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Physical–biological interactions in the life history of small pelagic fish in the Western Iberia Upwelling Ecosystem.
Get PDFThis paper reviews relevant investigations conducted in the Western Iberia Upwelling Ecosystem (WIUE) on the dynamics of small pelagic fish (SPF), its relationship to climate changes and processes related to the ‘ocean triad’ (enrichment, concentration, transport/retention). In the last decades, a decline in the productivity of several SPF species (e.g., sardine and horse mackerel) was observed in the WIUE, which is partially explained by environmental variability (e.g., changes in coastal upwelling). The main mechanism proposed to explain this decline is the increased frequency and intensity of upwelling events during the spawning season (winter) of these species, which is typically a period when convergence conditions prevail. Thus, this ‘anomalous’ situation promotes egg and larval dispersal away from the favourable coastal habitat (the shelf) and consequently has a negative impact on their survival and recruitment. However, the variability of local features like the Western Iberia Buoyant Plume (WIBP) and the Iberian Poleward Current (IPC) introduce important fluctuations in the transport patterns of the region, and could modulate the impact of these winter upwelling events in the survival of larvae. The retention on the shelf of larval sardine along convergence zones formed by the interaction of these two features plays an important role in their survival. Furthermore, the WIBP is a suitable environment for the growth of phytoplankton and for larval fish survival. From these findings it is clear that simplified Ekman transport models could not explain larval fish transport/retention patterns in this region and more realistic biophysical models should be used to simulate the local oceanographic conditions to understand larval dynamics and the success of recruitment of SPF in the Western Iberia
Interactions between small cetaceans and the purse-seine fishery in western Portuguese waters.
Get PDFMarine mammal interactions with Portuguese purse-seine fisheries operating in four different ports (Figueira da Foz, Sesimbra, Setúbal, Sines) were studied (July-October 2003). Observers accompanied commercial fishing vessels and\ud
monitored 48 fishing trips. An interview survey of skippers was also carried out (n = 36). Three species of marine mammals were observed in 31 sightings during the commercials trips but only the species Delphinus delphis and the category Delphinidae were observed to interact with fishing activities. Small cetaceans were observed to sink, gather or disperse school fishes and damage gear. Mean CPUE and fishing effort values did not change significantly in the presence of dolphins (H = 0.06 and H = 0, both p>0.05). Results from Figueira da Foz indicate that cetaceans are attracted to fishing grounds with a high abundance of their prey-species. Fishermen reported three by-catch events off Figueira da Foz. Compared with other fisheries, purse-seine fishing does not seem to be among the most damaging to marine mammals
Mapas Cognitivos Baseados em Regras Difusas: Modelação do Comportamento dos Pescadores da Frota de Cerco Portuguesa. Mestrado em Matemática Aplicada às Ciências Biológicas.
No full textThe implementation of fishing legislation and regulatory measures has traditionally been based on over-simplistic rules for regulating fishing effort that do not take fully into account the dynamics of fish populations nor those of the fishing feets. This has resulted in biologically and economically defficient advice. A clear understanding of how fishermen will respond to different factors is essential to design management plans that are sustainable in terms of fish resources and fishing activities
Assessment of catch statistics during the land-based whaling in Portugal
No full textWhaling has been known in Portugal since the 12th Century. However, the significant commercial\ud
interest of this activity began in the 19th Century and carried on through the 20th Century on\ud
the mainland and on the archipelagos of the Azores and Madeira. The purpose of this study is to\ud
conduct a global review of Portuguese whaling data and to obtain information on coastal catches of\ud
whales by the Portuguese land-based fleet during the 20th Century. Different periods of whaling can\ud
be discriminated considering the three Portuguese geographical locations but, globally, 89 years of\ud
land-based whaling in Portugal gave a total capture of 29,180 great whales. Captures included sperm,\ud
fin, humpback, sei, right and minke whales. Decline of the land-based whaling industry followed the\ud
decline of species in the exploited grounds
Discards from experimental trammel nets in southern European small-scale fisheries
No full textTrammel net discards in four southern European areas were considerable, with a total of 137 species (79.7% of the total) discarded 65, 105, 46 and 32 species in the Basque country (Spain), Algarve (Portugal), Gulf of Cadiz (Spain) and Cyclades islands (Greece), respectively. The overall discard rate in terms of catch numbers ranged from 15% for the Cyclades to 49% for the Algarve, with the high discard rate for the latter due largely to small pelagic fishes. Discards in the four areas consisted mainly of Trisopterus luscus (Basque country), Scomber japonicus (Algarve), Torpedo torpedo (Cadiz) and Sardina pilchardus (all three areas), and Diplodus annularis in the Cyclades. Strong seasonal variation in discarding was found, reflecting differences in métiers and the versatility of trammel nets as a gear. Discarding, both in terms of numbers of species and individuals decreased with increasing inner panel mesh size. The main reasons for discarding were: (1) species of no or low commercial value (e.g. Scomber japonicus; Torpedo torpedo), (2) commercial species that were damaged or spoiled (e.g. Merluccius merluccius), (3) undersized commercial species (e.g. Lophius piscatorius), and (4) species of commercial value but not caught in sufficient quantities to warrant sale (e.g. Sardina pilchardus). A decrease in soak time together with the appropriate choice of mesh sizes could contribute to a reduction in discarding and to improved sustainability and use of scarce resources in the small-scale, inshore multi-species fisheries of southern Europe
Interactions between small cetaceans and the\ud purse-seine fishery in western Portuguese waters
No full textMarine mammal interactions with Portuguese purse-seine fisheries operating in four different ports (Figueira\ud
da Foz, Sesimbra, Setúbal, Sines) were studied (July-October 2003). Observers accompanied commercial fishing vessels and\ud
monitored 48 fishing trips. An interview survey of skippers was also carried out (n = 36). Three species of marine mammals\ud
were observed in 31 sightings during the commercials trips but only the species Delphinus delphis and the category\ud
Delphinidae were observed to interact with fishing activities. Small cetaceans were observed to sink, gather or disperse\ud
school fishes and damage gear. Mean CPUE and fishing effort values did not change significantly in the presence of dolphins\ud
(H = 0.06 and H = 0, both p>0.05). Results from Figueira da Foz indicate that cetaceans are attracted to fishing grounds\ud
with a high abundance of their prey-species. Fishermen reported three by-catch events off Figueira da Foz. Compared with\ud
other fisheries, purse-seine fishing does not seem to be among the most damaging to marine mammals
Are edge bird populations doomed to extinction?\ud A retrospective analysis of the common guillemot\ud collapse in Iberia
No full textIn the first half of the XXth century, the common guillemot (Uria aalge) was the seabird with\ud
the largest breeding population in Atlantic Iberia (ca. 20,000 individuals), the low-latitude\ud
limit of the species breeding range. However, this population suffered a dramatic decline\ud
and is quasi-extinct at present. The decline was believed to be associated with reduced\ud
availability of pelagic prey fish due to climate change. In this study, we analyzed the population\ud
change of Iberian guillemots in the second half of the XXth century by means of a\ud
retrospective analysis. Our study showed that between 1960 and 1974 the guillemots in Iberia\ud
suffered a dramatic population crash (33.3% annual decline) and that subsequently, the\ud
population continued to decline at a slower annual rate (13.4%). Simulation models indicated\ud
that the factors driving the population crash should be related to adult survival,\ud
rather than reproduction. The analysis of environmental and fishery data suggested good\ud
climate conditions and higher or sustained availability of pelagic prey fish when the Iberian\ud
guillemots crashed. In contrast, relevant human-related factors were affecting adult mortality\ud
in that period, specially a rapid and large increase in the number of synthetic fishing\ud
nets. During the collapse, no conservation measures were undertaken to mitigate anthropogenic\ud
threats and it was assumed, in some extent, that this low-latitude edge population\ud
was somehow prone to extinction as a consequence of climate change. This study highlights\ud
that to carelessly attribute the decline of rear edge populations to climate change\ud
could be highly misleading if the population is suffering from other, particularly human,\ud
threats
Physical oceanography of the western Iberia ecosystem: latest views and challenges.
Get PDFThe present review is focused on the mesoscale physical processes recognized in the Western Iberia Ecosystem, complementing earlier reviews dedicated to larger scales. Recent studies support the idea that the mesoscale processes, superimposed on the larger scale variability, are the major factor controlling the ecosystem functioning in the region. A complex structure of interleaved alongshore slope, shelf and coastal currents that interact with eddies, buoyant plumes, upwelling filaments and fronts, surface layer expressions of the subsurface circulation and internal waves is revealed by the latest research. All of these contribute in different ways to have an effect on the ecosystem. The supposedly less variable winter circulation also exhibits significant mesoscale activity, in the form of eddy shedding from the poleward slope current, intermittent upwelling events and transient nearshore poleward flows. The present incomplete knowledge of this complex system presents a number of challenges and questions that must be addressed if we are to arrive at a satisfactory understanding and predictive capability for the system as a whole
MAPAS COGNITIVOS BASEADOS EM REGRAS DIFUSAS: MODELACAO DO COMPORTAMENTO DOS PESCADORES DA FROTA DE CERCO PORTUGUESA.
No full textCaracterização da pesca com arte de xávega na zona costeira adjacente ao estuário do Tejo. Mestrado em Pescas e Aquacultura.
No full textThe beach seine fishery is carried out along the Portuguese coast by small fishing communities. The fishery is characterised by a non-selective gear, significant bycatch and large amounts of discards. The catches and discards were monitored monthly on the Costa de Caparica, from October and November 2006 and April until September 2007. A total of 72 hauls were analysed, 36 in spring tides and 36 in neap tides. The specimens were identified, weighted and measured and the amounts of retained and discarded fish were determined for each haul. The amounts retained by fishermen, direct sale and sold on the fish resale market were also determined. A total of 49 fish species, 4 mollusc species and 1 crustacean species were identified. Sardina pilchardus (Walbaum, 1792), Scomber japonicus Houttuyn, 1782 and Trachurus trachurus (Linnaeus, 1758), represented 95% of the catches. The discards and juveniles ratio represented 13% and 53% of the total catches, respectively. The discards were mainly species with no or low commercial value and juveniles. Discard levels varied according to species. Catches were influenced by seasons but not by tide cycles. Discards do not varied between seasons. The catches of some species presented variations according to environmental factors. The overall estimate for the annual catches and discards values were 840 tonnes and 106 tonnes, respectively. It was concluded that catches amount are extremely variable and the percentage of discarded fish very high. The amount of discards is sometimes higher than the amount of retained fish, which shows the need for new mitigation measures