So what is Animal Satellite Tracking?
Welcome to my series on Animal Satellite Tracking. In the coming weeks, I hope to give provide you with a thorough review on what is now becoming the fastest and most popular technique used for researching animal ecology, and the best tool for science-based conservation.
What are the advantages?
Satellite tracking has the ability to track animals below the ocean's surface, across country borders and over vast distances in real time. It has provided conservation groups, scientists and policy makers with techniques to monitor species behaviour and survival, tools that were in previous decades only available to a select few. This information is critical for understanding the role of animals within the wide systems they operate and how they are likely to respond to variations in these systems due to climate change.
Some advantages of satellite tracking include –
Global coverage - animals can be followed across local, national and international borders
Newer tags allow a highly detailed analysis of spatial movements (which were previously impossible to observe)
Researchers do not have to spend a great deal of time in the field (such as in the cold of Antarctica!)
Animals need to be handled only once (traditional tags require recapture)
The tagged animal can be tracked from a computer anywhere in the world
The technology is most relevant in the marine environment, where it is nearly impossible to directly observe animals over extended periods. This is due to the three dimensional nature of movements within the ocean and the fact we cannot directly observe animals deep below the surface.
A few examples of how scientists use tracking information include:
Observing the movement patterns and speeds of migrating birds, fish or whales
Learning how deep seals dive when searching for food
Discovering where marine turtles feed between egg laying years
Discovering where a shark species aggregate for mating
This information is important for determining how best to manage the animals and the crucial habitat they require for survival. Whether determining breeding, feeding or mating grounds, satellite tags have opened our eyes to the unique behaviours of animals we have only ever rarely seen.
The Technical Bit
Modern satellite tracking involves an electronic tag or platform transmitter terminal (PTT) that relays information to polar-orbiting satellites operated by the National Ocean and Atmospheric Administration (NOAA) and the European Organisation for the Exploitation of Meterological Satellites (Eumetsat)1. On the satellites, Argos sensors pick up the signal before being re-transmitted to processing centres back on Earth and then to the scientist. This is the traditional system used due to its in-built location determination system and global coverage. The signals sent to the satellites are recorded in two ways; either the Argos satellites determine the location of the transmitting tag or a GPS unit on the tag uploads an accurate set of coordinates to the satellites. How the signal is actually transmitted is where the technology starts to get a little technical for this article but if you are interested you can see it in more detail on the ARGOS website.
The PTTs themselves are micro-processor controlled archival and transmitting tags, developed to record parameters from both the animal being tracked and the environment it inhabits. Information relayed to satellites can contain information on latitude and longitude (location on the earth), location accuracy, depth/altitude (including highest and lowest), time wet/dry, light levels and temperature. GPS tags can now also determine speed, altitude and record data at a much higher accuracy. All of this information can then be used to piece together the day to day life of the animal being tracked. Satellite tracking is now recognized as an essential research tool for understanding the broad and often hidden movement patterns of marine and terrestrial animals.
There are many types of satellite tags available to the researcher, each with their own advantages and disadvantages. The major tag categories are:
Transmitting (ARGOS) tags
For the past 30 years, Smart Position or Temperature Transmitting Tags (SPOT5, TAM, CTD, SRDL) have been the most popular tag type and are widely used by researchers, generally because you don't have to recapture your animal. Data on the animal's environment, location and behaviour is sent in real time and recorded by the ARGOS satellites before the tag's location is finally calculated via the ‘Doppler Effect' at ground stations. The more satellites the tag transmits information to, the higher the accuracy of the signal. In the marine environment, this technology is now considered inferior to a GPS based system due to its inaccuracy of over 1000 metres. This inaccuracy is because the animal needs to surface for a strong signal to be transmitted. However, SPOT5 tags still remain the cheapest and smallest option for near real time data collection and can be used on all species that are currently tracked by satellite.
Archival Tags and Pop-up tags
Archival (SPLASH) and Pop-up Archival Tags (PAT or PSAT) have been proven over the last 10 years to be the most effective way of tracking large scale movements of animals that don't regularly visit the ocean's surface. This is because the tags archive their data for later collection. They store information like pressure (depth), internal (body) and external temperature, ambient light level (time of day and geo-location) and swim or flight speed.
Archival Tags
Archival tags were first deployed in the 1990s and have developed rapidly over the past 10 years. The device is usually inserted into the abdominal cavity of a fish (mainly tuna), with the external sensor ‘stalk' emerging from the body. Data is generally collected at 2-4 minute intervals, however researchers can program the tags to maximize efficiency2. There are several computational algorithms that calculate latitude and longitude based on light levels; longitude from time of noon/midnight (or local moon) and latitude from measurements of day length. The accuracy of this tag type has been estimated to be less than 110km2.
Pop-up Tags
PAT tags are similar to Archival Tags but are attached to the outside of the host animal by a dart and wire or monofilament tether (Figure 4). The cable is designed to detach the tag from the animal either:
after a pre-determined time
when there has been no change in depth for a period of 4 days (if the animal has died) or
when the tagged animal swims to a depth that would damage the tag
It is then designed to float to the surface where it transmits its location, time of release and a summary of data to the ARGOS satellite system. PATs, like the one in figure 4, are made of a carbon fiber housing for streamlining and to protect them from the pressures of the oceans depths. The complete data set from archival or pop-up archival tags can only be retrieved if the tag is found, either retrieved by fishers or washed up on a beach near the study site. This is why scientists put out rewards for the return of satellite tags, often between $ 200 and $ 2000!
Rewards for returning satellite tags can be found at our site or at the Tag a Giant website.
GPS tags
GPS tags have become the ‘go-to' tag for researchers with a big budget. This tag type stores its location data before transmitting it to the ARGOS satellites in near real time. They are highly precise, giving an accuracy of less than 70 metres, and transmitting almost 4 times as many reliable locations during its time on the animal. This fine-scale accuracy has allowed scientists to analyse behaviours such as daily activity, home range size, accurate daily migration speeds and the advent of the ‘Daily Diary'.
Are there any disadvantages?
The two biggest disadvantages of satellite tags are the cost and the lack of time for which tags function. Currently oceanic tags, that relay information to satellites, last roughly for a maximum of 1 year due to failures in the battery, salt-water switch failure, antennae breakage, animal mortality and premature detachment. The key disadvantages are:
The ARGOS system is expensive, data accuracy is low and upload rates slow. Studies often discard 80 to 90% of fixes.
For GPS tags, the cost of data retrieval can be as much as a tag itself!
Tags may have an effect on animal behaviour, compromising data.
Tag loss is a major issue, mainly due to battery failure and unpredictability of the animals being tracked.
Transmitting tags must have the antennae above the water surface for successful transmission.
SPLASH and PAT tags are notoriously unpredictable in terms of recovery, with earlier studies yielding only 12% tag return.
Tags can only last to a maximum depth of 1500m.
Terrestrial satellite tags are generally too large for use on smaller animals such as birds, insects and mammals. There is currently no suitable technology for tracking the migration of the largest group of birds with importance to ornithologists, which are the medium to small song birds.
Until recently, tags broadcasting to ARGOS receivers have been a one-way system. This means that they could never be re-programmed once attached to the target species. Many transmissions are sent because the tag does not know if the signal has been recorded, thus reducing battery life. This is still the case with all cheaper models, including SPOT5 tags.
For a full list of references please see this blog post on our website.
Brendan is the President of the Tracking Research for Animal Conservation Society.
You can visit their website at www.tracsaustralia.com.au
