Various Reasons for Stranding

Animal Rescue & Rehabilitation Program

Various Reasons for Stranding


  1. Parasites may infest the skin, digestive tract, heart, and other internal organs of birds, marine mammals, and sea turtles. Animals normally contract parasites by feeding on other animals that carry them. Parasite infestations may make an animal ill and weak, and occasionally result in the animal's death (Welty, 1975; Ridgway, 1972).
  2. The parasites most often found in sea turtles are roundworms and flukes. Also, barnacles may encrust a turtle's shell and make swimming difficult (Marquez, 1990).
  3. Lice, ticks, and mites live on a bird's skin and feathers. Tapeworms, flukes, and roundworms are common internal parasites (Welty, 1975).
  4. Parasites that typically affect marine mammals include tapeworms, flukes, roundworms, lice, and barnacles (Ridgway, 1972).
  5. Gray whales are often infested with whale lice that are actually a type of amphipod.

  6. Two of the most common parasites of the California sea lion are roundworms, Anisakis spp. (found in the stomach), and the lungworm, Parafilaroides decorus. The lungworm lives in lung tissue, where it can make breathing difficult for its host. It develops gradually and is well established before the infestation becomes apparent. Affected individuals may become susceptible to pneumonia (Ridgway, 1972). Parasite infestations alone seldom debilitate otherwise healthy pinnipeds. They may harm the animals if they are weakened by other health conditions (Geraci and Lounsbury, 1993).
  7. Lungworm is one of the most common parasites afflicting California
    sea lions. The infestation is usually not harmful to them unless they
    are weakened by additional health problems.


  1. An animal in a weakened state often falls victim to viral, bacterial, and fungal infections.
    • Sea turtles.
      • Researchers have identified fibropapillomas in green sea turtles. Fibropapillomas are abnormal lobed tumorous growths on the skin. These growths appear between the scales and scutes, on the eyes and eyelids, in the mouth and viscera, on the back of the neck, and on the axillary ("armpit") and inguinal regions of the flippers. Fibropapillomas ultimately can be life threatening to free-ranging sea turtles by obscuring their vision and thus affecting their ability to feed, by becoming large enough to impair normal swimming, by interfering with respiration, or by predisposing them to secondary infections (Balazs and Pooley, 1991).

        Green sea turtles are sometimes afflicted with abnormal, lobed,
        tumorous growths on the skin called fibropapillomas.

    • Waterfowl and seabirds.
      • Diseases of waterfowl and seabirds vary with habitat and food preferences.
      • Infectious diseases may spread through entire waterfowl and seabird populations resulting in mass die-offs. Migrating waterfowl spread disease further. Infections include viral hepatitis, Newcastle disease, tuberculosis, tetanus, and botulism (Welty, 1975).
      • Aspergillosis, a fungal infection transmitted by airborne spores, is a common disease of waterfowl and seabirds. Aspergillosis outbreaks are most likely caused by lowered resistance or environmental factors (Dierauf, 1990; Welty, 1975).
    • Marine mammals.
      • Marine mammals may suffer from viral, bacterial, and fungal infections, including aspergillosis. In 1990, an outbreak of morbillivirus resulted in the deaths of at least 750 striped dolphins in the Mediterranean Sea (Geraci and Lounsbury, 1993).
      • Marine mammals may develop stomach ulcers, skin diseases, hepatitis, cancer, tuberculosis, and respiratory disorders such as pneumonia.


  1. Young marine mammals often are affected by storms and bad weather. Unable to nourish themselves, they lose blubber and become thin. The animals expend more energy to swim and to stay warm, causing them to lose more blubber. When an animal finally strands it is exhausted and emaciated (Geraci and Lounsbury, 1993).
  2. Storms and bad weather can cause young marine mammals to
    expend excessive energy to swim and stay warm. They are often
    exhausted and emaciated when they strand.


  1. Pups, calves, and chicks may become separated from their mothers during storms and in times of danger. Mothers may die, leaving young behind. Many of these young animals that rely on their mothers for food and protection may not survive on their own.
  2. Young animals like this pygmy sperm whale calf rely on their mothers for food and protection and cannot survive if they aren’t rescued.

  3. Some young seals and sea lions don't survive the natural separation process that occurs after they are weaned.


  1. Entanglement is an increasing threat to marine animals. Seabirds, marine mammals, sea turtles, fishes, and invertebrates can become trapped in nets, ropes, fishing line, or other lost or floating fishing gear. Discarded garbage such as plastic bags, sheets, and wrapping bands also entangle marine animals, making it difficult for them to breathe or take food. Without assistance, entanglement usually results in injury and death.
  2. Entanglement in items such as nets, ropes, and fishing line can cause
    sever injury and death in marine animals.

Ingestion of Non-Food Item

  1. Plastic is often mistaken as food by marine animals. Animals may mistake plastic pellets for fish eggs, or plastic bags for jellyfish. These objects can become lodged in the throat or restrict an airway, causing the animal to suffocate or drown.
  2. This sea turtle has ingested a fishing hook
    that must be surgically removed.

  3. Fish-eating birds and mammals, or manatees grazing on seagrasses, may accidentally swallow fishing hooks. A fishing hook lodged in the throat or digestive tract may cause discomfort and make eating difficult. The hook may puncture the gastrointestinal tract, causing infection that can be fatal.
  4. Foreign objects can obstruct the gastrointestinal tract and cause gastric inflammation, nausea, and loss of appetite, which may result in starvation (Dierauf, 1990).

Traumatic Injuries

  1. During storms, strong winds and waves may thrash seabirds along rocky shorelines, sometimes resulting in concussions or fractured limbs. Injuries also occur when birds are hit by cars or when chicks fall from nests.
  2. During storms and strong winds chicks can fall from nests.

  3. Predators such as sharks or killer whales may severely injure pinnipeds or dolphins.
  4. Some pinnipeds incur wounds from fights that erupt over territorial disputes during the mating season.
  5. In spite of regulations to protect them, marine mammals are sometimes shot because of conflicts over food between the mammals and fishermen.
  6. Head injuries seen on some sea turtles suggest blows to the head with blunt objects.
  7. Motor boats and other watercraft can cause substantial wounds to slow-swimming manatees and sea turtles.
  8. Motor boats and other watercraft can cause substantial wounds
    to slow swimming manatees (Trichechus manatus).

  9. All untreated wounds are prone to bacterial infections.

Habitat Loss

  1. Habitat is lost when natural homes of plants and animals are destroyed. This destruction occurs in different forms. Encroachment into sensitive habitats for human development, overharvesting of natural resources, and accidents such as oil spills. Animals forced out of their habitat may not be able to relocate or adapt to a new environment.
  2. Human encroachment has altered nearly every aspect of the Florida
    environment making areas that were once safe for manatees
    dangerous to their survival.


  1. Biotoxins.
    • Marine mammals sometimes are affected by natural toxins. One such toxin, ciguatoxin, occurs in tropical and subtropical areas. Ciguatoxin originates in dinoflagellates and algae, which are eaten by herbivorous reef fishes. Once ingested the toxins generally do not pass through the body; rather, they can accumulate in body tissues. Toxic fishes are in turn eaten by carnivorous fishes, marine mammals, and seabirds. The concentrations of toxins can reach dangerous levels in the tissues of these larger carnivorous animals. The resulting condition is known as ciguatera (Halstead, Auerbach, and Campbell, 1990).
    • Brevetoxin, originating in dinoflagellate blooms, was implicated in the deaths of 37 Florida manatees in 1982 (O'Shea, et al., 1991).
  2. Human-made toxic pesticides and industrial waste products run off into oceans, lakes, and rivers. They enter and move up the food chain in the same way as natural toxins, adversely affecting large marine animals.
  3. Recent studies suggest that chronic exposure to certain toxins can suppress a marine mammal's immune system, making it more susceptible to disease (DeSwart, et al., 1995).