The Silent Killers
Ghost nets are commercial fishing nets that have been lost, abandoned, or discarded at sea. Every year they are responsible for trapping and killing millions of marine animals including sharks, rays, bony fish, turtles, dolphins, whales, crustaceans, and birds. Ghost nets cause further damage by entangling live coral, smothering reefs and introducing parasites and invasive species into reef environments.
In addition, ghost nets affect the sustainability of well managed fisheries by damaging boats and killing species with economic value. They also impact the beauty of shorelines, resulting in expensive cleanup costs and financial loss for the tourism and diving industry.
The deadly effects of ghost nets can be felt far from their point of origin. Ghost nets drift with ocean currents for years, or even decades, traveling huge distances while continuing to catch and kill marine animals in a process called “ghost fishing”.
Entanglement in ghost nets can lead to exhaustion, suffocation, starvation, amputations of limbs, and, eventually, death of a marine animal. Entangled fish often act as bait, attracting larger predators such as turtles, sharks, and dolphins, which may themselves become entangled.
The Circle of Devastation
A drifting ghost net might eventually become so heavy due to its catch that it sinks to the bottom of the ocean. On the seabed, smaller ocean dwellers start feeding on the entangled marine animals, which, along with natural decomposition, reduces the weight of the net to the extent that it floats back up to the surface. Once the ghost net is again drifting with the ocean currents, it starts its cycle of ghost fishing, sinking and floating back up all over again. Due to the durability of modern fishing nets, this circle of devastation can continue for decades.
Why Do Ghost Nets End Up In The Ocean?
Research is ongoing to better understand why ghost nets end up in the ocean, yet the cause and magnitude of the negative impact of ghost nets on the economic and ecological resources in the Indian Ocean remains unknown.
The Olive Ridley Project focuses on identifying the key factors contributing to ghost nets in the Indian Ocean, some of which are:
- Bad weather conditions;
- Catch overload;
- Snagging on the bottom;
- Poor gear maintenance;
- High cost of retrieval;
- Fishery conflicts or vandalism;
- Poor or no access to disposal or recycling facilities;
- Illegal or unregulated fishing activities;
- Destructive fishing techniques.
Problematic Fishing Techniques that Create Ghost Nets
Many fishing techniques and practices are destructive to the marine environment by causing over-fishing, massive by-catch, damage to the sea bottom and coral reefs, and ghost fishing. Trawling and the use of gillnets, purse seine and FADs (Fish Aggregating Devices) are some of the problematic fishing techniques that create ghost nets. Pole and line, the primary fishing technique in the Maldives, is a low impact and sustainable fishing technique.
The dominant fishing gear in the Indian Ocean is gillnets. Gillnets contributes as much as 30-40% of the total catch in artisanal and semi-industrial fisheries.
Gillnets are sets of panels of uniform mesh size, which form a large net wall hanging vertically in the water. Suspended in the top- or mid-depths of the water (a drift gillnet), or anchored to the seafloor (bottom gillnet), gillnets trap fish by their gills. They are very effective – and particularly destructive.
Trawling involves dragging a large fishing net with heavy weights behind a boat, either mid-water or across the bottom. The net indiscriminately catches or crushes everything in its path. Consequently, by-catch is extremely high and nets are often lost due to snagging on the bottom.
Trawling is a common fishing technique in India and Sri Lanka.
Purse seine is a long wall of netting deployed around a school of fish and pulled tight, thus enveloping the school of fish (and any other animals) in a purse-like structure.
Purse seines targets pelagic fish of all sizes, including tuna, and are therefore frequently used in the western Indian Ocean, often in combination with FADs (see below).
Fish Aggregating Devices (FADs)
Fish Aggregating Devices (FADs) are man-made objects used to improve a vessel’s catch by attracting fish beneath them. FADs are usually a square of bamboo with netting and buoys attached, sometimes with a solar-powered GPS tracker on-board to allow the boat that deployed it to track it. The devices are either in a static location or deployed in the open ocean as drifting devices (dFADs).
Numerous dFADs have been found drifting in Maldivian waters. Some have even been traced back to specific boats operating in the Western Indian Ocean.
Searching for Answers
Through our research, we are still searching for the answers to the following questions:
- What is/are the major source(s) for the nets we find in the Maldives?
- How long can ghost nets remain in the oceans?
- Why are Olive Ridley sea turtles at such a risk? Why do we so often see juvenile turtles in nets?
- What breeding population are these turtles from?
- Do turtles released from a ghost net survive long term?
- How can we prevent these nets from entering the Indian Ocean?
- What can global consumers do to help mitigate this problem?
- How do we recycle or reuse the ghost nets that we find?
Marine fishing is vital in providing communities around the world with protein and a source of income. The Olive Ridley Project aim to work with fisheries in order to help prevent ghost nets from entering the Indian Ocean in the first place, and we hope that the research results will help to amend net or gear designs and influence fishing legislation.
Most ghost nets and entanglements go unnoticed. The Olive Ridley Project, in cooperation with our volunteers, have documented the entanglement of more than 185 sea turtles and removed over 120 ghost nets from Maldivian waters (as of February 2015).