Sighting of Stenella attenuata, the spotted dolphin, in Culebra Bay, Costa Rica, 1999-2000

Parallel to a zooplankton study (1999-2000) observations were made (from an inflatable boat), on the presence of dolphins along a transect (-8 km long) on the axis of Culebra Bay (24 km2), Gulf of Papagayo, Pacific coast of Costa Rica. Dolphins were found during 20 of the 31 boat surveys conducted. The only species of cetacean found in the bay was Stenella attenuata, the spotted dolphin. These sightings were more frequent during the rainy season, particularly during the month of May of both years. The presence of S. attenuata in Culebra Bay might be associated to the abundances of fish and mollusks (their presumed prey: for example, squids), as evidenced by fishery statistics available for this zone of the Pacific coast of Costa Rica.     

Morphometry and sexual dimorphism of the coastal spotted dolphin, Stenella attenuata graffmani, from Bahía de Banderas, Mexico

External measurements and size differences between the sexes were examined in the coastal spotted dolphin, Stenella attenuata graffmani , in Bahía de Banderas, on the Mexican Pacific coast. The dolphins were collected by local fishermen and 29 external characteristics were measured by members of the Marine Mammals Laboratory, University of Mexico. The length of each characteristic with respect to total length was analysed through adjustment of the data to a power equation. A stepwise discriminant analysis was applied to the absolute values and to those expressed as proportions to analyse the differences between the sexes. Results indicate that growth in these dolphins is generally negatively allometric, and most of the characteristics measured were, in both absolute and proportional terms, greater in male dolphins than in female dolphins. As found in many species of odontocetes, the discriminant analysis showed that the main differences between the sexes for this coastal subspecies include the relative positions of the umbilicus, the genital aperture and the anus. The morphometric data provided by this study, corresponding to 29 specimens of S. a. graffmani collected in a restricted locality of the Mexican Pacific coast, are particularly interesting to studies documenting latitudinal morphological differences in the coastal spotted dolphin.     

Isolation and genetic characterization of Toxoplasma gondii from striped dolphin (Stenella coeruleoalba) from Costa Rica

Toxoplasma gondii infection in marine mammals is of interest because of mortality and mode of transmission. It has been suggested that marine mammals become infected with T. gondii oocysts washed from land to the sea. We report the isolation and genetic characterization of viable T. gondii from a striped dolphin (Stenella coeruleoalba), the first time from this host. An adult female dolphin was found stranded on the Pacific Coast of Costa Rica, and the animal died the next day. The dolphin had a high (1:6400) antibody titer to T. gondii in the modified agglutination test. Severe nonsuppurative meningoencephalomyelitis was found in its brain and spinal cord, but T. gondii was not found in histological sections of the dolphin. Portions of its brain and the heart were bioassayed in mice for the isolation of T. gondii. Viable T. gondii was isolated from the brain, but not from the heart, of the dolphin. A cat fed mice infected with the dolphin isolate (designated TgSdCol) shed oocysts. Genomic DNA from tachyzoites of this isolate was used for genotyping at 10 genetic loci, including SAG1, SAG2, SAG3, BTUB, GRA6, c22-8, c29-2, L358, PK1, and Apico, and this TgSdCo1 isolate was found to be Type II.     

Complete amino acid sequence of the myoglobin from the Pacific spotted dolphin, Stenella attenuata graffmani.

The complete amino acid sequence of the major component myoglobin from the Pacific spotted dolphin, Stenella attenuata graffmani, was determined by the automated Edman degradation of several large peptides obtained by specific cleavage of the protein. The acetimidated apomyoglobin was selectively cleaved at its two methionyl residues with cyanogen bromide and at its three arginyl residues by trypsin. By subjecting four of these peptides and the apomyoglobin to automated Edman degradation, over 80% of the primary structure of the protein was obtained. The remainder of the covalent structure was determined by the sequence analysis of peptides that resulted from further digestion of the central cyanogen bromide fragment. This fragment was cleaved at its glutamyl residues with staphylococcal protease and its lysyl residues with trypsin. The action of trypsin was restricted to the lysyl residues by chemical modification of the single arginyl residue of the fragment with 1,2-cyclohexanedione. The primary structure of this myoglobin proved to be identical with that from the Atlantic bottlenosed dolphin and Pacific common dolphin but differs from the myoglobins of the killer whale and pilot whale at two positions. The above sequence identities and differences reflect the close taxonomic relationship of these five species of Cetacea.     

Differences in oscillatory whistles produced by spinner (Stenella longirostris) and pantropical spotted (Stenella attenuata) dolphins

Acoustic recordings of two closely related species, spinner dolphin (Stenella longirostris) and pantropical spotted dolphin (Stenella attenuata), were investigated from four different geographic locations: two in the Central Tropical Pacific, one in the Eastern Tropical Pacific and one in the Indian Ocean. The two delphinid species occur in tropical and warm temperate waters, with overlapping ranges. They produce very similar vocalizations, but at the same time their calls exhibit a certain degree of intraspecific variation among different geographic locations as has been observed in other delphinid species. Oscillatory whistles (whistles with at least two oscillations in their frequency contours) were identified and manually extracted from the recordings. Whistles with four or more maxima (oscillations) occurred only in spinner dolphins and they were present in all geographic regions investigated. In addition, the oscillatory whistles with two and three maxima were significantly more frequent in spinner than in spotted dolphins. The differences in oscillatory whistles for these two species seem to be consistent across study areas and therefore, could be used in addition to other whistle features to help distinguish between them.     

Postural instability and akinesia in a pantropical spotted dolphin,Stenella attenuata,in proximity to operating airguns of a geophysical seismic vessel

Aberrant behaviour including erratic locomotion was observed in a pantropical spotted dolphin 600 m ahead of an airgun array during 3D seismic explorations off Liberia in March 2009. The dolphin, presumably in acoustic distress, lifted its head and cervical region above the surface in an oblique, strikingly rigid posture during 5 min. Turbulent white-water evidenced a major propulsory thrust. Incremental postural instability and apparent exhaustion progressed to a catatonic-like state of akinesia as the dolphin rolled over onto one side, then its back before sinking virtually motionless close to the airgun array. Unless it recovered full locomotory control, asphyxiation was inevitable. Potential internal injury is discussed, both acoustic-mediated and from extreme exertion (exertional myopathy, rhabdomyolysis and myoglobinuric nephrosis). As behaviour was spatially and temporally closely associated with firing seismic airguns, we suggest a cause–effect relationship. Differential diagnoses of pre-existing morbidity, senescence, or intoxication are considered possible but unlikely.     

Seawater temperature measured at the surface and at two depths (7 and 12 m) in one coral reef at Culebra Bay, Gulf of Papagayo, Costa Rica

Superficial seawater temperature (SST) and at two depths (7 and 12 m) were measured non-continuously during the study of the corals and coral reefs of Culebra Bay (1993-1996). SST showed seasonal variations of approximately 4 degrees C. The highest average temperatures (27.0 +/- 0.1, range 23-29 degrees C) were during the rainy season from May to November and the lowest (22.9 +/- 0.3 degrees C, 15.5-29 degrees C) during the dry season from December to April. Cold fronts with 2-3 degrees C differences in SST frequently pass into the bay and remain there for several hours according to the tidal cycles. Differences of approximately 3 degrees C between SST and the bottom (5-10 m depth) were usually found, particularly at locations where bottom topography and tidal circulation produced tidal bores. The average temperatures recorded by data loggers placed at 7 and 12 m depth on a coral reef at the outer shores of Culebra Bay, were 27.1 +/- 0.02 degrees C (20.5-31.6 degrees C) and 25.8 +/- 0.04 (9.9-31.5 degrees C) respectively. The seasonal pattern of higher and lower temperatures corresponds respectively to the rainy and dry season of the northern Pacific coast of Costa Rica. Water temperature at 12 m was < 14 degrees C for some hours during an upwelling event whilst minimum temperatures at 7 m were > or = 22 degrees C. Negative temperature anomalies coincided with an increase of the NE-E winds intensity and there is a lunar and tidal component which influence diumal variations of temperature. These results suggest that coral reefs built by branching species (e.g. Pocillopora spp.) in Culebra Bay could be limited by both the influence of cold fronts and by seasonal upwellings which affect negatively those coral species, as reported for other locations in the tropical eastern Pacific.     

The diversity and distribution of the cetaceans of Costa Rica (Cetacea: Delphinidae, Physeteridae, Ziphiidae y Balaenopteridae)

The first complete checklist of Costa Rican cetaceans is presented with a total of 28 species (35% of the group's world diversity). Most of the species occur in the Pacific Ocean (89%) and most are considered oceanic (57%), common (54%) and resident (68%). The known distribution and status of each species are also provided.     

Hematological,serum, and plasma chemical constituents in pantropical spotted dolphins (Stenella attenuata) following chase,encirclement, and tagging

Hematology, serum chemistry, and plasma hormones were evaluated in 72 pantropical spotted dolphins (Stenella attenuata attenuata) from the eastern tropical Pacific in an attempt to define the degree of stress associated with chase and encirclement by a tuna purse seiner, and are here reported for the first time for this species. Dolphins had high levels of dopamine and moderately elevated levels of enzymes indicative of the expected muscle damage following exertion of the chase. The length of time between the start of the capture operation and blood sampling correlated with increases in platelet and white blood cell counts and mean cell hemoglobin concentration, while the length of time between net tie‐down and blood sampling influenced platelet, white blood cell, and eosinophil counts. Ten dolphins recaptured 1–3 d after their first capture had significantly lower serum creatinine kinase, thyroid (T4) and globulin levels compared to values in dolphins sampled at nominal first capture. Although small sample sizes and large individual variation limit interpretation, these data indicate a stress response occurred in all dolphins, but the extent of the response is within the expected range for adaptive responses previously measured in limited numbers of wild mammals.     

On Branchiostoma californiense (Cephalochordata) from the Gulf of Nicoya estuary, Costa Rica

The cephalochordates are represented by the lancelets, of which species of the genus Branchiostoma are the best known. In recent years, these organisms have been the center of activity of studies focusing on the phylogenetic relationships of the chordates. In 1980, a survey of the benthos at 48 stations in the Gulf of Nicoya estuary, Pacific coast of Costa Rica, yielded 265 specimens of the lancelet Branchiostoma californiense. A total of 48 specimens was also collected at an intertidal flat in the mid upper estuary. Of the 48 subtidal stations, only eight had B. californiense, and these sites all had a sand fraction above 72%. The remaining stations ranged in their sand content from as low as 1% to as high as 92%, with an average of 25.9%, with 29 stations having a sand content lower than 72%. Lower salinities and muddy sediments may limit the distribution of the lancelet further upstream. This information is useful when changes over decades in the ecology of the estuary need to be evaluated against the background of local, regional, and global dynamics.     

Variation of thermohaline properties in the Nicoya Gulf, Costa Rica

The time-space behavior of thermohaline properties of the water masses in the Gulf of Nicoya, a tropical estuary in the Costa Rican Pacific coast, was studied by sampling monthly from April 1992 to April 1993. The saline field has a seasonal maximum during April, a month before the maximum temperature is observed. Minimun values were observed during October and November, in the rainy season. A defined surface saline front is located towards the east of Negritos Islands; it is produced by the interaction of freshwater from the Tarcoles River and the oceanic waters that enter through the occidental coast of the gulf. The vertical distribution of temperature and salinity indicates a gulf whose internal area is highly stratified in the rainy season, and much less stratified, or even well mixed in the dry season. The outer area of the Gulf is stratified throughout the year.     

Composition, abundance and distribution of macrozooplankton in Culebra Bay, Gulf of Papagayo, Pacific coast of Costa Rica and its value as bioindicator of pollution

The abundance, distribution and composition of the macrozooplankton of Culebra Bay, Costa Rica (10 degrees 38' N - 85 degrees 40' W) were studied at four stations throughout the dry (February-May) and rainy (September-November) seasons of 2000. The samples were collected at two-week intervals using a 500 microm mesh net with a 0.5 m diameter opening. Copepods (23-31%) and ostracods (20-34%) were predominant throughout the year, followed by cladocerans (2.5-14%), zoea (6.6-9.5%), and siphonophores (2.5-7.2%). High densities of zooplankton were obtained in February and March with peak abundance on March 18. The lowest densities were observed on September 3 and November 5. Significant differences in abundances at each station were observed for the groups Acartia tonsa (Copepoda), Ctenophora, Medusae, Ostracoda, Zoea, and Amphipoda. Comparison of the dry and rainy seasons revealed significantly higher zooplankton abundance in the dry season and copepod domination of all stations; during the rainy season ostracods dominated the off-shore areas. Zooplankton abundance and distribution are influenced by upwelling, which occurs during the dry season in Culebra Bay.     

Mitogenomic differentiation in spinner (Stenella longirostris) and pantropical spotted dolphins (S. attenuata) from the eastern tropical Pacific Ocean

Spinner dolphins (Stenella longirostris) and pantropical spotted dolphins (S. attenuata) show high intraspecific morphological diversity and endemic subspecies in the eastern tropical Pacific Ocean (ETP). Previous studies of mitochondrial DNA have found low genetic differentiation among most of these groups, possibly due to demographic factors, ongoing gene flow, and/or recent divergence. These species were heavily depleted due to bycatch in the ETP yellowfin tuna fishery. Because understanding population structure is important for accurate management of the recovery of these species, we collected whole mitochondrial genome sequences from 104 spinner and 76 spotted dolphins to test structure hypotheses at multiple hierarchical taxonomic levels. Results show differences between subspecies of spinner and spotted dolphins, but no support for the division of existing offshore stocks of spotted dolphins. We compare these results to previous results of genome‐wide nuclear SNP data and suggest high haplotype diversity, female dispersal, and/or relative power of the two data sets explains the differences observed. Interestingly, increasing the amount of mitochondrial data (base pairs and genes) did not increase ability to delimit population units. This study supports a genetic basis for management units at the subspecies level, and provides critical information for mitigating historical and continued fisheries impacts.     

A biogeochemical model for the Gulf of Nicoya, Costa Rica

In agreement with the Broecker and Penn two-boxes model, I generated a biogeochemical balance model for the Gulf of Nicoya (Guanacaste, Costa Rica) using two nutrient reservoirs: surface water and deep water. The mixing zone was located at a depth of 20 m. There is a balance between surface waters descending to the bottom and upwelling waters that carry nutrients and other chemical elements to the surface. The main source of nitrogen (nitrate), was the outlet of the Tempisque and Tárcoles rivers. The Gulf of Nicoya is a net source of Dissolved Inorganic Nitrogen (DIN) with an availability rate of 87 x 10(3) mol day(-1) in the dry season and 3044 x 10(3) mol day(-1)in the rainy season. Dissolved Inorganic Phosphate (DIP) was estimated in 27 mol day(-1) in the dry season and 207 mol day(-1) in the rainy season. The dynamics of these biolimited nutrients, in relation to runoff seasonal variations, fits the biological processes reported for the gulf, for example, for variations in primary productivity levels, and maturity and reproduction seasons for species with short and long life cycles.     

Modeling the spatial distribution of the striped dolphin (Stenella coeruleoalba) and common bottlenose dolphin (Tursiops truncatus) in the Gulf of Taranto (Northern Ionian Sea,Central-eastern Mediterranean Sea)

Although the EU Marine Strategy Framework Directive (MSFD) is largely based on the establishment of environmental targets and associated proxies to achieve Good Environmental Status (GES), a full suite of ecological indicators for all the ecosystem components is not currently available for ongoing assessment and regular update of GES targets. This is because effective indicators and management actions aimed at preserving/rebuilding marine biodiversity should be found from the knowledge of the spatial distribution of target species and extension of critical habitats as well as their overlapping with human activities, pressure and impacts. In this regard, the spatial distributions of the striped dolphin Stenella coeruleoalba and the common bottlenose dolphin Tursiops truncatus in the Gulf of Taranto (Northern Ionian Sea, Central-eastern Mediterranean Sea) were investigated by means of a generalized additive model (GAM) and a Random Forest (RF) based on sighting data collected during standardized vessel-based surveys carried out from 2009 to 2015. Eight predictive variables were considered, taking into account both the local physiographic features and human activities existing in the investigated area, suggesting an innovative approach to habitat modeling. In particular, the explanatory variables depth, distance from industrial areas and distance from the coast proved to significantly influence the distribution of both dolphin species. In addition, the distribution of S. coeruleoalba and T. truncatus were also significantly shaped by the distance from the navy exercise areas and the fishing areas, respectively. On the contrary, the slope and the distance from the main commercial routes never provided any significant influence. The reliability of GAM and RF models in predicting the spatial distribution of both dolphins was tested by applying the Youden Index method to the ROC curves. The RF model allowed the projection of the expected presence/absence pattern of S. coeruleoalba and T. truncatus to produce the preference habitat versus non habitat map. In particular, the RF model predicted that the striped dolphin is widely present in the central and deeper part of the Gulf of Taranto. In contrast, the common bottlenose dolphin seems to be mainly distributed along the coasts in both the eastern and western sector of the basin. A clear overlapping of the preference habitats estimated for S. coeruleoalba and T. truncatus is shown north of Punta Alice and in front of Policoro as well as offshore from Ugento in the eastern and western parts of the investigated area, respectively. Finally, the critical habitats of S. coeruleoalba and T. truncatus are the outcome of both the influence of environmental conditions and anthropogenic pressures presently occurring in the Gulf of Taranto, basically indicating the need for conservation measures, especially considering that the area is expected to be considered for hydrocarbon prospecting. These results contribute to setting up a baseline reference for future assessment of environmental marine disturbances using cetaceans, which are considered a key group in the MSFD, as an ecological indicator.     

Spatio‐temporal patterns of genetic diversity in the Mediterranean striped dolphin (Stenella coeruleoalba)

Comparing the genetic composition of wild animals between geographic regions with distinct environments is common in evolutionary studies. However, genetic composition can also change through time in response to environmental changes but studies examining this are carried out less often. In this study, we characterize striped dolphin genetic composition in the Mediterranean Sea across both geography and time. We provide genotype data for 15 microsatellite loci and 919 bp of mtDNA control region, collected over 21 years across all main Mediterranean Sea basins. We investigated spatial genetic structure using both classical and Bayesian population structure methods, and compared it with temporal patterns of genetic change using time‐series statistics. We integrated the temporal datasets with known environmental pressures and data on social structure, to infer potential drivers of observed changes. Geographic analyses suggest weak differentiation for striped dolphin in the Mediterranean Sea, with evidence for a recent expansion. Temporal analyses show significant cyclical fluctuations in genetic composition over 21 years, which correspond well with recurrent morbillivirus epizootics. Similarly, social group composition shows changes in the relative number of juveniles and adults per group, and an overall increase in the number of adults per group relative to juveniles over the time period. We suggest that the observed changes in genetic and group composition could relate to specific dynamics of morbillivirus resistance. Overall, our study highlights the importance of tracking long‐term genetic variation and the potential for this species as a model in studying genetic adaptation to environmental stress.