Water Pollution's Impact: Seal's Health At Risk

Seals are semi-aquatic marine mammals that spend part of their lives on solid ground. They are playful and curious by nature, and their health is considered a barometer for the health of the marine environment. Unfortunately, human activities such as pollution and overfishing have severely impacted the seal population. One of the most pressing issues is plastic pollution, with microplastics, abandoned fishing gear, and other plastic waste threatening the lives of seals and other marine animals. Seals often ingest microplastics, which can lead to bioaccumulation of toxins and endocrine system disruption. Additionally, seals can become entangled in plastic debris, such as fishing lines and nets, which can result in gruesome deaths. Climate change, influenced by human activities, also poses a significant threat to seals, particularly with the disappearance of sea ice, which some pinniped species rely on for raising their pups.

Seals absorb and retain pollutants

Seals are semi-aquatic marine mammals that spend part of their lives on solid ground. They are carnivores, and most species consume fish. Seals are affected by water pollution because they do not migrate but live in the same region year-round. Their thick layers of blubber absorb and retain pollutants from industrial waterways. A 2005 study showed that the harbor seals of South Puget Sound were seven times more contaminated than those living in Canada's Georgia Strait.

Biologists use tissue samples from both live and dead seals to monitor the health of the ecosystem, measuring levels of PCBs, chemicals used in flame retardants (PBDEs), pesticides, and other highly toxic waste. While a ban on PCBs has reduced those toxins in recent years, the number of chemicals used in flame retardants has increased. Studies show that PBDE concentrations have been doubling every 3.5 years and have even been detected in the High Arctic.

Contaminants are stored in the blubber of seals, and these toxins pass from generation to generation through the milk of mothers to their offspring. Exposure to flame retardants causes physical abnormalities, impairs reproduction, and causes immune disorders in marine mammals. In recent years, researchers discovered a link between contaminants and the compromised immune systems of harbor seals. Weakened seals become vulnerable to parasitic infections, low body weight, and numerous viruses, often leading to fatalities.

Microplastics are also a concern for seals. These tiny pieces of plastic, usually defined as between 0.3 and 5mm in diameter, can be ingested by seals when they eat fish. A study of the feces of the fur seal in its eastern Pacific range found microplastics in over half of the seal specimens. While the seals' digestive systems can successfully excrete the plastic, long-lived toxins can latch onto the particles and enter the body. This bioaccumulation is a concern for scientists studying seals and other carnivorous mammals, including humans.

Plastic ingestion

Marine plastic debris is one of the most pressing environmental concerns, with over 8 million tonnes of plastic discarded into the oceans each year. Seals are playful and curious by nature, and their natural habitats are being invaded by plastic rubbish and ocean pollution, such as fishing lines, nets, packing straps, and plastic bags.

Seals often end up playing with and ingesting these plastic items, which can lead to painful injuries and even death. The ingested plastic can cause blockages and tears in the digestive system, and the toxins in the plastic can affect the endocrine system, causing hormonal imbalances, reproductive issues, and brain function alterations.

Microplastics, tiny pieces of plastic that come from the degradation of larger plastic items, are a major part of the problem. Due to their small size, seals and other marine animals often mistake them for food. These microplastics can be traced through every trophic level, from plankton to fish and then to seals, demonstrating how plastic contamination moves up the food chain.

The impact of plastic ingestion on seals can be devastating, with some seals suffering for months or years before eventually succumbing to their injuries or illnesses. The plastic waste can also tighten around the seal's body as it grows, leading to a slow and painful death.

The presence of plastic in the oceans is a direct result of negligent human behaviour, and it is essential that we take collective action to address this issue.

Bioaccumulation of toxins

Bioaccumulation is the process of toxic chemicals building up inside an organism's body. This occurs when an organism consumes or absorbs a chemical at a rate faster than it can excrete it. These chemicals are stored in cells and fatty tissue, particularly in fat cells, and are not exposed to direct physical or biochemical degradation. This means that they can collect and remain in an organism's body over time.

Pollutants such as polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs) are stored in the blubber of marine mammals at the top of the food chain, including seals. These toxins are passed from generation to generation through mothers' milk. Exposure to these toxins can cause physical abnormalities, behavioural changes, impaired reproduction, and immune disorders in marine mammals.

In addition to industrial chemicals, plastic pollution is also a significant source of bioaccumulated toxins in seals. Microplastics, in particular, are an emerging threat to the environment due to their prevalence, persistence, and ability to transport and release other pollutants. Seals can become entangled in plastic waste or ingest plastic debris, leading to a slow and painful death.

Entanglement in man-made debris

Seals are playful and curious creatures that often end up playing with plastic rubbish and ocean pollution, such as fishing lines, nets, packing straps, and plastic bags. This debris comes from land-based pollution, such as plastic blown into the sea from a beach, and ocean-based pollution, which comes from garbage disposed of by ships.

The impact of entanglement can be devastating for seals. As they grow, the plastic waste tightens around their necks, flippers, or mouths, leading to a slow and painful death. Even if they are successfully released from the entanglement, seals can suffer serious wounds that may become life-threatening.

The problem of entanglement is not limited to seals, as marine debris entangles and kills many other species, including corals, fish, and sea turtles. It is crucial to address the issue of plastic pollution and continue cleanup efforts to protect seals and other marine life from the harmful effects of entanglement.

To reduce the impact of entanglement on seals, it is essential to implement measures such as releasing marine animals from entanglement, cleaning up derelict fishing gear, raising public awareness, and reducing the amount of fishing gear lost at sea through government incentives.

Reproductive failure

Water pollution has been found to cause reproductive failure in seals. Polychlorinated biphenyls (PCBs) are believed to be responsible for low rates of reproduction in seals. A study of common seals in the Netherlands found that the population declined from over 3,000 to less than 500 between 1950 and 1975, with a sharp decline in pup production. High levels of PCBs in the tissue samples of these seals indicated that this was due to the consumption of contaminated fish.

Another study found that female adult seals were the most affected by plastic entanglement, which could result in death by wounds, asphyxiation, or inability to feed. Plastic entanglement has been found to decrease population growth rates, with one study projecting a decrease in population size of between 20.34% and 91.38% over a 30-year period.

Microplastics are also a concern, as they can be ingested by seals and other marine animals, leading to physical abnormalities, behavioral changes, impaired reproduction, and immune disorders. Seals are apex predators, and microplastics can be traced through every trophic level, moving up the food chain. While seals may be able to excrete the plastic waste, the toxins that latch onto the particles can cause endocrine disruption and alterations to the immune system.

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