Water Pollution's Impact: Seabird Health And Habitat

Seabirds are an integral part of marine ecosystems and are often used as indicators of the health of these environments. Water pollution, especially from plastic and oil, poses a significant threat to seabirds. Plastic pollution in the oceans has increased exponentially, with an estimated 15-51 trillion pieces of plastic currently in the oceans. Seabirds often mistake plastic for prey, leading to ingestion and health issues such as reduced stomach volume, kidney dysfunction, and higher concentrations of uric acid. Oil spills, both acute and chronic, can cause mass mortality among seabirds, affecting their waterproofing, buoyancy, and internal organs. Additionally, water pollutants can displace seabirds from their foraging habitats and reduce food availability. The impact of water pollution on seabirds highlights the delicate balance of marine ecosystems and the need for conservation efforts to protect these vulnerable species.

Oil spills

The toxic effects of oil spills on seabirds are primarily due to the presence of polycyclic aromatic hydrocarbons (PAHs), which are chemical constituents of petroleum oils. PAHs can cause endocrine disruption, compromising the birds' ability to recover and leading to unsustainable mortality. The ingestion of oil can also disturb thyroid homeostasis, which is vital for controlling energy metabolism. This disruption can result in lower body weight and condition, reducing the birds' chances of survival.

The impact of oil spills on seabirds can be long-lasting and devastating. The 1989 Exxon Valdez oil spill in Alaska's Prince William Sound resulted in the death of approximately 250,000 birds, with nearly three-quarters of them being Common Murres. While the population of Common Murres showed some resilience, recovering within a few years, the vulnerability of this species to oil spills underscores the need for better protection and conservation measures.

Plastic pollution

The detrimental effects of plastic pollution on birds include individual survival, growth and development, reproductive output, and physiology. Plastic pollution can also cause entanglement, nutritional deprivation, and damage or obstruction of the gut.

Seabirds are particularly vulnerable to plastic pollution due to their biology and migration patterns. For example, many species in the petrel and storm-petrel families migrate over vast areas of the sea, feeding on the water's surface where plastic collects. Unlike albatrosses and gulls, these birds cannot easily regurgitate plastic pieces, which instead pile up in their guts.

Furthermore, marine plastic is not evenly distributed, with currents and coastlines concentrating debris in hotspots. As a result, where a seabird species spends most of its time significantly shapes its exposure to plastic.

Recent studies have found that six of the ten species with the highest plastic exposure scores are already classified as vulnerable, threatened, or endangered. These include the Balearic and Yelkouan Shearwaters in the Mediterranean Sea and the Hawaiian Petrels in the Pacific Ocean.

Overall, plastic pollution poses a significant threat to seabirds, with increasing production and accumulation of plastic in the oceans leading to greater ingestion and associated health risks for these vulnerable species.

Bycatch and entanglement in fishing gear

Seabirds are attracted to fishing vessels and fishing operations, as offal and bait can be tempting sources of food. Unfortunately, this means that they frequently get hooked or entangled in fishing gear, especially in longline fisheries. Most birds are attracted to the baited hooks when the gear is being set, get hooked at the surface, and then dragged underwater where they drown.

Bycatch, or accidental hooking or entanglement in fishing gear, is a common threat to seabirds. Seabirds are most affected by set and drifting gillnets and longlines, while seines, trawls, traps, pots, and related equipment can capture and kill waterbirds.

Longlining is a commercial fishing method that commonly targets swordfish, tuna, and halibut, where hundreds or thousands of baited hooks hang at intervals along a single fishing line. The hooks often cause problems for marine turtles when swallowed, usually resulting in death. Sharks, non-target billfishes, and juvenile tunas are also often hooked.

With trawling, boats drag large nets along the seabed, catching almost everything in their path. They can damage coral reefs and, at shallow depths, catch marine turtles. Gillnets are mesh nets that allow fish to pass their heads and gill coverings through a hole in the mesh and then get stuck when they try to back out. They can be several miles long and up to 100 feet deep. Gillnets also trap everything larger than the net's mesh, including seabirds. The nets are very hard to see, blending in perfectly with the water and are difficult for cetaceans to detect by echolocation.

It is estimated that over 300,000 small whales, dolphins, and porpoises die from entanglement in fishing nets each year, making this the single largest cause of mortality for small cetaceans. Species such as the vaquita from the Gulf of California and Maui's dolphin from New Zealand face extinction if the threat of unselective fishing gear is not eliminated.

There are proven solutions to reduce bycatch, such as modifying fishing gear so that fewer non-target species are caught or can escape. In many cases, these modifications are simple and inexpensive and often come from fishers themselves. For example, the WWF created the International Smart Gear Competition to promote the development of such innovative technology. In another instance, the WWF introduced "circle" hooks, which are far less likely to be swallowed by turtles than J-shaped hooks, in the eastern Pacific longline fisheries. As a result, marine turtle deaths may be reduced by as much as 90% without adversely affecting swordfish and tuna catches.

Water pollutants

Plastic

Plastic is a pervasive water pollutant, with an estimated 15-51 trillion pieces in the oceans. Seabirds often mistake plastic debris for prey, ingesting it and leading to health issues and death. Plastic ingestion reduces stomach volume, causing starvation, and affects kidney function, cholesterol, and enzyme levels. It can also cause physical injuries, such as stomach scarring. Additionally, seabirds may use marine debris, such as fishing lines and synthetic ropes, to construct their nests, which can entangle them.

Oil Spills

Seabirds are particularly vulnerable to oil spills, especially those species that spend a lot of time on the water's surface, such as auks, seaducks, and divers. Oil spills can suffocate birds, destroy the waterproofing of their feathers, leading to hypothermia and reduced buoyancy, and cause liver damage and endocrine disruption if ingested. Even small amounts of oil exposure can have sublethal effects, impacting long-term breeding success and survival. Oil spills can also displace seabirds from their foraging habitats, reducing food availability.

Bycatch from Fishing Gear

Bycatch, or accidental hooking or entanglement in fishing gear, is a common threat to seabirds. Seabirds are attracted to fishing vessels and offal and bait, but this often leads to them becoming entangled or hooked, especially in longline fisheries. This can result in drowning or serious injuries. For endangered species like the Short-tailed Albatross, bycatch can pose a significant threat to their population.

Light and noise pollution

Light pollution has a detrimental impact on seabirds, including several globally threatened species. Artificial light can disorientate nocturnal seabirds, drawing them towards boats, oil platforms, and lighthouses, which often leads to fatal collisions. Coastal light pollution is particularly harmful to fledgling petrels and shearwaters, which become lured towards urban lighting as they attempt their first flights out to sea. Once grounded, these birds often cannot take off again and are vulnerable to starvation, dehydration, and predators.

Light pollution has also been shown to negatively impact the nocturnal aerial courtship of Bermuda Petrel.

Noise pollution has also been shown to have a negative impact on seabirds. Noise pollution can increase birds' stress levels, reduce their sizes, and negatively impact their reproductive success. Constant noise can act as an "acoustic blanket", muffling the audio cues that birds rely on to detect predators, competitors, and their own species. Nesting birds exposed to noise pollution must choose between staying on guard and finding food for their young.

Research has shown that birds exposed to the persistent noise of natural gas compressors exhibit symptoms similar to those in humans suffering from post-traumatic stress disorder.

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