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Abstract: Little is known about the long-finned pilot whale’s population size, structure, distribution and dynamics in the Western Mediterranean basin. The research region covered since 1992 in southeast Spain, at the edge of the Alboran Sea, is considered an important oceanographic transition zone between the Mediterranean and the Atlantic. The research ship Toftevaag carried out surveys covering a total of 10,173 nmi (18,840 km) from April to September each year, 1992-1997, all years pooled. Effort for ten-by-ten-mile quadrats was stratified by depth and sea state to ascertain encounter rates. Tracking of animals was used together with photo-identification in order to analyze home range of groups. Behavior was recorded ad libitum, and underwater video taping was used to analyze specific behavior patterns. One hundred and nine sightings of pilot whales were made. The average group size was 41.4 ± 58.4, ranging from 1 to 350. The average depth at encounters was 848.7 ± 281.2 m. ranging from 300 to 1800 m. Comparison of results on encounter rate and group size with those for other Mediterranean regions, together with site fidelity shown by photo-identification and observations of reproductive behavior, reflect the importance of the Alboran Sea to the species in the Mediterranean.
Guerra, A., González, A. F., Rocha, F.J., Sagarminaga, R. and Cañadas, A. 2002. Planktonic egg masses of the diamond-shaped squid Thysanoteuthis rhombus in the eastern Atlantic and the Mediterranean Sea. Journal of Plankton Research, 24(4): 333-338.
Abstract: Eight planktonic egg masses of the diamond-shaped Thysanoteuthis rhombus observed from 1995 and 2000 are described. Four were found in the western Mediterranean and the remaining ones off the Canary Islands. The egg masses from the Canary Islands are the first records for the eastern Atlantic. All were found near the surface during the end of summer and the beginning of autumn. The planktonic egg masses were dense, resilient oblong cylinder with rounded tips ranging from 80 to 130 cm in length and between 15 and 20 cm in diameter. Egg capsules dimensions ranged from 2.8 to 3.4 mm and total length of the newly hatched paralarvae between 2.5 and 2.8 mm. Each egg mass contained an estimated 24,100 to 43,800 eggs. Some new characters that should help identification of the paralarvae, such as arm formulae, presence of an incipient keel shaped membrane on some arms, and the type and chromatophore pattern are given. Ecological factors influencing the presence and distribution of these egg masses are discussed.
Abstract: The northeastern section of the Alboran Sea is currently under consideration as a Special Area for Conservation under the European Union’s Habitat Directive. Within this framework, the present study focuses on the distribution of cetaceans in this area and is part of the Spanish Ministry of the Environment’s “Program for the Identification of Areas of Special Interest for the Conservation of Cetaceans in the Spanish Mediterranean”. Shipboard visual surveys were conducted in 1992 and from 1995 to 2001 in the north-eastern Alboran Sea, covering 14,409 km. A total of 1,134 sightings of cetaceans were made. From the data collected, the distribution of seven species of odontocete was examined with respect to two physiographic variables, water depth and slope. Analyses of chi-square and fitting of GLMs demonstrated significant differences in distribution for all species, mainly with respect to depth. Kruskal-Wallis tests, factor analysis and discriminant function analysis showed that the species could be classified in two major groups, shallow-waters (short-beaked common dolphin and bottlenose dolphin) and deep-waters (striped dolphin, Risso’s dolphin, long-finned pilot whale, sperm whale and beaked whale) respectively. Preferred habitats in terms of water depth were areas deeper than 600 m for the deep-water group, and the shallower ranges from shore to 400 m for the other. The distribution of cetaceans was further matched with that of their most common prey in order to establish which habitats could be considered important for their feeding. The resulting analysis highlighted two areas in the region as important habitats for the conservation of the most vulnerable species in the Mediterranean, the bottlenose and the common dolphin.
Abstract: The recent decline in the Mediterranean population of Short-beaked Common Dolphins Delphinus delphis has been the subject of scientific controversy and political indifference. Research on these animals has been very limited and there has been no large-scale, systematic effort to assess and monitor their abundance and distribution. The consequent lack of data has prevented a good understanding of historical and ongoing trends. Nonetheless, literature and osteological collections confirm that common Dolphins were widespread and abundant in much of the Mediterranean Sea until the late 1960s and that their decline occurred relatively quickly. Today, Common Dolphins remain relatively abundant only in the westernmost portion of the basin (Alborán Sea), with sparse records off Algeria and Tunisia, concentrations around the Maltese islands and in parts of the Aegean Sea, and relict groups in the southeastern Tyrrhenian and eastern Ionian Seas. Otherwise, these dolphins are rare in, or completely absent from, Mediterranean areas where information is available. Circumstantial evidence and qualitative judgements by the authors suggest that the following factors may have contributed to the decline of Common Dolphins:
• reduced availability of prey caused by overfishing and habitat degradation,
• contamination by xenobiotic chemicals resulting in immunosuppression and reproductive impairment,
• environmental changes such as increased water temperatures affecting ecosystem dynamics, and
• incidental mortality in fishing gear, especially gill nets.
The cumulative importance of these factors is poorly understood, and as a result few conservation measures have been implemented. This paper reviews current knowledge and suggests priorities for action aimed at identifying and mitigating the main threats to Common Dolphins in the Mediterranean, with the ultimate goal of restoring the species’ favourable conservation status in the region.
Abstract: This paper examines the data for common dolphins collected during a general double-platform line transect cetacean survey carried out in waters around the Faroe Islands in 1995 (from southeastern Iceland to western Ireland) in order to determine the extent to which a correction factor can be estimated to account for animals missed on the trackline and for responsive movement towards the vessel. A major assumption of conventional distance-based methods is that all objects at zero distance from the line are detected (i.e. g(0) = 1). If this assumption is violated the estimated density and hence abundance will be negatively biased. It also assumes that animals do not respond to the survey vessel before they are detected by the observers. If the animals are attracted to the vessel, for example, this will result in a positively biassed estimate. The g(0) estimate was obtained using the method of Borchers et al. (1998). Visual inspection of the data suggested that the dolphins were attracted to the vessel and this was accounted for following the Buckland-Turnock (1992) approach. Coefficients of variation (CVs) and confidence intervals (CIs) were estimated using a non-parametric bootstrap procedure. During the survey, almost 1,700n.miles were sailed on primary research effort. There were 153 common dolphin sightings including 52 duplicates. The chosen model for the detection function incorporated perpendicular distance, group size and Beaufort sea state. The resulting estimate of g(0) was 0.7961 (CV=0.14). Density estimates obtained under an assumption of no responsive movement are almost four times higher than when it is taken into account, highlighting the importance of collecting appropriate data to allow analysis of this potential problem in cetacean surveys
Abstract: As part of a project to identify marine protected areas (MPAs) in Spanish Mediterranean waters, habitat preference models were developed using 11 years of survey data to provide predictions of relative density for cetacean species occurring off southern Spain. Models for bottlenose, striped, and short-beaked common dolphin described, firstly, probability of occurrence (using GLMs) and, secondly, group size (using linear models) as predicted by habitat type defined by a range of physical and oceanographic covariates. Models for Risso’s dolphin, long-finned pilot whale, sperm and beaked whales used only the first stage because of data limitations. Model results were used to define the boundaries of three proposed SACs (under the EU Habitats Directive) and one proposed SPAMI (under the Barcelona Convention). The study illustrates the value of habitat preference modelling as a tool to help identify potential MPAs. The analyses incorporate environmental data in a spatial prediction that is an improvement over simpler descriptions of animal occurrence. Contiguous areas covering a specified proportion of relative abundance can readily be defined. Areas with apparently good habitat but few observations can be identified for future research or monitoring programmes. Models can be refitted as new observations and additional environmental data become available, allowing changes in habitat preference to be investigated and monitoring how well MPAs are likely to be affording protection. The study represents an important contribution to the implementation of the Habitats Directive by the Spanish government by providing a robust scientific basis for the definition of SACs and providing results to inform conservation objectives and management plans for these areas. The results identified areas that are important for a number of cetacean species thus illustrating the potential for MPAs to improve cetacean conservation generally in the Alboran Sea, a region of great importance for supporting biodiversity and ecological processes in the wider Mediterranean Sea.
Abstract: The resolution of taxonomic classifications for delphinid cetaceans has been problematic, especially for species in the genera Delphinus, Tursiops and Stenella. The frequent lack of correspondence between morphological and genetic differentiation in these species raises questions about the mechanisms responsible for their evolution. In this study we focus on the genus Delphinus, and use molecular markers to address questions about speciation and the evolution of population structure. Delphinus species have a worldwide distribution and show a high degree of morphological variation. Two distinct morphotypes, long-beaked and short-beaked, have been considered different species named D. capensis and D. delphis, respectively. However, genetic differentiation between these two forms has only been demonstrated in the Pacific. We analysed samples from eight different geographical regions, including two morphologically defined long-beaked form populations, and compared these with the eastern North Pacific populations. We found high differentiation among the populations described as long-beaked instead of the expected monophyly, suggesting that these populations may have evolved from independent events converging on the same morphotype. We observed low genetic differentiation among the short-beaked populations across a large geographical scale. We interpret these phylogeographical patterns in the context of life history and population structure in related species.
Abstract: An EU-funded LIFE project was initiated off southern Spain in 2002, with the objective of developing a Conservation Plan for bottlenose dolphins in the area. Baseline information and monitoring of abundance and distribution is needed to determine if the conservation objectives are met in the long-term. To estimate abundance, 12,568 km of non-systematic line transects conducted from 2000 to 2003, with 72 sightings, were analysed using spatial modelling methods. Transects were divided into 4,575 small segments (average 2.8 km) with similar values for sightability conditions and environmental variables. The point estimate of bottlenose dolphin abundance in the area was 584 dolphins (95% CI = 278–744). The same method was applied to investigate changes in abundance since 1992 in the eastern section of the research area, where most dolphins were concentrated, stratifying by three groups of years. Point estimates were 111 dolphins for 1992-1997, 537 for 1998-2000 and 279 for 2001-2003. The higher abundance between 1998 and 2000 corresponded with the observation of an “immigrant” group of dolphins in these years. These results highlight the importance of long-term studies to understand natural variation in abundance in a specific area subject to conservation activities.
Abstract: Spatial modelling is increasingly being used as an alternative to conventional designbased line transect sampling to estimate cetacean abundance. This new method combines line transect sampling with spatial analysis to predict animal abundance based on the relationship of animals observed to environmental factors. It presents several advantages including: (1) the ability to use data collected from ‘platforms of opportunity’, (2) the ability to estimate abundance for any defined subarea within the study area, and (3) the possibility for increased precision if covariates explain sufficient variability in the data. One study has been conducted to compare spatial modelling with conventional line transect methods, but the use of covariates in the detection function and the inclusion of school size have not previously been investigated. In the present study, the density of striped dolphins Stenella coeruleoalba was estimated in western Mediterranean waters using spatial distance sampling models applying generalised additive models (GAMs). This estimate was compared with density values previously estimated in the same area using conventional line transect methods. The densities estimated were very similar: 0.494 animals km–2 (coefficient of variation, CV = 0.16) using spatial models and 0.489 animals km–2 (CV = 0.19) using conventional line transect methods. Densities were also similar when they were calculated in stratified areas defined during the original line transect study. The precision of the estimates from spatial modelling was higher than that of the estimates obtained from conventional line transect analysis, particularly in the subareas. The results confirm that spatial modelling is a good approach for estimating cetacean abundance.
Abstract: Mediterranean Sea common dolphins have recently been listed as ‘endangered’ in the IUCN Red list, due to their reported decline since the middle of the 20th century. However, little is know about the number or distribution of populations in this region. We analysed 118 samples from the Black Sea, Mediterranean Sea and eastern North Atlantic at nine microsatellite nuclear loci and for 428 bps of the mtDNA control region. We found small but significant population differentiation across the basin between the eastern and the western Mediterranean populations at both nuclear and mtDNA markers (microsatellite FST = 0.052, mtDNA FST = 0.107, P values B 0.001). This matched the differential distribution and habitat use patterns exhibited by this species in the eastern and the western parts of the Mediterranean Sea. The assignment test of a small number of samples from the central Mediterranean could not exclude further population structure in the central area of the basin. No significant genetic differentiation at either marker was observed among the eastern north Atlantic populations, though the Alboran population (inhabiting the Mediterranean waters immediately adjacent the Atlantic ocean) showed significant mtDNA genetic differentiation compared to the Atlantic populations. Directional estimates of gene flow suggested movement of females out of the Mediterranean, which may be relevant to the population decline. Phylogenetic analysis suggested that the observed population structure evolved recently.
Abstract: The Mediterranean sub-population of short-beaked common dolphin is believed to have suffered a steep decline in Mediterranean in recent years and in 2003 it was listed as endangered in the IUCN Red List of Threatened Species. Effective conservation will depend critically on our understanding of the relationship between the species and its habitats. The Alborán Sea, at the gates of the Mediterranean from the Atlantic, is believed to be the most important remaining habitat for this species in the basin and constitutes, therefore, a vital source of information on its ecology that is essential for the development of conservation measures. We used spatial modelling to estimate the abundance and to explore the habitat preferences of common dolphins in this area, examining regional, seasonal and interannual variations, as well as the influence of biological factors such as presence of calves, interspecific relationships and behaviour. From 1992 to 2004, 37,385 km of non-systematic line transects generated 738 sightings in a 19,189 km2 study area. The point estimate of abundance for the whole area was 19,428 (95%CI = 15,277 – 22,804) dolphins; an average density of 1 dolphin per sq km. Seasonal and geographical variations in abundance were detected, with higher average density in summer than in winter, and in the west (the area with a strong Atlantic influence) than in the east (the area with more Mediterranean characteristics). The different results in the Alborán Sea and the Gulf of Vera and their different physical/environmental characteristics suggest that exploration of similarities and differences in environmental features elsewhere in the Mediterranean may help us to understand why common dolphins have declined or redistributed to other unstudied areas. No overall trend in abundance was observed in the area of Alborán between 1992 and 2004, which contrasts with the apparent decline of this species in the rest of the Mediterranean Sea, and with the reported high levels of by-catch in Moroccan drift-nets in the southern Alborán Sea. However, a decline was observed in the eastern portion (Gulf of Vera) with a summer density three-fold lower in 1996-2004 than in 1992-1995. A potential link of this decline with prey depletion due to the exponential growth of aquaculture in the area is discussed. Clear differences in the habitat use were also found when examining the influence of biological factors. In particular, groups with calves and groups feeding preferred more coastal waters. This result could have important implications for the development of conservation measures in the Mediterranean.
Cañadas, A. Donovan, G., Desportes, G. and Borchers, D. En prensa. Distribution of short-beaked common dolphins (Delphinus delphis) in the central and eastern North Atlantic with an abundance estimate for part of this area. NAMMCO.
Abstract: This paper uses data from three programmes: (1) the NASS surveys undertaken throughout much of the central and eastern North Atlantic north of about 40°N in 1987, 1989, 1995 and 2001; (2) the MICA93 programme; and (3) the northeastern Atlantic segment of the SCANS survey in 1994. The data from all surveys were used to examine the distribution of common dolphins in the NE Atlantic. No sightings were made north of 57º. An initial attempt to examine distribution against four potential non-biological explanatory variables was made. A simple interpretation of the preliminary analyses presented here is that the primary areas for groups of common dolphins were in waters over 15°C and depths of 400-1000m (there does appear a link with shelf features), between around 49°-55°N especially between 20°- 30°W. An illustrative example of spatial modelling is presented.
Only for one year (and part of the total survey area) were there sufficient data to attempt to estimate abundance: 1995. The estimated abundance in the W Block of the NASS95 Faroese survey was 273,159 (CV = 0.26; 95% CI = 153,392 – 435,104) short-beaked common dolphins. This estimate is corrected for animals missed on the trackline (g(0)) and for responsive movement.
Abstract: Adapting state–space models (SSMs) to telemetry data has been helpful for dealing with location error and for modeling animal movements. We used a combination of two hierarchical Bayesian SSMs to estimate movement pathways from Argos satellite-tag data for 15 juvenile loggerhead turtles (Caretta caretta) in the western Mediterranean Sea, and to probabilistically assign locations to one of two behavioral movement types and relate those behaviors to environmental features. A Monte Carlo procedure helped propagate location uncertainty from the first SSM into the estimation of behavioral states and environment– behavior relationships in the second SSM. Turtles using oceanic habitats of the Balearic Sea (n ¼ 9 turtles) within the western Mediterranean Sea were more likely to exhibit ‘‘intensive search’’ as might occur during foraging when in deeper waters, but only larger turtles responded to variations in sea-surface height, suggesting they were better able than smaller turtles to cue on environmental features that concentrate prey resources or were more dependent on high-quality feeding areas. These findings stress the importance of individual heterogeneity in the analysis of movement behavior and, taken in concert with other descriptive studies of Pacific loggerheads, suggest that directed movements toward patchy ephemeral resources may be a general property of larger juvenile loggerheads in different populations. We discovered size-based variation in loggerhead distribution and documented use of the western Mediterranean Sea by turtles larger than previously thought to occur there. With one exception, only individuals .57 cm curved carapace length used the most westerly basin in the Mediterranean (western Albora´n Sea). These observations shed new light on loggerhead migration phenology.
