CHONDRICHTHYES CAUGHT DURING THE MEDITS SURVEYS IN … et al. 2010_Chondrichthyes caught... · Chondrichthyes caught during the Medits surveys in Italian waters 187 is a by-catch

Biol. Mar. Mediterr. (2010), 17 (1): 186-204

G. Relini, A. MAnnini, S. De RAnieRi1, i. Bitetto2, M.C. FolleSA3, V. GAnCitAno4, C. MAnFReDi5, l. CASCiARo2, l. Sion6

Centro Biolmar - DIP.TE.RIS., Università di Genova, V.le Benedetto XV, 3 – 16132, Genova, [email protected]

1Centro Interuniversitario di Biologia Marina (CIBM), V.le N. Sauro, 4 - 57128 Livorno, Italia.2COISPA Tecnologia & Ricerca, Via dei Trulli, 18/20 – 70126 Torre a mare (BA), Italia.

3Dipartimento Biologia Animale ed Ecologia, Università di Cagliari, V.le Poetto,1 - 09126 Cagliari, Italia.4Istituto per l’Ambiente Marino Costiero (IAMC), CNR, Via L. Vaccara, 61 - 91026 Mazara del Vallo (TP), Italia.

5Lab. Biologia Marina e Pesca, Dip.to B.E.S., Univ. di Bologna, V.le Adriatico, 1/N - 61032 Fano (PU), Italia.

6Dipartimento di Zoologia, Università di Bari, Via Orabona, 4 - 70125 Bari, Italia.

CHONDRICHTHYES CAUGHT DURING THE MEDITS SURVEYSIN ITALIAN WATERS

I CONDROITTI PESCATI DURANTE LE CAMPAGNE MEDITS NELLE ACQUE ITALIANE

Key-words: fish, trawl survey, biomass, Mediterranean Sea.

Abstract – Data on chondrichthyes fished during 16 surveys as part of the MEDITS project carried out from 1994 to 2009 on trawlable bottoms up to 800m depth in all seas around Italy are presented and discussed. From a total of 7 GSAs (10255 hauls) 38 elasmobranch species, including 21 rays and skates, 16 sharks and 1 chimaera, have been identified. Only 10 species occurred in all GSAs, 31 in the Strait of Sicily and 19 in the South Adriatic Sea. The number of species caught per year ranged from 23 to 31.

Introduction - Although the contribution of elasmobranchs to the market is low (in Italy during 2008, 1375t were landed, according to IREPA data) the by-catch discarded at sea is high and so the management of these fish needs particular attention above all in order to maintain biodiversity and the functions and services of the ecosystem. The interaction between species and the removal of top predators are crucial for the structure and function of the ecosystems. At present some species are threatened, often as a result of human activities. The main reasons for this is that these fish have a k-strategy life span: they grow slowly, mature at a relatively late age, have few young, low natural mortality rates and a very slow population increase (Hamlett 1999, 2005), they are generally top predators and some are rare. They are an important indicator of resource exploitation and the evolution of the community in an area, particularly where there are important multispecies fisheries. The non-sustainable exploitation of elasmobranchs implies an urgent need for a more systematic approach to the assessment and conservation of elasmobranchs.

Action Plans for the conservation of Cartilaginous Fish in the Mediterranean have been proposed at national and international level (in particular, UNEP MAP RAC/SPA 2003; FAO 1998). But there is an urgent need for our knowledge to be updated and no specific research on elasmobranchs has been financed or carried out for more than a year. Most of the data come from trawl surveys for demersal stock assessment (Relini, 2000 and Relini et al., 2000) or, in the case of pelagic fish, from longline fisheries. Some data were collected during the ELASMOIT project (Relini et al., 2010) supported by the Ministry for the Environment, Land and Sea Protection. There are 72 species present in Italian seas (plus 7 doubtful species) of which one is a chimaera, 41 are sharks and 30 are rays and skates (Vacchi and Serena, 2010). Some species are large, high-speed swimmers, which makes them very difficult to catch by bottom trawling.

At present there is no target fishery for elasmobranchs in Italy. All the landed catch

Chondrichthyes caught during the Medits surveys in Italian waters 187

is a by-catch of other fisheries. As mentioned above, the landed commercial catch in 2008 was 1375t, 63% of which was fished by otter trawlers and 54% were sharks.

Materials and methods - Data were collected during the Medits surveys carried out each year from 1994 to 2009 in the 7 GSAs (Geographical SubAreas established by GFCM-FAO in 2001) of Italian seas (Fig. 1) between May and July on all trawlable bottoms between 10m (Posidonia meadows excluded) and 800m depth. The sampling design was random stratified, five strata were established (see Tab. 1) and the number of hauls was proportional to the surface of strata and the position of hauls was the same in all years. The duration of the hauls was one hour at depths more than 200 m and half an hour at depths less than 200 m. The gear had a vertical opening of 2-2.5 m and small cod end (20 mm stretched mesh).

Fig. 1 - The seven Italian GSAs (9, 10, 11, 16, 17, 18, 19).Le sette GSA italiane (9, 10, 11, 16, 17, 18, 19).

Tab. 1 - The total number of hauls per stratum and GSA.Numero totale di cale per strato e GSA.

For information on gear, protocol of methods and processing of data, see Relini et al., 2008 and the website (www.sibm.it/SITO%20MEDITS/principalemedits.htm).

G. Relini et al.188

The number of hauls per GSA is given in Tab. 1 and a total of 10255 were performed during 16 surveys. Estimates of abundance indices (density n/km2, biomass kg/km2) were based on stratified random sampling and swept area method and were computed for two macrostrata: shelf (10-200 m depth) and slope (200-800 m depth).

For species caught in at least 12 out of 16 campaigns carried out (≥75%) a non- parametric Spearman’s rho value was estimated so as to test time trends.

The main references for identification and updated nomenclature are Fisher et al. (1987), Serena (2005), Serena et al. (2010) and Vacchi & Serena (2010).

The references give record of all the papers published by GSAs on elasmobranchs fished during Medits surveys.

Results - During the course of 16 years, 38 species (Tab. 2) including 21 rays and skates, 16 sharks and 1 rabit fish were collected and identified. Only 9 species (including 5 sharks) occurred in all GSAs, and another 10 were present in 6 GSAs.

Tab. 2 - List of species fished during Medits surveys (1994-2009) in each GSA.Lista delle specie catturate durante le campagne Medits (1994-2009) in ciascuna GSA.

The highest number of species was found in the Strait of Sicily (GSA16: 31 species), the lowest (19 species) in the South Adriatic Sea (GSA18). Eight species including 1


shark were found only in one GSA and three of them during one year only: they are Galeorhinus galeus (GSA10, 1995 and 2001), Dasyatis centroura (GSA19, 2002) Pteroplatytrygon violacea (GSA10, 2000 and 2002), Gymnura altavela (GSA19, 2006) Pteromylaeus bovinus (GSA17, ten years), Dipturus batis (GSA9, 1996) Leucoraja melitensis (GSA16, all years excluding 1994 and 2003) and Rostroraja alba (GSA16, 1995, 2000, 2003, 2005, 2007, 2008 and 2009).

The number of species caught per year (Tab. 3) was 23 in 1994, 30 in 1995 and fell to 23 in 1997, then increased with some fluctuation to 31 in 2008 and 2009.

Tab. 3 - List of species caught per year in all GSAs.Lista delle specie catturate ogni anno in tutte le GSA.

With regard to vertical distribution, the presence of species in different strata is reported (Tab. 4). In the last column on the right there are literature data on the vertical distribution of the species. In grey are the Medits data that conflict with the literature data and hence change the known vertical distribution of some species. There is interesting information about S. stellaris, T. marmorata and T. torpedo: whereas previously their vertical distribution was known up to 100 m depth, during the Medits surveys they were collected at more than 500 m depth. Sixteen species were found in all five strata, five in one stratum alone. The highest number of species occurred at the fourth and fifth strata, while the lowest was found at the second stratum, with a difference of five species. Five species were found only on the slope and six only on the shelf.

G. Relini et al.190

Tab. 4 - Species occurrence in different strata and literature data regarding depth range.Presenza delle specie nei diversi strati e dati della letteratura sulla distribuzione batimetrica.

Grey areas represent new data that conflict with the literatureLe aree in grigio si riferiscono a dati nuovi discordanti con quelli della letteratura

Data on numbers of individuals and biomass per GSA and year in the shelf (10-200 m) and in the slope (200-800 m) are given in Tabs. 5, 6, 7, 8, in which (when applicable) the Spearman rho values show the trend in each GSA.

The most abundant species on the shelf (Tab. 5) are S. canicula, R. asterias, R. brachyura and R. miraletus.

A clear negative trend occurs for S. acanthias in GSA 17, while positive trends are evident for R. brachyura (GSA11), M. mustelus (GSA16), R. clavata (GSA9 and GSA16), R. miraletus (GSA11) and S. blainvillei (GSA16). In 87 out of 110 series the data are insufficient to calculate the coefficient, in 24 there is no trend, 6 are positive and 1 negative as mentioned above.


Tab. 5 - Density index (n/km2) for shelf stratum (10-200 m depth) per GSA. Medits 1994-2009. Significant Spearman rho values are in bold.Indici di densità (n/km2) per la piattaforma (10-200 m) e per GSA. Medits 1994-2009. In grassetto i valori del rho di Spearman significativi.

(Segue/Follows)

G. Relini et al.192

The most abundant species On the slope (Tab. 7 and 8) are G. melastomus (GSA9), E. spinax (GSA9), S. canicula (GSA11), R. clavata (GSA11) and D. oxyrhincus (GSA11). In 103 out of 144 series the data are insufficient to calculate the Spearman coefficient; in 29 situations there are no trends, in two there are negative trends for biomass and three for density. There are ten positive trends for biomass and seven for density.

The trends of some common species on the shelf and on the slope in different GSAs are shown in Figs. 2-8. On the slope the biomass of R. clavata and S. canicula is quite different from one GSA to another. The highest values were reached in


Tab. 6 - Biomass index (kg/km2) for shelf stratum (10-200 m depth) per GSA. Medits 1994-2009. Significant Spearman rho values are in bold.Indici di biomassa(kg/km2) per la piattaforma (10-200 m) e per GSA. Medits 1994-2009. In grassetto i valori del rho di Spearman significativi.

(Segue/Follows)

G. Relini et al.194


Tab. 7 - Density index (n/km2) for slope stratum (200-800 m depth) per GSA. Medits 1994-2009. Significant Spearman rho values are in bold.Indici di densità (n/km2) per la scarpata (200-800 m) e per GSA. Medits 1994-2009. In grassetto i valori del rho di Spearman significativi. In grassetto i valori del rho di Spearman significativi.

Tab. 8 - Biomass index (kg/km2) for slope stratum (200-800 m depth) per GSA. Medits 1994-2009. Significant Spearman rho values are in bold.Indici di biomassa (kg/km2) per la scarpata (200-800 m) e per GSA. Medits 1994-2009. In grassetto i valori del rho di Spearman significativi.

(Segue/Follows)

G. Relini et al.196

Sardinia (GSA11) and the Strait of Sicily (GSA16). A clear positive trend occurs in GSA9 and GSA16. In GSA19 R. clavata was not fished, so in Fig. 4 the trend of T. nobiliana and S. canicula are shown. When the first species decreases the second increases; but this could be fortuitous.

On the slope G. melastomus was fished in all GSAs and all years (Fig. 5). The highest values of biomass were obtained in GSA9 (Ligurian and Northern Tyrrhenian Sea) and GSA11 (Sardinia) and in the last years also in GSA16 (Strait of Sicily) where there was an increasing trend of the catch. The lowest values were obtained in the northern and central Adriatic Seas, but this is due mainly to the reduced surface of the slope.


Fig. 2 - Biomass trends (kg/km2) of R. clavata and S. canicula in different years on the slope of GSA 9, 10 and 11.Andamenti della biomassa (kg/km2) di R. clavata e S. canicula in diversi anni sulla scarpata delle GSA 9, 10 e 11.

Kg/

Km

2K

g/K

m2

Kg/

Km

2

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Fig. 3 - Biomass trends (kg/km2) of R. clavata and S. canicula in different years on the slope of GSA 16, 17 and 18.Andamenti della biomassa (kg/km2) di R. clavata e S. canicula in diversi anni sulla scarpata delle GSA 16, 17 e 18.

Kg/

Km

2K

g/K

m2

Kg/

Km

2


Fig. 4 - Biomass trends (kg/km2) of T. nobiliana and S. canicula in different years on the slope of GSA19.Andamenti della biomassa (kg/km2) di T. nobiliana e S. canicula in diversi anni sulla scarpata delle GSA19.

Fig. 5 - Biomass (kg/km2) of G. melastomus caught in different years on the slope of seven GSAs.Biomassa (kg/km2) di G. melastomus presente nei diversi anni sulla scarpata delle sette GSA.

R. clavata and S. canicula were also caught in the shelf bottoms and the biomass trends of these two species and of the R. asterias in three GSA are shown in Fig. 6. The highest biomass was fished in Sardinia (GSA11) and in Sicily (GSA16). The biomass trends of some species fished on the shelf of Northern and Central Adriatic seas are given in Fig. 7. There was an exceptional catch of S. acanthias (304 kg/km2) in the 1998 survey, where normally the catch is between 3 and 22 kg/km2. The catch of M. mustelus is irregular. This species was caught in good quantity (31 kg/km2) in GSA19 during the 2009 survey (Fig. 8). The total biomass of chondrichthyes caught each year during the Medits surveys is given in Fig. 9. The highest values were obtained in Sardinia (GSA11) and Sicily (GSA16), while the lowest were in the Southern Adriatic (GSA18) and Ionian Seas (GSA19). There are no clear trend, positive or negative.

Kg/

Km

2

Kg/

Km

2

G. Relini et al.200

Fig. 6 - Biomass trends (kg/km2) of R. asterias, R.clavata and S. canicula in different years on the shelf of GSA 9, 11 and 16.Andamenti della biomassa (kg/km2) di R. asterais, R. clavata e S. canicula in diversi anni sulla piattaforma delle GSA 9, 11 e 16.

Kg/

Km

2K

g/K

m2

Kg/

Km

2


Fig. 7 - Biomass trends (kg/km2) of some species on the shelf of GSA17 in the period 1994-2009. The scale on the right is for S. acanthias.Andamenti della biomassa (kg/km2) di alcune specie della piattaforma delle GSA17 dal 1994 al 2009. La scala sulla destra è per S. acanthias.

Fig. 8 - Biomass trends (kg/km2) of some species of the shelf of GSA19 in the period 1994-2009. The scale on the right is for M. mustelus.Andamenti della biomassa (kg/km2) di alcune specie della piattaforma delle GSA19 dal 1994 al 2009. La scala sulla destra è per M. mustelus.

Conclusions - During the Medits surveys 16 sharks out of 22 demersal species listed in the checklist of Italian Fauna (Vacchi and Serena, 2010) were fished. All torpedos and 12 skats out of 16, 6 Myliobatiformes out of 9 (some are pelagic) were caught.

In a previous paper (Bertrand et al., 2000) dealing with elasmobranches caught in the whole area covered by the Medits surveys from 1994 to 1998, 44 species were described: 1 chimaera, 19 sharks and 24 rays and skates, of which 35 species are common to the present work. G. altavela, M. punctulatus and P. bovines were not fished in the period 1994-1998, while S. squatina, S. aculeata, Galeus atlanticus (not present in Italian waters), Hexanchus vitelus (=H. nakamurai only one record in Italy), Raja naevus, R. radula, R. undulate, Dasyatis tortonesei (not considered a valid species), Rhinoptera marginata are not mentioned in the present paper.

Kg/

Km

2K

g/K

m2

G. Relini et al.202

Fig. 9 - Trends of the total biomass of Chondrichthyes in the 7 GSAs.Andamenti della biomassa totale dei Condroitti nelle 7 GSA.


When we compare these data, we have to bear in mind the different areas and numbers of years considered. For the Italian seas important data come from the GRU.N.D. surveys carried out from 1985 to 1998 (Relini et al., 2000). During the Grund surveys all the species recorded in the present paper were found with the exception of Gymnura altavela. The species R. radula, R. naevus, R. rondeleti (not valid species), R. undulata, M. mobular and S. squatina fished in Grund surveys were not caught during the 1994-2009 Medits surveys. Although comparison and conclusions are not easy, we can recognize a reduction in the number of species of rays and the disappearance of the Squatina species. According to the Medits data, the situation of elasmobranches seems quite stable in the period 1994-2009 both in terms of number of species and biomass. This conflicts with some landing data collected during the Elasmoit project (Relini et al., 2010) which showed low numbers of species and individuals and poor quantity in weight.

In conclusion, we can say that during the Medits surveys there were no changes in the demersal elasmobranch population, whereas there are changes if we compare the Medits data with data collected before 1994. The main difference, as mentioned earlier, is the reduction in the number of rays and the disappearance of the Squatina species.

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