Putting seahorses on the map

By Jennifer Selgrath

Researcher Jenny Selgrath mapping a rare coral reef with local fishers. Amanda Vincent/Project Seahorse

Researcher Jenny Selgrath mapping a rare coral reef with local fishers. Amanda Vincent/Project Seahorse

If I asked you to map the location of, say, your local aquarium, you would whip out your smart phone and Google would tell you where it is. But what if I asked you to map the location of corals and other important habitats in the Danajon Bank, a coral reef ecosystem in the central Philippines and within the global center of marine biodiversity? You would have had trouble because that map did not exist — until now.

I moved to the Philippines to work on conserving coral reef ecosystems and seahorses, but I could not find an accurate map of things as simple as where different villages were located. I took a few trips to local government offices where friendly staff showed me the maps that they had on their walls. With that information and a bit of computer time I made a digital map of the villages I was going to do research in. A first step. But the next step was to make a map of coastal habitats (including the underwater ones), and that was going to more complicated.

Why map ocean habitats when I work for Project Seahorse? Seahorses are the most charming fishes in the sea, but a lot of seahorse populations are threatened. One major threat to seahorses is the loss of their habitats. In tropical oceans, seahorse habitats include corals, seagrass and mangroves. These connected habitats provide shelter for seahorses, and they also support a lot of other biodiversity.

But these habitats can be seriously degraded by overfishing, coastal development, pollution and climate change. An important step in protecting seahorses — and other amazing marine wildlife — is to know where their habitats are and how healthy those habitats are. To do this we need good maps.

Mapping things that are underwater is challenging, but I wanted to compare how useful two approaches were for conservation. One approach for making maps involved using satellite images and remote-sensing software. This is cutting edge because, for a number of technical reasons, like the sections of the light spectrum that satellites photograph, it’s been hard see what was underwater from space. New satellites have fixed some of these problems, opening up this possibility.

To make satellite-image-based maps, I did snorkeling surveys and took coordinates of the habitats I found. Those surveys helped identify color, texture and location patterns specific to each habitat in the satellite image. I made the remote-sensing maps in collaboration with Chris Roelfsema at the University of Queensland.

The second approach involved making habitat maps by interviewing local fishers to map the habitats that are in their fishing grounds. I interviewed approximately 250 fishers from 21 villages located in different regions of the Danajon Bank. Then I combined the maps each fisher drew into one map representing local knowledge about habitats. This is a lot less technical and expensive, and it can get fishers excited about protecting important habitats.

 

Remote-sensing map

When I compared these two approaches, both maps were fairly accurate, but each approach had different strengths for conservation programs. The remote-sensing map was slightly more accurate and did a better job of showing fine-scale details, such as indicating the amount of habitat edges present. This is important because some fishes, along with invertebrates such as scallops and lobsters, are strongly affected by habitat edges. Other species, however, such as highly mobile fishes, are not affected by habitat edges. Conservation programs focusing on them do not necessarily require such finely detailed maps.

Fisher map

The map I constructed with fishers was better at documenting habitats that were in murky waters (which the satellite-image map missed) and was informative about coarse habitat patterns. But the fisher maps were blank in places where the fishers did not fish, such as local marine protected areas (MPAs).

Because there are benefits to both techniques, at Project Seahorse we are planning to combine both maps to use in upcoming conservation projects. We recommend that conservation programs that are planning to make marine habitat maps identify their goals (i.e., what they are going to use the map for) early in the process so that they can make an informed decision about the best mapping approach to use.

If you want to learn more about the Danajon Bank, you can check out the iLCP photo exhibition in the Wild Reef exhibit at Shedd. And if you want to get involved with mapping and help protect seahorses, check out iSeahorse.org. iSeahorse is a new citizen science initiative that allows people to upload information and photos whenever they see seahorses in the wild. Information you provide will help us make maps of where seahorses are located around the world and will help us improve seahorse conservation.

Jenny Selgrath is a PhD student with Project Seahorse. Follow her on Twitter @JennySelgrath.