Luis Silva

Definition of fleet components in the Spanish artisanal fishery of the Gulf of Cádiz (SW Spain ICES division IXa)

Abstract The Spanish artisanal fishery in the Gulf of Cadiz is of a notably multi-gear and multi-species nature, with target species occurring seasonally, where a fleet composed of about 1000 vessels captures more than 50 commercial species. From this complexity arises the need for defining fleet components (FCs) (i.e., groups of vessels developing the same fishing pattern through the year), which allow the design of simpler and more efficient sampling schemes on the basis of understanding the behaviour of such components. To define the artisanal FCs, the daily landings by species and vessel during 1996 were considered. In a preliminary analysis, a total of 53 fishing trip types were objectively characterised from the species composition of these landings using hierarchical Cluster Analysis (CA) techniques. A non-hierarchical K-means CA was applied later to re-classify the 1996 data and to classify 1997 landings data by trip type. The red seabream (Pagellus bogaraveo), red-banded seabream (Pagrus auriga), octopus (Octopus vulgaris) and striped venus (Chamaela gallina) types stood out according to their importance in landed weight. In a second stage, only those vessels with more than 50 daily landings regularly distributed through the year were selected. A matrix with as many rows (cases) as selected vessels and 53 trip types ×12 months =636 columns (variables) was designed. A new CA was applied to group vessels which show similar fishing annual patterns. Eleven FCs were defined from these results. Two basic features of these components may be emphasised: they are highly related to the landing (home) ports and the fishing gears used, and they show definite seasonal fluctuations according to the main fishing trip types developed.

Timing variations and effects of size on the reproductive output of the wedge clam Donax trunculus (L. 1758) in the littoral of Huelva (SW Spain)

This study aimed to augment existing knowledge of the reproductive characteristics of Donax trunculus through analysis of timing variations and the influence of shell size on partial fecundity (PF) during the reproductive period. To achieve this objective, two reproductive timing characteristics were also studied: size at first maturity (SL 50 ) and the reproductive cycle using histology and image analysis techniques. SL 50 was 10.83 mm for females and 10.86 for males. Donax trunculus showed a continuous and simultaneous release of gametes and high oocyte regeneration ability during the reproductive period (from February to July). These reproductive characteristics impeded the estimation of total fecundity. However, throughout the reproductive period an increasing pattern of PF was observed followed by a significant drop at the end of the same period, which could be quantified (293,390 of vitellogenic and ripe oocytes). At the same time PF quantifications allowed for predicting and estimating the influence of shell length (SL) on the reproductive output as a function of oocyte typology (PF = 4.12 + 3.96 SL; r 2 = 0.86; all types). Levels of prevalence of a digenetic trematode-like parasite with castrate ability fluctuated between 0–20% depending on the time of the year and sex. In addition, the possible consequences of two different scenarios of population size structure on the reproductive output were simulated, and highlighted how beach areas supporting high levels of anthropogenic pressure (Isla Canela) could compromise future recruitments, producing 84% less oocytes than a beach with a lower level of disturbance (Donana).