Over three years, this work investigated the life history traits and the ecology of the two cryptic species of the genus Solea inhabiting the Adriatic Sea, one of the most exploited basins in the world, the common sole, Solea solea (Linnaeus, 1758), and the Egyptian sole, Solea aegyptiaca (Chabanaud, 1927). Both are valuable fishery resources landed in all the Adriatic harbors as a unique species, the common sole. The final aim was to understand their coexistence and provide useful information to support resource assessment and management in the Adriatic Sea. Preliminary information about the Egyptian sole presence directed research activity to the northwestern Adriatic area. The activities started with the monthly sample collection of both species’ specimens across one year. The two sampling approaches, fishery-dependent sampling at the Chioggia fishery market and fishery-independent sampling during the SoleMon survey, combined different information. Moreover, the involvement of fishermen provided further details about the aggregation areas of the Egyptian sole in correspondence with particular sand sediments in the Gulf of Venice, the “Aeolian dunes”. The all available data integration gave a clear picture of the Egyptian sole persistence area and spatial distribution. The comparison of the life history traits showed high similarity in the growth rate and trend, confirming their classification as cryptic species. The otolith analysis provided relevant information on the actual longevity of both species. For the first time, Egyptian soles older than 10 years were observed. The presence of very old individuals makes the populations more resilient, and this aspect is significant and deserves attention for the appropriate management of fishery resources. Furthermore, very old specimens among Egyptian soles suggested the presence of refuge areas, which could be the “Aeolian dunes” in the Gulf of Venice or the lagoons. The comparison of the reproductive cycle and strategy revealed distinctive traits between the two species. A shifted reproduction timing was observed. This aspect can be one of the reasons why the two species are considered reproductively isolated. Another main observation was the difference in the oocyte dimensions between the species. The smaller oocytes produced by Egyptian soles could have a lower survival probability than the bigger eggs produced by the common soles, and this could be one of the reasons why the first species is present in the Adriatic basin with a lower abundance. The feeding habits comparison confirmed that both species are benthophagous generalists. Their diet partially overlaps, but the use of feeding resources, a mixed strategy with varying degrees of specialization and generalization on different prey types, promotes the limitation of trophic competition. Both species showed low fullness values, due to the high digestion rate that characterizes Soleids. In conclusion, this study provided the main information on the biological and trophic characteristics of the two soles in the Adriatic Sea. The several hypotheses formulated and the huge amount of samples available can represent the starting point to investigate more and to develop new future research lines.
Nel corso dei tre anni, questo studio ha investigato i principali aspetti di life history e dell’ecologia delle due specie criptiche del genere Solea che popolano il mare Adriatico, uno dei bacini più sfruttati nel mondo, la sogliola comune, Solea solea (Linnaeus, 1758), e la sogliola egiziana, Solea aegyptiaca (Chabanaud, 1927). Entrambe le specie sono importanti risorse della pesca, sbarcate in tutti i porti adriatici come un’unica specie, la sogliola comune. Lo scopo ultimo di questo studio è stato quello di capire le modalità di coesistenza delle due specie e fornire informazioni utili a supporto delle attività di valutazione e gestione degli stock nel mare Adriatico. Sulla base di informazioni preliminari, l’attività di ricerca si è concentrata sulla zona nord ovest del bacino adriatico. Le attività sono iniziate attraverso il campionamento mensile di entrambe le specie nel corso di un intero anno. Sono stati utilizzati due approcci, campionamento fishery-dependent presso il mercato ittico di Chioggia e il campionamento fishery-independent durante il survey SoleMon, che hanno permesso di combinare differenti informazioni. Inoltre, la collaborazione con i pescatori locali ha fornito importanti dettagli circa la presenza di zone di aggregazione della sogliola egiziana in corrispondenza di peculiari substrati sabbiosi nel golfo di Venezia, chiamati “dune eoliane”. L’integrazione di tutte le informazioni disponibili ha fornito un quadro più chiaro sulle zone di persistenza e la distribuzione spaziale della sogliola egiziana. Il confronto dei tratti di life history ha mostrato tassi e trend di crescita molto simili, confermando la classificazione delle due specie come criptiche. L’analisi degli otoliti ha fornito rilevanti informazioni sulla longevità di entrambe le specie. Per la prima volta, sono state osservate sogliole egiziane con più di 10 anni di età. La presenza di individui longevi rende le popolazioni più resilienti e questo aspetto è significativo e merita attenzione per un appropriato approccio gestionale delle risorse alieutiche. Inoltre, individui molto anziani suggeriscono la presenza di zone rifugio anche per la sogliola egiziana, che potrebbero essere le “dune eoliane” o le lagune. Il confronto di ciclo e strategia riproduttivi ha rivelato tratti distintivi tra le due specie. È stato osservato uno shift nel picco riproduttivo e questo aspetto potrebbe essere una delle ragioni per cui le due specie sono considerate isolate a livello riproduttivo. Inoltre, le dimensioni delle uova prodotte dalla sogliola egiziana risultate significativamente inferiori potrebbero comportare una minore probabilità di sopravvivenza rispetto a quelle della sogliola comune. Questo potrebbe in parte motivare la ridotta abbondanza della prima specie in Adriatico. Il confronto delle abitudini alimentari ha confermato entrambe le specie come bentofaghe generaliste. La loro dieta si sovrappone parzialmente, ma l’uso delle risorse alimentari, una strategia mista con differenti gradi di specializzazione e generalizzazione su differenti tipi di prede, favorisce la limitazione della competizione trofica. Entrambe le specie hanno mostrato livelli molto bassi di fullness, a causa degli alti tassi di digestione tipici dei Soleidi. In conclusione, questo studio ha fornito le principali informazioni sulla biologia ed ecologia delle due specie in Adriatico. Le svariate ipotesi formulate e la grande disponibilità di campioni rappresentano un punto di partenza per approfondire diversi aspetti e sviluppare nuove linee di ricerca.
Common sole and Egyptian sole in the Adriatic Sea. A comparative investigation of the biology and ecology of two cryptic species
SABATINI, LAURA
2024
Abstract
Over three years, this work investigated the life history traits and the ecology of the two cryptic species of the genus Solea inhabiting the Adriatic Sea, one of the most exploited basins in the world, the common sole, Solea solea (Linnaeus, 1758), and the Egyptian sole, Solea aegyptiaca (Chabanaud, 1927). Both are valuable fishery resources landed in all the Adriatic harbors as a unique species, the common sole. The final aim was to understand their coexistence and provide useful information to support resource assessment and management in the Adriatic Sea. Preliminary information about the Egyptian sole presence directed research activity to the northwestern Adriatic area. The activities started with the monthly sample collection of both species’ specimens across one year. The two sampling approaches, fishery-dependent sampling at the Chioggia fishery market and fishery-independent sampling during the SoleMon survey, combined different information. Moreover, the involvement of fishermen provided further details about the aggregation areas of the Egyptian sole in correspondence with particular sand sediments in the Gulf of Venice, the “Aeolian dunes”. The all available data integration gave a clear picture of the Egyptian sole persistence area and spatial distribution. The comparison of the life history traits showed high similarity in the growth rate and trend, confirming their classification as cryptic species. The otolith analysis provided relevant information on the actual longevity of both species. For the first time, Egyptian soles older than 10 years were observed. The presence of very old individuals makes the populations more resilient, and this aspect is significant and deserves attention for the appropriate management of fishery resources. Furthermore, very old specimens among Egyptian soles suggested the presence of refuge areas, which could be the “Aeolian dunes” in the Gulf of Venice or the lagoons. The comparison of the reproductive cycle and strategy revealed distinctive traits between the two species. A shifted reproduction timing was observed. This aspect can be one of the reasons why the two species are considered reproductively isolated. Another main observation was the difference in the oocyte dimensions between the species. The smaller oocytes produced by Egyptian soles could have a lower survival probability than the bigger eggs produced by the common soles, and this could be one of the reasons why the first species is present in the Adriatic basin with a lower abundance. The feeding habits comparison confirmed that both species are benthophagous generalists. Their diet partially overlaps, but the use of feeding resources, a mixed strategy with varying degrees of specialization and generalization on different prey types, promotes the limitation of trophic competition. Both species showed low fullness values, due to the high digestion rate that characterizes Soleids. In conclusion, this study provided the main information on the biological and trophic characteristics of the two soles in the Adriatic Sea. The several hypotheses formulated and the huge amount of samples available can represent the starting point to investigate more and to develop new future research lines.File | Dimensione | Formato | |
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https://hdl.handle.net/20.500.14242/164809
URN:NBN:IT:UNIVPM-164809