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Research Project
MARE - Marine and Environmental Sciences Centre
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Publications
The use of parasites as biological tags for stock identification of Blue Jack Mackerel, Trachurus picturatus, in the North-eastern Atlantic
Publication . Vasconcelos, Joana; Hermida, Margarida; Saraiva, Aurélia; González, José Antonio; Gordo, Leonel Serrano
The 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.
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 measures
Publication . Sousa, Ricardo; Vasconcelos, Joana; Henriques, Paulo; Pinto, Ana Rita; Delgado, João; Riera, Rodrigo
Intertidal 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.
Stock assessment of the blue jack mackerel, Trachurus picturatus, in the North-eastern Atlantic
Publication . Vasconcelos, Joana; Sousa, Ricardo; Riera, Rodrigo; Delgado, João; Faria, Graça; Serrano Gordo, Leonel
A 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.
Filling biological information gaps of the marine topshell Phorcus sauciatus (Gastropoda: Trochidae) to ensure its sustainable exploitation
Publication . Sousa, Ricardo; Vasconcelos, Joana; Delgado, João; Riera, Rodrigo; González, José A.; Freitas, Mafalda; Henriques, Paulo
Topshells 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.
Deep Sea Chondrichthyes from Madeira and Nearby Seamounts (NE Atlantic)
Publication . Araujo, Teresa Mafalda Gonçalves Jardim de Freitas; Kaufmann, Manfred Josef
Chondrichthyes play a key role in the ecological balance of the ecosystems as predatory
species. However, more than one-third of these species are threatened by overfishing. The
lack of information on chondrichthyan species in the archipelago of Madeira led to this
study, which intended to provide reliable information on their taxonomy, biology,
population dynamics and fisheries. An updated checklist of cartilaginous fishes, new
records, taxonomic annotations, and clarification as well filling the gaps on life history of
several species were accomplished during this thesis. The checklist confirmed the
presence of 67 species of sharks, rays, and chimaeras. Another 14 species previously
referred for the area are now considered dubious records, and 5 species are withdrawn
from the list. Centrophorus uyato is here recorded for the first time from Madeira. Of the
species reported 24 are in the list of threatened species according to the IUCN European
Red List of marine fishes. Hydrolagus affinis and Chimaera opalescens are also first
recorded for the Madeira region, and their known range of distribution are extended. The
clarification and resolution of uncertainties over the identification of Deania calcea and
Deania hystricosa were accomplished through morphological and molecular studies, that
confirm that both are the same species. The knowledge of fish diversity of several
seamounts belonging to Madeira-Tore complex at different depth strata down to 2500 m
was increased, bridging the information gap regarding seamount associated
elasmobranchs. The checklist of cartilaginous fish species for Seine and Unicorn
seamounts confirmed the presence of 17 species in Seine and 11 in Unicorn,
corresponding to about 31% of the valid Chondrichthyes reported for the archipelago of
Madeira. The work herein presented contributed to increase the knowledge of fish
communities, diversity, and occurrence of Chondrichthyes in the archipelago of Madeira.
A reliable overview of Madeira’s elasmobranch fisheries and their evolution, between 1990 and 2020, is also provided. The study on the biology and population dynamics of
Centrophorus squamosus allowed to verify that the pressure of fishing did not cause
critical changes in the life history parameters of the species over 22 years. The
information obtained is essential to obtain the geographic distribution and depth of the
species, as well asto evaluate the fisheries impact on the biology and population dynamics
of this group, aiming to contribute to the development of suitable management strategies
to preserve these species, specifically the populations under pressure by the Madeiran
longline artisanal fishery.
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Funders
Funding agency
Fundação para a Ciência e a Tecnologia
Funding programme
6817 - DCRRNI ID
Funding Award Number
UID/MAR/04292/2013