Introduction

Five species of marine turtle are known to occur along the coast of Angola: the leatherback (Dermochelys coriacea), green (Chelonia mydas), loggerhead (Caretta caretta), olive ridley (Lepidochelys olivacea) and hawksbill (Eretmochelys imbricata) turtle.  Of these, the leatherback, green and olive ridley turtles have been confirmed as breeding on Angolan beach's, and nesting activities may well occur in most of the compatible sandy beaches along the whole coast-line of Angola.  The turtle nesting season in Angola extends from September to March, peaking between November and January.  Four species of marine turtle have been positively identified during our Angola survey work, with many more turtles remaining unidentified due to their distance from the survey vessel.  Turtles are particularly numerous within the offshore (> 1,000 m depth) licence blocks during August and September, when they apparently aggregate offshore prior to a coordinated inshore movement to the nesting beaches.  

Olive ridley turtle

Olive ridley turtles are by far the most numerous turtle species recorded during the offshore at-sea surveys, and this species is also the most abundant nesting species on Angolan beaches.  The majority of at-sea sightings have occurred at between 1,000 and 2,000 m water depth (although survey effort is also strongly biased for this depth range).  Although present in small numbers throughout the year, a clear peak in offshore olive ridley turtle density occurs between July and September.  Mating pairs of turtles have been observed during August, September and January, corresponding with the nesting season. 

Loggerhead turtle

There have been 12 confirmed sightings of loggerhead turtles during offshore survey work in Angola.  The sightings all occurred between August and November, in between 1,300 and 2,800 m water depth.  The status of loggerhead turtles in Angola remains unclear.  The species has not yet been confirmed to nest, but the observations reported here and occasional reports of bycatch in coastal fishing nets suggests that loggerhead turtles occur fairly regularly at sea off Angola.  It is possible that these animals represent a pelagic foraging population that nests outside of Angola.

Leatherback turtle

Leatherback turtles are the second most numerous turtle species on beaches in Angola, and the largest nesting population in the world is found further north in Gabon.  Despite this, at-sea sightings are relatively scarce.  Records to date include three individuals observed during late January/early February 2005 in the offshore licence blocks, an animal recorded close to the coast off Soyo in September 2005, and oceanic records in January and December 2006.  Possibly the long dive duration and brevity of time spent at the surface compared to other species is responsible for the lack of at-sea sightings.

Green turtle

A single green turtle was seen on the continental shelf off northern Angola during August 2005.  The deep-water emphasis of the survey effort probably explains the paucity of sightings of this species, which is likely to be more abundant in shallow and coastal waters where their sea-grass food occurs.

Offshore threats

Knowledge of Angola's turtle populations is poor, and recent interest has focussed predominantly on assessing nesting animals, their threats and habitat.  Although protection of nesting animals and beach habitat is clearly essential, it should be noted that male turtles never return to the beaches and females only return on annual cycles of several years.  The vast majority of a turtle's life is therefore spent at sea, and an understanding of their offshore distribution and threats is crucial to their protection within Angolan waters.  Two of the main threats affecting turtle populations worldwide are fishing bycatch and litter ingestion, and evidence for both has been documented off Angola.  Several turtles (olive ridley and leatherback) have been observed entangled in discarded fishing gear, and many of our sightings have involved animals associating with plastic and other litter drifting in the water.