Editor's note: The authors of the following essay work with the National Marine Protected Areas Center of the USA, established in 2000 to provide science, information, and tools for an effective national system of MPAs (http://www.mpa.gov)
By Charles Wahle, Rikki Grober-Dunsmore, and Lisa Wooninck
Policy-makers and stakeholders increasingly demand that new MPAs have clearly articulated conservation objectives and that user restrictions be demonstrably linked to significant environmental threats. These concerns are often reflected in disputes over whether a proposed MPA must be a no-take reserve to be truly effective, or whether recreational fishing for pelagic species could be permitted without compromising the integrity of the underlying benthic communities - often the primary target of MPA protections.
In such situations, managing recreational fishing through "vertical zoning" that restricts fishing to the MPA's upper waters might represent a practical way to facilitate existing uses consistent with the site's primary conservation goals. Clearly, the advisability of this management strategy depends on the scope of the MPA's conservation objectives (i.e., benthic communities vs. the entire water column), the degree to which its benthic and pelagic communities are linked ecologically and vulnerable to fishing, and the MPA's ability to monitor and enforce complex fishing restrictions.
To date, the answer to this timely question has been in the eye of the beholder. Without a more transparent scientific basis for evaluating potential threats posed by common activities such as recreational fishing, MPAs will continue to spark opposition from user groups that question their underlying ecological rationale and equitability. In November 2005, the US National Marine Protected Areas Center convened 30 fisheries scientists, marine ecologists, MPA practitioners, and key recreational fishing leaders in Monterey, California, to address this increasingly critical issue. The purpose of this diverse gathering was to synthesize what is currently known about benthic-pelagic (BP) linkages in US marine ecosystems, to identify significant gaps in our scientific understanding of BP linkages, and to lay the preliminary groundwork for practical guidelines and best practices for managing recreational fishing in MPAs.
Benthic-Pelagic Linkages in Marine Ecosystems - General Trends
The workshop participants synthesized current knowledge about the strength, direction and complexity of benthic-pelagic linkages among different taxa and ecosystems. While local BP linkages will differ, three important general trends emerged from the group:
- First, BP linkages can generally be expected to be stronger and more direct in shallow water habitats (i.e., seafloors 50-100m deep); among coastal pelagic fish species (e.g. jacks, mackerel, bluefish); in predictable spawning aggregations that feed heavily on the benthos; in upwelling zones and other areas of localized biophysical coupling; and in habitats with pronounced three-dimensional relief (e.g., coral reefs, shallow sea mounts, kelp beds).
- Second, BP linkages may be generally weaker and more indirect in deeper habitats where pelagic predators rarely encounter benthic prey and among oceanic pelagic species (e.g., tuna, sharks, marlin).
- Third, there are many circumstances in which ecologically important interactions are likely to be complex, unpredictable, and/or poorly understood. Local ecological factors contributing to complex BP linkages include multiple interactions within and among trophic levels (e.g., with mid-water forage or bait fish); complex behaviors and life histories among key local species; the ephemeral appearance of highly mobile predators; and/or the size of pelagic predator populations.
Thus, while the extreme ends of the BP linkages spectrum are relatively straightforward and intuitive, the vast ecological center is considerably less clear for designers of future MPAs.
Implications of Benthic-Pelagic Linkages for MPA Design
Based on these general ecological trends in the potential occurrence and importance of BP linkages, the workshop participants agreed on some preliminary rules of thumb to help guide MPA planners when evaluating proposals to allow pelagic recreational fishing in an MPA. Vertical zoning of fishing might be appropriate to consider in areas with weak and indirect BP linkages, where pelagic fishing may not impact protected benthic communities. In contrast, vertical zoning might not be an appropriate management design in areas with strong and direct BP linkages, where pelagic fish prey heavily upon benthic or mid-water species. Finally, for the many areas in which the nature, direction, strength, and predictability of the BP linkages are poorly understood, a more precautionary and adaptive approach to MPA design might be most appropriate to adopt, pending additional scientific information about the site.
By identifying the general circumstances in which we may know enough to evaluate the advisability of using vertical zoning of fishing to design and manage benthic-focused MPAs, these scientists, fishermen and managers overcame significant differences in experience and perspective on an important and contentious marine policy issue. Ongoing follow-up actions include developing a more detailed scientific publication, organizing a scientific working group to address the emerging research needs on BP linkages, and working with the recreational fishing community to develop best practices for low impact pelagic fishing by, and for, fishermen. Ultimately, we hope that the workshop's results, and the subsequent efforts that it has already spawned, will help inform a new direction of science-based collaboration in MPA policy deliberations in the United States and abroad.
For more information:
Charles M. Wahle, Director, MPA Science Institute, National Marine Protected Areas Center, National Oceanic and Atmospheric Administration (NOAA), Monterey and Santa Cruz, CA, USA. Tel: +1 831 242 2052; E-mail: charles.wahle [at] noaa.gov