Conservation engineering: Saving marine turtles
Marine turtles have been swimming the world's oceans since before the dinosaurs roamed the earth, more than 110 million years ago. Turtles are an important component of the marine ecosystem and serve as indicators of the health of the environment in which they live. Their aesthetic appeal draws conservationists and tourists from around the world to nesting beaches throughout the region, generating income for local communities. In many countries, marine turtles are used for their meat, egg and shell, representing a traditional source of food for human populations. However, these treasures of ancient times are now on the brink of extinction. All seven sea turtle species are globally endangered including the five species that swim in Bangladesh territorial waters and are listed as "threatened" or "endangered" in the IUCN Red Data Book. The proposed revision of Bangladesh Wildlife Preservation (Amendment) Act 1974 has also included the marine turtles in the list of protected species. The species are: Dermochelys coraicea (Leatherback), Chelonia mydas (Green Turtle), Lepidochelys olivacea (Olive Ridley), Eretmochelys imbricata (Hawksbill) and Caretta caretta (Loggerhead).
Human activities have driven global marine turtle populations to dangerously low levels. Dirty fishing by commercial fishing operations is one of the greatest threats to marine turtle survival. Commercial fishing gear, including dredges, gillnets, long-lines and trawls is the greatest threat to marine turtles. The seven species remaining today have become seriously depleted due to excessive harvesting, destruction of nesting and feeding habitats, and accidental taking in fisheries operations. Actions need to be taken now before we lose these majestic marine turtles forever.
The CMS Conference of Parties (COP) has identified them as a group of species which deserves priority action. The Secretariat, assisted by the experts of the Scientific Council and in cooperation with the Marine Turtle Specialist Group of the IUCN Species Survival Commission, has taken steps towards this aim in the African and in the Indian Ocean region. Co-operative efforts to conserve globally threatened marine turtles received a boost in June 2001 with the completion of the Memorandum of Understanding on the Conservation and Management of Marine Turtles and their Habitats of the Indian Ocean and South-East Asia (IOSEA).
The Memorandum is the second of its kind to be concluded under the auspices of the Convention on Migratory Species. Bangladesh is a signatory to the Memorandum too. The Memorandum of Understanding puts in place a framework through which States of the region -- as well as other concerned States -- can work together to conserve and replenish depleted marine turtle populations for which they share responsibility. It acknowledges a wide range of threats to marine turtles, including habitat destruction, direct harvesting and trade, fisheries by-catch, pollution and other man-induced sources of mortality.
The signatory States of the Memorandum meet every two years to discuss issues and progress made in terms of policy, legislation, programmes related to the conservation and management of marine turtles by the respective states. The Fifth Meeting of the Signatory States to the Memorandum of Understanding on the Conservation and Management of Marine Turtles and their Habitats of the Indian Ocean and South-East Asia was held in Bali, Indonesia, from 20 to 23 August 2008 and Bangladesh participated as one of the twenty-seven signatory states.
Every year hundreds and thousands of dead marine turtles wash ashore on the beaches of Bangladesh (Fig. 1). Many of these marine turtles die by either drowning getting entangled in the fishing nets or hit by the mechanised fishing trawlers or killed by fishermen to free their nets. The turtles breathe air and when entangled in the nets cannot come up to the surface to breathe and drown. On several occasions the nesting female turtle is killed by the stray dogs or other predator animals on land and sometimes by the urchins for fun. All these contribute to the decline of the marine turtle population.
It is important to know that one in ten thousand hatchlings survive and one of the surviving thousand reach maturity and IT TAKES 25-30 YEARS FOR A TURTLE TO REACH MATURITY.
Marine turtles are migratory in nature and show a great degree of nesting site fidelity which means that a female hatchling born in St. Martin's Island if survives and reaches adulthood will come to nest in St. Martin's Island. Praise the Lord for the marine turtle's instinct and bio-navigational memory. For this reason it swims vast distances to come to the shores and nest on the same sandy beaches where it was born. It is during this migration and their brief stay (mainly for reproductive activities) in the coastal offshore waters that many of the turtles get entangled in fishing nets and either drown or are killed by the fishermen to free their nets. These dead turtles wash ashore on the mainland and island beaches.
The exact numbers are not known for the whole of the 710 km Bangladesh coastline; however for the last several years' information from St. Martin's Island, Teknaf Peninsula, Sonadia Island, Sandweep, Kutubdia, Nijhum dweep, Hatiya, Kuakata and Sunderbans beaches indicated that the number of dead turtles that washed ashore was more than a thousand on average per annum. The number increases during the winter months that coincide with the increased frequency of nesting females and increased intensity of fishing activities. Considering the comparatively low species diversity and numbers of female marine turtles successfully nesting in Bangladesh than the neighbouring India and Myanmar this is alarming for the marine turtle populations in the Bay of Bengal and the Indian Ocean.
Sea turtles, mainly Pacific Ridleys (approx 95%) and some Green Turtles (approx. 4%) and other species (approx 1%) get killed in the fishing nets in Bangladesh coastal waters. Generally the fishermen use behundi jal (in deep water trawls) and lakkha jal (in shallow waters, both with funnel-shaped bag nets and with codend) for fishing. Many of the sea turtles also get entangled in the Marine Set Bag Nets (MSBN) and Estuarine Set Bag Nets (ESBN) (similar to behundi jal except that it is fixed and used in coastal areas affected by tide) (Fig. 2).
Conservation engineering in this case is the integration and application of standard engineering principles for biology and conservation. For example, conserving endangered species like marine turtles by either reducing the capture of the target species or by-catch or allowing escape of unwanted or endangered species from the fishing nets. Turtle Excluder Device (TED) is one such example applicable to the marine turtles and the commercial fishing industry. The use of TEDs has a lot of implications in the economy and shrimp export industry of Bangladesh. If the readers may recall that back in 1997 USA banned importing shrimps from Bangladesh due to the fact that shrimp trawls contributed to the mortality of marine turtles and that Bangladesh was not using any TEDs, for which the shrimp producers and exporters made huge uproar. This non-compliance may have a backlash and the industry may suffer as Bangladesh is not on the recently published list of US State Department certified TED users (US State Dept., 2008/350, May 2, 2008). European and other CMS signatory countries are also planning to use the TEDs as a means of compliance indicator.
The use of TEDs is to be made mandatory for fishing nets used by fishermen in the Bay of Bengal and in the coastal areas has been suggested by many of the conservationists. The truth however is that most of the campaigners in Bangladesh have no clear idea about the TEDs. It may sound depressing but most if not all, have not seen a TED let apart its use and benefits. The fishermen are further down the line to know about it. Not only the nets used in shrimp trawls but other fishing nets are also equally detrimental to the sea turtle populations.
The use of TEDs by shrimp trawlers in many countries have shown that it has reduced the number of turtles killed by approximately 50 percent. Trawl nets (Figure 3) are used to catch some species of fish, prawns and scallops. Unfortunately, trawl nets also catch a wide variety and sometimes large quantity of unwanted species. Sea turtles, sting rays and sharks can also be incidentally caught in the trawl net. Turtle Excluder Devices have been developed to reduce the capture of turtles and other large non-target species in commercial trawl nets.
What are TEDs? TEDs usually include a metal grid, much like a storm-water-drain grate (hard TEDs) or a panel of large mesh webbing (soft TEDs) that is installed at an angle between 40° and 60°. This creates a physical barrier that allows shrimps and other animals smaller than the bar spacing of a hard TED or mesh webbing of a soft TED to pass through the TED and into the codend. Sea turtles, other large animals and debris slide along the TED to an exit hole cut in the top (top opening TED) or bottom of the TED (bottom opening TED). The exit hole may be partially covered by a flap of webbing to reduce the possibility of losing shrimps or other target fish species.
TEDs come in many designs and like other fishing gear; no single design of TED is suitable for all fishing conditions. Catch loss associated with these devices should be minimal, with indications that they may improve the quality or the quantity of the shrimp catch.
How TEDs work in a trawl net: TEDs are a modification to the trawl net that allow larger animals to escape after being taken into the net, as it is difficult to prevent or reduce the number of unwanted bycatch animals that enter the trawl net in the first instance.
TEDs are usually fitted into a trawl net at the beginning of the codend (Figure 4). At this point in the net, water-flow is fastest and maximises the ability of a TED to separate target animals, such as shrimps and scallops, from non-target animals, such as sea turtles, sharks, dolphins.
So much of money is earned by the government and the private sector from the resources harvested from the marine environment, however, little is paid back for the conservation and management of these resources and the ecosystems that support these virtually bountiful resources. The relevant government agencies particularly the Ministry of Environment and Forest, Ministry of Fisheries and Livestock, Coast Guard (under the Ministry of Defence) and the fishing and boat-owners associations should open dialogues to convince the commercial fishing enterprises to use TEDs in their trawl nets. NGOs may be engaged to do the groundwork for motivating the fishing communities and associations.
NGOs may organize workshops designed to have hands-on demonstration of the TEDs and its use in the actual fishing so that the participants, including policy makers and the users -- the fishermen -- get practical experience and see for themselves the amount of bycatch and other non-target species that get trapped and thrown overboard as waste. Moreover the fisher communities would know the technicalities of constructing appropriate TEDs using locally available materials and are convinced and mandated to make and use it in their fishing nets. The fishers also need to be educated and made aware through organizing repeated sessions about the benefits of using TEDs and responsible fishing. The Department of Fisheries (DOF), Department of Environment (DOE) and the Coast Guard may monitor the fishing vessels on the use of TEDs and data collected on the catch and by-catch may allow the fishers and concerned government agencies to see for themselves the benefits of using TEDs thus reducing marine turtle mortality due to fishing.
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