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Impact of a winter upwelling event on the distribution and transport of sardine (Sardina pilchardus) eggs and larvae off western Iberia: a retention mechanism.
Get PDFA hydrographic and ichthyoplanktonic survey was conducted on the western Iberia Peninsula shelf-slope, with the objective of assessing the influence of wind-driven flow on the transport and survival of sardine early life history stages. Measurements were taken during a 2-week period of an 'upwelling-favourable' wind event. An offshore displacement of the surface low salinity Western Iberia Buoyant Plume (WIBP) was observed well off the shelf break. Below the plume, the current was southward over the mid- and inner-shelf. Offshore, the flow was poleward in the northern part of the survey area and equatorward in the south. A convergence zone was detected along the outer shelf and upper slope where the buoyant plume was apparently trapped and deepened. In general, eggs and larvae were distributed according to the spreading of the low salinity surface waters, and also within the convergent band. Older larvae were retained within the latter feature. The role of wind forcing on the plume and its interaction with the slope flow were analysed. A mechanism of larvae retention was formulated based on simplified models of the observed shelf-slope circulation
Sardine regime shifts off Portugal: a time series analisys of catches anf wind conditions
No full textGrowth and reproduction of horse mackerel, Trachurus trachurus (carangidae).
Get PDFThere is a broad knowledge of the growth and reproduction of Trachurus trachurus, although important gaps still exist. Horse mackerel are a long-lived species, reaching up to 40 years of age. They have isometric growth, although the alometric parameter b may vary throughout the year and in relation to latitude. Growth to age 3 is rapid compared to slower growth later in life. Phenomena of density dependent growth have been observed in the northeast Atlantic. Horse mackerel are an asynchronous species. The following stages of atresia have been validated in horse mackerel: alpha, beta, and delta. The transition in females from the spawning state to post spawning is very fast. The spawning fraction in horse mackerel is estimated to be between 8.3% and 20.9%. Horse mackerel have a long spawning season (up to 8 months), which varies according to geography. Length at first 28 maturity is between 16 and 25 cm, most commonly around 21 cm. Males mature at a slightly smaller length than females. The age at first maturity for females has been estimated to range from 2 to 4 years, depending on the geography. Batch fecundity has been estimated to range between 172–209 oocytes per gram-female-weight. Female spawning lasts between 65 and 94 days. An individual female can release from 5 to 16 batches during\ud
the spawning period. The estimated potential annual relative fecundity ranges from 1040 to 3280 oocytes per\ud
gram-female-weight
Distribuição, Abundância e Evolução do Manancial de\ud Sardinha Presente na Plataforma Continental Portuguesa entre 1995 e 2002.
No full textA sardinha (Sardina pilchardus, Walb.) é um dos mais importantes recursos pesqueiros portugueses,\ud
tanto em termos económicos como sociais. O IPIMAR realiza regularmente campanhas de rastreio\ud
acústico para a monitorização deste recurso. O resultado destas campanhas é divulgado, sob a forma\ud
de relatório, junto da administração e das associações de produtores. Não existe, no entanto, nenhuma\ud
publicação que permita a consulta e a referência destes relatórios pela comunidade científica, sendo\ud
portanto este o principal objectivo deste trabalho. A presente publicação apresenta os resultados da\ud
série de campanhas acústicas dirigidas a sardinha realizadas entre 1995 e 2002, bem como a evolução\ud
temporal deste recurso durante este período
Quatifying the roles of competing static gears: comparative selectivity og longlines and monofilament gill nets in a multi-species fishery of the Algarve (southern Portugal)
No full textOFFSHORE FORAGING OF MEDITERRANEAN\ud GULLS LARUS MELANOCEPHALUS\ud IN PORTUGAL DURING THE WINTER
No full textMovements and behaviour of Mediterranean Gulls Larus melanocephalus were\ud
observed along the Atlantic coast of central Portugal in December 2001. The\ud
observations suggest that at least part of the Mediterranean Gull population wintering in\ud
central Portugal feeds extensively at sea and possibly during the night. In the morning,\ud
Mediterranean Gulls flew in straight lines towards the coast, where they settled on water\ud
to roost in flocks of several tens of birds. Because there were no gulls near the coast at\ud
sunrise, it is assumed that these arrivals were Mediterranean Gulls that had spent the\ud
night out at sea. With an estimated ‘ground speed’ corrected for wind speed, it was\ud
estimated that the birds could have covered several tens of kilometres offshore between\ud
sunrise and the peak of coastal arrivals. One late afternoon, there were no roosting birds\ud
at the coast, but foraging birds were observed which were apparently successful. The\ud
question is raised whether the foraging activity is solely restricted to the hours around\ud
sunrise and sunset, or whether it is truly nocturnal. Changes in prey availability\ud
resulting from vertical migrations in the water column may have influenced diurnal\ud
patterns in foraging activity of the gulls. Alternatively, the possible utilisation of\ud
discards cannot be ruled out, since night-active purse seine vessels normally discharge\ud
discards early morning. However, outside the breeding season, the Mediterranean Gull\ud
is so far only known to attend trawlers during the day
Estudo Morfométrico das Populações de Biqueirão (Engraulis encrasicholus L.) da Península Ibérica e Golfo da Biscaia. Universidade do Algarve, Faculdade de Ciências do Mar e do Ambiente, Relatório de estágio do curso de Licenciatura em Biologia Marinha e Pescas Faro 2002
No full textCenso das populações de aves marinhas nidificantes no Arquipélago da Berlenga em 2002: Calonectris diomedea, Phalacrocorax aristotelis e Uria aalge
Get PDFO Arquipélago das Berlengas é o local mais importante da costa continental\ud
portuguesa para a nidificação de aves marinhas. Aqui localizam-se as únicas\ud
populações nidificantes em Portugal Continental de Pardela-de-bico-amarelo\ud
Calonectris diomedea e de Airo Uria aalge, bem como o maior núcleo reprodutor de\ud
Corvo-marinho-de-crista Phalacrocorax aristotelis. No ano de 2002 foram estudadas\ud
as populações nidificantes destas espécies. Os efectivos de Pardela-de-bico-amarelo,\ud
comparativamente ao censo realizado em 1999, mostraram-se relativamente estáveis,\ud
tendo sido contabilizados 123 casais em incubação. No entanto, o sucesso reprodutor\ud
foi menor que em anos anteriores, chegando apenas 30 juvenis ao estado de voador. Os\ud
ninhos artificiais instalados desde 1999 apresentaram resultados positivos, registando\ud
uma ocupação crescente relativamente ao total de ninhos ocupados. Relativamente ao\ud
Corvo-marinho-de-crista foram estimados 79-105 casais, valores semelhantes aos\ud
verificados em 1995, ano em que foi efectuado o último censo completo, sugerindo,\ud
aparentemente, estabilidade no efectivo da população reprodutora. No que diz respeito\ud
ao Airo, foram observados apenas 17 e 13 indivíduos, em dois censos efectuados,\ud
tendo sido confirmada a nidificação de um casal apenas. Tendo em conta os dados\ud
obtidos até ao momento, e uma vez que a espécie apresenta um declínio acentuado, a\ud
manterem-se as causas responsáveis pela tendência actual, é provável que se extinga\ud
como reprodutora no nosso país nos próximos anos
Sardine slipping during purse-seining off northern Portugal
No full textObservations aboard purse-seiners demonstrated that deliberate lowering of the net to\ud
allow pelagic fish to escape (‘‘slipping’’) was frequent off northern Portugal during the\ud
second semester of 2001. Some slipping occurred in 25 of 30 trips observed, and the\ud
quantities slipped were significantly higher when the net was set on dense echo-sounder\ud
marks. During the 12 weeks of the study, the sampled fleet (nine vessels) landed 2196 t\ud
and deliberately released an estimated 4979 t (CV 33.6%). More than 95% of the total\ud
catch was sardine. Data provided by the skippers in the absence of shipboard observers\ud
led to considerably lower estimates of slipped quantities. The main reason for slipping\ud
was daily quota limitations, but illegal size and mixture with unmarketable bycatch\ud
were also reported. These results demonstrate the existence and potential magnitude of\ud
slipping, but indications of large seasonal and regional variations make extrapolations\ud
for the entire fishery impractical