Download pdf - Biology and ®shery of Octopus vulgaris

7/27/2019 Biology and shery of Octopus vulgaris

1/13


2/13

Relini, 1984; Tursi and D'Onghia, 1992; Belcari and

Sartor, 1993). However, the trawlers can

only exploit the part of the population living on a

soft, sandy or muddy bottom. Octopuses inhabit-ing rocky substrates are caught with pots on a com-

mercial scale, where several km2 areas are covered by

a web of strings holding thousands of pots (Mangold,

1983b).

The biology and shery of O. vulgaris in the

Mediterranean Sea have been previously studied,

but the majority of studies refer to individuals kept

in laboratory conditions (Nixon, 1966, 1971, 1979;

Boucaud-Camou et al., 1976; Nixon and Maconna-

chie, 1988) or caught in littoral waters (Kayes, 1974;

Ambrose and Nelson, 1983). Some studies deal withthe biology of this species taken by trawlers. Thus,

Mangold-Wirz (1963) made a detailed study of the

general biology, Mangold and Boletzky (1973) dealt

with growth and reproduction biology, Guerra (1975)

determined the sexual development and Guerra (1978)

analysed the diet.

Sanchez and Obarti (1993) studied the biology and

shery of O. vulgaris populations living in littoral

waters from 535 m in the central Spanish Mediter-

ranean coast, where the species is collected with pots

by local shermen.The present work has been developed in a nearby

area of the Western Mediterranean and is a general

study on the biology and shery ofO. vulgaris caught

by trawlers at depths of 50100 m.

2. Material and methods

The sampling programme was carried out from

August 1995 to August 1996, on-board commercial

bottom trawling vessels operating off the port ofPalma de Mallorca (Fig. 1). The haul data (date,

position, duration, depth and course) and the weight

by species of the total commercial catch were

recorded. All the hauls were performed between a

depth of 50100 m.

Monthly sizefrequency distributions ofO. vulgaris

were measured on-board. Apart from this species,

another octopus, Eledone moschata Lamarck, 1799,

is present in this shery but, although shermen

recognise them, they are not classied into species.

Thus, both species appear pooled together under the

`octopuses' category in the statistics of the central

auction wharf of Mallorca. In order to determine theproportion of these two species in the catches, the

weight of each one was estimated from representative

samples.

Monthly samples of O. vulgaris were taken to the

laboratory for processing. For each specimen the

following measurements were noted: dorsal mantle

length (ML, in mm), total body weight (BW, in g), sex

and maturity stage.

To calculate the relationship between dorsal mantle

length and total body weight, the formula TWaMLb

was used. Calculations were made for each sex sepa-rately and also for both sexes pooled. The slopes and

the intercepts for males and females were compared

using the methods described in Zar (1984). The allo-

metry of the growth in weight was tested by a Stu-

dent's t-test for males, females and both sexes pooled.

The sex ratio was estimated for each season of the year

and it was tested by a Chi-square test. In all the

statistical tests applied in this study, a signicance

level () of 0.05 was considered.

The following three-stage maturity scale (adapted

from Sanchez and Obarti, 1993) was used:

Fig. 1. The study area in the Balearic Sea (Western Mediterra-

nean).

238 A. Quetglas et al. / Fisheries Research 36 (1998) 237249


3/13

Immature (I): ovary whitish, very small and with

no signs of granulation in females; spermatophoric

organ transparent in males.

Maturing (II): ovary yellowish with a granularstructure; spermatophoric organ with white streaks.

Mature (III): ovary very large with plenty of

eggs; spermatophoric sac with spermatophores.

The weight of the gonads was recorded by taking

the weight of the testis and the spermatophoric com-

plex for males and the weight of ovary for females. For

males, the relationship between total body weight and

gonad weight was obtained. For females, a logarith-

mic transformation of the ovary weight (OvW) was

made: log (1OvW), and used to eliminate negativeOvW values (Bartlett, 1947).Stomach contents were analysed and prey identied

from their remains (eyes, mandibles or appendages in

Crustacea; cephalopod beaks; otoliths) after making a

comparison with a reference collection and published

descriptions (Zariquiey-Alvarez, 1968; Perez-Gan-

daras, 1983; D'Angello and Gargiullo, 1991). The

following indices were used (Hyslop, 1980; Cortez

et al., 1995):

Occurrence index (OCI): the ratio between the

number of stomachs with one type of prey presentand the total number of stomachs with food, eachstomach being counted as many times as the

number of different types of prey it contained.

Emptiness index (EMI): the percentage of

specimens with no food in their stomachs.

Finally, monthly statistics of octopus catches (in kg)from January 1981 to August 1996 for the total

Mallorca eet were collected. In order to determine

if landings showed any periodicity, two time-series

analysis techniques (Bloomeld, 1976) were used.

The rst one was the least-squares tting, which

consists of nding the sinusoidal function that best

ts the data. The function has the following form:

y "x A cos3t B cos3t

where 3 is the frequency of the series searched for, "x

the mean of the catch data, and A and B are as follows:

A 2

n

t

n1

xt "xcos 3tY B 2

n

t

n1

xt "xsin 3t

n and xt being the number of points and the value ofx

in time t (in months), respectively.

The second technique was spectrum analysis, which

consists in computing the Fourier transform of the

series. The spectrum obtained indicates the relative

importance of each frequency in a time series. The

peaks in the spectrum indicate the existence of moreenergetic frequencies, being the importance of a given

frequency determined by the high of its corresponding

peak.

Table 1

Parameters of the relationship between mantle length (ML) and body weight (BW) from previous studies and the present work

Sex a b n r Area Size range

(cm)

Source

M 0.350 2.988 584 0.979

F 0.542 2.804 434 0.969 Catalonia (Western Mediterranean) Guerra and Manrquez, 1980MF 0.420 2.917 1018 0.969 322

M 0.757 2.74 37 0.95 4.921.5

F 0.587 2.83 55 0.97 South Africa (Atlantic Ocean) 4.621.5 Smale and Buchan, 1981

MF 0.718 2.80 92 0.97 4.621.5

M 3.306 2.323 155 0.90 822

F 1.654 2.576 165 0.92 Valencia (Western Mediterranean) 926 Sanchez and Obarti, 1993

MF

M 0.442 2.882 168 0.95 516

F 0.413 2.916 175 0.94 Mallorca (Western Mediterranean) 516 Present work

MF 0.437 2.889 343 0.94 516

A. Quetglas et al. / Fisheries Research 36 (1998) 237249 239


4/13

3. Results

3.1. Lengthweight relationships and size-frequency

distributions

The results of the relationship between dorsal man-

tle length and total body weight are shown in Table 1.

No signicant differences were observed when the

slopes and the intercepts were compared between

sexes (0.20


5/13

maximum number in MayJune and a minimum in

NovemberDecember. Maturing females were caught

from May to August.

Formales, the relationship between total bodyweight

and gonad weight (GoWtestisspermatophoriccomplex weight) gave these parameters (Fig. 4(a)):

GoW 0X541 0X014TWY with n 167

and r 0X92

For females, the relationships between log (1OvW)and log (ML) are presented in Fig. 4(b).

3.3. Diet

The occurrence-index (OCI) values for the prey

items found in the stomachs are shown in Table 2.

Major taxonomic groups are summarised in Fig. 5(a).

O. vulgaris fed basically on crustaceans (mainly dec-

apods) and shes, although it occasionally included

gastropods and cephalopods in its diet. Percentages of

the number of prey types found in the stomachs are

shown in Fig. 5(b). Stomachs with one or two types of

prey were most common, but those with three or four

types were also rather common. The emptiness index

(EMI) was analysed seasonally (Fig. 6). There was agradual decrease of this index from winter to summer,

increasing again in autumn.

3.4. Fishery

Two species of octopuses, O. vulgaris and E.

moschata, were caught in this shery which targeted

sh. Both species were pooled for sales, although they

were separated into sizes. It was noticed that another

octopus, E. cirrhosa Lamarck, 1798, would sporadi-

cally appear, but it generally inhabits deeper waters,

Fig. 2. (Continued).



6/13

and is caught in small quantities, mostly by trawlers

targeting the Norway lobster (Nephrops norvegicus

Linnaeus, 1758).

Bimonthly percentages ofO. vulgaris, E. moschataand the rest of the commercial catch are shown in

Fig. 7. The relative importance of octopuses increased

gradually from $20%, in the rst months of the year,up to $40% in JuneJuly. Subsequently, theydecreased abruptly to $20% in AugustSeptember,before increasing again thereafter.

Although E. moschata appeared regularly through-

out the year (Fig. 7), its catches were lower than those

ofO. vulgaris. In addition, the importance ofOctopus

in relation to Eledone increased gradually from

December to July.The mean and standard deviation of monthly land-

ings from January 1981 to August 1996 are shown in

Fig. 8(a). Catches increase progressively from Janu-

ary to March, going down thereafter. Finally, after a

clear minimum in AugustSeptember they increased

again. The catch rates (kg/h) throughout the year are

shown in Fig. 8(b). The highest catch rates were

obtained from April to July, while during the rest of

the year they remained at low levels.

As suggested by the visual analysis of the monthly

octopus landings, two oscillations seemed to exist: an

approximately annual periodicity superimposed on a

higher oscillation. To characterise this higher oscilla-

tion, the series was analysed by the least-squares

tting method. As a result, a period of 92 monthswas obtained, with "x 1521X04 kg, A4710.64 kgand B1626.95 kg. Monthly landings from January1981 to August 1996 and the sinusoidal function

obtained (extrapolated until January 2000) are shown

in Fig. 9(a). If this periodicity were to be maintained,

an increase of landings until the year 2000 would be

expected.

In order to determine the lower oscillation, a

spectrum analysis was applied to the series, and the

trend and the larger periodicities in the data were

eliminated by ltering the periods longer than 24months. The spectrum analysis (Fig. 9(b)) revealed

a clear peak at a frequency of 310.083 months1

(corresponding to a period of 12 months) with

two other peaks at 320.167 and 330.250 months1

(periods of 6 and 4 months, respectively). These

two last peaks were located at frequencies that are

multiples of the rst one (32231 and 33331),thus indicating that they were probably related

to the harmonics of the 12-month periodicity.

The presence of harmonics indicates that the

periodicity of 12 months is not strictly sinusoidal.

Fig. 3. Bimonthly percentage of maturity stages of (a) males and (b) females.



7/13

Other higher frequency peaks may not be signi-

cant.

4. Discussion

It is known that O. vulgaris migrates to the coast

during the rst months of the year, and remains close

to it (mainly at a depth between 30 and 60 m) during

the reproductive period (Mangold-Wirz, 1963). The

results obtained in the present work show that this

migration is reected in some aspects of the biology

and shery population exploited by trawlers, which

are forbidden to sh over 50 m depth.

The rst effect of this displacement can be observed

in the sizefrequency distribution. Octopuses

Fig. 4. (a) Scatter diagram of gonad weight vs. total body weight for males. (b) Relationship between the logarithmic transformation of ovary

weight (OvW) and the logarithm of mantle length (ML).



8/13

Table 2

The occurrence index (OCI) for the prey items found in the

stomachs

Occurrence Index (OCI)

CRUSTACEA 65.75

AMPHIPODA 4.50

Gammaridea 4.50

ISOPODA 1.00

DECAPODA 60.25

Decapoda indeterminate 8.75

DECAPODA NATANTIA 3.25

Natantia indeterminate 2.25

Caridea indeterminate 0.25

Alpheidae indeterminate 0.25

Thoralus cranchii 0.25

Philocheras sculptus 0.25

DECAPODA REPTANTIA 48.25

ANOMURA 19.25

Anomura indeterminate 2.00

Galathea sp. 1.75

Galathea intermedia 11.50

Galathea strigosa 0.25

Galathea bolivari 0.75

Paguridea indeterminate 2.00

Paguristes eremita 0.75

Pagurus prideaux 0.25

BRACHYURA 29.00

Brachyura indeterminate 15.00

Liocarcinus sp. 0.25

Liocarcinus corrugatus 8.75

Liocarcinus pusillus 0.25

Pilumnus spinifer 0.25

Xantho pilipes 0.25

Ebalia sp. 0.75

Ebalia granulosa 0.25

Ebalia tuberosa 1.25

Oxyrhyncha indeterminate 0.25

Parthenopidae indeterminate 0.25

Inachus dorsettensis 0.25

Eurynome spinosa 0.25

Atelecyclus rotundatus 1.00

MOLLUSCA 6.50

POLIPLACOPHORA 0.50

GASTROPODA 3.25

Trachidae indeterminate 1.50

Turritella communis 0.25

Raphitoma reticulata 0.25

Naticarius intricatoides 0.25

Naticarius hebraeus 0.50

Calliostoma granulatum 0.50

CEPHALOPODA 2.75

Cephalopoda indeterminate 1.75

Sepiolidae indeterminate 0.50

Alloteuthis media 0.25

Table 2

(Continued)

Occurrence Index (OCI)

Loligo vulgaris 0.25

TELEOSTEI 27.00

Teleostei indeterminate 12.00

Gobidae indeterminate 13.00

Carapus acus 0.25

Ophichthus rufus 0.25

Gaidropsarus vulgaris 0.25

Blennius ocellaris 0.75

Capros aper 0.25

Centracanthus cirrus 0.25

Not identified 0.75

Fig. 5. Percentages of (a) the major taxonomic groups and (b) the

number of prey types found in the stomach contents.



9/13

disappear progressively from trawling grounds

when they reach a 1112 cm ML size. This size

coincides with the minimum mean length obtained

by Sanchez and Obarti (1993), whose work was

carried out in a depth range of 5 to 35 m in a nearby

area of the Spanish Mediterranean coast. The largest

individuals analysed in our study (16 cm ML) were

clearly smaller than those obtained by these authors

(26 cm ML).

The movement to the coast is probably related to theneed of rocky substrates where females could lay eggs

(Mangold-Wirz, 1963), so mature females would

always be found in littoral waters. The fact that no

mature females were caught throughout the year of

sampling is in accordance with this. Mangold and

Boletzky (1973) and Guerra (1975) found mature

females but their specimens were caught by trawlers

working between depths of 2090 m and 25100 m,

respectively. The absence of mature females in ourwork could be explained if they were in waters

shallower than the minimum depth sampled (50 m).

The results of Sanchez and Obarti (1993) conrm this

because important percentages of mature females

appeared regularly in their samples.

Sanchez and Obarti (1993) found a protracted and

somewhat irregular reproductive period, lasting from

January to July. Guerra (1975) suggested that this

period could occur from March to September, with

a maximum in May to July. Mangold and Boletzky

(1973) extended this period to October. Taking intoaccount the results obtained by all these authors it can

be noticed that, although reproduction could last from

January to October, it reaches a maximum from April

to July. The only maturing females caught during the

present work were from May to August, in good

agreement with these results.

Bearing in mind the results about the reproductive

period, it is now possible to interpret the sizefre-

quency distribution obtained. Recruits, in the sense of

small animals, are mainly present from September to

April. Following Mangold-Wirz (1963), the speci-mens of 6.5 to 7 cm ML are 8 months old. Thus,

the octopuses of 67 cm ML caught from September

to April, would have been spawned from January to

August, which coincides with the reproductive period.

The interruption of spawning from September to

Fig. 6. Seasonal changes of the emptiness index (EMI) for the

digestive tracts analysed.

Fig. 7. Bimonthly composition of octopus catches (O. vulgaris and E. moschata) and the rest of the commercial catch.



10/13

December is reected in the low percentage of speci-

mens of that size from May to August.

It is known that data on the feeding habits of

octopuses are biased by the sampling method used

(Sanchez and Obarti, 1993; Cortez et al., 1995). Thus,

stomach contents studies would underestimate the

proportion of molluscs, while studies based on debris

found near the middens would overestimate it. The

results obtained in this work conrm the importance of

crustaceans in the diet of octopuses, as have studiesfrom other authors (Nigmatullin and Ostapenko, 1976;

Guerra, 1978; Sanchez and Obarti, 1993). The impor-

tance of shes was higher when compared to the

values obtained by Guerra (1978), Smale and Buchan

(1981) and Sanchez and Obarti (1993), but similar to

those found by Nigmatullin and Ostapenko (1976).

Seasonal changes in feeding intensity were in

accordance with Cortez et al. (1995). The EMI was

higher during the colder seasons (especially in winter).

These results agree with the fact that, in general,

cephalopods respond to temperature increases by

increasing their food intake (Mangold and Boletzky,

1973; Mangold-Wirz and Boucher-Rodoni, 1973;

Mangold, 1983a).

From the point of view of shery, apart from O.

vulgaris, another species, E. moschata, occurs regu-

larly throughout the year. The results of the present

study show that O. vulgaris is always more abundant

and its importance, in relation to Eledone, increases

gradually from December to July, although it

decreases thereafter.Octopuses represented 2040% of the total catch

for the trawlers. Sanchez and Obarti (1993) recorded

that 36.26% annual catch of O. vulgaris from the

Spanish Mediterranean coast was made by pots, the

rest being caught by trawl. The high percentage of clay

pots catches in the total octopus catch is due to the fact

that this kind of shing takes only large specimens,

whereas trawls catch all sizes, specially small ones. In

our work, the highest catch rates were obtained in

spring and at the beginning of the summer, while

during the rest of the year they remained at low levels.

Fig. 8. (a) Mean and standard deviation for monthly octopus landings of the total Mallorcan fleet from January 1981 to August 1996. (b)

Catch yields (kg/h) obtained during the sampling period.



11/13

Sanchez and Obarti (1993) observed that the most

productive times were at the end of the spring and

beginning of summer when the octopuses caught were

larger, and in autumn when the number of specimens

was higher.

Landings of octopuses show a cyclic behaviour

throughout the year. After a minimum in August

September, they increase gradually until March,

before decreasing. This minimum could be explained

by the fact that until August, as was cited above,

octopuses disappear progressively from trawling

grounds and, moreover, they are not replaced by

recruits from May to August. The lack of recruits

during these months would also explain the decrease

Fig. 9. (a) Monthly octopus landings from January 1981 to August 1996 and the sinusoidal function that best fits the data. (b) The spectrum

obtained from the time series; DF16.



12/13

of catches from April to August. Octopus population

would recover only by means of the recruitment since,

like the majority of cephalopod species, they die after

reproduction (Mangold and Boletzky, 1973; O'Dorand Wells, 1987). The September to April catches

would increase by recruitment and also by the growth

in weight of individuals.

Although many of the exogenous changes that

affect a shery occur at time scales much shorter than

a year (Mendelssohn and Cury, 1987), applications of

time-series analysis to monthly catches are scarce

(Saila et al., 1980; Mendelssohn, 1981; Mendelssohn

and Cury, 1987; Jeffries et al., 1989).

To our knowledge, this is the rst study where time-

series analysis is applied to a cephalopod shery.Since octopuses landings showed a cyclic behaviour

throughout the year, as cited above, the 12-month

cycle revealed by the spectrum analysis would simply

reect the annual biological cycle of the species. This

marked seasonality in landings has also been observed

in other cephalopod species (Sanchez and Martn,

1993; Cunha and Moreno, 1994; Guerra et al.,

1994; Pierce et al., 1994), being related to their short

life span, rapid population turnover and the reproduc-

tion behaviour of the species (Sanchez and Martn,

1993).It is only in recent years that the catch data from

ofcial statistics is well-documented. This allows us to

observe uctuations in landings along the year, but

little can be done to analyse trends for longer periods

of time. The periodicity of 92 months found in the time

series could be signicant, but a longer series would be

needed to conrm the signicance of this periodicity.

Acknowledgements

This study was carried out within the framework of

the project `Discards of the Western Mediterranean

trawl eets' (Contract ref. DG-XIV, MED/94/027).

We wish to express our gratitude to the crew of the

trawlers Bellver and Mar Jupe II for their kindness

during the on-board boat sampling. Special thanks

also to Dr. Sebastia Monserrat (Department of Phy-

sics, Universitat Illes Balears) for his help in the

analysis of the time-series data and to Dr. Chris

Rodgers and Catalina Ballester for the English

version.

References

Ambrose, R.F., Nelson, B.V., 1983. Predation by Octopus vulgaris

in the Mediterranean. P.S.Z.N. I.: Mar. Ecol. 4(3), 251261.Bartlett, M.S., 1947. The use of transformations. Biometrics 3, 39

52.

Belcari, P., Sartor, P., 1993. Bottom trawling teuthofauna of the

northern Tyrrhenian Sea, Sci. Mar. 57(2-3) 145-152.

Bloomfield, P., 1976. Fourier Analysis of Time Series: An

Introduction. John Wiley and Sons, Inc., New York, pp. 258.

Boucaud-Camou, E., Boucher-Rodoni, R., Mangold, K., 1976.

Digestive absortion in Octopus vulgaris (Cephalopoda: Octo-

poda). J. Zool., Lond. 179, 261271.

Cortez, T., Castro, B.G., Guerra, A., 1995. Feeding dynamics of

Octopus mimus (Mollusca: Cephalopoda) in northern Chile

waters. Mar. Biol. 123, 497503.

Cunha, M.M., Moreno, A., 1994. Recent trends in the Portuguesesquid fishery. Fish. Res. 21, 231241.

D'Angello, G., Gargiullo, S., 1991. Guida alle conchiglie

Mediterranee. Fabbri, Milano, pp. 223.

Guerra, A., 1975. Determinacion de las diferentes fases del

desarrollo sexual de Octopus vulgaris Lamarck, mediante un

ndice de madurez. Inv. Pesq. 39(2), 397416.

Guerra, A., 1978. Sobre la alimentacion y el comportamiento

alimentario de Octopus vulgaris. Inv. Pesq. 42(2), 351364.

Guerra, A., Manrquez, M., 1980. Parametros biometricos de

Octopus vulgaris. Inv. Pesq. 44(1), 177198.

Guerra, A., Sanchez, P., Rocha, F., 1994. The Spanish fishery for

Loligo: Recent trends. Fish. Res. 21, 217230.

Hyslop, E.J., 1980. Stomach content analysis A review of

methods and their application. J. Fish. Biol. 17, 411429.

Jeffries, P., Keller, A., Hale, S., 1989. Predicting winter flounder

(Pseudopleuronectes americanus) catches by time series

analysis. Can. J. Fish. Aquat. Sci. 46, 650659.

Kayes, R.J., 1974. The daily activity pattern of Octopus vulgaris in

a natural habitat. Mar. Behav. Physiol. 2, 337343.

Mangold, K., 1983a. Food, feeding and growth in cephalopods,

Mem. natn. Mus. Vict., 44 8193.

Mangold, K., 1983b. Octopus vulgaris. In: Boyle, P. (Ed.).

Cephalopod Life Cycles. Vol. I, Academic Press, London, pp.

335364.

Mangold, K., von Boletzky, S., 1973. New data on reproductive

biology and growth of Octopus vulgaris. Mar. Biol. 19,

712.

Mangold-Wirz, K., 1963. Biologie de cephalopodes benthiques et

nectoniques de la mer catalane. Vie et Milieu (Suppl.) 13, 1

285.

Mangold-Wirz, K., Boucher-Rodoni, R., 1973. Nutrition et

croissance de trois Octopodides mediterraneens. Etude pre-

liminaire. Rapp. Comm. int. Mer Medit. 21, 789791.

Mendelssohn, R., 1981. Using Box-Jenkins models to forecast

fishery dynamics: Identification, estimation and checking. Fish.

Bull. 78(4), 887896.

Mendelssohn, R., Cury, P., 1987. Fluctuations of a fortnightly

abundance index of the Ivorian coastal pelagic species and

associated environmental conditions. Can. J. Fish. Aquat. Sci.

44, 408421.



13/13

Nigmatullin, Ch.M., Ostapenko, A.A., 1976. Feeding of Octopus

vulgaris Lam. from the Northwest African coast. ICES, C.M.

1976/K 6, 115.

Nixon, M., 1966. Changes in body weight and intake of food by

Octopus vulgaris. J. Zool., Lond. 150, 19.Nixon, M., 1971. Some parameters of growth in Octopus vulgaris.

J. Zool., Lond. 163, 277284.

Nixon, M., 1979. Hole-boring in shells by Octopus vulgaris Cuvier

in the Mediterranean. Malacologia 18, 431443.

Nixon, M., Maconnachie, E., 1988. Drilling by Octopus vulgaris

(Mollusca: Cephalopoda) in the Mediterranean. J. Zool., Lond.

216, 687716.

O' Dor, R.K., Wells M.J., 1987. Energy and nutrient flow. In: P.R.

Boyle (Ed.), Cephalopods Life Cycles. Vol. II. Comparative

Reviews, Academic Press, pp. 109133.

Perez-Gandaras, G., 1983. Estudio de los cefalopodos ibericos.

Sistematica y bionoma mediante el estudio morfometrico

comparado de sus mandbulas. Tesis Doctoral, UniversidadComplutense de Madrid.

Pierce, G.J., Boyle, P.R., Hastie, L.C., Shanks, A., 1994.

Distribution and abundance of the fished population of Loligo

forbesi in UK waters: Analysis of fishery data. Fish. Res. 21,

193216.

Relini, G., Orsi-Relini, L., 1984. The role of cephalopods in the

inshore trawl fishing of the Ligurian Sea. Oebalia, 10, N.S. 37

58.

Saila, S.B., Wigbout, M., Lermit, R.J., 1980. Comparison of some

time series models for the analysis of fisheries data. J. Cons.Int. Explor. Mer. 39, 4452.

Sanchez, P., Martn, P., 1993. Population dynamics of the exploited

cephalopod species of the Catalan Sea (NW Mediterranean),

Sci. Mar. 57(2-3), 153159.

Sanchez, P., Obarti, R., 1993. The Biology and Fishery of Octopus

vulgaris Caught with Clay Pots on the Spanish Mediterranean

Coast. In: Okutani, T., R.K. O'Dor, T. Kubodera (Eds.), Recent

Advances in Fisheries Biology. Tokai University Press, Tokyo.,

pp. 477487.

Smale, M.J., Buchan, P.R., 1981. Biology of Octopus vulgaris off

the east coast of South Africa. Mar. Biol. 65, 112.

Tursi, S., D'Onghia, G., 1992. Cephalopods of the Ionian Sea

(Mediterranean Sea). Oebalia 18, 2543.Zar, J.H., 1984. Biostatistical analysis. Prentice-Hall Inc., Engle-

wood Cliffs, pp. 718.

Zariquiey-Alvarez, R., 1968. Crustaceos decapodos ibericos. Inv.

Pesq., 32, pp. 510.
