Partial Protection in Mexican MPA Only Marginally Effective in Restoring Reef Ecosystem

by Katie Huang

Loreto Bay National Park (LBNP) is a marine protected area (MPA) in the Gulf of California, Mexico, which bans fishing in some areas and allows limited amounts in others. However, since only a small region of the MPA is completely protected, it is possible that the benefits of a no-take area do not offset the effects of the permitted fishing. From 1998 to 2010, Rife et al. (2013) surveyed the biomasses of fish in sites within the LBNP and in open control areas and compared the data from before and after the MPA was established. They found that the biomasses of protected and open area fish were not significantly different. Although the biomasses of herbivorous and zooplanktivorous fish increased significantly within the MPA’s restricted area, the authors did not observe changes in apex predator and carnivore biomasses which suggests that the reef ecosystem is still unhealthy even after 13 years of protection. Possible explanations include poor enforcement of regulations as well as the small size of the restricted area, and management solutions should address these issues to make the LBNP more effective.

Rife et al. surveyed 22 sites, 14 within LBNP and eight controls, throughout August and September from 1998 to 2010. One of the sites was located within the no-take zone and another in an area that restricted the types of gear fishers could use. The authors conducted underwater surveys, counting, identifying, and estimating the lengths of fish along up to seven transects in each site, focusing on larger reef fish instead of small, cryptic species. From the length data, they used allometric measures to extrapolate fish weight and biomass. In order to ensure that observed differences between the open and protected areas were not simply due to natural variation, Rife et al. compared data from before and after the MPA was established. Since the MPA implemented its management strategy in 2003, data from 1998–2002 were considered “before” and 2003–2010 were treated as “after.” The authors also grouped the no-take and restricted gear areas within LBNP together under a “restricted” categorization separate from the “rest of park” since they observed no significant differences between them. Using statistical analyses, they compared the changes in mean biomass after protection and in temporal variance among the restricted, rest of park, and control areas. To compare catch trends, they analyzed data from fisheries databases for both MPA and open access areas from 1999 to 2009.

The authors found significant differences in total fish biomass between the restricted area and the other LBNP sites from before to after the MPA was established, due to increases in the abundances of herbivorous and zooplanktivorous species. However, there were no significant improvements in apex predator and carnivore biomasses, nor were there changes in temporal variance between the two areas. Other studies have found that no-take MPA protection can lead to increases in apex predator and carnivore biomasses within a few years, so these results suggest that regulations within the LBNP have not been effective in helping the recovery of target species, potentially because the restricted areas are so small. From the catch data, they found that fewer fish were being reported as being caught in the MPA over time, but it is possible that these results were due to unreported catches by recreational and out-of-area fishers. Between the MPA and open areas, Rife et al. observed no significant differences in total fish biomass, biomasses of fish trophic groups, or temporal variance from before to after the MPA establishment, even after 13 years of monitoring. In both regions, about 70% of the total biomass was composed of herbivores and zooplanktivores instead of the expected apex predators, suggesting that anthropogenic effects are preventing the reef ecosystem from recovering. The authors recommend that in order to improve the LBNP MPA, it should enforce existing regulations more strictly, expand the size of the no-take zone, and ban certain types of fishing gear that target apex predators. With only partial protection, the MPA has been extremely limited in its effectiveness.

Rife A.N., Aburto-Oropeza O., Hastings P.A., Erisman B., Ballantyne F., Wielgus J., Sala E., Gerber L., 2013. Long-term effectiveness of a multi-use marine protected area on reef fish assemblages and fisheries landings. Journal of Environmental Management 117, 276–283. http://fb4.myweb.uga.edu/pubs/lbnp.pdf

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