Preprint volume - SIBM

Pre-print Volume - Posters
MANAGEMENT OF THE COASTAL ZONE COMMITEE
G. RIZZO, T. MARČETA, V. MATOZZO, M. BRESSAN, M.G. MARIN
Department of Biology, University of Padova, Via U. Bassi, 58/B – 35121 Padova, Italia.
mgmar@bio.unipd.it
NEW INSIGHT ON CLAM POPULATION (CHAMELEA GALLINA) IN THE
CHIOGGIA DISTRICT: MORPHOMETRIC AND PHYSIOLOGICAL DATA
CHAMELEA GALLINA NEL COMPARTIMENTO MARITTIMO DI CHIOGGIA:
DATI MORFOMETRICI E FISIOLOGICI DI POPOLAZIONE
Abstract – The population of the clam Chamelea gallina (Mollusca, Bivalvia) was studied in two sites of the
Chioggia district, Caleri and Chioggia, from June 2009 to February 2010. Some preliminary results
concerning spatial and temporal distribution, mortality, physiological and reproductive condition,
recruitment and growth rate are presented.
Key-words: Chamelea, Chioggia, North Adriatic, fisheries.
Introduction – In the early 1980’s, Chamelea gallina landings were up to 100,000 t/yr
along the western Adriatic Sea coasts (Froglia, 1989). Overexploitation, recruitment
failure and mortality outbreaks have severely depleted clams stocks, leading to a
reduction in total catches in Chioggia district, from almost 3000 t in 2007 to about 850
t in 2009 (CO.GE.VO., unpubl.). In this context, the research project “CLODIA”
(Sviluppo sostenibile degli ambienti costieri) funded by Regione Veneto aims at
providing new insight on spatial and temporal distribution, mortality, physiological and
reproductive condition, recruitment and growth rate of the species, potentially useful
for resource restocking and management. Some preliminary results are presented.
Materials and methods – Clams were monthly sampled (from June 2009 to February
2010) along a 250 m transect parallel to the coast at Caleri (45°06.214 N; 12°20.660 E)
and Chioggia (45°10.590 N; 12°19.670 E). A conventional dredge provided with a
bag-shaped sampling mesh with a rigid mouth (40 cm width, 20 cm height) and a 9 mm
mesh size was used to collect both juveniles (25 mm). Size frequency distribution in the dredged area was obtained
measuring (antero-posterior axis), counting and weighting clams. Clam mortality was
tentatively estimated by measuring weight percentage of empty shells. Percentages of
mature animals were obtained by microscopic observation of smears of gonadal tissue.
The condition index (CI), expressed as meat dry weight x 100/shell dry weight, was
determined, and the survival-in-air test was performed.
Results – In Tab. 1, C. gallina morphometric data are reported. On average, juveniles
were more abundant at Caleri (49 clams per m 2 ) than at Chioggia (18 clams per m 2 ),
whereas commercial size clams were less than 10 animals per m 2 at Caleri, and 5
animals per m 2 at Chioggia. A new age class (0+, mode=5 mm) was recruited at Caleri
starting from September, with a mode shift to 7 mm in February. Clams of 15-22 mm
shell length were the most abundant at Chioggia (1+, putatively). Average percentages
of empty shells were 27% at Caleri and 33% at Chioggia, with a peak for both sites in
January (53%). As for CI, no influence of the sampling site was recorded (mean
CI=5.5), whereas a statistically significant influence of the sampling time (Kruskall-
Wallis, p