Silva Monica A.

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Monica A.

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  • Preprint
    The forgotten whale : a bibliometric analysis and literature review of the North Atlantic sei whale Balaenoptera borealis
    ( 2012-07) Prieto, Rui ; Janiger, David ; Silva, Monica A. ; Waring, Gordon T. ; Goncalves, Joao M. A.
    1. A bibliometric analysis of the literature on the sei whale Balaenoptera borealis is presented. Research output on the species is quantified and compared with research on four other whale species. The results show a significant increase in research for all species except the sei whale. Research output is characterized chronologically and by oceanic basin. 2. The species’ distribution, movements, stock structure, feeding, reproduction, abundance, acoustics, mortality and threats are reviewed for the North Atlantic, and the review is complemented with previously unpublished data. 3. Knowledge on the distribution and movements of the sei whale in the North Atlantic is still mainly derived from whaling records. Movement patterns and winter distribution are not clear. Surveys in some known summering areas show that the species has changed its distribution in parts of its previously known range. 4. With the present information, it is impossible to determine whether or not the North Atlantic sei whale population is subdivided into biological units. Abundance estimates are fragmentary and cover a restricted part of the summering habitat. 5. In the North Atlantic, sei whales seem to be stenophagous, feeding almost exclusively on calanoid copepods and euphausiids. On feeding grounds, they are associated with oceanic frontal systems, but how they find and explore these structures has not been fully investigated. 6. The available data on vital rates are based on whaling-derived studies and are 25 years old or older. Despite increasing human and environmentally induced pressures, there are no current estimates for mortality and population trends. 7. Current research needs include the clear definition of stock units, reliable abundance estimates, studies of distribution and migration that incorporate the identification of wintering areas, acquisition of up-to-date data on reproduction and mortality, and investigations into the consequences of environmental changes for the species.
  • Article
    Multi-state open robust design applied to opportunistic data reveals dynamics of wide-ranging taxa: The sperm whale case.
    (Ecological Society of America, 2019-03-04) Boys, Rebecca M. ; Oliveira, Claudia ; Pérez‐Jorge, Sergi ; Prieto, Rui ; Steiner, Lisa ; Silva, Monica A.
    Capture–mark–recapture methods have been extensively used to estimate abundance, demography, and life history parameters of populations of several taxa. However, the high mobility of many species means that dedicated surveys are logistically complicated and expensive. Use of opportunistic data may be an alternative, if modeling takes into account the inevitable heterogeneity in capture probability from imperfect detection and incomplete sampling, which can produce significant bias in parameter estimates. Here, we compare covariate‐based open Jolly‐Seber models (POPAN) and multi‐state open robust design (MSORD) models to estimate demographic parameters of the sperm whale population summering in the Azores, from photo‐identification data collected opportunistically by whale‐watching operators and researchers. The structure of the MSORD also allows for extra information to be obtained, estimating temporary emigration and improving precision of estimated parameters. Estimates of survival from both POPAN and MSORD were high, constant, and very similar. The POPAN model, which partially accounted for heterogeneity in capture probabilities, estimated an unbiased super‐population of ~1470 whales, with annual abundance showing a positive trend from 351 individuals (95% CI: 234–526) in 2010 to 718 (95% CI: 477–1082) in 2015. In contrast, estimates of abundance from MSORD models that explicitly incorporated imperfect detection due to temporary emigration were less biased, more precise, and showed no trend over years, from 275 individuals (95% CI: 188–404) in 2014 to 367 (95% CI: 248–542) in 2012. The MSORD estimated short residence time and an even‐flow temporary emigration, meaning that the probability of whales emigrating from and immigrating to the area was equal. Our results illustrate how failure to account for transience and temporary emigration can lead to biased estimates and trends in abundance, compromising our ability to detect true population changes. MSORD models should improve inferences of population dynamics, especially when capture probability is low and highly variable, due to wide‐ranging behavior of individuals or to non‐standardized sampling. Therefore, these models should provide less biased estimates and more accurate assessments of uncertainty that can inform management and conservation measures.
  • Article
    Sperm whale codas may encode individuality as well as clan identity
    (Acoustical Society of America, 2016-05-19) Oliveira, Claudia ; Wahlberg, Magnus ; Silva, Monica A. ; Johnson, Mark P. ; Antunes, Ricardo ; Wisniewska, Danuta M. ; Fais, Andrea ; Goncalves, Joao M. A. ; Madsen, Peter T.
    Sperm whales produce codas for communication that can be grouped into different types according to their temporal patterns. Codas have led researchers to propose that sperm whales belong to distinct cultural clans, but it is presently unclear if they also convey individual information. Coda clicks comprise a series of pulses and the delay between pulses is a function of organ size, and therefore body size, and so is one potential source of individual information. Another potential individual-specific parameter could be the inter-click intervals within codas. To test whether these parameters provide reliable individual cues, stereo-hydrophone acoustic tags (Dtags) were attached to five sperm whales of the Azores, recording a total of 802 codas. A discriminant function analysis was used to distinguish 288 5 Regular codas from four of the sperm whales and 183 3 Regular codas from two sperm whales. The results suggest that codas have consistent individual features in their inter-click intervals and inter-pulse intervals which may contribute to individual identification. Additionally, two whales produced different coda types in distinct foraging dive phases. Codas may therefore be used by sperm whales to convey information of identity as well as activity within a social group to a larger extent than previously assumed.
  • Article
    Endo- and ectoparasites of large whales (Cetartiodactyla: Balaenopteridae, Physeteridae) : overcoming difficulties in obtaining appropriate samples by non- and minimally-invasive methods
    (Elsevier, 2015-11-22) Hermosilla, Carlos ; Silva, Liliana M. R. ; Prieto, Rui ; Kleinertz, Sonja ; Taubert, Anja ; Silva, Monica A.
    Baleen and sperm whales, belonging to the Order Cetartiodactyla, are the largest and heaviest existent mammals in the world, collectively known as large whales. Large whales have been subjected to a variety of conservation means, which could be better monitored and managed if physiological and pathophysiological information, such as pathogen infections, could already be gathered from free-swimming animals instead of carcasses. Parasitic diseases are increasingly recognized for their profound influences on individual, population, and even ecosystem health. Furthermore, a number of parasite species have gained importance as opportunistic neozoan infections in the marine environment. Nonetheless, traditional approaches to study parasitic diseases have been impractical for large whales, since there is no current routine method for the capture and handling of these large animals and there is presently no practical method to obtain blood samples remotely from free-ranging whales. Therefore, we here not only intend to review the endo- and ectoparasite fauna of large whales but also to provide new insights in current available methods for gathering parasitological data by using non- or minimally invasive sampling techniques. We focus on methods, which will allow detailed parasitological studies to gain a broader knowledge on parasitoses affecting wild, free-swimming large whale populations.
  • Article
    Sei whale movements and behaviour in the North Atlantic inferred from satellite telemetry
    (Inter-Research, 2014-12-01) Prieto, Rui ; Silva, Monica A. ; Waring, Gordon T. ; Goncalves, Joao M. A.
    The stock structure of the sei whale Balaenoptera borealis in the North Atlantic is unknown, despite years of commercial hunting. New and up-to-date data on distribution and movements are essential for the creation of plausible hypotheses about the stock structure of this species. Between 2008 and 2009 satellite tracks of 8 sei whales were obtained, 7 during spring and 1 in late September. Using a hierarchical switching state-space model we investigated the movements, behaviour and the role of distinct areas in their life history. Two distinct phases corresponding to migratory and foraging movements were identified. A migratory corridor between the Azores and the Labrador Sea is clearly identifiable from the data. Behaviour consistent with foraging was observed frequently in the Labrador Sea, showing that it constitutes an important feeding ground. A link between the Labrador Sea and other feeding grounds to the east is deemed likely. The data also support a discrete feeding ground in the Gulf of Maine and off Nova Scotia. A possible link between the feeding grounds in the Labrador Sea and wintering grounds off northwestern Africa is proposed.
  • Preprint
    Sex bias in biopsy samples collected from free-ranging dolphins
    ( 2009-01-16) Querouil, Sophie ; Freitas, Luis ; Dinis, Ana ; Alves, Filipe ; Cascao, Irma ; Prieto, Rui ; Silva, Monica A. ; Magalhaes, Sara ; Matos, Jose A. ; Santos, Ricardo S.
    Biological samples of free-ranging dolphins are increasingly used to gain information on population structure and ecology. In small cetaceans, the gender of individuals usually cannot be determined at sea, and population sex ratio has to be inferred indirectly. We used molecular sexing to determine the gender of 340 biopsy samples of bottlenose dolphins, Tursiops truncatus, spotted dolphins, Stenella frontalis, and common dolphins, Delphinus delphis, collected around the Azores and Madeira. Sex ratio was globally skewed in favor of males, and differed between species and archipelagos. Skew was probably influenced by the selectivity of biopsy collectors and seasonal or year-round predominance of males in natural populations. Skew was also influenced by sampling duration and intensity. In the Azores, when several samples were successively collected within the same group, the proportion of female samples decreased as a function of sample order. This trend indicated a tendency for females to increasingly avoid the boat while samples were being collected. It showed that males and females reacted differently to the perturbation caused by the biopsy sampling process (i.e. sample collection and driving style).
  • Preprint
    Spatial and temporal distribution of cetaceans in the mid-Atlantic waters around the Azores
    ( 2013-02) Silva, Monica A. ; Prieto, Rui ; Cascao, Irma ; Seabra, Maria I. ; Machete, Miguel ; Baumgartner, Mark F. ; Santos, Ricardo S.
    Cetaceans living in offshore waters are under increasing pressure from anthropogenic activities. Yet, due to the lack of survey effort, relatively little is known about the demography or ecology of these populations. Spatial and temporal distribution of cetaceans in mid-Atlantic waters were investigated using a long term dataset collected from boat surveys and land-based observations around the Azores. From 1999 to 2009, 7307 cetacean schools were sighted during 271717 km of survey effort. In 4944 h of land-based observations, 2968 cetacean groups were detected. Twenty-four species were recorded: seven baleen whales, six beaked whales, eight dolphin species, Physeter macrocephalus, Kogia breviceps and K. sima. Overall, Delphinus delphis was the most frequently sighted species but its encounter rate decreased in June- November, coinciding with presence of Stenella frontalis in the region. Tursiops truncatus, P. macrocephalus and Grampus griseus were frequently encountered yearround, whereas large baleen whales showed a distinct peak in encounter rates in March-May. Mesoplodonts were fairly common and appear to be present throughout the year. These findings fill-in a significant gap in the knowledge of cetaceans occurring in a poorly studied region of the North Atlantic, providing much needed data to inform management initiatives.
  • Article
    Environmental drivers of large-scale movements of baleen whales in the mid-North Atlantic Ocean
    (Wiley Open Access, 2020-03-21) Pérez‐Jorge, Sergi ; Tobeña Morcillo, Marta ; Prieto, Rui ; Vandeperre, Frederic ; Calmettes, Beatriz ; Lehodey, Patrick ; Silva, Monica A.
    Aim Understanding the environmental drivers of movement and habitat use of highly migratory marine species is crucial to implement appropriate management and conservation measures. However, this requires quantitative information on their spatial and temporal presence, which is limited in the high seas. Here, we aimed to gain insights of the essential habitats of three baleen whale species around the mid‐North Atlantic (NA) region, linking their large‐scale movements with information on oceanographic and biological processes. Location Mid‐NA Ocean. Methods We present the first study combining data from 31 satellite tracks of baleen whales (15, 10 and 6 from fin, blue and sei whales, respectively) from March to July (2008–2016) with data on remotely sensed oceanography and mid‐ and lower trophic level biomass derived from the spatial ecosystem and population dynamics model (SEAPODYM). A Bayesian switching state‐space model was applied to obtain regular tracks and correct for location errors, and pseudo‐absences were created through simulated positions using a correlated random walk model. Based on the tracks and pseudo‐absences, we applied generalized additive mixed models (GAMMs) to determine the probability of occurrence and predict monthly distributions. Results This study provides the most detailed research on the spatio‐temporal distribution of baleen whales in the mid‐NA, showing how dynamic biophysical processes determine their habitat preference. Movement patterns were mainly influenced by the interaction of temperature and the lower trophic level biomass; however, this relationship differed substantially among species. Best‐fit models suggest that movements of whales migrating towards more productive areas in northern latitudes were constrained by depth and eddy kinetic energy. Main conclusions These novel insights highlight the importance of integrating telemetry data with spatially explicit prey models to understand which factors shape the movement patterns of highly migratory species across large geographical scales. In addition, our outcomes could contribute to inform management of anthropogenic threats to baleen whales in sparsely surveyed region.
  • Preprint
    Ranging patterns of bottlenose dolphins living in oceanic waters : implications for population structure
    ( 2008-10) Silva, Monica A. ; Prieto, Rui ; Magalhaes, Sara ; Seabra, Maria I. ; Santos, Ricardo S. ; Hammond, Philip S.
    Very little is known about the ecology of common bottlenose dolphins (Tursiops truncatus) living in oceanic waters. This study investigated the ranging and residence pattern, of bottlenose dolphins occurring in the Azores (Portugal), the most isolated archipelago in the North Atlantic. Data were collected during standardized boat-based surveys conducted over a 6-year period in an area of approximately 5,400 km2 (main study area). To investigate the extent of movements of individual animals. non-systematic surveys were also conducted outside this area. Only 44 individuals out of 966 identified were frequently sighted within and between years. The remaining individuals were either temporary migrants from within or outside the archipelago, or transients. Resident dolphins showed strong geographic fidelity to the area. Long-distance movements (of almost 300 km), consistent with foraging or exploratory trips. were observed among non-resident dolphins. Home range size was estimated for 31 individuals sighted ≥ 10 times. Range areas of these dolphins varied in size and location, but considerable overlap was observed in the areas used, suggesting the absence of habitat partitioning between resident and non-resident dolphins. Estimates of home range size of bottlenose dolphins in the Azores were found to be considerably larger than those previously reported for this species. It is hypothesized that dolphins living in the Azores carry out extensive movements and have large home ranges in response to the lower density and patchy distribution of prey compared to other areas. The extensive ranging behaviour and the lack of territoriality provide an opportunity for interbreeding between dolphins associated with different islands, thus preventing genetic differentiation within the population of the Azores.
  • Article
    Temporal patterns in acoustic presence and foraging activity of oceanic dolphins at seamounts in the Azores
    (Nature Research, 2020-02-27) Cascão, Irma ; Lammers, Marc O. ; Prieto, Rui ; Santos, Ricardo S. ; Silva, Monica A.
    Several seamounts have been identified as hotspots of marine life in the Azores, acting as feeding stations for top predators, including cetaceans. Passive acoustic monitoring is an efficient tool to study temporal variations in the occurrence and behaviour of vocalizing cetacean species. We deployed bottom-moored Ecological Acoustic Recorders (EARs) to investigate the temporal patterns in acoustic presence and foraging activity of oceanic dolphins at two seamounts (Condor and Gigante) in the Azores. Data were collected in March–May 2008 and April 2010–February 2011. Dolphins were present year round and nearly every day at both seamounts. Foraging signals (buzzes and bray calls) were recorded in >87% of the days dolphin were present. There was a strong diel pattern in dolphin acoustic occurrence and behaviour, with higher detections of foraging and echolocation vocalizations during the night and of social signals during daylight hours. Acoustic data demonstrate that small dolphins consistently use Condor and Gigante seamounts to forage at night. These results suggest that these seamounts likely are important feeding areas for dolphins. This study contributes to a better understanding of the feeding ecology of oceanic dolphins and provides new insights into the role of seamount habitats for top predators.
  • Preprint
    A review of interactions between cetaceans and fisheries in the Azores
    ( 2010-03) Silva, Monica A. ; Machete, Miguel ; Reis, Dalia ; Santos, Marco ; Prieto, Rui ; Damaso, Carla ; Pereira, Joao Gil ; Santos, Ricardo S.
    1. Interactions between cetaceans and fishing activity in the Archipelago of the Azores were examined using information contained in grey literature and previously unpublished data collected by observer programmes and research projects from 1998 to 2006. Together with a brief description of the economics, gear, fishing effort, and past and ongoing monitoring projects, levels of cetacean bycatch and interference were reported for each major fishery. 2. Cetaceans were present in 7% (n=973) and interfered in 3% (n=452) of the fishing events monitored by observers aboard tuna-fishing vessels. Interference resulted in a significantly higher proportion of events with zero catches but it was also associated with higher tuna catches. 3. There was a decreasing trend in the proportion of tuna-fishing events with cetacean presence or interference throughout this study, as well as a reduction in the estimates of dolphins captured annually by the whole fleet. 4. Observers reported cetacean depredation in 16% of the sets for demersal species and in 2% of the sets for swordfish. Cetacean presence and depredation were associated with higher overall catches and higher catches per unit effort in demersal fisheries. Bottlenose dolphins (Tursiops truncatus) were responsible for most depredation events in demersal fisheries, whereas in the swordfish fishery, depredation was associated with the presence of killer whales (Orcinus orca). There were no reports of cetacean bycatch in these fisheries. There were also no reports of cetaceans interacting in the experimental deep-sea fisheries that were examined. 5. Available data suggests that levels of interaction between cetaceans and Azorean fisheries are generally low and that the economic impact of cetacean interference is probably small. However, for several traditional fisheries there are no accurate data to determine levels of cetacean interaction. We recommend that existing observer programmes be expanded to increase observer coverage of the demersal and swordfish fisheries and allow monitoring of other existing and emerging fisheries.
  • Article
    Predicting interactions between common dolphins and the pole-and-line tuna fishery in the Azores
    (Public Library of Science, 2016-11-16) Cruz, Maria João ; Menezes, Gui ; Machete, Miguel ; Silva, Monica A.
    Common dolphins (Delphinus delphis) are responsible for the large majority of interactions with the pole-and-line tuna fishery in the Azores but the underlying drivers remain poorly understood. In this study we investigate the influence of various environmental and fisheries-related factors in promoting the interaction of common dolphins with this fishery and estimate the resultant catch losses. We analysed 15 years of fishery and cetacean interaction data (1998–2012) collected by observers placed aboard tuna fishing vessels. Dolphins interacted in less than 3% of the fishing events observed during the study period. The probability of dolphin interaction varied significantly between years with no evident trend over time. Generalized additive modeling results suggest that fishing duration, sea surface temperature and prey abundance in the region were the most important factors explaining common dolphin interaction. Dolphin interaction had no impact on the catches of albacore, skipjack and yellowfin tuna but resulted in significantly lower catches of bigeye tuna, with a predicted median annual loss of 13.5% in the number of fish captured. However, impact on bigeye catches varied considerably both by year and fishing area. Our work shows that rates of common dolphin interaction with the pole-and-line tuna fishery in the Azores are low and showed no signs of increase over the study period. Although overall economic impact was low, the interaction may lead to significant losses in some years. These findings emphasize the need for continued monitoring and for further research into the consequences and economic viability of potential mitigation measures.
  • Preprint
    Historic and recent occurrences of pinnipeds in the Archipelago of the Azores
    ( 2009-10-03) Silva, Monica A. ; Brito, Cristina ; Santos, Sara. V. ; Barreiros, Joao Pedro
    The Archipelago of the Azores (Portugal) is located between 37º and 41ºN and 25º and 31ºW and crosses the Mid-Atlantic Ridge. It is the most isolated archipelago in the Atlantic, situated 1600 km west of mainland Portugal and 3500 km from the eastern coast of the United States of America. At present, the only population of seals occurring in the Portuguese territory is found on Desertas Islands, Archipelago of Madeira, where a colony of 24 Mediterranean monk seals, Monachus monachus (Hermann, 1779), still persists (Pires and Neves 2001). Nonetheless, historical accounts reported by Frutuoso (1983) dating from the early to late 1500's mention sightings of "sea wolves" (the old Portuguese folk term for the Mediterranean monk seal) at several sites along the Azorean Island of Santa Maria. Little is known about the occurrence of monk seals in this area over the past five centuries, but the species certainly did not escape deliberate killing by the first settlers. While the early monk seal reports by Frutuoso (1983) are the only ones referring to the presence of colonies of seals in the Azores, more recently several sightings and strandings of vagrant seals of other species have been noted. Here we summarize historical knowledge describing colonies of Mediterranean monk seals in the Azores, review published records of pinnipeds from the 20th century and report new sightings and strandings of seals in the Azores.
  • Preprint
    Macro- and micro-geographic variation of short-beaked common dolphin’s whistles in the Mediterranean Sea and Atlantic Ocean
    ( 2013-09) Papale, Elena B. ; Azzolin, Marta A. ; Cascao, Irma ; Gannier, Alexandre ; Lammers, Marc O. ; Martin, Vidal M. ; Oswald, Julie N. ; Perez-Gil, Monica ; Prieto, Rui ; Silva, Monica A. ; Giacoma, Cristina
    Genetic studies have shown that there are small but significant differences between the short-beaked common dolphin populations in the Atlantic Ocean and those in the Mediterranean Sea. The short-beaked common dolphin is a highly vocal species with a wide sound production repertoire including whistles. Whistles are continuous, narrowband, frequency-modulated signals that can show geographic variation in dolphin species. This study tests whether the differences, highlighted by genetic studies, are recognisable in the acoustic features of short-beaked common dolphin’s whistles in the two adjacent areas of the Atlantic Ocean and the Mediterranean Sea. From a selected sample of good quality whistles (514 recorded in the Atlantic and 193 in the Mediterranean) 10 parameters of duration, frequency and frequency modulation were measured. Comparing data among basins, differences were found for duration and all frequency parameters except for minimum frequency. Modulation parameters showed the highest coefficient of variation. Through discriminant analysis we correctly assigned 75.7% of sounds to their basins. Furthermore, micro-geographic analysis revealed similarity between the sounds recorded around the Azores and the Canary archipelagos and between the Bay of Biscay and the Mediterranean Sea. Results are in agreement with the hypothesis proposed by previous genetic studies that two distinct populations are present, still supposing a gene flow between the basins. This study is the first to compare shortbeaked common dolphin’s whistles of the Atlantic Ocean and the Mediterranean areas.
  • Article
    Baleen whale acoustic presence and behaviour at a Mid-Atlantic migratory habitat, the Azores Archipelago
    (Nature Research, 2020-03-16) Romagosa Verges, Miriam ; Baumgartner, Mark F. ; Cascão, Irma ; Lammers, Marc O. ; Marques, Tiago A. ; Santos, Ricardo S. ; Silva, Monica A.
    The identification of important areas during the annual life cycle of migratory animals, such as baleen whales, is vital for their conservation. In boreal springtime, fin and blue whales feed in the Azores on their way to northern latitudes while sei whales migrate through the archipelago with only occasional feeding. Little is known about their autumn or winter presence or their acoustic behaviour in temperate migratory habitats. This study used a 5-year acoustic data set collected by autonomous recorders in the Azores that were processed and analysed using an automated call detection and classification system. Fin and blue whales were acoustically present in the archipelago from autumn to spring with marked seasonal differences in the use of different call types. Diel patterns of calling activity were only found for fin whales with more calls during the day than night. Sei whales showed a bimodal distribution of acoustic presence in spring and autumn, corresponding to their expected migration patterns. Diel differences in sei whale calling varied with season and location. This work highlights the importance of the Azores as a migratory and wintering habitat for three species of baleen whales and provides novel information on their acoustic behaviour in a mid-Atlantic region.
  • Preprint
    Incorporating information on bottlenose dolphin distribution into marine protected area design
    ( 2011-10-12) Silva, Monica A. ; Prieto, Rui ; Magalhaes, Sara ; Seabra, Maria I. ; Machete, Miguel ; Hammond, Philip S.
    The steady growth of the whale-watching activities in the Azores and its concentration in a small area that partly overlaps the home range of a resident group of bottlenose dolphins (Tursiops truncatus) was one of the driving forces to proposing part of the range of this group as a Marine Protected Area (MPA). We used 6-years of data collected during boat surveys to investigate how dolphins used the candidate MPA (cMPA) and whether they showed any preference for the cMPA over adjacent areas. We also estimated the fraction of the resident individuals and group’s range included in the cMPA and examined whether there were any temporal changes in its use. Mean daily encounter rate of bottlenose dolphins was higher inside than outside the cMPA. Dolphin sightings inside the cMPA were nearly double than what was predicted by the survey effort. Dolphins used the cMPA with similar intensity throughout the years. Resident dolphins were frequently sighted in the cMPA. However, less than 20% of the known range (650 km2) and 41% (39 km2) of the core area of the group lay within the cMPA. The reliability in the use of the cMPA over a 6-year period suggests its importance for the dolphin population remained relatively stable but its surface area was clearly insufficient to satisfy the spatial requirements of the resident group. Based on these findings, we proposed to the Regional Government of the Azores to extend the boundaries of the cMPA. Accordingly, the modified protected area established in 2008 includes 100% of the core area of the resident group of bottlenose dolphins. This study provides an example of how information on cetacean habitat-use patterns may be used to design ecologically meaningful protected areas for this group.
  • Article
    Interspecific hybridization in pilot whales and asymmetric genetic introgression in northern Globicephala melas under the scenario of global warming
    (Public Library of Science, 2016-08-10) Miralles, Laura ; Oremus, Marc ; Silva, Monica A. ; Planes, Serge ; Garcia-Vazquez, Eva
    Pilot whales are two cetacean species (Globicephala melas and G. macrorhynchus) whose distributions are correlated with water temperature and partially overlap in some areas like the North Atlantic Ocean. In the context of global warming, distribution range shifts are expected to occur in species affected by temperature. Consequently, a northward displacement of the tropical pilot whale G. macrorynchus is expected, eventually leading to increased secondary contact areas and opportunities for interspecific hybridization. Here, we describe genetic evidences of recurrent hybridization between pilot whales in northeast Atlantic Ocean. Based on mitochondrial DNA sequences and microsatellite loci, asymmetric introgression of G. macrorhynchus genes into G. melas was observed. For the latter species, a significant correlation was found between historical population growth rate estimates and paleotemperature oscillations. Introgressive hybridization, current temperature increases and lower genetic variation in G. melas suggest that this species could be at risk in its northern range. Under increasing environmental and human-mediated stressors in the North Atlantic Ocean, it seems recommendable to develop a conservation program for G. melas.
  • Article
    Assessing performance of Bayesian state-space models fit to Argos satellite telemetry locations processed with Kalman filtering
    (Public Library of Science, 2014-03-20) Silva, Monica A. ; Jonsen, Ian ; Russell, Deborah J. F. ; Prieto, Rui ; Thompson, Dave ; Baumgartner, Mark F.
    Argos recently implemented a new algorithm to calculate locations of satellite-tracked animals that uses a Kalman filter (KF). The KF algorithm is reported to increase the number and accuracy of estimated positions over the traditional Least Squares (LS) algorithm, with potential advantages to the application of state-space methods to model animal movement data. We tested the performance of two Bayesian state-space models (SSMs) fitted to satellite tracking data processed with KF algorithm. Tracks from 7 harbour seals (Phoca vitulina) tagged with ARGOS satellite transmitters equipped with Fastloc GPS loggers were used to calculate the error of locations estimated from SSMs fitted to KF and LS data, by comparing those to “true” GPS locations. Data on 6 fin whales (Balaenoptera physalus) were used to investigate consistency in movement parameters, location and behavioural states estimated by switching state-space models (SSSM) fitted to data derived from KF and LS methods. The model fit to KF locations improved the accuracy of seal trips by 27% over the LS model. 82% of locations predicted from the KF model and 73% of locations from the LS model were <5 km from the corresponding interpolated GPS position. Uncertainty in KF model estimates (5.6±5.6 km) was nearly half that of LS estimates (11.6±8.4 km). Accuracy of KF and LS modelled locations was sensitive to precision but not to observation frequency or temporal resolution of raw Argos data. On average, 88% of whale locations estimated by KF models fell within the 95% probability ellipse of paired locations from LS models. Precision of KF locations for whales was generally higher. Whales’ behavioural mode inferred by KF models matched the classification from LS models in 94% of the cases. State-space models fit to KF data can improve spatial accuracy of location estimates over LS models and produce equally reliable behavioural estimates.
  • Article
    Estimating common dolphin bycatch in the pole-and-line tuna fishery in the Azores
    (PeerJ, 2018-02-12) Cruz, Maria João ; Machete, Miguel ; Menezes, Gui ; Rogan, Emer ; Silva, Monica A.
    Small-scale artisanal fisheries can have a significant negative impact in cetacean populations. Cetacean bycatch has been documented in the pole-and-line tuna fishery in the Azores with common dolphins being the species more frequently taken. Based on data collected by observers on ∼50% of vessels operating from 1998 to 2012, we investigate the influence of various environmental and fisheries-related factors in common dolphin bycatch and calculate fleet-wide estimates of total bycatch using design-based and model-based methods. Over the 15-year study dolphin bycatch occurred in less than 0.4% of the observed fishing events. Generalized additive modelling results suggest a significant relationship between common dolphin bycatch and duration of fishing events, sea surface temperature and location. Total bycatch calculated from the traditional stratified ratio estimation approach was 196 (95% CI: 186–205), while the negative binomial GAM estimated 262 (95% CI: 249–274) dolphins. Bycatch estimates of common dolphin were similar using statistical approaches suggesting that either of these methods may be used in future bycatch assessments for this fishery. Our work shows that rates of common dolphin bycatch in the pole-and-line tuna fishery in the Azores are low, despite considerable variations between years. Dolphins caught were released alive although the fate of these individuals is unknown. Continued monitoring will provide a better understanding of dolphin bycatch and more accurate estimates essential in the development of potential mitigation measures.
  • Article
    Stable isotopes reveal winter feeding in different habitats in blue, fin and sei whales migrating through the Azores
    (The Royal Society, 2019-08-14) Silva, Monica A. ; Borrell, Asunción ; Prieto, Rui ; Gauffier, Pauline ; Bérubé, Martine ; Palsbøll, Per J. ; Colaço, Ana
    Knowing the migratory movements and behaviour of baleen whales is fundamental to understanding their ecology. We compared δ15N and δ13C values in the skin of blue (Balaenoptera musculus), fin (Balaenoptera physalus) and sei (Balaenoptera borealis) whales sighted in the Azores in spring with the values of potential prey from different regions within the North Atlantic using Bayesian mixing models to investigate their trophic ecology and migration patterns. Fin whale δ15N values were higher than those recorded in blue and sei whales, reflecting feeding at higher trophic levels. Whales' skin δ15N and δ13C values did not reflect prey from high-latitude summer foraging grounds; instead mixing models identified tropical or subtropical regions as the most likely feeding areas for all species during winter and spring. Yet, differences in δ13C values among whale species suggest use of different regions within this range. Blue and sei whales primarily used resources from the Northwest African upwelling and pelagic tropical/subtropical regions, while fin whales fed off Iberia. However, determining feeding habitats from stable isotope values remains difficult. In conclusion, winter feeding appears common among North Atlantic blue, fin and sei whales, and may play a crucial role in determining their winter distribution. A better understanding of winter feeding behaviour is therefore fundamental for the effective conservation of these species.