Intensive beach management as an improved sea turtle conservation strategy in Mexico

We evaluate the role of intensive beach management, meaning intense patrolling and nest reburial to a central hatchery, as a strategy for improving the success of sea turtle conservation at nesting sites in Mexico. We report the results of an experimental program at Playa Cuixmala, Jalisco, western Mexico. Sea turtle conservation efforts in Mexico have, in general, poor results because of lack of funds, which leads to insufficient beach protection and severe negative effects of nest removal on hatching success and sex ratios. Alternative strategies are needed to optimize limited resources. We predicted that intensive beach management, which included intense patrolling and careful nest reburial, could be an effective way to maximize nest survival and hatchling release under limited financial and human resources. The results of our 9-year study were very positive. Survival rate increased several fold during the study period. Hatching success and sex ratios were not significantly different between in-situ and removed nests. Survival in removed nests was, however, much higher that in-situ nests, because of predation and beach erosion. In total, the small (3 km length) Playa Cuixmala became the second most productive sea turtle nesting beach in the region because of these concentrated efforts. Intense beach management can be an important technique for sea turtle conservation, and can be properly applied to small beaches or the most productive sections of large beaches.     

Conservation and the scarecrow effect: Can human activity benefit threatened species by displacing predators?

Most wild animals show direct negative responses to human disturbance; however, disturbance may also have positive indirect effects by altering species interactions. In the Caribbean, introduced mongooses (Herpestes javanicus) are an important diurnal predator of the nests of critically endangered hawksbill sea turtles (Eretmochelys imbricata). We asked whether daytime visitor activity could benefit hawksbills by reducing mongoose activity in nesting habitat. We used track monitoring sites to measure how mongooses alter their space use in response to fluctuating human beach use and availability of hawksbill nests, and we estimated the indirect impact of human disturbance on nest predation for 5 years of hawksbill nesting. Human activity substantially decreased mongoose use of nesting habitat. Mongoose activity increased with abundance of nests and was lower at the edge than the interior of patches of beach vegetation, but neither factor altered relative sensitivity to disturbance. We estimated that, in addition to deterring mongooses from accessing nests on the open beach, human activity has the potential to reduce predation of nests in vegetation by up to 56% at our site, with the greatest per capita impact at low (<50) visitor numbers. Many forms of human activity negatively affect sea turtles, but our study indicates that there are positive aspects of daytime use of nesting beaches. Optimizing the trade-off between positive and negative impacts of disturbance could provide a useful approach for regulating tourist activity in critical habitat for threatened species.     

Edge effects on nesting success of cavity-nesting birds in fragmented forests

Forest fragmentation leads to the creation of isolated forest patches and habitat edges with subsequent impact on forest-interior bird species. Although the effects of fragmentation and edge on avian nesting success are well documented for open cup-nesting species in eastern deciduous forests in North America, it is unclear whether these effects are common for all birds nesting in predominantly forested landscapes. In particular, edge effects on nesting success of cavity-nesting birds are poorly understood. Using natural cavity nests, we examined nesting success of four species of cavity-nesting birds (two nonexcavators and two excavators), the yellow-rumped flycatcher (Ficedula zanthopygia), the great tit (Parus major), the great spotted woodpecker (Picoides major), and the grey-faced woodpecker (Picus canus) in relation to forest edges in Zuojia Nature Reserve, Jilin province, northeastern China. Our primary objective was to assess whether distance to the edge of agricultural lands was related to nesting success for cavity-nesting birds in fragmented forests. A total of 439 natural cavity nests of the four species were located and monitored during four breeding seasons. Probability of nest success was influenced by distance to forest edge for nonexcavators, but not for excavators. The rate of nesting success of the two nonexcavators, yellow-rumped flycatcher and the great tit, increased with distance from the edges. For all cavity nests, nesting success was 0.43 at 0-100 m, 0.56 at 101-200 m, 0.68 at 201-300 m, 0.61 at 301-400 m, 0.77 at 401-500 m from the edges. Nesting success ranged from 0.57 for the yellow-rumped flycatcher to 0.89 for the Grey-faced Woodpecker. Failed nests were often occupied by nest-site competitors (accounting for 68%). However, predation only accounted for 20% of all nest failures. Our results suggest that negative edge effects do exist for some cavity-nesting birds, especially for nonexcavator species.     

Vegetation and sand characteristics influencing nesting activity of Caretta caretta on Sekania beach

Despite its relatively small length (650 m), Sekania beach on Zakynthos island (Ionian sea) is the single most important Caretta caretta L. nesting beach in the Mediterranean Sea. The aim of this work was to tackle the possible relationships of sand and vegetation characteristics with the nesting activity of sea turtle C. caretta. The vegetation structure and distribution along the sandy beach was studied with the use of line transect method. Grouping of plant species was revealed through an ordination method. Plant groups were distinguished and mapped. Sand texture, pH, and organic matter were measured on the transects. Nesting activity was also mapped on the beach and hatching success was recorded. It was concluded that where sand salinity is high enough to prevent vegetation development, wet sand is located at a threshold depth for excavating an egg chamber. It seems that well-sorted sand grains favor nesting activity on the beach. The increase of fine sand - from east to west - is proportional with the reduction of nesting density. The data collected for this study are organized in a GIS database, which could be the basis for the establishment of an integrated monitoring system for Sekania beach.     

Low reproductive success of leatherback turtles, Dermochelys coriacea, is due to high embryonic mortality

We examined the mechanism responsible for low reproductive success in leatherback turtles (Dermochelys coriacea) at Playa Grande, Costa Rica: low egg fertilization versus high rates of embryonic death. Leatherbacks at this beach had a high rate of fertility (=93.3%±2.5%, n=819). We incubated 10 eggs from every clutch encountered of 19 females during 3 months of the 1998-1999 nesting season. Fertility rate of some females decreased during the nesting season, but overall was high. Detection of fertility was difficult using standard methods because fertility rates cannot be determined accurately from nests excavated after hatching because of egg decomposition. Removal and incubation of eggs from nests provided a better estimate. Embryonic death, particularly in the beginning of incubation before embryos are visible to the unaided eye, was the cause of low hatching success in this population. Hatching success increased with increasing fertility and differed between females, with some mothers having 71-81% success and others 23-32%. Embryonic death and not low egg fertility drives poor recruitment at Playa Grande. Improved conservation of this species at Playa Grande will require a better understanding of the mechanism behind embryonic death.     

A review of sea turtle nesting activity along the Mediterranean coast of Turkey

Many parts of the Turkish coastline are important nesting grounds for sea turtles. The aim of this study was to assess the present state of sea turtle populations along the coastline of Turkey, by evaluating research conducted at various nesting grounds from 1979 to 2000. The results of the evaluation indicate that the Turkish coastline is the most important nesting area for Chelonia mydas, and the third most important nesting area for Caretta caretta after Greece and Libya (if nesting estimates for Libya are correct) in the entire Mediterranean. The most important C. caretta nesting beaches in Turkey are Dalyan (11.9%), Kumluca (11.3%), Belek (27.9%), Kizilot, (8.9%) and Anamur (8.8%), while those for C. mydas are Kazanli (24.1%) and Akyatan (54.4%). These sites are classified as “Nesting Areas of 1st Degree Importance”. Annual mean nest numbers along the coastline of Turkey are estimated to be ca. 2000 for C. caretta and 650 for C. mydas. Assuming that each adult female sea turtle nests three times per season, the annual numbers of nesting females along the beaches of Turkey range between about 500 and 800 for C. caretta and 130 and 300 for C. mydas. Annual nesting densities along the 204 km beach strip, which includes 17 important nesting grounds in Turkey, were 11.3 nests/km for C. caretta and 19.2 nests/km for C. mydas.     

Effectiveness of different conservation measures for loggerhead sea turtle (Caretta caretta) nests at Zakynthos Island, Greece

In this paper, we evaluate the effectiveness of different well-tested conservation techniques in an effort to successfully protect sea turtle nests. From an eight-year study on the island of Zakynthos, West Greece, we have experimentally investigated the effectiveness of two different conservation techniques applied to loggerhead sea turtle nests and provided statistical measures to evaluate their conservation value. The categories of nests evaluated include: (i) nests incubated in situ, (ii) translocated into a beach hatchery, or (iii) protected by metal cages. Results of the analysis showed significant interannual variations in hatching success as obtained for each one of the three groups of nests. Significant differences were also observed when comparing hatching success data among the three groups of nests during the eight-year period. Overall, our results indicate that relocation of nests laid at highly threatened locations and the placement of protective cages on nests in situ provide adequate conservation measures that could allow an increase in hatchling production; although their choice and application should be based on the specific conditions and threats of each nest.     

An analysis of the role of local fishermen in the conservation of the loggerhead turtle (Caretta caretta) in Pontal do Ipiranga, Linhares, ES, Brazil

The role of researchers and fishermen in the clutch management of loggerhead sea turtles was evaluated for 10 nesting seasons at Pontal do Ipiranga TAMAR station, Linhares, ES. The comparison of nests transferred by researchers and locals (carebeiros) showed that clutches transferred by researchers presented higher clutch size. Clutch size between nests transferred by carebeiros and left in situ did not show significant differences. Hatching success was significantly higher for clutches left in situ than for those transferred to other places in the beach or to hatcheries. The clutches transferred exclusively by researchers achieved a higher hatching success than those transferred partially or totally by carebeiros. The relocation time of clutches collected by carebeiros and handed to researchers affected hatching success. It is recommended that clutches be left in situ, provided they have adequate conditions for monitoring, but careful clutch translocation, independent of the interval elapsed after laying, may also constitute a viable technique for the conservation of sea turtles in the region.     

Signage reduces the impact of human disturbance on little tern nesting success in Portugal

This study evaluated the influence of human disturbance in nesting success of little tern (Sterna albifrons) and its interaction with the intrinsic seasonal variation in the birds’ breeding biology. During 2003-2005 we studied little tern nesting ecology in southern Portugal in two different types of habitat: their natural habitat (sandy beaches) and a man-made habitat (salinas). In both habitat types, annual variations were found in the distribution of nest initiation over the breeding season and in the size of the clutches. The percentage of nests producing hatched chicks varied between 26.7% and 66.4% in different years and habitats. The main causes of hatching failure varied between years and habitats, but predation, flooding and human activities were very common. No consistent differences in breeding parameters or nesting success were found between habitats. On sandy beaches, the effect of protective measures (warning signs and wardening) on nesting success, together with differences between years and within each breeding season, were assessed using a logistic regression model. The presence/absence of protective measures was the most important predictor of nesting success, with birds being up to 34 times more likely to succeed with protective measures. Seasonal declines were found for clutch size and egg volume, and season was also an important predictor of nesting success, with nests more likely to succeed earlier in the season. Hence, earlier breeders will be those that benefit more from protective measures, suggesting that conservation efforts for little tern can be maximised if concentrated earlier in the season.     

Effects of landscape composition, habitat features, and nest distribution on predation rates of simulated turtle nests

We investigated predation of simulated turtle nests in an effort to understand how land-use patterns and the availability of nesting habitat may affect turtle recruitment in a region where human populations and associated development are increasing. Simulated nests were patterned after those created by painted turtles (Chrysemys picta), a common aquatic turtle in our study area, and distributed in four patterns (clustered and near pond, scattered and near pond, clustered and far from pond, and scattered and far from pond) around 36 ponds. Landscape composition (500-2000 m from pond perimeters) and habitats surrounding pond edges (an area extending 250 m from the shore of each pond) were then compared with rates of predation at each pond. Nest-site characteristics also were compared to the fate of individual nests. Landscape composition and habitats surrounding ponds apparently had little influence on predation rates. Nest distribution and the immediate habitat features associated with each nest did affect vulnerability to predation. Clumped nests were preyed upon at a higher rate than scattered nests, and nests close to ponds (within 50 m) were more vulnerable to predators than those created far (100-150 m) from a pond. Counter to our expectations, proximity to edge habitats (other than the shore of a pond) reduced the probability that a nest would be detected by predators. Also, nests placed near roads and suburban lawns had a reduced likelihood of predation whereas those placed in agricultural areas or disturbed sites had a greater probability of being preyed upon. Our results suggest that predation of simulated turtle nests may be a consequence of their distribution and location relative to the foraging activities of common nest predators, especially raccoons (Procyon lotor). Efforts to enhance recruitment among declining populations of turtles should consider the abundance and distribution of nesting habitat. Providing additional nesting sites away from predator foraging habitats may reduce nest predation and increase the recruitment of hatchlings into a population.     

Managing predation on ground-nesting birds: The effectiveness of nest exclosures

Ground-nesting birds have declined world-wide, probably partly due to high nest predation. A non-lethal method for decreasing predation uses protective cages at nests. Tests have mainly looked at the effect of such nest exclosures on hatching success and adult predation, but several additional aspects need to be explored for a comprehensive evaluation of this conservation technique. Here, we test the effect of nest exclosures in two common European shorebirds: northern lapwing (Vanellus vanellus) and redshank (Tringa totanus), measuring hatching success, incubation length, hatching synchrony, hatchability, partial clutch loss, chick condition, and adult predation. In both species, protected nests had higher hatching success than unprotected nests. Taking into account incubation time, nest abandonment, hatchability and partial clutch loss, protected nests still hatched more young than unprotected controls. In lapwings, but not in redshanks, protected nests were incubated longer, but this did not impair the condition of lapwing chicks. Protected redshanks suffered increased predation on incubating adults, which often sit on the nest until a predator is close by. Our results emphasize the need for caution in the use of nest exclosures, particularly in redshanks and other species with similar incubation behaviour. Exclosures can, however, be a useful management tool in shorebirds that leave their nest early, when an approaching predator is still far away.     

Long-term conservation efforts contribute to positive green turtle Chelonia mydas nesting trend at Tortuguero, Costa Rica

Worldwide, green turtle Chelonia mydas populations have declined and the species is classified as globally endangered. Tortuguero, Costa Rica, hosts the largest remaining green turtle rookery in the Atlantic basin. Tortuguero green turtles have been hunted since pre-Columbian times. Monitoring and conservation of the green turtle population began in 1955. The long-term efforts provide an excellent opportunity to evaluate the success of sea turtle conservation action and policies. Nest counts conducted 1971-2003 were analyzed to: (1) determine the nesting trend, (2) estimate rookery size and (3) identify events and policy decisions influencing the trend. A nonparametric regression model indicates a 417% increase in nesting over the study period. Rookery size was defined as the mean number of nests 1999-2003 and estimated at 104,411 nests year⁻¹, corresponding to 17,402-37,290 nesting females year⁻¹. A comparison with 34 index populations verifies Tortuguero as one of the two largest green turtle rookeries worldwide. Events and policy decisions in Costa Rica, Nicaragua, and Panama that comprise the main nesting, feeding and mating grounds for the Tortuguero population are likely to have had the greatest influence on green turtle survivorship. Conservation efforts and policies catalyzing increased hatchling production and decreased adult and juvenile mortality since 1963 have contributed to the positive nesting trend. The trend demonstrates that long-term conservation efforts can reverse nesting declines and offers hope that adequate management can result in recuperation of endangered sea turtle species.     

Vulnerability of ground-nesting waterbirds to predation by invasive American mink in the Cape Horn Biosphere Reserve, Chile

Biological invasions constitute one of the most important threats to biodiversity. This is especially true for “naïve” birds that have evolved in the absence of terrestrial predators in island ecosystems. The American mink (Mustela vison) has recently established a feral population on Navarino Island (55°S), southern Chile, where it represents a new guild of terrestrial mammal predators. We investigated the impact of mink on ground-nesting coastal waterbirds with the aim of deriving a vulnerability profile for birds as a function of different breeding strategies, habitat, and nest characteristics. We compared rates of nest survival and mink predation on 102 nests of solitary nesting species (Chloephaga picta, Tachyeres pteneres), on 361 nests of colonial birds (Larus dominicanus, Larus scoresbii, Sterna hirundinacea), and on 558 artificial nests. We calculated relative mink and bird densities at all nest sites. Nests of colonial species showed the highest nest survival probabilities (67-84%) and no predation by mink. Nest survival rates for solitary nesting species were lower (5-20%) and mink predation rates higher (10-44%). Discriminant analyses revealed that mink preyed upon artificial nests mainly at shores with rocky outcroppings where mink were abundant. High nest concealment increased the probability for predation by mink. Conservation planning should consider that invasive mink might severely affect the reproduction success of bird species with the following characteristics: solitary nesting, nesting habitat at rocky outcrop shores, and concealed nests. We recommend that work starts immediately to control the mink population with a priority in the nesting habitats of vulnerable endemic waterbirds.     

Distribution, use and selection of nest type by Komodo Dragons

We report the abundance, patterns of distribution and physical characteristics of Komodo dragon (Varanus komodoensis) nests on Komodo Island in Indonesia. A total of 46 Komodo dragon nesting sites were identified, of these 26 nests were considered active for the 2002/2003 season. The distribution of nests coincided with large coastal valleys in northern Komodo Island. There was a significant preference by breeding females to utilize the mound nests (61%) over both open hillside (19.5%) and ground nests (19.5%). Further, within these mound nests, females discriminated for nests based on habitat characteristics, especially sunlight exposure. The main implications for management and conservation drawn from this study is that there is a small number of females nesting annually on the largest island within Komodo National Park. Further, continuation of nesting surveys could provide a cost effective accurate way to gather important long term demographic information on this species.     

Monitoring predators to optimize their management for marine turtle nest protection

The fundamental conservation focus for Hobe Sound National Wildlife Refuge (HSNWR), Florida is to provide protected nesting habitat for three threatened or endangered marine turtle species. Turtle nesting and hatching spans from early spring to fall each year. Left unchecked, nest predation by raccoons and armadillos would destroy most turtle nests. Predators are removed to protect nests, primarily with a one person-month contract using control specialists. We maximized the efficiency of predator removal by using a passive tracking index to: (1) optimize the timing and strategy for predator removal, (2) minimize labor by identifying areas where predator removal would have maximal effect, (3) examine beach invasion patterns of predators, (4) assess efficacy of removal efforts, (5) provide anticipatory information for future turtle nesting seasons, and (6) serve as a detection method for invasion by additional species known to depredate turtle nests. An overall nest predation rate of 28% resulted, whereas the rate for the previous year was 42% when the same level of contracted predator removal was applied, but without monitoring predators. One year before that, predator removal was done without contracts with specialists and predation was 48%. Up to 95% of the nests were destroyed in the years prior to predator removal. Using 2000 data on numbers of nests, clutch sizes, and emergence rates, we estimated the number of hatchlings that would have been lost assuming that the predation rates observed from four predator removal scenarios at HSNWR would have occurred in 2000. Historical predation of 95% would have resulted in 120,597 hatchlings lost in 2000. Predator removal as part of regular refuge operations would have reduced this number to 62,481. Addition of a contract with control specialists would have further reduced the number lost to 53,778. Addition of temporal and spatial monitoring for predator removal reduced losses to 36,637.     

Habitat management of little terns in Japan’s highly developed landscape

The little tern (Sterna albifrons) is a species of shorebird that nests in colonies on sandy beaches and riverbanks with little vegetation cover. In Japan, the natural breeding habitats of the terns have decreased drastically, and the species is listed under the category “vulnerable” in the Red List of the Government of Japan. To reduce the effects of habitat loss on the terns, conservationists are attempting to create and manage artificial colony sites in highly developed landscapes, such as reclaimed lands located in Tokyo Bay, central Japan. We present the factors that contribute to breeding success for this species and the habitat characteristics related to nest-site selection in the artificial colony sites along Tokyo Bay. Our data show that around 3 ha of a building rooftop without vegetation cover could sustain more than 2000 little tern nests. We found a strong positive relationship between colony size and hatching success, observing that a colony size of more than 100 lowered predation rates of eggs. On sites built upon white crushed-concrete, nest densities were high and predation rates of eggs were low. We also found that feeding rates were affected by foraging habitats, of which the best types were the shoreline of sandy beaches and mud flats. The 40 km dispersal range of the breeding terns, inferred from distribution data, should be considered when establishing a network of the multiple colony sites.     

Floating platforms increase reproductive success of common loons

Many southern populations of the common loon (Gavia immer) face threats from lead and methylmercury contamination, lake acidification, shoreline development and human recreation. It is now clear that the task of conserving loon populations will depend upon mitigating these varied threats. In a controlled experiment, we examined the efficacy of using floating nest platforms to increase reproductive success of loons and thus help sustain local populations. Platforms were attractive nesting sites both on lakes that had consistently hatched chicks from natural sites and on lakes where chick production had been sporadic. When compared to natural nest sites, platforms increased hatching success by 69% and fledging success by 32%, apparently through reduction in mammalian egg predation. A well-managed effort to introduce nesting platforms might be a viable strategy to help sustain threatened populations.     

Lighting the way: Towards reducing misorientation of olive ridley hatchlings due to artificial lighting at Rushikulya, India

Sea-finding behavior in sea turtle hatchlings is modified by the visual cues provided by artificial beach front lighting. The consequent landward movement of hatchlings in response to coastal electric lighting reduces their survival rates. We assessed the potential impact of coastal lighting at Rushikulya, an important mass nesting site of the olive ridley sea turtle (Lepidochelys olivacea) in the Indian Ocean region. We examined the response of hatchlings to light characteristics in an experimental setup, as well as to the existing lighting regimes along the beach, using arena trials. Previous studies on other species indicate preferential orientation towards low wavelength and high intensity light. Our study confirms these preferences among hatchlings from the Indian Ocean population of olive ridleys. In addition we also found that wavelength and intensity could have an interactive effect upon hatchling orientation. Hatchlings at the study site respond both to visible point sources of light and to sheer glows of light. Though beach plantations of introduced Casuarina equisetifolia are generally considered to have negative impacts on sea turtle nesting beaches, we found that they acted as an effective light barrier when planted about 50 m away from the high tide line. We developed a model of the expected impact of artificial lighting on hatchling orientation during mass hatching events of previous years, and predict as much as 50% misorientation in some years. We also developed a map representing the misorientation of hatchlings due to artificial lighting based on arena trials in different regions of the beach. The results of the study helped identify focal areas for light management on the beach, which could be critical for the survival of this population.     

Observations on loggerhead sea turtle Caretta caretta activity during three nesting seasons (1977–1979) in Zakynthos,Greece

Data collected during the 1977, 1978 and 1979 seasons showed that a remarkable sea turtle population of unknown size and origin utilizes Zakynthos' small southern beaches as nesting areas. Preliminary surveys indicate that nesting activity on Sekania, Dafni and Gherakas beaches averaged 18·1 emergences and 10·77 nestings per night, most of which were concentrated on Sekania beach. Observed adults and young were identified as Caretta caretta with a mean carapace length of 80·4 cm for females and 40·4 mm for hatchlings. The importance of this newly discovered rookery is emphasized and the need to maintain present population levels through realistic conservation measures is discussed.     

Implications of intraguild predation for sea turtle nest protection

In the United States, raccoons Procyon lotor are often removed from sea turtle nesting beaches to decrease egg mortality. However, raccoons also consume ghost crabs Ocypode quadrata, another common egg predator. Reducing predator populations can benefit secondary predators, inflating total predation pressure and leading to a decline in prey species. We used track and burrow counts to compare raccoon and ghost crab abundance at four beaches in Florida, USA, that differ in management activity and determined predation rates on loggerhead Caretta caretta nests by each predator. Mean raccoon abundance (range 0.12-0.46 tracks plot⁻¹ night⁻¹) and ghost crab density (0.09-0.19 burrows m⁻²) were inversely correlated. Ghost crabs were largest at the site with the fewest raccoons. The stable nitrogen isotope ratios of ghost crabs (mean 9.8‰) were positively correlated with body mass, indicating larger ghost crabs feed at a higher trophic level and suggesting large ghost crabs may consume more loggerhead eggs. The highest rates of egg predation by both predators (31%) occurred where raccoon abundance was lowest and ghost crab abundance was highest, suggesting ghost crab burrows may facilitate predation by raccoons. Our data suggest that predation by raccoons limits ghost crabs and that removing raccoons can increase ghost crab abundance and sea turtle egg mortality. Although predator removal can be effective when nest predation rates are quite high, maintaining moderate raccoon densities may be important for controlling ghost crabs. These results highlight the importance of understanding food web connectivity in developing management strategies to achieve conservation goals, especially when the species of concern are threatened or facing extinction.