Repository logo
 
Loading...
Profile Picture

Search Results

Now showing 1 - 10 of 29
  • Swimming abilities of temperate pelagic fish larvae prove that they may control their dispersion in coastal areas
    Publication . Baptista, Vânia; Morais, Pedro; Cruz, Joana; Castanho, Sara; Ribeiro, L.; Pousão-Ferreira, P.; Leitão, Francisco Miguel de Sousa; Wolanski, E.; Teodosio, Maria Alexandra
    The Sense Acuity and Behavioral (SAAB) Hypothesis proposes that the swimming capabilities and sensorial acuity of temperate fish larvae allows them to find and swim towards coastal nursery areas, which are crucial for their recruitment. To gather further evidence to support this theory, it is necessary to understand how horizontal swimming capability varies along fish larvae ontogeny. Therefore, we studied the swimming capability of white seabream Diplodus sargus (Linnaeus, 1758) larvae along ontogeny, and their relationship with physiological condition. Thus, critical swimming speed (U-crit) and the distance swam (km) during endurance tests were determined for fish larvae from 15 to 55 days post-hatching (DPH), and their physiological condition (RNA, DNA and protein contents) was assessed. The critical swimming speed of white seabream larvae increased along ontogeny from 1.1 cm s(-1) (15 DPH) to 23 cm s(-1) (50 and 55 DPH), and the distance swam by larvae in the endurance experiments increased from 0.01 km (15 DPH) to 86.5 km (45 DPH). This finding supports one of the premises of the SAAB hypothesis, which proposes that fish larvae can influence their transport and distribution in coastal areas due to their swimming capabilities. The relationship between larvae's physiological condition and swimming capabilities were not evident in this study. Overall, this study provides critical information for understanding the link between population dynamics and connectivity with the management and conservation of fish stocks.
  • Environmental influence on commercial fishery landings of small pelagic fish in Portugal
    Publication . Teixeira, Célia M.; Gamito, Rita; Miguel de Sousa Leitão, Francisco; Murta, Alberto G.; Cabral, Henrique N.; Erzini, Karim; Costa, Maria José
    Small pelagic fishes are particularly abundant in areas with high environmental variability (zones of coastal upwelling and areas of tidal mixing and river discharge), and because of this, their abundance suffers large inter-annual and inter-decadal fluctuations. In Portugal, the most important species in terms of landings are European sardine, Atlantic horse mackerel and Atlantic chub mackerel. Small pelagic fish landings account for 62.8 % of the total fish biomass and represent 32.7 % of the economical value of all catches. We have investigated trends in landings of these small pelagic fishes and detected the effects of environmental factors in this fishery. In order to explain the variability of landings of small pelagic fishes, we have used official landings (1965-2012) for trawling and purse seine fisheries and applied generalized linear models, using the North Atlantic Oscillation index (NAO) (annual and winter NAO index), sea surface temperature (SST), wind data (strength and North-South and East-West wind components) and rainfall, as explanatory variables. Regression analysis was used to describe the relationship between landings and SST. The models explained between 50.16 and 51.07 % of the variability of the LPUE, with the most important factors being winter NAO index, SST and wind strength. The LPUE of European sardine and Atlantic horse mackerel was negatively correlated with SST, and LPUE of Atlantic chub mackerel was positively correlated with SST. The use of landings of three important species of small pelagic fishes allowed the detection of variations in landings associated with changes in sea water temperature and NAO index.
  • The Influence of environmental factors and fishing pressure on catch rates of diplodus vulgaris
    Publication . Baptista, Vânia; Campos, Carlos J. A.; Leitão, Francisco
    The variability of coastal marine resources has been linked to environmental variability but the impacts of artisanal nearshore fishing activity and environmental factors interact in different ways. Time series, Min/Max Autocorrelation Factor, Generalised Least Squares and Dynamic Factor Analyses models were applied to examine the role of environmental factors (SST, NAO Index, Upwelling Index, Wind Magnitude, Easterly Wind Component, Northerly Wind Component, Coastal River Discharges) and fisheries effort on commercial catch rates of Diplodus vulgaris in the Northwest, Southwest and South Portuguese coast. Environmental factors were found to affect short-term variations of catch rates with a time lag of 2 years, according to the regions and seasons. In the Northwest, autumn wind magnitude and summer river discharges were positively correlated with D. vulgaris catch rates. In the Southwest, D. vulgaris catch rates were negatively associated with variations in winter sea surface temperature. In the South, catch rates were positively associated with yearly westerly wind component and yearly, winter and autumn river discharges whilst negatively associated with the North Atlantic Oscillation (NAO) Index. These results indicate that both large-scale climatic patterns and local hydrological factors can have an influential role in determining the abundance of D. vulgaris stocks. Fishery assessment should therefore incorporate information on ecosystem and environmental effects to help managers to make informed decisions on how to best regulate coastal fisheries.
  • On the presence of the Ponto-Caspian hydrozoan Cordylophora caspia (Pallas, 1771) in an Iberian estuary: highlights on the introduction vectors and invasion routes
    Publication . Seyer, Thomas; Morais, Pedro; Amorim, Katherine; Leitão, Francisco; Martins, Flavio; Teodosio, Maria
    Several non-native invertebrate and vertebrate species have been detected in the Guadiana Estuary (SW-Iberian Peninsula, Europe) during the 21st century. In June 2015, the non-native hydroid Cordylophora caspia (Pallas, 1771) was detected for the first time in this estuary, which motivated an assessment of its distribution during late Spring and Summer 2016. The main goals of this paper were to: i) report the presence of Cordylophora caspia and its distribution in the Guadiana Estuary, ii) record the substrates colonized, salinity, and water temperatures at locations where the species was detected, iii) evaluate possible introduction vectors and invasion routes; and iv) discuss the potential impacts and management options. Cordylophora caspia occupied a 25-km stretch of the estuary with salinities between 0.2 and 13.8 and occupied a variety of human-made substrates. Shipping was the most likely introduction vector of C. caspia, which might have originated from populations in the Atlantic Ocean or the Mediterranean Sea. Currently, the potential ecological impacts are likely low since the population size is small due to an apparent shortage of suitable habitat. Economic effects are minimal at present because there are no major industries along the basin extracting water from the estuary. An integrated ecohydrological approach-i.e. freshets released from dams to control the populations of Cnidaria-was proposed to minimize or mitigate the potential negative effects of this species in the Guadiana Estuary.
  • The Atlantic blue crab Callinectes sapidus Rathbun, 1896 expands its non-native distribution into the Ria Formosa lagoon and the Guadiana estuary (SW-Iberian Peninsula, Europe)
    Publication . Morais, Pedro; Gaspar, Miguel; Garel, Erwan; Baptista, Vânia; Cruz, Joana; Cerveira, Inês; Leitão, Francisco; Teodosio, Maria
    The Atlantic blue crab Callinectes sapidus Rathbun, 1896 is native in the western Atlantic, however it is a non-indigenous species across Europe since 1900, among other world regions. In this paper, we report the first occurrences of this species in the Ria Formosa lagoon and in the Guadiana estuary (SW-Iberian Peninsula, Europe) which occurred in 2016 and July 2017, respectively. We hypothesize that the introduction of this species into these ecosystems might be due to the expansion of the Guadalquivir estuary population through natural processes (larval advection, active movement), or due to unintended introduction events after being transported aboard fishing boats, or, less likely, through ballast water. Changes in Guadiana's river flow after the construction of the Alqueva dam might also explain the presence of another non-indigenous species in the Guadiana estuary. The hypotheses presented, regarding the introduction of the Atlantic blue crab into these ecosystems and of its co-occurrence with other decapod species, are framed in a broader context to serve as a future research framework. The use of the Atlantic blue crab as a new fishing resource is also proposed, namely if it is to be used exclusively by local communities and if no deleterious impacts upon other fisheries and the ecosystem occur from this new fishery.
  • Survival estimates of bycatch individuals discarded from bivalve dredges
    Publication . Miguel de Sousa Leitão, Francisco; Range, Pedro; Gaspar, Miguel
    The fate of released bycatch is an issue of great interest for fisheries research and management. Survival experiments were carried out to assess the survival capacity of animals damaged and discarded during clam dredging operations. Three common bycatch species, two fish (Trachinus vipera; Dicologlossa cuneata) and one crab (Polybius henslowii), were collected during the sorting of catches from a commercial dredging boat. An arbitrary score scale was used to quantify the type and extent of damage to the organisms. Onboard, damaged individuals were placed in tanks containing seawater which were subsequently transferred to the laboratory. Survival experiments were conducted during the subsequent 48h. D. cuneata exhibited the lowest mortality after 48h (54%), followed by P. henslowii (65%) and T. vipera (81%). Despite the magnitude of the percentage mortalities determined, the average number of individuals estimated to die during a 15 minutes tow (standard commercial fishing time) was relatively small: 1.2, 3.24 and 11 for D. cuneata, T. vipera and P. henslowii, respectively. Nevertheless, when these figures are extrapolated to cover all the dredging fleet the impact of this practice on the populations of the species studied can be significant, particulary for D. cuneata.
  • Northerly wind trends along the Portuguese marine coast since 1950
    Publication . Leitão, Francisco; Relvas, Paulo; Canovas, Fernando; Baptista, Vânia; Teodosio, M. A.
    Wind is a marine coastal factor that is little understood but has a strong interaction with biological productivity. In this study, northerly wind trends in three regions of the Portuguese coast (Northwestern: NW, Southwestern: SW, and Southern: S) were analyzed. Two datasets with long-term (ICOADS: 1960-2010) and short-term data (Satellite: 1989-2010) were used to complement one another. The study revealed the northerly wind yearly data to be non-stationary and highly variable between years. Overall, the northerly wind intensity increased throughout the 1960s regardless of the area and dataset. Between 1960 and 2010, the northerly wind increased at a linear rate of 0.24, 0.09, and 0.15ms-1 per decade in the NW, SW, and S coastal regions, respectively. The rate was higher in recent decades (1988-2009), with the wind intensity increasing by 0.4, 0.3, and 0.3ms-1 per decade in the NW, SW, and S regions, respectively. Analyses of the sudden shifts showed significant increases in northerly wind intensities after 2003, 2004, and 1998 in the NW, SW, and S coast, respectively. Exceptions were found for autumn (September for short-term data), when a decrease in northerly winds was observed in recent decades, regardless of the area, and for summer, when no changes in wind trends were recorded in the NW and SW. The long-term data also showed a major increase in northerly winds in winter (January and February), which is the recruitment season for many small and medium-sized pelagic fish. The increase in the intensity of the northerly winds over the past two decades and the past half-century occurred at a higher rate than was estimated by the IPCC for the next century.
  • The role of environmental and fisheries multi-controls in white seabream (Diplodus sargus) artisanal fisheries in Portuguese coast
    Publication . Leitão, Francisco; Baptista, Vania; Teodosio, Maria; Hughes, Samantha Jane; Vieira, Vasco; Chícharo, Luís
    Evaluating the effects of fishing and environmental factors on fish populations are fundamental tenets of fisheries science. In this study, we assess associations between environmental variables (sea surface temperature; North Atlantic Oscillation index; upwelling; wind magnitude; westerly winds; northerly winds; river discharge) and fishing variables (fishing effort) in Diplodus sagus catch rates accounting for regional analyses (northwest coast; southwest coast and Algarve-Algarve south coast). Different time series models for data fitting (multi-model approach) were used. The models were lagged, according to species fishing recruitment age based on the hypothesis that fisheries catches depend on larvae recruitment and survivorship. D. sargus catch rates across areas were unrelated to fishing effort but correlated to environmental variables, with seasonal events explaining much of the variability in trends. On the northwestern coast, the catch rates were mainly set by sea surface temperature (SST) and wind magnitude; however, southwestern coast catch rates were set by NAO winter. On the south coast, only one statistical model (SST, upwelling and westerly winds) associated spring conditions with D. sargus catch rates. The multi-model approach revealed autumn, winter and spring seasonal effects to be related with northwest, southwest and Algarve coastal catch rates, respectively, indicating a possible coastal longitudinal gradient related with given periods of spawning and larval availability. The metadata analysis yielded different results from the regional analyses. In summary, marine resource management should take regional environment characteristics and variability into account when determining sustainable catch rates in given areas for species with high habitat site fidelity.
  • Relative sensitivity of soft-bottom intertidal macrofauna to increased CO2 and experimental stress
    Publication . Range, Pedro; Martins, M.; Cabral, Sara; Piló, David; Ben-Hamadou, Radhouan; Chicharo, Maria Alexandra Teodosio; Miguel de Sousa Leitão, Francisco; Drago, T.; Oliveira, A. P.; Matias, D.; Chícharo, Luís
    We used a controlled CO2 perturbation experiment to test hypotheses about changes in diversity, composition and structure of soft-bottom intertidal macrobenthic assemblages, under realistic and locally relevant scenarios of seawater acidification. Patches of undisturbed sediment were collected from 2 types of intertidal sedimentary habitat in the Ria Formosa coastal lagoon (South Portugal) and exposed to 2 levels of seawater acidification (pH reduced by 0.3 and 0.6 units) and 1 unmanipulated (control) level. After 75 d the assemblages differed significantly between the 2 types of sediment and between field controls and the ex situ treatments, but not among the 3 pH levels tested. The naturally high values of total alkalinity buffered seawater from the changes imposed on carbonate chemistry and may have contributed to offsetting acidification at the local scale. Observed differences on biota were strongly related to the organic matter content and grain-size of the sediments, particularly to the fractions of medium and coarse sand. Soft-bottom intertidal macrofauna was significantly affected by the stress of being held in an artificial environment, but not by CO2-induced seawater acidification. Given the previously observed variations in the sensitivities of marine organisms to seawater acidification, direct extrapolations of the present findings to different regions or other types of assemblages do not seem advisable. However, the contribution of ex situ studies to the assessment of ecosystem-level responses to environmental disturbances could generally be improved by incorporating adequate field controls in the experimental design.
  • Biomass-density data analysis: a comment on Cabaco et al. (2013)
    Publication . Vieira, Vasco M. N. C. S.; Miguel de Sousa Leitão, Francisco; Mateus, Marcos
    Appropriate use of mathematics and statistics is fundamental for sound interpretations of ecological results and to prevent inaccurate conclusions. Throughout the article by Cabaco etal. (2013) emerge cases of biased data analyses including absence of statistical tests, application of unsuited tests, inconsistent geometrical interpretation of xy data scatter, among others. These biases congregated into incorrect conclusions including (i) reporting a generalized nutrient limitation of seagrass meadows, (ii) proposing the intraspecific biomass-density relation of seaweeds as an ecological indicator, when results report little more than randomness, thus suggesting this relation is unsuited as an ecological indicator; (iii) contradicting general ecological theory without any statistical evidence; and (iv) misassociating their results to the ones by other authors.Synthesis. In order to help ecological researchers pinpoint sources of bias, we point out mistakes related to xy data analysis in Cabaco et al. (2013) that can occur in any subject area and flag others specific to biomass-density relations.