Hellenic Waters Research Articles

Morphometric description and biological notes on the rare kitefin shark Dalatias licha (Chondrichthyes: Dalatidae) from the Hellenic waters.

Deep-sea sharks are among the less studied and most endangered elasmobranchs existing in the Mediterranean Sea, and therefore scientific research should be prioritized towards this vulnerable group of species. The aim of this study is to provide a morphometric description of the vulnerable kitefin shark by recording 55 standard morphometric measurements and to present its main biological features based on the examination of six historical specimens that were captured as by-catch by commercial bottom trawlers in the Hellenic waters.

Shedding light on the deep: The case of the velvet belly lanternshark in the North Aegean Sea.

Main biological features were assessed for the first time in the deep-water shark Etmopterus spinax from Hellenic waters by examining 150 individuals caught incidentally in the bottom-trawl commercial fishery off Skyros island. Females outnumbered males and the overall sex ratio was 1.38:1. Females ranged from 122 to 311 mm in total length (LT ) and males from 129 to 270 mm LT , both exhibiting positive allometric growth. Total length-total mass relationships and frequency distributions did not show significant differences between females and males. Sexual dimorphism was not either found by analysing 56 different morphological characteristics. The effect of sex and season was more prominent on the gonadosomatic and hepatosomatic indices compared to the relative condition factor. Most of the individuals were sexually immature, with two specimens classified as mature, one gravid female reaching 311 mm LT with undeveloped gonads and enlarged uteri with embryos, and one male reaching 270 mm LT with enlarged gonads and rigid claspers with hooks. The present study highlights the importance of the sampling location as a breeding and nursery ground for E. spinax in the eastern Mediterranean Sea that should be taken into account for the species' conservation considering its intrinsic characteristics, which make it vulnerable to fishing pressure.

Reproductive strategy of Scyliorhinus canicula (L., 1758): a holistic approach based on macroscopic measurements and microscopic observations of the reproductive organs

Understanding reproductive features of elasmobranchs that affect population recovery and natural mortality is essential for conservation management planning. Considering macroscopic and microscopic observations of the reproductive tract in 2253 individuals, sampled in Hellenic waters over a 7-year period, four reproductive stages were described. The presence of advanced spermatocyst stages in immature testes supported the early gamete development and long maturation process. The simultaneous presence of follicles of all developmental stages in mature ovaries indicated a protracted egg-laying season. An extended reproductive period was also supported by monthly records of egg-laying females, sexually active males, large egg cases and high values of the gonadosomatic (GSI) and hepatosomatic (HSI) indices. Size at maturity was similar for both sexes. Females and males exhibited no depth segregation compared with individuals of different maturity stages regardless of sex. Sex, size and maturity stage significantly affected GSI, HSI and the relative condition factor. All three somatic indices showed a similar monthly variation, supporting a fat assimilation rate that follows maturation rate, with both affecting physiological condition. The severe population decline that Scyliorhinus canicula has recently undergone should focus our attention on future research supporting robust population modelling to help management of the species.

First record of the isopod Idotea hectica (Pallas, 1772) (Idoteidae) and of the brachyuran crab Matuta victor (Fabricius, 1781) (Matutidae) in the Hellenic waters

The presence and the establishment of Idotea hectica is reported for the first time in the Hellenic seas on the basis of three adult specimens and a juvenile collected from Posidonia oceanica meadows close to the main town of Rhodes Island, Aegean Sea. Common and contrasting characters between this and other species of the genera Idotea and Pentidotea are briefly discussed. Furthermore, following a westward expansion along the eastern Mediterranean coasts, Matuta victor was discovered for the first time in Hellenic waters on the basis of a single specimen from the northeast of Rhodes Island.

New marine gastropod records for the Hellenic waters

BackgroundThe Hellenic Seas are influenced by on-going environmental changes and the introduction of alien species, which are expected to have an impact on their biodiversity. This study contributes to the knowledge of the Hellenic marine gastropod biodiversity, expanding data over the entire Greek territory, during the period from October 2008 to March 2017.ResultsThis work presents 45 species of gastropods not previously reported from Greece or reported only once, belonging to 19 families. From those species, one (Horologica sp.) is, most probably, an undescribed species, 17 are new for the Eastern Mediterranean Sea and 40 are new for the Hellenic fauna. Main taxonomic characteristics and ecological information such as habitat, distribution and origin, are given and discussed.ConclusionsBy this report, the Hellenic gastropod biodiversity is enriched by 40 new records, out of which, 17 are new for the Eastern Mediterranean Sea, 4 are Lessepsian migrants previously reported for the Mediterranean Sea and 1 is probably a new species.

First Record of the African Surgeonfish Acanthurus monroviae (Osteichthyes: Acanthuridae) In the Hellenic Waters

Acanthurus monroviae inhabits the African coasts from Morocco to South Africa and the Canaries. It is distributed in various tropical and subtropical seas all around the world. The species feeds mainly on benthic algae and forms large schools that overwhelm other herbivorous fish species. It has been recorded at the Brazilian coasts and at the Western Mediterranean Sea. One individual was reported at the south-eastern basin of the Mediterranean on the coasts of Israel. The present study describes the first record of the species in the Hellenic waters that was captured by spear fishing at Salamina Island by one of the authors.

Occurrence of the first non-indigenous ascidian Phallusia nigra Savigny, 1816 (Tunicata: Ascidiacea) in Greek waters

The ascidian Phallusia nigra is listed among the non-indigenous species of the Mediterranean Sea and its first occurrence in Hellenic waters is noted here. The westward expansion of the black sea squirt from the north Levantine coast, up to the Aegean Sea has been revealed by scuba diving, as established populations were recorded offshore and in one of the harbours of Rhodes Island. Maintenance conditions of the species in captivity are briefly discussed.

Description of the first Lessepsian squid migrant, Sepioteuthis lessoniana (CEPHALOPODA: Loliginidae), in the Aegean Sea (Eastern Mediterranean)

Loliginid squids of the Sepioteuthis lessoniana complex are widely spread in the Indo-Pacific Ocean, where they constitute a commercially important resource for neritic fisheries. Sepioteuthis lessoniana is the only Lessepsian squid migrant till now, recorded for the first time in the Mediterranean in 2002 along the Turkish Levantine coasts. Two maturing males, with mantle lengths 193 mm and 244 mm, have been recently caught near the coasts of Rhodes Island (SE Aegean), extending the species distribution northward, into Hellenic waters. Their identity was confirmed by comparison of the main body, beak characteristics and morphometric measurements with those available in the literature for this species. Suspected expansion of the Lessepsian loliginid into the Aegean Sea, due to the gradual warming of the sea, is discussed.

On the finding of the Indo-Pacific fish Scomberomorus commerson in Rhodes (Greece)

The occurrence of the Indo-Pacific fish Scomberomorus commerson was observed for the first time in the Hellenic waters of the SE Aegean Sea during the spring 2008. The record may represent a first indication of a population expansion of this alien species along the southern coasts of the Aegean Sea.

Allochthonous and vagrant ichthyofauna in Hellenic marine and estuarine waters

A review of the non-indigenous ichthyofauna occurring in the Hellenic marine and estuarine waters is presented, including Atlantic origin colonizers, aquaculture introduced and Lessepsian alien species. 34 non-native species have been registered. The majority of allochthonous fish are Lessepsian immigrants, which represent approximately 80% of the ascertained non-native ichthyofauna in Hellenic waters; their establishment, spread, habitat, abundance and interaction with indigenous fish are discussed.

Possible influence of reared gilthead sea bream (Sparus aurata, L.) on wild stocks in the area of the Messolonghi lagoon (Ionian Sea, Greece)

AbstractMorethan25%of Greek¢shfarmsand20%of Greekhatcheries of gilthead sea bream (Sparus aurata)andsea bass (Dicentrarchus labrax) are located along theWestern Hellenic coast. The part of sea bream pro-duction is about 60% of thetotalproductionof thesespecies. During the last decade, a spectacular in-creaseinboththenumberoffarmsandtheirproduc-tion, accompanied by a substantial price decreaseand modi¢cation of their structure and functioning,has been recorded. These changes resulted in themaintenanceincagesoflargeindividuals(morethan500g) of gilthead sea bream which are potentialspawners. The study, based on both the maturitystage and the decrease in individual mean weightsduring the reproductive period of the species, con-¢rmed reproduction in cages. In parallel, during thelast5yearsaremarkableincrease(about80%)inseabream landings from the ¢sh trap ¢sheries of theMessolonghi-Etoliko lagoon, which is a typical nur-sery for the species, was recorded.The increase wasaccompanied by a decrease both in price and meansize of the 0-group individuals. The possible in£u-ence of the rearingactivities inthearea, thedensity-dependent mechanisms and the negative impacts ofthis unintentional enhancement of the traditionallagoon¢sheriesof theareaarediscussed.Keywords: aquaculture, gilthead sea bream, eco-logical impact, carrying capacity, density depen-dence, Messolonghi-EtolikolagoonIntroductionThe rapid expansion of aquaculture is accompaniedbyan increasedawareness concerning the impact of¢sh rearingonthe environment.These environmen-taleiectsareexpressedatalargevarietyof¢eldsandspatiotemporal scales (Machias, Karakassis, Gian-noulaki, Papadopoulou, Smith & Somarakis 2005).However,therecentspectacularevolutionof theHel-lenicaquacultureindustry,basedmainlyongiltheadseabream(Sparusaurata)andseabass(Dicentrarchuslabrax), masks the potential environmental conse-quences on the coastal zone. In particular, duringthe last 20 years both the number of ¢sh farms andtheir production have increased greatly from12 and100t in 1985, to 269 and 85000t in 2004 respec-tively (source: Mariculture Federation of Greece),with the relative contribution of the two species re-maining rather stable during this period (60% of seabream). In Hellenic waters, the impacts of ¢sh farmsonthemarineecosystemhavebeenwidelyinvesti-gated,includingeiectsonthewaterqualityininten-sive rearing areas (Western Hellenic coast: Belias,Bikas, Dassenakis & Scoullos 2003), on the sea bedand the watercolumn (Aegean and Ionian Sea: Kar-akassis,Tsapakis, Hatziyanni, Papadopoulou & Plaiti2000) and on possible changes of ¢sh assemblagestructureanddiversityclosetotheseafarms(AegeanSea: Machias, Karakassis, Labropoulou, Somarakis,Papadopoulou& Papaconstantinou2004).Worldwide, the interactions between wild andfarmed populations are frequently focused on the

Update of marine alien species in Hellenic waters

The list of marine alien species in Hellenic waters is updated taking into account new findings (published and unpublished data). According to the present work, the number of these species has increased from 90 (known until end 2003) to 128. Most of them are zoobenthic species followed by fish and macroalgae. An interannual analysis revealed an important increase of alien species during the last years. The study of their geographic distribution showed that their majority is present in the southeastern Aegean. More than 55% of them are well established, while about 40% are casual records. Their main pathway of introduction seems to be the Suez Canal followed by shipping, whereas the Straits of Gibraltar, aquaculture and the Straits of Dardanelles appear to play a less important role in their invasion of Hellenic waters. These findings are discussed considering environmental and anthropogenic factors.

Life-history patterns of fishes in the Hellenic Seas

Abstract. The available quantitative information (age, growth, maturation and mortality) for 103 fish stocks in Hellenic Seas was analysed here in the context of life-history theory and compared with similar information from other areas of the world. The results showed that the fish species and stocks inhabiting Hellenic waters are generally small in size, have low longevity, mature at an early age and size, and probably suffer high adult mortality rates. Such a pattern most probably is an adaptation to the synergetic combination of highly oligotrophic conditions and high subtropical temperatures prevailing in Hellenic waters and is consistent with life-history theory. Finally, the auximetric grid was used to compare the growth of four species, each represented by more than six stocks. The results revealed that the growth spaces occupied by the four species reflect their strikingly different feeding habits, especially with respect to the size of prey and the relative importance of fish prey to their diet.

The phylum Sipuncula in the eastern Mediterranean: composition, ecology, zoogeography

The bibliography concerning the Mediterranean Sipuncula is reviewed, particularly that from the eastern Mediterranean. Additional data are provided from macrobenthic samples collected between 1974 and 1997 in the Hellenic waters. A total of 17 species are recorded, five of which (Sipunculus norvegicus, Golfingia elongata, Nephasoma lilljeborgi, Thysanocardiacatharinae and Aspidosiphon (Akrikos) mexicanus) are reported for the first time in Hellenic waters. Three more species (Onchnesoma squamatum squamatum, Aspidosiphon (Aspidosiphon) elegans, Apionsoma (Apionsoma) trichocephalus) which are found exclusively in the extreme eastern basin (Israel, Egypt) raises the number of eastern Mediterranean Sipuncula species to twenty.

Selectivity experiments in the NE Mediterranean: the effect of trawl codend mesh size on species diversity and discards

In the present study we compare the overall performance of the 14 mm (from knot-to-knot) diamond-shaped codend (14D), presently used in Hellenic waters, with those of 20 mm square-shaped (20S) and 20 mm diamond-shaped (20D) trawl codends. The experiments took place at 12 stations in the western Aegean Sea and were based on the covered codend method (cover codend: 10 mm from knot-to-knot, 10D). The results of applying multivariate techniques, to the different station/codend combinations suggest that they form groups which differ from each other in terms of species composition, species diversity, and catch numbers/weights per hour of fishing. In general, the 10D covers of 20D and 20S were separated from the 10D covers of 14D. The 20D and 20S codends were generally grouped together and separated from those of 14D and 10D. Finally, the 14D codend either form groups by themselves or group together with the 10D cover codends. In addition, the results indicated that the 20D and 20S codends, when compared with 14D, allow significantly more individuals and number of species to escape through the meshes and are characterised by considerably higher commerical/non-commercial ratios in terms of both weight and number. In absolute numbers and weights 14D caught a very large quantity of non-commercial species whereas the weight of the commercial species caught was among the lowest. The commercial/non-commercial ratios of 20D were higher than those of 20S and, in absolute numbers and weights, 20S caught relatively more non-commercial species than 20D. These facts clearly indicate that 14D is harmful in terms of species diversity for the Hellenic demersal stocks and hence its use should be prohibited.

Size selectivity of diamond and square mesh codends for four commercial Mediterranean fish species

In the present study, we compared the size selectivity of the 14 mm (knot-to-knot) diamond-shaped codend (14D), presently used in Hellenic waters, with those of 20 mm square-shaped (20S) and 20 mm diamond-shaped (20D) codends for four commercially important demersal species (Merluccius merluccius, Micromesistius poutassou, Trisopterus minutus capelanus and Lepidorhombus boscii). Codend selectivity was estimated using the covered codend method. Our results suggested that 14D was not selective for any of the target species and the proportion retained by 14D ranged between 0.88 and 1. In addition, only in the case of M. merluccius did the results suggest that 20S is significantly more selective and retains fewer under-sized fish than 20D. With the exception of M. merluccius, the direct estimation of the 14D L50 values was not possible, because of the small number of specimens retained by the cover codend of 14D. The L50 value of M. merluccius for 14D was lower than its currently enforced minimum landing size (MLS) and length at 50% maturity. In contrast, for 20S and/or 20D codends, even though the estimated L50values were generally close to, or higher than, the species’ MLS, the L50 value of 20S for M. merluccius and that of 20D for L. boscii, were much smaller than their lengths at 50% maturity, a fact indicating that even the use of 20S and 20D, respectively, provides small opportunities for reproduction. Hence, the appropriate mesh sizes for these two species must be greater than 20 mm and their MLS must be raised. In contrast, forT. m. capelanusand M. poutassou, the L50values of 20D (but not of 14D) were close to their lengths at 50% maturity, a fact indicating that 20D is appropriate for these two species. The above mentioned facts clearly showed that: (a) 14D is harmful, in terms of size of landed fish, for the Hellenic demersal stocks and hence its use should be discontinued and (b) the use of a single appropriate mesh size for the Mediterranean trawl fishery as a whole is impossible because of its multispecies nature and the diVerent body sizes of species involved. Since the majority of the individuals escaping through the meshes of 20D or 20S are immature and under-sized (i.e. their length is smaller than MLS), the replacement of 14D by either 20D or 20S, the former being the codend mesh size proposed by EU for the entire Mediterranean, will be accompanied by increased yield per recruit. ? 1997 International Council for the Exploration of the Sea

Climatic variability and the anchovy/sardine ratio in Hellenic waters

In the present work, the monthly anchovy (Engraulis encrasicolus) and sardine (Sardina pilchardus) commercial catches, the anchovy/sardine commercial catch ratio as well as different climatic parameters in Hellenic waters (air and sea surface temperature AIRT and SST, sea level pressure SLP, N-S wind component NSW, and wind speed cubed WISC) over the 1964 to 1989 period were analyzed using spectral and cross-spectral analyses. The monthly anchovy and sardine catches as well as the anchovy/sardine catch ratio all exhibited a pronounced seasonal cycle that is related to the behaviour of sardine and anchovy and the nature of the purse seine fishery. Spectral analysis of the monthly sardine catches and anchovy/sardine catch ratio in the Hellenic waters also revealed cycles of 2.7 yr whereas that of anchovy catches revealed a prominent peak at 4.6 yr and secondary ones at 3.6 and 1.9 yr. Cross-spectral analysis resolved significant coherence between the anchovy/sardine ratio and SLP at 2.7 yr and marginally with NSW and WISC at 2.7 and 5.3 yr, respectively. The corresponding phase spectra showed that increased SLP and NSW over the north Aegean Sea proceed and are associated with decreased anchovy/sardine ratio with a lag of about 2.5 months for SLP and 6 months for NSW whereas increased WISC over the north Aegean proceed and are associated with increased anchovy/sardine ratio with a lag of 28 months. Cross-spectral analysis also resolved significant coherence between the anchovy catches and AIRT and SLP at 2.7 yr, NSW at 1.8 yr and WISC at 5.3 yr. The corresponding phase spectra showed that increased SLP, AIRT and NSW over the north Aegean Sea proceed and are associated with decreased anchovy catches with a lag of about 2 months for SLP, 16 months for AIRT and 6 months for NSW whereas increased WISC over the same area proceed and are associated with increased anchovy catches with a lag of 30 months. In contrast, cross-spectral analysis resolved no significant coherence between sardine catches and all five climatic variables. Possible mechanisms underlying such patterns are discussed.