Gimme Shelter: Challenges for Marine Protected Areas

By January 30, 2013 Ocean Solutions


Marine Protected Areas: What are they? How are they supposed to work? How can we tell if they work? And most importantly how can we make them work better?

Simply put a Marine Protected Area (MPA) is in essence a National Park, just underwater. In practice what that means is that it is an area with restrictions on fishing (this ranges from a full no-take zone to limiting only for recreational fishers, to only being able to fish certain times of the year, really the list goes on and on).
spillover effect
The idea being that this is an area that will be able to protect fish from being caught by fishers so they can grow larger and have more offspring. This is important because as fish age (and get larger) they produce exponentially more offspring. An MPA also provides juvenile fish with a safe place to settle and grow into adults without the threat of trawlers and other fishing boats catching them. The idea is that there will be a spillover effect causing some of the fish in the MPA to leave and go to areas that fishermen do have access to.

The potential for this is really a win-win situation. The environment benefits because of the protection of fish and other species within the boundaries of the MPA, as well as the safeguarding of the habitat which in some cases can take decades, even centuries to regrow after being destroyed. Fishermen benefit because there will be more fish, and larger fish present outside of the reserves for them to catch and sell.

Are MPAs Working?

>Well unfortunately that is a bit harder to figure out than it may seem. On the surface it seems like an easy question take the number and size of the fish before the MPA was created and compare it to the number and size after the MPA. Sounds simple enough right? Wrong. Basically, as with most things, every MPA is different, and every species protected by the MPA is different. TunaSome things like tuna which have extremely large home ranges may pass through MPAs but because they travel so much they just as quickly leave the area they are protected in, so in reality MPAs have basically no impact on tuna populations. On the other hand species like grouper which have fairly small home ranges do very well in an MPA, as evidenced by the Exuma Cays Land and Sea Park, the oldest MPA in The Bahamas (established in 1958). Here researchers see that there are more grouper and that on average the grouper are bigger than their unprotected counterparts.

Graph represents average biomass (a measurement of density and size) of grouper in a variety of habitat types both inside (solid gray bar) and outside the Exuma Cays Land and Sea Park. Take from Chiappone and Sealey. 2000. Bulletin of Marine Science.

Another factor to consider in developing MPAs is that many fish species spend a long time during their larval stage living in the plankton and being moved around by ocean currents. This means that often fish that are spawned inside an MPA settle and become a juvenile outside its boundaries. This can also happen in reverse as well. The good news is that this means there is a constant influx of new genetic material into the MPA. The bad news is it means that the larvae that leave the MPA now face all of the fishing pressure put on fish all over the world.

Next time I’ll post more about how these issues can be managed and other innovative ways some MPAs are being designed to maximize their efficacy.

But in the meantime, do you think MPAs are necessary?

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