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- Considerations on the biology of Plesionika narval (Fabricius, 1787) in the Northeastern AtlanticPublication . Sousa, Ricardo; Henriques, Paulo; Biscoito, Manuel; Pinto, Ana Rita; Delgado, João; Dellinger, Thomas; Pinho, Mário RuiLife history traits of Plesionika narval were studied in the Northeastern Atlantic, Madeira archipelago including growth, age, sexual maturity, recruitment pattern and mortality. A total of 28,262 specimens were sampled over a period of 8 years comprising two time series from 1991 to 1995 and 2004 to 2008. The relative growth pattern showed a negative allometric nature of growth for combined sexes, males, females, non ovigerous and ovigerous females. Estimated asymptotic carapace length (CL∞) and growth coefficient (K) showed higher values in females (CL∞=30.21 mm, K=0.450 year-1 ) comparatively to males (CL∞=28.61 mm, K=0.430 year-1 ), resulting in better overall growth performance in females. The maximum life span (tmax) was estimated at 6.81 years for combined sexes, 6.97 for males and 6.66 for females, however 99.95% of the individuals were younger than 3 years. Although a seasonal spawning season was evident from late summer to late autumn, reproduction may be prolonged throughout the year since ovigerous females are present in all months and achieving sexual maturity at 14.61 mm. The recruitment pattern was continuous throughout the year with a major peak occurring in spring. The total mortality (Z) and fishing mortality (F) were higher in females than in males while natural mortality (M) was similar between groups.
- First observations of hermaphroditism in the patellid limpet Patella piperata Gould, 1846Publication . Sousa, Ricardo; Henriques, Paulo; Vasconcelos, Joana; Faria, Graça; Riera, Rodrigo; Pinto, Ana Rita; Delgado, João; Hawkins, Stephen J.Hermaphroditism is thought to be an advantageous strategy common in marine molluscs that exhibit simultaneous, sequential or alternating hermaphroditism. Several species of patellid limpets have previously been shown to be protandrous hermaphrodites. The present study aimed to confirm whether this phenomenon occurs in Patella piperata. Transitional forms of simultaneous protandrous hermaphroditism were found in intermediate size classes of P. piperata, in Madeira (North-eastern Atlantic). Sequential hermaphroditism was confirmed after histological analysis. The overall sex-ratio was biased towards females but approached similar proportions in the larger size classes. Analysis of size at sex change showed that at a shell length of 36 mm 50% of the population probably have changed sex. The results reported confirm the occurrence of sequential hermaphroditism. These findings are of utmost importance to the understanding of the reproductive biology of this species with direct effect on management and conservation of this traditionally harvested limpet.
- The protection effects of marine protected areas on exploited molluscs from an oceanic archipelagoPublication . Sousa, Ricardo; Henriques, Paulo; Vasconcelos, Joana; Pinto, Ana Rita; Delgado, João; Riera, Rodrigo1. Limpets are one of the most successful intertidal algal grazers in the north-eastern Atlantic. They provide valuable ecosystem services, playing a pivotal role in maintaining rocky shore ecological balance and have an important economic value, being subject to high levels of exploitation in several oceanic archipelagos. Limpets represent one of the most profitable economic activities of small-scale fisheries in the Madeira archipelago. However, limpets are extremely vulnerable to anthropogenic impacts, such as overharvesting, habitat fragmentation, and pollution. 2. The protection effects and the effectiveness of marine protected areas (MPAs) on the population dynamics of two historically highly exploited limpet species, Patella aspera and Patella candei, were analysed through a comparative study of size, reproduction, and biomass in the Madeira archipelago. 3. The effects of protection from MPAs on limpet populations resulted in a differential increase on size at first maturity, shell size, and capture per unit effort according to the degree of protection. 4. Old and enforced MPAs showed the best-preserved limpet populations in the study area, and both variables (age and enforcement) best explained the observed variability among the MPAs studied. 5. A thorough and multidisciplinary study is necessary to obtain a reliable picture of commercial stocks of the two targeted species (P. aspera and P. candei). Genetic analysis and studies on the food source of limpets may shed light to develop integrative conservation strategies.
- Long-term population status of two harvested intertidal grazers (Patella aspera and Patella candei), before (1996–2006) and after (2007–2017) the implementation of management measuresPublication . Sousa, Ricardo; Vasconcelos, Joana; Henriques, Paulo; Pinto, Ana Rita; Delgado, João; Riera, RodrigoIntertidal limpets are subject to harvesting pressure in regions, e.g. oceanic islands, where marine organisms are a more accessible source of protein. These molluscs are very sensitive to human exploitation which often results on a decrease of their densities and an over-representation of immature individuals, because of the loss of large sized reproductive specimens. Two species of exploited limpets (Patella aspera and Patella candei) were assessed throughout 21 years, before (1996–2006) and after (2007–2017) the implementation of conservation measures for their sustainable management in Madeira (North-eastern Atlantic Ocean). Different levels of anthropogenic pressure were also taken in account in this comparative study: (i) proximity to coastal settlements (“Near” vs. “Far”) and (ii) accessibility to the coast (North vs. South), that may be considered surrogates of harvesting pressure on the intertidal of Madeira. The present results showed that the stocks of P. aspera and P. candei are slightly recovered after regulatory measures entered into force, with an increase of mean shell length and dominance of reproductive individuals (> 40 mm). P. aspera populations showed a clearer effect mainly due to the higher exploitation rate relative to P. candei. Conservation measures prompted a positive effect on both exploited limpet species, but further assessment studies are necessary to address the evolution of stocks over time.
- Two sympatric, not externally discernible, and heavily exploited deepwater species with coastal migration during spawning season: implications for sustainable stocks management of Aphanopus carbo and Aphanopus intermedius around MadeiraPublication . Vasconcelos, Joana; Sousa, Ricardo; Henriques, Paulo; Amorim, Antonieta; Delgado, João; Riera, RodrigoSeveral artisanal fisheries target deep species. These stocks are highly sensitive to overfishing because of their slow growth and late maturation. This vulnerability is higher if species concentrate during spawning season in coastal areas, as occur with scabbardfish (Aphanopus spp.). We herein explore if two Aphanopus species (A. carbo and A. intermedius) that coexist show migration patterns to coastal areas during spawning. We analysed specimens of both species throughout 4 years (2014-2017) in a weekly basis and compare morphological parameters to the distance of the coast [coastal (< 12 nm) vs. offshore (> 12 nm)]. Both species showed coastal patterns of migration during the spawning season (October-December), with 65.90% of total specimens of A. carbo and 51.60% of A. intermedius being caught at < 12 nm during this season. Fishing events were also more numerous at < 12 nm to the coast during spawning season (46.6%) relative to non-spawning season (32.6%). A series of management measures, e.g. October 46 December season, were developed to preserve Aphanopus stocks in the NE Atlantic Ocean.
- Disentangling exploitation of the intertidal grazer Phorcus sauciatus (Gastropoda: Trochidae) in an oceanic archipelago: implications for conservationPublication . Sousa, Ricardo; Vasconcelos, Joana; Riera, Rodrigo; Delgado, João; González, José A.; Freitas, Mafalda; Henriques, PauloHarvesting of intertidal grazers such as topshells is known to affect negatively the exploited populations by altering population structure and decreasing abundance. Phorcus sauciatus has a wide geographic distribution in the North‐eastern Atlantic Ocean and is subject to increasing levels of harvesting pressure due to the expansion of human population on coastal areas. The effect of proximity to human settlements and coastal accessibility on the size structure and abundance of P. sauciatus popula‐ tions was examined in Madeira archipelago. Mean size, proportion of reproductive individuals, and abundance of this species were generally smaller in areas closer to human settlements and in more accessible coastal areas. Marine protected areas re‐ turned the highest mean sizes evidencing their effectiveness in preserving the size structure of this species. The results highlight the necessity to regulate the harvest of P. sauciatus in Madeira archipelago, as well as the implementation of management measures aiming at the sustainable exploitation and conservation of this species, ex‐ ploited in this region since the early 15th century.
- Filling biological information gaps of the marine topshell Phorcus sauciatus (Gastropoda: Trochidae) to ensure its sustainable exploitationPublication . Sousa, Ricardo; Vasconcelos, Joana; Delgado, João; Riera, Rodrigo; González, José A.; Freitas, Mafalda; Henriques, PauloTopshells 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 com pared 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 indivi duals 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 mod erately 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.
- Potential impact of harvesting management measures on the reproductive parameters of the limpets Patella aspera and Patella candei from Madeira IslandPublication . Sousa, Ricardo; Vasconcelos, Joana; Riera, Rodrigo; Pinto, Ana Rita; Delgado, João; Henriques, PauloIntertidal and shallow subtidal molluscs are highly sensitive to overharvesting because of their restricted habitat, limited mobility and easy access to humans. Several parameters have been previously used to determine their exploitation status, e.g. sizes, abundances and reproductive stages. Herein the reproductive parameters of two exploited limpets, Patella candei and the protandrous hermaphrodite Patella aspera were examined. Limpets were collected “before” (1996–2006) and “after” (2007–2017) the implementation of management measures aiming to preserve limpet populations in Madeira Island (NE Atlantic Ocean). The proportion of reproductive in dividuals increased approximately 14% after the implementation of management measures for both species. An increase in the size and age at first maturity of both species (from 34.6 to 37.5 mm in P. aspera and from 33.4 to 37.4 mm in P. candei) also occurred after such implementation. “Before” samples of P. aspera showed male biased populations (1.7:1) shifting towards a balanced sex ratio (1:1) after the regulations. No “before” nor “after” sex ratio variations were observed in P. candei populations. Reproductive parameters revealed feasible to determine the efficiency of the implementation of management measures and to detect a slight improvement in reproductive potential of both limpet species.
- Deep stocks avoid competition migrating horizontal and vertically: The example of two scabbardfishes (Aphanopus spp.) targeted by long-liners in grounds next to an oceanic archipelagoPublication . Vasconcelos, Joana; Henriques, Paulo; Sousa, Ricardo; Amorim, Antonieta; Delgado, João; Riera, RodrigoFishing is occurring all over the globe, with an increase trend of exploiting deep stocks. Several species are currently targeted from the deep ocean, and some artisanal fisheries developed fishing gears, e.g. long lines, with limited impact to the environment but scarce information is available on biological aspects of these exploited stocks. In the Macaronesian region and specifically in Madeira archipelago, two Aphanopus sympatric species have been extensively exploited for decades but no detailed information is available on the spatial and vertical distribution of both species (Aphanopus carbo and Aphanopus intermedius). Currently, they represent an important percentage of landings from artisanal fishermen of Madeira (27% of the total catches in 2017). We herein observed that they showed a pattern of depth segregation, where adults of both species are more abundant (ca. 80%) at deeper seafloor (> 2500 m). A. intermedius was more numerous in fishing areas with greater seafloor depth (> 4500 m) compared to A. carbo. This pattern may be explained by a food source overlap between both species, and also the vertical segregation within the same species may be considered as a pattern to avoid cannibalism. Also, migration patterns were found in both species being more pronounced for A. intermedius where > 86% of individuals were collected offshore (> 12 n.m.). The present results constitute a step forward to start developing integrative management actions to preserve stocks of both species in the medium and long term in the study region.