Reasons why marine animals may strand

Stranded Whale

Reasons why marine animals may strand have been identified recently and are recapped in the post below.

THERE are many reasons why a marine animal may beach itself or become stranded, according to Ezemvelo KZN Wildlife marine ecologist, Jennifer Olbers.

A litany of possible external or internal factors could cause a dolphin, for example, to beach itself though no definitive theory has been proved.

“There remains uncertainty as to why marine animals strand. Below are some of the accepted theories that may separately or in combination with others, contribute to a stranding event.

Natural factors (from national response plan as edited by Ken Findlay)Reasons why marine animals may strand:

Social cohesive nature of odontocetes – Toothed whales form highly social groups, often in numbers exceeding 100. It is believed if one animal (leader or key whale) in the group is sick or injured and enters shallow water to strand, the remaining group members will follow the sick animal in response to distress calls and also strand.

Disease or parasitic infection – Most animals carry a number of external and internal parasites. However, when parasite numbers exceed normal levels (which varies per species), this may affect the animal’s health, feeding and navigational ability.

Coastal topography – Toothed whales use echo-location to detect and navigate sea floor topography and may be misled by a gently sloping ocean floor of a shallow bay (such as Doctors Reef in St. Helena Bay). A gentle slope will deflect, rather than reflect echo-location pulses, leading the animals to believe they are in deeper water. Many stranding ‘hot spots’ around the world are characterised by a gently sloping, shallow bay.

Anomalies in the Earth’s magnetic field – It has been proposed that some species navigate using the Earth’s magnetic field. Cetacean mass stranding events in certain regions of the world have been linked to geomagnetic anomalies which occur when local magnetic fields shift during sun spot activity.

Abandoned neonates and malnourished juveniles – Abandoned neonates are particularly common in southern right whales and some coastal dolphin species. Malnourished humpback whale juveniles are also known to strand, probably as a result of inability to forage independently or the premature death of the mother.

Severe oceanographic and weather conditions – Animals may come ashore following a severe storm with extreme wind and oceanographic conditions.

Predatory interactions – Animals may congregate or be herded close to shore in response to threats from predators. This may lead to distress and confusion in the shallower water and result in animals stranding. Furthermore, animals may strand with injuries sustained from predation (such as pectoral fins or tail flukes missing from shark or killer whale attacks). Alternatively, animals may follow their prey inshore or up onto the beach, becoming stranded.

Natural toxins – Animals may strand in response to natural toxins such as algal blooms.



Anthropogenic factors (from national response plan as edited by Ken Findlay)Reasons why marine animals may strand:

Noise interference – Anthropogenic ocean noise arises from vessel traffic, seismic surveying, oil and gas exploration and military operations using low and mid-frequency sonar. Noise is believed to impact upon the behaviour, perceptions and physiology of marine animals, in particular cetacean species that rely on evolutionary adaptations to use acoustics for navigation, avoidance of predators, foraging for food and reproduction. Deep diving beaked whale species may be particularly susceptible to anthropogenic ocean noise, and mass strandings of Cuvier’s beaked whales around the world have been linked to anthropogenic noise (in some of these cases, animals have shown decompression sickness-like symptoms suggesting behavioural or physiological impacts).

Toxins – Anthropogenic toxins (such as mercury or persistent organic pollutants from fertilisers and other man-made products) present in the ocean may result in animals becoming poisoned and stranding due to poor health or death.

Sustained injury – Many animals wash up on the beach, either dead or in poor condition, as a result of anthropogenic injury, such as those from ship strikes, propeller cuts and entanglements in fishing gear. Furthermore, animals may strand as a direct result of entanglement in gear or discarded material.”

If a marine animal is found on the shore, it is best to call for help immediately.

“We encourage the public to first contact the authorities and continue to keep the animal comfortable while the authorities or trained personnel are en-route,” said Olbers.

11 reasons why marine animals may strand

She offers the following advice for ensuring a dolphin’s comfort while waiting for authorities to arrive:

  • Do not return the animal to the water
  • If possible, place the animal on the beach facing away from the water – don’t drag it by the tail or flippers. If you cannot lift it, leave it
  • Dig holes for the flippers so there is no pressure placed on them by lying at awkward angles
  • Place a tarpaulin above the animal for shade, if possible
  • Place wet towels over the body and keep them wet
  • Do not pour water near or in the blowhole (this will drown the animal)
  • Keep noise levels as low as possible
  • Keep crowds at a few metres away from the animal
  • Be aware of the animal’s movement. Dolphins can give a nasty blow with their tails.

Reasons why marine animals may strand is just one more piece of evidence that includes noise pollution as a causative factor. The list keeps growing every day.