I cetacei del Golfo di Corinto, Grecia

Il Golfo di Corinto, nella Grecia centrale, è un bacino semichiuso di 2400 km2. Con le sue ampie piattaforme continentali, ripi-de zone di scarpata e acque profonde fino a 900 m, il Golfo è letteralmente un piccolo “mediterraneo”, non solo perché circondato da terre e rilievi montuosi, ma anche per la varietà degli ecosistemi marini che ospita. Tre specie di cetacei sono presenti in queste acque: 1) la stenella striata (Stenella coerule-oalba), un delfino tipico di ambienti pelagici; 2) il delfino comune (Delphinus delphis), che in Mediterraneo è osservabile sia in ambien-te pelagico sia in zone di scarpata e presso la costa; 3) il tursiope (Tursiops truncatus), tipico della piattaforma continentale. In ag-giunta, il Golfo ospita un quarto odontoce-to: un solo esemplare di grampo (Grampus griseus)...

Optimizing abundance estimates of striped dolphins in the Gulf of Corinth, Greece

Monitoring cetacean abundance is often challenged by insufficient funding and/or effort. Large sample sizes are required to obtain reliable estimates via Capture Mark Recapture (CMR) models. Dataset simulations and power analysis can be used to assess 1) minimum sample size to achieve reliable estimates within one sampling season, and 2) the number of repeated estimates required to detect abundance trends. We used photo-identification data from June-September 2012 to estimate abundance of striped dolphins Stenella coeruleoalba in the Gulf of Corinth, Greece, using CMR models. To evaluate minimum sample size needed within one sampling season, we used dataset simulations in program MARK and compared accuracy and precision obtained with increasing sample sizes. We then used Gerrodette’s inequality model to perform a power analysis and compare the smallest annual percent declines detectable by decennial monitoring plans based on 1) one estimate per year, 2) one estimate every two years, and 3) one estimate every five years. The effect of different levels of precision of the estimates (CV=0.01-0.04) was also investigated. Population abundance was estimated at 1,309 (SE=62.45; CV=0.05; 95% CI=1,192–1,437) for open models and at 1,293 (SE=53.66; CV=0.04; 95% CI=1,192–1,403) for closed models. These estimates are substantially larger that those obtained in a previous CMR study on 2009 data, and need to be validated. To obtain reasonably accurate estimates within one sampling season, simulations indicated a minimum sample size of 8 capture occasions, with minimum capture probabilities of 0.5 for closed models and 0.7 for open models. Furthermore, a power analysis indicated that the smallest annual declines (5%–12.5%) could be detected by monitoring plans providing one estimate every two years. High levels of precision are required (CV=0.01 to detect a 5% annual decline). This information is being used to set monitoring goals and optimize the available resources

Striped dolphin abundance in the Gulf of Corinth, Greece: dataset simulations help improve sampling design

Estimating wildlife population abundance is essential to evaluate the extinction risk of local populations and support conservation management. Photographic Capture mark-recapture (CMR) is a widely-used technique to assess cetacean abundance. However, reliability of estimates is strongly dependent on sample size. CMR software such as MARK can be used to simulate datasets sampled from virtual populations of known size. Population size can be estimated with CMR models from such datasets and, being the real abundance (Ntrue) known, is then possible to assess the models’ performance under different sample size scenarios. We used photo-identification data from June-September 2012 to estimate population size (N) as well as capture and survival probability (p and phi, respectively) of striped dolphins Stenella coeruleoalba in the semi-enclosed Gulf of Corinth. We then used these estimates to simulate datasets obtained with different levels of sampling effort. Finally, we estimated N from the simulated datasets and 1) compared the accuracy and precision of estimates obtained with closed and open population CMR models with samples of different size and 2) identified an 'optimal' sampling strategy. Reliable estimates (100% included in a ± 50 interval around Ntrue) with both models were obtained with 7+ capture occasions and a minimum capture probability of 0.5 for closed and 0.7 for open models. These results provide a way forward for improved sampling design

The dark side of hybridization: quantifying prevalence of anthropogenic introgression for conservation

Hybridization, the interbreeding of individuals from genetically distinct populations, has been considered until recently a relatively rare event across animal species. However, it is with the development of molecular techniques that hybrids have been increasingly detected, suggesting hybridization may be a more widespread phenomenon than originally thought. Hybrids are not necessarily less fit and, under given circumstances, they may also bear more successful adaptive traits with respect to their parental populations. Hybrids can also re-integrate with parental populations by backcrossing, leading to various levels of introgression. Whereas natural hybridization is considered a positive evolutionary force and a source of evolutionary novelty, conservation-wise hybridization caused by human impacts (anthropogenic hybridization, AH) may threaten the genetic integrity of many wild plant and animal taxa. AH has been recently recognized as an increasing threat for biodiversity worldwide due to human induced changes in species abundance and distribution, removal of reproductive barriers, and introduction of non-native and domestic species. Conservation issues raised by AH may range from wasted reproductive effort in threatened, parental species, when the hybrids are sterile, to various degrees of genetic swamping when introgression takes place. We present a review of AH cases focusing on the hybridization between wild species and their and domesticated counterparts. By summarizing factors and conditions that most facilitate AH, we discuss the most relevant implications from both an evolutionary and conservation-wise points of view. In particular, we emphasize the importance of developing of demographic models to accurately estimate the current and future extent of admixture in parental populations in order to explore and accordingly identify the most appropriate management and conservation recommendations

Bottlenose dolphin abundance in the Northern Evoikos Gulf, Greece

The Mediterranean subpopulation of the common bottlenose dolphin Tursiops truncatus has been classified as Vulnerable in the IUCN Red List. However, population size data are only available for a few Mediterranean subareas, hampering understanding of bottlenose dolphin status and trends. To contribute baseline information, we assessed bottlenose dolphin abundance in the Northern Evoikos Gulf, a 960 km2 semi-enclosed basin in central Greece exposed to high heavy-industry and fishing impacts. Boat-based surveys covering the entire Gulf were conducted in October 2010 and March-April 2011, totalling 3340 km of navigation over 39 survey days. A total of 54 dolphin groups were encountered (mean size 10.0 animals, SD=5.90, range 1–30, based on 84 group size samples recorded at 60 min intervals). Dolphin group follows averaged 94 min (SD=74.3, n=54, range 2–282 min), totalling 84 h 20 min of individual photo-identification effort across 457 km. Of 5890 digital photos taken (at 18 megapixel resolution), 3141 high quality images portraying single dorsal fins were selected. The dorsal fins of 95 individuals had natural marks allowing for long-term identification. Based on the number of photos portraying marked vs. unmarked individuals, we estimated a marked proportion of 0.92. The hypothesis of population closure was rejected by the Stanley and Burnham closure test (χ2=31.34181, df=8, p=0.0012). We therefore used an open capture-recapture model (POPAN package) in program MARK 7.1 to estimate bottlenose dolphin abundance in the study area. The model yielded a population of 100 marked animals (95% C.I.=95–106), resulting in a total population of 109 (95% C.I.=101–117). We recommend continued photo-identification effort in the Northern Evoikos Gulf and contiguous waters, for longer-term status and trends analyses

Studying Species Demography and Distribution in Natural Conditions: Hidden Markov Models

International audienceThis chapter shows how hidden Markov models (HMMs) can be used to develop capture–recapture and occupancy models, traditionally used to study the dynamics of populations and the distribution of species in a context of imperfect detection. It shows how the HMM formulation permits the estimation of hidden variables in two different case studies. These case studies include: estimating the prevalence of dog–wolf hybrids with uncertain individual identification; and estimating the distribution of a wolf population with species identification errors and heterogeneous detection. The hidden variables encountered in the study of animal populations are living/dead; developmental states, which are generally discrete, such as sexual maturity; epidemiological states; or social states. HMM will be used to model species distribution in a case featuring identification errors and heterogeneous detection. The main advantage of the HMM approach lies in the ability to infer the ecological states of individuals and species which are partially observable: these are hidden variables

Revised abundance estimates of striped and short-beaked common dolphins in the Gulf of Corinth, Mediterranean Sea

Santostasi N.L., Bonizzoni S., Bearzi G., Eddy L., Gimenez O. 2016. Revised abundance estimates of striped and short-beaked common dolphins in the Gulf of Corinth, Greece. Proceedings of the 30th Annual Conference of the European Cetacean Society, Funchal, Madeira, 14-16 March 2016. Revised abundance estimates of striped and short-beaked common dolphins in the Gulf of Corinth, Greece Nina Luisa Santostasi1,4, Silvia Bonizzoni1,2,3, Giovanni Bearzi1,2,3, Lavinia Eddy1,2, Olivier Gimenez4 1) Dolphin Biology and Conservation, Piegaro PG, Italy; [email protected] 2) OceanCare, Wädenswil, Switzerland 3) Texas A&M University at Galveston, Galveston TX, USA 4) Centre d’Ecologie Fonctionnelle et Evolutive, CNRS, Montpellier, France Reliable population abundance estimates are essential for conservation, but remain challenging to obtain for cetaceans. The Gulf of Corinth, in Greece, hosts local populations of striped and short-beaked common dolphins. We estimated the combined abundance of the two species (the latter only found in mixed-species groups) in years 2011-2014 using photographic identification and capture-recapture models. We considered a subset of 22,039 high-resolution, high-quality photos featuring appropriately marked dorsal fins. The proportion of unmarked individuals was calculated based on the number of photographs of marked and unmarked dorsal fins obtained daily. Our 4-year average estimate was 1,504 individuals (95% CI 1,376-1,644). This estimate is almost twice as large as a published estimate obtained in 2009 with comparable methods (835 animals; 95% CI 631-1,106). An actual 80% population increase was ruled out. The 2009 sample (23 sampled groups and 116 capture histories) was 2.7 times smaller than the one in 2011-2014 (average of xxxx sampled groups and 311 capture histories per year). Additionally, it only covered the central portion of the Gulf. To better understand the discrepancy, we tested if either insufficient spatial coverage or insufficient sample size in 2009 may have resulted in underestimation of population abundance. First, spatial resampling of the 2012 dataset within the smaller area sampled in 2009 yielded no significant difference in abundance. Second, through randomly re-sampling, we reduced the 2012 sample size to that of 2009. We performed 100 permutations, extracted a capture matrix from each simulated sample and re-estimated abundance. The resulting point estimates were extremely variable, ranging between 716 and 3,174 animals. In conclusion, while spatial coverage did not seem to affect abundance estimates, reducing the number of sampled groups negatively affected accuracy. Simulations such as those outlined here can improve abundance estimates by ensuring that they rely on an appropriate sample size

Short‐beaked common dolphins in the Gulf of Corinth are critically endangered

1. Local populations ('subpopulations') of globally abundant species can be exposed to human impacts that threaten their viability. Given the value of cetacean subpopulations as Evolutionary Significant Units, keystone and umbrella species, it is important to assess their conservation status separately and propose area-specific conservation measures. 2. We used a threat assessment process and applied IUCN Red List criteria to a regional population of short-beaked common dolphins Delphinus delphis in the semi-enclosed Gulf of Corinth, Greece. Available population-specific information about abundance and trends were compiled. The geographic range of the population (Area of occupancy and Extent of occurrence) was estimated, and the probability of extinction calculated through stochastic population modelling. 3. The subpopulation qualified as Endangered according to criterion A (population size reduction over three generations) and B (geographic range), and as Critically Endangered under criterion C (population size and decline) and D (very small or restricted population). The probability of extinction was estimated to be ≥ 50% in three generations, qualifying the subpopulation as Critically Endangered under criterion E (quantitative analysis). We concluded that the subpopulation should be classified as Critically Endangered. 4. Considering the high extinction risk faced by this subpopulation we recommend that a) immediate action is taken to mitigate anthropogenic impacts known or suspected to have a negative impact on cetaceans in the area (particularly commercial fishing, underwater noise, pollution and maritime traffic) and b) a Marine Protected Area is established in the Gulf of Corinth as a management tool for enforcing conservation action and facilitating the recovery of common dolphins

Assessing the dynamics of hybridization through a matrix modelling approach

International audienceHybridization affects the evolution and conservation status of species and populations. Because the dynamics of hybridization is driven by reproduction and survival of parental and admixed individuals, demographic modelling is a valuable tool to assess the effects of hybridization on population viability, e.g., under different management scenarios. While matrix models have been used to assess the long-term consequences of hybridization between crops and wild plants, to our knowledge they have not been developed for animal species. Here, we present a new matrix population model to project population dynamics in a system with two parental species or populations that interbreed. We consider the dynamics of males and females of the two parental groups as separate components, each described by species-specific vectors of initial abundance and projection matrices. Then we model hybridization as the production of hybrid fertile offspring due to the interaction of reproductive individuals of different parental species. Finally, we apply the model to two real-world case studies regarding a terrestrial and a marine mammal species in the presence of hybridization. Specifically, we investigate 1) the genomic extinction probability of two interbreeding dolphin species within a semi-enclosed gulf in Greece, under different hybrids’ fitness scenarios, 2) the possible outcomes of wolf x dog hybridization events for an expanding wolf population in Italy, under different reproductive isolation scenarios, 3) the sensitivity of the probability of genomic extinction to the main demographic parameters in the two case studies

Assessing dolphin extinction risk in presence of hybridization

Hybridization has been documented in several marine mammal species. Human disturbance can increase hybridization rates by affecting species distribution and abundance. Depleted species, in particular, may face genomic extinction due to lack of conspecific mates and high introgression rates. Understanding how introgressive hybridization can lead to genomic extinction helps identify the management action needed to protect threatened species and populations. However, data on hybridization rates and fitness parameters (i.e., fertility and survival) of parental and admixed individuals are often missing. In such cases demographic models can be used to: 1) project population dynamics under possible hybrid and parental fitness hypotheses (i.e., hybrid vigour, outbreeding depression) and 2) identify the main demographic parameters affecting population extinction. Here, we present a new matrix population model to project hybridization dynamics, and we use it to evaluate the hybridization outcomes for two odontocete populations interbreeding in the semi-enclosed Gulf of Corinth, Greece: the common dolphin Delphinus delphis and the 60-fold more abundant striped dolphin Stenella coeruleoalba. We projected hybridization dynamics for 100 years under different fitness scenarios for parental and admixed individuals. We performed a sensitivity analysis to identify the main demographic parameters affecting the probability of genomic extinction of the two populations. Common dolphins were predicted to go extinct in one generation time (16 years), regardless of the scenario. The growth rate of striped dolphins was affected by hybridization, and their population could eventually reach genomic extinction—except for scenarios where the fitness of admixed individuals was lower than that of parentals. The probability of extinction of both striped and common dolphins was most affected by the survival of mature and juvenile individuals. For common dolphins, the low initial abundance was also important. Our study shows that hybridization represents an additional and important threat that may contribute to the eradication of local populations