Abstract
AbstractTopshells play a pivotal role in intertidal rocky ecosystems and are adapted to harsh thermal and hydric stress. Phorcus sauciatus, a common grazer in the Macaronesian region (Madeira and the Canaries), has rarely been studied due to its restricted geographic distribution compared with Phorcus lineatus. Monthly samples were taken throughout 2017 to analyse biological parameters and evaluate the harvesting effect on the stocks of this species in Madeira. Individuals of the first age classes (<4 years) were dominant (~89%), while immature individuals were more abundant during the summer season. The spawning season occurs between March and August, especially from March to June. The size at first maturity was 12.95 mm long (1.68 years), with a continuous recruitment pattern throughout the year. Yield-per-recruit analysis (Y/R) showed that maximum production is achieved at a fishing mortality of 1.7 year−1, corresponding to a Y/R of 0.023 g. Currently, Phorcus sauciatus seems to be moderately exploited in Madeira, but urgent conservation measures, such as a landing obligation, the establishment of a minimum catch size of 15 mm length, and a closed season (February–May), are warranted to preserve stocks of this species in the medium to long term.
Highlights
Topshells, limpets and winkles are among the most successful intertidal algal grazers in the North-eastern Atlantic Ocean and the Mediterranean Sea (Templado & Rolán, 2012)
The size distribution estimated for P. sauciatus from the Madeira archipelago is in accordance with what was previously
The relative growth coefficient obtained for the combined sexes revealed a negative allometric growth for this gastropod, which implies a disproportional increase in total weight in relation to the increase in individual shell growth
Summary
Limpets and winkles are among the most successful intertidal algal grazers in the North-eastern Atlantic Ocean and the Mediterranean Sea (Templado & Rolán, 2012). Topshells are exposed to different levels of thermal and hydric stress that result in specific morphological and biological characteristics related to adaptations to the harsh environmental conditions on rocky shores (Ramírez et al, 2005; Donald et al, 2012; Henriques et al, 2017). They play a pivotal role in the intertidal ecological balance and are frequently used as biological indicators of anthropogenic impacts (Sousa et al, 2018). Local information on the population structure and distribution of P. sauciatus is available from the north-west Iberian Peninsula (Rubal et al, 2014) and the Canary Islands (Ramírez et al, 2005, 2009; Alfonso et al, 2015)
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