Forward masking in a bottlenose dolphin Tursiops truncatus : Dependence on azimuthal positions of the masker and test sources

Forward masking was investigated by the auditory evoked potentials (AEP) method in a bottlenose dolphin Tursiops truncatus using stimulation by two successive acoustic pulses (the masker and test) projected from spatially separated sources. The positions of the two sound sources either coincided with or were symmetrical relative to the head axis at azimuths from 0 to ±90°. AEPs were recorded either from the vertex or from the lateral head surface next to the auditory meatus. In the last case, the test source was ipsilateral to the recording side, whereas the masker source was either ipsi- or contralateral. For lateral recording, AEP release from masking (recovery) was slower for the ipsi- than for the contralateral masker source position. For vertex recording, AEP recovery was equal both for the coinciding positions of the masker and test sources and for their symmetrical positions relative to the head axis. The data indicate that at higher levels of the auditory system of the dolphin, binaural convergence makes the forward masking nearly equal for ipsi- and contralateral positions of the masker and test.

DDT in Crimea coastal waters and blubber of Black Sea cetaceans

This research is based on the multi-year data on the distribution of organochlorine pesticides of the DDT group in the water of the coastal Black Sea areas of Crimea, obtained in expeditions of the “Professor Vodyanitsky” research vessel from 1999 to 2020. Study of content of DDT and its metabolites (DDTs) in the blubber of three species of Black Sea cetaceans that were astrand on the Black Sea coast from the 1980s to the 2020s was grounded on own and literature data. While there was an overall significant variability in ∑DDT content during the study period, there was a significant downward trend in their concentrations in the water of coastal areas of Crimea. Despite the significantly decreased DDTs pollution of the habitat of the Black Sea marine mammals over the last 10 years, high concentrations of DDTs were accumulated in their blubber, the maximum value of the sum of DDTs concentrations reached (163 µg/g of lipids) in the blubber of adult depleted bottlenose dolphin. The minimum concentrations were determined in the blubber of a newborn harbour porpoise female. In blubber samples up to 70% was of DDE, DDD - from 21 to 24%, and the concentration of the initial DDT varied from 6 to 14%. Based on the analysis of own and literature data, it is assumed that in the modern period, as compared to the 1990s, there is a downward trend in the content of the DDTs in the blubber of Black Sea cetaceans.

Characterization of Circulating Androgens, Cortisol and Estrogens During Normal, Abnormal and False Pregnancy in Bottlenose Dolphins (Tursiops truncatus) Under Managed Care

The few hormone studies on bottlenose dolphin (Tursiops truncatus) pregnancy with different reproductive outcomes, e.g., normal birth, stillbirth and abortion, have mostly focused on progestagens or relaxin. However, recent analysis of androgens, glucocorticoids and estrogens has shown they are also biomarkers of cetacean pregnancy. Therefore, our objective was to examine circulating concentrations of androgens, glucocorticoids and estrogens during bottlenose dolphin pregnancies with different reproductive outcomes, including normal pregnancy (NORM, n = 27), failure to thrive (FTT, n = 17), perinatal loss (PNL, n = 20), early loss (EL, n = 12) and false pregnancy (FP, n = 16), to determine if they could be potential indicators of reproductive or fetal health. We analyzed longitudinal serum samples (n = 654) from 57 bottlenose dolphins and 92 reproductive events for testosterone, androstenedione, cortisol, estradiol and estrone conjugates. Testosterone concentrations were higher during EL compared to NORM and lower during FP at MID (day 121 – 240 post ovulation/conception) and LATE (day 241 – end of FP) stages (months post conception/ovulation [MPC, MPO] seven through ten, P < 0.05). During FTT, androstenedione concentrations were increased compared to NORM pregnancies in the EARLY and LATE stages (P ≤ 0.05), and concentrations were reduced during FP (P < 0.05). For cortisol, FTT pregnancies had higher concentrations compared to NORM during all stages (P < 0.05), while PNL had higher cortisol during EARLY and LATE stages (P < 0.05). Estradiol concentrations were lower for EL and FP compared to NORM (P < 0.05), while estrone conjugates were only reduced during FP (P < 0.05). Based on our results only cortisol may be a useful predictor of PNL, while both cortisol and androstenedione were useful for distinguishing FTT pregnancies. Similarly, both testosterone and estradiol during EL and FP were different from NORM. Our data indicate a suite of pregnancy specific hormone biomarkers to evaluate maternal and fetal health in bottlenose dolphins should include cortisol, androgens and estrogens. This research also highlights the importance on non-progestagen hormones as sentinels of cetacean pregnancy and fetal health.

Site Fidelity and Residency of Tursiops truncatus off the Aragua Coast, Venezuela-First Records of Long Residency

This study represents the first comprehensive analysis of the residency patterns of a coastal population of bottlenose dolphin off the coast of Aragua, Venezuela, over a multi-year period. Using photo-identification, the most recent study (2019-2020) identified 56 individuals with the time between encounters from one to 344 days between the first and last sighting. Site Fidelity (SF) and Residence (RES) indices were calculated and Agglomerative Hierarchical Clustering (AHC) modeling was performed, with three patterns of residence obtained: resident (25%), semiresident (17.86%) and transient (57.14%). These results were contrasted with remodeled data from a previous study (2006-2007), showing similar patterns: resident (24.44%), semi-resident (28.89%) and transient (46.67%). Importantly, two individuals were found to have been resident over the extended period. A breeding female sighted for the first time in 2004 and again in 2020 (16 years) and the other from 2005 to 2020 (15 years). This region is an important area for marine mammals, known to support a resident reproductive population over many years, as well seabirds, sea turtles, whale sharks and fishermen. We recommend that consideration be given to designating the waters as a Marine Protected Area to safeguard the existing population and provide benefit to the surrounding marine environment.

Patterns and Trends in Cetacean Occurrence Revealed by Shorewatch, a Land-Based Citizen Science Program in Scotland (United Kingdom)

Shorewatch is a citizen science project, managed by Whale and Dolphin Conservation (WDC), that records the occurrence of cetaceans during regular, standardized watches from a series of locations along the coast of Scotland (United Kingdom). Observer training and a clearly defined protocol help deliver a valuable source of information about cetacean occurrence and activity along the coast. Between 2005–2018, over 52000 watches generated over 11000 sightings of at least 18 cetacean species. Generalized Additive Models based on sightings for the five most commonly sighted species (bottlenose dolphin, harbor porpoise, minke whale, Risso’s dolphin, and common dolphin), at those sites with the longest time series, demonstrated seasonal, geographical and year-to-year differences in their local occurrence and relative abundance. Bottlenose dolphins are mainly present at observation sites located on the east coast of Scotland, being uncommon on the west coast, while harbor porpoise and minke whale are principally present at sites located on the west coast. The seasonality observed in cetacean occurrence is consistent with peak abundance in summer months described by previous studies in the area. Mean depth around the observation sites is the static variable that apparently has the greatest influence on species presence and number of sightings, except for Risso’s dolphin. All the species except bottlenose dolphin showed upward trends in occurrence and number of sightings over the period 2012–2018. Evidence of temporal autocorrelation was found between results from consecutive watches at the same site on the same day as well as between results from consecutive days at the same site. The power to detect declines in local abundance over a 6-year period depends on the underlying sighting rate of each cetacean species, the number of watches performed and the rate of decline. Simulations performed to determine the power to detect a decline suggest that the current intensity of observation effort in some observation sites, of about 2500 watches per year, may offer good prospects of detecting a 30% decline of the most frequently sighted species (95% of the time) over a 6-year period, although a more even distribution of observation effort in space and time is desirable. The data could potentially be used for monitoring and 6-yearly reporting of the status of cetacean populations.

Skin lesion and mortality rate estimates for common bottlenose dolphin (Tursiops truncatus) in the Florida Panhandle following a historic flood

Increasing evidence links prolonged freshwater exposure to adverse health conditions, immune deficiencies, and mortality in delphinids. Pensacola, Florida, experienced a record-breaking flood event in April 2014, after which, skin lesions evident of freshwater exposure were observed on common bottlenose dolphins (Tursiops truncatus). Here we assess the potential consequences of the flood on bottlenose dolphin health and mortality. Data from an ongoing study were used to evaluate the relationship between skin lesions (progression, prevalence, and extent) and the flood with respect to changing environmental conditions (salinity). Annual stranding records (2012–2016) from Alabama to the eastern Florida Panhandle were used as an indicator of dolphin health to test the hypothesis that the flood event resulted in increased annual mortality rates. Although salinities remained low for several months, results suggest that there was not the widespread skin lesion outbreak anticipated. Of the 333 unique individuals detected only 20% were seen with skin lesions. There was a significant increase in the proportion of dolphins seen post-flood with lesion extent above background levels (≥ 5%; p = 0.001), however, there were only 11 cases with lesion extent greater than 20%. Skin lesion prevalence increased overall following the flood (p < 0.001), but pairwise comparisons revealed a delayed response with significant increases not detected until the following fall (p = 0.01), several months after salinities returned to expected levels. Regression modeling revealed no significant effects of year, region, or year x region on mortality rates, except in Alabama, where increased mortality rates were likely due to residual impacts from the Deepwater Horizon Oil Spill. This study takes advantage of a natural experiment, highlighting how little is understood about the conditions in which prolonged freshwater exposure leads to negative impacts on dolphin health.