Coastal Migration Research Articles

Tracking animal movements via collaborative acoustic telemetry networks: Multiscale habitat use, phenology, and management insights.

Estuaries support diverse fish and invertebrate communities, including resident species that rely on estuarine habitats year-round and transient migratory species. The unique movement patterns of these animals connect habitats within and far beyond the estuary and are integrally linked to fisheries management objectives. With a focus on Chesapeake Bay, this study leveraged data from collaborative acoustic telemetry networks in the northwest Atlantic to assess habitat use and phenology of movements for seven species of fish (cownose rays, dusky sharks, smooth dogfish, alewife, striped bass, common carp, and blue catfish) and one invertebrate (horseshoe crabs). A total of 288 acoustically tagged individuals were detected >3.2 million times (6,743 to 2,095,717 detections per species) on receivers across ~20.5 degrees of latitude spanning the North American Atlantic seaboard from Florida, USA, to New Brunswick, Canada. Common metrics of movement and phenology grouped these species as resident (common carp, blue catfish, horseshoe crabs), primarily resident in estuaries (juvenile striped bass), and coastal migrant (cownose rays, dusky sharks, smooth dogfish, alewife); maximum distance traveled varied by three orders of magnitude among these species. Further analysis of phenology for coastal migrants elucidated the timing and duration of these species' use of Chesapeake Bay. Collectively, movements linked habitats within Chesapeake Bay and connected the estuary to coastal ecosystems both to the north (e.g., alewife) and south (e.g., cownose rays), creating networks of fisheries management jurisdictions that varied in complexity and identified opportunities for enhancement to current management or co-management of some species. Our results elucidate the importance of estuaries to species with diverse movement behaviors, identify scales and pathways of habitat connectivity via animal movements, and highlight the utility of collaborative acoustic telemetry networks for quantifying movements relevant to both ecological research and fisheries management.

Diamond Gymnura natalensis and duckbill Aetomylaeus bovinus rays undertake nationwide coastal migrations.

Migration is a critical aspect of ocean ecosystems, and understanding this phenomenon answers ecological and management questions. Given the difficulty in tracking ocean animals across large distances, the extent to which different ray species perform long-distance movements, such as migrations, remains unknown. This study used passive acoustic telemetry to track the movements of endemic diamond Gymnura natalensis and critically endangered duckbill Aetomylaeus bovinus rays along the South African coastline using a collaborative nationwide network of coastal acoustic receivers for up to 7 years. Duckbill rays were detected significantly more frequently than diamond rays, but both species moved between the south and east coasts of South Africa (traveling up to 1167 km). Tagged individuals were detected significantly more often in their tagging locations during summer months but traveled significantly further distances during winter months. Furthermore, movement models fitted to individual duckbill rays' annual net-squared displacement identified most individual annual movements as migratory. This evidence suggests that both diamond and duckbill rays make eastward winter migrations and return to specific areas along the coastline during the summer months. The exceptions to this were diamond rays tagged on the east coast that were not found to migrate seasonally, which supports previous research that there is intraspecific variability in migrations for ray species. These findings have implications for understanding ray migration not only on a global scale but also locally for spatial management interventions and population delineation.

A multi-scale tracking approach for conserving large migratory fish in an open coastal environment

Coastal habitats serve essential roles in the life cycles of migratory fishes, impacting both local and regional population stability. Conservation efforts for coastal fish often rely on spatial approaches within designated boundaries to mitigate threats and enhance production. However, in open coastal environments, migratory behaviours can extend beyond these protected areas, exposing individuals to potential threats or population bottlenecks elsewhere in their range. To improve conservation outcomes, a comprehensive understanding of movements across the entire migratory range is essential. Aquatic telemetry is a valuable tool for studying these behaviours, but must be adapted to address questions at multiple spatial and temporal scales. In this study we demonstrate how a combination of telemetry techniques can capture both local and regional fish behaviours. We begin by introducing the implications of migratory behaviours for fish conservation in open coastal environments, using the Wadden Sea as an example where additional research and management are needed to address fish declines. We then present a case study which uses the Dutch Wadden Sea to illustrate how a multi-scale telemetry approach can enhance both fundamental knowledge and conservation strategies for migratory fish. Within this case study, we present the general movement strategies exhibited by coastal migrants, alongside an overview of telemetry techniques applicable for open coastal systems. We then apply a size-based assessment using a reference tag to estimate the suitability of common Wadden Sea species for long-term tracking. Drawing from these results, we select four example species to showcase how species-specific understanding of fish life history and abundance can guide tracking studies, accompanied by illustrative examples using telemetry data. Expanding from this case study, we transition to a broader discussion were we provide overarching perspectives on tracking in open coastal ecosystems and offer recommendations to enhance future tracking studies in the Wadden Sea. The integration of telemetry methodologies aligns research and management with fish movement over multiple scales, improving our understanding of fish behaviors and contributing to more effective conservation strategies.

New age constraints for human entry into the Americas on the north Pacific coast

The timing of the initial peopling of the Americas is unresolved. Because the archaeological record necessitates discussion of human entry from Beringia into southern North America during the last glaciation, addressing this problem routinely involves evaluating environmental parameters then targeting areas suitable for human settlement. Vertebrate remains indicate landscape quality and are a key dataset for assessing coastal migration theories and the viability of coastal routes. Here, radiocarbon dates on vertebrate specimens and archaeological sites are calibrated to document species occurrences and the ages of human settlements across the western expansion and decay of the Cordilleran Ice Sheet (CIS) during the Late Wisconsin Fraser Glaciation in four subregions of the north Pacific coast of North America. The results show archaeological sites occur after glacial maxima and are generally consistent with the age of other securely dated earliest sites in southern North America. They also highlight gaps in the vertebrate chronologies around CIS maxima in each of the subregions that point to species redistributions and extirpations and signal times of low potential for human settlement and subsistence in a key portion of the proposed coastal migration route. This study, therefore, defines new age constraints for human coastal migration theories in the peopling of the Americas debate.

Striped Bass Movement in a Large Southeastern River System

Abstract Migratory behaviors of coastal Striped Bass Morone saxatilis are diverse and vary by latitude along the U.S. Atlantic Coast. Northern populations (e.g., north of Cape Hatteras, North Carolina) are anadromous, with spawning occurring in tidal freshwater/brackish rivers and adults leaving spawning locations during the winter to conduct north–south coastal migrations. The central Atlantic comprises a mixture of potamodromous and anadromous types, completing the natural continuum of behavioral modes along latitudinal ecotones. Southern populations (e.g., south of Cape Hatteras, North Carolina) are typically resident and potamodromous, completing full life cycles within river systems, and do not migrate along the Atlantic Coast. There are limited studies that have investigated daily movement of Striped Bass in the Southeast and no studies have documented movement of Striped Bass in the Great Pee Dee River, particularly with reference to spawning migrations. The objective of this study was to describe daily movement patterns and centers of attraction (e.g., spawning and resting stages) of Striped Bass in the Great Pee Dee River, South Carolina. We implanted 10 fish with hydroacoustic transmitters between 2013 and 2016. We describe daily movement and behavior using the state-space model with a two-dimensional spatial coordinate system. We recorded a total of 94,857 data points across all individuals and receivers. We observed two movement patterns. One group completed a seasonal migration (i.e., were recorded swimming upstream or downstream) that coincides with spring spawning season. A second group was present in the lower river section and Winyah Bay during the winter for 3 consecutive years but were never observed migrating up the Great Pee Dee River during the spring. One individual was documented swimming 80 river km north in the Atlantic Intracoastal Waterway, suggesting there are important overwintering locations outside their natal river. Additionally, there were significant gaps in observations for all individuals, particularly in the summer. It is possible that fish are leaving the main stem in search of thermal refuge within small tributaries. Identifying these overwintering areas and tributaries that serve as summer refuge is needed to determine stressors and fishing pressure of this important species.

Bidirectional movements of Nathusius’ pipistrelle bats (Pipistrellus nathusii) during autumn at a major migration corridor

Migration is well documented for many species throughout the animal kingdom. Although migration is also a common behaviour in bats, it is rarely studied due to the cryptic nature of the phenomenon. Recoveries of banded individuals have shown that Nathusius' pipistrelles (Pipistrellus nathusii) can fly more than 2000 km between their summer and winter ranges in Europe, but further details of how and where they move between the endpoints of their seasonal journeys remain elusive. Here, we used three-dimensional acoustic tracking at a coastal migration corridor to elucidate the flight behaviour of Nathusius' pipistrelles during late summer. Analyzing 432 recorded flight trajectories, we show that the majority of bats followed the expected southerly direction, parallel to the coastline, on all nights, and flying at the optimal speed for long-distance travel with minimal energy expenditure. However, on one day with stronger winds, about 20 % of the bats flew in the opposite, i.e. northerly, direction. The observation of a proportion of individuals flying antiparallel to the mass of migrating conspecifics within the same movement corridor highlights that individuals may follow contrasting movement strategies at the same time and place, presumably depending on environmental conditions. We argue that it is possible for Nathusius’ pipistrelles to fly back and forth (south and north) during autumn migration, spending more time on this migration corridor than required for a straight one-way flight. This highlights the urgent need to protect migration corridors along coastlines, particularly as wind energy development continues.

30,000 years of fishing in the Philippines: New ichthyoarchaeological investigations in Occidental Mindoro

Marine adaptations are considered to have been significant factors in the evolution of our species (Homo sapiens). As humans dispersed from Africa around 100 kya, marine resources provided essential nutrients in island environments of the tropical Southeast Asian seas. The Philippine archipelago has revealed significant evidence of early human settlement during this period of coastal migration. Yet, despite being a global marine biodiversity hotspot, few studies have investigated prehistoric marine adaptations there. In this study, we focus on the analysis of fish bones from three sites in Occidental Mindoro, Philippines: Bubog I, Bubog II, and Bilat Cave with the aim of enhancing the understanding of H. sapiens' coastal adaptations and maritime interactions since at least 32,000 BP. We utilized expanded skeletal element identification protocols to determine the lowest taxonomic level possible, combined with diversity indices. The analyses indicate that H. sapiens on Mindoro mostly exploited near-shore environments, with temporal variations in fishing practices reflecting differences in site occupation intensity and periods of climate-mediated habitat change. Inter-site variations in fishing practices are likely related to disparities in local marine habitats. Spatiotemporal differences in marine environments influenced the development of diverse fishing methods and technologies, demonstrating a detailed knowledge of local aquatic environments and the adaptability of modern humans in Island Southeast Asia since the Pleistocene.

A compromised shore: seachange migration and landscape politics on the Central Coast of New South Wales, 1945–2001

The second half of the twentieth century saw major coastal landscape changes around Australia driven by seachange migration. This article examines the experience of New South Wales’ Central Coast, whose population increased nearly tenfold and was the site of ongoing debates about environmental risk and loss. Over time, a compromise emerged regionally and nationally that allowed continuing coastal migration but with distinct bounds on further development. This article examines how this compromise accompanied the rise of the Australian environmental state, melded with the institutionalisation of the sustainability movement, and can be placed in a broader history of political settlements.

A paleogenome from a Holocene individual supports genetic continuity in Southeast Alaska

Many specifics of the population histories of the Indigenous peoples of North America remain contentious owing to a dearth of physical evidence. Only few ancient human genomes have been recovered from the Pacific Northwest Coast, a region increasingly supported as a coastal migration route for the initial peopling of the Americas. Here, we report paleogenomic data from the remains of a ∼3,000-year-old female individual from Southeast Alaska, named Tatóok yík yées sháawat (TYYS). Our results demonstrate at least 3,000 years of matrilineal genetic continuity in Southeast Alaska, and that TYYS is most closely related to ancient and present-day northern Pacific Northwest Coast Indigenous Americans. We find no evidence of Paleo-Inuit (represented by Saqqaq) ancestry in present-day or ancient Pacific Northwest peoples. Instead, our analyses suggest the Saqqaq genome harbors Northern Native American ancestry. This study sheds further light on the human population history of the northern Pacific Northwest Coast.

A coupled agent-based model for France for simulating adaptation and migration decisions under future coastal flood risk

In this study, we couple an integrated flood damage and agent-based model (ABM) with a gravity model of internal migration and a flood risk module (DYNAMO-M) to project household adaptation and migration decisions under increasing coastal flood risk in France. We ground the agent decision rules in a framework of subjective expected utility theory. This method addresses agent’s bounded rationality related to risk perception and risk aversion and simulates the impact of push, pull, and mooring factors on migration and adaptation decisions. The agents are parameterized using subnational statistics, and the model is calibrated using a household survey on adaptation uptake. Subsequently, the model simulates household adaptation and migration based on increasing coastal flood damage from 2015 until 2080. A medium population growth scenario is used to simulate future population development, and sea level rise (SLR) is assessed for different climate scenarios. The results indicate that SLR can drive migration exceeding 8000 and 10,000 coastal inhabitants for 2080 under the Representative Concentration Pathways 4.5 and 8.5, respectively. Although household adaptation to flood risk strongly impacts projected annual flood damage, its impact on migration decisions is small and falls within the 90% confidence interval of model runs. Projections of coastal migration under SLR are most sensitive to migration costs and coastal flood protection standards, highlighting the need for better characterization of both in modeling exercises. The modeling framework demonstrated in this study can be upscaled to the global scale and function as a platform for a more integrated assessment of SLR-induced migration.

Ice and ocean constraints on early human migrations into North America along the Pacific coast

Founding populations of the first Americans likely occupied parts of Beringia during the Last Glacial Maximum (LGM). The timing, pathways, and modes of their southward transit remain unknown, but blockage of the interior route by North American ice sheets between ~26 and 14 cal kyr BP (ka) favors a coastal route during this period. Using models and paleoceanographic data from the North Pacific,we identify climatically favorable intervals when humans could have plausibly traversed the Cordilleran coastal corridor during the terminal Pleistocene. Model simulations suggest that northward coastal currents strengthened during the LGM and at times of enhanced freshwater input, making southward transit by boat more difficult. Repeated Cordilleran glacial-calving events would have further challenged coastal transit on land and at sea. Following these events, ice-free coastal areas opened and seasonal sea ice was present along the Alaskan margin until at least 15 ka. Given evidence for humans south of the ice sheets by 16 ka and possibly earlier, we posit that early people may have taken advantage of winter sea ice that connected islands and coastal refugia. Marine ice-edge habitats offer a rich food supply and traversing coastal sea ice could have mitigated the difficulty of traveling southward in watercraft or on land over glaciers.We identify 24.5 to 22 ka and 16.4 to 14.8 ka as environmentally favorable time periods for coastal migration, when climate conditions provided both winter sea ice and ice-free summer conditions that facilitated year-round marine resource diversity and multiple modes of mobility along theNorth Pacific coast.

Nathusius’ bats, Pipistrellus nathusii, bypass mating opportunities of their own species, but respond to foraging heterospecifics on migratory transit flights

In late summer, migratory bats of the temperate zone face the challenge of accomplishing two energy-demanding tasks almost at the same time: migration and mating. Both require information and involve search efforts, such as localizing prey or finding potential mates. In non-migrating bat species, playback studies showed that listening to vocalizations of other bats, both con-and heterospecifics, may help a recipient bat to find foraging patches and mating sites. However, we are still unaware of the degree to which migrating bats depend on con-or heterospecific vocalizations for identifying potential feeding or mating opportunities during nightly transit flights. Here, we investigated the vocal responses of Nathusius’ pipistrelle bats, Pipistrellus nathusii, to simulated feeding and courtship aggregations at a coastal migration corridor. We presented migrating bats either feeding buzzes or courtship calls of their own or a heterospecific migratory species, the common noctule, Nyctalus noctula. We expected that during migratory transit flights, simulated feeding opportunities would be particularly attractive to bats, as well as simulated mating opportunities which may indicate suitable roosts for a stopover. However, we found that when compared to the natural silence of both pre-and post-playback phases, bats called indifferently during the playback of conspecific feeding sounds, whereas P. nathusii echolocation call activity increased during simulated feeding of N. noctula. In contrast, the call activity of P. nathusii decreased during the playback of conspecific courtship calls, while no response could be detected when heterospecific call types were broadcasted. Our results suggest that while on migratory transits, P. nathusii circumnavigate conspecific mating aggregations, possibly to save time or to reduce the risks associated with social interactions where aggression due to territoriality might be expected. This avoidance behavior could be a result of optimization strategies by P. nathusii when performing long-distance migratory flights, and it could also explain the lack of a response to simulated conspecific feeding. However, the observed increase of activity in response to simulated feeding of N. noctula, suggests that P. nathusii individuals may be eavesdropping on other aerial hawking insectivorous species during migration, especially if these occupy a slightly different foraging niche.

Migration timing affects the foraging ecology of Fraser River sockeye salmon stocks in coastal waters of British Columbia, Canada

Coastal migrations of juvenile Pacific salmon Oncorhynchus spp. have evolved to take advantage of optimal ocean foraging conditions and maximize early marine growth and survival. The growth and survival of salmon during the early marine period is affected by both the diversity of encountered coastal habitats, with varying productivity and plankton phenology, and stock-specific migration timings that determine the match-mismatch with their prey. In 2015 and 2016, we investigated temporal and spatial patterns in environmental conditions and zooplankton prey as well as diets and stock composition of juvenile Fraser River sockeye O. nerka during their outmigration through the tidally mixed Discovery Islands and Johnstone Strait in British Columbia (Canada). Three groups of sockeye diet profiles reflected variations in environmental conditions and prey communities. First, in the Discovery Islands, earlier migrating stocks primarily encountered and foraged on small, energy-poor zooplankton prey (barnacles and cladocerans). Second, later migrating stocks foraged mainly on larger, more energy-rich copepod and larvacean prey. And third, in the highly mixed waters of Johnstone Strait, large energy-rich calanoid copepods dominated diets irrespective of migration timing and year. Foraging success was typically low throughout the areas sampled and across the migration period, which may amplify the importance of prey nutritional quality. Our findings highlight the importance of accounting for spatial and temporal differences in foraging environments for migrating species such as juvenile salmon. Furthermore, we demonstrate that the timing of stock migration affects the foraging conditions experienced.

River‐of‐origin assignment of migratory Striped Bass, with implications for mixed‐stock analysis

AbstractObjectiveThe Striped Bass Morone saxatilis is an anadromous teleost with a native range extending north from the Gulf of Mexico into Canadian waters. Far‐ranging coastal migrations support one of the most popular recreational fisheries in the United States. Identifying the underlying population genetic structure of the spawning populations and the genetic markers capable of differentiating among them advances our understanding of these economically and ecologically important fish and enables more targeted management to occur.MethodsWe used a restriction site‐associated DNA sequencing approach to identify neutral and adaptive single‐nucleotide polymorphisms (SNPs), and we determined the population genetic structure of 438 adult Striped Bass sampled from nine spawning locations along the Atlantic coast from the Roanoke River, United States, to the Miramichi River, Canada.ResultThe two Canadian populations (Shubenacadie and Miramichi rivers) were genetically distinct from U.S. populations and from each other. Neutral loci differentiated Striped Bass from U.S. waters into four genetically distinct populations: Roanoke River, Hudson–Kennebec River, Upper Chesapeake Bay–Potomac River–Delaware River, and Choptank River (eastern Chesapeake Bay). Outlier loci further differentiated the Delaware River from the Chesapeake Bay tributaries, suggesting that there may be local adaptation in the face of gene flow. We identified 1300 highly informative SNPs (the top 10% [with respect to the genetic differentiation index FST] of the full suite of 13,361 SNPs in our study) capable of assigning fish with at least 90% accuracy to their river of origin; through simulations, we established their applicability for conducting robust mixed‐stock analyses of the coastal migratory Striped Bass fishery.ConclusionThis study demonstrated that neutral and adaptive loci together provide evidence for fine‐scale population structure of migratory Striped Bass, and these loci provide the most informative genetic panel for mixed‐stock analysis of Striped Bass to date, capable of assigning fish to their spawning river of origin.

Understanding the Drivers of Coastal Flood Exposure and Risk From 1860 to 2100

AbstractGlobal coastal flood exposure (population and assets) has been growing since the beginning of the industrial age and is likely to continue to grow through 21st century. Three main drivers are responsible: (a) climate‐related mean sea‐level change, (b) vertical land movement contributing to relative sea‐level rise, and (c) socio‐economic development. This paper attributes growing coastal exposure and flood risk from 1860 to 2100 to these three drivers. For historic flood exposure (1860–2005) we find that the roughly six‐fold increase in population exposure and 53‐fold increase in asset exposure are almost completely explained by socio‐economic development (>97% for population and >99% for assets). For future exposure (2005–2100), assuming a middle‐of‐the‐road regionalized socio‐economic scenario (SSP2) without coastal migration and sea‐level rise according to RCP2.6 and RCP6.0, climate‐change induced sea‐level rise will become the most important driver for the growth in population exposure, while growth in asset exposure will still be mainly determined by socio‐economic development.

The macroeconomic effects of adapting to high-end sea-level rise via protection and migration

Climate change-induced sea level rise (SLR) is projected to be substantial, triggering human adaptation responses, including increasing protection and out-migration from coastlines. Yet, in macroeconomic assessments of SLR the latter option has been given little attention. We fill this gap by providing a global analysis of the macroeconomic effects of adaptation to SLR, including coastal migration, focusing on the higher end of SLR projections until 2050. We find that when adapting simultaneously via protection and coastal migration, macroeconomic costs can be lower than with protection alone. For some developing regions coastal migration is even less costly (in GDP) than protection. Additionally, we find that future macroeconomic costs are dominated by accumulated macroeconomic effects over time, rather than by future direct damages, implying the need for immediate adaptation. Finally, we demonstrate the importance of including autonomous adaptation in the reference scenario of economic assessment studies to avoid overestimation of adaptation benefits.

One Shell of a Problem: Cumulative Threat Analysis of Male Sea Turtles Indicates High Anthropogenic Threat for Migratory Individuals and Gulf of Mexico Residents

Human use of oceans has dramatically increased in the 21st century. Sea turtles are vulnerable to anthropogenic stressors in the marine environment because of lengthy migrations between foraging and breeding sites, often along coastal migration corridors. Little is known about how movement and threat interact specifically for male sea turtles. To better understand male sea turtle movement and the threats they encounter, we satellite-tagged 40 adult male sea turtles of four different species. We calculated movement patterns using state-space modeling (SSM), and quantified threats in seven unique categories; shipping, fishing, light pollution, oil rigs, proximity to coast, marine protected area (MPA) status, and location within or outside of the U.S. Exclusive Economic Zone (EEZ). We found significantly higher threat severity in northern and southern latitudes for green turtles (Chelonia mydas) and Kemp’s ridleys (Lepidochelys kempii) in our study area. Those threats were pervasive, with only 35.9% of SSM points encountering no high threat exposure, of which 47% belong to just two individuals. Kemp’s ridleys were most exposed to high threats among tested species. Lastly, turtles within MPA boundaries face significantly lower threat exposure, indicating MPAs could be a useful conservation tool.

Surfing the tide: Homeward migration of sea trout (Salmo trutta) in a Patagonian river

This study evaluates the influence of marine and freshwater conditions on the timing of river entry and upstream migration of sea trout (Salmo trutta) in the Grande River of Tierra del Fuego, Patagonia. We analysed the in-river catch-and-release records from a group of fishing lodges that dominate the Grande River fishery during January-April 2008 (n=5029 fish) as a function of environmental variables: tidal amplitude, stage in the lunar cycle, river discharge, and river water temperature along the homeward migration season. We discuss the value of the daily catch rate as an abundance index in the Grande river, then analyse the temporal structure of the tidal cycle in the Grande River estuary, a macro-tidal environment with a mean tidal amplitude of 5.7m, and analyse the fit of a generalized additive model to trout catches on a daily basis in four sections along the river to identify the environmental variables that may affect trout abundance throughout the homeward migration. Fish catches in each section of the river were differentially affected by specific environmental variables: tidal amplitude had a positive and significant effect on catches in the lower river sections, whereas water temperature and river discharge significantly affected catches in upper sections (positive effect of temperature; negative effect of discharge). Catches in the lower section clearly reflect the river entry stage of the homeward migration, with a bi-modal shape significantly correlated with the tidal cycle. The first peak was composed mainly of larger multi-sea-winter trout that move upstream, whereas the second one had a wider range of fish lengths, including a large proportion of small and maybe nonreproductive trout that overwinter in the lower river. Based on our results, we conclude that the large tides in the Grande River estuary strongly affect the river entry timing of sea trout. The underlying mechanisms of this effect may be a combination of increased olfactory recognition and increased tidal transport modulated by the seasonal tidal cycle, which operates on trout during coastal migration to produce the pulses observed in the Grande River sea trout run. In the middle and upper sections of the river, where the tidal effect at river entry was dissipated as upstream migration progressed, trout catches increased with water temperature and decreased with river discharge, which may operate through their influence on in-river migration rate and abundance, but also through changes in catchability.

Phylogeographic analysis of the Bantu language expansion supports a rainforest route

The Bantu expansion transformed the linguistic, economic, and cultural composition of sub-Saharan Africa. However, the exact dates and routes taken by the ancestors of the speakers of the more than 500 current Bantu languages remain uncertain. Here, we use the recently developed "break-away" geographical diffusion model, specially designed for modeling migrations, with "augmented" geographic information, to reconstruct the Bantu language family expansion. This Bayesian phylogeographic approach with augmented geographical data provides a powerful way of linking linguistic, archaeological, and genetic data to test hypotheses about large language family expansions. We compare four hypotheses: an early major split north of the rainforest; a migration through the Sangha River Interval corridor around 2,500 BP; a coastal migration around 4,000 BP; and a migration through the rainforest before the corridor opening, at 4,000 BP. Our results produce a topology and timeline for the Bantu language family, which supports the hypothesis of an expansion through Central African tropical forests at 4,420 BP (4,040 to 5,000 95% highest posterior density interval), well before the Sangha River Interval was open.

The age of the opening of the Ice-Free Corridor and implications for the peopling of the Americas

SignificanceThe Ice-Free Corridor (IFC) has long played a key role in hypotheses about the peopling of the Americas. Earlier assessments of its age suggested that the IFC was available for a Clovis-first migration, but subsequent developments now suggest a pre-Clovis occupation of the Americas that occurred before the opening of the IFC, thus supporting a Pacific coastal migration route instead. However, large uncertainties in existing ages from the IFC cannot preclude its availability as a route for the first migrations. Resolving this debate over migration route is important for addressing the questions of when and how the first Americans arrived. We report cosmogenic nuclide exposure ages that show that the final opening of the IFC occurred well after pre-Clovis occupation.