Human activities threaten sea turtles at virtually every stage of their lives, from the moment eggs are laid on a beach to the decades adults spend migrating across open ocean. Fisheries bycatch and coastal development consistently rank as the top two threats in expert assessments, but they sit alongside a long list of other pressures: plastic pollution, climate-driven nest feminization, illegal harvesting, chemical contamination, invasive predators, and vessel strikes, among others. No single threat operates in isolation. What makes the situation especially precarious is that sea turtles are slow to mature and reproduce, so population losses can take years or decades to become visible.
Fisheries Bycatch
Being accidentally caught in fishing gear is widely considered the most serious at-sea threat to sea turtles. Trawl nets, gill nets, and longlines all capture turtles that surface to breathe or forage near the seabed. A global analysis of bycatch impacts found that net and trawl gear impose significantly higher mortality and bycatch impact scores on turtle populations than longline gear, largely because turtles caught in nets are more likely to drown before the gear is retrieved.1Ecosphere. Impacts of fisheries bycatch on marine turtle populations worldwide: toward conservation and research priorities The problem is not just active fishing fleets. An estimated 640,000 tons of fishing gear is lost, abandoned, or discarded worldwide each year, and these “ghost nets” continue drifting and trapping marine life for years or even decades.2Conservation Letters. Ghostnet impacts on globally threatened turtles, a spatial risk analysis for northern Australia
Ghost nets with larger mesh and smaller twine, the kind used in pelagic drift-net fisheries, are especially dangerous because turtles become tangled more easily. Research in northern Australia estimated that roughly 8,700 recovered ghost nets had caught somewhere between 4,900 and 14,600 turtles, assuming each net drifted for about a year.3PubMed. Understanding the sources and effects of abandoned, lost, and discarded fishing gear on marine turtles in northern Australia Data from the Indian Ocean paints a similar picture: among injured turtles documented over 12 years, about 75% of morbidity or mortality cases were attributed to human causes, and the single most common injury source was ghost-net entanglement, accounting for roughly two-thirds of all cases. Injuries ranged from deep flipper lacerations to traumatic amputations.4PLoS ONE. Evaluation of sea turtle morbidity and mortality within the Indian Ocean from 12 years of data shows high prevalence of ghost net entanglement
Turtle excluder devices, or TEDs, are one of the most effective mitigation tools available. In Australian prawn trawl fisheries, nets equipped with TEDs reduced turtle catches by 99%.5Fisheries Research. The impact of turtle excluder devices and bycatch reduction devices on diverse tropical marine communities in Australia’s northern prawn trawl fishery Those same devices also dramatically reduced catches of larger sharks and rays. In the Mediterranean, TEDs prevented all potentially live-caught turtles from ending up in the net’s collection bag, though some vessels experienced commercial catch losses in the range of 17–20%, which complicates adoption.6Aquatic Conservation: Marine and Freshwater Ecosystems. Turtle Excluder Devices for Multispecies Bottom Trawls in the Mediterranean: Current Performance and the Need for Further Adjustments Getting fishers to adopt TEDs remains an ongoing challenge, and researchers stress that designs need further refinement, ideally with direct fisher input, to reduce those economic trade-offs.
Plastic Pollution and Ingestion
Plastic debris harms sea turtles in two main ways: they eat it, and they get tangled in it. All seven species of marine turtle have been documented ingesting plastic. Turtles are visual predators, so they often mistake floating bags, balloon fragments, and thin plastic film for food like jellyfish. Indirect ingestion also occurs when turtles eat prey organisms that have already accumulated microplastics in their tissues.7ICES Journal of Marine Science. Plastic and marine turtles: a review and call for research
The consequences go beyond a one-time stomach blockage. Hard plastic fragments can cause internal lacerations and intestinal obstruction. Over longer periods, the bigger problem may be what researchers call dietary dilution: plastic sitting in the gut takes up space that food would normally occupy, reducing the turtle’s drive and ability to eat. A study on green turtles found that while small amounts of plastic in the stomach actually coincided with increased food intake, once plastic accumulated throughout the gastrointestinal tract, food consumption dropped. Turtles with higher plastic loads were more likely to be underweight or emaciated.8PubMed. Exploring plastic-induced satiety in foraging green turtles Buoyant material trapped in the intestines can even interfere with a turtle’s ability to dive properly, and chemical additives like phthalates can leach from ingested plastics into body tissues over time, potentially disrupting hormone systems.7ICES Journal of Marine Science. Plastic and marine turtles: a review and call for research
Coastal Development and Light Pollution
Sea turtles depend on sandy beaches to nest, and decades of coastal construction have steadily chipped away at the quality and availability of those beaches. Hard-armoring structures like seawalls and rock revetments are especially problematic. When female turtles encounter these barriers while searching for a nesting site, they frequently abort the attempt. Research on Florida beaches showed that green turtles nested at significantly lower densities near hard-armored sites, and nesting success for both loggerheads and greens dropped when turtles encountered these structures compared to beaches with no obstructions.9Frontiers in Marine Science. Responses of three nesting sea turtle species to hard-armoring structures The energy a female turtle spends crawling up a beach, encountering a wall, turning around, and trying again elsewhere is not trivial for an animal that may nest multiple times per season.
Artificial lighting adds another layer of harm. Sea turtle hatchlings instinctively orient toward the brightest horizon to find the ocean, which under natural conditions is the open sky reflected off the water. Beachfront lights from hotels, roads, and houses overwhelm that natural cue. On Pinellas County beaches in Florida, more than a third of all hatchling emergences between 2018 and 2023 resulted in disorientation events, with hatchlings heading inland instead of toward the surf.10PLoS One. Disorientation patterns of loggerhead sea turtle (Caretta caretta) hatchlings in Pinellas County, Florida, USA Studies in Taiwan confirmed that when artificial light intensity exceeds natural ambient light, hatchlings become either misoriented (heading in a consistent but wrong direction) or disoriented (heading in no consistent direction at all).11PubMed Central. The Effect of Light Pollution on the Sea Finding Behavior of Green Turtle Hatchlings on Lanyu Island, Taiwan Disoriented hatchlings that wander the beach are easy prey for crabs, birds, and other predators, and those that wander inland face dehydration and exhaustion.
Climate Change and the Disappearance of Males
Sea turtles have temperature-dependent sex determination: the temperature of the sand during a critical window of egg incubation determines whether a hatchling develops as male or female. Warmer sand produces more females. As global temperatures climb, this mechanism is pushing entire populations toward extreme female bias. A global analysis of 64 nesting sites found that 57 already showed female-skewed sex ratios, with 17 sites producing more than 90% female hatchlings.12PubMed. Climate warming and sea turtle sex ratios across the globe
One of the starkest examples comes from Australia’s Great Barrier Reef. At the warmer northern nesting beaches, researchers found that over 99% of juvenile and subadult green turtles were female, and this extreme skew has persisted for more than two decades. Southern beaches, which are cooler, still showed a female bias but a more moderate one, around 65–69%.13PubMed. Environmental Warming and Feminization of One of the Largest Sea Turtle Populations in the World A near-total loss of males does not immediately collapse a population because a single male can mate with multiple females, but it reduces genetic diversity and leaves populations with no buffer if males decline further.
Rising seas create a separate but related threat. Higher water levels increase the frequency of nest inundation, where saltwater washes over buried eggs. Experiments on green turtle eggs showed that six hours of saltwater exposure cut hatching success by about 30% compared to unexposed controls.14PubMed Central. Nest inundation from sea-level rise threatens sea turtle population viability Shorter flooding events of one to three hours were less damaging, but as storm surges and tidal reach increase with sea-level rise, prolonged inundation events will become more common.
Illegal Harvesting and the Egg Trade
Despite legal protections in most countries, sea turtles continue to be hunted for their meat, eggs, and shells. Researchers estimate that over 1.1 million marine turtles were illegally exploited between 1990 and 2020, spanning 65 countries or territories. Over the most recent decade tracked, the rate sat above 44,000 turtles per year.15PubMed. Global patterns of illegal marine turtle exploitation The trade covers a range of uses, from turtle eggs sold as aphrodisiacs or protein sources, to shells carved into jewelry, to meat eaten as a cultural delicacy.16Ecology and Society. Motivations and sensitivities surrounding the illegal trade of sea turtles in Costa Rica
Egg poaching is particularly insidious because sea turtles take decades to reach reproductive maturity. Removing a clutch of eggs today eliminates hatchlings that would not have contributed to the breeding population for 20 to 30 years, so the population impact stays hidden long after the theft. In many coastal communities, enforcement is limited and economic incentives to poach remain strong. In places like Costa Rica and the wider Caribbean, conservation programs that guard nesting beaches have had real success, but they need sustained funding and community buy-in to be effective over the long term.16Ecology and Society. Motivations and sensitivities surrounding the illegal trade of sea turtles in Costa Rica
Chemical Contamination
Sea turtles sit relatively high in the food chain and are long-lived, which makes them susceptible to bioaccumulation of toxic metals and persistent organic pollutants. Studies on loggerhead turtles in the Mediterranean have measured concerning concentrations of mercury, cadmium, lead, and arsenic in internal organs. Mercury accumulated most heavily in the liver, cadmium and arsenic in the kidneys, and lead in muscle tissue.17PubMed Central. Bioaccumulation and biomagnifications of toxic metals in tissues of loggerhead turtles (Caretta caretta) from the Mediterranean Sea coast, Egypt These metals enter the marine environment through industrial runoff, agricultural chemicals, and fossil-fuel combustion, and they magnify up the food web with each trophic level. At high enough levels, heavy metals compromise immune function, interfere with reproduction, and damage organ systems, though the exact population-level consequences for sea turtles are still being studied.
Degraded water quality also shrinks the dietary options available to turtles. In highly urbanized coastal areas of southeastern Brazil, researchers documented that habitat degradation led to low algal diversity on the seabed, which in turn restricted the diet of green turtles relying on those foraging grounds.18PubMed. Coastal habitat degradation and green sea turtle diets in Southeastern Brazil A turtle that can only find a few species of algae is both nutritionally limited and more vulnerable if any one food source disappears.
Invasive Predators on Nesting Beaches
Human activity has introduced a range of non-native predators to sea turtle nesting beaches around the world. Black rats, feral pigs, and mongooses are among the most destructive. A global review catalogued 36 species known to predate sea turtle eggs, and eight of those were invasive species brought to islands by humans.19Marine Biology. Predation of sea turtle eggs by rats and crabs On one island monitored in the study, overall hatching success was about 65%, with roughly 3% of eggs lost directly to nest predation, though rates vary enormously by site.
Feral swine can cause outsized damage. On one North Island nesting site, feral pigs caused nearly total nest destruction in 2010 and 2011, wiping out an entire season’s reproductive output before management programs kicked in.20Acta Oecologica. Feral swine harming insular sea turtle reproduction: The origin, impacts, behavior and elimination of an invasive species In the Caribbean, introduced mongooses prey on hawksbill turtle eggs, and the problem is amplified by habitat fragmentation. Hawksbills prefer to nest along vegetation edges, but in fragmented beach habitat those edges are also the corridors mongooses use to hunt, turning what was once a safe nesting strategy into an ecological trap.21PubMed Central. Predicting species interactions from edge responses: mongoose predation on hawksbill sea turtle nests in fragmented beach habitat
Vessel Strikes, Dredging, and Underwater Noise
Boat traffic poses a direct physical hazard to turtles that surface to breathe in busy waterways. Studies on loggerhead sea turtles have documented characteristic injuries from boat encounters: parallel propeller slashes across the shell, continuous wounds from the motor’s lower housing, and torn-away sections of the carapace from blunt-force impact.22Journal of Experimental Marine Biology and Ecology. Influence of small vessel operation and propulsion system on loggerhead sea turtle injuries Many of these injuries are fatal, and even non-lethal strikes can leave turtles vulnerable to infection and impaired swimming.
Dredging operations, used to deepen ports and channels, present risks of entrainment (turtles being sucked into dredging equipment), vessel strike, and habitat disturbance. Research on flatback turtles during an active dredging operation found that turtles actually increased their use of the dredging area while it was being worked, rather than avoiding it. They also changed their dive behavior, taking longer and deeper resting dives in the now-deeper water.23Biological Conservation. Effects of a dredging operation on the movement and dive behaviour of marine turtles during breeding This counterintuitive attraction to dredging areas raises the risk of direct injury from the equipment.
Underwater noise from vessel engines also appears to alter turtle behavior. A study tracking a free-ranging green turtle in the Galapagos found that increasing vessel noise caused the turtle to become more vigilant while swimming, spending more time scanning rather than foraging or resting. This behavioral shift may not sound like much, but it can change how turtles allocate their daily energy budget, potentially reducing the time available for feeding and rest over extended periods.24PubMed. Anthropogenic noise predicts sea turtle behavioural responses
Disease Linked to Degraded Environments
Fibropapillomatosis is a tumor-forming disease that has become increasingly common in sea turtles, particularly green turtles, and its spread appears to be linked to degraded coastal environments. The disease causes large external and internal growths that can impair a turtle’s vision, movement, and ability to feed. In Texas, researchers found that fibropapillomatosis prevalence correlated with environmental indicators associated with nutrient pollution, including river water discharge, organic carbon levels, and phosphorus concentrations.25PubMed Central. Occurrence of Fibropapillomatosis in Green Turtles (Chelonia mydas) in Relation to Environmental Changes in Coastal Ecosystems in Texas and Florida: A Retrospective Study The suspected pathway is that nutrient runoff from agriculture and development fuels algal blooms and shifts the microbial environment in ways that promote the herpesvirus responsible for the disease.
In Akumal Bay, Mexico, a popular snorkeling destination, green turtles are experiencing rising rates of fibropapillomatosis in what researchers describe as an area of intense and prolonged tourism pressure. The disease is associated with stress-induced immunosuppression, and the combination of high human density and degraded water quality appears to be making turtles more susceptible.26Aquatic Conservation: Marine and Freshwater Ecosystems. Sick of attention: The effect of a stress‐related disease on juvenile green sea turtle behaviour in the face of intense and prolonged tourism This is a case where multiple human pressures converge: nutrient pollution weakens habitat quality, tourism adds chronic stress, and compromised immune systems let an opportunistic pathogen flourish.
Tourism and Direct Human Disturbance
Sea turtle tourism generates significant conservation funding and public awareness, but it is not without trade-offs. Even well-managed turtle-watch programs affect the animals they are meant to protect. Studies of guided nesting-watch programs in Florida noted that turtles observed during egg-laying often displayed camouflaging behavior, holding still rather than continuing their normal nesting routine, which suggests they were reacting to the group’s presence even when they appeared undisturbed.27Global Ecology and Conservation. Using behavior indices and vital rates to determine the conservation impact of wildlife tourism: Guided sea turtle watch programs in Florida In unmanaged or loosely managed settings, the effects can be worse. Crowds on nesting beaches, flashlight use, and physical contact with turtles can cause females to abandon nesting attempts entirely.
The challenge is finding the right balance. Tourism revenue often funds the very beach patrols and hatchery programs that protect turtles, so shutting it down entirely can be counterproductive. But in high-traffic areas like Akumal Bay, the sheer volume of daily snorkelers creates conditions of chronic disturbance that contribute to stress and, potentially, disease susceptibility. Managing group sizes, restricting viewing distances, and limiting the hours during which beaches are open to visitors are all strategies being used, though enforcement is spotty in many countries. The broader tension is one familiar across wildlife conservation: the animals most worth protecting are often the ones most accessible to tourism, and accessibility is both their best funding source and one of the threats they face.