Survey Results for Greece - area G1: North Aegean Sea

by A. Kallianiotis, K. Sophronidis, P. Vidoris & A. Adamidou

            Introduction

In the 62 hauls effected in the north Aegean Sea during Medits-GR’99 survey, 177 species were recognized until today. From these, there were recognized 126 species of fishes, 25 species of cephalopods and 26 species of crustaceans.

The most abundant species (in kg) in the northern Aegean Sea were: Sardina pilchardus, Micromesistius poutassou, Engraulis encrasicolus, Merluccius merluccius, Illex coindetii, Argentina sphyraena, Raja clavata, Lepidopus caudatus, Parapenaeus longirostris, Scyliorhinus canicula, Lophius budegassa, Trisopterus minutus capelanus, Spicara flexuosa, Lophius piscatorius, and Mullus barbatus.

A more detailed analysis of the results concerning the target species is given below.

            Global comments for Fish, Crustaceans and Cephalopods, Survey 1999

            Fish

Aspitrigla cuculus

This species was present at depths from 50 to 500 m with the maximum occurrence at 100-200 m (3.5 kg/kmē). The overall biomass (1.1 kg/kmē) and density index (90 N/kmē) were generally low.

Citharus linguatula

This species was present at depths from 10 to 500 m with the maximum occurrence at 10-50 m. The overall biomass (9.2 kg/kmē) and density index (353 N/kmē) are higher than these of Medits’98 (5.4 kg/kmē and 182 N/kmē respectively). The maximum length of individuals was 25 cm, whereas the minimum 8 cm. Male individuals were 51.12% of the total catches, females were 34.31%, while the rest 14.57% were immature individuals.

Eutrigla gurnardus

In general a small total biomass index (1 kg/kmē) - higher than last year (0.2 kg/kmē) - and a low-density index (50 N/kmē) was found for this species. It was present only at depths ranging from 50-200 m, while it is not fished at greater depths. The minimum length of individuals was 9 cm whereas the maximum 20 cm. Male individuals were the 36.36% of the total catches; females were 34.54%, while the rest 29.09% were immature ones.

Galeus melastomus

This species was present at the slope, at depths from 200 to 800 m, almost equally distributed at the zone 200-500 and 500-800 m. The overall biomass and density index were respectively 3.8 kg/kmē and 37 N/kmē.

Helicolenus dactylopterus

It was absent in depths less than 100 m and appeared mainly in greater depths, with an overall biomass index of 3.2 kg/kmē and density index of 20 N/kmē. Last year the total biomass index was lower (1.9 kg/kmē). The maximum presence has been recorded at the slope (6.1 kg/kmē). Male individuals were the 39.24% of the total catches; females were the 35.44%, while the rest 25.32% were immature ones. The maximum length of individuals was 31 cm and the minimum 5 cm.

Lepidorhombus boscii

It was mainly found in depths greater than 100 m, with overall biomass index (3.6 kg/kmē) and density index (67 N/kmē). The indices that were calculated for the Medits’98 were a little higher (3.9 kg/kmē) than those found during this year. The maximum length of individuals was 35 cm and the minimum 6 cm. Females were the 37.92%, male ones were the 50.13% while the rest 11.95% were immature.

Lophius budegassa

The total biomass index for this species this year was 18.4 kg/kmē presenting a small decline with respect to those of last year (19.2 kg/kmē). It was present at all zones with the highest biomass index (31.4 kg/kmē) and density index (143 N/kmē) found at the zone of 10-200 m. The maximum length of individuals was 64 cm whereas the minimum 6 cm. Male individuals were the 28.73% of the total catches, females were the 25.07%, while the rest 46.2% were undetermined.

Lophius piscatorius

It was distributed at depths from 50-500 m, with a total biomass index of 11.6 kg/kmē, almost the double than the previous survey. The highest biomass (22.4 kg/kmē) and density index (2 N/kmē) were found at the slope (200-800 m). The highest biomass index found on Medits’98 at the same zone was 11.5 kg/kmē and the total biomass index was 6 kg/kmē. The maximum length of individuals was 111 cm whereas the minimum 13 cm.

Merluccius merluccius

It was the most widespread species found during Medits’99 as it was present in 53 from 62 hauls at all depths. It was the second most abundant in weight and the fifth most abundant in number of all 36 target species. The overall biomass index (56.6 kg/kmē) observed was higher compared to that of previous year (44.6 kg/kmē) and of Medits’97 (54.4 kg/kmē). The highest value of biomass index (71.2 kg/kmē) and density index (1686 N/kmē) were obtained at the zone of 10-200 m. A significant proportion of the specimens fished this year (73.5%) was up to 25 cm in length. The length distribution shows two cohorts, the first one of small fishes with a modal length at 13-14 cm and the second cohort of adults with a modal length at 25-26 cm, respectively. The biggest individual was of 73 cm whereas the minimum length found was 6 cm. Male individuals were the 30.42% of the total, female individuals were the 35%, while the rest 34.59% were immature.

Micromesistius poutassou

It was the most abundant in weight and in number of all 36 target species. During this year the biomass index and density index were respectively 74.3 kg/kmē and 4488 N/kmē. It was present at depths between 100-800 m, with the highest biomass index (107.5 kg/kmē) and density index (8407 N/kmē) at the zone of 10-200 m. Comparing the present results to those of the previous year (13.3 kg/kmē total biomass index and 195 N/kmē density index), we note an important increase in both indices of this species. Due to the migratory behaviour of the species it is probably the presence of big shoals in the hauls that greatly increased the abundance this year. The maximum length of individuals was 38 cm and the minimum 9 cm. Male individuals were the 21.84% of the total number, females were the 22.53%, while the 55.63% were immature.

Mullus barbatus

This species was abundant at depths less than 100 m, while it was present until the depth of 500 m. The total biomass index was 11.2 kg/kmē and the density index was 350 N/kmē. In this species we observe a significant decrease in both indices, in respect to the ones of last year (18.1 kg/kmē and 642 N/kmē). The higher values were obtained at depths from 10 to 200 m (22.9 kg/kmē) and (718 N/kmē) respectively. Size of individuals ranged from 10 to 25 cm, while the 50.36% of them were males, the 42.96% females, and the 6.68% immature individuals.

Mullus surmuletus

This species was found generally in very low quantities at depths from 100-500 m and was more frequent until 200 m. The total biomass index was 0.5 kg/kmē and density indices 9 N/kmē. Last year this species was more abundant, having a biomass index of 2.6 kg/kmē. Size of individuals ranged from 14 to 21 cm, while 58.33% of them were males and 41.67% females.

Pagellus acarne

The overall biomass index of this fish (0.2 kg/kmē) presented a decrease with regard to the survey of ’98 (0.8 kg/kmē). It was mainly found at swallow waters 10-50 m (1.4 kg/kmē) and it was absent at depths greater than 100 m. Lengths of individuals ranged from 11 to 16 cm. The 66.67% of them were males, the 26.67% females, and the 6.67% immature ones.

Pagellus bogaraveo

It was also found in low quantities (overall biomass 6.5 kg/kmē and density indices 95 N/kmē respectively) in depths from 50 to 800 m, with the maximum occurrence (12.5 kg/kmē) at the slope. These values are higher in regard to these of Medits’98 (overall biomass 4.2 kg/kmē). Size of individuals ranged from 13 to 31 cm. The 30.61% were males, the 20.41% females, and the 48.98% immature.

Pagellus erythrinus

It appeared at depths from 10-200 m, with higher biomass index (13.4 kg/kmē) found in same zone and total biomass index of 6.5 kg/kmē. The values of this year are lower than the ones of Medits’98 (biomass index 14.5 kg/kmē in the zone 10-200 m and total biomass index 7.0 kg/kmē). Size of individuals ranged from 12 to 27 cm. The 29.41% of them were males and the 70.59% females.

Phycis blennoides

It was present at all depths except in the stratum 10-50 m, with total biomass index of 4.3 kg/kmē. This species was presented in low quantities at swallow waters (<100 m), while it was abundant in the slope (7.5 kg/kmē). During Medits’98, the biomass index at depths of 200-800 m was higher than this year (14.8 kg/kmē). Size of individuals ranged from 2 to 46 cm and the 68% of the individuals were up to 12 cm in length. The 6.06% of them were males, 12.28% females and 81.66% were immature.

Raja clavata

It was the forth most abundant species in weight among the 36 target species at the region of the Northern Aegean Sea. A small decrease at the overall biomass index value (26.7 kg/kmē) of this species was noted, compared to these of Medits’98 (27.5 kg/kmē). Present at all depths except the zone 10-50 m, but generally more abundant at the continental shelf where it shows the highest biomass index (32.9 kg/kmē). Size of individuals ranged from 16 to 82 cm, with 58.28% females and 41.72% males.

Scyliorhinus canicula

This species was found in 35 hauls in N. Aegean Sea at depths from 10-500 m. However it was mainly fished at depths from 50-200 m with a total biomass index of 19.4 kg/kmē and density indices of 186 N/kmē. The size of individuals ranged from 11 to 68 cm, with 48.8% females, 49.5% males, and the 1.7% not determined.

Solea vulgaris

It was present only in swallow waters at depths ranging from 10-100 m. It has shown an extremely low total biomass index (0.9 kg/kmē) a little higher than the values obtained in Medits’98 (0.6 kg/kmē). Even in the zone of 10-200 m, the biomass (1.9 kg/kmē) and density indices (11 N/kmē) were low. Specimen lengths ranged from 7 to 33 cm, with 61.54% females, 15.38% males, and the 23.08 immature.

Spicara flexuosa

It was present at depths less than 200 m. The total biomass index (15.3 kg/kmē) shows a stability in the abundance compared to that of 1998 (13.5 kg/kmē) and 1997 (14.3 kg/kmē). The highest biomass and density were observed at depths from 10 to 50 m (95.1 kg/kmē and 3152 N/kmē respectively). Size of individuals ranged from 8 to 19 cm, the 36.71% of them were males, the 60.81% females, and 1.1% immature ones.

Trachurus mediterraneus

The total biomass and abundance indices for this species were 5.9 kg/kmē and 153 N/kmē respectively, lower than the values of last year survey (10.3 kg/kmē and 258 N/kmē). It was present at depths 10 to 500 m while the highest density index (315 N/kmē) and biomass index (12.1 kg/kmē) occurred at the continental shelf. The differences found between the years in the abundance can be attributed at the migratory behaviour and the distribution pattern of the species. Sizes ranged between 7 and 24 cm. The 32.30% were males, the 56.01% were females, and the 11.68% were immature individuals.

Trachurus trachurus

It was present at depths until 500 m and it was the forth most abundant in number of individuals of the 36 target species in the region of Northern Aegean Sea (1161 N/kmē). The abundance of the species (9.8 kg/kmē) presented an important decrease with respect to the results of Medits’98 (20.7 kg/kmē). It was mainly present in the zone 50-100 m, where the highest density (5918 N/kmē) and biomass indices (43.3 kg/kmē) were found.

This is due to the fact that the majority of the catches were young fishes (min 5 cm). There is one modal length class at 10-11 cm. The biggest individual was 48 cm, and the sex ratio was 5.21% males, 2.0% females, and 92.79% immature.

Trigloporus lastoviza

It was present only in swallow waters at depths ranging from 10-200 m. It has shown an extremely low total biomass (0.5 kg/kmē) and density indices (21 N/kmē). The highest biomass index (3.5 kg/kmē) and density index (128 N/kmē) were recorded at the zone of 10-50 m.

Trisopterus minutus capelanus

The third most abundant in number (1595 N/kmē) of the 36 target species. It was present at depths from 10 to 500 m and the total biomass index was 18.4 kg/kmē, double than last year (9.7 kg/kmē). It was principally present at depths from 10 to 200 m. where the maximum biomass index was observed (37.7 kg/kmē). In the same zone it has the highest density index (3260 N/kmē). On Medits’98 we found the same pattern but lower biomass indices (19.8 kg/kmē) in the depth zone of 10-200 m.

A clear predominance of young fishes was also noted for this species, as the 96% of the individuals was up to 13 cm in length. This year, there is one modal length class at 11 cm. The lengths ranged from 5 to 20 cm, from which the 9.34% were males, the 11.74% were females, and the 78.91% were immature.

Zeus faber

This species was found in all depths until 500 m, although it was more abundant from 100 to 200 m. The highest biomass index (13.3 kg/kmē) was obtained in the zone of 10-200 m, while the total biomass index was 6.6 kg/kmē. Similar pattern and a little higher index were also found during the cruise of ’98 (total biomass index 6.9 kg/kmē). The maximum length of individuals was 50 cm and the minimum 8 cm. Female individuals were 50.0% of the total number, male were 30.77%, while 19.23% were immature.

Engraulis encrasicolus

Non-targeted species. It was the third most abundant in weight (71.1 kg/kmē) and the second in number (8741 N/kmē) of all species fished during Medits’99 in Northern Aegean Sea. This species was found in depths between 10-200 m while it was absent at deeper waters. The pattern of distribution of the species showed a small abundance in the stratum 10-50 m (34.1 kg/kmē), a maximum occurrence between 50 and100 m (451.4 kg/kmē). Its abundance decreased in the stratum 100-200 m (45.5 kg/kmē). In the super-stratum 10-200 m, the observed biomass and density indices were respectively 147 kg/kmē and 18077 N/kmē, lower than the corresponding values of Medits’98. Lengths ranged from 6 to 16 cm, with 46.64% being males, 38.09% females, and 15.27% immature.

It was caught at only 24 out of 62 hauls, mainly in the Thermaikos gulf (8 hauls) while last year we had fished anchovy in 22 hauls.

Sardina pilchardus

No-target species. It was the most abundant in weight (154.3 kg/kmē) and in numbers (12742 N/kmē) of all species fished in Northern Aegean Sea. It was found at 22 out of 62 hauls during the Medits’99 in our area. Last year sardine was fished in 27 hauls. It was mainly fished in the depth zone of 10-200 m where exhibits the higher biomass index (319.1 kg/kmē) and density index (26351 N/kmē). The higher abundance was found at the stratum 10-50 m (124.1 kg/kmē), showing a continuous decrease with depth increasing.

Comparing these data with the data of Medits’98 we find a different distribution pattern and a remarkable increase in the abundance of the species (total biomass index of ’98: 37.3 kg/kmē). The minimum length of individuals was 6 cm, whereas the maximum 20 cm. The 31.55% of the individuals were found to be females, the 29.96% males, and the 38.49% immature.

            Crustaceans

Aristeus antennatus

Not found at all in our region during the cruises of Medits ’96, ’97, ’98, and ’99.

Aristaeomorpha foliacea

This species was found only in the zone of 500-800 m in two hauls (8 individuals in haul 28 and 1 specimen in haul 25) in extremely low total biomass (0.1 kg/kmē) and total density indices (3 N/kmē). During the cruise of Medits’98 the total biomass index observed was similar (0.1 kg/kmē). The size range was 27-51 mm of carapace length. The 66.67% of the individuals were found to be females and 33.33% males

Nephrops norvegicus

Low biomass index (0.5 kg/kmē) in shallow waters (10-200 m) and higher values (9.5 kg/kmē) in the zone of 200-800 m were observed for this species. The total biomass index was 5.2 kg/kmē. A similar pattern was also found in the ’98 survey. The size range was 18-73 mm of carapace length. The 40.0% of the individuals were found to be females and 54.67% males, while 5.33% were undetermined individuals.

Parapenaeus longirostris

It was the second most abundant in number (3706 N/kmē) and the fifth most abundant in weight (20.7 kg/kmē) of all target species in the Northern Aegean Sea. This species had presented the same characteristics with lower biomass indices (16.6 kg/kmē) and density indices (2242 N/kmē) in Medits’98 survey. It was generally fished in all depths, although the maximum of its biomass was observed in the zone of 200-500 m. The minimum carapace length of individuals was 7 mm, whereas the maximum 40 mm. The 53.1% of the individuals were found to be females and the 45.1% males. In some specimens (1.8%) sex was not identified due to the bad situation of the shrimps.

            Cephalopods

Eledone cirrhosa

It was the second most abundant in weight (9.3 kg/kmē) of the 6 target cephalopods species of the Northern Aegean Sea. It was generally present at all depths except the zone of 10-50 m and 500-800 m. The highest biomass index (10 kg/kmē) was obtained in the stratum of 10-200 m. The total biomass index level of this species decreased from 10.9 kg/kmē in 1998 to 9.3 kg/kmē this year. The minimum length of individuals was 2 cm, whereas the maximum 16 cm. The 44.1% of the individuals were found to be females, the 46.08% males, and the 9.8% immature.

Eledone moschata

Present at depths of 10-500 m and absent at greater depths. It has shown relatively low total biomass index (5.5 kg/kmē), while in the zone of 10-50 m the biomass index takes its higher value (37.9 kg/kmē). Comparing with Medits’98 results (6.6 kg/kmē) we noticed a decrease in total biomass index. The minimum length of individuals was 3 cm, whereas the maximum 15 cm. The 25.58% of the individuals were found to be females, the 38.37% males, and the 36.05% immature.

Illex coindetii

It was the third most abundant in weight of all target species and the most abundant from the 6 target cephalopods species of the Northern Aegean Sea, having a total biomass index (37.2 kg/kmē). The density index of the species was 421 N/kmē. A significant increase was observed with respect to the total biomass index found on Medits’98 (11.2 kg/kmē). This species was fished at all depths, however it was more abundant in the stratum of 200-500 m. The highest biomass index (50.1 kg/kmē) was obtained in the zone of 200-800 m, significantly higher than last year (15.8 kg/kmē). Size ranged from 3 to 39 cm, with the 37.12% female individuals, the 51.44% males, and the 11.44% immature ones.

Loligo vulgaris

This species was poorly caught in our region. This year it was present mainly at depths from 10 to 100 m, same as last year survey. The biomass index is low (0.1 kg/kmē) and identical to the corresponding of Medits’98 (0.1 kg/kmē). Lengths ranged from 4 to 18 cm. The 12.5% of the individuals were male and 87.5% immature, while we didn’t found females.

Octopus vulgaris

In the Medits’99 survey this species presents a small decline in the overall biomass index (5.8 kg/kmē) with respect to ’98 data (8.7 kg/kmē). It was found down to 500 m with the higher abundance observed in shallow waters between 10 and 50 m (24.1 kg/kmē). Minimum length was found to be 5 cm and maximum 15 cm. The 72.22% were female individuals, and the 27.78% males.

Sepia officinalis

It was fished only in the depth zone of 50-100 m, where its biomass index is relatively low (2 individuals fished during the whole survey). The total biomass index was 0.1 kg/kmē. A minor decrease was observed with respect to the total biomass index of last year (0.5 kg/kmē). Lengths ranged from 10 to 13 cm.

            Comments by stratum, Survey 1999

            Stratum 10-50 m

It is the stratum with the greater density and biomass indices. In this depth zone, 19 out of 36 target species were found. Among the crustaceans, only P. longirostris appeared. All target species of cephalopods - except E. moschata - were present.

The most abundant species in total weight were Merluccius merluccius (101 kg/kmē), Spicara flexuosa (95.1 kg/kmē), Citharus linguatula (51.3 kg/kmē), Scorpaena notata (48.4 kg/kmē), and Pagellus erythrinus (48.1 kg/kmē). Finally, high density indices of Spicara flexuosa (3152 N/kmē), Merluccius merluccius (2719 N/kmē), Trisopterus minutus capelanus (1785 N/kmē), Trachurus trachurus (1617 N/kmē), and Citharus linguatula (1219 N/kmē) were also observed.

            Stratum 50-100 m

In this stratum we found this year 29 out of 36 target species. From the four crustaceans target species P. longirostris and N. norvegicus were present, while from the six target species of cephalopods E. cirrhosa, E. moschata, I. coindetii, O. vulgaris, and S. officinalis were present.

In total weight, the most abundant species were Merluccius merluccius (68.5 kg/kmē), Lophius budegassa (57.6 kg/kmē), Scyliorhinus canicula (56.6 kg/kmē), Raja clavata (47.9 kg/kmē), and Trisopterus minutus capelanus (44.2 kg/kmē). The most abundant species in terms of total density were Trachurus trachurus (5918 N/kmē), Trisopterus minutus capelanus (3871 N/kmē), Parapenaeus longirostris (3453 N/kmē), Merluccius merluccius (1736 N/kmē), and Citharus linguatula (875 N/kmē).

            Stratum 100-200 m

This depth zone is the richest in terms of species composition as it contains the highest proportion of the target species (27 out of 36). From the crustaceans two species (N. norvegicus and P. longirostris) appeared. From the six target species of cephalopods, E. cirrhosa, E. moschata, I. coindetii and O. vulgaris were present.

The species with the higher biomass indices were Micromesistius poutassou (223.9 kg/kmē), Merluccius merluccius (56.5 kg/kmē), Raja clavata (42.9 kg/kmē), Trisopterus minutus capelanus (37.6 kg/kmē) and Parapenaeus longirostris (31.5 kg/kmē). The species with the higher density indices were Micromesistius poutassou (17510 N/kmē), Parapenaeus longirostris (6290 N/kmē), Trisopterus minutus capelanus (3738 N/kmē), Merluccius merluccius (1096 N/kmē), and Trachurus trachurus (918 N/kmē).

            Stratum 200-500 m

In this stratum we found 25 out of 36 target species. Among the crustaceans, two species were present again, with the highest of their biomass indices, N. norvegicus and P. longirostris. From the target species of cephalopods were present E. cirrhosa, and I. coindetii.

The species with the higher biomass indices were Illex coindetii (87.7 kg/kmē), Micromesistius poutassou (73.6 kg/kmē), Merluccius merluccius (73.1 kg/kmē), Lophius piscatorius (39.8 kg/kmē) and Parapenaeus longirostris (37.8 kg/kmē). The species with the higher density indices were Parapenaeus longirostris (6126 N/kmē), Micromesistius poutassou (1440 N/kmē), Illex coindetii (723 N/kmē), Merluccius merluccius (446 N/kmē), and Pagellus bogaraveo (312 N/kmē).

            Stratum 500-800 m

In this stratum only 13 of the target species were found including three species of crustaceans (A. foliacea, N. norvegicus, and P. longirostris), and one species of cephalopods (Illex coindetii).

Helicolenus dactylopterus (10.8 kg/kmē) was the most abundant species in this depth zone, whereas Nephrops norvegicus (9.4 kg/kmē), Phycis blennoides (4.3 kg/kmē), Micromesistius poutassou (4.2 kg/kmē) and Merluccius merluccius (4.0 kg/kmē) were also abundant. Finally, the highest density index was observed for Parapenaeus longirostris (142 N/kmē), Nephrops norvegicus (120 N/kmē), Phycis blennoides (74 N/kmē), Helicolenus dactylopterus (49 N/kmē), and Micromesistius poutassou (22 N/kmē).

            Discussion

The global analysis of the data for the Northern Aegean Sea, irrespectively of depth zones, shows that, in weight, the most abundant fish target species were the following: M. poutassou (74.3 kg/kmē), M. merluccius (56.6 kg/kmē), R. clavata (26.7 kg/kmē), L. budegassa (18.4 kg/kmē), and T. minutus capelanus (18.4 kg/kmē). Furthermore, the most abundant fish target species in number were: M. poutassou (4488 N/kmē), T. minutus capelanus (1595 N/kmē), T. trachurus (1161 N/kmē), M. merluccius (947 N/kmē), and S. flexuosa (3706 N/kmē).

The most abundant crustacean target species in weight and number were P. longirostris (20.7 kg/kmē and 3706 N/kmē), and N. norvegicus (5.2 kg/kmē and 108 N/kmē).

From the six cephalopods species, I. coindetii (37.2 kg/kmē and 421 N/kmē), and E. cirrhosa (9.3 kg/kmē and 54 N/kmē) were found to be the most abundant.

A general decrease in abundance compared to the results of Medits’98 was recorded this year. From the 36 target species, 15 species of fish, crustaceans and cephalopods present lower biomass indices this year while 14 species show an increase in their biomass indices with respect to the indices of last year. Two species (Loligo vulgaris and Aristaeomorpha foliacea) present stability in their biomass indices and one species (Aristeus antennatus) was not found, as last year.

The most significant differences have been noticed in M. poutassou (13.3 kg/kmē; 74.3 kg/kmē), I. coindetii (11.2 kg/kmē; 37.2 kg/kmē), M. merluccius (44.6 kg/kmē; 56.5 kg/kmē), T. minutus capelanus (9.7 kg/kmē; 18.4 kg/kmē), L. piscatorius (5.9 kg/kmē; 11.6 kg/kmē), M. barbatus (18.1 kg/kmē; 11.2 kg/kmē), and T. trachurus (20.7 kg/kmē; 9.8 kg/kmē) in Medits’98 and in Medits’99 respectively.