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Sharkbites Saturday

Can you keep me safe? What can MPAs do for Sharks


White, T. D., Carlisle, A. B., Kroodsma, D. A., Block, B. A., Casagrandi, R., De Leo, G. A., … & McCauley, D. J. (2017). Assessing the effectiveness of a large marine protected area for reef shark conservation. Biological Conservation207, 64-71.

What is an MPA?

What do you think about when you hear the word MPA? You might have heard it in the news or from a friend who is really into science and conservation. Well, MPA stands for Marine Protected Area, and it is exactly that, an area designated for conservation purposes where human activities are either regulated, limited, or restricted. The first MPA in the states was established in 1903 by President Theodore Roosevelt and this was Pelican Island National Wildlife Refuge in Vero Beach Florida. Since then we’ve established more than 1,200 U.S. MPAs and includes coastal watersheds, estuaries, and inland lakes.

Beyond the States, MPAs have expanded at a remarkable rate (Figure 1). Many of these restrict fishing and are designated “No-Take Zones” which allow for overfished species to take refuge and replenish their numbers. Acting as sanctuaries, they are currently the last pockets of highly biodiversed coastal ecosystems.

Figure 1. Map illustrating existing Marine Protected Areas as of 2014 alongside Exclusive Economic Zones. Image Credit: By Daniel Stone, National Geographic

Can they protect sharks?

Over the last few years shark populations have declined significantly because their fins are of immense commercial value. MPAs are thought to be effective tools for their protection, however, these are huge fish with capabilities of swimming great distances in and out of MPAs. Therefore, how can we be sure? First, we would need to document how much time do they spend outside an MPA and second, figure out the mortality risks they are exposed to during that time.

The Study

A research team led by Timothy White decided to tackle on this question using the grey reef shark population (Figure 2) which were known to be abundant in coral reefs ecosystems of the Indo-Pacific. Their study was done in the 54,000 km2 U.S. Palmyra Atoll National refuge located in the Central Pacific Ocean, close to other islands exposed to fishing pressures.

Figure 2. Grey reef sharks. Image credit: http://animal-wildlife.blogspot.com

To track the sharks’ movements in and out of the MPA they used both satellite and conventional tags. They deployed instruments on 11 sharks, which included high resolution satellite position-only tags (SPOTs) that allowed them to get accurate location for each individual during any large-scale movement. The tags send a signal to the researchers every time the shark’s dorsal fin breaks to the surface. The conventional tags were used to not only study their movements but also observe how frequently sharks die from being fished. They tagged 262 sharks and recovered the tags from fisherman over a period of three years.

What they found

Five out of the 262 conventional tags were retrieved from local fishermen outside the MPA. All sharks were female ranging from 130-155 cm in length. Two were caught 223 km from the MPA and three from 366 km away. The fisherman used single-hook hand lines aboard aluminum skiffs to fish.

Six out of the eleven SPOT tags were retrieved with 1280 dorsal fin breaking surface detection recordings. The average time percent spent beyond the MPA boundary per shark was 28%. All sharks were male and found feeding in open ocean away from the Palmyra Atoll.

Is this enough data?

You may be thinking, wow, out of so many tags, very little were retrieved; and what happened with the five satellite tags that did not transmit data? Well, this is a huge part of why there are so many gaps in our knowledge about shark population status and their natural history. Studying sharks is a huge and hard task because most of the time we don’t know where they are. However, the data collected in this study is enough for us to infer on the importance of MPAs for the grey reef shark population seeing as they spend a considerable amount of time within the MPA and use it as refuge from fisherman.

What does this mean?

The retrieved conventional tags tell us that sharks around the Palmyra Atoll are at risk of being fished whenever they swim beyond the boundaries. The researchers created a fishing effort density map out of data collected from 193 vessels (Figure 3) and their results show heavy fishing pressures (measured as time boats spent out fishing) near the edges of the MPA closer to the Atoll. Based on the map they created, absence of an MPA around Palmyra would have severe consequences for the grey reef shark population which would have continued to decline until they were none left. MPAs are of utmost importance to replenish shark populations and other fisheries!

Similarly, the satellite tag detections support that sharks use the habitat around the Atoll within the MPA for their core activities such as feeding and resting further supporting that large and remote MPAs in the ocean do offer substantial protection for this species. Furthermore, it implies that the further establishments of large MPAs will allow for more refuge for these mobile predators. We need MPAs!

Figure 3. A fishing effort density map for 193 commercial fishing vessels as determined through remote sensing of vessel Automatic Identification System (AIS) transmissions. Grid size is
0.25°. Resource: White et al, 2016


To the researchers’ surprise, their use of satellite tags uncovered surprising shark behaviors such as high detection signals in the pelagic (open water) environment for one of the individuals when it is believed that grey reef sharks spend most of their time near the reefs. Another surprise was that they captured the longest movement on record for this species. A single individual swam 926 km, out of which 810 km was beyond the MPA, Wow, that is a long distance for a 4-5ft fish!

Bigger Picture

Sharks are amazing creatures but this project doesn’t only apply to sharks. Whales, dolphins, and turtles are also big and highly mobile creatures that need sanctuary from excess fishing. As the general public we can urge our governments to establish Marine protected areas in order to help conserve these important species. They play an enormous role in marine food webs that support the very fish we eat. As citizens, we have the power to exert pressure on our administrators and fight for a healthier planet and its biodiversity.

Have a Sharktastic Saturday!

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