CIESM Congress 2001, Monaco, article 0234

Rapp. Comm. int. Mer Médit., 36,2001

234

Sharks and rays occupy, an high level in the trophic webs and are char-

acterised by a K strategy (1). This determines an high sensibility to even

relatively low fishing pressure (2), but in the Mediterranean very few

assessments and standardised data are available (3,4).

Material and methods

Six bottom trawl surveys, from Alboran to Aegean Sea, were carried out

between April and June (1994–99) within the MEDITS International pro-

gram (5). Biomass indices (BI; kg/km

) and standing stocks (swept area

method assuming a full catchability) were estimated from the database

produced by IFREMER. The BI were referred to 4 arbitrary geographical

areas identified by using a land-oriented criterion: Western(WA; Morocco,

Spain and France coasts), Western Central(WCA;Tyrrhenian, Corsica,

Sardinia and Sicily coasts), Eastern Central(ECA;Adriatic, Ionian and

Albanian), and Eastern(EA;Aegean Sea). The BI by dept strata were

pooled in 4 levels (– = less than 0.1, + = between 0.1 and1, o = between 1

and 10, O = more than 10 kg/km

Results and discussion

Overall, 6336 tows were performed and 45 species of elasmobranchs

identified (Tab.1): 18 sharks, 2 angelsharks, 4 stingrays, 3 skates, 14 rays,

3 electric rays and 1 rabbitfish. Single or sporadic captures were recorded

e.g. for Dasyatis violacea, Hexanchus griseus, Mustelus asterias, Raja

batis. For some species, these figures re?ect a true rarity (Rhinoptera

marginata) or population reduction (Squatina spp.), but in other cases

(Galeus atlanticus) some misclassification problem cannot be excluded.

Scyliorhinus canicula, Raja clavata, Galeus melastomusandSqualus

acanthiasshowed both high occurrence (>5% of the hauls) and abundance

(> 10 kg/km

or > 10% of relative biomass). Three faunistic groups can be

fied in regard to depth distribu

n: a

)well represented on all depths

such as R. clavata and S. canicula; b

)with preference for the shelf such as

Dasyatis pastinacaand M. mustelusand c

)for the slope such as C. gra

sand Etmopterus spinax. Only an handful of species have abu

evels of practical interest and just some are actually commercialised, bu

the large-sized species (M

sand Squalus spp.) show signs of depletion

although it were evidenced zones of relatively high density (likely danger-

ous hauls usually not explored by fis

)

.From the geographical point

of view, some species are abundant in all areas (S. canicula, R. clavata,

Torpedo marmorata, R. asterias, C. monstrosa), while others are most

common in the west (T. nobiliana, R. alba, Oxynotus centrina) or in the

east (S. acantias, R. radula, R. naevus, R. brachiura); some species are

localised into restricted areas (Hexachus griseusandRaja miraletusin the

Tyrrhenian,M. mustelus in the Adriatic Sea, or R. brachiuraandR. undu-

latain the Aegean Sea). Globally speaking the eastern basins (Adriatic and

Aegean Seas) show higher standing stocks, mainly due to the wider conti-

nental shelf. The good catches of R. clavata, the most abundant ray in the

Mediterranean, seems to re?ect mainly an higher ecological performance

than a true resilience to exploitation; in fact, concentrations (up to 100

kg/km

) likely closer to the “virgin” conditions are found only locally in

the Gulf of Lion, Corsica, Sardinia and Greece waters. It is worth noting

that up 64% of the total

biomass is located in the

Aegean Sea, where trawling

deeper than 400 m is practi-

cally absent. These prelimi-

nary results are only a first

step toward a future assess-

ment aimed at the manage-

ment of the elasmobranchs

stocks. Nevertheless, also

the analysis of M

EDITS

data

evidences clear signs of suf-

ferance for most of sharks

and rays and the risks of

local extinction for some

once common species

(Squatina spp.).

References

1 - Hoenig, J. M. and S. H.

Gruber., 1990. Life-history

patterns in the elasmobranchs:

implications for fisheries

management.NOOATech. Rep.

NMFS, 90: 1-16.

2 - Walker, P.A., 1996. Sensitive

skates or resilient rays? Annu.

Rep. Neth. Inst. Sea. Res.1996:

60-61.

3 - Muñoz-Chápuli, R., 1985.

Análisis de las capturas de

escualos demersales en el

Atlántico NE (27°N-37°N) y mar

de Alborán (Mediterráneo

occidental).Inv. Pesq. 49(1):

121-136..

4 - Bonfil, R., 1994. Overview of

world Elasmobranch fisheries.

FAOFisc.Tec. Pap.341.

5 – Bertrand, J., L, Gil de Sola,

C. Papakostantinou, G. Relini and

A. Souplet., 1997. An

international bottom trawl

survey in the Mediterranean: the

EDITS

Program.ICES CM

1997/Y: 03 16.

CATCH COMPOSITION AND ABUNDANCE OF ELASMOBRANCHS BASED ON THE MEDITS PROGRAM

Romano Baino

*, Fabrizio Serena

, Sergio Ragonese

, Javier Rey

and Paola Rinelli

ARPAT, Livorno, Italy - gea@arpat.toscana.it;

IRMA-CNR, Mazara del Vallo, Italy

Centro Oceangràfico, Fuengirola, Spain;

Istituto Sperimentale Talassografico-CNR, Messina, Italy

Abstract

Species composition and distribution from international trawl surveys are analysed in relation to geographical areas and depth. Data were

gathered in six campaigns carried out in 1994-99 along the whole European Mediterranean coasts with standardised gear and methodology.

Depths from 10 to 800 m were explored. For fortyfive species, the biomass indexes, standing stocks and frequencies of occurrence are

reported.

Keywords : elasmobranchii, trawl surveys, demersal, stock assessment, biomass

FrequencyStanding stock

Depth

biomass index

Species

ofbiomass

distribution

by geographical area

occurencepositive

(m)

(kg/km

)

hauls

%tons%0-5050-100100-200200-500500-800WAWCAECAEAOverall

Centrophorus granulosus

116

1528

2,75,50,13,1

2,9

Centrophorus uyato

318

1,01,7

0,6

Chimaera monstrosa

524

2056

-oO

8,53,31,44,5

4,0

Dalatias licha

152

780

3,32,80,80,2

1,5

Dasyatis centroura

0,0

Dasyatis pastinaca

778

oo+

0,12,90,21,9

1,5

Dasyatis tortonesi

0,1

0,0

Dasyatis violacea

0,00,0

0,0

Etmopterus spinax

1173

19%

2248

+oo

9,26,50,93,1

4,3

Galeorhinus galeus

126

0,10,20,10,4

0,2

Galeus atlanticus

0,0

Galeus melastomus

1702

27%

6891

12%

+OO

48,516,73,03,3

13,3

Heptranchias perlo

723

+oo

0,73,9

0,7

1,4

Hexanchus griseus

440

0,03,1

0,8

Hexanchus vitulus

0,3

0,1

Mustelus asterias

0,7

0,2

Mustelus mustelus

111

2645

Oo+++

0,11,118,70,3

5,1

Mustelus punctulatus

0,0

Myliobatis aquila

626

0,34,30,1

1,2

Oxynotus centrina

380

+o++

0,61,9

0,4

0,7

Raja alba

125

o--

0,8

0,0

0,2

Raja asterias

252

1575

oooo+

2,23,51,34,4

3,0

Raja batis

0,20,0

0,0

Raja brachyura

532

++oo-

0,4

2,8

1,0

Raja circularis

0,20,00,1

0,1

Raja clavata

1000

16%

8151

15%

oOOOo

4,614,97,927,0

15,7

Raja fullonica

0,00,00,0

0,0

Raja melitensis

705

++o

4,9

0,0

1,4

Raja miraletus

422

1729

oooo-

1,36,42,02,7

3,3

Raja montagui

107

882

++oo-

0,92,40,12,7

1,7

Raja naevus

348

++o+

0,30,00,11,8

0,7

Raja oxyrinchus

301

1899

+oOo

1,08,10,33,7

3,7

Raja polystigma

171

568

oooo

2,42,60,00,2

1,1

Raja radula

181

o++

0,00,20,9

0,3

Raja undulata

+--

0,1

0,0

Rhinoptera marginata

0,0

Scyliorhinus canicula

1761

28%

8396

15%

oOOOo

19,314,411,819,8

16,2

Scyliorhinus stellaris

301

+o+++

0,71,20,2

0,6

Squalus acanthias

327

6682

12%

OooOo

0,31,231,314,1

12,9

Squalus blainvillei

196

1490

++oo+

6,61,32,1

2,9

Squatina aculeata

0,3

0,0

Squatina squatina

0,1

0,0

Torpedo marmorata

317

1239

oooo-

4,33,30,91,9

2,4

Torpedo nobiliana

531

+++o+

2,12,10,00,5

1,0

Torpedo torpedo

+-+-

0,00,20,00,0

0,1

TOTALS633655158

11412289103106

Tab.1 – List of the elasmobranchs species caught in the MEDITS surveys, their occurrence, biomass, depth distribution