Abstract
Exploitation of organisms can prompt the reduction in the number and size of target populations consequently affecting reproductive output and replenishment. Here, we investigated the effects of exploitation on the population structure of a protandrous patellid limpet, Patella aspera, an overexploited Macaronesian endemic. Timed dives were used to collect animals across eleven islands of Macaronesia. Individuals were inspected for sex, size, and gonad stage. Using catch effort (time per person) per island coastal perimeter as a surrogate for exploitation intensity, we found that limpet abundance (CPUE) and mean size tended to decrease with exploitation intensity. When considering the sex of animals separately, the size of the largest male, but not females, decreased with exploitation. In contrast, the size of the smallest male remained relatively consistent, whereas the size of the smallest female decreased significantly with exploitation. As exploitation is mostly targeting larger individuals, results suggest that males are compensating the removal of larger females, by undergoing sex change at smaller and presumably earlier sizes. These results have wider implications for the conservation of P. aspera, as a reduction in female size will likely affect the numbers of oocytes produced, hence fecundity. Regulations promoting the protection of the larger‐sized animals should be enforced to safeguard the replenishment of the population.
Highlights
In a time when over 28% of all the world’s fish stocks are either overexploited or depleted and when another 61% is fully exploited and in imminent danger of overexploitation (FAO 2014), it is paramount that the impact of fishing on the ecology of marine populations, communities, and ecosystems is better understood
Other patellid limpets can be found throughout the Macaronesia, we focus on P. aspera because: (1) it has a wide distribution occurring in all islands, (2) there is still debate regarding the taxonomic status of other patellid limpets (P. candei complex) (Côrte-Real et al, 1996; Faria et al, 2016; Sá-Pinto, Branco, Harris, & Alexandrino, 2005; Weber & Hawkins, 2002), and (3) it is the most exploited species with the highest economical value (Martins, 2009; Martins et al, 1987; Navarro et al, 2005)
MARTINS et al be intense on islands (Erlandson & Rick, 2010) leading to overexploitation of stocks and, in extreme cases, local extinction of species (e.g., Patella candei in Lanzarote, Weber & Hawkins, 2002)
Summary
In a time when over 28% of all the world’s fish stocks are either overexploited or depleted and when another 61% is fully exploited and in imminent danger of overexploitation (FAO 2014), it is paramount that the impact of fishing on the ecology of marine populations, communities, and ecosystems is better understood. Both in the Azores (e.g. Martins et al, 2008) and in the Canaries (e.g. Navarro et al, 2005), significant reductions in abundance and size of limpets have been documented, especially in the most heavily exploited islands. In sequential hermaphrodite species, size-selective fishing can lead to sperm or egg limitation and reproductive failure in harvested populations (Alonzo & Mangel, 2004; Hamilton et al, 2007), in species with a fixed sex change.
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