VICTIM NO.3: THE SHARK
Sharks are among the oldest creatures to have lived on earth that evolved 400 million years ago, even before dinosaurs had arrived. They are the apex predators of the marine ecosystem and play a very important role in the ecosystem by regulating the energy flow. Without sharks, life is not sustainable as far as the underwater world is concerned and indirectly affects the terrestrial ecosystem. There are over 400 species of sharks all over the world and around 160 species in the oceans of India. Sharks can be oviparous, viviparous or ovoviviparous which are respectively egg laying, giving birth to live young and laying eggs inside the body. The male sharks use their pelvic fin to fertilize the female shark. They have a gestation period of about 22 months and most of the shark species give birth once in two years according to NOAA. (National Oceanic and Atmospheric Administration) Hammerhead sharks and whale sharks give birth to live young similar to mammals. Some sharks such as tiger sharks are ovoviviparous which means that they lay eggs inside their body and the young are born from the mother.
Like every other creature on the planet, sharks face threats due to anthropogenic activities such as extensive fishing, plastic pollution, global warming, climate change that have resulted in the near extinction of various species, and rendered many other vulnerable and endangered. A few examples of the major threats faced by sharks due to human interruption include shark finning, sharks as bycatches and entanglement in ghost nets. This article is focused on emphasising the various issues faced by sharks due to ghost nets that are discarded by fishermen.
So, what are ghost nets? Ghost nets are commercial fishing nets that have been lost, thrown or abandoned into the sea which end up being the silent killers of aquatic life. When fishermen discard waste or damaged nets in the ocean, they travel far and wide resulting in the adverse effects of ghost nets prevailing far from their site of entry into the water. This is because the water currents carry the nets across oceans. One such example of finding ghost nets far from their point of entry into the water is finding ghost nets near the coast of Maldives. Maldives has a protected coastline where fishing near the coast is banned but ghost nets are regularly found near its coast. Different types of fishing gear have various mesh sizes and the species caught in the ghost nets depend on the size of their mesh.
The effects of ghost nets on marine life include suffocation, entanglement, starvation and eventually the death of the animal. The nets trap small fish which act as prey for larger fishes such as sharks, dolphins which also get entangled in the nets. The major causes for ghost nets are the methods of fishing. Gill nets, trawlers are some examples of massively used fishing gears. In India, gill nets are the dominant fishing gear. Gill nets are basically long net walls hanging in the water. They have uniform mesh size with different sets of panels. They trap the fish by their gills and are the most productive and cause irreparable damage. Sharks are heavily affected by gill nets in various places of the world.
The misconception about sharks and their behaviour towards humans alone have led to the death of millions of sharks. A study conducted in South Africa on the number of sharks that were caught using gill nets to prevent them from attacking the bathers in the coast reveals a shocking total of 591 great white sharks that were caught in the gill nets over a period of 14 years from 1974 – 1988.
However, ghost fishing is not much of a problem in depths >200m as the ghost fishing nets do not have a long fishing life owing to high rates of biofouling (accumulation of algae, small plants, microorganisms on wetted surfaces that have a mechanical function causing structural deficiencies) that deep in the water. There is not much information available regarding the extent of damage ghost nets have on marine life. There is mostly only numerical data available on the species that are affected by ghost nets. Qualitative data is very much necessary to assess the condition of the marine life and to know in what ways we can help conserve aquatic species, especially apex predators like sharks.
To do that first we need to be aware of the effects of ghost nets on the ocean life and how it got there in the first place.
To propagate this message, we are making a film called tangled seas, the first of its kind that discusses about the problems of ghost nets in the Indian subcontinent.