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Differing sepion morphology of cuttlefish in the Gulf of Aden, supported by ecological diffferences, suggesting that the stocks generally reported as Sepia pharaonis may comprise two separate species.



By Hashim Sakaf
(formerly) Marine Science and Resources Research Centre
Labour Island, Khormaksar, Aden, Republic of Yemen

Submitted by David J Currie


Abstract
Cuttlefish caught in the Gulf of Aden make an important contribution to the fisheries landings of the Republic of Yemen. The cuttlefish most commonly found along the eastern part of Yemen’s Gulf coast are closely similar in their external appearance to those found in the western part. Both have historically been reported as being the Pharaon Cuttlefish, Sepia pharaonis (Ehrenberg 1831). The systematics of the genus Sepia have been generally based on external appearance, including regarding the characteristics of the suckers of the tentacular clubs. However, these may not always provide a definitive basis for taxonomic separation. Colouration differences are also unreliable. Previous scientific literature has not ascribed particular importance to the sepion (cuttlebone) as a major criterion in taxonomic classification, but this study suggests that morphological differences in the sepion may indeed be valuable. Differences in the morphology of sepia taken from presumptive Sepia pharaonis caught in the western and eastern regions of the Gulf of Aden suggest that the populations in the two regions may represent two separate species.

Introduction

The Yemen cuttlefish fishery

The Yemeni coastline of the Gulf of Aden measures approximately 1 550 km from Bab Al Mandab, the narrow strait separating the country’s southwest peninsula from the African continent, to the border with Oman in the East (Figure 1). The coastline is divided administratively into eastern and western fishing regions. This division reflects differences in seabed type and species distributions.

Sepia range map
Figure 1: Map showing the Gulf of Aden and the western and eastern cuttlefish fishing regions of Yemen.

Cuttlefish are commonly caught along the Gulf of Aden coast of the Republic of Yemen and make an important contribution to the fisheries landings of the country. FAO (Food and Agriculture Organization of the United Nations) statistics for 2003-2007 show cuttlefish/squids as representing between 5% and 10% of Yemen’s total marine capture fisheries landings (Table 1).

2003 2004 2005 2006 2007
Cuttlefish & squids (t) 11269 21900 24100 16797 9531
Total marine capture (t) 228116 256300 238400 229660 179916
Cuttlefish & squids as % of total 5% 9% 10% 7% 5%

Table 1: Yemen marine capture fisheries landings 2003-2007: Cuttlefish/squid and Total (t) (FAO).

Statistics held by the Yemen Ministry of Fish Wealth indicate that those total landings of cuttlefish and squids reported by FAO for 2003-2007 comprise more than 98% cuttlefish and less than 2% squids (Ministry of Fish Wealth, Republic of Yemen; Annual Statistics 2000 to 2007).

The value of the cuttlefish resource in the Gulf of Aden was first recognized by Japanese exploratory trawling surveys in 1966 and has been subject to various scientific studies since: Druzhinin (1973), Aoyama and Nguyen (1979), Bouhlel (1981), Sanders (1981), Sanders and Bouhlel (1981), Hashim & Koithara (1992).

Nine species of cuttlefish have been reported from the Gulf of Aden and Arabian Sea: Sepia pharaonis, Sepia prashadi, Sepia omani, Sepia lattmanus, Sepia trigonina, Sepia brevimana, Sepia braggi, Sepia murravi, and Sepiella inermis: Wooster et al. 1967, Nesis (1982), Roper et al. 1984. Among these species S. pharaonis (Ehrenberg 1831) and S. prashadi (Winckworth 1936) are present in commercial quantities in Yemen waters, and S. pharaonis makes up around 96% of the country’s total cuttlefish landings. (Ministry of Fish Wealth, Republic of Yemen; Annual Statistics 2000 to 2007).

The cuttlefish resource in Yemen is exploited by both large commercial trawlers and artisanal fishermen.

The western fishing area, from Bab Al Mandab to Bir Ali, (see Figure 1) has a narrow continental shelf and is mostly rough ground not suited to trawling. There are some restricted areas that are suitable for trawling between Ras Alara and Ahwar, with depths of 10-50 m and a seabed of gravel and small rocks. This substrate type is also favoured by cuttlefish for spawning.

The eastern fishing ground stretches from Mukalla to Al Ghaida, with much of it suitable for bottom trawling. An estimated 90% of Yemen’s trawlers fish in this area. The shelf is wider than in the western region, and fishing takes place at depths between 10-200 m.

Since 1999 Yemen’s artisanal fishermen have been targeting cuttlefish during the spawning seasons. The cuttlefish are easy to catch in shallow waters and fetch a good price. In addition there is a strong market support system, with easy availability of fishing gear and a good network of traders supplying ice and insulated boxes. Since 2003 large foreign trawlers have been refused licenses to fish in shallow areas and this has also added to the increase in the artisanal fishery.

A large proportion of the cuttlefish landed are mature, with the females carrying eggs, but the effect on the sustainability of the resource of targeting these animals is not known. Little stock assessment work has been reported for cuttlefish populations in the region.

Aspects of the biology of the cuttlefish of the Yemen coast

As part of a series of studies of the cuttlefish fishery in Yemen carried out by the Marine Science Research and Resource Centre (MSRRC), Aden, during the period 2002-2005, samples were collected regularly along the length of the Gulf coast for recording of length and weight, sex, stage of maturity, and sepion morphology. Data were collected also on fishing effort and landings (Sakaf, in press).

The data indicate that in the western region, there are two spawning seasons, the first starting in February or March and lasting until April; the second running mid-July to October, with peak landings in August and September, but with some differences from area to area according to ecological conditions. In February and March large numbers of cuttlefish appear in shallow inshore waters of the western region. Fishermen report that during this period of the northeast monsoon, strong winds are followed by a fall in offshore water temperatures (probably due to upwelling of deeper cooler waters) and it may be that the migration of the cuttlefish is connected to these temperature changes. The start of the second spawning season in July coincides with the peak of the southwest monsoon. Again large numbers of mature cuttlefish appear in shallow coastal waters at this time.

In the eastern region the first spawning season also starts in February or March but lasts longer than in the west, continuing typically until May. In contrast to the pattern in the western region, the spawning cuttlefish in the East are found during this period mainly at depths of more than 40 metres. These stocks are not usually exploited by the artisanal fleet as the depths are too great for the small boats to deal with. In the second spawning season in the eastern region, however, which starts earlier than in the West, in mid-June, cuttlefish move into shallower waters with the start of the southwest monsoon and commence spawning. There is a large concentration of cuttlefish in the area from Mukalla to Al Ghaida in June and July, in areas where the shallow waters show high temperatures. Nutrients supplied by the monsoonal upwellings create a region of high productivity in this area. Similar to the western region, peak spawning is in August and September. Fishing by artisanal vessels in the region takes place from June to November.

There is limited oceanographic data for the coastal waters of the northern Gulf and further study is needed on the ecological and biological basis of the spawning periods.

There are thus a number of seasonal and behavioural differences between the populations of presumptive Sepia pharaonis in the eastern and western regions of the Yemen coast of the Gulf of Aden.

Materials and methods

Sepion (cuttlebone) study

A total of 970 sepion samples were collected in August 2003 from presumptive Sepia pharaonis landed in the western region between Ras Al-Ara and Makalla, and 1 339 samples from the eastern region between Makalla and the border with Oman. The samples were taken from approximately equal numbers of males and females and almost all were from mature animals.

The location and date of sampling, and the number of sepion samples collected are shown in Table 2.

Eastern region: Fish landing centre Date of sampling Number of sepion samples collected
Mukalla 16 August 2003 106
Shihir 17 August 2003 215
Quasyir 19 August 2003 180
Sayhut 21 August 2003 112
Qishin 25 August 2003 130
Nashtun 27 August 2003 286
Dabut 29 August 2003 310
Total 1339

Western region: Fish landing centre Date of sampling Number of sepion samples collected
Ras Al Ara 2 August 2003 83
Imran 4 August 2003 125
Fukum 5 August 2003 240
Aden (Sera) 7 August 2003 72
Ahwar 10 August 2003 270
Bir Ali 12 August 2003 180
Total 970

Table 2: Sepion sampling details.

The lectotype specimen for Sepia pharaonis is held at the Museum of Natural History, Humboldt University, Berlin. It was collected by Hemprich & Ehrenberg in 1831 during a sample survey carried out in the area from the Red Sea to the Massaua archipelago in Eritrea, and thus at the western end of the Yemen coast. The lectotype (and also a paralectotype) was examined manually and by x-ray.

Results

There were a number of marked differences between the sepion samples collected from cuttlefish landed in the western region and those from the eastern region, although externally the cuttlefish were indistinguishable by colour, shape, or by the count or orientation of the tentacular clubs. Most noticeably, the rostrum of the sepion is inclined dorsally in most samples from the western region and ventrally in most samples from the eastern region. Also the ventral striations cover a greater proportion of the total sepion length in the western samples (approximately 70%) than in the eastern samples (less than 60%) (see Figure 2). These and a number of other morphological differences are summarised in Table 3.

Sepia sepion

Figure 2: Comparison of sepia (cuttlebones) from two groups of cuttlefish inhabiting (a) the western region and (b) the eastern region, of the Yemen coast of the Gulf of Aden.

Features Western region Eastern region
Striation (ventral view) Striations cover 71% of the total length of the cuttlebone. Striations cover 57% of the total length of the cuttlebone.
Rostrum a. lateral view The rostrum inclines towards the dorsal plane. The rostrum inclines towards the ventral plane.
Rostrum b. dorsal view The base of the rostrum has a triangular form with smooth edges. The base of the rostrum has a trapezoid form with serrated edges.
Inner cone The inner cone is thicker and consists of hard material, U shaped with a long fork. The inner cone is thin and of soft material, V-shaped and elongated with serrated edges.
Dorsal margin The lower part of the sepion and rostrum are white in colour without any thin coating. The lower part of the sepion and rostrum are covered with thin light chitinous material.

Table 3: Comparative features of sepion samples from the western and eastern regions of the Yemen coast of the Gulf of Aden.

Manual and x-ray examination of the lectotype and paralectotype held at the Museum of Natural History, Humboldt University, Berlin confirmed the rostrum of the sepion in these two samples to be inclined dorsally.

Discussion

The cuttlefish most commonly found in the eastern region of Yemen’s Gulf coast are closely similar in their external appearance to those found in the western region. Both have historically been reported as being the Pharaon Cuttlefish, Sepia pharaonis (Ehrenberg 1831).

The systematics of the genus Sepia have been generally based on external appearance, including regarding the characteristics of the suckers of the tentacular clubs. However, these may not always provide a definitive basis for taxonomic separation. Colouration differences are also unreliable.

Previous scientific literature has not ascribed particular importance to the sepion (cuttlebone) as a major criterion in taxonomic classification, but this study suggests that morphological differences in the sepion may indeed be valuable.

The fundamental differences noted in the structure and appearance of the sepia from presumptive S. pharaonis inhabiting the western and eastern regions of the Yemen coast of the Gulf of Aden suggest that the cuttlefish most commonly caught in the western and eastern regions might in fact represent two distinct species.

Conclusion

The marked morphological differences between the sepia of cuttlefish sampled from the western and eastern regions of the Yemen coast of the Gulf of Aden suggest that they may represent two separate species. The variant found in the western region appears to conform to the lectotype and so is likely to be Sepia pharaonis. The variant found in the eastern region may be a previously undescribed species.

Acknowledgements

Hashim Sakaf, a respected Yemeni scientist who devoted much of his professional life to the study of cuttlefish in Yemen, died suddenly from a heart attack in April 2007 while still in his forties and before his paper reporting the possible presence of a previously undescribed species of cuttlefish could be published. The paper was submitted posthumously to The Cephalopod Page in his memory by a colleague, David Currie. Thanks are also due to Dr. Thomas von Rintelen of the Museum of Natural History, Humboldt University, Berlin who carried out the examination of the lectotype and to Dr. Martin Collins of the British Antarctic Survey who gave valuable advice on the presentation of the data.

David Currie requests taking responsibility for any remaining deficiencies or errors in this paper. As the editor and webmaster for The Cephalopod Page, I am taking these last few words to express my gratitude and respect to David for honoring his friend and colleague, Hashim Sakaf, by insuring that this work is shared. - James

References

Aoyama, T. and T-T. Nguyen. 1979. Stock assessment of cuttlefish of the coast of the Peoples Democratic Republic of Yemen. Ocean Research Institute, University of Tokyo, Japan.

Bouhlel, M. 1981. Stock assessment of cuttlefish studies with application of cohort analysis method. Report to MSRRC, Aden.

Druzhinin, A. 1973. Fishery resources of the Gulf of Aden and some adjacent areas. FAO (FI: SF/ DP 9/ 12 PDY / 64 / 501/ 7), 299pp.

Hashim, M. A. and Koithara, P. 1992. Observations on the bionomics and fisheries of cuttlefish, Sepia pharaonis, in the Gulf of Aden. MSRRC internal report.

Ministry of Fish Wealth, Republic of Yemen, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007. Annual Fisheries Statistics (in Arabic).

Nesis, K.N. 1982. Short determination of cephalopods of the world’s oceans. Published in Moscow. 357 pp. (in Russian).

Roper, C.F.E., M.J. Sweeny and C.E.Nauen. 1984. Cephalopods of the world. FAO Fisheries Synopsis 3 (125). 277 pp.

Sanders, M.J. 1981. Revised stock assessment for the cuttlefish Sepia pharaonis taken off the coast of the People’s Democratic Republic of Yemen. FAO (RAB/77/008/13).

Sanders, M.J. and M Bouhlel. 1981. Interim report of a mesh selectivity study conducted in the P.D.R.Y. on the cuttlefish Sepia pharaonis. FAO (RAB/77/008/41). 35 pp.

Wooster W.S., Schaepher M.B. and Robinson M.K. Atlas of the Arabian Sea for fishery oceanography. IMR Reference 67-12, Univ. Calif. 1967, 35 pp.



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