Many pelagic and coastal-pelagic species in the Eastern Tropical Pacific migrate throughout the region at different times of the year. A comprehensive regional management plan must include adequate protection for key species at particular sites or at moments during the year when they are particularly vulnerable.

It is difficult to follow a shark for a long period of time, so positional tags are used to determine their routes. The choice of tags depends very much on the size and behaviour of the species involved.

The information obtained from the different tags used in these studies will show us how the different populations migrate throughout the region, and whether there are physical ‘corridors’ along which the migrations occur.

By placing temperature and depth sensors on the tags, it is also possible to understand their diving behaviour and relate this to vulnerability from different fishing gear.

PAT-tagging: challenges and regional coverage

The first satellite tags used in this project were PAT tags on scalloped hammerhead sharks at Malpelo Island; 9 tags have been placed during cruises carried out in 2006, 2007 and 2008. Subsequently, 5 smalltooth sandtiger sharks were also fitted with these tags.

Tags were programmed to pop off after 9 to 12 months, but we encountered retention problems, and most tags lasted from 7 to 15 days. However, one tag remained on a hammerhead shark for close to 5 months and a second tag placed on a Smalltooth sandtiger shark detached on the preset date, nine months after attachment.

Similar tags were also placed on Galapagos sharks in the Galapagos Islands in 2006, as part of a study by George Shillinger from Stanford/TOPP, who double tagged 12 sharks with SPOT and PAT tags.

In 2007, 3 PAT tags and 7 SPLASH tags were also placed on whale sharks at Las Perlas Archipelago, in Panama, and on one whale shark (SPOT tag) in the Galapagos Island.

In Cocos Islands, we’ve tagged three PAT tags on scalloped hammerhead sharks and one SPOT tag on a silky shark during June 2008.

Many pelagic and coastal-pelagic species in the Eastern Tropical Pacific migrate throughout the region at different times of the year. A comprehensive regional management plan must include adequate protection for key species at particular sites or at moments during the year when they are particularly vulnerable.

It is difficult to follow a shark for a long period of time, so positional tags are used to determine their routes. The choice of tags depends very much on the size and behaviour of the species involved.

The information obtained from the different tags used in these studies will show us how the different populations migrate throughout the region, and whether there are physical ‘corridors’ along which the migrations occur.

By placing temperature and depth sensors on the tags, it is also possible to understand their diving behaviour and relate this to vulnerability from different fishing gear.

SPOT-tagging hammerheads

Due to the problems encountered with the PAT tags, we were keen to switch to SPOT tags for hammerheads.

SPOT tags are attached to the dorsal fin of the shark, and emit signals whenever they are on the surface. Like the other types of tags, it records a variety of measurements, such as temperature, salinity, and depth. Unlike PAT tags, which broadcast their data at the end of their useful life, SPOT Tags are permanently attached to the animal and regularly send their recorded data to satellites. These tags are primarily designed for use on animals that are commonly found at the ocean’s surface, where regular broadcast to a satellite is possible.

To apply SPOT tags, we faced the challenge of catching hammerheads without unduly harming them.

Hammerheads are often caught on longlines but display a much higher mortality than other sharks – as ram ventilators they need to remain in constant motion so that water can flow through their gills.

We did not have much luck catching them until our July 2007 cruise in the Galapagos Islands, when we were finally able to place SPOT tags on two males.

Now that we have been able to catch and tag them, we will be trying to place our tags on the sharks just before they leave the islands, in late February.

Making sense of the data collected

Once the information from the tags has been retrieved and (in the case of the PAT tags) positions have been determined, we can use this information to determine whether there are particular pathways in the region that these creatures are using as their migratory routes.

First, we show whether individuals cross national boundaries, and estimate the amount of time they spend in Marine Protected Areas in comparison to the time spent in the open ocean.

We can also use GIS programs to overlay bathymetry (sea floor depth and profile), sea surface temperature and other physical attributes of the region to understand whether movements are associated with particular features or events.

For those tags which provide us with temperature and depth information, we can determine whether individuals show a preference for a particular depth or temperature regime, or whether they use different parts of the water column at different times of year or in different places. For example, a Galapagos shark spent most of its time at depths between 50-100 m while in the Galapagos Marine Reserve, but used surface waters to a much greater degree when travelling in the open ocean. This would have implications when determining its vulnerability to shallow longline fishing gear.

What our interactive map shows

Migramar researchers can post their tracks on our interactive animated map at any time – either in near-real time as they receive new position locations from the satellites, or at the end of a particular study once the tracks have been analyzed.

The aim of the map is to provide a platform for all oceanic tracks in the region, regardless of the species, and thus build a composite picture of migratory pathways, which can be used by decision makers and stakeholders when discussing a whole range of marine-related issues, such as dive tourism ordination, fisheries regulations, oceanic protected areas, and connectivity and regional marine management plans.

(1) The first conclusion we can make from the tracks placed on the map to date, is that the animals we tagged venture further afield than the Marine Protected Areas in which they began.

(2) Several hammerhead sharks cross international boundaries, at least one hammerhead tagged in Malpelo Island moves south of Coco´s Island. A second shark tagged in Malpelo moves south parallel to the South American coast into Ecuador waters later on returning near Malpelo.

(3) Furthermore, one hammerhead tagged in Galapagos makes an oceanic journey of over 1500 kilometres in a northwesterly direction. This tells us that while these animals may display site fidelity and residence for parts of the year, they also travel huge distances at particular times.

(4) The silky shark that was tagged at Cocos island was subsequently caught by a fishing vessel. The tag continued to send signals to the satellites, and we tracked it to the village of Punta Arenas, Costa Rica, only 38 days after it was tagged.

(5) The hammerhead sharks tagged in Coco´s Island remained with the tags for shot periods of time: from 1 to 6 days. However one of this sharks moved west of Coco´s Island over a sea range covering 127 km before the tag detached.

The big picture

This project allows us to document open ocean movements, and can be combined with the results of the ultrasonic tagging projects to provide an overall view of the spatial dynamics and connectivity of the populations in the region. In the future, this work will be integrated with genetic studies to determine the level of mixing within the region.

We can use this information to evaluate the contribution that the Marine Protected Areas make to the conservation of the species tagged, and to provide technical input for ocean resource management issues such as zoning schemes, mobile marine reserves and fisheries regulations.

Read how this project contributes to the big picture.