
Figure 2 shows the relationship between the DML and the IN, for males and females.
No difTerences were found (F=O.78; p>0.38).
Figure 3 shows the relationship between the TSL and the IN. No difTerences were
[ound between males and females (F=O.57; p>0.45).
Figure 4 shows the relationship between the GI and the D.ML, for immature (figure 4a)
and mature individuals (figure 4b). The regression coefficient indicates that the gro\v1h rate of
the statoliths is higher in the immature animals, decreasing in mature squids.
Discussion
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The preparation of the statoliths is a highly time consuming task. Nevertheless, the
analysis ofthe statoliths
s~em
to be the most appropriate approach in the ageing of L. 17ilgaris.
_ The use_ of both, the image analysis system and the light microscope is strongly suggested for
this type of analysis.
This study indicates that the males live longer than the females and that the statolith
grow fast er in the former and slower in the latter. Similar results are referred to by Lipinski &
Durholtz (1994) for L. mlgaris reynaudii. Thus, the statolith length can be considered as an
indicator ofthe age ofthe individuals.
The gro\\1h index of the statolith decreases gradually with the gro\v1h of the
individuals, particularly between the immature and the mature period. This result might be
related with the onset ofthe sex-ual maturation and with higher energetic demand caused by the
growth of the gonads. Similar results are described for other cephalopods by Guerra &
Sanchez (1985), Morris & Aldrich (1985), Lipinski (1986), Arkhipkin'& Scherbich (1991) and
Raya (1994).
Due to the high unreadable number ofincrements which were observed in the statoliths
of L. \'1dgaris, it was conc1uded that, the aecuraey of the age readings depends on the proper
mounting, grinding and polishing of the statolith. So, great eare is necessary during these
tasks. Furthermore, the increments have been considered as daily gro\\1h rings. Further
investigation is neeessary to validate this assumption.
Acknowledgements
This work was funded by the Commission of the European Communities within the
frame of the EEC research programme in the fisheries seetor (AlRI-CT92-0573). V.
Bettencourt had a scholarship (BM/2565/91-IG), granted by Junta Naeional de Investigal;äo
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Cientifiea e Tecnol6gica. We would like also to thank to Dr. Angel Guerra for adviee and
suggestions.
References
Arkipkin AI. and Seherbieh Z.N., 1991. Creeimiento y estructura intraespeeifiea del calamar,
Illex argcntinlls (Castellanos, 1960) (Ommastrephidae) en invierno y primavera en el
Atlantico sudocidental. Scicnta A1arina 55(4): 619-627.
Coelho, M. L.; Quinte1a J.; Bettencourt Y.; Mattos Silva G.& Villa H. 1994 Population
biolob'Y of the squid Loligo l'1JIgaris in the coastal v..'aters of the Algarve, Southem
Portugal. Fishcrics rcscarch (21): 87 - 102.
Guerra A y Sänchez P., 1985. Crecimiento relativo deI estatolito de Sepia ojjicillalis
(Cephalopoda, Sepioidea) de la Ria de Vigo.lnvestigati6n Pcsqllcra. 49(4): 545-557.
Guerra A, Rocha F., and Castro B. G., 1993. Statolith Workshop. Eurosquid Report. Vigo,
30 June - 2 July, 1993. Instituto de Investigaeiones Marinas (CSIC), Vigo. Spain: 10pp.
Guerra A, Rocha F., 1994. The life history of Loligo l'1JIgaris and Loligo forbesi
(Cephalopoda: Loliginidae) in Galician waters (NW Spain). Fisheries research (21): 43-69.
Lipinski M. R. and Durholtz M. D., 1994. Problcms assoeiatcdwith ageillg squidfrom their
statoliths: towards a morc stmcturcd approach. In: Rodhouse P. G., Piatkowski U. &
Lu C. c., (eds.). Southem Ocean eephalopods: life cycles and populations. A11tartic
Seicl1ce, 6: 215-222.
Morris C. C. and Aldrieh F. A, 1985 Statolith length and increment number for age
determination in squid Illex illeccbrosus (Le Sueur, 1821) (Cephalopoda:
Ommastrephidae) NAFO Sei. COllnc. Studies, 9: 101-106.
Lipinski M., 1986. Methods for the validation of squid age from statoliths. Journal mar. biol.
Ass. UK., 66(2): 505-526.
Natsukari, Y and Komine, N., 1992. Age and growth estimation ofthe European squid, Loligo
l'1Jlgaris, based on statolith mierostrueture. J. Afar. Biol. Assoe. UK, (72): 271 - 280.
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Ngoile M. A. K., 1987. r"lshc/}' bi%gy 0/ Ihe squid Lo/igo /orbesi (Cepha/opoda:
Loli~illidae) ill Scollhis walers. Tesis Doctoral, Universidad de Aberdeen, 218 pp.
Raya c.P., Fernandez-Nunuz t\1.M., Balguerias E. and Hernandez-Gonzalez C.L. , 1994.
Progress towards ageing cuttlefish Sepia hicrreda, from Northwestern African coast using
statoliths. Marine Ecology Progress Series, 114: 139-147.
Rocha, F. 1994. Aspcclos biologicos Y ccol6gicos de Loligo ru/garis )' L. /orbesi
(Cephalopoda, Loligillidac) Cll las coslas dc Galicia (NrV de Espalia). Tesis Doctoral.
Universidad de Oviedo. 240 pp.
Sokal R. R. and RohlfF. 1., 1981. BiomclI)'. 2 nd. Ed. W. H. Freeman and Company. N. Y.:
859pp.
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_
...
400
350
300
a) Females
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= 41.98 X 1\2.54
r2 = 0.80
n = 142
Y
:: 250
=
-...:J 200
:; 150
Q 100
5~ _-t-_-t-_--+-_~__t_-_+_-_-___<_-_--______I
-l--r
0.00
0.25
0.50 0.75
1.00
1.25
1.50
1.75
2.00
2.25
2.50
TSL (mm)
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b) Males
Y = 39.39 X 1\2.85
n=129
r2=0.77
0.25
0.50
0.75
1.00
1.25
1.50
1.75
2.00
2.25
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2.50
TSL (mm)
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females
+
males
... indetenninate
Figure 1 - DML - TSL relationship from a) females and b) males.
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I
I
2.50 T
I
I
I
I1
II
I Y = 0.S93
I
--::-
---
..:.l
2.00 t
r2
=
+ 0.00429 X
0.66
n = 152
I
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1
1
1.50
.
rI
t-
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(
~
er. 1.00
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T
I
0.50
0.00 I
0
100
50
150
200
Increment number
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•
•
females
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males
..... indeterminate
Figure 3 - TSL - fi\! relationship to total individuais.
250
300
400
350
.- 300
§ 250
-- 200
...J
:;;150
Q
100
50
0
a) Females
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Y = 0.143 xl\1.35
n = 69 r2 = 0.74
--
50
0
•
100
150
200
•
250
300
Increment Number
-=
.-
E
-...J
~
Q
400
350
300
250
200
150
100
50
0
...
b) Males
Y = 0.197 X 1\1.35
n = 71
r2
.
= 0.68
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~
..
0
50
100
150
200
250
300
Increment Number
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females
•
males
... indeterminate
Figure 1 - D:ML - IN relationship from a) females and b) males.
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2
a)
1.8
1.6
Y = 1.49-0.0037 X
r2 = 0.22
n :=: I 12
1.4
1.2
1
0.8
0.6
0.4
0.2
o
-+-_._-+-
-_--+
--I--_ _
o
50
100
150
200
+--~-_+__--_<---____<
250
300
350
400
DML(mm)
2
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b)
1.8
1.6
Y = I. 13 - 0.0009 X
r2 == 0.26
n= 39
1.4
1.2
1
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.. "
•
0.8
.~
0.6
0.4
0.2
0+-------+--------+---+----_+__---+-----1
o
50
100
150
200
250
300
350
400
DML (mm)
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females
•
males
... indeterminate
Figure 4 - Growth index ofthe statolith: a)juveniles imatures and b) adults matures
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