Spatial distribution patterns of the striped venus clam (Chamelea gallina, L. 1758) natural beds in the Gulf of Cádiz (SW Spain)

VENUSEstudio integral de los bancos naturales de moluscos bivalvos en el Golfo de Cádiz para su gestión sostenible y la conservación de sus hábitats asociado

Spatial distribution and community structure of megabenthic bivalves in the subtidal area of the Gulf of Cádiz (SW Spain)

VENUSEstudio integral de los bancos naturales de moluscos bivalvos en el Golfo de Cádiz para su gestión sostenible y la conservación de sus hábitats asociado

Investigación y gestión pesquera como elementos clave para alcanzar la sostenibilidad de la pesquería de chirla Chamelea gallina (Linnaeus, 1758) en las aguas españolas del Golfo de Cádiz

Fondos FEMP Andalucí

First insights into population parameters and spatial distribution of the two morphotypes of Mactra stultorum (brownish and whitish) (Linnaeus, 1758) (Mollusca: Bivalvia) along the southwestern Spanish coast

The aim of this study was to address an analysis of spatial distribution, reproduction, population parameters and secondary production of the natural beds of the well-defined morphotypes of the clam Mactra stultorum (brownish and whitish variants) along the SW Spanish coast. The main findings showed that the presence and the frequencies of both morphotypes increased near the estuaries of rivers, particularly the Guadalquivir River. However, subtle differences in habitat preferences have been revealed and the brownish variant showed a wider and deeper distribution. High similarity in the gonadal development was recorded for both variants. It started in January, continued into late winter and early spring and ended with a spawning period from April to August. An energy storage-utilization cycle, coupled to the reproductive and resting periods and driven by sea water temperature variations and food availability, was also observed. The abovementioned period of gamete emissions resulted in a recruitment pattern with a one-time settlement period per year. Von Bertalanffy growth functions provided an asymptotic length of 46.7 mm (whitish) and 50 mm (brownish) and growth constants of 0.55 (whitish) and 0.50 yr−1 (brownish). The mean annual biomass (B ̅) ranged between 0.062 (whitish) and 0.076 g AFDW m−2 yr−1 (brownish) (AFDW: ash-free dry mass). Individual somatic production showed the highest value at 32 and 34 mm shell length, and annual production (P) ranged between 0.075 and 0.113 g AFDW m−2 yr−1, resulting in renewal rate (P/B ̅) values between 1.21 and 1.37, for the whitish and brownish variants, respectively. These results provide basic knowledge about the reproduction and population dynamics of this species along the Atlantic coast, particularly in the sandflats near the estuary of the Guadalquivir River. They could also shed additional light upon taxonomic differentiation and clarify the ecological role of both variants when compared with two bivalve sympatric species of the intertidal and subtidal areas.Versión del editor1,48

Abundance prediction and influence of environmental parameter in the abundance of Octopus (Octopus vulgaris Cuvier, 1797) in the Gulf of Cadiz

Understanding the processes that influence octopus abundance is important in order to manage the fishing grounds and offer advice on the exploitation of this important resource. Fluctuations in abundance of exploited stocks may be due to a great variety of factors. However, in short-lived animals such as cephalopods, in which abundance depends on strength of the recruitment, it is well known that population abundance is highly influenced by the environmental conditions. In this study we investigated the relationship between octopus (Octopus vulgaris) catches from the fishery located in the area off the Gulf of Cadiz (Spanish South Atlantic Region) and several hydrographic and oceanographic parameters such as sea surface temperature, surface chlorophyll-a, inorganic surface turbidity and climatic indicators such as the NAO index, rain, WeMoi Index, AMO index and or Guadalquivir River discharges. In addition, a recruitment index was obtained from fishery-independent surveys, which was also used to investigate its effect on annual catches. Results revealed that abundance of octopus showed a significant negative relationship with rain in the previous year as well as a positive effect of the recruitment index. We have obtained a model using the rain and the recruit index to forecast the catches. This model explained a high percentage of variation in annual catches and was used to forecast the next year’s catch providing results within the expected confidence intervals. This represents a potentially useful tool to guide fishery managers since no assessment of the species is currently conducted in the area