Appendix 4. Geographical distribution of two subspecies of Sepia officinalis LINNE off the northwestern coast of Africa

by

Hiroshi Hatanaka

INTRODUCTION

Six species of cuttlefish are found off the northwestern coast of Africa (Cabrera, 1970), Among them, Sepia officinalis LINNE is the major target for trawlers operating in the area. Sepia officinalis occurs from northern Europe to southern Africa. Four sub-specimens, geo-graphically separated, have been reported:

Sepia	officinalis	filliouxi LAFONT
S.	o.	officinalis LINNE
S.	o.	hierredda RANG
S.	o.	vermiculata QUOY et GAIMARD

However, the morphological differences are so small that their identification is difficult (Adam, 1941; 1952; 1966; Okutani, 1967).

In the Sahara coastal and Cape Verde Divisions where the fishing grounds for cuttlefish, are located, two subspecies, officinalis and hierredda, were reported by Adam (1941) and Cabrera (1970), who indicated that the distribution patterns of the two subspecies were different.

In this report, the author discusses the distribution, off the northwestern coast of Africa, of the two subspecies of Sepia officinalis LINNE using for that purpose material collected from Japanese trawlers.

MATERIAL AND METHODS

About 3,200 specimens (Table 1) have been collected from Japanese research and commercial trawl catches. This work started in 1967 when our laboratory initiated regular investigations on bottom fish resources in CECAF waters.

According to Adam (1941), the identification of the subspecies can be based on the shape of the rostrum on the shell; the transverse rows of modified suckers on hectocotylus can in addition be used for males. He reported that the rostrum is covered by a chitinous hood at least as far as the shells of adult specimens belonging to the two northern subspecies, i.e. filliouxi and officinalis are concerned; on the contrary, the rostrum of the two southern subspecies, i.e. hierredda and vermiculata is never covered; the hectocotylus has 5-7 rows in the northern subspecies and 8-13 rows in the southern ones.

In the material used for this study two types of rostrum are found. One, soft and translucent, is covered by a chitinous hood; the other is hard and opaque. Females larger than 15 cm (mantle length) can easily be identified, without extracting the shell from the body, by passing the finger tip over the end of the mantle. For the email specimens under 15 cm, the identification of the type of rostrum is difficult without extracting the shell from the body for direct examination. For specimens smaller than about 8 cm which have no chitinous hood, it is hard to identify the type of rostrum, even through direct observation.

On the other hand, modified suckers present on the hectocotylus of males are considerably smaller than normal suckers. Peripheric suckers, between normal and fully modified ones, are also of intermediate size. These are, therefore, difficult to distinguish. The sucker modification seems to be incompleted in the specimens smaller than 12 cm, and generally it is difficult to count the rows for individuals smaller than 10 cm (mantle length).

The specimens with soft rostrum have 5-8 rows, whereas the specimens with hard rostrum have 7-14 rows of modified suckers (Fig. 1). Therefore, these two groups could correspond to the northern and southern subspecies reported by Adam (1941). As Sepia filliouxi is encountered only in northern Europe and vermiculata only in southern Africa, the group with soft rostrum was identified as S, o. officinalis, and the group with hard rostrum as S. o. hierredda.

RESULTS

Among the 3,089 specimens larger than 8 cm in mantle length, 2,694 were identified as belonging to the subspecies officinalis, and 395 to the hierredda subspecies. The specimens attributed to the subspecies officinalis were caught in the northern part down to the shores of Mauritania included, and hierredda specimens were caught from the coasts of Mauritania (south of Cape Blanc) to those of Guinea (Table 2 and Fig. 2). However, because of the lack of material from the Senegalese waters, the southern boundary of the subspecies officinalis could not be accurately determined.

Off the shores of Mauritania where both subspecies overlap, officinalis was found at all depths lesser than 110 meters, but hierredda occured only in shallower waters (Table 2).

DISCUSSION

Present results are closer to those published by Adam (1941) than to those of Cabrera (1970) (Fig. 3). Cabrera (1970) was of the opinion that officinalis is replaced by hierredda at the latitude of the Canary Islands. Although the material used in this report has been collected outside the 12 miles-limit in the CECAF Division Sahara littoral, at least the cuttlefish caught commercially by Japanese trawlers in this sector belonged to the officinalis subspecies.

According to Adam (1941), the subspecies officinalis is distributed north of the bay of Lévrier and hierredda south of the bay. But his material collected off Mauritania consisted only of two specimens.

SUMMARY

The geographical distributions of two subspecies of Sepia officinalis LINNE off the northwestern coast of Africa, has been analysed using samples collected from Japanese trawlers. The main results are the following:

(1) The southern boundary of Sepia officinalis officinalis coincides approximately with the border between Mauritania and Senegal.

(2) The northern limit of Sepia o. hierredda is at the latitude of Cape Blanc.

(3) Off the coast of Mauritania where the distribution areas of the two subspecies overlap, S. o. hierredda is found mainly in the waters shallower than 50 meters.

REFERENCES

Adam, W. 1941: Résultats scientifiques des croisières du navire-école belge "Mercator", III (4), Cephalopoda. Mém. Mus. r. Hist. Nat. Belg. Sér. 2, 21, 84-107.

Adam, W. 1952: Résultats scientifiques des expéditions océanographiques belges dans les eaux côtières africaines de l'Atlantique Sud, (1948-1949). Céphalopodes. Résultats. scient. Expéd. océanogr. Belg. (1948-49), II (3), 9-15

Adam, W. and W.J. Rees 1966: The John Murray Expedition 1933-34. Scientific Report, XI (1), A Review of the Cephalopod Family Sepiidae. Trust. Brit, Mus. (Nat. Hist.).

Cabrera, R.C.G. 1970: Espèces du genre Sepia du Sahara espagnol. Rapp. P.-v. Réun. Cons, int. Explor. Mer. 159, 132-139.

Okutani, K. 1967: "Mongoika" in African Coast. Venus, 25 (2). 78-79.

Table 1 Size and origin of the samples used in this report

Fig. 1. Frequency distribution of transverse rows of modified suckers for the two groups sorted according to the type of rostrum.

Table 2 Depth distribution of the two subspecies in each fishing grounds

Fig. 2. Geographical distribution of the two subspecies of Sepia o. officinalis off the northwestern coast of Africa.

Fig. 3. Limits of distribution of the two subspecies of Sepia officinalis as given in the literature and in the present report.