Abstract
Age and growth studies provide critical data for clam fishery management. Three ageing techniques, thin sections and acetate peel replicas – which involve shell sectioning – and surface growth rings were used to estimate the age and growth of Chamelea gallina populations in the mid-western Adriatic Sea. Their results were compared to identify the most reliable and least time-consuming approach. There were no significant differences between the two shell sectioning techniques (χ2 = 4.66, df = 3, p = 0.198), which were described by the same von Bertalanffy (VBF) growth curve parameters (L∞ = 43.9, k = 0.26, t0 = -0.84), whereas significantly different L∞ and k values were found between the two shell sectioning techniques and surface growth rings (L∞: χ2 = 13.62, df = 1, p < 0.001; k: χ2 = 9.18, df = 1, p < 0.002; these statistics refer to the comparison between acetate peels and surface growth rings).The latter approach proved unreliable and error-prone, as it underestimated age and overestimated the growth rate (L∞ = 26.4, k = 1.91, t0 = - 0.11). Although the thin sections and acetate peel techniques both provide reliable age and growth estimates, the former approach was less time-consuming. Our analyses demonstrated that shell growth is slower in the cold season and in older specimens and that it has slowed down over the past few decades.
Highlights
Chamelea gallina (Linnaeus, 1758) is an infaunal filter-feeder clam of the Veneridae family (Bivalvia: Lamellibranchiata: Veneridae) that inhabits the fine well-sorted sand biocenosis described by Péres and Picard (1964)
This study examines the age structure and growth rate of C. gallina populations harvested in the mid-western Adriatic Sea by three techniques – thin sections, acetate peel replicas and shell surface growth rings – to identify the most accurate and least time-consuming method
Indices of age precision within readings performed by the same reader were very low (APE = 1.22%; average coefficient of variation (ACV) = 4.34%), reflecting good method consistency and reproducibility
Summary
Chamelea gallina (Linnaeus, 1758) is an infaunal filter-feeder clam of the Veneridae family (Bivalvia: Lamellibranchiata: Veneridae) that inhabits the fine well-sorted sand biocenosis described by Péres and Picard (1964). It is widespread in the Mediterranean and Black Seas and along the eastern Atlantic coast. In Italy it inhabits a narrow coastal strip at depths ranging from 0 to 12 m up to 1–2 nautical miles (nm) off the coast (Morello et al, 2006). It is abundant in the central and northern Adriatic. In Italian territorial waters its Minimum Conservation Reference Size (MCRS) has been reduced from 25 mm total length (TL) [Council Regulation (CE) No 1967/2006, 2006 of the European Community (EC)] to 22 mm TL [Delegated Regulation (UE) No 2016/2376, 2016 of the European Union (EU) and Commission Delegated Regulation (EU) 2020/3, 2020]
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