by Kyra Hartog, RJD Intern
With fisheries collapsing around the world, Marine Protected Areas (MPAs) have emerged as a potential solution to allow fish stocks to recover to a level at which they may be harvested sustainably. There are several types of MPAs, ranging from areas with some fishing allowed to no-take reserves. Though MPAs are widely considered as fishery recovery tools, there has been little empirical evidence showing the benefit a fishery may receive from an MPA. In addition, fishermen generally believe that an MPA will come with an economic cost, possibly related to decreased catch rates and increased boat travel time. In their recent paper, Kerwath et. al (2010) demonstrate the effectiveness of the no-take Goukamma MPA off the coast of South Africa with no apparent cost to fishermen.
The focus species of this study was the roman (Chrysoblephus laticeps), a seabream endemic to the South coast of South Africa that inhabits rocky reefs. The species is targeted as part of a larger fishery directed toward rocky-reef dwelling predatory fish. Due to lifestyle characteristics such as long lifespan and broadcast spawning reproduction, the roman is vulnerable to overexploitation and has been heavily depleted along the South African coast. Fishermen have been required to report species and boat catch data since 1985, providing five years of roman catch data before the Goukamma MPA was implemented in 1990. The study then examined catch data for ten years following the MPA’s implementation. The specific metrics used in this study were catch per unit effort (CPUE), which was used as an indicator for roman abundance, and total roman catch.
The researchers found that in the years leading up to and during the first year of the Goukamma MPA implementation (1985-1991), total roman catch decreased. A year after the MPA was implemented, roman catch began to increase. While there was no visible trend in CPUE before the MPA, researchers saw an increase in CPUE in the vicinity of the MPA after its implementation. Other areas further away from the Goukamma MPA exhibited neither positive nor negative effects with respect to CPUE or total catch. The researchers also did not see any increased travel time for fishermen due to the availability of access points to the fishery outside of the MPA.
The analysis of fishery data suggests to the researchers that the Goukamma MPA was effective in terms of fishery management and conservation of the roman. Though the exact reasons as to why the MPA was effective have not been investigated, it is believed that spillover and larval export from the MPA are the main contributors to the increase in CPUE around the MPA. When roman inside the MPA are protected, the biomass of the species will increase inside the area until the species has recovered sufficiently. Spillover of adults will occur, as the fish are able to grow without pressure from fishing. After males and females have recovered to pre-exploitation numbers, further CPUE increases can be attributed to recruitment of larval roman. The currents in the area can allow pelagic larvae to stay in the area of the MPA, where they can then settle out, grow and become available to the fishery.
This study gives strong positive evidence for MPA use as a fishery management tool. It provides empirical evidence for fishery recovery without great cost to the local fishermen. This study can be cited as reason to implement MPAs in areas around the world where species similar to the roman are in decline due to exploitation.
Kerwath, S. E., Winker, H., Götz, A., & Attwood, C. G. (2013). Marine protected area improves yield without disadvantaging fishers. Nature Communications, 4, 1–6. doi:10.1038/ncomms3347