The Collapse of a Wedge Clam Fishery in the Spanish Mediterranean Coast and Recovery Problems

Abstract

[EN] In the sandy shores of the Spanish Mediterranean, Donax trunculus (Linnaeus, 1758) has a high commercial interest. In the Gulf of Valencia, poor management of fishing activity led to its closure in June 2015. The objective of this study was to analyze the evolution of the catches of D. trunculus before the closure of the fishery as well as the biomass and density of the population in the months following the closure, plus 2 y later. The area of study was located in the main fishing area of the Gulf of Valencia, which belongs to the fleet of the Gandia Fishermen's Guild. The fishing beds for this clam are found on sandy sediments in shallow waters (between 0 and 2 m). During the 10 y previous to the fishery closure, the annual catch per unit effort of D. trunculus suffered a sharp decrease, falling from values between 37 and 42 (kg small vessel(-1) d(-1)) during the period 2004-2008 to 5.5 in 2014. After the closure, the biomass and density of the wedge clam showed a seasonal pattern, with maximum values in summer, as well as notable differences in densities along the shore in each sampled month. Furthermore, a different size-frequency distribution across depth, with smaller individuals in the shallower areas, was observed. Nevertheless, a general and considerable decline for biomass and density from 2015 (monthly mean of commercial biomass ranged from 24 to 48 kg ha(-1)) to 2017 (from 4 to 13 kg ha-1) was noted. This indicates that the closure did not improve the state of the population. There are several hypotheses that could explain this decline such as overfishing, changes in environmental conditions, higher predation (in benthic and planktonic phases), and the reduction of food availability. Therefore, there would be a need to study them in greater depth, as well as to increase the understanding of the spatial dynamics and connectivity of the Donax beds.