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- Effects of alterations in fresh water supply on the abundance and distribution of Engraulis encrasicolus in the Guadiana estuary and adjacent coastal areas of south PortugalPublication . Chícharo, Luís; Chicharo, Alexandra; Esteves, E.; Andrade, José Pedro; Morais, P.A reduction of inflow to the Guadiana River on the border between Portugal and Spain may directly contribute to the degradation of fish habitats. Changes are expected to the spawning behaviour of Engraulis encrasicolus adults, to the migration patterns of larvae in the estuary, and to the catches of fisheries in the lower part of the river and adjacent coastal areas. Spawning of E. encrasicolus occurs in the lower part of the estuary and in the adjacent coastal areas. However, high abundances of larvae have been registered in the middle and upper parts of the estuary, the most productive region of the estuary, that with the estuarine turbidity maximum (ETM). In a year of normal inflow, such as the hydrologic year 1987-1988, some retention of larvae occured in this area. However, in an abnormal hydrologic year with a low inflow (1999-2000), and with an increase in freshwater inflow during the spring months, a disturbance to the migration pattern seems to have affected the survival of larvae in the estuary. High river flow, probably associated with an increased input of nutrients, appears to have important und positive effect on adult numbers, because anchovy fishery catches in the adjacent coastal area increased under these conditions.
- Seal and polar bear behavioral response to an icebreaker vessel in northwest GreenlandPublication . Lomac-MacNair, Kate; Andrade, José Pedro; Esteves, EduardoIcebreaker vessels are important scientific tools, enabling access and research within the polar regions of the world, including the High Arctic. These vessels have the potential to overlap with marine mammal habitats in infrequently studied areas. Marine mammal behavioral responses to icebreaker vessel presence and distance at which responses occur are not well documented or understood. During the Petermann 2015 Expedition on the icebreaker Oden, seal and polar bear (Ursus maritimus) data were collected in Petermann Fjord (Northwest Greenland), the adjacent Nares Strait region, and transit to and from Thule, Greenland over 31 days (July 30 to August 30, 2015). We examined behavioral responses from 4 pinniped species: bearded seal (Erignathus barbatus), ringed seal (Pusa hispida), harp seal (Pagophilus groenlandicus), and hooded seal (Crystophora cristata), as well as the polar bear to an icebreaker vessel in a rarely studied region of northwest Greenland. We investigated the rate of flush response, entering the water from a previously hauled out (i.e., resting) location on ice in relation to seal distance to the vessel. Our results showed a significant difference (independent t-test, P <= 0.001) between seal distance to the vessel when a flush response occurred (mean = 467.1 m, SD = 212.39 m) and when no flush response occurred (mean = 1334.0 m, SD = 433.89 m). There were fewer flush responses by seals to the icebreaker at distances >600 m and no flush responses by seals to the icebreaker at distances >800 m. We used a logistic model to describe the relationship between the proportion of seals that flushed and distance from the icebreaker. Results of the logistical model showed the estimated distance at which 50% of the seals flushed to be 709.45 m (SE = 9.24, t = 76.8, P < 0.0001). Three polar bears were recorded during the transit, and a behavioral response (e.g., look, approach, move away) was recorded for all 3 sightings. Our preliminary findings are relevant to assess potential impacts of increasing vessel activity in the High Arctic and to assist in the development of effective monitoring and mitigation strategies.
- Comparison of RNA/DNA ratios obtained with two methods for nucleic acid quantification in gobiid larvaePublication . Esteves, E.; Chicharo, Alexandra; Pina, T.; Coelho, M. L.; Andrade, José PedroIn this paper, RNA and DNA contents and RNA/DNA ratios obtained with two fluorometric methods for the extraction and quantification of nucleic acids in individual estuarine gobiid larvae are compared. A total of 141 gobiid larvae, collected in the Mira and Guadiana estuaries (Portugal), were analysed. This study indicated that the nucleic acids content and RNA/DNA ratios of individual larvae varied with the procedure used. The two methods yielded similar log DNA values but different log RNA and log (RNA/DNA). The differences could be due to a number of factors related to specific steps of tested protocols. Comparison of nucleic acids contents and calibration of the two methods by regression analysis provided a reasonable basis for comparison although differences between estimates were evident.
- Status of the Guadiana estuary (South Portugal) during 1996-1998: an ecohydrological approachPublication . Teodosio, Maria; Chícharo, Luís; Galvão, Helena M.; Barbosa, Ana B.; Marques, M. Helena; Andrade, José Pedro; Esteves, E.; Miguel, Cláudia; Gouveia, IsabelThe aims of this study were to monitor basic hydrological and ecological characteristics of the Guadiana Estuary (1996–1998) before the construction of the Alqueva dam. This work was carried out to determine how environmental factors affect seasonal and tidal variations of plankton populations in the estuary. The available information on the subcatchment of the estuary (e.g., urban, agricultural and forested areas) was integrated into a geographic information system-based software program. Mean monthly river flow varied markedly on a seasonal and yearly basis. River flow near Mértola (ca 50 km upstream from the mouth) reached 3400×106 m3 in winter and decreased to 42×106 m3 in summer. With respect to nutrients, nitrogen to phosphorus ratios indicated some limitation by phosphorus, except at the end of summer, when nitrogen limitation appeared. During this period, cyanobacterial blooms usually occurred in the upper/middle estuary. Estuarine Turbidity Maximum may significantly influence the retention of zooplankton in the estuary. The fish larval life cycle, especially sensitive to environmental alterations, showed high ratios of ribonucleic to desoxyribonucleic acids indicating good physiological condition. It was concluded that an ecohydrological approach, allowing integration of different elements from the cellular to the habitat level into a geographic information system, can contribute to a better understanding of the processes that influence the aquatic biota of the estuary. The approach will be a useful assessment tool for monitoring the estuary following dam completion.
- The distribution of estuarine fish larvae: nutritional condition and co-occurrence with predators and preyPublication . Esteves, E.; Pina, T.; Teodosio, Maria; Andrade, José PedroFish larvae were collected monthly between March and September 1997 in the Mira and Guadiana estuaries (southern Portugal). Hydrological parameters were registered and zooplankton samples were obtained simultaneously. Densities of fish larvae (ind·100 m–3) were calculated from 211 samples and larval nutritional condition measured as RNA/DNA ratios were obtained for 346 individuals, using a fluorimetric method for nucleic acid quantification. Correlating variables were further studied using multiple regression analysis in order to assess the relative importance of abiotic and biotic factors affecting within-year trends in abundance and nutritional condition of estuarine fish larvae. Results indicated that: 1) the abundance of fish larvae seems conditioned by temperature and predation; and 2) their nutritional condition is dependent on temperature and prey availability. Temperature is an important variable structuring estuaries and therefore conditions the behaviour and physiology of fish larvae. Furthermore, the co-occurrence of predators and larvae might be related to similar feeding patterns or comensalism. Whenever feeding conditions are suitable, they usually determine enhanced growth and nutritional condition. However, predation seems to control this latter relationship through its effect on larval mortality.
- Gross and histological observations of ovarian development in twaite shad, Alosa fallax fallax, from Rivers Mira and Guadiana (Portugal)Publication . Esteves, E.; Pina, T.; Andrade, José PedroIn order to describe the stages of oogenesis of twaite shad, Alosa fallax fallax, 265 females were collected between March and June 1997, February and June 1998 and January and April 1999 in the Rivers Mira and Guadiana. From the histological study of ovaries a total of eight developmental stages were delineated. Gross examination of paired ovary revealed that they could be placed into one of seven maturity stages according to their stage of development. Two stages of atresia, alfa and beta,were identified. Upon cessation of spawning, the ovaries still contained some oocytes at various stages of development but with a greater number of atretic oocytes. The simultaneous occurrence of tes at different stages of development in the ovary indicates asynchronous oocyte development. Oocyte size frequency distributions do not show a gap in size between cortical alveoli and vitellogenic oocytes during the spawning season. This may represent the ability of twaite shad to push oocytes through vitellogenesis from a previtellogenic condition during the spawning period. This has important implications for twaite shad fecundity, because fish with this type of oocyte development depend on timates of batch fecundity and spawning frequency to determine potential annual fecundity.