Published on 26 August 2018

Reviewing a study on marine protected area efectiveness for reef shark conservation

I have been doing some work reviewing the literature on marine protecte areas (MPAs) and how effective they are in protecting mobile species. This recent paper from White et al. (2017) demonstrates how large MPAs are capable of providing a high degree of protection, although incomplete, to mobile pelagic species such as the grey reef shark. The paper in question is:

Timothy D. White, Aaron B. Carlisle, David A. Kroodsma, Barbara A. Block, Renato Casagrandi, Giulio A. De Leo, Marino Gatto, Fiorenza Micheli, Douglas J. McCauley (2017). Assessing the effectiveness of a large marine protected area for reef shark conservation, Biological Conservation, Volume 207, Pages 64-71, ISSN 0006-3207, https://doi.org/10.1016/j.biocon.2017.01.009.

Critical review

In this paper a group of researchers from Stanford University share their findings about the effectiveness of a large no-take marine protected area (MPA), the U.S. Palmyra Atoll National Wildlife Refuge, on the population of grey reef shark (Carcharhinus amblyrhynchos). The grey reef shark is a declining species classified as near threatened in the Red List of Threatened Species (Smale, 2009).

As a result of targets set by the United Nations Convention on Biological Diversity (UNCBD), the number of MPAs has significantly increased, doubling the total protected area in recent years (De Santo, 2013). MPAs are steadily becoming larger and being set in remote locations away from human populations (Lubchenco & Grorud-Colvert, 2015), triggering concerns as their creation rate has outpaced research on their effectiveness (McCauley, 2014). While positive effects of smaller MPAs on sedentary species have been largely documented (Claudet et al., 2006; Miller et al., 2012; Russ et al., 2008), there is uncertainty on whether highly mobile and poorly understood species like the grey reef shark benefits or not from larger and remote MPAs (White et al., 2015).

To determine the amount of time grey reef sharks spend outside of the MPA boundaries, 50 nautical miles (NM) from the atoll shores, the team used both conventional and satellite tags on the sharks. In the following years 5 conventional tags were retrieved from local fishermen who caught the sharks. Most likely more tagged sharks were fished but communication issues with the most remote communities and the lack of involvement from commercial vessels in the study prevented their recovery. Furthermore, only half of the satellite tags proved to be effective. Similar studies previously relied on acoustic telemetry, which detects tagged sharks when they approach a static sensor. A significant improvement over acoustic telemetry, satellite-based tags keep emitting signals but not without flaws. The battery life of the tags is limited and because tags would only transmit when the dorsal fin of the shark comes out of the water, large underwater movements went untracked, resulting in some data gaps. In total, 273 sharks were included in the study, a relatively low sample size considering that the number of grey reef sharks at Palmyra is estimated to be around 9,000 individuals (Bradley et al., 2017).

Palmyra Atoll

Palmyra Atoll viewed from the northwest, 2011. Photo credit: Erik Oberg/Island Conservation.

Using public data from the Automatic Identification System (AIS), a vessel transmitting system designed to prevent collisions, researchers were able to estimate industrial fishing activities across the region. The study pioneers the use of AIS to estimate fishing efforts but must be looked at cautiously as only large and modern vessels possess this technology, allowing smaller vessels to go undetected. The lack of international regulation also means that AIS transponders can be turned off at will. Recent estimates set to 30% the amount of large fishing vessels not consistently transmitting (McCauley et al., 2016). A machine learning algorithm was used on 2 years of data, showing high levels of fishing activities outside the MPA boundaries and virtually none within the boundaries.

Combining the results of shark tracking and AIS data, the team was able to demonstrate that the Palmyra Atoll MPA provides grey reef sharks with substantial yet incomplete protection. The recovered tags by Kiribati fishermen and the satellite data proved how some of the sharks ventured into pelagic waters beyond the 50 NM boundary, becoming vulnerable to fishing. One of the satellite-tracked sharks was detected 810 km away from the MPA; the largest known distance roamed by a grey reef shark, exceeding by far the 134 km recorded by Heupel et al. (2010). The results highlight the potential of AIS in fisheries management and protection enforcement, proven by the nation of Kiribati who successfully prosecuted a company for illegal fishing using AIS data as evidence (Lubin, 2016). The study offers useful insight on how grey reef sharks interact with commercial and local fishermen off the MPA limits and how a boundary expansion could increase protection even further. For a complete evaluation on its effectiveness it would also be beneficial to look at how the MPA may or may not protect grey reef sharks against other major threats such as plastic pollution, ocean acidification or noise pollution (Hilborn, 2015).

References

Bradley, D., Conklin, E., Papastamatiou, Y. P., McCauley, D. J., Pollock, K., Pollock, A., Caselle, J. E. (2017). Resetting predator baselines in coral reef ecosystems. Scientific Reports, 7, 43131. 10.1038/srep43131

Claudet, J., Pelletier, D., Jouvenel, J., Bachet, F., & Galzin, R. (2006). Assessing the effects of marine protected area (MPA) on a reef fish assemblage in a northwestern mediterranean marine reserve: Identifying community-based indicators. Biological Conservation, 130(3), 349-369. 10.1016/j.biocon.2005.12.030

De Santo, E. M. (2013). Missing marine protected area (MPA) targets: How the push for quantity over quality undermines sustainability and social justice. Journal of Environmental Management, 124, 137-146. 10.1016/j.jenvman.2013.01.033

Heupel, M. R., Simpfendorfer, C. A., & Fitzpatrick, R. (2010). Large–Scale movement and reef fidelity of grey reef sharks. Plos One, 5(3), e9650. 10.1371/journal.pone.0009650

Hilborn, R. (2015). Marine protected areas miss the boat. Science, 350(6266), 1326.

Lubchenco, J., & Grorud-Colvert, K. (2015). Making waves: The science and politics of ocean protection. Science, 350(6259), 382.

Lubin, G. (2016). Satellite watchers busted an illegal fishing vessel, and they're coming for others around the world. https://www.businessinsider.com.au/global-fishing-watch-catches-illegal-fishing-vessel-2016-11

McCauley, D. J. (2014). Mega-parks need greater oversight. Nature News, 515(7525), 28. 10.1038/515028a

McCauley, D. J., Woods, P., Sullivan, B., Bergman, B., Jablonicky, C., Roan, A., Worm, B. (2016). Ending hide and seek at sea. Science, 351(6278), 1148.

Miller, I., Cheal, A. J., Emslie, M. J., Logan, M., & Sweatman, H. (2012). Ongoing effects of no-take marine reserves on commercially exploited coral trout populations on the great barrier reef. Marine Environmental Research, 79, 167-170. 10.1016/j.marenvres.2012.05.008

Russ, G. R., Cheal, A. J., Dolman, A. M., Emslie, M. J., Evans, R. D., Miller, I., Williamson, D. H. (2008). Rapid increase in fish numbers follows creation of world's largest marine reserve network. Current Biology, 18(12), R515. 10.1016/j.cub.2008.04.016

Smale, M.J. 2009. Carcharhinus amblyrhynchos. The IUCN Red List of Threatened Species 2009. e.T39365A10216946. http://dx.doi.org/10.2305/IUCN.UK.2009-2.RLTS.T39365A10216946.en. Downloaded on 22 July 2018

White, E. R., Myers, M. C., Flemming, J. M., & Baum, J. K. (2015). Shifting elasmobranch community assemblage at Cocos island—an isolated marine protected area. Conservation Biology, 29(4), 1186-1197. 10.1111/cobi.12478

Creative Commons License
This work is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 New Zealand License.