SCRS/2004/079 Col. Vol. Sci. Pap. ICCAT, 58(2): 589-595 (2005)

SIZE FREQUENCY COMPOSITION OF THE MEDITERRANEAN SPEARFISH ( BELONE, RAFINESQUE) CATCHES IN THE TYRRHENIAN SEA AND IN THE STRAIT OF MESSINA IN 2003

A. Di Natale, A. Mangano, A. Celona, M. Valastro1

SUMMARY

The Mediterranean spearfish continues in increasing its importance on the market, in parallel with the apparent increasing of its presence. Following the previous experience, several data have been collect by Aquastudio during the landing control carried out in the last year, particularly in the coastal areas of the central and southern Tyrrhenian Sea and in the Strait of Messina. Trends in LJFL means and RW means are slightly different between them, possibly due to higher number of weight samples. A preliminary estimate revision of the catches is also presented.

RÉSUMÉ

L’importance du makaire-bécune de la Méditerranée ne cesse de croître sur le marché, parallèlement à l’augmentation apparente de sa présence. A la suite de l’expérience antérieure, plusieurs données ont été recueillies par Aquastudio au cours du contrôle des débarquements réalisé l’année dernière, notamment dans les zones côtières du centre et du sud de la mer Tyrrhénienne et dans le Détroit de Messine. Les tendances des moyennes de longueur maxillaire inférieur-fourche (LJFL) et des moyennes de poids vif sont légèrement différentes, en raison peut-être du nombre plus élevé d’échantillons de poids. Une révision des estimations préliminaires des captures est également présentée.

RESUMEN

Sigue produciéndose un incremento de la importancia comercial del Tetrapturus pfluegeri + T. belone mediterráneo, junto con un aparente aumento de su presencia. Tras las anteriores experiencias, Aquastudio ha recopilado varios datos durante el control de los desembarques realizado el año pasado, sobre todo en las zonas costeras del mar Tirreno central y meridional y el Estrecho de Messina. Las tendencias en la LJFL media y el RW medios presentan ligeras diferencias, debidas posiblemente al mayor número de las muestras de peso. También se presenta una revisión preliminar de la estimación de las capturas.

KEYWORDS

Population structure, Potential yield, Artisanal fishery, Catch composition, Size distribution, Mediterranean spearfish, By-catch

1 Aquastudio Research Institute, Via Trapani 6, 98121 Messina, Italy. 589 1. Introduction

As reported in a previous paper (Di Natale et al. SCRS/02/161), the Mediterranean spearfish, Tetrapturus belone Rafinesque 1810, is the only spearfish known to have only a limited regional distribution. It lives in the Mediterranean sea (Anonimous 1973; Bini 1968; Nakamura 1985; Postel 1964; Rodriguez-Roda & Howard 1962; Tortonese 1961, 1975), even if a few specimens seems to have been caught even in the Atlantic ocean, but in the immediate surroundings of the Straits of Gibraltar. In the 1960s it was considered distributed even in the tropical Atlantic Ocean (Robins & De Sylva 1960) but later Robins & De Sylva (1963) attributed the specimens from the Atlantic to another , Tetrapturus pfluegeri.

The reproduction of this species is known in the Straits of Messina, where eggs, larvae and juveniles have been reported (Spartà 1953, Spartà 1961, Cavaliere 1962). It is suspected that reproduction may also occur in other several Mediterranean areas.

This species is not a target species, except for the traditional harpoon fishery in the Straits of Messina. For all the other fisheries targeting large pelagic species, like the gillnet fishery, the long-line fishery, the trolling lines and the big-game fishery, it is a by-catch component. Catches are very rarely reported in scientific papers and this fact creates serious difficulties in assessing the real relevance of this species.

According to the our knowledge of the fishery, the Mediterranean spearfish is usually sold on the local markets and consumed fresh, reaching good prices in several places, due to the high quality and taste of its meat.

2. Methods

The methodology adopted to collect the size frequencies of the Mediterranean spearfish (Tetrapturus belone) along all the coasts of the southern and central Tyrrhenian Sea (Italian Regions: Sicily, Calabria, Basilicata, Campania and Lazio) and in the Straits of Messina was the same adopted in the past in various projects (Di Natale et al. 1992, 1995b, 1998, 2002; Di Natale 1999).

The basic structure of the landing ports was kept in the same manner (Ponza in the Central Tyrrhenian Sea, Lipari and Milazzo in the Southern Tyrrhenian Sea). In addition to those traditional landing points used for sampling, we included the Straits of Messina, with a landing point in the small fishermen village of Ganzirri, where the traditional harpoon fishery is still practised.

In most of the places, the landing control was carried out regularly (two weeks per month), while in another place (Ganzirri) it was on opportunistic basis, trying to cover all the positive fishing days.

The lower jaw fork length (LJFL) measure was used as a standard length, because sometimes the short bill could be damaged or broken, while the round weight (RW) was used as a standard weight measure, thanks to the habit to land these fishes fresh and not gutted.

Data sets concerning length or weight show different samples, because it is not always possible to get both measures from the same fish, according to the opportunities or the situation at landing. In some cases, several fishes were weighted together and it was not possible to use these data, besides to get the total landed weight.

The data sets were treated separately for gillnets and harpoons, due to possible differences.

3. The data

In 2003 it was possible to collect a total of 684 data on Tetrapturus belone: among these, only 44 were length data (LJFL), while 484 were weight (RW) data. Other data, coming from a total of 200 fishes, were used only to obtain the total landings, because they are related to fishes weighted together in small groups by the fishmongers.

About 55% of the samples were originated from the harpoon fishery, while the others from the gillnet fishery. No data were available from the ling-line fishery.

The few length data (LJFL) are presented in Figures 1 to 3, showing the length frequencies by classes of 2.

590 The length frequency, based on the low number of fishes sampled in 2003, shows peaks at 146, 148 and 156 cm for the gillnet fishery; the minimum size was 139 cm, while the maximum was 163 cm, with an average of 148,42 cm. No peaks were detectable for the harpoon fishery, where the minimum size was 118 cm, while the maximum was 166 cm, with an average length was 142,74. In total, the peak was between 148 to 149.9 cm, with a minimum lengthy of 118 cm, a maximum at 166 cm and an average of 144,47 cm

The weight data are more important in number, even considering that 200 fishes were not include, because they were weighted together in groups. As concerns the harpoon fishery, the peak was at 12 kg, with a minimum weight of 5 kg, a maximum at 29 kg and an average of 12.74 kg. In the gillnet fishery the peak was at 10 kg, with a minimum weight of 5 kg, a maximum at 29 kg and an average of 14.16 kg. In total, the peak was at 10 kg, with a minimum weight of 5 kg, a maximum at 29 kg and an average of 13.13 kg (figures 4 to 6).

Both maximum length and weight have been lower that the maximum measures reported in previous years (Di Natale et al. 2002).

4. Discussion

From the above-mentioned data and from the data sets available for the previous years (Di Natale et al. 2002) it was possible to obtain a summary table (Table 1) showing the most important reference points in each year (number of samples, minimum maximum and mean values, standard deviations). Considering the mean values as the most reliable reference points, the last two graphs (Figures 7 and 8) show some trends for the period 1994 to 2002.

As concerns the mean length (LJFL), there is a triple-dome pattern, with the lowest values in 1994, 1998 and 2001 and the highest values in 1997, 1999 and 2003 (Figure 7). The limited size of the sample (n = 331) clearly affects the reliability of the general figure, but the length data are quite difficult to collect for landing operational reasons. The general trend appears as moderately positive (r2= 0.0765), but no length data were available in 2002.

The graph showing the trend of the mean weight values shows some differences, but the sample was more then five times the previous one and quite significant (n= 1802). Even here there is a triple-dome pattern, more smoothed, with the lowest values again in 1994, 1998 and 2001 and the highest values in 1996, 1999 and 2002 (Figure 7); differences in peaks between length and weight data might be due to the different components in samples. As concerns the general trend, showed by the linear regression, it is slightly negative (r2= 0.0147).

Even considering the strong improvement in data in 2003 (+54,7% of the previous total) the interpretation of the above reported data is still not clear, because the factors affecting the situation of this fishery are the same reported in the previous paper (Di Natale et al. 2002). According to the last data, it seems that the presence of this species in the last year was increasing even considering that no relevant data are available from the long-line fishery, the most practised in the Mediterranean sea, able to provide good catches of this non-target species. If this fact reflects an increasing in the total population, or a higher availability to the fishery or another possible reason is unclear.

It is also important to take into account the fact that the oceanographic conditions in 2003 in the Mediterranean were very peculiar, with high water temperatures in the upper stratum from late May to October. This situation prolonged the spawning period of several large pelagic species, causing a modification in the usual behaviour. It might be the case that the same happened for the Mediterranean spearfish.

Its importance on the market is still increasing, due to the good taste of the fish and to the less availability of fresh on the local Mediterranean market, as a consequence of the driftnet ban.

According to some speculative estimates made in the past (Di Natale et al. 1995b) and even more recently (Di Natale et al. 2002) the hypothesis to have more than 100 tons of catches for this species in the Mediterranean sea appears now very conservative. As a matter of fact, taking into account the consistency of the various fleets, the trend in catches per each gear and the catches reported in the sampling ports, the previous estimated amount for the whole Mediterranean area might be not so far from the total catch of this species obtained in 2003 by the Italian fleet only. The very small attention provided to this species by the official statistics everywhere in the Mediterranean is clearly affected by the scattered landings and the previous lower importance of the quantities.

591 Due to the still poor knowledge on this species and to the possibility that the stock might be not very consistent, it should be useful to better follow the landings (including those from long-lines), with the purpose to have a much more detailed figure of the Mediterranean spearfish situation. The inclusion of this species in the EC Data Collection Programme might help to improve the current knowledge on Tetrapturus belone.

5. Bibliography

ANON, 1973. Catalogue raisoné des Poissons des mers Marocaines. 2eme Partie. Bull. Inst. Peche Marit. Maroc, 21: 350. BINI G., 1968. Atlante dei Pesci delle Coste Italiane. Mondo Sommerso Ed., Roma, vol. VI: 61-62. CAVALIERE A., 1960. Notizie su biologia e pesca di Tetrapturus belone Raf. Boll. Pesca Piscic. Idrobiol. XV (2). COSTA F., 1991. Atlante dei Pesci dei Mari Italiani. Mursia Ed., Milano: 17-18 DI NATALE A., G. Labanchi, A. Mangano, A. Maurizi, L. Montaldo, E. Navarra, A. Pederzoli, S. Pinca, V. Placenti, G. Schimmenti, E. Sieni, G. Torchia, M. Valastro, 1992 - Gli attrezzi pelagici derivanti utilizzati per la cattura del Pescespada (Xiphias gladius) adulto: valutazione comparata della funzionalità, della capacità di cattura, dell'impatto globale e della economia dei sistemi e della riconversione. Report to: Ministry of Merchant Marine, Direction General for Fishery and Aquaculture, Roma: 350 p. + 60 suppl. DI NATALE, A., A. Mangano, A. Maurizi, L. Montaldo, E. Navarra, S. Pinca, G. Schimmenti, G. Torchia, M. Valastro. 1995a. A review of driftnet catches by the Italian fleet: species composition, observers data and distribution along the net. Third Expert Consultation on Stock of Large Pelagic Fishes in the Mediterranean Sea, Fuengirola, Spain, 1994): ICCAT, SCRS/94/81, Col.Vol.Sci.Pap. XLIV (1): 226-235. DI NATALE A., A. Mangano, E. Navarra, M. Valastro, 1995b. Osservazioni sulla pesca dei grandi nei bacini tirrenici e dello Stretto di Sicilia (prosecuzione). Report to: Ministry of Agricultural, Food and Forestry Resouces, Direction General for Fishery and Aquaculture, Rome, 322-329. DI NATALE A., A. Mangano, E. Navarra, M. Valastro, 1998. Osservazioni sulla pesca dei grandi Scombroidei nei bacini tirrenici e dello Stretto di Sicilia. In. Le Ricerche sulla Pesca e sull'Acquacoltura nell'Ambito della Legge 41/82. Parte 1. M.P.A., Roma: 189-198. DI NATALE A., A. Mangano, A. Celona, E. Navarra, M. Valastro. 2002. Size frequency composition of the Mediterranean spearfish catches in the Tyrrhenian Sea and in the Strait of Messina in the period 1994-2002. ICCAT/GFCM Expert Consultation on Stock of Large Pelagic Fishes in the Mediterranean Sea, Malta: ICCAT, SCRS/02/161. DI NATALE A., 1999. La ricerca sulla pesca: I Grandi Pelagici. In. Le Ricerche sulla Pesca e sull'Acquacoltura nell'Ambito della Legge 41/82. Parte 4: Relazioni. M.P.A., Roma, 1999; Biol. Mar. Medit., 7(4): 46-58. ROBINS C.R. and D.P. De Silva, 1960. Description and relationships of the , Tetrapturus belone, based on western north Atlantic specimens. Bull. Mar. Sci. Gulf Caribb., 10(4): 383-413. ROBINS C.R. and D.P. De Silva, 1963. A new western Atlantic Spearfish, Tetrapturus pflueggeri with a redescription of the Mediterranean Spearfish, Tetrapturus belon. Bull. Mar. Sci. Gulf Caribb., 13 (1): 84-122. RODIGUEZ RODA J. and J.K. Howard, 1962. Presence of Istiophoridae along the South Atlantic and the Mediterranean coast of Spain. Nature 196 (4853): 495-496. SPARTA’ A., 1953. Uova e larve di Tetrapturus belone Raf. (Aguglia imperiale). Boll. Pesca Piscic. Idrobiol., VIII (1): 1-8. SPARTA’ A., 1961. Biologia e pesca di Tetrapturus belone Raf. e sue forme post-larvali. Boll. Pesca Piscic. Idrobiol., XV (1): 20-24. TORTONESE E., 1961. Mediterranean fishes of the family Istiophoridae. Nature, 192 (4797: 80 p. TORTONESE E., 1975. Osteichthyes. Pesci Ossei. In: Fauna d’Italia. Calderini Ed., Bologna, vol. XI: 374-376.

592 Table 1. Summary table showing most important reference points (no. of samples, minimum-maximum relaible reference points, standard deviations).

1999 1999 2000 2000 2001 2001 2002 2003 2003 1994 1995 1996 1997 1998 1999 2000 2001 2003 gillnet harpoon gillnet harpoon gillnet harpoon harpoon gillnet harpoon no. LJFL 11 50 22 3 11 18 18 0 106 106 0 66 66 0 0 44 13 31 mean LJFL 114,45 142,28 141,86 151 134,18 146,67 146,67 140,82 140,82 126,73 126,73 144,47 148,92 142,74 min LJFL 78 102 109 141 109 102 102 102 102 95 95 118 139 118 max LJFL 165 181 171 170 170 174 174 181 181 193 193 166 163 166 St.Dev.LJFL 26,1127 22,0297 21,004 16,462 22,1035 20,0088 20,0088 17,2184 17,2184 23,6952 23,6952 13,3684 6,8125 15,031 no. RW 49 110 29 15 42 116 67 49 265 99 166 466 106 360 226 484 134 350 mean RW 12,46 14,02 14,4 13,93 11,95 13,88 14,65 12,84 13,38 14,42 12,75 12,63 11,76 12,89 13,64 13,13 14,13 12,74 min RW 4 2 3 4 4 3 353341,41,465555 max RW 33 36 24 21 22 30 30 24 36 30 36 35 35 31 30 29 29 29 St.Dev.RW 7,2914 7,5232 4,924 4,9959 4,5596 4,3924 4,6726 3,7768 5,3798 5,4541 5,2523 5,9001 8,3794 4,9257 4,1335 4,5597 4,8725 4,378

GILLNET no = 13

20,00

15,00

10,00

5,00

0,00

LENGTH CLASSES (cm)

Figure 1.

ALL GEARS no = 44

15,00

10,00

5,00

0,00

LENGTH CLASSES (cm)

Figure 2.

GILLNET no = 13

20,00

15,00

10,00

5,00

0,00

LENGTH CLASSES (cm)

Figure 3.

593 20,0

18,0

16,0 No. 134

14,0

12,0

10,0

8,0

6,0

4,0

2,0

0,0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 WEIGHT CLASSES (kg)

Figure 4 - Weight classes of Mediterranean spearfish catches obtained by the gillnet fishery in 2003 in the Tyrrhenian Sea.

Figure 4. Weight classes of Mediterranean spearfish catches botained by the gillnet fishery in 2003 in the Tyrrhenian Sea.

HARPOON no = 350

15,00

10,00

5,00

0,00

WEIGHT CLASSES (kg)

Figure 5. Harpoon fishery

ALL GEARS no = 484

15,00

10,00

5,00

0,00

WEIGHT CLASSES (kg)

Figure 6. All gears.

594 Figure 7 - MEAN LENGTH IN Tetrapturus belone

160

150

140

130

120

110

100

90

80 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003

Figure 7. Mean length in Tetrapturus belone.

16

15

14

13

12 11 10 9 KG y = -0,0315x + 13,515 8 R2 = 0,0147 7 6 5 4 3 2 1 0 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003

Figure 8. Mean weight data series in Tetrapturus belone.

595