Benefits of Marine Reserves to Fishers through Spillover

 Murray Hosking

(a more extensive paper on this subject is found here)

Evidence that fish in marine reserves will ‘spillover’ to the benefit of fishers in adjacent waters, is available in scientific literature in both New Zealand and overseas. There are many papers that should adequately satisfy even the most ardent critic that well managed marine reserves satisfy their principal purpose, which is to protect natural habitats, ecosystems and biodiversity for scientific study. An important proviso is that there is adequate compliance and enforcement of the ‘no take’ principle.

Many sites attest to the fact that, given time, exploited fish species will increase in size and numbers and that there will be a cascade of effects through trophic levels as a result. The reserve at Leigh records significant changes in habitat as a result of 30 years plus of protection from harvest. The technical literature also records spillover of rock lobster so as to maintain adjacent catch levels. At Long Island (Kokomohua) Marine Reserve the very territorial blue cod show some limited movement beyond reserve boundaries to the benefit of local fishers.

Whether there are benefits, through the movement of target fish into surrounding waters, will depend on the species concerned and their mobility, as well as the size of the reserve. Studies at the no-fishing zone in estuaries and waters alongside the Kennedy Space Centre in the USA do show evidence of spillover from recovery of some tagged trophy fish species outside the ‘no-take’ zone, though not for fish species that remain close to their limited home range inside the reserve. The best evidence of spillover on these estuaries is the behaviour of recreational fishers who frequent the reserve margins. Is it a coincidence that several world record trophy fish were caught in proximity to the reserve in the late 1980s?

Evidence from elsewhere is more clear. There are more than 400 community-based no-take Marine Protected Areas in Philippine coastal waters. While some have taken time to show results due to poor siting and other environmental factors, all of the reserves are known to have resulted in increased fishery yields outside the reserve boundaries. Scallop beds adjacent to closed areas on the Georges Bank (off New England, USA) have shown dramatic recovery within a few years.

Notwithstanding those clear results, fisheries scientists are generally cautious about the promise of adjacent increases in yield. While reserves can generate increased fish numbers and larger fish, dispersal depends on the species. It certainly does no harm to have more eggs and larvae in the water from allowing large, fecund individual fish to survive and reproduce. The jury is still out whether there are any spillover benefits to commercial or recreational fishing outside the near vicinity of reserves. Apart from their prime role to protect marine biodiversity within their boundaries, the greatest benefit to ‘spill over’ from marine reserves may well be the capacity to reinstate lost ecosystem processes and to provide information that can be vital to fisheries management.

Forget science, though. The best evidence of local ‘spillover’ is surely the behaviour of fishers at Kapiti, Cathedral Cove, Long Island and even at Taputeranga and other marine reserves, who habitually fish the ‘margins’ with good results.