Browsing by Author "Pereira, Jorge M."
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- Seasonal variation in seabird abundance and bycatch at artisanal bottom-set net fisheries in the southern Iberian Atlantic coastPublication . Pereira, Jorge M.; Ramos, Jaime A.; Almeida, Ana; Marçalo, Ana; Carvalho, Flávia; Fagundes, Isabel; Gonçalves, Jorge Manuel Santos; Frade, Magda; Oliveira, Nuno; Nascimento, Tânia; Paiva, Vitor H.Bycatch is a major cause of seabird mortality, yet most studies focus on industrial fisheries, with limited knowledge on artisanal fisheries. This study investigates the seasonal abundance of seabirds off the southern-eastern coast of mainland Portugal, their attendance at artisanal bottom-set net fisheries, and observed bycatch, using onboard observations and fishermen interviews. From March 2020 to November 2022, 24,643 seabirds were observed attending fishing vessels in 183 daily fishing trips (98.4 % of 186 trips), spanning 20 species across 7 families, with 25 seabirds recorded as bycatch. Lesser black-backed and Yellow-legged gulls (Larus fuscus and Larus michahellis) were the most abundant species, followed by Audouin's gulls (Ichthyaetus audouinii), Great shearwaters (Ardenna gravis), and Northern gannets (Morus bassanus). During summer, the abundance of Yellow-legged and Audouin's gulls (local breeders) and Lesser black-backed gulls (non-breeding species) increased with fishery catch per unit effort. Great shearwaters were more affected by gear type, exhibiting higher attendance and bycatch in trammel nets during autumn. 65 % of Great shearwater bycatch occurred during a single fishing event, probably from fishermen cleaning nets and discarding fish and viscera during net setting. Fishermen interviews identified Northern gannets and Great cormorants (Phalacrocorax carbo) as the most frequently bycaught species, particularly in winter when onboard observations were limited. These findings underscore the impact of artisanal fisheries on seabird populations and highlight the importance of combining onboard data with fishermen interviews to improve bycatch estimates and inform conservation efforts. Our study also suggests that fishermen behaviour during fishery operations significantly influence seabird bycatch.
- The impact of breeding Yellow-Legged Gulls on vegetation cover and plant composition of Grey Dune habitatsPublication . Portela, Diogo; Pereira, Jorge M.; Cerveira, Lara R.; Paiva, Vitor H.; Ramos, Jaime A.The establishment of large populations of yellow-legged gull Larus michahellis in coastal and urban areas can lead to strong changes in vegetation cover and composition through creating physical disturbance in the vegetation and impacting the soil quality through defecation. In this study, we evaluated the effects of breeding yellow-legged gull populations on tall and short vegetation cover and plant species composition in old (occupied for 13 years) and new (occupied for 3 years) colony sites in grey dunes of the Algarve, southern Portugal. In each site, sampling plots were used to measure the percentage of vegetation cover in areas with and without breeding gulls. In the old colony site, the cover by tall vegetation was substantially reduced and the cover by short vegetation substantially increased in the areas where gulls are breeding in comparison with the adjacent areas. In the new colony sites, there were only minor differences. The increase in cover of short vegetation in the breeding area of the old colony site was mostly by nitrophilous species (Paronychia argentea and Malcolmia littorea) and should be explained by the decrease in vegetation cover of tall plant species and by feces deposition. Tall and slow-growing species Suaeda maritima and Helichrysum italicum covers were negatively affected. Our results showed that yellow-legged gulls affected vegetation cover and composition of grey dunes after 3 years of consecutive breeding, and this should be considered in the management of these habitats where breeding yellow-legged gulls are increasing.