1,720,973 research outputs found
Sometimes they come back and disappear again
No full textStarting from 2004 the razor clam Ensis minor disappeared in the Gulf of Trieste (Italy)
to reappear in 2008 when a similar species, Solen marginatus, crashed. E. minor peaked in 2011, when at least three successive recruitment events occurred. The species is difficult to rear and no restocking seem feasible. The density in 2012 was quite high in spite of a really bad February’ sea, and the fishery obtained good economic income. Scarce recruitment was observed in 2013 and no settlement was found up to the end of 2014. Presently E. minor is going low but S. marginatus is growing in densities again. These observations are difficult to explain: it could be a natural cycle perhaps based on competition between species.
But the decrease in population density in beach restoration site (where E. minor disappeared, as survey results showed in September, 2014) could be a proxy for some tentative explanation: even if the cycles could be natural events it’s interesting to underline that both species did not recover after beach restoration. So the possibility that beach restoration can be at least in part responsible for the simultaneous absence of Ensis and Solen should be taken in account
Survey on Chamelea gallina bedsin the Lignano area (Gulf of Trieste, Adriatic Sea)
No full textFollowing the mass mortality which occurred in 1996, the rebuilding of the Striped Venus clam(Chamelea gallina) stock was complicated due to recruitment failure and low grawth rate, as suggested by seasonal surveys. Thin sections of shell were obtained from twenty clams randomly extracted for every survey and it was observed that the cleft was formed in the autumn as acertained in previous surveys. Stock management based on minimum size and quantities only is discussed. At present, in spite of the effort to manage the population made by both the Public Authority and fishermen soon after 1996, the depletion of the area is almost complete as resulted from surveys done in 2009 and 201
Solénidos En Italia
No full textI Solenidi in Italia sono stati per anni un'importante risorsa della pesca costiera. In Seguito importanti oscillazioni sia nel reclutamento che nel tasso di accrescimento hanno da una parte ridotto l'importanza di Ensis minor, mentre dall'altra Solen marginatus, specie meno pregiata, è diventata la risorsa più importante. Vengono discussi i dati forniti dalle Autorità marittime e quelli ottenuti dai mercati ittici. La pesca con draga idraulica è comunque in declino ed emerge un potenziale conflitto gestionale con la pesca in immersione
DEFINITION OF A NEW FORMULA FOR THE CALCULATION OF THE TOTAL HEIGHT OF THE FAN SHELL PINNA NOBILIS IN THE MIRAMARE MARINE PROTECTED AREA (TRIESTE, ITALY)
No full textFour years of monitoring of Pinna nobilis population in Miramare Marine Protected Area (Trieste, Italy) have led to the development of a new equation for indirect calculation of total shell height (Htot) for this bivalve,endemic to the Mediterranean Sea. As the formulas listed in the cited literature are not corroborated by in situ measured growth data, it was necessary to describe a specific formula for Miramare population. This exponential equation was called MirExp. A specific growth curve has also been created with this formula and the data collected every year from 2008 to 2011. This curve shows that in Miramare P. nobilis grows faster in its early years than
what is reported in other studies carried out in Croatia and Spain. Population density is also the highest among those reported in consulted papers, which make reference to studies conducted in various Mediterranean protected and non-protected areas
What went eventually wrong in the clam fishery in the Gulf of Trieste (Italy) (Prophecies, science and empiricism)
No full textThe collapse of clam fishery in the Gulf of Trieste is not surprising even if the fishery pressure declined year after year since the beginning of the 00’ties. The failure is referred mainly to baby clam Chamelea gallina, suffering extended depletion far to be justified, due to strong regulation imposed by the fishermen Consonsortium, supported partly by results of periodic surveys. In order to find some explanation an analysis was conducted on the hystorical data collected by our institution with special attention to the length-shell weight ratio, possibly a comprehensive index of the status of both environment and clam wellness. The data set contains clams processed in early 80’ies (from commercial fishery), in the 94-2000 interval and in 2009, the last two from surveys done with the same sampling gear. The results of the first data set are quite high (over 1.3) but as obtained from commercial clams must to be treated cautiously, the minimum (0.6) being in 1999-2000 (after a mass mortality occurred in 1996) and recovering (over 1) in 2009, but with very low clams density. The clam beds was moreover severely reduced by extending seagrass covering and molluscs vanishing beyond 5 meters depth, where once the most fishery pressure was exerted. The phenomena involved are complex and cannot be resolved simply by looking at exploitation even if in the 90’ies it was heavy and without control in spite of law severity and the buy-back project leaved “de facto” the operating boats equal in numbers . The hope of stock recovery is at the present quite low due to growth rate lower than previously supposed, but in the Gulf of Trieste this was clear since the mid of 90’ties to the fishermen and the scientific operators. Some encouraging signal may be found in Chlorophyll-a water content that, since 2006, seems progressively increasing and the recovery of length - shell weight ratio observed could be a positive response to food availability
The Mapping of Clam Beds for the Fishery Assessment and Management in theNorthern Part of the Gulf of Trieste
No full textThe Gulf of Trieste is characterized by quite shallow waters (less 25 meters depth, Stravisi 2003) with
the most important tidal amplitude in the Mediterranean enhanced by basin geometry. The study area is
located on the northern part of Adriatic Sea, between Tagliamento and Isonzo river mouths where important
clam beds are exploited by local fleet armed with hydraulic dredges mainly on sandy bottom ranging from 2
till 6 meters depth.
Thanks to exhaustive geomorphological research done by Gordini et al [2003] it was possible to obtain
a detailed picture of the bottom features that can also be used to improve the knowledge of 3D (Fig.1)
distribution of the infaunal mollusc populations, to ameliorate the assessment and fishery management and
this achievement should be obtained using the GIS tools.
Here we examine the results of the surveys conducted in August and December 2009 on the Chamelea
gallina beds to support the fishermen organisation and Maritime Authority of the Monfalcone District. From
August to December the numbers/m2 of clams exhibits a general decrease even if the maximum is reached at
higher level due to the recruits become vulnerable to the sampling gea
ANALISI DI DATI BIOACUSTICI OTTENUTI MEDIANTE ECHOSOUNDER PER LA VALUTAZIONE DELLA COMPONENTE ITTICA DELL' AREA MARINA PROTETTA DI MIRAMARE
No full textLe tecniche acustiche attive, essendo metodi non invasivi, rappresentano un valido strumento, complementare ai censimenti visivi ("visual census"), per lo studio e il monitoraggio della componente ittica all'interno di un'area marina protetta. Nel periodo compreso tra Aprile e Novembre 2006, l'utilizzo di un echosounder scientifico split-beam ha permesso di ottenere stime quantitative della distribuzione spaziale dei popolamenti ittici dell'AMP di Miramare (Golfo di Trieste, Alto Adriatico) e di individuare potenziali aree di aggregazione ittica. La zona della barriera, la zona del FAD (fish aggregating device) e la zona al limite settentrionale dell'AMP si caratterizzano per la frequenza con cui si sono rilevati elevati valori di densita ittica nel corso del periodo di campionamento. I risultati ottenuti dal presente studio costituiscono utili informazioni per la gestione e la valutazione dell'efficacia di gestione della AM
Isotopic composition, growth rates and biological behaviourof Chamelea gallina and Callista chione from the Gulf of Trieste (Italy)
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