HOW EFFECTIVE ARE MARINE RESERVES?

A project funded jointly by the Hawaii Department of Land and Natural Resources and Sea Grant

Coral reefs are an extremely important natural resource, supplying food and income for millions of people. Unfortunately many coral reefs are threatened by human activities such as unsustainable fishing. This problem is particularly severe in developing countries where detrimental effects of large-scale removal of fish from reefs are often compounded by use of fishing methods, such as explosives and poison, which seriously damage coral reef habitat. Habitat damage severely reduces the chance of long term recovery of reef fish communities.

Marine reserves ('no fishing zones') are gaining popularity as tools for conserving coral reef habitat and fishes. The rationale for such reserves is not simply to 'lock away' fish from fishermen, but rather to create refuges inside which fish populations can thrive and replenish adjacent fished areas through natural processes of larval settlement and emigration of juvenile and adult fish. In many respects ma rine reserves are analogous to interest yielding bank accounts. The fish inside the reserve are equivalent to the account capital. Surplus fish which 'spillover' into adjacent fished areas are equivalent to interest yielded by the account. Provided that reef fish 'capital' is not eroded (e.g., by poaching), the reserve will continue to yield 'interest' (i.e., will supply fish to be caught outside the reserve)

Despite considerable theoretical benefits and the establishment of hundreds of marine reserves worldwide, hard evidence supporting reserve effectiveness is almost non-existent. Key questions in reserve design, such as optimum size, number, habitat content and location remain unanswered. Lack of data has led to establishment of reserves on an arbitrary basis. Such reserves may simply be ineffective and at worst may promote overconfidence, resulting in further overexploitation of coral reef resources.

In Hawaii we have been assessing the effectiveness of existing reserves with the aim of improving design of future reserves. Specific research goals include gaining a better understanding of movement patterns, habitat use, dispersal rates and population dynamics of coral reef fish in and around marine reserves. The rate at which fish disperse from marine reserves is determined using 'tag and release' methodology. Reef fish are first captured in marine reserves by angling and 'nightscooping' (diving on the reef at night, stunning fish with underwater lights and capturing them with soft meshed handnets). Captured fish are then fitted with ID tags (displaying a reward message, telephone number and unique ID code) and released at their point of capture. The proportion of tagged fish subsequently recaptured outside the reserve, together with the distance between release and recapture sites, indicates how 'resident' each species is in the reserve. There are a number of statistical analysis options for tag and release data

Tag and release techniques are useful for determining dispersal rates but provide no information on daily movement patterns and habitat use of reef fish. Such information is critical for designing effective marine reserves because in order to protect fish, reserves must be large enough to completely encompass fishes daily movements. If too many reef fish regularly cross reserve boundaries into adjacent fished areas and get caught, reserves will not be effective! Acoustic telemetry (ultrasonic 'tracking') is a technique that has been used successfully to determine daily movement patterns of fish ranging in size from 15cm goatfish to 5m tiger sharks. When using this technique, reef fish are captured, equipped with a miniature ultrasonic transmitter , released and followed in a 17ft boat equipped with a hydrophone and receiver. The next step in increased tracking efficiency will be a kayak equipped with acoustic telemetry equipment (receiver, hydrophone and power source) interfaced to a Global Positioning System (GPS) unit, depth finder and laptop computer. The kayak makes no engine noise and can follow fish into extremely shallow water. The tracker simply follows the transmitter signal (heard through headphones) while the computer records relevant data.

While understanding fish movement and dispersal patterns is important in designing effective refuges, actual performance of refuges is best determined by monitoring temporal variation in fish populations in reserves and adjacent areas. In theory fish population size should gradually increase inside marine reserves, relative to fished areas, following establishment of a reserve. The clear waters surrounding coral reefs enable divers to count fish at sample sites situated at different locations in the reef system. The same sites are revisited at monthly intervals and over time a picture of population changes is developed. Sampling protocols must provide sufficient statistical power to detect population changes otherwise results obtained are meaningless! Fortunately some excellent software for determining statistical power of monitoring programs is now available on the web.

Results obtained to date have been encouraging. Most commercially important reef fish studied have shown high site fidelity (high residency), relatively small home ranges and predictable, repeated patterns of daily movements and habitat use. These behavioural characteristics make such species well suited to protection in marine reserves. Further experiments are underway to determine how quickly reef fish increase in numbers after a reserve is established and how many fish a reserve will export to support adjacent fisheries.

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e-mail Carl Meyer at carlm@hawaii.edu