Hatching success of sea turtle eggs can be reduced by a variety of biotic and abiotic factors. This study of the nesting ecology of leatherback (
Dermochelys coriacea
) and green (
Chelonia mydas
) ...sea turtles, investigated how several environmental factors and beach characteristics on Bioko Island, Equatorial Guinea influence sea turtle reproductive success. Average hatching success was 40.4% for green turtles and 41.73% for leatherback turtles. For leatherback turtles, clutch elevation relative to the high tide line (HTL) was found to be the most influential factor in determining hatching success, highlighting the sensitivity of this species to sea-level rise (SLR). Multiple linear regression analysis demonstrated that nest distance to vegetation, temperature, sand grain size, location on the beach, and sand conductivity also played significant roles in leatherback clutch hatching success. For leatherback clutches, 33% percent of nests were affected by inundation and 17% by predation. An optimum clutch elevation range for leatherback turtles was identified, where a distinct increase in hatching success was observed between − 0.286 and − 0.0528 m above the HTL. For green sea turtles, 64% of experimental nests were affected by predation, confounding conclusions about the roles of environmental characteristics in green turtle hatching success. We propose further investigation into influential characteristics in green turtle nests and confirmation of the observed optimum elevation range on Bioko Island and other nesting grounds. Identified sensitivities of each species to SLR and beach characteristics will be used to encourage the government of Equatorial Guinea to consider the vulnerability of their resident turtle populations when planning for future coastal development.
Sea level is expected to rise 44 to 74 cm by the year 2100, which may have critical, previously un-investigated implications for sea turtle nesting habitat on Bioko Island, Equatorial Guinea. This ...study investigates how nesting habitat will likely be lost and altered with various increases in sea level, using global sea level rise (SLR) predictions from the Intergovernmental Panel on Climate Change. Beach profiling datasets from Bioko's five southern nesting beaches were used in GIS to create models to estimate habitat loss with predicted increases in sea level by years 2046-2065 and 2081-2100. The models indicate that an average of 62% of Bioko's current nesting habitat could be lost by 2046-2065 and 87% by the years 2081-2100. Our results show that different study beaches showed different levels of vulnerability to increases in SLR. In addition, on two beaches erosion and tall vegetation berms have been documented, causing green turtles to nest uncharacteristically in front of the vegetation line. We also report that development plans are currently underway on the beach least susceptible to future increases in sea level, highlighting how anthropogenic encroachment combined with SLR can be particularly detrimental to nesting turtle populations. Identified habitat sensitivities to SLR will be used to inform the government of Equatorial Guinea to consider the vulnerability of their resident turtle populations and projected climate change implications when planning for future development. To our knowledge this is the first study to predict the impacts of SLR on a sea turtle nesting habitat in Africa.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
This study uses satellite telemetry to track post-nesting movements of endangered green turtles (Chelonia mydas) (n = 6) in the Gulf of Guinea. It identifies a migratory corridor linking breeding ...grounds of Atlantic green turtles nesting on Bioko Island, Equatorial Guinea, to foraging grounds in the coastal waters of Accra, Ghana. Track lengths of 20-198 days were analyzed, for a total of 536 movement days for the six turtles. Migratory pathways and foraging grounds were identified by applying a switching state space model to locational data, which provides daily position estimates to identify shifts between migrating and foraging behavior. Turtles exhibited a combination of coastal and oceanic migrations pathways that ranged from 957 km to 1,131 km. Of the six turtles, five completed their migration and maintained residency at the same foraging ground near the coastal waters of Accra, Ghana until transmission was lost. These five resident turtles inhabit heavily fished waters and are vulnerable to a variety of anthropogenic threats. The identification of these foraging grounds highlights the importance of these coastal waters for the protection of the endangered Atlantic green turtle.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Island Biogeography Reveals the Deep History of SIV Worobey, Michael; Telfer, Paul; Souquière, Sandrine ...
Science (American Association for the Advancement of Science),
09/2010, Letnik:
329, Številka:
5998
Journal Article
Recenzirano
Simian immunodeficiency virus (SIV) lineages have been identified that are endemic to Bioko Island. The time the island formed offers a geological time scale calibration point for dating the most ...recent common ancestor of SIV. The Bioko viruses cover the whole range of SIV genetic diversity, and each Bioko SIV clade is most closely related to viruses circulating in hosts of the same genus on the African mainland rather than to SIVs of other Bioko species. Our phylogeographic approach establishes that SIV is ancient and at least 32,000 years old. Our conservative calibration point and analyses of gene sequence saturation and dating bias suggest it may be much older.
Satellite telemetry was used to track inter-nesting, post-nesting, and foraging movements of six green turtles that nested on Bioko Island, Equatorial Guinea at the end of the 2019 nesting season, as ...well as foraging movements of five green turtles after the 2018 nesting season (
n
= 11 across two seasons), from the same nesting population. These tracks were fit with a switching state-space model to characterize movements and then analyzed in relation to environmental and anthropogenic factors. Inter-nesting movements of two turtles included separate oceanic loops, in which turtles traveled > 40 km away from nesting beaches. Four complete migrations were observed to two distinct foraging grounds, with two turtles migrating west for an average of 1064 km to the coastal waters of Ghana, and two migrating south for an average of 1563 km to a newly discovered foraging ground in the coastal waters of Angola. All migrations included intermittent foraging at stopover sites, including one period of possible oceanic foraging. Turtles at both foraging grounds maintained distinct core use areas in shallow, near-shore (< 20 km from coast) waters. Spatial and depth data reveal critical habitats for this population throughout inter-nesting, post-nesting, and foraging behaviors. Tracks spanned nine countries, highlighting the need for multi-national cooperation in the development of marine conservation management plans in the area. The long distances covered by these turtles suggests that fisheries bycatch and direct harvest throughout the East Atlantic may impact this population. Additionally, spatial and dive depth data can inform zonal fishing regulations and provide the information needed to modify fishing practices and gear in ways likely to reduce sea turtle bycatch.
Bushmeat hunting is extensive in west and central Africa as both a means for subsistence and for commercial gain. Commercial hunting represents one of the primary threats to wildlife in the region, ...and confounding factors have made it challenging to examine how external factors influence the commercial bushmeat trade. Bioko Island, Equatorial Guinea is a small island with large tracts of intact forest that support sizeable populations of commercially valuable vertebrates, especially endemic primates. The island also has a low human population and has experienced dramatic economic growth and rapid development since the mid-1990's. From October 1997 - September 2010, we monitored the largest bushmeat market on Bioko in Malabo, recording over 197,000 carcasses for sale. We used these data to analyze the dynamics of the market in relation to political events, environmental legislation, and rapid economic growth. Our findings suggest that bushmeat hunting and availability increased in parallel with the growth of Equatorial Guinea's GDP and disposable income of its citizens. During this 13-year study, the predominant mode of capture shifted from trapping to shotguns. Consequently, carcass volume and rates of taxa typically captured with shotguns increased significantly, most notably including intensified hunting of Bioko's unique and endangered monkey fauna. Attempts to limit bushmeat sales, including a 2007 ban on primate hunting and trade, were only transiently effective. The hunting ban was not enforced, and was quickly followed by a marked increase in bushmeat hunting compared to hunting rates prior to the ban. Our results emphasize the negative impact that rapid development and unenforced legislation have had on Bioko's wildlife, and demonstrate the need for strong governmental support if conservation strategies are to be successful at preventing extinctions of tropical wildlife.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Background
Non-native wild pigs (
Sus scrofa
) threaten sensitive flora and fauna, cost billions of dollars in economic damage, and pose a significant human–wildlife conflict risk. Despite growing ...interest in wild pig research, basic life history information is often lacking throughout their introduced range and particularly in tropical environments. Similar to other large terrestrial mammals, pigs possess the ability to shift their range based on local climatic conditions or resource availability, further complicating management decisions. The objectives of this study were to (i) model the distribution and abundance of wild pigs across two seasons within a single calendar year; (ii) determine the most important environmental variables driving changes in pig distribution and abundance; and (iii) highlight key differences between seasonal models and their potential management implications. These study objectives were achieved using zero-inflated models constructed from abundance data obtained from extensive field surveys and remotely sensed environmental variables.
Results
Our models demonstrate a considerable change in distribution and abundance of wild pigs throughout a single calendar year. Rainfall and vegetation height were among the most influential variables for pig distribution during the spring, and distance to adjacent forest and vegetation density were among the most significant for the fall. Further, our seasonal models show that areas of high conservation value may be more vulnerable to threats from wild pigs at certain times throughout the year, which was not captured by more traditional modeling approaches using aggregated data.
Conclusions
Our results suggest that (i) wild pigs can considerably shift their range throughout the calendar year, even in tropical environments; (ii) pigs prefer dense forested areas in the presence of either hunting pressure or an abundance of frugivorous plants, but may shift to adjacent areas in the absence of either of these conditions; and (iii) seasonal models provide valuable biological information that would otherwise be missed by common modeling approaches that use aggregated data over many years. These findings highlight the importance of considering biologically relevant time scales that provide key information to better inform management strategies, particularly for species whose ranges include both temperate and tropical environments and thrive in both large continental and small island ecosystems.
Hatching success of sea turtle eggs can be reduced by a variety of biotic and abiotic factors. This study of the nesting ecology of leatherback (Dermochelys coriacea) and green (Chelonia mydas) sea ...turtles, investigated how several environmental factors and beach characteristics on Bioko Island, Equatorial Guinea influence sea turtle reproductive success. Average hatching success was 40.4% for green turtles and 41.73% for leatherback turtles. For leatherback turtles, clutch elevation relative to the high tide line (HTL) was found to be the most influential factor in determining hatching success, highlighting the sensitivity of this species to sea-level rise (SLR). Multiple linear regression analysis demonstrated that nest distance to vegetation, temperature, sand grain size, location on the beach, and sand conductivity also played significant roles in leatherback clutch hatching success. For leatherback clutches, 33% percent of nests were affected by inundation and 17% by predation. An optimum clutch elevation range for leatherback turtles was identified, where a distinct increase in hatching success was observed between - 0.286 and - 0.0528 m above the HTL. For green sea turtles, 64% of experimental nests were affected by predation, confounding conclusions about the roles of environmental characteristics in green turtle hatching success. We propose further investigation into influential characteristics in green turtle nests and confirmation of the observed optimum elevation range on Bioko Island and other nesting grounds. Identified sensitivities of each species to SLR and beach characteristics will be used to encourage the government of Equatorial Guinea to consider the vulnerability of their resident turtle populations when planning for future coastal development.
Hawai'i is home to 'o'opu nākea (Awaous stamineus), a culturally significant, endemic, goby that exhibits an amphidromous life cycle characterized by a marine larval stage followed by post-larval ...recruitment to streams, where they live to become reproductive adults. However, it was recently suggested that their migration to the ocean might not be obligatory, as originally thought. Despite their importance in Hawaiian traditions and the ecology of Hawaiian freshwater ecosystems, we still lack a full understanding of their migratory patterns and life history due to the difficulties in determining the environmental migratory cues that set the timing and location of their migratory paths. This study examined environmental factors, such as mean annual rainfall, streamflow, and water chemistry, to determine if they play a role in whether A. stamineus spend their larval period in the ocean or their entire life cycle in freshwater streams. We sampled A. stamineus (n = 90) from three streams (Kahana, Kahalu'u, and Waimānalo) on the island of O'ahu, Hawai'i that represented the range of hydroclimatic gradient in wet-habitat conditions on the windward side of the island and characterized their migratory pattern using elemental analysis of sagittae, the largest pair of otoliths (calcareous ear structures). Based on otolith strontium:calcium and barium:calcium ratios, we determined if individuals spent their larval period in the ocean or the stream. We found that 100% of individuals displayed clear evidence of marine residence during their larval phase, regardless of the environmental factors the fish experienced. This study highlights the necessity of stream-ocean connectivity for the survival of A. stamineus and emphasizes the importance of stream-mouth conservation and management as it is a critical transition zone in stream-ocean-stream migratory pathways.
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