Turtle Density Research Articles

Combining UAVs and multi-sensor dataloggers to estimate fine-scale sea turtle density at foraging areas: a case study in the central Mediterranean

Knowledge of the distribution and density of marine species is key to understanding habitat use and interactions with human activities. Yet such information for sea turtles remains scarce, especially at foraging areas, where low turtle density represents an additional challenge in comparison to turtle aggregations at coastal breeding areas. Aerial surveys with aircraft are an efficient method for collecting these data over broad scales, while more novel unoccupied aerial vehicles (UAVs) are better suited for finer-scale data collection. However, their use is less developed, especially in offshore areas. Here we explored, for the first time in the Mediterranean, the potential of UAV surveys to estimate turtle density (surface and total) at foraging areas and its temporal trend. Between 2017 and 2023, we conducted 427 flights in the Pelagian Islands Archipelago (PIA), Italy, a regionally important foraging area of the loggerhead sea turtle Caretta caretta. To convert from surface to total density, we used data from multisensor biologgers deployed on 22 turtles to calculate the proportion of time turtles are visible from aerial surveys (availability time proportion, ATP). Results show that the mean surface turtle density in the PIA (0.336-0.477 turtles km-2) is among the highest reported globally for a loggerhead turtle foraging area. Such densities make it possible to assess population trends through periodic UAV surveys, which are less expensive than aircraft surveys and which can minimize the typical biases of aerial surveys (distance sampling, perception, and misidentification). A standardized methodology is needed for meaningful comparisons, including ATP at the visible depth layer vs. surface.

Morphological variations and demographic responses of the Mediterranean pond turtle Mauremys leprosa to heterogeneous aquatic habitats

Human activities affect terrestrial and aquatic habitats leading to changes at both individual and population levels in wild animal species. In this study, we investigated the phenotype and demographics of the Mediterranean pond turtle Mauremys leprosa (Schweigger, 1812) in contrasted environments of Southern France: two peri-urban rivers receiving effluents from wastewater treatment plants (WWTP), and another one without sewage treatment plant. Our findings revealed the presence of pesticides and pharmaceuticals in the three rivers of investigation, the highest diversities and concentrations of pollutants being found in the river subsections impacted by WWTP effluents. Principal component analysis and hierarchical clustering identified three levels of habitat quality, with different pollutant concentrations, thermal conditions, nutrient, and organic matter levels. The highest turtle densities, growth rates, and body sizes were estimated in the most disturbed habitats, suggesting potential adult benefits derived from harsh environmental conditions induced by pollution and eutrophication. Conversely, juveniles were the most abundant in the least polluted habitats, suggesting adverse effects of pollution on juvenile survival or adult reproduction. This study suggests that turtles living in polluted habitats may benefit from enhanced growth and body size, at the expense of reproductive success.

Sea turtle density surface models along the United States Atlantic coast

Spatially explicit estimates of marine species distribution and abundance are required to quantify potential impacts from human activities such as military training and testing, fisheries interactions, and offshore energy development. There are 4 protected species of sea turtle (loggerhead, green, Kemp’s ridley, and leatherback) commonly found along the east coast of the USA, our study area, and which require impact assessments. Data from 7 different survey organizations were used to create density surface models for the 4 sea turtle species utilizing 1.2 million km of line-transect surveys. A substantial portion (29.7%) of available sightings were not identified to the species level. Not including these sightings would underestimate density, so a conditional random forest model was used to assign unidentified sightings to species. Higher densities of loggerhead, green, and Kemp’s ridley sea turtles were predicted south of the Outer Banks in cool months, transitioning northwards in late spring to occupy seasonal neritic habitats. The highest leatherback densities were predicted off the coasts of Georgia and Florida. Leatherbacks were also predicted throughout offshore areas. The predicted distribution patterns generally matched satellite tracking and strandings data, indicating the models reproduced established seasonal movements. Surveys rarely detect sea turtles smaller than 40 cm, so these age classes are not represented. The models are the first for the study area to apply availability bias estimates developed in or near the study area and attempt to classify unidentified sightings to the species level, providing an updated, critical tool for conservation management along the eastern seaboard.

Distribution patterns of nearshore aggregations of olive ridley sea turtles (Lepidochelys olivacea) in Rushikulya, Odisha, India: Implications for spatial management measures

Abstract Sea turtles are known to migrate large distances between their foraging and breeding grounds. Olive ridley turtles migrate annually in November to the east coast of India from their foraging grounds in the Bay of Bengal and form large aggregations at Gahirmatha and Rushikulya, two globally significant mass nesting rookeries in Odisha. However, little is known about the spatial and temporal variation in their nearshore distribution prior to the mass nesting events, which typically occur between February and April. Inter‐ and intra‐annual variations in the density and distribution of olive ridley turtles were examined in the nearshore waters of Rushikulya from 2012 to 2022. The densities of turtles were estimated for each field season and aggregations were spatially delineated using minimum convex polygons. There was considerable interannual variation in turtle abundance, which typically increased from December to February in Rushikulya. Turtle densities in nearshore waters did not correspond to the presence or absence of mass nesting, thus suggesting that management decisions cannot be based only on nesting beach estimates. Turtle aggregations in Rushikulya were spatially and temporally dynamic and were typically concentrated around the nesting beach. However, they occupied only a small fraction of the area designated as a no‐fishing zone, which suggests that these regulations need to be reassessed. As the no‐fishing zones impose high costs on fishers, it is critical to look at alternative protection measures, such as dynamic spatial closures, developed in consultation with local fishers.

Consequences of Heatwave on Density of Freshwater Turtle Populations in Water Plans of Northeastern Algeria

Aquatic turtles are ectotherm animals whose activities are conditioned by their environment. The objective of this study is to asses the heatwave effects on the abundance of aquatic turtles. The resulting study was conducted from spring to fall 2022, in a water plan next to Guerbes Sanhadja wetlands eco complex, known for the density of aquatic turtles it hosts. Temperature and rainfall data, as well as satellite images and field photography, were utilised to monitor the drying of the water plain. . Freshwater turtles were counted remotely every one hour from a specific location. The results obtained confirm the resumption of aquatic turtle activity, particularly marked in summer, but the persistence of heatwave, with abnormally high air temperatures and very low rainfall, caused the gradual drying up of the water plan and a sharp drop in turtle’s numbers.

Green turtles shape the seascape through grazing patch formation around habitat features: Experimental evidence.

Understanding how megaherbivores incorporate habitat features into their foraging behavior is key toward understanding how herbivores shape the surrounding landscape. While the role of habitat structure has been studied within the context of predator-prey dynamics and grazing behavior in terrestrial systems, there is a limited understanding of how structure influences megaherbivore grazing in marine ecosystems. To investigate the response of megaherbivores (green turtles) to habitat features, we experimentally introduced structure at two spatial scales in a shallow seagrass meadow in The Bahamas. Turtle density increased 50-fold (to 311 turtles ha-1 ) in response to the structures, and turtles were mainly grazing and resting (low vigilance behavior). This resulted in a grazing patch exceeding the size of the experimental setup (242 m2 ), with reduced seagrass shoot density and aboveground biomass. After structure removal, turtle density decreased and vigilance increased (more browsing and shorter surfacing times), while seagrass within the patch partly recovered. Even at a small scale (9 m2 ), artificial structures altered turtle grazing behavior, resulting in grazing patches in 60% of the plots. Our results demonstrate that marine megaherbivores select habitat features as foraging sites, likely to be a predator refuge, resulting in heterogeneity in seagrass bed structure at the landscape scale.

Interspecific interactions among three species of sea turtle using a common resting area.

Interspecific interactions among three species of sea turtle using a common resting area.

Fine‐scale movement and habitat use of juvenile, subadult, and adult green turtles (Chelonia mydas) in a foraging ground at Ningaloo Reef, Australia

Abstract The residence, home range, and habitat use of juvenile (42.0–63.5 cm midline curved carapace length, CCL), subadult (68.6–84.6 cm CCL), and adult (81.9–104.2 cm CCL) green turtles (Chelonia mydas) was investigated using passive acoustic telemetry in Ningaloo Marine Park, north‐western Australia. Eighty‐one turtles ranging in size from 42 to 104 cm CCL were captured on their foraging grounds and tagged with acoustic tags. Individuals were monitored for up to 913 days (range 48–913 days, median 367 days). Turtles of all sizes demonstrated very high fidelity to their foraging area. Residence declined with turtle body size and home range increased with turtle body size, with an average 50% kernel utilization distribution (KUD) area of 0.29, 0.47, and 0.57 km2 for juveniles, subadults, and adults, respectively. Juveniles occurred only in shallow inshore habitat dominated by seagrass and macroalgae‐covered pavement. Subadults and adults selected macroalgae‐covered pavement, sandy areas of the lagoon, and macroalgae‐dominated patch reefs within the lagoon. At high tide, juveniles were approximately 200 m closer to the shore than at low tide, but there was no tidal pattern of space use in subadult and adult turtles. Less than 5% of turtles departed the array within 6 months and there was no evidence of developmental migrations in subadults. The results highlight the conservation potential for go‐slow areas to minimize boat strike in areas of high turtle density, given the small and stable home ranges. Furthermore, the spatial segregation of juveniles, subadults, and adults will result in variability in the susceptibility of individuals to boat strike. The influencing factors that drive the developmental migrations of turtles to consecutive habitats as they grow, as well as movement away from foraging grounds in response to changes in habitat quality, are complex. The ability of acoustic telemetry to provide long‐term data on all size classes of turtles within foraging areas provides a tool to enable the long‐term monitoring of turtle populations, which is required for at‐risk populations and/or habitats.

Population density and abundance of Green Turtles (Chelonia mydas) in one of the largest feeding grounds in the Egyptian Red Sea

Green turtles (Chelonia mydas) are globally endangered and very little is known about their population in Egypt’s Red Sea. Abu Dabbab Bay was believed to contain one of the most dense and important green turtle feeding grounds in the Egyptian Red Sea. The results of our surveys suggest that Abu Dabbab Bay is a high density feeding ground with 612±61.9 turtles/km2 and a mean population size of 104±10 turtles. The density and abundance of green turtles in Abu Dabbab bay has at least doubled, depending upon survey month, in a ten year span This increase could be the result of reduced shark populations in the Red Sea, a temporary reduction of tourist numbers from the Covid 19 pandemic, and/or local initiatives by private stakeholders to reduce disturbance. Regular monitoring the is needed to better understand the reasons for future population trends.

Incorporating Geographical Scale and Multiple Environmental Factors to Delineate the Breeding Distribution of Sea Turtles

Temperature is often used to infer how climate influences wildlife distributions; yet, other parameters also contribute, separately and combined, with effects varying across geographical scales. Here, we used an unoccupied aircraft system to explore how environmental parameters affect the regional distribution of the terrestrial and marine breeding habitats of threatened loggerhead sea turtles (Caretta caretta). Surveys spanned four years and ~620 km coastline of western Greece, encompassing low (<10 nests/km) to high (100–500 nests/km) density nesting areas. We recorded 2395 tracks left by turtles on beaches and 1928 turtles occupying waters adjacent to these beaches. Variation in beach track and inwater turtle densities was explained by temperature, offshore prevailing wind, and physical marine and terrestrial factors combined. The highest beach-track densities (400 tracks/km) occurred on beaches with steep slopes and higher sand temperatures, sheltered from prevailing offshore winds. The highest inwater turtle densities (270 turtles/km) occurred over submerged sandbanks, with warmer sea temperatures associated with offshore wind. Most turtles (90%) occurred over nearshore submerged sandbanks within 10 km of beaches supporting the highest track densities, showing the strong linkage between optimal marine and terrestrial environments for breeding. Our findings demonstrate the utility of UASs in surveying marine megafauna and environmental data at large scales and the importance of integrating multiple factors in climate change models to predict species distributions.

Spatial distribution of sea turtles on South Atlantic subtropical reefs

Environmental conditions have a strong influence on sea turtle population dynamics. Sea turtles spend most of their lives in foraging areas; however, there is a lack of information on how oceanographic and biological parameters determine habitat use and density. Here, we estimated density of green turtles Chelonia mydas and hawksbill turtles Eretmochelys imbricata in a South Atlantic foraging area (Arraial do Cabo, Brazil). We also investigated the influence of environmental variables (wind fetch, temperature, depth, and visibility) and benthic composition on the distribution of turtles. Surveyed sites were split between a colder, more wave-exposed location (western), and a warmer, more sheltered location (eastern). To ensure that these mobile and sparsely distributed species were adequately surveyed, underwater visual censuses (timed transects) were conducted. Sea turtle densities were significantly different between warm/sheltered and cold/wave-exposed locations. C. mydas were almost 10 times more frequently sighted than E. imbricata. The local distribution of E. imbricata mirrored large-scale latitudinal patterns, where this tropical species is dominant on warmer reefs (similar to habitat conditions found at the eastern location). It was not possible to assess the environmental influence on E. imbricata sightings due to their low density. C. mydas were frequently sighted in the cold/exposed sites and negatively correlated with depth. Overall, the density of E. imbricata and C. mydas suggests that Arraial do Cabo is an important feeding ground in the western Atlantic Ocean. This study highlights that visual census can produce reliable density estimates of sea turtles in foraging areas.

Effects of urban demand for food and water on physicochemicals and biotic structure of riverine wetlands in the Pampean plain

ABSTRACT Riparian areas of riverine plains develop extensive floodable areas named riverine wetlands, which are essential to the water cycle balance and ecosystem dynamics. In this study, we contrasted the hydrological and physicochemical variables of riverine wetlands of both peri-urban areas impacted by intensive farming and those of rural areas with the indicators of the biotic structure (taxonomic richness, Shannon diversity and total density) of benthic diatoms, phytoplankton, zooplankton, macroinvertebrates, chironomids, fishes, turtles, and birds. The study was performed on riverine waters of the Pampean plain, Argentina, with four seasonal samplings conducted in 2017–2018. Our results showed that the significant deepening of the groundwater level caused by aquifer overexploitation in peri-urban areas, as well as the declining surface water quality with higher phosphorus and total nitrogen concentrations, affected the taxonomic richness, diversity, and total density of the biotic assemblages of riverine wetlands. The taxonomic richness of birds, turtles, phytoplankton, chironomids, and fishes was the most sensitive to land use. Phytoplankton, chironomid, and fish diversity showed the greatest differences between rural and peri-urban riverine waters, while the total density of chironomids and birds showed the greatest differences according to land use. The results suggest that the socioeconomic development in those riverine wetlands that still maintain conditions close to the natural ones needs to be subject to guidelines derived from integrated basin management and sustainable urban planning.

Sequential overgrazing by green turtles causes archipelago-wide functional extinctions of seagrass meadows

After centuries of decline, green turtle (Chelonia mydas) populations are showing handsome localized recoveries due to dedicated conservation efforts. This calls into question how much herbivory can be sustained by seagrass meadows that these turtle populations feed on. In our study, we documented the long-term impacts of green turtle foraging on seagrass meadows in the Lakshadweep archipelago, Indian Ocean. We tracked green turtle densities and seagrass areal extent in five atolls across the archipelago since 2005. Turtle densities first grew to record levels in the seagrass meadow of the Agatti lagoon around 15 years ago. Within a few years of intense herbivory, the meadow underwent radical biomass reduction and compositional shifts, leading to functional extinction and ultimately, bare sand. This trajectory of decline wtas repeated in every atoll, with turtle aggregations persisting 2 to 6 years before meadows were depleted, depending on their initial size. By 2019, all large meadows had declined, and in 2020, green turtles were distributed at low densities in every meadow. The meadows were limited to small patches of early successional species, maintained in a state of protracted recovery by constant, low-level herbivory. We measured the impacts of turtles on two key ecosystem services, a habitat for fish communities and stored organic carbon. Turtle overgrazing resulted in massive declines in seagrass fish diversity, biomass, and abundance, and major reductions in sediment-stored carbon. Apart from being important conservation flagships, green turtles are strong ecosystem interactors, and can potentially cause trophic cascades or functional extinction of seagrass ecosystems.

Turtle density around Mussau Island, Papua New Guinea: with notes on the practicality of in-water distance sampling

Despite sea turtles in Papua New Guinea being culturally important and heavily harvested, no in-country density estimates have been previously established. We provide the first estimates of sea turtle density in Papua New Guinea from two locations around Mussau Island where turtle consumption is banned due to religious beliefs. We obtained density estimates using a low-cost, in-water distance sampling method. Our monitoring shows that the island has a high density of sea turtles (almost exclusively Chelonia mydas). At Lolieng, a site with a steep reef drop off, we recorded a mean of 7.4 turtles ha−1 (s.d. = 2.6) at the reef crest during low tide (across all sampling occasions), which is comparable to high density sites globally. By comparison, we recorded a much lower estimate of 1.1 turtles ha−1 (s.d. = 0.4) at Nae, a site with an extensive, low profile reef system. Additionally, our modelling shows that tidal cycle is an essential covariate for assessing sea turtle density for in-water distance sampling. We advocate that Papua New Guinea needs to invest in long-term monitoring at a national scale to track the sustainability of this important cultural resource, and that in-water distance sampling is a low cost monitoring method that potentially could be used for this purpose albeit subject to certain caveats.

A Sea Turtle Population Assessment for Florida's Big Bend, Northeastern Gulf of Mexico

Coastal waters of Florida’s Big Bend, Gulf of Mexico (GOM) once supported one of the largest sea turtle fisheries in the United States. To fill an information gap in this region on abundance and distribution of sea turtles, we used vessel—based distance sampling and active capture methods to characterize current foraging aggregations near the St. Martins Marsh Aquatic Preserve. Over 10 sampling periods between 2012—2018, we completed 513 km of transects and recorded 819 turtles among 4 species—green turtle (Chelonia mydas, n = 624), Kemp’s ridley (Lepidochelys kempii, n = 147), loggerhead (Caretta caretta, n = 47), and a single hawksbill (Eretmochelys imbricata). Turtle densities in 4 study plots within the 200 km2 study site ranged from 57—221 immature green turtles/km2, 16—56 immature Kemp’s ridleys/km2, and 1—14 juvenile—to—adult loggerheads/km2. Of 200 green turtles captured, 67.5% showed skin tumors consistent with fibropapillomatosis, a frequency similar to that from urbanized estuaries of Florida’s east coast. The largest green turtles (> 60 cm straight standard carapace length), abundant in the southern portion of our study area, are of note because this size class is uncommonly recorded within US territorial waters. Analyses of green turtle mtDNA haplotypes found contributions from rookeries in the western GOM, Mexican Caribbean, and Costa Rica. Although Big Bend protected areas were principally designed to conserve marine and coastal habitats, these regulatory zones have also effectively encompassed a hotspot for foraging sea turtles.

Patterns of nesting behaviour and nesting success for green turtles at Raine Island, Australia

To understand how turtles use the nesting habitat at Raine Island across a nesting season, and how the turtles respond to the restoration of the island’s dune systems, we identified 534 nesting events for 39 green turtles Chelonia mydas across 2 breeding seasons using data derived from satellite tags. Tracked turtles laid between 4 and 10 clutches of eggs. Patterns of nesting success varied between individuals, within and between seasons. Nesting success was higher in 2018-19 (57%) than 2017-18 (45%), and in both years, nesting success was lowest between October and early January (<50%). In 2017-18, increased rainfall in January corresponded with increased nesting success (>50%). The density of female turtles ashore was lower in 2018-19, and likely explains higher nesting success in 2018-19 because competition for nest space was lower. In 2017-18, females had more attempts per clutch, and the attempts were around 90 min longer. Consequently, energy required to lay a clutch of eggs in 2017-18 was significantly higher than in 2018-19, highlighting potential costs of lower nesting success rates on reproductive output. The area of beach re-profiled as an intervention in 2014 and 2017 was a nesting hotspot in 2017-18. However, in 2018-19, the area was not used to the same extent, and the nesting hotspot occurred on the north-eastern unaltered beach. Collectively, the tracking of turtles across the whole nesting season enabled us to assess overall beach use and nesting site fidelity of green turtles at Raine Island. Results will aid future planning and management of beach restoration activities at turtle nesting sites.

Effects of stocking density of Chinese soft‐shelled turtle and interactions between cultivated species on growth performance and the environment in a turtle–rice coculture system

AbstractExperiments were performed to investigate the effects of stocking density (6, 8, 10, and 12 turtles/m2) of Chinese soft‐shelled turtles (Pelodiscus sinensis) and coculture interactions on growth performance and environment in a turtle–rice coculture system. The average yields of rice grain and rice straw in four turtle–rice coculture (TR) groups were significantly higher than those in a rice monoculture with fertilizer (RMF) group and a rice monoculture (RM) group (p < .05). The yield of turtles increased gradually with increasing stocking density until reaching 10 turtles/m2, and the yield of TR10 was 1,297.51 ± 106.31 g/m2. The death rate in TR6, TR8, and TR10 groups was significantly lower than that in the turtle monoculture (TM) group (p < .05), whereas the specific growth rate and weight gain in TR6, TR8, and TR10 groups were significantly higher than those in the TM group (p < .05). The nitrogen and phosphorus use efficiencies in the TR groups were significantly higher than those in the TM and RM groups (p < .05). The water environment was improved in the TR group. The results suggest that an appropriate stocking density (10 turtles/m2) of turtles in the coculture system can effectively increase the yield of turtles and reduce the impacts on the environment compared with the TM.

Road mortality of freshwater turtles in Palawan, Philippines

The impact of road mortality on freshwater turtle populations on a global scale could be significant enough to cause the extinction of sensitive species. Essential data on roadkill abundance, composition, spatial patterns, and temporal distribution is needed for crafting mitigation strategies. To provide such information, a survey was conducted along the highway section (67 km) connecting Aborlan and Puerto Princesa City in Palawan, Philippines. Collection of data was done four times a month from January 2010 to December 2015. A total of 127 road-killed turtles belonging to two species of the Geoemydidae family were recorded, 102 (80.3%) of which were classified as the Southeast Asian Box Turtle (Cuora amboinensis) and 25 (19.7%) were identified as the Asian Leaf Turtle (Cyclemys dentata). The increase in road traffic noticed during the survey period possibly caused the corresponding increase in the roadkill counts of C. amboinensis, which is a more common species. Concurrently, the decline in the road-kill counts of C. dentata may indicate a severe drop in the population of this less common species. Roadside habitat types, time of the day, and presence of water bodies are found to be important predictors of road-killed turtles. High densities of road-killed turtles clustered in short segments of the road which identified as hotspots. Effective mitigating measures to curve down the impact of road mortality on turtle populations must be implemented and focusing the conservation strategies along the hotspots is considered an efficient and practical option.

A turtle population study in an isolated urban wetland complex in Ontario reveals a few surprises

We report on the results of the first mark–recapture survey of freshwater turtles in an isolated urban wetland complex in one of Canada’s fastest growing municipalities. Although we found turtles in every surveyed wetland, the density and assemblage of turtles in smaller wetlands were significantly different than in larger wetland bodies. We also documented two species of turtles that were thought to be absent from this wetland complex, the Northern Map turtle and Eastern Musk turtle. We noted that a wetland that was bisected by a high-traffic road showed a male-skewed sex ratio in the population of Midland Painted turtles but not in the population of Eastern Snapping turtles. As a whole, the sex ratios inside the wetland complex were not skewed. These results reinforce the conclusions of a previous study of a single wetland within this same complex that had found a correlation between road mortality and a male-skewed sex ratio in Midland painted turtles. We discuss population sources and sinks within the complex and the importance of protecting the overland corridors that support the safe turtle movements within this provincially significant wetland complex.

Densities and drivers of sea turtle populations across Pacific coral reef ecosystems.

Sea turtle populations are often assessed at the regional to sub-basin scale from discrete indices of nesting abundance. While this may be practical and sometimes effective, widespread in-water surveys may enhance assessments by including additional demographics, locations, and revealing emerging population trends. Here, we describe sea turtle observations from 13 years of towed-diver surveys across 53 coral islands, atolls, and reefs in the Central, West, and South Pacific. These surveys covered more than 7,300 linear km, and observed more than 3,400 green (Chelonia mydas) and hawksbill (Eretmochelys imbricata) sea turtles. From these data, we estimated sea turtle densities, described trends across space and time, and modelled the influence of environmental and anthropogenic drivers. Both species were patchily distributed across spatial scales, and green turtles were 11 times more abundant than hawksbills. The Pacific Remote Island Areas had the highest densities of greens (3.62 turtles km-1, Jarvis Island), while American Samoa had the most hawksbills (0.12 turtles km-1, Ta’u Island). The Hawaiian Islands had the lowest turtle densities (island ave = 0.07 turtles km-1) yet the highest annual population growth (μ = 0.08, σ = 0.22), suggesting extensive management protections can yield positive conservation results. Densities peaked at 27.5°C SST, in areas of high productivity and low human impact, and were consistent with patterns of historic overexploitation. Though such intensive surveys have great value, they are logistically demanding and therefore have an uncertain budget and programmatic future. We hope the methods we described here may be applied to future comparatively low-cost surveys either with autonomous vehicles or with environmental DNA.