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- Tunas off northwest Africa: The epipelagic diet of The Bigeye and Skipjack tunasPublication . Romero, Joana; Catry, Paulo; Hermida, Margarida; Neves, V C; Cavaleiro, Bárbara; Gouveia, Lídia; Granadeiro, José PedroTunas are among the most exploited top predators worldwide, with negative impacts on some of their stocks. Changes in their population abundance can impact marine food-webs and have the potential to alter entire ecosystems. To better understand the impacts of the exploitation of tuna stocks in the most critical habitats, basic knowledge on the diet of these species in each region is required. Here, we describe the diet of the two most fished tuna species in the archipelago of Madeira, the Bigeye tuna Thunnus obesus and the Skipjack tuna Katsuwonus pelamis, based on stomach contents analysis. To gain further insights into the diet, and also better assess the possible bias caused by the occurrence of live bait in stomachs, we compared tuna mercury values with those of two other predators with similar diets that are not directly targeted by fisheries, and with Bigeye and Skipjack tunas from other ocean basins. Bigeye tunas fed mostly on Atlantic chub mackerel Scomber colias and mackerel Trachurus sp., which together contributed with 85% of total prey weight. Only 7.5% of prey weight was constituted by mesopelagic prey, including myctophids and cephalopods. Skipjack tunas had an epipelagic diet (NF = 97%), with the Atlantic chub mackerel representing half of the total prey weight, despite Longspine snipefish Macroramphosus scolopax and Sand smelt Atherina sp. accounting for 62.9% of the total number of prey. There were interannual variations in diet likely linked to interannual pelagic community shifts. Bait did not bias the results of the stomach analysis of these tunas and bait species were observed to be part of the natural diet of both tuna species. Baseline data provided by this study should allow for more informed decisions for an efficient ecosystem-based fisheries management.
- Methods to detect spatial biases in tracking studies caused by differential representativeness of individuals, populations and timePublication . Pujol, Virginia Morera; Catry, Paulo; Magalhães, Maria; Peron, Clara; Reyes‐González, José Manuel; Granadeiro, José P.; Militão, Teresa; Dias, Maria P.; Oro, Daniel; Dell'Omo, Giacomo; Müller, Martina; Paiva, Vitor H.; Metzger, Benjamin; Neves, V C; Navarro, Joan; Karris, Georgios; Xirouchakis, Stavros; Cecere, Jacopo G.; Zamora‐López, Antonio; Forero, Manuel G.; Ouni, Ridha; Romdhane, Mohamed Salah; De Felipe, Fernanda; Zajková, Zuzana; Cruz‐Flores, Marta; Grémillet, David; González‐Solís, Jacob; Ramos, RaülAim Over the last decades, the study of movement through tracking data has grown exceeding the expectations of movement ecologists. This has posed new challenges, specifically when using individual tracking data to infer higher-level distributions (e.g. population and species). Sources of variability such as individual site fidelity (ISF), environmental stochasticity over time, and space-use variability across species ranges must be considered, and their effects identified and corrected, to produce accurate estimates of spatial distribution using tracking data. Innovation We developed R functions to detect the effect of these sources of variability in the distribution of animal groups when inferred from individual tracking data. These procedures can be adapted for their use in most tracking datasets and tracking techniques. We demonstrated our procedures with simulated datasets and showed their applicability on a real-world dataset containing 1346 year-round migratory trips from 805 individuals of three closely related seabird species breeding in 34 colonies in the Mediterranean Sea and the Atlantic Ocean, spanning 10 years. We detected an effect of ISF in one of the colonies, but no effect of the environmental stochasticity on the distribution of birds for any of the species. We also identified among-colony variability in nonbreeding space use for one species, with significant effects of population size and longitude. Main conclusions This work provides a useful, much-needed tool for researchers using animal tracking data to model species distributions or establish conservation measures. This methodology may be applied in studies using individual tracking data to accurately infer the distribution of a population or species and support the delineation of important areas for conservation based on tracking data. This step, designed to precede any analysis, has become increasingly relevant with the proliferation of studies using large tracking datasets that has accompanied the globalization process in science driving collaborations and tracking data sharing initiatives.
- Migratory Connectivity and Non‐Breeding Habitat Segregation Across Biogeographical Scales in Closely Related Seabird TaxaPublication . Morera‐Pujol, Virginia; Catry, Paulo; Magalhães, Maria; Péron, Clara; Reyes‐González, José Manuel; Granadeiro, José Pedro; Militão, Teresa; Dias, Maria P.; Oro, Daniel; Igual, José Manuel; Dell'Omo, Giacomo; Müller, Martina; Paiva, Vitor H.; Metzger, Benjamin; Neves, Verónica; Navarro, Joan; Karris, Georgios; Xirouchakis, Stavros; Cecere, Jacopo G.; Zamora‐Marín, José Manuel; Forero, Manuela G.; Afán, Isabel; Ouni, Ridha; Romdhane, Mohamed Salah; Felipe, Fernanda De; Zajková, Zuzana; Cruz‐Flores, Marta; Grémillet, David; González‐Solís, Jacob; Ramos, RaülIn highly mobile species, Migratory Connectivity (MC) has relevant consequences in population dynamics, genetic mixing, conservation and management. Additionally, in colonially breeding species, the maintenance of the breeding geographical structure during the non‐breeding period, that is, a strong MC, can promote isolation and population divergence, which ultimately can affect the process of lineage sorting. In geographically structured populations, studying the MC and differences in environmental preferences among colonies, populations, or taxa can improve our understanding of the ecological divergence among them.We investigated the MC and non‐breeding ecological niche of three seabird taxa from the genus colonies, we assess the level (from taxa to colony) at which MC and non‐breeding spatial and environmental segregation emerge. At a taxon level, we found a clear difference in the non‐breeding distributions between Cory's. and Scopoli's shearwaters, and a clear ecological divergence between Cory's and Cape Verde shearwaters. At an intermediate aggregation level, we found that birds breeding in proximity had similar non‐breeding habitat preferences, while birds breeding in very distant colonies (and therefore classified in different populations) had different non‐breeding habitat preferences. Furthermore, within each taxon, we found more structure (i.e. stronger MC) and non‐breeding divergence at an intermediate aggregation level than at the colony scale, where MC was weak. Main Conclusions These results suggest that conspecifics from nearby colonies mix in common non‐breeding areas, but not with birds from more distant colonies or different taxa. These results support the need for management and conservation strategies that take into account this structure when dealing with migratory species with high connectivity.