Loading...
2 results
Search Results
Now showing 1 - 2 of 2
- First long‐term study of live observations of loggerhead and leatherback turtles in southern Portugal with relevance for conservationPublication . Castro, Joana; Hughes, Ashley Payne; Cid, André; Patrício, Ana Rita; Laborde, Marina I; L. Matos, FábioMost of the information available on loggerhead turtles (Caretta caretta) andleatherback turtles (Dermochelys coriacea) for the southern coast of Portugal isbased on stranding data, and to a less extent on telemetry data, with very littleinformation derived from sightings of live animals.2. This work reports sightings data of loggerhead and leatherback turtles off thesouth coast of Portugal collected during dedicated surveys on board a researchboat, from 2016 to 2022.3. The sightings data corrected for effort confirm the recurrent presence ofloggerhead turtles in the study area, with a higher sightings rate in May and June.Conversely, leatherback turtles were only sporadically observed in some years.4. This study highlights the importance of the southern waters of Portugal forloggerhead turtles as a recurrent area used by individuals of this species, probablyfrom different origins within the North Atlantic and the Mediterranean, in linewith previous studies.5. The southern coast of Portugal, however, is heavily exploited by fisheries, and themain cause of death among sea turtles is bycatch. The results presented willtherefore help inform future management measures aiming to reduce interactionswith fisheries (e.g., limiting some fishing gears in the months with more sightings).6. Since the study area is probably used by loggerhead turtles from differentRegional Management Units, the impacts of conservation measures imposedlocally may also have beneficial effects at a regional scale.
- The effects of vessel traffic on the behavior patterns of common dolphins in the tagus estuary (Portugal)Publication . Silva, M. M.; Alves Jesus, Nádia; Castro, Joana; Luís, Ana RitaThe impact of vessels on dolphin populations has been extensively studied worldwide. The common dolphin, Delphinus delphis, has been observed in the Tagus estuary for the past two centuries, and during the last several years, these sightings seem to have increased. This area has high levels of maritime traffic throughout the year, both commercial and recreational. To understand the possible effects of vessel traffic on dolphins’ behavior, land-based observations were carried out from March 2022 to March 2023. For a total of 67 events (48.9 h of dolphin sightings), differences in behavioral budgets were noted. Although “neutral reaction” was the most observed response when vessels were in the vicinity of dolphins, “negative reaction” was also common and five times more abundant than “positive reaction”. The GEE model showed statistical differences between these reaction types (positive, neutral, and negative). Markov chains’ analysis revealed distinct patterns in the behavioral transition probabilities, as dolphins were more likely to switch to a traveling state when vessels were nearby. This study is the first step towards understanding a potential impact source in the area since it is expected that tourism companies expand due to the increase in dolphin sightings in the estuary.