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- Endoparasites of Trachurus picturatus (Pisces: Carangidae) from the Madeira and Canary Islands: selecting parasites for use as tagsPublication . Costa, Graça; Garcia Santamaria, Maria Teresa; Vasconcelos, Joana; Borges Perera, Clara; Moreira, Egberto MeloIn order to evaluate the use of parasites as biological tags to identify populations of the oceanic horse mackerel, Trachurus picturatus, two samples of 100 fish each, caught off the Madeira and Canary Islands from January to June 2009, were examined for the presence of anisakids, trypanorhynchs, acanthocephalans and liver coccidians. In T. picturatus from Madeira, prevalence of the coccidian Goussia cruciata reached 82%, whereas prevalence of the nematode Anisakis sp., the acanthocephalan Rhadinorhynchus cadenati and the trypanorhynch Nybelinia lingualis were 12.0%, 8.9% and 7.0%, respectively. In samples from the Canary Islands, prevalence of G. cruciata was 8.0%, Anisakis sp. and R. cadenati reached 5.0% and 42.0% respectively, and N. lingualis was not recovered. The absence of N. lingualis and the lower prevalence of Anisakis sp. appear to be related to the smaller size of the oceanic horse mackerels examined from the Canary Islands. Although significant differences in prevalence of two parasites, G. cruciata and R. cadenati, were found between the two regions investigated (χ2=125.13, df=1, p=0.000 and χ2=40.77, df=1, p=0.000), only G. cruciata was considered useful as a biological tag for the identification of populations of T. picturatus. In order to reach sound conclusions, an expansion of the temporal and spatial sampling strategy is recommended.
- 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.
- Stock assessment of the blue jack mackerel, Trachurus picturatus, in the North-eastern AtlanticPublication . Vasconcelos, Joana; Sousa, Ricardo; Riera, Rodrigo; Delgado, João; Faria, Graça; Serrano Gordo, LeonelA total of 49,151 blue jack mackerel, Trachurus picturatus, (Bowdich) was collected in Madeira Island (North-eastern Atlantic) between 2002 and 2016 to evaluate pos sible influence of fishing on landings and reproductive parameters. A decreasing trend in the length composition was observed over the study period and length at first maturity decreased by 2.78 cm TL. Maximum yield per recruit decreased from 2002 to 2016 but the corresponding fishing mortality was constant (Fmax = 0.4/ year). Considering the fishing mortality level in 2016, it is evident that the stock may be exploited beyond its sustainability limit. Amendments of the purse-seine fishing regulations and implementation of measures to reduce fishing effort are suggested.
- Identifying populations of the Blue Jack Mackerel (Trachurus picturatus) in the Northeast Atlantic by using geometric morphometrics and otolith shape analysisPublication . Vasconcelos, Joana; Vieira, Ana R.; Sequeira, Vera; González, José A.; Kaufmann, Manfred; Gordo, Leonel SerranoThe population structure of the blue jack mackerel (Trachurus picturatus, Osteichthyes, Carangi dae), in the northeast Atlantic is still unknown. To identify any dis tinct population units, three areas were selected: waters off Madeira, Peniche (mainland Portugal), and the Canary Islands. Knowledge of population structure is an aspect of the population dynamics of a spe cies that is essential to effectively assess the existence of stocks and manage fisheries. In this study, geo metric morphometrics and otolith shape analysis were successfully applied for population identifica tion. Multivariate analysis of vari ance (MANOVA) revealed no body shape differences between males and females in each area studied, and therefore the sexes were com bined for the analysis. The results of the discriminant analysis showed that a low misclassification occurred among areas; 78.0% of individuals were correctly classified. MANOVA performed on the otolith normalized elliptic Fourier descriptors revealed significant areal differences, but no difference between sexes. An overall classification success of 73.3% in the canonical discriminant analysis was achieved. These results indicate the usefulness of both otolith and body shape analysis for differentiation of blue jack mackerel stocks from the northeast Atlantic and indicate the existence of at least three distin guishable populations of this specie
- Age and growth of the pink dentex Dentex gibbosus (Rafinesque, 1810) caught off the Madeira ArchipelagoPublication . Alves, Adriana; Vasconcelos, JoanaA total of 146 otoliths were extracted for age readings from 68 females (23.2-90.1 cm TL), 76 males (22.0-81.3 cm TL) and 2 undetermined (30.3-38.0 cm TL), between April 2004 and December 2007. The maximum age obtained from whole otoliths was 11 years. Differ ences in the growth rhythms were observed between the sexes (females: L∞=134.4, K=0.092 and t0=−0.406; males: L∞=135.9, K=0.078 and t0=−0.894; and all fish were: L∞=149.8, K=0.078 and t0=−0.784). Pink dentex attain 50% of their maximum theoretical length during their fourth year of life. The weight-length relationship (W = q Lfb) were de termined separately for each sex and for all fish: for females q=0.01094 and b=3.033, for males q=0.10002 and b=3.047 and for all, q=0.01027 and b=3.046. According to the F-test, there were no significant differences between the weight-length relations obtained for fe males and males (F-test, F=2.2526, p=0.06646).
- Deep-sea sharks as by-catch of an experimental fishing survey for black scabbardfishes (Aphanopus spp.) off the Canary Islands (NE Atlantic)Publication . Freitas, Mafalda; Costa, Luísa; Delgado, João; Jiménez, Sebastián; Timóteo, Viriato; Vasconcelos, Joana; González, José A.The deep-sea sharks associated as by-catch of the Madeiran midwater drifting longline fishery for scabbardfishes (Aphanopus spp.) were investigated by means of an experimental survey at 800-1200 m depth within the Canary Islands Exclusive Economic Zone, whose fishing grounds have been exploited during the past 15 years. Nine species of chondrich thyans were identified, belonging to five families: Pseudotriakidae, Centrophoridae, Etmopteridae, Somniosidae and Chi maeridae. Data on length, weight and sex ratio for the 436 chondrichthyan individuals caught in the March 2009 survey are given. Several voucher specimens of each species caught were deposited in the collections of the Natural History Museum of Funchal.
- 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.
- The use of parasites as biological tags for stock identification of Blue Jack Mackerel, Trachurus picturatus, in the North-eastern AtlanticPublication . Vasconcelos, Joana; Hermida, Margarida; Saraiva, Aurélia; González, José Antonio; Gordo, Leonel SerranoThe use of parasites as biological tags for discriminating stocks of blue jack mackerel, Trachurus pic turatus (Osteichthyes, Carangidae), in the northeast Atlantic Ocean is assessed herein. In this study the following parasites have been selected as possible biological tags: Anisakis spp. (Nematoda: Anisakidae), Rhadinorhynchus sp. (Acanthocephala: Rhadinorhynchidae), Nybelinia sp. (Cestoda: Tentaculariidae) and Bolbosoma sp. (Acanthocephala: Polymorphidae). Anisakis spp. was the most prevalent parasite taxon found in all localities, attaining higher values in fish from Peniche, mainland Portugal. The occurrence of Rhadinorhynchus sp. in fish from all studied areas was rare (prevalence <10%) but significantly different between localities, with higher values in both archipelagos. Nybelinia sp. specimens were only detected in fish from Madeira and cystacanths ofthe genus Bolbosoma were never detected. The distinctive pattern of infection of these parasite species points to the existence of three stocks of blue jack mackerel in the northeast Atlantic: one in Portuguese mainland waters, one in Madeira archipelago and another in the Canary archipelago. These results support the management strategy which treats the three populations studied as separate stocks.
- 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.