Browsing by Author "Ullah, Hadayet"
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- An analysis of the impacts of climatic variability and hydrology on the coastal fisheries, Engraulis encrasicolus and Sepia officinalis, of PortugalPublication . Ullah, Hadayet; Miguel de Sousa Leitão, Francisco; Baptista, Vânia; Chícharo, LuísThe notion that climate change may impact coastal fish production suggests a need to understand how climatic variables may influence fish catches at different time scales. Evidence suggests that the effect of climatic variability and fishing effort on landed catches (as proxy of fish abundance) may vary at the regional scale. This study aims to assess the sensibility of two commercial species with a short life cycle (Engraulis encrasicolus and Sepia officinalis) to climatic and fisheries effects across different regions of the coast of Portugal: northwestern, southwestern and southern Portugal. The effect of environmental explanatory variables, i.e. NAO index, sea surface temperature (SST), upwelling (UPW) index, river discharge, wind magnitude (WmaG), wind direction (Wdir), and fishing variables (fishing effort) on catch rates time series were studied between 1989 and 2009. The sensibility of the species studied to climatic variability differed among regions and were explained by different climatic variables. River discharge had a significant effect on catch rates of the two species, region independently. However, wind driven phenomenon and UPW were the variables that better explained the observed fishing trends across the three regions. Changes in catch rate trends among the studied regions, at a given time, were mostly associated with the reproduction periods of the species. Therefore, regional analyses will significantly contribute to a better understanding of the relationship between climate change and coastal fisheries, aiming to improve integrated coastal zone management.
- Effects of elevated CO2 and nutrients on the community metabolism of a Cymodocea nodosa bedPublication . Khan, Faisal; Alexandre, Ana; Ullah, Hadayet; Santos, RuiWe assessed the combined effects of elevated CO2 and nutrients on the metabolism of a benthic community dominated by the seagrass Cymodocea nodosa (Ucria) Ascherson in a mesocosm experiment. C. nodosa plants and their associated community were exposed to two CO2 levels simulating future (700 ppm, pH 7.84) and current (360 ppm, pH 8.12) conditions, and two nutrient levels (enriched and ambient concentration) in a total of four treatments (-C-N, -C+N, +C-N, +C+N). Net community production (NCP) was estimated from changes in the concentration of dissolved inorganic carbon in the seawater in light incubations using benthic chambers. The variation pattern of NCP with the ordinance was consistent for all treatments. Although differences among treatments were not statistically significant, average NCP values were lowest under CO2 enrichment conditions. NCP was lower at a high CO2 level and ambient nitrogen concentration compared to when nutrient availability was higher, suggesting that the low nutrient availability may modulate the community response to CO2 enrichment. The results obtained suggest that the stimulation of the net community production of C. nodosa by elevated CO2 concentrations may be curtailed by low nutrient availability.
- Establishing relationships between climatic variables and coastal fisheries of PortugalPublication . Ullah, Hadayet; Chícharo, Luís; Leitão, Francisco Miguel de SousaThe notion that climate change may impact coastal fish production suggests a need to understand how climate variables may influence fish catch on a small and large scale. The direct or indirect effects of climate change have been shown to affect catch in productive estuarine and coastal ecosystems. However, the effect of climatic variability and fishing effort on landing catches (as proxy of fish abundance) varied accordingly local and regional scale. Therefore, two studies were conducted. In the first study, an area with similar oceanographic environmental conditions, (Northwestern coast of Portugal) was selected, aiming to analyze the relationships between both climate and fishery variables on catch rates of important commercial and mostly short life cycle species (Alosa alosa, Alosa fallax, Engraulis encrasicolus, Sardina pilchardus, Sepia officinalis and Trachurus trachurus). In addition, particular emphasis was given to explore the effects of freshwater discharge from the three main rivers on the selected species landing trends. Therefore, time series of commercial landings of NW-Atlantic (northwestern Portugal) from 1989 to 2009 were analyzed using min/max autocorrelation factor analysis (MAFA) and dynamic factor analysis (DFA). These techniques were used to explore the relationships between the response variables (annual landings per unit effort) and explanatory variables [NAO index, sea surface temperature (SST), an upwelling (UPW) index, river discharge and fishing effort]. The results of the study confirmed that river discharge was the most important explanatory variables affecting coastal fisheries, followed by SST and UPW. In particular, seasonal river discharge became the explanatory variables that better explain the variability of the two most important small pelagic, Engraulis encrasicolus and Sardina pilchardus. Likewise, results also elucidated that change or reduction in river discharge during spawning event, might become detrimental for other species as well. The key finding of this study is that even within a small area with different rivers regimes and similar oceanographic conditions, the effect of environmental variables might be different on the same species/ population. In the other study, the sensibility of the species to climatic variability and fisheries was evaluated across regions: south, southwestern and northwestern Atlantic coast of Portugal. Similar statistical techniques were used for exploring data information that also includes the period from 1989 to 2009. The sensibility of the species studied to climatic variability differed accordingly the regions. However, results showed that wind and river discharge were the variables that mostly affect fishing trends, independently of different region. Thus, this study will significantly contribute to a better understanding of the relations between climate change and coastal fisheries variability, aspect that need to be considered for the integrated coastal management and development of new policies under the scope of climatic conditions.
- Influence of environmental variables and fishing pressure on bivalve fisheries in an inshore lagoon and adjacent nearshore coastal areaPublication . Vânia, Baptista; Ullah, Hadayet; Teixeira, Célia M.; Range, Pedro; Erzini, Karim; Leitão, FranciscoClimate changes affect marine ecosystems and the survival, growth, reproduction and distribution of species, including those targeted by commercial fisheries. The impact of climate change has been reported for many fish species, but studies focusing on the effects of climate on bivalve resources are lacking. In Portugal, the harvesting of bivalves is an old and artisanal activity, of special importance along the Algarve coast (South of Portugal). This study aims to evaluate the influence of climatic, environmental and fisheries factors on the landings of intertidal coastal lagoon and coastal bivalve species (subtidal nearshore species). The environmental and fisheries parameters considered to affect the landings of bivalves in the eastern Algarve were: fishing effort (number of fishing events), sea surface temperature, North Atlantic Oscillation (NAO) index, upwelling index, wind magnitude and direction and river discharges. Analysis of time series data using min/max autocorrelation factor analysis and dynamic factor analysis showed that, for most species, fishing effort was positively related with landings per unit effort trends in the following year. Lagoon bivalve species (Cerastoderma edule and Ruditapes decussatus) responded to different environmental variables than the coastal bivalve species (Chamelea gallina, Pharus legumen, Donax spp. and Spisula solida). Upwelling index had a significant effect on the lagoon bivalves while the NAO index, wind magnitude and direction, and river discharges only affected the coastal species. This study highlighted the need to adapt fishing effort regimes, while considering the background effects of environmental variability, in order to improve fisheries management.