Hybridization mechanisms between the endangered marble trout (Salmo marmoratus) and the brown trout (Salmo trutta) as revealed by in-stream experiments

Populations of the marble trout (Salmo marmoratus) are critically declining due to introgression by brown trout (S. trutta) strains. Hybrids between the two forms are fertile and presently predominant in most rivers of the species’ range.The involved hybridization mechanisms have been studied through two large scale in-stream experiments (Driselpoh and Stopnikarca) as 50% of each species have been stocked at the age of one year in fishless streams, each fish being individually marked. Diagnostic molecular markers were applied to test a partial reproductive isolation between the two species. Emphasis was put on survival and growth patterns of stocked fish (parental generation) as well as on fish hatched within the stream (F₁ generation).No evidence of a partial reproductive barrier between the two species was observed. Survival of the parental generation depended on the year in both streams, as well as on the species in Stopnikarca, but was identical for both species in Driselpoh. In both streams survival of instream hatched individuals measured from 0+ to 2+ was lower for brown trout. In Driselpoh, F₁ 0+, 1+ and 2+ hybrids were larger than pure individuals. Larger hybrids were only observed in Stopnikarca when analyses focused on individuals in inter-specific competition suggesting that heterosis and stress effects may explain the observed size differences.Our results point out important ecological differences between marble and brown trout and have shown that hybridization can easily take place. The findings indicate that high F₁ hybrid presence, survival and heterosis effects may impede marble trout rehabilitation in the area.     

Potential factors controlling the population viability of newly introduced endangered marble trout populations

While several population viability analyses (PVAs) have been performed on anadromous salmonids, less attention has been given to stream-living salmonids. In this work, we explore the role of PVA as a tool in the recovery of threatened stream-living salmonid species. The analysis has been performed with reference to marble trout Salmo marmoratus, a salmonid with a limited geographic distribution and at risk of extinction due to hybridization with the non-native introduced brown trout. Demographic parameters, such as survival, fecundity and density-dependent patterns were estimated from an eight year on-going monitoring program of two translocated marble trout populations in pristine, previously fishless streams (Zakojska and Gorska) in the Soca and Idrijca river basins (Slovenia). To explore the importance of disturbance events such as floods on marble trout population dynamics, we performed a PVA under three scenarios: (1) occurrence of both severe and moderate floods; (2) occurrence of only moderate floods; (3) no flood events. Our analysis shows that population viability is threatened only by severe flood events, otherwise the two populations prove to be fairly stable with population abundance fluctuating around stream carrying capacity. A sensitivity analysis performed on model parameters highlighted that density-dependence in first-year survival and the magnitude of reduction in population size after a severe flood are the two most crucial parameters affecting population abundance and quasi-extinction probability, respectively. While only extreme floods can drive the population to extinction, the increase in juvenile survival when population abundance collapses after a major flood may allow the populations to quickly recover from few reproductive individuals back to stream carrying capacity.     

Ecological consequences of invasive lake trout on river otters in Yellowstone National Park

The introduction of lake trout (Salvelinus namaycush) to Yellowstone Lake in Yellowstone National Park has contributed to a significant decline in the endangered Yellowstone cutthroat trout (Oncorhynchus clarki bouvieri), leading to concern over the persistence of this subspecies but also to piscivorous predators in this community. We assessed the impact of lake trout on a key piscivore, the river otter (Lontra canadensis) in two lakes in Yellowstone National Park. Yellowstone Lake continues to support a native cutthroat trout population, although the recent introduction of lake trout has dramatically impacted the cutthroat trout population. Nearby Lewis Lake has an entirely introduced fish fauna of lake trout, brown trout (Salmo trutta), and Utah chub (Gilia atraria) but lacks cutthroat trout. Analysis of otter scat from Yellowstone Lake implicated trout (lake or cutthroat trout) as a major prey item (57% of scat), whereas stable isotopes identified longnose suckers (Catostomus catostomus) as the primary prey there (58% of diet). By contrast, scat from Lewis Lake implicated minnows, presumably Utah chub, as the primary prey for otters occupying that lake (86%), while stable isotopes implicated brown trout (64%) over both lake trout and Utah chub (36% combined). Our data establish the importance of alternative prey to otters and suggest that lake trout-induced reductions in cutthroat trout may not be catastrophic for otter populations here. These data do not necessarily exonerate lake trout, as their impact on other species, most notably grizzly bears (Ursus arctos) and piscivorous birds, has been documented to be substantial, and further data on the nutritional value of alternate prey are required to confirm or refute a working hypothesis that otter populations will continue to thrive in the face of the lake trout invasion.     

Do native species limit survival of reintroduced Atlantic salmon in historic rearing streams?

Reintroduction of extirpated populations creates a unique context that can exacerbate the effects of interactions among species. Thus, reintroduced populations may be particularly vulnerable to predators and competitors, including native species with which they historically coexisted. In this study, we evaluated the effect of native fishes on survival of reintroduced Atlantic salmon (Salmo salar) in the Connecticut River basin, where the native salmon population is extinct. Juvenile salmon are stocked annually in many Connecticut River tributaries. We sampled salmon reintroduction sites across tributaries with different fish communities to determine whether native fish reduce the success of salmon reintroductions (N = 19 site-years). Increased density of slimy sculpin (Cottus cognatus), a native generalist predator, was associated with reduced recruitment of reintroduced salmon. Salmon first-summer survival declined with increased sculpin density across sites, and low first-summer survival led to reduced densities of overyearling salmon the subsequent year. Hierarchical partitioning analysis showed that the negative relationship between sculpin and salmon was independent of potentially confounding variation in other fish community or habitat characteristics. Negative effects of native, historically-sympatric species, particularly generalist predators, can impede restoration of extirpated populations.     

Hatchery introgression blurs ancient hybridization between brown trout (Salmo trutta) lineages as indicated by complementary allozymes and mtDNA markers

Populations living on the periphery of a species range are subjected to intense habitat pressures that stress their vulnerability to threats. South Iberian brown trout (Salmo trutta) populations are located on the southwestern boundary of the species range in Europe. This region has been described as a contact zone between Atlantic and Mediterranean populations in other fish species, and allozyme data detected natural hybridization between native Atlantic and Mediterranean brown trout in this area. Nevertheless, native pattern of populations relationships are threatened by hybridization with exogenous hatchery fish. Allozyme data and complete mtDNA control region sequences were used to analyse the ongoing processes of human mediated hybridization between native and hatchery brown trout in this region. Estimates of the persistence of hatchery genes detected a high level of introgression in some of the sampled locations (hatchery ancestry more than 25% in GF-1, GF-2 and GF-3), but results differed from both kinds of markers. The low intrapopulation diversity (H_s = 0.051) indicated that genetic drift could explain discrepancies between markers. At individual level, the complementary use of both markers detected more hatchery origin fish than those detected by the use of a single technique. Based on these results, the importance of considering a large number of genetic markers to evaluate introgression accurately is emphasized. The ability of the current management policies to the protection and conservation of marginal populations that retain complex and special evolutionary histories such as those studied is also questioned.     

Survival of the western pond turtle (Emys marmorata) in an urban California environment

The western pond turtle Emys (formerly Clemmys) marmorata is declining throughout its range, primarily due to loss of habitat via urbanization and conversion to agriculture. Urban waterways present several important challenges to freshwater turtle populations, but they also present an opportunity to maintain declining species in a ubiquitous habitat that has high public visibility. The arboretum waterway on the University of California, Davis campus is an example of an extensively altered urban habitat that supports a relatively large E. marmorata population. Over the last 6 years, we monitored the turtle population inhabiting the arboretum waterway to determine the demographic health of the population, and the challenges and opportunities that urban environments pose for pond turtles. Since 1993, the naturally existing arboretum pond turtle population has declined by approximately 40% and has shown little natural recruitment. During this time, we also introduced 31 headstarted turtles into the arboretum. Headstarting is the process of raising juveniles in captivity until they have outgrown their period of greatest vulnerability to predators, and then releasing them into the wild. Our headstarting results demonstrate that this contentious strategy is a viable option for adding young turtles to the population, although it does not address the causes of decline. Over the course of our study, we encountered nine species of non-native turtles in the waterway, and these appear to be a serious threat to the native species. As more habitat becomes urbanized, it is increasingly important to understand how freshwater turtles, such as E. marmorata, adapt to urban waterways and the impact of non-native turtles on native turtle species. Our strong feeling is that urban waterways can provide habitat for viable populations of freshwater turtles and showcase them to the public, but both the aquatic and terrestrial habitat must be managed according to the biological requirements of individual species.     

Does natural acidity mediate interactions between introduced brown trout, native fish, crayfish and other invertebrates in West Coast New Zealand streams?

The presence of introduced brown trout (Salmo trutta) on the distribution of native crayfish (Paranephrops planifrons), native galaxiid fishes (Galaxias spp.) and invertebrate fauna was investigated in 18 West Coast New Zealand streams (8 with trout and 10 without trout) differing in chemical characteristics. Gut contents of trout, crayfish and eels were also examined to evaluate whether competition or predation could be linked to the patterns found. Abundances of crayfish and galaxiids were significantly lower in streams with trout, but in streams without trout, substrate size was one of the most important factors determining crayfish abundance. In contrast to crayfish, other macroinvertebrates were more abundant in trout streams than streams without trout and significantly more taxa were found in streams with trout. Macroinvertebrate abundance was related to environmental factors, such as pH, substrate, depth and total nitrogen. Gut content analysis showed an overlap in diet (mostly invertebrates) between trout and eels. Crayfish, however, had a more omnivorous diet where detritus was the most frequently occurring food material. Differences in chemical characteristics marked the streams with and without trout. Thus, trout were not present in streams with pH < 6.0. Crayfish and galaxiids were present in streams with pH ranging from 4.1 to 7.9, and those with pH < 6.0 may function as trout-free refuges where larger populations of these species may persist. However, other macroinvertebrate taxa may be more negatively affected by acidification than by trout. By protecting naturally acidic, brown water streams, New Zealand crayfish and galaxiid fish populations can be conserved within geographic areas where trout are present.     

Does restocking with Japanese quail or hybrids affect native populations of common quail Coturnix coturnix?

Natural populations of the common quail Coturnix coturnix may hybridize in the wild with non-native individuals (Japanese quail Coturnix japonica or hybrids) as a result of restocking for hunting purposes. Several laboratory studies suggest that this could lead to a decline in the impulse to migrate in the common quail, and a drop in the frequency of phenotypes showing this tendency. This could lead to an increase in common quail populations in North Africa and a decrease in Europe. This paper provides new data on the proportion of hybrids in Catalonia (Northeast Spain) over 24 years (1983-2006) showing how restocking with Japanese quail or hybrids affects native populations of common quail. The first hybrids were detected in 1990 with an estimate of 4.65% of non-native individuals during the breeding season of wild common quail populations. No increase in non-native or hybrid numbers was detected during the study period, indicating that restocking poses no serious conservation problems at present. However, this may change in the near future, either with or without changes in the current scenario. A prudent policy with regard to restocking with non-native individuals is suggested. Moreover, further studies are needed to clarify the extent of this conservation problem.     

An acidic snowmelt event in a new jersey stream: Evidence of effects on an indigenous trout population

Van Campens Brook is a circumneutral stream in northwestern New Jersey that supports reproducing populations of brook trout (Salvelinus fontinalis), brown trout (Salmo trutta) and rainbow trout (Oncorhynchus mykiss). A short-term pH depression occurred in the stream following a snowmelt in the spring of 1984. A stream pH of 4.5 was recorded shortly after the onset of the snowmelt and the pH remained depressed (5.2) a week later. Stream pH did not fall below 6.2 following other rain and snowmelt events monitored during 1985–1987. An electrofishing survey conducted in 1985 revealed a near-total absence of 1984 year-class rainbow trout, spring spawners that are highly sensitive to acidity. Brook and brown trout spawning appeared to be unaffected. Rainbow trout reproductive success was good during 1985–87.     

Options for liming rivers to ameliorate acidity — A UK perspective

The options for large scale liming of river systems are reviewed with particular reference to the River Tywi in Wales, a major salmonid river with a reservoir in the upper catchment. For hydrological source area liming the cost of lime transport is high due to remoteness and inaccessibility. The concern of potential damage to wetland mires of conservation value is considered. Re-treatment intervals are expected to be 5–10 years, but results from sub-catchment experiments indicate that treatment longevity and the pattern of ecological recovery are uncertain. Flow-related dosing systems for rivers avoid impacts on wetlands but would treat only the main river. Reliability may be problematical though the reservoir provides a margin of safety against system failure. Reservoirs can be limed to treat the main river outflow. This avoids the problems of power supply. For the River Tywi, the financial costs of both direct treatment methods are lower than for catchment liming and comparable with estimates of the economic benefit to the fishery. The system currently operated on the Tywi is reservoir treatment. Results from the first 3 years demonstrate colonization of the main river by acid intolerant invertebrate taxa and clear increases in populations of juvenile Atlantic salmon, Salmo salar L. and sea/brown trout. Salmo trutta L.     

Evidence of indirect impacts of introduced trout on native amphibians via facilitation of a shared predator

Hyperpredation occurs when non-native prey facilitate invasive predators, which then suppress native prey. Direct impacts of introduced fish on amphibians are well studied, but the role of fish in supporting shared predators has not been considered. We present evidence for indirect effects of trout on amphibians through snake predation. Analyses of the diet, distribution and density of the Pacific coast aquatic garter snake (Thamnophis atratus) relative to the sympatric common garter snake (Thamnophis sirtalis) in the Klamath Mountains of California suggest that trout introductions facilitated expansion of T. atratus by providing alternative prey. T. atratus diet included trout and amphibians whereas T. sirtalis preyed solely upon amphibians. The distribution and density of T. atratus matched that of introduced trout instead of native amphibians. Populations of T. atratus could reach high densities in the absence of high densities of amphibians. When the snakes opportunistically prey upon amphibians whose numbers are already directly impacted by trout, they can cause significant additional declines. When T. atratus was present in lake basins, native Cascades frogs (Rana cascadae) were rarer than in basins without T. atratus. This case differs from other hyperpredation studies because the two prey species also interact via intraguild predation. Given the worldwide practice of stocking fish into aquatic habitats, it is important to understand the consequences of the practice on food-web structure and ecosystem functioning. Bottom-up impacts of introduced predators should be considered as well as top-down so that managers can incorporate the range of ecosystem-level effects into conservation goals and decisions.     

Habitat characteristics of adult frosted elfins (Callophrys irus) in sandplain communities of southeastern Massachusetts, USA

Changes to land use and disturbance frequency threaten disturbance-dependent Lepidoptera within sandplain habitats of the northeastern United States. The frosted elfin (Callophrys irus) is a rare and declining monophagous butterfly that is found in xeric open habitats maintained by disturbance. We surveyed potential habitat for adult frosted elfins at four sites containing frosted elfin populations in southeastern Massachusetts, United States. Based on the survey data, we used kernel density estimation to establish separate adult frosted elfin density classes, and then used regression tree analysis to describe the relationship between density and habitat features. Adult frosted elfin density was greatest when the host plant, wild indigo (Baptisia tinctoria), density was >2.6 plants/m² and tree canopy cover was <29%. Frosted elfin density was inversely related to tree cover and declined when the density of wild indigo was <2.6 plants/m² and shrub cover was ?16%. Even small quantities of non-native shrub cover negatively affected elfin densities. This effect was more pronounced when native herbaceous cover was <36%. Our results indicate that management for frosted elfins should aim to increase both wild indigo density and native herbaceous cover and limit native tree and shrub cover in open sandplain habitats. Elimination of non-native shrub cover is also recommended because of the negative effects of even low non-native shrub cover on frosted elfin densities. The maintenance of patches of early successional sandplain habitat with the combination of low tree and shrub cover, high host plant densities, and the absence of non-native shrubs appears essential for frosted elfin persistence, but may also be beneficial for a number of other rare sandplain insects and plant species.     

Ecology of the native and introduced crayfishes Austropotamobius pallipes and Procambarus clarkii in southern Spain and implications for conservation of the native species

The former and present distribution of white clawed crayfish (Austropotamobius pallipes) in the province of Granada (southern Spain) is studied. Before 1980 it was widely distributed but at present only 16 populations exist. The decline is related to the presence of the freshwater red-swamp crayfish (Procambarus clarkii), an American species, vector of the aphanomycosis disease, introduced to the Iberian Peninsula in 1974 and now widely distributed in the watercourses and marshes of southern Spain. To establish an appropriate conservation policy for A. pallipes at its southernmost distribution limit, we studied watercourses from two river basins, Genil and Guadiana Menor, (tributaries of the Guadalquivir River). P. clarkii inhabits the medium to lower reaches of these two river basins (with its upper limit at 820 m a.s.l.). The distribution of this species was best explained by the effect of three of the 12 analyzed variables: altitude, water-current and minimum winter temperatures. From our results, the repopulation of the native crayfish is almost impossible in those reaches inhabited by P. clarkii. However, based on the habitat selection study, it is clear that upper reaches are unsuitable for the red-swamp crayfish, where the native white-clawed crayfish may have greater survival possibilities, and these sites can be used for future restocking projects.     

Management regimes for a plant invader differentially impact resident communities

Management of plant invaders causes disturbance and the compounding effects of both invasion and management on biodiversity merit rigorous assessment. We explored the impacts of both plant invasion and management disturbance in coastal dune communities of Australia invaded by the introduced shrub bitou bush (Chrysanthemoides monilifera ssp. rotundata). We compared the effects of intensive, manually based invader control with those of extensive control (mainly herbicide spraying from aircraft) across fore dune communities. We examined one management regime, which was typically intensive, in hind dune communities. Our main aim was to test the prediction that intensive methods would achieve better biodiversity outcomes than extensive approaches in fore dune communities. We found that extensive management created native species complements that diverged from non-invaded sites while intensive management approached non-invaded site conditions. However, intensively managed sites were also richer in other exotic species than extensively managed sites. Thus, while biodiversity outcomes were better under intensive management, the risk profile of such sites was increased by the greater array of exotics that could potentially replace the original invader. The positive effects of management evident on some fore dunes were not found in hind dunes, where managed sites had the highest exotic species richness and similar bitou bush seedling abundance as both non-invaded and bitou-invaded sites. Hind dune managed sites were also compositionally distinct from non-invaded sites. Thus fore and hind dune communities exhibited different responses to bitou management regimes.     

Relationship of biotic and abiotic factors to recruitment patterns in Margaritifera margaritifera

We investigated relationships of biotic and abiotic factors to recruitment patterns of the endangered freshwater pearl mussel (Margaritifera margaritifera) in 10 Swedish streams. We found that the maximum proportion of gravid mussels did not differ between streams with and without recent recruitment. Moreover, the mean glochidial load on trout (Salmo trutta), which was positively related to adult mussel density, did not differ significantly between these stream types. Thus, the larval stages of the freshwater pearl mussel were not related to recruitment failure. Instead, recruitment is probably hindered at the next stage in the life history of the mussels, the benthic stage, and may be related to sedimentation as turbidity was four times greater in streams lacking recent recruitment than in streams with recent recruitment. Furthermore, we found that juvenile mussel density was positively related to the number of glochidial infections per stream area in streams with ongoing recruitment, indicating that successful recruitment in these streams may depend on both mussel and trout density. Future research should thus examine biotic interactions between mussels and trout as well as the effects of sedimentation on benthic-living mussels.     

Microsatellite analysis of genetic population structure of the endangered cyprinid Anaecypris hispanica in Portugal: implications for conservation

The endangered fish species Anaecypris hispanica is restricted to eight disjunct populations in the Portuguese Guadiana drainage. The genetic structure of these populations was studied in order to determine levels of genetic variation within and among populations and suggest implications for conservation of the species. Based on five microsatellite loci, the null hypothesis of population homogeneity was tested. Tests for genetic differentiation revealed highly significant differences for pairwise comparisons between all populations, and substantial overall population subdivision (F_ST=0.112). All sampled populations contained unique alleles. Our findings indicate marked genetic structuring and emphasise limited dispersal ability. The high levels of genetic diversity detected within and among A. hispanica populations suggest, however, that the observed fragmentation and reduction in population size of some populations during the last two decades, has impacted little on levels of genetic variability. Data imply that most A. hispanica populations should be managed as distinct units and that each has a high conservation value containing unique genetic variation. It is argued that geographic patterns of genetic structuring indicate the existence of eight management units.     

Agricultural insect pest compromises survival of two endemic Braya (Brassicaceae)

Agro-ecosystems support a vast array of non-native insects, but the potential of these insects to invade and degrade natural ecosystems is largely unknown. Plutella xylostella L. (diamondback moth) is a global agricultural pest that is not native to North America. It feeds on members of the Brassicaceae family, including the endangered Braya longii (Fernald) (Long’s braya) and threatened B. fernaldii (Abbe) (Fernald’s braya) which are endemic to the limestone barrens of Newfoundland, Canada. The immigration of P. xylostella from overwintering sites in the United States to this rare natural ecosystem was monitored with pheromone traps between 2003 and 2005. After their mass immigration in early summer, females lay eggs on an average of 30% of the B. longii and 16% of the B. fernaldii population. Larval feeding reduces the mean seed output of infested plants by 60%, from 10.8 to 4.3 seeds/fruit, and damages 26% of their leaves. There are residual and long-term effects of this herbivory, as many dead braya had higher numbers of eggs, and subsequent leaf and fruit damage one to three years before they died. High summer air temperatures and low precipitation allowed this pest to become multivoltine, resulting in additive damage to braya individuals. Presently, insufficient attention is directed to the impacts of agricultural pests on native ecosystems and rare host plants; hence, there is a need for both the conservation and agricultural communities to cooperate in mitigating the impacts of these pests on native biodiversity.     

Disperser communities and legacies of goat grazing determine forest succession on the remote Three Kings Islands, New Zealand

Many remote islands are degraded as a result of deforestation and browsing of vegetation by introduced goats. Goat eradication is therefore a focus for island restoration, but there are few long-term records of change on islands after eradications. In 1946, three permanent plots were established immediately after goats were eradicated from Great Island (Manawa Tawhi), 60 km from northern New Zealand, and provide a 57-year record of change across a sequence of forest succession. Since 1946, the native and non-native bird communities that disperse 75% of the woody flora have increased from six to eight species and bird-dispersed woody plants in plots have increased from 7 to 11 species. After 1946, palatable trees were recruited in the plots. Unpalatable understorey sedges, present when goats were abundant, have persisted and may impede tree seedling establishment. Of the bird-dispersed woody plant species, 41% occur in the plots compared with 67% of the non-bird-dispersed species. Large-seeded species were unable to germinate away from parents until native pigeons Hemiphaga novaeseelandiae were present during the last decade. Forest succession is a consequence of interactions between the legacy of goat grazing and current disperser communities. Survival of seed-limited rare plants is not guaranteed in these circumstances. Although non-native goats no longer influence succession directly, non-native birds have been and remain important components of the disperser community. Our study supports the view that a whole-ecosystem understanding of the interactions between native and non-native species is needed to predict the consequences of eradications on islands worldwide.     

Phylogeography and conservation of the populations of Zootoca vivipara carniolica

The lizard Zootoca vivipara has both oviparous and viviparous populations which belong to distinct clades. This study aims to elucidate the geographic distribution, phylogeography and conservation priority of the oviparous subspecies, Zootoca vivipara carniolica, that has recently been identified in Slovenia. We studied seven Slovenian populations, two northeastern Italian populations and five northwestern Italian populations. The seven cytochrome b haplotypes that we identified from the Slovenian and Italian oviparous populations form a monophyletic basal clade. The high homogeneity of the Slovenian and northeastern Italian populations (nucleotide diversity π=0.06%) is a striking contrast with the pattern observed in northwest Italy where each of the five populations studied presents a private haplotype (π=1.03%). The results obtained suggest that all the extant lineages of Z. v. carniolica have originated in an Italian refuge. The reproductive and phylogenetic distinctiveness of Z. v. carniolica clearly justifies conservation of its populations, especially in Italy where the highest genetic diversity and the most ancestral haplotype were observed.     

Genetic isolation and morphological divergence of Black Sea bottlenose dolphins

The Black Sea is a semi-enclosed body of water that differs from the adjacent Mediterranean Sea in terms of its biodiversity, oceanographical and ecological characteristics. There is growing international concern about pollution in the Black Sea and other anthropogenic threats to its fauna. The bottlenose dolphin (Tursiops truncatus) is one of three species of cetaceans living in the Azov-Black Sea basin. Despite considerable research on bottlenose dolphins elsewhere, the extent of human impacts on the Black Sea populations is unknown. Previous attempts to award special conservation status to Black Sea cetaceans have failed specifically because policy makers have viewed their ecological and evolutionary uniqueness as equivocal. This study assessed divergence between Black Sea, Mediterranean Sea and Atlantic Ocean bottlenose dolphins for 26 cranial measurements (n = 75 adult bottlenose dolphin skulls) and mitochondrial DNA (n = 99 individuals). Black Sea bottlenose dolphins are smaller than those in the Mediterranean, and possess a uniquely shaped skull. As in a previous study, we found the Black Sea population to be genetically distinct, with relatively low levels of mtDNA diversity. Population genetic models suggest that Black Sea bottlenose dolphins have so little gene flow with the Mediterranean due to historical isolation that they should be managed separately.