The globe is criss-crossed with borders and boundaries, designating countries and states each with its own culture, identity and regulations. However, these geopolitical borders were created by humans for humans and animals follow their own geography, wonderfully oblivious to the way we have divided up their world. Animals often require different habitats and environmental conditions for mating, breeding and feeding and so migrate between areas in order to find the resources they need. Some migration routes are relatively short, perhaps just between one side of a mountain range to another, but some species will travel for thousands of miles. A wide range of animal groups make such mammoth migrations; including birds, mammals, fish, invertebrates and reptiles. Species which make these epic journeys have adapted to time their movements in response to external and internal cues. External cues include a range of environmental signals; including day length, local climate and availability of food. While internal cues may include body condition or the bodies internal, circadian, rhythms. Once they are underway, animals may navigate with the aid of the sun, stars, magnetic fields, winds, currents and even smell, however, the exact mechanisms remain unknown in many animals. Whether by instinct or learned group experience individuals can follow the same routes and return to ancestral breeding and feeding grounds year on year.
Because of the large distances, the different habitats and the multiple National borders through which they pass, conserving migratory species presents a particular challenge. The first difficulty is tracking species to find out where they actually go. The advent of modern satellite tracking devices has made this a little easier but even then attaching a tag to wild animals, sensitive to human disturbance, is not always straightforward. Even once a migration route is known, countries along that route need to agree shared conservation goals and enact them under their local policies and procedures. If a conservation threat persists at just one step along the way, the species is put in jeopardy so it is imperative that nations work together.
To help facilitate the conservation of migratory species, a number of global platforms exist including the Convention on Migratory Species (CMS), which is an environmental treaty under the umbrella of the United Nations Environment Programme. First signed in Bonn in 1983, this year the Convention celebrates its 35th anniversary. Outside of formal agreements like the CMS, countries work together through a variety of conservation programmes and non-governmental organisations. Conservation initiatives that benefit migratory species include promoting sustainable habitat conservation, policing illegal trade, by-catch prevention and reducing disturbance from marine noise.
Green Turtle Chelonia mydas
Ascension Island has the second largest nesting population of the green turtle in the entire Atlantic Ocean and the largest nesting population of any marine turtle species in all of the UK Overseas Territories. The long-term population monitoring programme on Ascension shows that since 1977 numbers of nests on Long Beach have increased exponentially from around 1,000 to almost 10,000. This is an encouraging trend indeed, and charts the recovery of the green turtle population following the cessation of harvesting for meat in the 1930s.
The use of satellite-telemetry tags has allowed for the movements of green turtles to be monitored in real-time with GPS signals of their location broadcast to a satellite each time they surface to breathe. It has been established that the green turtles nesting on Ascension migrate from their feeding-grounds off the coast of Brazil every 3-4 years to lay their eggs – a journey that takes approximately 5 - 6 weeks.
Hawksbill Turtle Eretmochelys imbricata
Smaller numbers of critically endangered hawksbill turtles are also found in the nearshore habitats of the Island. Hawksbills have not been recorded nesting on Ascension and from their sizes it seems likely that the individuals found here are sexually immature juveniles.
From 2003-2009 staff from AI Conservation Office and recreational divers captured and tagged around 30 hawksbill turtles to study how long they spend around the Island. So far four of these turtles have been recaptured, with an average time between tagging and recapture of over four years. During this time the turtles had grown an average of about 3 cm per year suggesting that Ascension may serve as developmental habitat for juvenile hawksbills until they move on to their adult foraging and/or nesting sites, likely to be in Brazil or West Africa.
Ascension Island Migratory Species is one of a complimentary suite of stamps being issued in 2018 by British Overseas Territories including British Antarctic Territory, Falkland Islands, South Georgia and South Sandwich Islands and Tristan da Cunha.
4 value issue 65p, 65p, £1.00, £1.00
Designer: Andrew Robinson
Process: Stochastic lithography
Perforation: 13 ¼ x 13 ½ per 2cms
Stamp size: 42 x 28mm
Sheet layout: 20 (2 x 10 Se-tenant pairs)
Release date: 5 December, 2018
Production Co-ordination: Creative Direction (Worldwide) Ltd