:: Methodological techniques
The molecular genetic techniques allow us to understand the natural changes of the DNA of the individuals of cetaceanís population. Either genes analyses, nuclear or mitochondrial DNA can be applied on the study of these populations.
The mithocondrial DNA studies are based on the amplification of fragments of genetic material through the PCR technique. This specific analysis allows individualís identification, rebuild phylogenetic relationships, and study geographic patterns of intraspecific genetic changes. Currently, the D-loop is the most used fragment of mithocondrial DNA to study cetaceansí populations.
This fragment is highly variable and allows study the intraspecific diversity and determines the genetics differentiation level between populations. Other low variable fragments such as the COI or the NADH5 can also be used, especially when the D-loop presents high polymorphism.
Other analysis based on the use of micro satellites, which are short repetitive fragments of genomic DNA. These fragments analysis (also based on the PCR technique) allows, between other things, identify the components of a group, familiar relationships between individuals and the consanguinity level.
The genetic analyses require samples from the target species that contains genetic material. These samples can be collected directly from the animal using biopsies darting or through skin samples that animals (e.g. sperm whale) naturally left at the sea surface. The first case produces better quality samples but may cause greater stress on the animals.
Thanks to the differences in form, number and position of small cuts and scars on the dorsal fins (dolphins) and on flukes (sperm whales) of the animals, the photo-identification technique, which consists of taking pictures of the individual fins, allows us to differentiate between individuals relatively well.
For a better application of this method it is important to relate it with a construction of an image database. Nowadays, the photo-identification databases are built with informaticsí software, which can help on the individualís identification. Is currently in course the Europhlukes project, which aim to develop a European Network of providers and end-users of a European Cetacean Photo-ID system.
Knowing which animal was observed where, when, with whom and which under environmental conditions can provide knowledge of their numbers, habitat, migration patterns and social structure.
Telemetry involves surveying a target object at distance. Several telemetry techniques have been successfully used in wild animal, including cetaceans. Some of these techniques transmit information using electromagnetic waves of radio frequency.
The common radio telemetry transmitters emit an impulse series with regular intervals on VHF (138 a 180 MHz). This transmitters use a directional antenna to receive signal. On most cases using VHF telemetry in cetaceans, the receptorís position is the only obtained information, and normally limited to 3 nautical miles. This kind of telemetry also demands large efforts from the operators.
Other radio telemetry is to use satellites for the signals detection. Its use had increased on the study of cetaceans, and the most common one is the Argos. On this case, the transmitters (PTTs - Platform Transmitter Terminals) sent signals by UHF that are received by satellites at about 850 Km above the earth surface. This method only requires effort to install the PTTs and covers a wider range than the VHF transmitters.
Other techniques acquire and electronically record the information in situ, but require further recover of the equipment. The TDRs (Time-Depth recorders) is the most optimized instrument to study the cetaceans diving behavior.
All telemetry systems applied to animals demand electronic equipment to be tagged. This constitutes a major problem on the cetaceans, especially due to tagging and stress on the animals. Instruments using the sucker system are easy to apply, non-destructive, reduce stress to minimum, but only for short periods (two days maximum). Perfect for recoverable instruments like the TDRs. For longer periods the instruments are set under the animalís skin, being potentially stressful.
The cetaceans are one of the most difficult animals to study because of their life living and behavior. Part of their life can only be known with the help of technology. Telemetry plays an important role studying the movements and behaviors of the tagged individuals, help understanding how the cetaceans use their habitat.