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Diet of common dolphins, Delphinus delphis, off the Portuguese continental coast
No full textDiet of common dolphins off the Portuguese coast was studied based on the examination of stomach contents of 50 stranded and incidentally caught animals. The relative importance of each prey species was assessed through occurrence, numerical and biomass indices. Common dolphins preyed on a large variety of items but four fish and two cephalopod species appeared to form the basis of their diet. Overall, sardine (Sardina pilchardus) was the most important prey, as given by all the indices used to measure prey relative importance. Although common dolphins preyed mostly on pelagic species, they seemed able to explore habitats with distinct features and employ various foraging strategies. A comparison between the diet of dolphins of different sex and size groups was not indicative of major differences. Common dolphins incidentally caught in fishing nets had taken a higher proportion of sardines, the target species of the fishery
Genetic variability and isolation of Cory's shearwater Calonectris diomedea) colonies of the N.E. Atlantic
No full textDNA fingerprinting was used to compare levels of genetic variability within and among eight colonies of Cory’s Shearwater (Calonectris diomedea borealis) in the Madeira, Azores, Canarias, and Berlenga archipelagoes in the Northeast Atlantic. Fingerprint diversity, as measured by one probe and two restriction enzymes, showed very little correlation with population size, suggesting that genetic diversity reflects historical rather than current population sizes. Mean band sharing between pairs of colonies did not show any relation with between-population geographic distance. However, all between-population similarity indexes were lower than the corresponding within-population similarity index, a trend that suggests a small\ud
degree of population structure across the breeding range of this subspecies. Despite banding recordss uggesting high levels of philopatry, gene flow seems sufficient to prevent considerable divergence at these loci. Alternative and equally plausible explanations for the results also are discussed
Patterns of activity and burrow attendance in Cory's Shearwater Calonectris diomedea as revealed by a novel logging technique
No full textWe monitored the attendance and activity of Cory's Shearwater Calonectris diomedea on Berlenga Island, Portugal, during the breeding season. To achieve this, we developed a novel logging technique to record the date and time of entrances and departures from the burrows, as well as the identity of each member of a pair. The technique enabled nonintrusive assessment of the activity of burrow-nesting animals over prolonged periods and provided very reliable information. Our study showed that males attended the nests more frequently than females during the pre-laying and chick-rearing periods. We did not find such differences during the incubation period, and both members spent similar amounts of time incubating the eggs. An index of activity (denned as number of entrances plus exits from the nest) achieved higher scores during the pre-laying and incubation periods, but the activity decreased significantly during the chick-rearing period. We did not find any effect of moonlight on the levels of activity, hour of arrival at the colony or time spent inside the burrows in breeding birds
Nutritional condition and starvation in Sardina pilchardus (L.) larvae off southern Portugal compared with some environmental factors
No full textThe aim of this study was to determine the condition and the incidence of starvation among field-caught Sardina pilchardus larvae, using RNA/DNA ratios and to compare them with various abiotic and biotic factors. S. pilchardus larvae were collected off southern Portugal, during April and May 1992. A highly sensitive fluorometric method for quantifying larvae nucleic acid was applied. Sardine larvae were generally in good condition. The means of the RNA/DNA ratios were relatively high and low percentages of starving larvae (RNA/DNA ratio <1.3) were recorded, ranging from 0 to 12.5%. These two results were associated with high prey availability, which contributes to enhanced condition, and with a high density of potential predators, which may result in fewer larvae in poor condition
Maturation and gill-net selectivity of two small sea breams (genus Diplodus) from the Algarve coast (south Portugal)
No full textiplodus annularis and Diplodus bellottii, two species of small sea breams from the Algarve coast (south Portugal), were studied to obtain information on the spawning period, first maturity, weight–length relationship and gill-net selectivity curves. These species are important in local gill-net catches, and there is no information on their biology and selectivity in the Algarve waters. Spawning lasts for 6 months. Total length (TL) at first maturity for females was 13.4 cm in case of D. annularis and 11.4 cm in case of D. bellottii. The relationships between weight and length were W=0.0132 TL3.096 for D. annularis and W=0.0093 TL3.193 for D. bellottii. The Sechin method was used to estimate gill-net selectivity curves. The estimated selectivity curves correspond closely to the catch curves of the legal mesh size (60 mm), but were narrower for the other meshes. D. annularis and D. bellottii will be caught using the legal mesh size in the following length ranges: 13–19 cm and 11–19 cm
Starvation percentages in field caught Sardina\ud pilchardus larvae off southern Portugal
No full textStarvation has been proposed as a major event only in small larvae that are learning to feed on planktonic\ud
prey. However, there are few comparisons of percentages of starving larvae either among locations, times or phases of larval\ud
development. The percentage of starvation of Sardina pilchardus larvae of different lengths was analysed in four distinct\ud
areas off southern Portugal. A highly sensitive fluorometric method for RNA/DNA quantification was applied to field\ud
caught S. pilchardus larvae during April and May 1992. Using in situ determination of critical RNA/DNA ratio (1.3), we\ud
classified as starving only a small percentage (2.22%) of first-feeding (<8 mm) sardine larvae, but bigger larvae appeared\ud
to be more vulnerable to starvation. We concluded that sardine larvae analysed were generally in good condition (total percentage\ud
of starving larvae - 4.64%), but with some variation within each region
An experimental study of gill net and trammel net\ud 'ghost fishing' off the Algarve (southern Portugal)
No full textFour 100 m lengths of both monofilament gill nets and trammel nets were deployed at\ud
depths between 15 and 18 m off the coast of the Algarve (south of Portugal) between April 1995 and\ud
June 1996. The nets were set on a natural rocky bottom with one end cut loose to simulate lost nets.\ud
Changes in net structure (net height, effective fishing area, movement, colonisation, wear and tear) and\ud
their catches (species, sizes, numbers, and biomass) were monitored by divers. Similar patterns were\ud
observed in all the nets, with a sharp decrease in net height and effective fishmg area, and an increase in\ud
visibility within the first few weeks. Net movement was negligible except in the case of interference\ud
from other fishing gears. Catch rates were initially comparable to normally fished gd.l nets and trammel\ud
nets in this area, but decreased steadily over time. No sea birds, reptiles or mammals were caught in any\ud
of the 8 nets. Catches were dominated by fish (89% by number, at least 27 species), in particular by sea\ud
breams (Sparidae) and wrasscs (Labridae). Under the conditions experienced throughout the study the\ud
fishlng hfetime of a 'lost' net is between 15 and 20 wk. Based on an exponential model, we estimated that\ud
100 m lengths of gill net and trammel net will catch 314 and 221 fish respectively over a 17 wk period.\ud
However, we consider this to be an underestimate due to high rates of predation and scavenging by\ud
octopuses, cuttlefish, moray eels, conger eels, and other fish such as the wrasse Coris julis. When the\ud
nets were surveyed in the following spring. 8 to 11 mo after being deployed, they were found to be\ud
completely destroyed or heavily colonised by algae and had become incorporated into the reef
Beached bird surveys in Portugal 1990-1996
Get PDFBetween 1990 and 1996 a large proportion of the Portuguese coast was systematically surveyed for dead seabirds during the winter (October to March). About 5330 Km of beaches were walked during this period and 2660 dead seabirds were recorded. Razorbill Alca torda was the most common species, followed by Gannet Morus bassanus, Yellow-legged Gull Larus cachinnans and Lesser Black-backed Gull L. fuscus. Together, these species accounted for 73.7% of all corpses found. Most casualties were found in the central area of the Portuguese coast. Beaches in these regions face predominant northwesterly winds and are close to an important upwelling area which represents a potentially good feeding zone for seabirds. Oil contamination of the corpses was generally low, especially when compared with those recorded in similar surveys in some northern European countries. Deaths due to entanglement in fishing gear were significantly lower than those reported in previous surveys and they apparently no longer represent a major threat to seabirds in the Portuguese coast
Fish mouth dimensions and size selectivity in a Portuguese longline fishery
No full textThe relationship between fish total length (TL) and mouth size in six species was investigated in light of the implications for the modelling of size selectivity of hooks. Significant non-linear relationships were found in three species, suggesting that optimal size at capture is not a linear function of hook size. These results strongly support the choices made in modelling skew-normal selectivity with optimal size at capture as a function of hook size