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Forage species with high biomass, such as anchovies and sardines, play a key role in pelagic ecosystems and make up a significant proportion of the world's capture fisheries production. In recent years, condition indices have gained interest as significant indicators for assessing the effects of environmental and human pressures on these species and the quality of their habitats. In the present study, we examined, for the first time in the North Aegean Sea (eastern Mediterranean), the year‐round variation in somatic and gonadal condition, energy density, and percentage of lipid content of anchovy (Engraulis encrasicolus) and sardine (Sardina pilchardus). Energy density was measured with bomb calorimetry and percentage lipid content with the fatmeter, a portable electronic device. Finally, the monthly changes in gonadal and energetic condition were examined in relation to the annual cycle of temperature and mesozooplankton biomass, simulated by the implementation of a coupled hydrodynamic‐biogeochemical model (POM‐ERSEM). There was a strong relationship between fish energy density (kJ g−1) and percentage dry weight. Furthermore, the mean monthly energy density and fatmeter measurements were strongly correlated, especially in sardine. Overall, the monthly changes in energetic condition were indicative of the species' different strategies for energy acquisition and allocation to reproduction (capital vs. income breeding): sardine exhibited low energy density and percentage lipid content during the winter spawning period (November–March) and markedly higher energetic condition from spring to autumn (April–October). Anchovy spawning period, as inferred from gonadal condition, lasted from April to September, i.e., during the warm period of the year but its energy density and percentage lipid content did not exhibit any seasonal changes and were markedly lower than in sardine from April to October. Finally, the simulated mesozooplankton biomass was higher from January to July, which corresponded to the second half of the spawning season for sardine, but first half of the spawning season for anchovy. [ABSTRACT FROM AUTHOR]

Mesopelagic fishes hold an important position in marine food webs, serving as a link between lower trophic levels and top predators and transferring energy from their deep mesopelagic habitat to shallower oceanic layers. Despite their ecological importance, research on mesopelagic fishes' diet and feeding habits in the Mediterranean Sea is far from thorough. The present work attempts to assess the preying patterns and diet composition of four myctophid (Benthosema glaciale, Ceratoscopelus maderensis, Myctophum punctatum, Notoscopelus elongatus) and two sternoptychid (Argyropelecus hemigymnus, Maurolicus muelleri) species from the Corinthian Gulf (Ionian Sea, Greece), sampled during pelagic trawl surveys in 2018 and 2019. Stomach vacuity was high for myctophids caught during daytime, a pattern which sternoptychids did not follow. Estimated trophic indices revealed high dietary diversity (Shannon's H' index) for most investigated species, but a narrow trophic niche breadth (Levins' normalized Bn index). Copepods and various marine crustaceans were dominant in all diets, classifying them under the zooplanktivorous trophic guild, while A. hemigymnus exhibited high concentrations of particulate organic matter in their stomachs and N. elongatus exhibited consumption of fish. Diet overlap was significant among most studied mesopelagic species, as indicated by Shoener's S index and confirmed by both the multidimensional scaling ordination and a hierarchical cluster analysis. Information on mesopelagic fishes' diet composition in this poorly studied part of the Mediterranean is useful in further assessing and parameterizing marine food webs and midwater trophic interactions, as well as in quantifying the ensued energy transfer to top predators of commercial interest or conservation concerns. [ABSTRACT FROM AUTHOR]

The assessment of the economic impacts of marine invasive species is fundamental for adopting mitigation measures, yet such impacts have been underreported in the Mediterranean Sea. The silver-cheeked toadfish (Lagocephalus sceleratus) is a toxic pufferfish that since its introduction has seriously disturbed small-scale fisheries along the eastern Mediterranean coast. This species depredates on fishing gears, causing damage to nets, longlines and commercial catches. To quantify its economic impact on small-scale fisheries, we interviewed 141 fishers from Crete (Cretan and Libyan Sea) and the Ionian Sea (Greece) during May 2020–December 2022. The mean annual economic cost resulting from L. sceleratus depredation was estimated at EUR 6315 ± 2620 per vessel in Crete and EUR 258 ± 120 in the Ionian Sea. Additionally, observer surveys carried out on board small-scale fishing vessels in Crete showed that depredation probability was significantly influenced by fishing depth, sea surface temperature, gear type (nets, longlines) and region (Cretan, Libyan Sea). L. sceleratus was caught more frequently and in higher numbers in the Libyan Sea. In response to depredation, fishers in Crete have altered their fishing tactics in terms of fishing in deeper waters, reducing fishing time and changing the technical characteristics of fishing gears. Our results underscore the adverse impacts of L. sceleratus on Greek small-scale fishers, emphasizing the need for region-specific management plans where the species establishes large populations. [ABSTRACT FROM AUTHOR]

Reliable stock identification constitutes an integral component of effective fishery management. Current methods for the identification of putative stock units comprise the analysis of both phenotypic and genetic variability. The present study examined the spatial variation in otolith morphology (shape and asymmetry) and genetic composition of 395 wild-caught Gilthead seabream (Sparus aurata) specimens, collected from the Aegean and Ionian Seas (eastern Mediterranean) between 2014–2018. The degree of scale regeneration (SRD, % of regenerated scales) was used as an indicator to assess the potential presence of aquaculture escapees in the wild-caught samples. Otolith shape and asymmetry analyses showed a phenotypic discrimination between northwestern Aegean and Ionian Gilthead seabream populations. Genetic analyses of nine microsatellite markers revealed higher levels of genetic variation in the wild compared with samples obtained from aquaculture farms. Despite the absence of genetic structure among the wild-caught seabream populations, a low but statistically significant genetic differentiation was found between reared fish and fish collected in the field. The SRD was considered effective in detecting the presence of aquaculture escapees that may have escaped in either early or late rearing phases. [ABSTRACT FROM AUTHOR]

For many mesopelagic fishes, even basic knowledge regarding their biology is missing, greatly impeding their effective management. Here we present length-weight relations for 16 mesopelagic fishes sampled during research surveys in the Greek seas (eastern Mediterranean). The following species were studied: Benthosema glaciale (Reinhardt, 1837); Ceratoscopelus maderensis (Lowe, 1839); Diaphus holti Tåning, 1918; Diaphus metopoclampus (Cocco, 1829); Diaphus rafinesquii (Cocco, 1838); Hygophum benoiti (Cocco, 1838); Hygophum hygomii (Lütken, 1892); Lampanyctus crocodilus (Risso, 1810); Lobianchia dofleini (Zugmayer, 1911); Myctophum punctatum Rafinesque, 1810; Notoscopelus elongatus (Costa, 1844); Symbolophorus veranyi (Moreau, 1888) [Myctophidae]; Argyropelecus hemigymnus Cocco, 1829; Maurolicus muelleri (Gmelin, 1789) [Sternoptychidae]; Stomias boa (Risso, 1810); Chauliodus sloani Bloch et Schneider, 1801 [Stomiidae].With the exception of Diaphus holti and Symbolophorus veranyi, parameter b diverged significantly from isometry. Only two species (Benthosema glaciale and Chauliodus sloani) displayed negative allometry, while for the remaining 12 species a positive allometry was found, with the highest parameter b values estimated for Stomias boa and Diaphus rafinesquii. The median value of parameter b for all species was 3.236 and 50% of its values ranged from 3.173 to 3.323. Some variations of the parameter b were observed between our findings and other studies from the Atlantic and the western Mediterranean. [ABSTRACT FROM AUTHOR]