Niche overlap and diet composition of three sympatric coastal dolphin species in the southwest Atlantic Ocean

Sympatric species are expected to differ in ecological requirements to minimize niche overlap and avoid competition. Here we assess the trophic interactions among three coexisting dolphin species from southern Brazil: the franciscana dolphin (Pontoporia blainvillei), the Guiana dolphin (Sotalia guianensis), and the Lahille's bottlenose dolphin (Tursiops truncatus gephyreus). We evaluated temporal variation in carbon (δ¹³C) and nitrogen (δ¹⁵N) isotope values of bone collagen to examine potential dietary shifts resulting from increased fishing activity over the past three decades. We estimated the degree of niche overlap among these species and the contribution of potential prey sources to their diet. δ¹⁵N values were consistent among species and across years, while δ¹³C values increased for Guiana dolphins and decreased for bottlenose dolphins, suggesting changes in diet and/or foraging habitats through time. The similar δ¹³C and δ¹⁵N values and the high niche overlap between Guiana and bottlenose dolphins indicate that these species are primarily feeding on demersal prey. The franciscana diet is primarily composed of pelagic prey, resulting in a lower niche overlap in comparison with the other dolphin species. Our study provides further information about the foraging ecology of this unique dolphin community in southern Brazil with implications for its management and conservation.     

SHORT-TERM EFFECTS OF BOAT TRAFFIC ON BOTTLENOSE DOLPHINS, TURSIOPS TRUNCATUS, IN SARASOTA BAY, FLORIDA

Coastal cetaceans are subject to potential injury or disturbance from vessels. In Sarasota, Florida, where about 120 resident bottlenose dolphins, Tursiops truncatus , share the inshore waters with over 34,000 registered boats, disturbance potential is high. We assessed specific behavioral responses of individual dolphins to boat traffic. We conducted focal animal behavioral observations during opportunistic and experimental boat approaches involving 33 well-known identifiable individual bottlenose dolphins. Dolphins had longer interbreath intervals (IBI) during boat approaches compared to control periods (no boats within 100 m). Treatment IBI length was inversely correlated with distance to the nearest boat in opportunistic observations. During 58 experimental approaches to 18 individuals, a video system suspended from a tethered airship was used to observe subsurface responses of focal dolphins as boats under our control, operating at specified speeds, were directed near dolphins. Dolphins decreased interanimal distance, changed heading, and increased swimming speed significantly more often in response to an approaching vessel than during control periods. Probability of change for both interanimal distance and heading increased when dolphins were approached while in shallow water. Our findings provide additional support for the need to consider disturbance in management plans for cetacean conservation.     

Faunistical data on the Croatian Orthoptera with four species newly recorded in the country

We present 914 records of Croatian Orthoptera, representing 124 taxa from 178 localities. The list is compiled based on the Hungarian Natural History Museum collections, private collections, and authors’ observations. The first faunistical records for Croatia are given for a bush-cricket (Leptophyes intermedia), two crickets (Modicogryllus truncatus, Oecanthus dulcisonans), and a grasshopper species (Epacromius tergestinus).     

The Effects of Isolation,Grouping and Population Density on Fecundity of Bulinus truncatus

Summary

Bulinus truncatus is the intermediate host of Schistosoma haematobium, a trematode parasite causing bladder bilharziasis in man. In the struggle against this disease, control of snail populations is an important goal and expansion of our knowledge of the reproductive activity of Bulinus is relevant in this regard.

In this study the effects of various factors on the fecundity of Bulinus were investigated in specimens kept under continuous water refreshment conditions. The results are considered to be more indicative of the natural situation than results obtained under the current use of discontinuous water refreshment.

Isolated snails produce considerably higher numbers of egg masses and eggs than grouped snails. The effect of grouping on isolated snails, and the reverse situation, is very rapid, being fully effective within one week. The increase in fecundity of isolated snails is most probably caused by the absence of copulatory activity, since transfer of semen is known to curtail egg laying in freshwater pulmonate snails. Egg mass production was shown to decrease with increasing population density. This may be caused either by the difference in space available or by the possible difference in copulatory activity. Isolated snails showed a faster body growth than grouped snails.

The possible role of hormones involved in establishing the above effects and the consequences of the results for snail control programs are discussed.     

Fine-scale sociality reveals female–male affiliations and absence of male alliances in bottlenose dolphins (Tursiops truncatus) in the Shannon Estuary,Ireland

Knowledge of social behavior at an individual level is central to our understanding of complex mammalian societies. In this study, we analyzed the fine-scale sociality of wild bottlenose dolphins in the Shannon Estuary, Ireland, by examining associations between members of the whole population and between specific female and male dolphins. We carried out 51 boat-based individual focal follows on 18 identifiable bottlenose dolphins over 90.8 hr (39 days) between 2014 and 2016. Additionally, we conducted 353 boat-based surveys (with 607 sightings) between 2012 and 2015, and identified 121 distinct adult/juvenile dolphins. The mean group size of focal dolphin groups was 7.2 ± 4.1 (range = 1–20) and the mean fission-fusion rate was 3.06 ± 1.35 changes/hr. The most frequent composition of within-group affiliate pairs was female–male. Focal males spent more time with female nearest-neighbors than male nearest-neighbors (p = .013). Differences between female and male activity budgets were not strongly supported (p = .13). There was no evidence for male alliance formation in the Shannon Estuary population, and all of the known-sex top-ranked associates (7) of known males (n = 10) were females. This research reveals a distinct bottlenose dolphin society with female–male affiliations and an absence of male alliances.     

Environmental drivers of habitat use by common bottlenose dolphins (Tursiops truncatus) in the Indian River Lagoon,Florida, USA

Anthropogenic impacts in estuarine systems can influence marine mammal habitat use, population dynamics, fitness, and mortality events. The objective was to examine habitat use among the resident common bottlenose dolphin (Tursiops truncatus) population inhabiting the Indian River Lagoon, Florida, and the influences of variation in environmental factors and prey availability in 2003–2015. We utilized photo-identification surveys, stratified random samples of prey, and environmental variables collected monthly. Kernel density estimation was used to determine the magnitude-per-unit area of dolphins across the IRL by wet and dry seasons each year, the values were used as a response variable in classification and regression tree analyses with fish community and environmental variables as predictors. Spatial patterns in dolphin density in the IRL were associated with salinity and dissolved oxygen levels, which are in part associated with freshwater discharges of nutrient and algae laden waters from the region's storm water management system. These findings isolate locations of concern for management of dolphin habitat, and anthropogenic drivers of dolphin distributions requiring further research.     

Bioactivity of fenchone and Plectranthus glandulosus oil against Prostephanus truncatus and two strains of Sitophilus zeamais

The toxic, repellent and reproduction inhibitory effects of Plectranthus glandulosus essential oil and one of its major compounds, fenchone, were evaluated against adult Prostephanus truncatus (Horn) and for two strains of Sitophilus zeamais Motschulsky from Cameroon and Germany. Maize grains were coated with the oil at 0, 10, 20, 40 and 80 μl/40 g grain and fenchone at 0, 20, 40, 80 and 120 μl/40 g grain. Mortality was assessed over a 7‐day period, followed by the determination of F₁ progeny production. The repellence of the two products was evaluated at five rates (0.5, 1, 3, 5, 10 μl/half disc) in a choice bioassay on filter paper. The oil and fenchone caused significant dose‐dependent mortality to the three insects, with the oil achieving 100% and 90% mortality for the two S. zeamais strains and P. truncatus, respectively, within 1 day of exposure at the dosage of 80 μl/40 g grain. The insects were less susceptible to fenchone compared with the crude oil. The German strain of S. zeamais was susceptible to the oil than the Cameroonian strain. At the dosage of 20 μl/40 g grain, S. zeamais F₁ progeny emergency was completely inhibited by the oil, while 80 μl/40 g grain treatment with fenchone prevented also insect emergence. Plectranthus glandulosus oil generally evoked a maximum per cent repellency of 100% for the three insects, but fenchone caused 55–60% to S. zeamais and 80% to P. truncatus. These results suggest that fenchone, though a major constituent of P. glandulosus oil, may only be a minor component of its bioactivity.     

截形叶螨药剂防治对比试验

截形叶螨(Tetranychus truncatus Ehara)在云南昆明主要为害大棚花卉,尤其对月季(Rosa chinensis)为害严重。使用玻片浸液法,选用6种化学杀螨剂和1种植物叶面保护剂对该叶螨进行室内药效测定;同时,选取真除螨、主力和植物叶面保护剂等3种杀螨剂实施田间防治试验。结果表明,室内施药48h后,真除螨2 000、3 000倍液杀螨效果达100%;田间喷药3d后,真除螨4 000倍液能达到30%的防治效果,可有效降低害螨数量。建议每年截形叶螨为害严重的5～11月期间,在保护地栽培的月季上连续施用真除螨。害螨发生高峰期前,可使用植物叶面保护剂,减少害螨的取食。     

OCCURRENCE,DISTRIBUTION, SITE FIDELITY,AND SCHOOL SIZE OF BOTTLENOSE DOLPHINS (TURSIOPS TRUNCATUS) OFF SAN DIEGO,CALIFORNIA

The occurrence, distribution, site fidelity, and school size of bottlenose dolphins (Tursiops truncatus) in the coastal waters of north San Diego County, California were assessed during a six-year boat-based photoidentification study. A total of 146 photographic surveys were conducted between January 1984 and December 1989. Dolphin schools were encountered on 79% of all surveys, and 2, 869 individuals were observed in 145 separate schools. Three-hundred seventy-three dolphins were individually identified. All schools were sighted within 1 km of shore, and more than two thirds of the schools were encountered in the southern half of the 32-km long study area. School size (mean = 19.8, SD = 18.40) and the number of dolphins encountered per survey (mean = 26.8, SD = 22.30) were highly variable. Low resighting rates of known individuals provided little evidence for longterm site fidelity. When our six-year photoidentification database was combined with previous data, 404 dolphins were identified in the study area from September 1981 to December 1989. Jolly-Seber population estimates during the 1984-1989 study period varied between 234 and 285. The combination of regular dolphin occurrence, low site fidelity by known individuals, and the continuous increase in the rate at which new dolphins were identified indicates that numerous different individuals were visiting the study area across and within years. The open California coastline differs in habitat structure and prey distribution from more protected study areas where bottlenose dolphins display site fidelity. These habitat differences may help to explain the observed intraspecific behavioral variability of this species.