Konstantinos Touloumis

Elasmobranchs are among the most threatened marine taxonomic groups in the Mediterranean Sea. Moreover, knowledge of batoid life‐history strategies and spatial distribution is limited, despite being essential to stock assessments and effective management. This study focuses on batoid species collected across the North Aegean Sea, Greece, from 2014 to 2021. Conversion factors and length at maturity were estimated to assess biological traits of batoids. Random forests and generalized additive models were used to detect underlying spatial distribution patterns of species occurrence and abundance, respectively. Overall, 3,920 specimens were measured from at least 13 species, with Rajiformes being the most common order, whereas Torpedo marmorata was the sole Torpediniformes recorded in the area. Females were larger than males in all species, and sizes at which 50% of fish reached maturity were among the lowest in the Mediterranean Sea. Predictions suggested that Dipturus oxyrinchus , Raja clavata and Raja polystigma had the broadest distribution, whereas Raja radula and Torpedo marmorata were found mostly in coastal waters. Additionally, only D . oxyrinchus was spatially segregated by sex, whereas spatial and bathymetric segregation was associated with ontogeny for Leucoraja naevus , R. clavata and R. polystigma . Our findings contribute to our understanding of the biology and behavioural patterns of batoid species in the North Aegean Sea and are of relevance to the development of conservation plans in the area.

Non-targeted fish species contribute significantly to the structure and functioning of marine ecosystems, but they remain largely understudied. In this study, species distribution models (SDMs) were applied using the MaxEnt algorithm to assess current and future habitat suitability for 103 non-targeted species in the Mediterranean Sea. Based on trawl survey data from 2010 to 2022, and nine environmental variables, SDMs were calibrated and projected under three climate change scenarios (SSP1-1.9, SSP2-4.5, SSP5-8.5) for two future periods (2040–2050, 2090–2100). Among the environmental layers, depth, distance to the coast and sea bottom temperature explained most of the species’ distribution. Results indicate a general decline in suitable habitats for 97% of the species, particularly under the high emissions scenario SSP5-8.5 by 2100, independent of habitat type, with slightly greater declines for higher-trophic level species. Several species are projected to be at high risk of local or regional extinction. Moreover, future species distributions exhibited large spatial shifts of the centroids compared to the present-day, mainly explained by the contraction of suitable habitats rather than by expansion to new areas. Areas in the central and eastern basin of the Mediterranean Sea exhibited the highest levels of species turnover, indicating their potential higher vulnerability under climate change. These findings highlight the importance of integrating non-targeted species into conservation planning and fisheries management, as well as the need to prioritize areas that can sustain biodiversity in a rapidly changing Mediterranean ecosystem.

Deep-sea bamboo coral assemblages are often undescribed in the eastern Mediterranean Sea. Their structural complexity provides essential habitats for many species and promotes high biodiversity that is poorly known. In this study, we examined the effects of coral presence on biodiversity of benthic communities from a scientific trawl survey in the North Aegean Sea carried out in 2018. Genetic analyses did not support the first species identification of the coral as Isidella elongata (Esper, 1788). All searches resulted in matches belonging to Acanella specimens, a genus with a disputed taxonomic validity since its initial description. Quantitative data from macrobenthos in coral assemblages revealed the presence of at least 45 species. Additionally, few species of economic importance were exclusively detected in the haul associated with coral assemblages, which also hosted the highest species richness. Our results highlight the importance of such ecosystems as diversity hotspots in the marine environment, which are heavily impacted by human activities and are extremely important to commercial fisheries.

Following an introduction to the nature of fisheries catches and their information content, a new development of CMSY, a data-limited stock assessment method for fishes and invertebrates, is presented. This new version, CMSY++, overcomes several of the deficiencies of CMSY, which itself improved upon the “Catch-MSY” method published by S. Martell and R. Froese in 2013. The catch-only application of CMSY++ uses a Bayesian implementation of a modified Schaefer model, which also allows the fitting of abundance indices should such information be available. In the absence of historical catch time series and abundance indices, CMSY++ depends strongly on the provision of appropriate and informative priors for plausible ranges of initial and final stock depletion. An Artificial Neural Network (ANN) now assists in selecting objective priors for relative stock size based on patterns in 400 catch time series used for training. Regarding the cross-validation of the ANN predictions, of the 400 real stocks used in the training of ANN, 94% of final relative biomass (B/k) Bayesian (BSM) estimates were within the approximate 95% confidence limits of the respective CMSY++ estimate. Also, the equilibrium catch-biomass relations of the modified Schaefer model are compared with those of alternative surplus-production and age-structured models, suggesting that the latter two can be strongly biased towards underestimating the biomass required to sustain catches at low abundance. Numerous independent applications demonstrate how CMSY++ can incorporate, in addition to the required catch time series, both abundance data and a wide variety of ancillary information. We stress, however, the caveats and pitfalls of naively using the built-in prior options, which should instead be evaluated case-by-case and ideally be replaced by independent prior knowledge.

Following an introduction to the nature of fisheries catches and their information content, a new development of CMSY, a data-limited stock assessment method for fishes and invertebrates, is presented. This new version, CMSY++, overcomes several of the deficiencies of CMSY, which itself improved upon the “Catch-MSY” method published by S. Martell and R. Froese in 2013. The catch-only application of CMSY++ uses a Bayesian implementation of a modified Schaefer model, which also allows the fitting of abundance indices should such information be available. In the absence of historical catch time series and abundance indices, CMSY++ depends strongly on the provision of appropriate and informative priors for plausible ranges of initial and final stock depletion. An Artificial Neural Network (ANN) now assists in selecting objective priors for relative stock size based on patterns in 400 catch time series used for training. Regarding the cross-validation of the ANN predictions, of the 400 real stocks used in the training of ANN, 94% of final relative biomass (B/k) Bayesian (BSM) estimates were within the approximate 95% confidence limits of the respective CMSY++ estimate. Also, the equilibrium catch-biomass relations of the modified Schaefer model are compared with those of alternative surplus-production and age-structured models, suggesting that the latter two can be strongly biased towards underestimating the biomass required to sustain catches at low abundance. Numerous independent applications demonstrate how CMSY++ can incorporate, in addition to the required catch time series, both abundance data and a wide variety of ancillary information. We stress, however, the caveats and pitfalls of naively using the built-in prior options, which should instead be evaluated case-by-case and ideally be replaced by independent prior knowledge.

The size selectivity of trammel nets was investigated in the northern Aegean Sea using 10 different inner-panel mesh sizes ranging from 16 to 70 mm nominal mesh size (bar length). Selectivity estimates were made for the eight most abundant target and bycatch fish species, namely black scorpionfish, Scorpaena porcus Linnaeus, 1758; annular seabream, Diplodus annularis (Linnaeus, 1758); red mullet, Mullus barbatus Linnaeus, 1758; surmullet, Mullus surmuletus Linnaeus, 1758; round sardinella, Sardinella aurita Valenciennes, 1847; European hake, Merluccius merluccius (Linnaeus, 1758); greater weever, Trachinus draco Linnaeus, 1758; and blotched picarel, Spicara flexuosum Rafinesque, 1810, which accounted for 51.5% by number and 42.7% by weight of the fish caught with trammel nets in the sea trials. The SELECT method was used to estimate the selectivity parameters. Five different selectivity functions (i.e., normal scale, normal location, gamma, log-normal, and bi-normal) were applied with the bi-normal function providing the best fit as it had the lowest deviance value for all species and the lowest values for the dispersion parameter (D/df). The mesh size of 16 mm in most of the cases retained specimens below the size at first maturity (L_m). The mesh size of 19 mm seems more appropriate for red mullet, surmullet, and blotched picarel, the mesh size of 22 mm for annular seabream and round sardinella, while for European hake and black scorpionfish, the mesh size larger than 26 mm would be more appropriate.

A recent study of the Anthemis collections in the Balkans indicated that the taxa of the Anthemis macedonica group (A. macedonica subsp. macedonica, A. macedonica subsp. thracica, A. meteorica, A. orbelica) exhibit noteworthy morphological patterns not evaluated before. We applied morphometric approaches (principal components analysis, PCA; factor analysis on mixed data, FAMD) by considering 19 qualitative and 20 quantitative morphological characters, together with three ratios, in 26 populations of this group. Furthermore, the chromosome numbers and karyotype morphology were investigated in eight populations of the group, covering the taxa participating in the study. Our results revealed that the southernmost populations of the group represent a hitherto unknown species confined to serpentine: it is described here as Anthemis serpentinica Goula & Constantinidis. The morphological evidence supports the proximity of A. macedonica and A. orbelica, which would be better considered as subspecific entities of the same species. On the contrary, A. meteorica and A. thracica are retained as independent entities at species level. All taxa share the same diploid chromosome number of 2n = 2x = 18 with similar but not identical karyotypes. A brief description of all taxa, based on recent new collections, and a dichotomous key are presented. Lectotypes are designated for Anthemis macedonica and A. meteorica.

Aim: We explored the range shifts of alien and native birds, the responses of alien and native β‐diversity to abiotic factors, and the effect of native diversity on alien β‐diversity in two time periods.Location: Great Britain.Time period: 1968–1972, 2007–2011.Taxa studied: Breeding birds.Methods: We estimated range shifts of alien and native species between the periods 1968–1972 and 2007–2011. Following, β‐diversity of alien and native communities was estimated by Jaccard pairwise index (β_tot) and partitioned into richness difference and replacement component for each period. We built abiotic generalized dissimilarity models including abiotic factors for alien and native β_tot and their components and a biotic model for aliens including native taxonomic and functional diversity as predictors.Results: Most alien and half native species expanded into new regions during the 40‐year period. The native species range shifts did not exhibit a clear pattern along the longitudinal or latitudinal gradient, while alien species tended to move north‐westwards. The richness difference was the dominant component of alien β‐diversity, and the replacement component contributed mostly to native β‐diversity. Alien β‐diversity responded similarly but less strongly than native β‐diversity, to the abiotic gradients. Temperature‐related variables, distance and precipitation were the most important abiotic drivers of native and alien β‐diversity. The biotic model of alien β‐diversity explained more deviance than the abiotic model.Main conclusions: Alien species expanded into new regions over the 40 years, with alien β‐diversity driven mostly by species gains. The effect of environmental filtering on alien communities was weaker compared with native communities but was slightly reinforced in the second period compared with the first period, highlighting the role of environmental change in shaping diversity patterns. Native diversity played a key role in driving alien β‐diversity, through biotic interactions or/and by reflecting climatic suitability or niche availability for aliens.

Context: Sharks are frequently caught as bycatch in trawl fisheries in the North Aegean Sea. However, very little information exists on their biology and ecology in the area. Aims: Biological parameters and spatial segregation of sharks in relation to size class, sex, depth and geographic location were examined. Methods: Morphological characteristics and generalised additive models were used to explore biological traits and aggregating behaviour respectively, by using data from the Mediterranean International Trawl Survey between 2014 and 2021. Key results: Overall, 7761 specimens were measured, with Scyliorhinus canicula, Galeus melastomus and Squalus blainville being the most common species. Scyliorhinus canicula was found in shallow coastal waters, whereas the remaining species were detected in deeper waters. Conclusions: Females were larger and heavier than males and the weight–length relationships corroborated size differences between sexes in all species, whereas allometric growth did not share the same patterns as those from the Mediterranean Sea. Generalised additive models showed that the distribution of dominant species is bathymetric and geographically dependent. Additionally, the depth and geographic segregation patterns are highly associated with ontogeny and not sex. Implications: These findings highlighted the importance of incorporating elasmobranch behavioural characteristics in the poorly developed management regulations in the North Aegean Sea.