A report authored by Craig Dahlgren and commissioned by the Wildlife Conservation Society (WCS) reviews the benefits of no-take marine reserves (LINK to .pdf). This comprehensive report titled: Belize’s Lobster, Conch, and Fish Populations Rebuild in No-Take Zones, focuses on Belizian reefs, but I imagine these data are very useful for the Bahamas as well. The report is long, ~90 pages, and I have’t looked it over in great detail yet. However, below I provide excerpts of some of the important findings:
“MPAs are designated expanses of sea where some or all uses of marine resources are restricted to enhance the management or conservation of marine resources. MPAs may be created for a variety of purposes – fisheries management, biodiversity conservation, recreational uses, or to address the conservation needs of sensitive species or habitats.
Increasingly, MPAs are divided into zones where different levels of protection are conferred. MPAs or zones within MPAs that have been shown to have the greatest positive impact on the resources within them are ones in which resource extraction, such as fishing, is prohibited.
The most commonly reported benefits from no-take zones around the world relate to their ability to conserve populations of exploited species.
Recovery of exploited species within no-take zones as opposed to fished areas may take as little as 1-6 years, but full recovery of populations to near-pristine levels may take decades.”
The report provides three explanations for the increased productivity and demographic health of populations within protected areas. The final hypothesis is an interesting one, but I couldn’t find any evidence for in the report. Anyone else have any ideas if reserves preserve local genetic diversity tied to behavioral variation?
1. Larger females
“The number of eggs that female fish produce increases exponentially with size, so the more abundant populations of larger fish within no-take zones increase by orders of magnitude over unprotected areas.”
2. Older females
“Similarly, because fish in no-take zones survive to older ages and larvae hatched from eggs spawned from older and larger individuals have a greater chance of survival and higher growth rates, fish spawned in no-take zones have a greater probability of reaching juvenile stages.”
3. Larger (and more) males
“Increases in the size of males can also increase reproductive output of crustaceans such as the Caribbean spiny lobster, as larger males are more likely to successfully reproduce and increase the number of fertilized eggs brooded by females. For fishes that change sex from female to male, e.g., parrotfishes and grouper, the conservation benefits within no-take zones include preserving natural sex ratios that can become skewed towards females in fished populations and cause females to change to males at smaller sizes, potentially reducing reproductive output.”
4. Increased Genetic Diversity
“Finally, because fishing selectively removes some of the more aggressive and faster-growing individuals from populations, characteristics that have a genetic component, fishing selectively removes some of the fittest individuals from the population and, in so doing, may exert selective pressures on the evolution of species. Preserving these beneficial traits within no-take zones may maintain the genetic diversity of species.”
I hope this is valuable! My guess is that a more expert reader will find much more in this report than I.
- WCS Glovers Reef Research Station – www.wcsgloversreef.org
- Dahlgren, C. 2014. Belize’s Lobster, Conch, and Fish Populations Rebuild in No-Take Zones. WCS Technical Report.*
*Note that I am not exactly sure how to cite this one.