Exploitation Patterns of the Cuttlefish, <I>Sepia Officinalis</I>

BULLETIN OF MARINE SCIENCE, 71(1): 187–196, 2002

EXPLOITATION PATTERNS OF THE CUTTLEFISH, SEPIA OFFICINALIS (CEPHALOPODA, SEPIIDAE), IN THE MEDITERRANEAN SEA

Paola Belcari, Paolo Sartor, Pilar Sanchez, Montserrat Demestre, Alexis Tsangridis, Panagiotis Leondarakis, Eugenia Lefkaditou and Costas Papaconstantinou

ABSTRACT Exploitation patterns of the cuttlefish Sepia officinalis in the Mediterranean Sea were studied by investigating the fishing activity in three ports located in the Catalan (Spain), Ligurian (Italy) and Thracian (Greece) Seas. Monthly collection of data on commercial landings, fishing effort and demographic structure of the catches of S. officinalis was undertaken between July 1998 and June 1999. S. officinalis was exploited simultaneously or sequentially by different gears, whose importance changed in each port. Bottom trawling accounted for the majority of the landings at all ports, followed by the medium size trammel nets. Traps played an important role in the cuttlefish landings in the Catalan Sea, while beach seines and small size trammel nets contributed to a minor part of the landings of Kavala and Livorno, respectively. A marked seasonality in the landings of different gears was observed. Trammel net and trap landings comprised mostly adult specimens of large size, while trawl and beach seine catches also contained small individuals.

The cuttlefish, Sepia officinalis L. 1758, is among the commercially most important and appreciated species of cephalopods: during the period 1980–1995 annual world landings ranged from about 15,000 to 29,000 t (FAO Yearbook, 1995, 1997). This species is traditionally exploited by the demersal fisheries of the Mediterranean, especially in Italy and Spain (Guerra, 1991; Sanchez and Martín, 1993; Belcari et al., 1998; Sartor et al., 1998; Belcari, 1999). In all areas where it is exploited, S. officinalis provides a good example of a multigear fishery, being caught simultaneously or sequentially by different gears (Guerra, 1991); Pinczon du Sel and Daguzan (1997) and Dunn (1999) reported for the Bay of Biscay and the English Channel respectively, that the landings from bottom trawling (otter and beam trawl) are supplemented with those obtained using different kinds of artisanal gears, such as trammel nets and traps. Resource competition and interference between fishing vessels are generally referred to as technical interactions. Knowledge of technical interaction is valuable for fishery management. Potential technical interactions can be identified through the exploitation pattern. At present, for the Mediterranean sea, investigations of gear interactions are still scarce and mostly concern finfish (Aldebert et al., 1993; Demestre et al., 1997). Despite the fact that many cephalopod fisheries have experienced a period of expan- sion during recent years (Caddy and Rodhouse, 1998), the fisheries studied in more detail are mostly related to squid species (Rosenberg et al., 1990; Pierce and Guerra, 1994; Caddy, 1995). Regarding S. officinalis, the available studies on exploitation mainly concern the Atlantic waters (Boucaud-Camou, 1988; Pinczon du Sel and Daguzan, 1997; Dunn, 1999).

187 188 BULLETIN OF MARINE SCIENCE, VOL. 71, NO. 1, 2002

This paper describes the exploitation patterns of the cuttlefish in three different areas of the Mediterranean, according to the region fished and the gears employed.

MATERIAL AND METHODS

The study was carried out by collecting data on characteristics of the fishing fleet, commercial landings, fishing effort and demographic structure of the species in three ports along the Mediterra- nean coast: Vilanova i la Geltrú (Catalan Sea, Spain), Livorno (Ligurian Sea, Italy) and Kavala (Thracian Sea, Greece) (Fig. 1). The most representative gears interacting in exploitation of S. officinalis were selected: in the three study ports, the cuttlefish was caught using traditional bottom trawl and trammel nets with inner panel mesh size of around 60–70 mm (medium size trammel nets). In addition, traps were utilised in Vilanova, beach seine in Kavala and trammel nets with inner panel mesh size from 40 to 50 mm (small size trammel nets) in Livorno. From July 1998 to June 1999, data on landings of cuttlefish were collected in each studied port on a fortnightly basis directly at the auction and/or at the landing point: a minimum of 3 d of observation each fortnight was carried out. Fishing effort data were collected monthly by consult- ing the official archives and through interviews with fishermen. To estimate the monthly total landings, the sampled data were raised according to the total fishing days of the fleet in that month. A closed season of 4 mo for the towed gears was enforced in the Greek seas, as a measure to control fishing effort. In the Mediterranean fisheries, S. officinalis is not discarded (Sartor et al., 1998); for this reason we considered that landings were equivalent to catches. Catch per unit effort (CPUE) was ex- pressed as kg fishing d−1 boat−1 for trawling and beach seine, kg 1000−1 m of net/boat for trammel nets, kg 100 traps−1 boat−1 for traps. In each port, the monthly size structure of S. officinalis was obtained by measuring a sample of the specimens landed by each gear. Mantle length (ML) was measured to the nearest 0.5 cm below. The total of specimens measured was 3475 in Vilanova (1401 for trawl, 921 for medium size trammel net, 1153 for traps), 7246 in Livorno (4067 for trawl, 1782 for medium size trammel net, 1397 for small size trammel net) and 2232 in Kavala (1018 for trawl, 521 for medium size trammel net, 693 for small size trammel net). Monthly size distributions, weighed according to the monthly catches by each gear, were used to estimate annual distributions.

Figure 1. Map of the study area with sampling ports. BELCARI ET AL.: CUTTLEFISH EXPLOITATION IN MEDITERRANEAN SEA 189

Table 1. Characteristics of fishing fleets by port and gear (n = total number of vessels; hp = total horsepower; GRT = total gross registered tonnage, tons). * = vessels using trawl net or purse seine, according to the season.

Psort Tsrawler Pturse seiner A*rtisanal flee Mixed nphTGnpR hTGnpR hTGnpR hTGR V1ilanova i la Geltrù 4461,63 18,063. 1748,69 4885. 6531,65 3---36. L7ivorno 2560,37 56777. 20,19 2319. 6030,41 2---39. K3avala 1655,87 8224. 1831,43 7326. 6636,32 23084. 15,50 251.

RESULTS

Trawling was the fishing operation accounting for the majority of the overall horsepower and tonnage in all the studied ports (Table 1). The trawlers of Kavala were clearly more powerful, with an average value of 452 hp (± 87.9), compared to those of Vilanova (162 hp ± 136.0) and Livorno (236 hp ± 82.4). The trawlers in the three ports carry out their activity on different fishing grounds that vary according to the season and/or to the most important target species. Normally, these vessels perform 1-d trips returning to their home port every day. The small-scale fishery was also found to be an important activity in these ports. It is carried out by a large number of boats, but with limited horsepower and tonnage. Vessel size was quite similar in the three ports, with a mean power of about 54 hp. Among artisanal gears, trammel net was the most commonly employed. Several other gears, such as gillnet, long lines, traps, beach seine, fyke nets, etc. were utilized depending on the ports. The activity of the artisanal fleets varied throughout the year as well as the use of each gear and, consequently, the most important target species. Purse seiners represented a fairly important fraction of the fleet in Vilanova and Kavala, while in Livorno they were less abundant (Table 1). Bottom trawl was the gear accounting for the highest fraction of the commercial landings of S. officinalis (Table 2). An important fraction of the annual landings came from the medium size trammel nets, ranging from 15% to 41% of annual landings (Table 2). The remaining fraction of the biomass landed was ascribable to additional artisanal gears, which differed in each port: traps in Vilanova, small size trammel nets in Livorno and beach seine in Kavala. Traps played an important role in the cuttlefish exploitation in Vilanova, accounting for 40% of the annual landings, whereas the contribution of small size trammel nets and beach seines in Livorno and Kavala was less important (Table 2). The landings of the different gears were characterized by a clear seasonality (Fig. 2). Exploitation of S. officinalis by trawling was concentrated between November and Feb- ruary, depending on the port. Trammel nets mostly caught cuttlefish in spring-summer,

Table 2. Sepia officinalis. Landings (in tons) obtained in the year of sampling (July 1998−June 1999), by port and gear. In addition to medium size trammel net, the other artisanal gears were: traps (Vilanova), small size trammel net (Livorno) and beach seine (Kavala).

Alrtisanal Teraw Mledium siz Tota trammel nets V6ilanova 292. 254. 80. 56. L7ivorno 17. 134. 171. 27. K2avala 14. 642. 107. 81. 190 BULLETIN OF MARINE SCIENCE, VOL. 71, NO. 1, 2002

Figure 2. Sepia officinalis. Monthly patterns of the landings by port and gear. BELCARI ET AL.: CUTTLEFISH EXPLOITATION IN MEDITERRANEAN SEA 191 showing the highest values from March to April. A similar trend was shown by the traps in Vilanova. Monthly CPUE showed the same overall seasonal pattern as observed for landings (Fig. 3). The trend in CPUE for trawlers was found to be similar in Vilanova and Livorno, with highest values (8–9 kg d−1 boat−1) in autumn-winter. Kavala showed notably higher CPUE values in the second fortnight of February. The highest CPUE of the trammel nets were obtained from March to June in the three studied ports, Vilanova showing the highest values. The trap fishery in Vilanova was temporally restricted, but highly remunerated (30–40 kg 100−1 traps, on average). Differences in the exploitation patterns of the different gears were also detected by analysing the size composition of the landings (Fig. 4). Catches showed a wide size range, especially in Vilanova and in Kavala, from 4 to 32 cm ML. The bulk of landings was in specimens measuring less than 20 cm ML. Trawling was responsible for the smallest individuals captured in Livorno; this was essentially due to the catches registered in July, when the landings were mostly composed of specimens smaller than 6 cm ML. The mode of the annual trawl catch of Livorno was 8 cm ML, while those of Vilanova and Kavala were 12 and 11 cm ML, respectively. Some differences in the selectivity of the gears can be evidenced particularly in Livorno and Kavala, trawl landings exhibited smaller-sized specimens than those caught by medium size trammel nets. The size composition of the landings due to traps was very similar to that of medium size trammel nets; the exploitation patterns of beach seine and small size trammel nets, although accounting for only a small portion of the catch, proved to be similar to that of trawling, mostly composed of medium-small sized individuals (Fig. 4).

DISCUSSION

Together with the common octopus, Octopus vulgaris, S. officinalis undoubtedly represents one of the most important coastal fishery resources of the Mediterranean Sea (Voss, 1973; Belcari and Sartor, 1993; Sanchez et al., 1998). In the Mediterranean area, cuttlefish is an established resource that is exploited on industrial and small-scale levels, even including recreational angling. Historically, cap- ture and utilization of cuttlefish has been very important in this area and discards are practically absent in Mediterranean fisheries (Sartor et al., 1998). In some other areas this resource, previously discarded, has come to be appreciated only in more recent decades and a rapid increase in the landings is being observed (Dunn, 1999). The results of the present study show that, in the three ports investigated, bottom trawling is responsible for the majority of S. officinalis landings. Previous studies carried out in Atlantic waters confirm the primary role played by trawling (otter and beam trawl) in the exploitation of this species (Boucaud-Camou, 1988; Bravo de Laguna, 1989; Dunn, 1999) The high trawl catches observed in Kavala are not necessarily ascribable to a major abundance of the resource in this area: the effectiveness of the more powerful fleet and the larger size of the specimens, especially when compared to those captured in Livorno, could partly explain the greater amount of the landings. 192 BULLETIN OF MARINE SCIENCE, VOL. 71, NO. 1, 2002

Figure 3. Sepia officinalis. Monthly patterns of the Catch Per Unit Effort (CPUE) by port and gear. BELCARI ET AL.: CUTTLEFISH EXPLOITATION IN MEDITERRANEAN SEA 193

Figure 4. Sepia officinalis. Length frequency distributions of the annual landings by port and gear. 194 BULLETIN OF MARINE SCIENCE, VOL. 71, NO. 1, 2002

However, while multispecific demersal fisheries are not specifically oriented to cuttlefish, the species is undoubtedly among the primary targets of the small scale fishery, for which it represents the greater part of the earnings at certain periods of the year. As a consequence, highly specialized artisanal gears have been developed, such as traps, in which catches are practically monospecific. Traps are also commonly used for cuttlefish in the Atlantic ocean, a practice that has been increasing in recent years (Bakhayokho and Ito, 1991; Pinczon du Sel and Daguzan, 1997; Dunn, 1999). The exploitation pattern emerging from this study is mainly an outcome of the well- known features of S. officinalis ecology. Its short life span and terminal spawning, the extended spawning period with seasonal peaks and the seasonal migrations between shal- low and deeper waters (Mangold-Wirz, 1963; Mangold 1966; Boletzky, 1983; Ezzedine- Najai, 1984; Guerra and Castro, 1988; Boucaud-Camou and Boismery, 1991; Boucaud- Camou et al., 1991; Bouchaud, 1991; Le Goff and Daguzan, 1991) makes this species vulnerable to different gears during its life cycle. In the studied areas, the species moves inshore for spawning at the end of winter, thus becoming available to the artisanal gears, while from autumn to winter it retreats to deeper waters where it is mostly exploited by trawlers. Thus, fishing grounds for the different types of gear do not substantially over- lap, artisanal gears being used in areas where bottom trawling is not possible or not al- lowed. The size at 50% of maturity of females estimated in the Ligurian Sea was around 10 cm ML (Bartoli, 1999); similar or slightly higher values have been reported for other Mediterranean areas (Mangold-Wirz, 1963; Ezzedine-Najai, 1984; Manfrin-Piccinetti and Giovanardi, 1984). An important fraction of the trawl landings, especially in Livorno, consisted of immature specimens, while catches of medium size trammel nets and those of traps were mostly composed by adult individuals, frequently larger than the minimum size at maturity. From results of the present study, intensive exploitation of the earliest stages of cuttlefish seems to be rather occasional. However, trawling undoubtedly affects smaller specimens and mostly individuals that have not yet reached maturity. On the other hand, trammel nets and traps mainly affect spawners. Furthermore, a possible impact of traps might be related to the high mortality of the eggs that remain attached inside (Arkley et al., 1996). Stable, long term monitoring is required in order to understand the dynamics of the resource and the associated fleets. The results of the present study clearly indicate that further investigations on population dynamics as well as a system for monitoring the fishing are needed in order to produce a framework for implementation of management measures of this resource.

ACKNOWLEDGMENTS

We wish to thank all the fishermen and fishermen associations for their collaboration during the sampling and providing useful information about the activity of the fleets. The study was carried out within an E.U. research project focused on the evaluation of the cephalopod fisheries in Medi- terranean sea (DG XIV Study n° 97/0054). BELCARI ET AL.: CUTTLEFISH EXPLOITATION IN MEDITERRANEAN SEA 195

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ADDRESSES: (P.B.,P.S.) Dipartimento di Scienze dell’ Uomo e dell’ Ambiente, Università di Pisa, Via Volta 6, 56126 Pisa-Italy. (P.S.,M.D.) Instituto de Ciencias del Mar, CSIC, Passeig Maritim 3749, 08003 Barcelona, Spain. (A.T.,P.J.) Fisheries Research Institute, NAGREF, Nea Peramos, 64007 Kavala- Greece. (E.L.) NCMR, Aghios Kosmas, Helliniko, 16604 Athens, Greece. CORRESPONDING AUTHOR: (P.B.) E-mail: .