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Coastal Management

How sea turtles with backpacks can help establish highways for ocean health

Pendoley, K., Schofield, G., Whittock, P., Ierodiaconou, D., Hays, G., (2014).  Protected species use of a coastal marine migratory corridor connecting marine protected areas.  Marine Biology. 161:1455-1466.
DOI 10.1007/s00227-014-2433-7

Credit: Paul Whittock.

Credit: Paul Whittock. Flatback turtle on beach.

Background

It is a big scary world out there if you are a migrating ocean animal. Oil and gas exploration is so loud that it is almost impossible to communicate with your kin, massive cargo ships plow through your path and offshore energy farms pop up along your migration route. Then every which way you swim, a net or baited hook threatens to end your life.

Encountering each obstacle decreases the chance of a migrating ocean animal’s survival, making it an exhausting feat to reach their feeding or breeding destination, let alone to merely exist. Thankfully, marine protected areas (MPAs) can be a welcome oasis for many species, including endangered sea turtles, sharks, cetaceans (whales and dolphins), and commercially important fish. Many ocean stakeholders are starting to realize the importance of sustaining healthy and diverse species populations, and are supporting the implementation of MPAs as a tool to achieve this.

However, there is a weak link in the armor. Outside the boundaries of MPAs, protection ceases which partially negates their effectiveness. Creating protected pathways or corridors that link protected zones is a simple and elegant solution that may extend the conservation benefits of MPAs and still accomodate planned allocation of human activity. A study done in Australia enlists the help of some charismatic ocean inhabitants to suggest where some corridors could be established.

 

Materials & Methods

Every 1-3 years around 20,000 female flatback sea turtles (Natator depressus), considered vulnerable in Western Australia, return to their natal beach to nest. During this time, about every two weeks, gravid females lay up to four clutches of eggs from November through January.

From 2005-2012, Pendoley et al., successfully tracked the migratory routes of 73 female flatback sea turtles from four nesting sites outside marine reserves. By harnessing only healthy turtles with various styles of satellite transmitter backpacks, they were able to reveal the turtles’ adventures to and from breeding and foraging areas.

So how did scientists build a backpack that can help promote ocean health?

Credit: Gail Schofield

Figure 1: Female adult flatback turtle with transmitter. Credit: Gail Schofield.

Step #1: Transmitters were mounted with a plate lined with grooved neoprene padding to allow water flow beneath. This makes sure the backpacks ‘cramp their stylez’ as little as possible for smooth sailing.

Step #2: Instead of a measly human backpack that has two straps, six straps made of nylon seatbelt webbing were used to thread through the plate and velcro the transmitter over the first and second vertebral scutes (the bony plates that run along the middle of the shell). More straps = more securing power & precise placement, a double whammy!

Step #3:   Zinc staples were also used to prevent slippage of the straps but they were also meant to corrode over time to facilitate easy removal … and voila!  See Figure 1.

Although there was some evidence of carapace wear as there often is with this kind of method, external flipper tags & passive infrared transponders (PIT) were used to identify individuals to ensure they were not tracked for more than one season.

After cleaning up the data by removing outliers, controlling for the bias of tagging, breeding and feeding sites, turtle-friendly expressways were revealed based on cumulative track length.

 

Results & Significance

Figure 1.  State and Commonwealth Marine Reserves are outlined in black, and laid over cumulative track length.

Figure 1. State and Commonwealth Marine Reserves are outlined in black, and laid over cumulative track length shown in yellow, orange and red.

By layering the coordinates of established state and national MPAs it was revealed that 52% of the corridor passed through 11 MPAs.  See Figure 1. This means more than half of the work to designate this turtle highway is already done!  To figure out which species might also flap their fins with glee if the turtle corridor is protected, available distribution data of local marine mammals, reptiles and sharks were analyzed. Tracking data of humpback whales showed that their migration routes traverse 96% of the corridor, implicating multi-species benefits. And although data is quite limited for other species, it was shown that is potential corridor benefits for 20 other species including blue whales, whale sharks, olive ridley turtles, dugongs, sea snakes, sharks and crocodiles.

However, a good portion of the corridor intersects with multi-use areas. For example, concentrated oil and gas activity, two economically significant shipping ports, and recreational fishing and boating areas currently occupy parts of the delineated corridor. This represents the kind of Holy Grail information that marine spatial planners or MPA managers may use to establish high-priority linkages that give safe passage to many species from one MPA to another. However, more tracking data is needed to confirm the frolicking habits of species within the corridor and further information regarding timing of usage by different species may necessitate year-round protection of the corridor.

Of course, migratory pathways may change, keeping us on our toes. As well, enforcement is an ever-present challenge in marine management due to a lack of economic resources, political will and international coordination. However, this demonstrates an encouraging multi-species approach that can be repeated in other areas of the world. At the very least, it can kick start appropriate data collection to ensure both humans and marine life can use the very thing we depend on, and the very thing that connects us: the big blue sea.

 

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