Borchers D.L.,University of St. Andrews |
Zucchini W.,University of Gottingen |
Heide-Jorgensen M.P.,Greenland Institute of Natural Resources |
Canadas A.,Alnilam Research and Conservation |
Langrock R.,University of St. Andrews
Biometrics | Year: 2013
We develop estimators for line transect surveys of animals that are stochastically unavailable for detection while within detection range. The detection process is formulated as a hidden Markov model with a binary state-dependent observation model that depends on both perpendicular and forward distances. This provides a parametric method of dealing with availability bias when estimates of availability process parameters are available even if series of availability events themselves are not. We apply the estimators to an aerial and a shipboard survey of whales, and investigate their properties by simulation. They are shown to be more general and more flexible than existing estimators based on parametric models of the availability process. We also find that methods using availability correction factors can be very biased when surveys are not close to being instantaneous, as can estimators that assume temporal independence in availability when there is temporal dependence. © 2013, The International Biometric Society.
Druon J.-N.,European Commission - Joint Research Center Ispra |
Panigada S.,Tethys Research Institute |
David L.,EcoOcean Institute |
Gannier A.,British Petroleum |
And 7 more authors.
Marine Ecology Progress Series | Year: 2012
The development of synoptic tools is required to derive the potential habitat of fin whales Balaenoptera physalus on a large-scale basis in the Mediterranean Sea, as the species has a largely unknown distribution and is at high risk of ship strike. We propose a foraging habitat model for fin whales in the western Mediterranean Sea relying on species ecology for the choice of predictors. The selected environmental variables are direct predictors and resource predictors available at daily and basin scales. Feeding habitat was determined mainly from the simultaneous occurrence of large oceanic fronts of satellite-derived sea-surface chlorophyll content (chl a) and temperature (SST). A specific range of surface chl a content (0.11 to 0.39 mg m-3) and a minimum water depth (92 m) were also identified to be important regional criteria. Daily maps were calibrated and evaluated against independent sets of fin whale sightings (presence data only). Specific chl a fronts represented the main predictor of feeding environment; therefore, derived habitat is a potential, rather than effective, habitat, but is functionally linked to a proxy of its resource (chl a production of fronts). The model performs well, with 80% of the presence data <9.7 km from the predicted potential habitat. The computed monthly, seasonal and annual maps of potential feeding habitat from 2000 to 2010 correlate, for the most part, with current knowledge on fin whale ecology. Overall, fin whale potential habitat occurs frequently during summer in dynamic areas of the general circulation, and is substantially more spread over the basin in winter. However, the results also displayed high year-to-year variations (40 to 50%), which are essential to consider when assessing migration patterns and recommending protection and conservation measures. © Inter-Research 2012.
Dinis A.,Madeira Whale Museum |
Dinis A.,University of Madeira |
Dinis A.,The Interdisciplinary Center |
Alves F.,Madeira Whale Museum |
And 9 more authors.
African Journal of Marine Science | Year: 2016
The bottlenose dolphin Tursiops truncatus is one of the most frequently sighted cetacean species in the Madeira Archipelago (North-East Atlantic); however, little is known about its population ecology in these waters. Photo-identification undertaken during systematic, non-systematic and opportunistic surveys conducted between 2001 and 2012 was used to assess group dynamics, site fidelity, residency and movement patterns of bottlenose dolphins in the archipelago. Three different patterns of residency were assigned, based on individual sighting histories. Group size ranged between 2 and 90 individuals (median 12), with no significant monthly difference in group size. All resident dolphins formed a core, complex network with migrant and transient dolphins. In contrast, satellite clusters were formed exclusively by transient individuals. The lagged identification rate (LIR) model indicated that a dolphin remained in the area for an average of 90 days, whereas the average time an individual spent outside the study area was approximately 313 days. The Madeira Archipelago appears to be only a section of a much larger home range for this population, with the dolphins exhibiting three different patterns of occurrence that associate with each other. The information gained about this poorly studied population contributes to the overall knowledge of bottlenose dolphins in insular oceanic habitats. © 2016 NISC (Pty) Ltd
Wierucka K.,Information and Research on Cetaceans |
Verborgh P.,Information and Research on Cetaceans |
Meade R.,Information and Research on Cetaceans |
Colmant L.,Information and Research on Cetaceans |
And 4 more authors.
Marine Ecology Progress Series | Year: 2014
Long-finned pilot whales Globicephala melas are a commonly encountered species in the Mediterranean Sea. In 2006-2007, an outbreak of the dolphin morbillivirus in the Western Mediterranean resulted in increased mortality of this species. The aim of this study was to determine whether survival rates differed between clusters of Spanish Medi - terranean pilot whales, and how the epizootic in - fluenced these survival rates. Photo-identification surveys were conducted between 1992 and 2009. Association indices were used to define clusters of individuals that associate with each other more frequently than with others. Based on a Cormack-Jolly- Seber survival rate model, apparent survival rate estimates varied from 0.821 to 0.995 over 11 clusters for the 1992-2009 period. When the effect of the morbillivirus outbreak was modeled, 3 clusters with distinctly lower survival rates from previous models presented lower estimates after the outbreak (survival rate dropped from 0.919 [95% CI: 0.854-0.956] to 0.547 [95% CI: 0.185-0.866]), suggesting a negative influence of the epizootic or other unknown additive factors on certain clusters. This information is critical for the conservation of long-finned pilot whales, since they are listed as 'data deficient' in the Mediterranean Sea by the IUCN and as 'vulnerable' in the Spanish National Catalogue of Endangered Species. © Inter-Research 2014.
Esteban R.,Conservation Information and Research on Cetaceans |
Verborgh P.,Conservation Information and Research on Cetaceans |
Gauffier P.,Conservation Information and Research on Cetaceans |
Gimenez J.,Gema Inc |
And 7 more authors.
Journal of the Marine Biological Association of the United Kingdom | Year: 2014
Killer whales have been described in the Gulf of Cadiz, southern Spain, in spring and in the Strait of Gibraltar in summer. A total of 11,276 cetaceans sightings coming from different sources (dedicated research surveys, whale watching companies and opportunistic observations) were used to create two presence-'pseudo-absence' predictive generalized additive models (GAM), where presence data were defined as sightings of killer whales and 'pseudo-absence' data as sightings of other cetacean species. One model was created using spring data when killer whales' main prey, Atlantic bluefin tuna, enter the Mediterranean Sea, and the other model used summer data when Atlantic bluefin tuna return to the Atlantic Ocean. Both model predictions show that killer whales are highly associated with a probable distribution of bluefin tuna during their migration throughout the study area, constraining their distribution to the Gulf of Cadiz in spring and the Strait of Gibraltar in spring and summer. Knowledge of the distribution of killer whales in the study area is essential to establish conservation measures for this population. © 2013 Marine Biological Association of the United Kingdom .