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Age, growth, mortality and population structure of Polititapes aureus (Mollusca: Bivalvia) in the Gulf of Gabes, Tunisia

Derbali Abdelkarim

Oceanological and Hydrobiological Studies

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2024

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Vol. 53, No. 2

102--110

EN

The population dynamics of Polititapes aureus from Tunisia were investigated monthly during a one-year period (2018). The possible future commercial benefits of the species as a significant resource of artisanal fisheries require better knowledge of its population dynamics. This study provides the first insight into population parameters by investigating its population structure, growth, mortality, and exploitation rate. Allometric relationships between body size and length were determined. The shell length/total weight ratio indicated a positive allometric growth and was expressed as TW = 0.0002 SL3.103. Length frequency data were analyzed to estimate population parameters using FiSAT ΙΙ software. P. aureus showed lower growth rate (K = 0.46 yr-1) and asymptotic length (L∞ = 38.80) compared to those obtained for other bivalve species (mean values: K = 0.61 and L∞ = 55.02). Longevity (Tmax) and the growth performance index (φ’) were 7.95 yr-1 and 2.84, respectively. Total mortality (Z) was estimated from the length-converted catch curve at 0.85 yr-1 and fishing mortality (F) at 0.03 yr-1. Both values of natural mortality (M = 0.82 yr-1) derived from bivalve literature and based on Pauly’s (1980) empirical equation (M = 0.83 yr-1) developed for fish were comparable. The most intensive growth occurred during the first three years. The data presented herein are crucial for appropriate fisheries management and conservation of clams.

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Stock mapping, size structure and biological parameters of the clam Polititapes aureus in the shellfish production area of the southern Tunisian waters (Central Mediterranean)

Derbali Abdelkarim, Jarboui Othman

Oceanological and Hydrobiological Studies

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2021

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Vol. 50, No. 2

128--136

EN

The clam Polititapes aureus is one of the most abundant shellfish species in the southern Tunisian waters. Its current exploitation status and management are becoming a major concern for fishing industry in Tunisia. The significant ecological role of the species and possible future commercial benefits require a better knowledge of its stock. This research is the first attempt to investigate its current status in an area with the largest shellfish production. The obtained results showed a scattered distribution. The stock density ranged from 0 to 124 ind. m−2, and biomass values varied from 0 to 300 g m−2. This results in a remarkable biomass of 201.2 (± 64.6) t and high abundance reaching 91.3 ± 32.9 million individuals, estimated an area of 4182 ha. The species distribution was also investigated, with the size ranging from 4.9 to 35.34 mm. The overall sex ratio (F:M) was 1.26:1, which significantly deviated different from parity (1:1). The main environmental factors were identified and several abiotic parameters were found to strongly affect the spread of the clam species. The clam reproduce well and is expected to almost meet the domestic market demand through artisanal fishery.

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Taphonomy of mass mollusc shell accumulation at Amvrakikos Gulf lagoon complex sandy barriers (NW Greece)

Tsolakos Konstantinos, Katselis George, Theodorou John A.

Oceanologia

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2021

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No. 63 (2)

179--193

EN

The preservation status of the mollusc shell accumulation of sandy barriers at the Amvrakikos Gulf lagoon complex was studied. Taphonomic shell analysis of dead mollusc depositions was undertaken in the summer of 2016 at Amvrakikos lagoon complex within the Tsoukalio and Logarou sandy barriers, which showed significant differences among the major abundant bivalve species of Cerastoderma glaucum and Polititapes aureus. Both hydrodynamic transport and differential exposure to environmental conditions differ among the accumulated shells depositions of the lagoonal sandy barriers. The heavier and more durable shells of C. glaucum are frequently found concentrated at the Tsoukalio lagoon accumulations and show a higher intensity of fragmentation whereas at Logarou lagoon the bioerosion and abrasion is more intense. On the other hand, the lighter, thinner, and thus more fragile shells of P. aureus show higher concentration and intensity of fragmentation and bioerosion at Logarou lagoon sandy barriers. The continuous deposition of shells at Tsoukalio lagoonal sandy barriers, contrary to the long-term deposition at Logarou lagoon, explains the different types of accumulations among the lagoons which are attributed to the geomorphology of the sandy shores as well as the morphological characteristics of the different shells.