MPA News asked three scientists what they considered to be fair or unfair assurances to stakeholders on the fishery effects of marine reserves. The scientists, who have each published previously in MPA News, were:

  • Trevor Willis of the University of Bologna, Italy (see “The Science of Marine Reserves: How Much of It Is Science?”, MPA News 5:6)
  • Ben Halpern of the University of California Santa Barbara, USA (see “Moving the Discussion About Marine Reserve Science Forward”, MPA News 5:7)
  • Tundi Agardy of Sound Seas, a US-based NGO (see “Dangerous Targets And Inflexible Stances Threaten Marine Conservation Efforts”, MPA News 3:11)

The following pieces are in the words of each scientist:

Trevor Willis: “The biggest promise that should not be made is that local fishery yield will increase”

The biggest promise that should not be made is that local fishery yield will increase. Sure, one can raise the possibility that it could happen, but even if the peculiarities of a particular place allow local replenishment outside reserve boundaries to occur, it will take time. The problem is that we have no empirical means of predicting whether (and if so, when) yield per se will benefit from reserves for particular places and species – only general theoretical principles. It is even more difficult to obtain data that demonstrate contributions to production from reserves, and the best examples we have so far come from tropical multi-species fisheries. Temperate examples are hard to come by. A more realistic promise might be to postulate no loss to the fishery if a reserve is implemented (there are a couple of examples where this has happened – catch per unit effort did not decrease even though the area fished was reduced). If benefits to local yield accrue in the future, great, but it is a dangerous promise to make.

We can now be fairly certain that not fishing in a particular area will protect a resident proportion of a population that was previously fished. This allows those individuals to grow and provide a source of recruits that will disperse outside the reserve (how far depends on the species). From the fisheries perspective, this is the old idea of “insurance” against recruitment overfishing. Such measures may have prevented some of the catastrophic collapses of previously productive fisheries, and may yet prevent future ones. It certainly does no harm to have more eggs in the water.

One of the more important things that might be more effectively communicated to stakeholders is that the biological effects of MPAs are not yet well-known. This should be regarded as a good reason to implement them, rather than an argument against them. Our limited experiences to date indicate that reserves are likely to reinstate “lost” ecosystem processes and, as such, provide valuable controls for learning about the effects of fishing. At a time when fishery biologists are beginning to embrace concepts of ecosystem-based fishery management, it is surprising how little emphasis has been put upon the idea of using unfished reserves to determine general management goals. It is absolutely safe to promise that no-take reserves can serve this function, for the greater good of a given fishery. Such concepts are less tangible and therefore more difficult to communicate than “it will give you more fish”, but are long-term functions for reserves that can potentially ensure the productivity of a fishery better than any local-scale spillover.

For more information:
Trevor J. Willis, Centro Interdipartimentale di Ricerca per le Scienze Ambientali, Universita di Bologna, Via Sant’ Alberto 163, 48100 Ravenna, Italy. Tel: +39 0544 937 314; E-mail:

Ben Halpern: “Some species will rebound sufficiently and quickly enough to provide rapid and large benefits to some fishermen”

It is always difficult, and dangerous, to make promises, but there are fisheries effects of marine reserves that one can almost certainly expect, and some that one can be almost certain will not happen. Here I focus on just two of the many of each kind. It is also important to remember that fishermen are only one of many stakeholders with interest in marine resources, such that reserve goals, and therefore expectations, should always represent a balance of these interests.

Highly likely: 1) Some species will rebound sufficiently and quickly enough to provide rapid and large benefits to some fishermen. The scallop example from the Georges Bank closures off of New England, USA, where catches in adjacent waters increased dramatically within a few years, is an excellent example of this (MPA News 2:3). In general, fast-growing species that recruit frequently, are not highly mobile, and that have not been decimated by fishing should rebound more quickly, although there will always be exceptions. 2) In the long term (10-20 years), larger-scale reserve networks will be better at sustaining more stable, and maybe more abundant, fish populations than could traditional gear and effort regulations. This stability (and abundance) results from reserves allowing large, fecund individuals to survive and reproduce, whereas traditionally regulated fisheries (except for extremely effective slot fisheries) will always target and remove the largest individuals first (significantly reducing reproductive output and the population stability provided by this output).

Highly unlikely: 1) Every single species will benefit from the creation of marine reserves. This is almost certainly not true, and it is hard to imagine any single management strategy that could do this. 2) Marine reserves will replace the need for any other form of management. Unless reserve networks are very large (>50% of the total area), there will always be a need for other regulations for at least some species outside the reserves.

For more information:
Ben Halpern, National Center for Ecological Analysis and Synthesis, University of California, Santa Barbara, CA 93106, USA. E-mail:

Tundi Agardy: “It is better to focus on the undisputed benefits”

I am confident we can say that MPAs are an important – perhaps the most important – tool for conserving marine habitat to protect biodiversity (and, to a lesser extent, to conserve ocean wilderness). Well-designed and -executed MPAs can prevent habitat destruction, fisheries overexploitation, and damage to ecosystem dynamics caused by selective removal of ecologically important species at the site. MPA designations raise attention and political will to better address even indirect threats like pollution. There is also some evidence of “biodiversity spillover”, or increased species richness in adjacent areas.

What is more contentious is the extent to which MPAs, and the newer MPA networks modeled on larval dispersal, can enhance or restore fisheries in adjacent areas. While build-up of biomass has been shown to occur outside MPAs in some areas (e.g., scallops on Georges Bank), it is hardly a universal phenomenon, and the problem of displaced effort is a real one with which MPA planners have to contend.

It is better to focus on the undisputed benefits: protection of unique areas, maintenance of biodiversity, conservation of essential fish habitat, and protection of culturally important areas. Stakeholders should be told that MPAs can help reduce user conflicts and better integrate the management efforts of different agencies, both necessary to attain the goals listed above. Scientists should be truthful about uncertainties, and stress how MPAs can further ecological knowledge and understanding about management effectiveness and potential. But we should admit that deriving these many benefits requires active management and enforcement, costly as these things can be.

For more information:
Tundi Agardy, Sound Seas, 6620 Broad Street, Bethesda, MD 20816, USA. Tel: +1 301 229 9105; E-mail: