Lack of recovery symptoms of an endangered and harvested mollusc in the last 20 years

Abstract

Molluscs are subjected to intense harvesting in many areas around the world. Conservation measures have been developed to preserve populations of an overexploited gastropod species, the abalone Haliotis tuberculata coccinea. This species was surveyed in subtidal localities throughout coastal Tenerife, Canary Islands over the last two decades (1994–2014). A clear indicator of non-recovery was observed in the decrease of mean size throughout the last two decades, even after the inclusion of this species in the Regional Catalogue of Endangered Species. The mean size of abalones decreased from 33.5 mm (1994) to 28–29 mm (2002 and 2014), corresponding to sub-adult individuals. The structure of size classes was typical of an overexploited species, with reduced occurrence of large individuals (>50 mm). Several factors might explain this pattern such as illegal harvesting, proliferation of featureless benthos and a decrease of suitable habitats for colonization and settlement. Complementary conservation actions are urgently needed to preserve this species in the area studied.

Filling biological information gaps of the marine topshell Phorcus sauciatus (Gastropoda: Trochidae) to ensure its sustainable exploitation

“…The low frequency of specimens in the age classes between 4 and 9 years (~11%) seems to be a consequence of intensive size-selective exploitation of the larger topshells, resulting in a decrease in the reproductive output. The reproduction of this species is gamete density-dependent, as occurs in other gastropods, such as the patellids Patella candei crenata and P. aspera (Riera et al ., 2016; Sousa et al ., 2017).…”