Threats
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Threats belong to two categories: natural and anthropogenic or human induced threats.
Natural threats can be either Biotic (disease, predation at sea and predation at nesting sites) or Abiotic (flooding/storms, driftwood, seaweed etc).
Anthropogenic (human caused) threats include: degradation and/or loss of nesting habitat, sand compaction from driving vehicles, horse riding on nesting beaches, sand raking and/or removal, marine pollution and disease, incidental catch by fisheries (specifically shrimp trawlers and long lines), boat collisions with speeding boats, tourism development, etc. Currently, the biggest threat to sea turtles is the fishing activity, with thousands of incidental catches each year.
In addition, another anthropogenic impact is Climate Change.
Over the last 10.000 years, turtles have been adapting to a constantly changing climate. Taking into account the projected scenarios for climate change, it is clear that temperature rises and climatic fluctuations are no longer entirely based on natural processes and are also affected by anthropogenic processes such as industry and the production of greenhouse gases.
Climate Change
There is a direct effect of global warming on nesting beaches as higher sand temperatures produce more females and cooler nests more males.
- Any sea level rise may lead to the loss of nesting and feeding habitats;
- Increased ocean temperatures can lead to coral bleaching and other damage to turtle feeding habitats;
- Changes in ocean currents can modify migration paths and feeding patterns;
There is therefore an urgent need to study the possible climate change scenarios. It may be the case that many of the nesting beaches of today will not be the nesting beaches of tomorrow. Studying the scenarios of climate change for different geographical locations may allow conservationists time to identify future nesting sites.
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Future Scenarios for temperature rise linked to GHG emissions
Source: NOAA
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Fishing
Throughout their lives, turtles of differing ages and species travel extensively throughout the Mediterranean Sea. During their movements, the turtles come into contact with a great deal of fishing activity, nearly all of which is potentially lethal to them. It is estimated that at least 6,000-8,000 Mediterranean sea turtles are caught by fishing activities every year (Demetropoulos). The main species caught is the loggerhead turtle - Caretta caretta.
There are three main types of fishing techniques employed by the Mediterranean fishing industries which cause the incidental capture of sea turtles. They are long-line fishing, trawl-net fishing and drift-net or gill-net fishing.
- Long-line fishing: each fishing unit consists of a floating 'mother-line', 300m long, from which hang the hooked 'groundlines', each 25m long, at 20m intervals. Units can be strung together in great chains. It is not unusual for 200 units to be strung together to reach a length of 60Km. This method of fishing is usually used to catch Swordfish and Albacore in the Mediterranean.
- Trawl-net fishing: a boat drags an enclosed net behind it. The net forms a sock shaped enclosure catching any matter that enters it. The mesh of the trawl net tends to be very small as this type of fishing is primarily used for shrimping.
- Drift-net or gill-net fishing: uses a huge net, essentially an area of mesh; it is not fixed into any assembly. The mesh of the net is just large enough to allow the heads of the fish to pass through while trapping them at their gills. The net is usually dragged behind a single boat in a loop or may be fastened to two boats on a parallel course. This type of fishing is usually used to catch tuna, swordfish and albacore.
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A Loggerhead turtle caught in fishing nets
Dennis Alen, Centre for Marine Conservation- Washington DC
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Tourism
The building of hotels, shops and restaurants has encroached on the turtles' nesting grounds. Artificial lighting from hotels, bars and restaurants in the beach areas can also lead to disorientation, as the turtles usually follow the reflection of the water to find their way back to the sea.
Watch "Turtles in Trouble" |
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Nesting beach in Zakynthos:
Tourism is negatively affecting the quality and accessibility of the nesting beaches by sea turtles.
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Small Garbage and pollution
Every year, in addition to the 150 million people living along the Mediterranean coastline, over 200 million tourists contribute more than 15 million tons of garbage. Garbage is becoming an overwhelming threat to this fragile ecosystem as the waters of this beautiful "enclosed sea" take more than 100 years to renew.
The most common and destructive objects are made from extremely durable, lightweight, versatile and inexpensive plastic. With varying sizes, colours and shapes, these items are often mistaken for food by sea creatures and sea birds. For example, floating plastic pellets (a by-product of plastic manufacturing) resemble fish eggs, and plastic bags in the water look like jellyfish, a favourite food of sea turtles. It is estimated that five-hundred billion to one trillion plastic bags are produced worldwide each year! Billions end up in the sea and on the shores. Turtles who mistakenly eat them may suffocate or suffer a blocked digestive tract, causing them to feel full though in reality they may be starving to death! Additionally, air bubbles in plastics consumed can prevent turtles from diving for food.
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Rubbish accumulated on a nesting beach in Syria
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