Given the economic importance of the smooth clam (Callista chione) in Italy, this thesis work aimed at investigating some aspects of the biology (age, growth, reproduction), fishing activity (distribution and extension of fishing areas) and habitat (macro-benthic community living associated) where the resource lives, which is harvested in Italy by means of hydraulic dredges in the Chioggia, Venice and Monfalcone maritime districts. To adopt management measures that guarantee the conservation of the resource over time as well as the environmental and fishing sustainability, it is fundamental to have a thorough knowledge on the basic biological aspects of the species. At present, a Minimum Conservation Reference Size (MCRS) does not exist for the smooth clam in Italy, although the size of the landed product is around ≥40 mm in shell total length (TL). Samples were collected monthly - whenever possible - between December 2018 and November 2020. Three laboratory techniques were adopted and compared for age determination: backlighting (RI), thin cross sections (SL) and count of hinge growth rings (UMBO). The size range of the analyzed individuals was 18.5 - 79.5 mm. 246 specimens were analyzed by RI and SL techniques and the estimated age range was 1 - 20 years. 232 individuals were analyzed by mean of the UMBO technique and the estimated age ranged between 1 and 16 years. From the comparison between techniques the APE and ACV values resulted always below the reference ones, therefore indicating the consistency of readings. Furthermore, in the comparison between pairs of techniques, the LogLikelihood ratio test did not show any statistically significant difference, so that the 3 models were described by the same VBGF growth curve parameters (L∞= 87.1, k = 0.11, t0= - 1.75). The 1st year of life is reached between 19-23 mm TL, while the size of 40 mm TL is reached within the 4th year. The study of the growth rate has shown that the smooth clam is a long-lived species and it has a very fast growth during the first year of life, which at the second year is already more than halved, while remains quite fast up to 7 years of life and then decreases from the seventh year. The growth rate is slower in late summer – early autumn, when the deposition of the hyaline dark band occurs. To investigate the reproductive cycle of the species, the microscopic analysis of the gonads showed that the smooth clam reproduces throughout the year, despite of the inter-individual gonads asynchrony encountered. The study of the distribution of the species in the north-western Adriatic Sea, by information from bibliography, meetings and stakeholders, has highlighted the patchy distribution of the species, which lives in clusters scattered on sandy bumps. For this reason, it is necessary to adopt an ad hoc sampling design to monitor the status of the resource. The preliminary qualitative analysis of the macro-benthic community characterizing the study area, showed a dominance of bivalves (28.3% of the total species), followed by gastropods and crustaceans of the Malacostraca class (both 17.4% of the total species). This analysis also highlighted the presence of some sensitive species, which could be more impacted by the dredging activity. Considering the results gained in this thesis work, it is fundamental to deepen the knowledge on biological aspects of the species, the effects of dredging on the benthic communities and on the surrounding environment, as well as on the survival of the species after being released into the sea. All these is required to suggest management measures which aim at guaranteeing the sustainability of the resource and the environment where it lives, as well as to ensure a long-lasting socio-economic and environmental well-being.
Nota l’importanza economica del fasolaro (Callista chione) in Italia, il presente lavoro di tesi ha investigato alcuni aspetti della biologia (età, accrescimento, riproduzione), della pesca (distribuzione ed estensione degli areali di pesca) e dell’habitat (comunità macro-bentonica associata) in cui vive la risorsa, pescata in Italia per mezzo di draghe idrauliche presso le marinerie di Chioggia, Venezia e Monfalcone. Per adottare misure gestionali volte alla conservazione della risorsa nel tempo e alla sostenibilità ambientale e dell’attività di pesca, è fondamentale una conoscenza precisa sulla biologia di base della specie. Ad oggi il fasolaro in Italia non ha una Taglia Minima per la Conservazione delle Specie (MCRS), tuttavia il prodotto sbarcato è intorno a ≥40 mm di lunghezza. I campioni analizzati sono stati collezionati tra dicembre 2018 e novembre 2020, se possibile ogni mese. Per determinare l’età sono state confrontate 3 tecniche: retroilluminazione (RI), sezioni longitudinali sottili (SL) e conta degli anelli di crescita nell’umbone (UMBO). Il range di taglia degli individui analizzati era tra 18.5 e 79.5 mm. 246 individui sono stati analizzati mediante RI e SL e il range di età stimato era compreso tra 1 e 20 anni, mentre 232 individui sono stati letti con la tecnica dell’UMBO con range di età stimato tra 1 e 16 anni. Dal confronto tra tecniche, i valori di APE e ACV sono risultati al di sotto dei valori di riferimento indicando la bontà delle letture. Inoltre, il LogLikelihood ratio test, nel confronto tra coppie di tecniche, non ha mostrato differenze statisticamente significative, per cui i 3 modelli sono risultati descritti dagli stessi parametri della curva di VBGF (L∞= 87.1, k= 0.11, t0= -1.75). Il 1° anno di età risulta raggiunto tra 19-23 mm, mentre la taglia di 40 mm è raggiunta entro il 4° anno. Lo studio del tasso di accrescimento ha evidenziato che il fasolaro è una specie longeva, con accrescimento estremamente rapido durante il primo anno di vita, per poi più che dimezzare dal secondo, mantenersi relativamente rapido fino a ca. 7 anni e poi diminuire soprattutto dal settimo anno. Il tasso di crescita risulta più lento in tarda estate – inizio autunno quando è deposta la banda ialina. Per investigare il ciclo riproduttivo, l’analisi microscopica delle gonadi ha mostrato che la specie è in riproduzione continua durante tutto l’anno, nonostante sia stata evidenziato uno sviluppo gonadico asincrono tra gli individui. L’indagine per comprendere la distribuzione della specie in Adriatico nord-occidentale (informazioni da bibliografia grigia, riunioni e stakeholders) ha evidenziato che la specie vive in banchi sparsi su dossi sabbiosi e la sua distribuzione non è omogenea nella fascia batimetrica, per cui è necessario, ai fini del monitoraggio della risorsa stessa, adottare metodologie di campionamento ad hoc. L’analisi preliminare di campioni di benthos per descrivere qualitativamente la comunità macrozoobentonica che caratterizza l’area di studio, ha rivelato una dominanza di bivalvi (28.3% delle specie totali), seguita da gasteropodi e da crostacei della classe Malacostraca (entrambi il 17.4% sul totale). Tale analisi ha evidenziato anche la presenza di alcune specie sensibili, che potrebbero risultare maggiormente impattate dall’attività di dragaggio. Alla luce dei risultati emersi, è essenziale approfondire le conoscenze della biologia della specie, degli effetti del dragaggio sulle comunità bentoniche e sull’habitat circostante, e sulla sopravvivenza della specie dopo il rilascio in mare, al fine di proporre misure gestionali che, con un approccio ecosistemico, mirino alla sostenibilità della risorsa e dell’ambiente in cui vive, per garantire un benessere socio-economico e ambientale duraturo.
STUDIO DEGLI ASPETTI BIO-ECOLOGICI DEL FASOLARO CALLISTA CHIONE (LINNAEUS, 1758) IN FUNZIONE DI UNA GESTIONE SOSTENIBILE DELLA PESCA
FABBRI, SARA
2021/2022
Abstract
Given the economic importance of the smooth clam (Callista chione) in Italy, this thesis work aimed at investigating some aspects of the biology (age, growth, reproduction), fishing activity (distribution and extension of fishing areas) and habitat (macro-benthic community living associated) where the resource lives, which is harvested in Italy by means of hydraulic dredges in the Chioggia, Venice and Monfalcone maritime districts. To adopt management measures that guarantee the conservation of the resource over time as well as the environmental and fishing sustainability, it is fundamental to have a thorough knowledge on the basic biological aspects of the species. At present, a Minimum Conservation Reference Size (MCRS) does not exist for the smooth clam in Italy, although the size of the landed product is around ≥40 mm in shell total length (TL). Samples were collected monthly - whenever possible - between December 2018 and November 2020. Three laboratory techniques were adopted and compared for age determination: backlighting (RI), thin cross sections (SL) and count of hinge growth rings (UMBO). The size range of the analyzed individuals was 18.5 - 79.5 mm. 246 specimens were analyzed by RI and SL techniques and the estimated age range was 1 - 20 years. 232 individuals were analyzed by mean of the UMBO technique and the estimated age ranged between 1 and 16 years. From the comparison between techniques the APE and ACV values resulted always below the reference ones, therefore indicating the consistency of readings. Furthermore, in the comparison between pairs of techniques, the LogLikelihood ratio test did not show any statistically significant difference, so that the 3 models were described by the same VBGF growth curve parameters (L∞= 87.1, k = 0.11, t0= - 1.75). The 1st year of life is reached between 19-23 mm TL, while the size of 40 mm TL is reached within the 4th year. The study of the growth rate has shown that the smooth clam is a long-lived species and it has a very fast growth during the first year of life, which at the second year is already more than halved, while remains quite fast up to 7 years of life and then decreases from the seventh year. The growth rate is slower in late summer – early autumn, when the deposition of the hyaline dark band occurs. To investigate the reproductive cycle of the species, the microscopic analysis of the gonads showed that the smooth clam reproduces throughout the year, despite of the inter-individual gonads asynchrony encountered. The study of the distribution of the species in the north-western Adriatic Sea, by information from bibliography, meetings and stakeholders, has highlighted the patchy distribution of the species, which lives in clusters scattered on sandy bumps. For this reason, it is necessary to adopt an ad hoc sampling design to monitor the status of the resource. The preliminary qualitative analysis of the macro-benthic community characterizing the study area, showed a dominance of bivalves (28.3% of the total species), followed by gastropods and crustaceans of the Malacostraca class (both 17.4% of the total species). This analysis also highlighted the presence of some sensitive species, which could be more impacted by the dredging activity. Considering the results gained in this thesis work, it is fundamental to deepen the knowledge on biological aspects of the species, the effects of dredging on the benthic communities and on the surrounding environment, as well as on the survival of the species after being released into the sea. All these is required to suggest management measures which aim at guaranteeing the sustainability of the resource and the environment where it lives, as well as to ensure a long-lasting socio-economic and environmental well-being.File | Dimensione | Formato | |
---|---|---|---|
Tesi_Fabbri.pdf
embargo fino al 21/02/2025
Descrizione: Tesi sperimentale Sara Fabbri (1101774)
Dimensione
3.49 MB
Formato
Adobe PDF
|
3.49 MB | Adobe PDF |
I documenti in UNITESI sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
https://hdl.handle.net/20.500.12075/12501