• Document: E. Possenti (*), P. Sartor (*), S. De Ranieri (**)
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Atti Soc. tosc. Sci. nat., Mem., Serie B, 114 (2007) pagg. 91-98, figg. 9 E. Possenti (*), P. Sartor (*), S. De Ranieri (**) Reproductive biology of females of Plesionika edwardsii (Brandt, 1851) (Crustacea, Decapoda, Pandalidae) in the northern Tyrrhenian Sea (Western Mediterranean) Abstract - Individuals of P. edwardsii were collected on soft Introduction bottoms from 300 to 450 m depth through experimental traps and samplings on commercial trawlers from December 2003 The pandalid decapod crustacean Plesionika edward- to April 2006. A total of 4919 specimens (2385 females, 1451 sii (Brandt, 1851) is a nektobenthic species, present males and 1083 undetermined) was analysed. Sex was mac- roscopically determined: adult and subadult males show the in a wide bathymetric range: in Mediterranean it has masculine appendix on the second pair of pleopods. Sizes been recorded from 100 to 650 m depth (Colloca et ranged from 10 to 29 mm carapace length (CL) for females, al., 1998). P. edwardsii is a gregarious species, able from 11 to 26 mm CL for males. Sex ratio was in favour of to perform nictemeral vertical migrations, mainly for females along all the investigated period. Females with mature feeding (Relini et al., 1999). ovaries and ovigerous ones were observed all year long, except P. edwardsii is one of the largest Pandalid species, in December, even though sexual maturity peaked from March the maximum size reported for the Mediterranean Sea to July. Physiological size at first maturity (size where 50% is 30 mm CL (carapace length) (Colloca, 2002). The of females shows mature ovaries) and the functional one (size species, called «striped soldier shrimp» thanks to the where 50% of females is ovigerous) were 18.5 and 20.2 mm CL, respectively. Absolute fecundity ranged from about 1,000 longitudinal, dark red stripes on the abdomen (Fisher to about 20,000 eggs for ovigerous female. A positive correla- et al., 1987; Relini et al., 1999), is of commercial inter- tion between number of eggs and size was obtained. est, and it is included in the FAO catalogue of species of interest to fisheries (FAO, 2005). Landings mainly Key words - Plesionika edwardsii, crustaceans, decapoda, comes from fishing with traps and trawling (De Ranieri, reproductive biology, fecundity, resource assessment, north- 2005). In spite of this, a targeted fishery for P. edwardsii ern Tyrrhenian Sea, Western Mediterranean. is still absent, so that this resource can be considered as underexploited. Riassunto - Biologia riproduttiva delle femmine di Plesionika In expectation of a future increase of fishing pressure, edwardsii (Brandt, 1851) (Crustacea, Decapoda, Pandalidae) it is important to deepen the information on biology nel Mar Tirreno settentrionale (Mediterraneo occidentale). I campioni mensili del gamberetto Plesionika edwardsii, raccolti and population dynamic of this species, still scarce and da dicembre 2004 ad aprile 2006, sono stati ottenuti sia attra- scattered. verso campagne di pesca con nasse sperimentali, sia tramite This study has been focused on the reproductive biol- campionamenti effettuati a bordo di pescherecci a strascico, in ogy of P. edwardsii, in order to provide information on zone comprese tra 300 e 450 m di profondità, caratterizzate da reproductive period, maturity size and fecundity. fondali fangosi con ripide pendenze. Sono stati analizzati 4919 esemplari (2385 femmine, 1451 maschi e 1083 indeterminati). Il sesso è stato determinato macroscopicamente: i maschi adul- Materials and methods ti e subadulti possiedono l’appendice mascolina, localizzata sul secondo paio di pleopodi. La struttura in taglie è risultata compresa tra 10 e 29 mm di lunghezza del carapace (LC) per Data collection le femmine e tra 11 e 26 mm LC per i maschi. La sex ratio è Sampling was performed both with experimental traps risultata spostata a favore delle femmine per tutto il periodo (Sartor et al., 2006) and through embarks on a profes- investigato. Femmine con ovari maturi e femmine ovigere sono sional bottom trawler of Porto Ercole fleet (Grosseto, state osservate in tutti i mesi dell’anno, ad eccezione di dicem- Italy). Data were collected monthly in the period 2003- bre, anche se il picco di maturità sessuale è risultato compre- 2006 to the South of Giannutri Island, in the northern so tra marzo e giugno. La taglia di prima maturità fisiologica Tyrrhenian Sea. Muddy bottoms from 300 to 450 m (taglia alla quale il 50% delle femmine ha ovari maturi) e quella depth were investigated, in a zone far more than 20 funzionale (taglia al

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