15 - Perspectives

FSAs beyond MPAs

A common question we get from fishers, community groups, fishery, and marine protected area(MPA) managers is “How do we manage the use of spawning aggregations with MPAs, and if not, what is the most effective tool?” It is a hard question to answer, but here is a little more about how MPAs can at least be part of the solution.

Fish spawning aggregations (FSAs) are integral components of coral reef ecosystems. They are the only reproductive opportunities for many reef species and their persistence is important for replenishing fish populations, for the health of many exploited species and for the benefit of coastal fishing communities. Transient aggregations are particularly important and are formed by many larger reef species for short periods each year when they gather in their hundreds to tens of thousands. The movements of transient aggregators to and from aggregations can be extensive, representing an important component of adult connectivity and biomass flux across reefs. Because transient aggregations are highly predictable, they are often the focus of fishing. Indeed, many are in decline because few are effectively managed.

Marine protected areas (MPAs) are widely and heavily advocated as conservation tools for coral reef ecosystems, and are increasingly promoted for fishery management. MPAs can help to preserve coral reef habitat, and, because many reef-associated species are relatively sedentary as adults, ‘no-take’ MPAs can effectively protect sub-populations of such species from fishing. This protection allows them to grow larger and persist at higher densities than in nearby exploited areas. MPAs are being introduced in many tropical coastal areas to address both conservation and fishery management. In some cases they are the only protective measure in place.

Unfortunately, species that form transient spawning aggregations are not well protected by MPAs as a sole measure because they are not sedentary, because most are also fished outside of the reproductive season (and hence outside of aggregations) and because MPAs are not typically located in the habitat where most transient aggregations occur. The majority of MPAs are smaller in area than 10 km2, far smaller than the typical home range (inclusive of annual migration distances of 10s to 100s of km to and from spawning sites) areas of most aggregating fishes and are typically located close to shore. Many aggregations, however, form in outer reef and reef drop-off areas, offshore locations not regularly incorporated into MPAs, partly because their protection is difficult to enforce. Moreover, since most aggregating species are also fished outside of the spawning season some control on fishing effort is called for.

As we learn more about transient FSAs, appreciate their role in coral reef ecosystems and coastal fisheries, and as management embraces a more holistic ecosystem approach we recognize the importance of outer reef drop-off habitat for biodiversity and its increasing exposure to fishing (e.g. Olavo, G., Costa, P.A.S, Martins, A.S. and Ferriera, B.P. (2011) Shelf-edge reefs as priority areas for conservation of reef fish diversity in the tropical Atlantic. Aquatic Conservation Marine Freshwater Ecosystem 2011 Published online in Wiley Online Library wileyonlinelibrary.com. DOI: 10.1002/aqc.1174). Aggregations are key life history events for many fish species, including some that are threatened and are easily overfished. The deep reef habitat and associated reef slope and reef passage areas are refuges for heavily fished shallow water species and home to a distinctive deep reef fish assemblage. This habitat also contains many transient spawning aggregation sites. MPA’s and MPA networks need to incorporate such habitats and aggregating species need to be managed well beyond MPA boundaries if they are to persist as healthy populations and continue to contribute significantly to food security and societal well-being. (See also: Protecting the Spawning and Nursery Habitats of Fish: The Use of MPAs to Safeguard Critical Life-History Stages for Marine Life: http://depts.washington.edu/mpanews/MPA77.pdf )