Figure 1
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Figure 8
Frequency of prey groups for each size class of thornback ray
| N | Size class (cm) | Annelida | Cephalopoda | Crustacea | Teleostei | Other |
|---|---|---|---|---|---|---|
| 2 | 40–50 | 0 | 0 | 0.15 | 0 | 0.23 |
| 29 | 50–60 | 0.001 | 1.71 | 4.62 | 9.23 | 2.8 |
| 35 | 60–70 | 0.004 | 2.03 | 11.91 | 18.58 | 4.99 |
| 27 | 70–80 | 0.002 | 0.97 | 6.48 | 20.56 | 3.69 |
| 11 | 80–90 | 0.004 | 0.28 | 3.76 | 7.18 | 0.84 |
Diet composition of R_ clavata presented as percentage numerical composition (N%), percentage weight of prey items (W%), percentage frequency of occurrence (F%) and percentage index of relative importance (IRI%)
| Prey | N% | W% | F% | IRI% |
|---|---|---|---|---|
| Nematoda | ||||
| Unidentified nematode | 3.37 | 0.01 | 5.00 | 0.80 |
| Cephalopoda | ||||
| Loligo sp. | 2.25 | 5.64 | 5.00 | 1.88 |
| Octopus sp. | 0.16 | 0.08 | 0.45 | 0.01 |
| Crustacea | ||||
| Decapoda | ||||
| Aegaeon cataphractus | 0.16 | 0.11 | 0.45 | 0.01 |
| Natantia | ||||
| Caridea | 24.88 | 12.41 | 17.73 | 31.42 |
| Parapenaeus longirostris | 4.82 | 2.63 | 2.73 | 0.97 |
| Solenocera membranacea | 0.80 | 0.29 | 0.45 | 0.02 |
| Stomatopoda | ||||
| Squilla mantis | 4.17 | 7.14 | 3.64 | 1.96 |
| Erugosquilla massavensis | 0.16 | 0.02 | 0.45 | 0.00 |
| Brachyura | ||||
| unidentified Brachyura | 29.53 | 7.71 | 10.45 | 18.51 |
| Medorippe lanata | 0.96 | 0.79 | 1.36 | 0.11 |
| Gonoplax rhomboides | 0.32 | 0.19 | 0.45 | 0.01 |
| Anapagurus petiti | 0.48 | 0.07 | 0.45 | 0.01 |
| Athelecyclus roduntatus | 0.16 | 0.19 | 0.45 | 0.01 |
| Teleostei | ||||
| Boops boops | 0.48 | 3.47 | 0.45 | 0.09 |
| Merluccius merluccius | 0.48 | 1.27 | 0.91 | 0.08 |
| Gobius sp. | 0.32 | 0.70 | 0.45 | 0.02 |
| Trachurus trachurus | 1.77 | 9.12 | 4.55 | 2.35 |
| Micromesistius poutassou | 0.64 | 4.29 | 0.91 | 0.21 |
| Mullus barbatus | 0.96 | 10.27 | 2.73 | 1.46 |
| Mullus surmuletus | 0.16 | 1.37 | 0.45 | 0.03 |
| Sardina pilchardus | 0.32 | 2.23 | 0.91 | 0.11 |
| Spicara smaris | 0.32 | 3.18 | 0.45 | 0.08 |
| Trachurus mediterraneus | 0.16 | 0.30 | 0.45 | 0.01 |
| Engraulis encrasicolus | 1.12 | 1.28 | 0.45 | 0.05 |
| Gadiculus argenteus | 0.16 | 0.22 | 0.45 | 0.01 |
| Triglidae | 0.48 | 1.87 | 0.45 | 0.05 |
| Serranus hepatus | 0.16 | 0.62 | 0.45 | 0.02 |
| Unidentified fish | 8.19 | 9.20 | 12.27 | 10.14 |
| Other | 12.04 | 13.32 | 24.55 | 29.59 |
Von Bertalanffy growth parameters for R_ clavata
| Sex | Growth parameters | ||
|---|---|---|---|
| L∞ (cm) (95% CI) | K (year−1) (95% CI) | t0 (year) (95% CI) | |
| Males | 101.71 (53.67−149.76) | 0.18 (−0.060 to 0.410) | −0.07 (−2.910 to 2.779) |
| Females | 106.54 (73.18−139.89) | 0.16 (0.029−0.286) | −0.28 (−1.981 to 1.427) |
Comparison of von Bertalanffy growth parameters by region
| Region | N | Sex | L∞ (cm) | K (year−1) | t0 (year) | Maximum age (year) | Study |
|---|---|---|---|---|---|---|---|
| UK waters | – | M | 88.3 | 0.22 | −1.30 | – | Taylor & Holden 1964 |
| F | 127.3 | 0.10 | −2.50 | – | |||
| Irish Sea and Bristol Channel | – | M | 85.6 | 0.21 | −0.60 | – | Holden 1972 |
| F | 107.0 | 0.13 | −0.60 | – | |||
| Carmarthen Bay, United Kingdom | – | M + F | 139.2 | 0.09 | −2.63 | 12 | Ryland & Ajayi 1984 |
| Irish Sea, Northeast coast | – | M + F | 105.0 | 0.22 | 0.45 | – | Brander & Palmer 1985 |
| Irish Sea, southeast coast | – | M | 96.8 | 0.19 | −1.36 | – | Fahy 1991 |
| – | F | 107.8 | 0.15 | −1.01 | – | ||
| Italy, Sicily Channel | 200 | M | 116.7 | 0.106 | −0.41 | – | Cannizzaro et al. 1995 |
| 224 | F | 126.5 | 0.098 | −0.51 | – | ||
| North Sea | – | M | 98.0 | 0.17 | −0.43 | – | Walker 1999 |
| – | F | 118.0 | 0.14 | −0.88 | – | ||
| Irish Sea | 258 | M | 106.5 | 0.14 | −1.74 | 8 | Gallagher et al. 2005 |
| F | 139.5 | 0.093 | −1.84 | 8 | |||
| Caernarfon Bay, North of Wales | 54 | M | 100.9 | 0.18 | −0.95 | 7 | Whittamore & McCarthy 2005 |
| 135 | F | 117.6 | 0.16 | −0.70 | 9 | ||
| Portugal | 85 | M | 121.5 | 0.11 | −0.11 | – | Serra-Pereira et al. 2005 |
| 115 | F | 130.5 | 0.10 | −0.13 | – | ||
| 200 | M + F | 130.5 | 0.10 | −0.14 | 10 | ||
| North-East Mediterranean | 53 | M | 61.9 | 0.22 | −1.79 | – | Yeldan et al. 2008 |
| 37 | F | 95.7 | 0.92 | −2.60 | – | ||
| 90 | M + F | 79.7 | 0.13 | −2.70 | 8 | ||
| North Aegean Sea, Saros Bay | 98 | M | 79.99 | 0.23 | −1.09 | 7 | Yığın 2010 |
| 128 | F | 95.00 | 0.15 | −1.10 | 8 | ||
| 226 | M + F | 99.99 | 0.15 | −1.08 | 8 | ||
| Gulf of Gabes, Tunisia | 530 | M | 100.8 | 0.14 | 1.13 | 12 | Kadri et al. 2014a |
| 750 | F | 114.6 | 0.11 | 1.23 | 15 | ||
| West Algerian coast | 166 | M | 100.0 | 0.35 | −0.68 | – | Adda-Hanifi et al. 2017 |
| 397 | F | 105.0 | 0.46 | −0.20 | – | ||
| North Aegean Sea | 28 | M | 101.71 | 0.18 | −0.07 | 8 | this study |
| 76 | F | 106.54 | 0.16 | −0.28 | 8 |
Age frequency distribution for R_ clavata from the North Aegean Sea
| Age | Males | Females | Combined | |||
|---|---|---|---|---|---|---|
| Groups | n | % | n | % | n | % |
| 4 | 5 | 25 | 12 | 19.3 | 17 | 20.7 |
| 5 | 6 | 30 | 20 | 32.3 | 26 | 31.7 |
| 6 | 2 | 10 | 12 | 19.4 | 14 | 17.1 |
| 7 | 3 | 15 | 11 | 17.7 | 14 | 17.1 |
| 8 | 4 | 20 | 7 | 11.3 | 11 | 13.4 |
Length–weight relationship parameters of thornback ray by region
| Study | Region | Sex | N | Length(cm) | Weight (g) | Relationship Parameters | ||||
|---|---|---|---|---|---|---|---|---|---|---|
| Min. | Max | Min. | Max | a | b | r2 | ||||
| Filiz & Mater 2002 | North Aegean Sea | M + F | 31 | 20.5 | 99.0 | 28.9 | 2614.3 | 0.0016 | 3.29 | 0.93 |
| Borges et al. 2003 | Southern Portugal | M + F | 13 | 13.7 | 54.0 | 7.8 | 758.2 | 0.0014 | 3.36 | 0.99 |
| Mendes et al. 2004 | Coast of Portugal | M + F | 63 | 30.6 | 86.2 | 110 | 4590 | 0.0025 | 3.23 | 0.96 |
| Demirhan et al. 2005 | Southeast Black Sea | M | 23 | 48.0 | 95.0 | 620 | 5000 | 0.0005 | 3.02 | 0.96 |
| F | 29 | 34.3 | 88.2 | 170 | 5450 | 0.0003 | 3.70 | 0.94 | ||
| Rosa et al. 2006 | Azores Archipelago | M + F | 404 | 37.0 | 89.0 | 270.0 | 5110.0 | 0.0058 | 3.02 | 0.93 |
| İşmen et al. 2007 | Gulf of Saros | M + F | 112 | 6.0 | 60.0 | 5 | 4610 | 0.01300 | 3.12 | 0.99 |
| İlkyaz et al. 2008 | Aegean Sea | M + F | 24 | 29.0 | 51.3 | – | – | 0.0335 | 2.89 | 0.96 |
| Yeldan et al. 2008 | Northeast Mediterranean | M + F | 90 | 29.3 | 64.6 | 110 | 1120 | 0.0034 | 3.10 | 0.99 |
| Yığın & İşmen 2009 | North Aegean Sea | M | 98 | 11.0 | 76.0 | 6.30 | 2900 | 0.00146 | 3.34 | 0.99 |
| F | 128 | 10.0 | 88.0 | 5.00 | 4622 | 0.00181 | 3.31 | 0.99 | ||
| M + F | 226 | 10.0 | 88.0 | 5.00 | 4622 | 0.00163 | 3.32 | 0.99 | ||
| Bök et al. 2011 | Marmara Sea | M + F | 24 | 12.2 | 70 | 0.015 | 2628 | 0.00001 | 2.87 | 0.89 |
| Yemişken 2017 | Gulf of Iskenderun | M + F | 66 | 6.1 | 42.6 | 2 | 1387 | 0.0100 | 3.16 | 0.99 |
| M | 27 | 6.8 | 33.8 | 4 | 648 | 0.110 | 3.12 | 0.99 | ||
| F | 39 | 6.1 | 42.6 | 2 | 1387 | 0.0096 | 3.17 | 0.99 | ||
| Around Gökçeada | M + F | 19 | 6.8 | 46.3 | 6 | 2650 | 0.0127 | 3.13 | 0.80 | |
| In this study | North Aegean Sea | M + F | 104 | 43.1 | 89.9 | 588.7 | 5192.8 | 0.0041 | 3.10 | 0.93 |
| M | 28 | 43.1 | 82.7 | 588.7 | 3492 | 0.0223 | 2.68 | 0.88 | ||
| F | 76 | 50.2 | 89.9 | 654.1 | 5192.8 | 0.003 | 3.18 | 0.95 | ||