Spillover - what does it Mean?
Spillover of fish from Marine Reserves to benefit fishers – Murray Hosking
Evidence that fish in marine reserves will “spillover” to the benefit of fishers in adjacent
waters is reported in scientific literature in both New Zealand and overseas. There are many
papers that should adequately convince 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. 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, New Zealand,
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, NZ, even the very territorial blue
cod show some 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.
The empirical evidence to establish spillover is now compelling. Researchers (1) established
good evidence of spillover near Cape Canaveral in the 1990’s, and some of the early
research results were generated at the reserve at Leigh around the same time in studying
both snapper and rock lobster. There are research papers which indicate that spillover is a
factor of size of reserve, extent of exploitation before reservation, and the availability of
nursery stock to recover previous levels of exploited species. These will affect the extent
and rapidity of recovery and of spillover.
It is apparent that there is acceptance at official levels in Europe (2) and the Mediterranean,
Australia (3) and the United States, backed by research. Research and case studies have
been recorded from sites in Mexico, the Philippines, West Hawaii, Columbretes
(Mediterranean), the Californian Channel Islands, the Red Sea, St Lucia, and several
Australian Marine Parks, as well as the Cape Canaveral and New Zealand sites noted above.
Studies have covered a wide range of targeted food, aquarium and game fish, rock lobster,
molluscs and crabs. These studies clearly accept the fact of spillover although recognise that
its extent and value will vary in different circumstances.
1
Johnson,DR; Funicelli,NA; Bohnsack,JA: ‘Effectiveness of an Existing No-Take Fish Sanctuary within the
Kennedy Space Center, Florida’, North American Journal of Fisheries Management 19, 1999.
2
Fenberg P.B.*, Caselle J., Claudet J., Clemence M., Gaines S., García-Charton J.A., Gonçalves E., GrorudColvert K., Guidetti P., Jenkins S., Jones P.J.S., Lester S., McAllen R., Moland E., Planes S. and Sørensen T.K.
(2012) The science of European marine reserves: status, efficacy and needs. Marine Policy 36(5), 1012-1021.
doi:10.1016/j.marpol.2012.02.021
3
‘The economics of marine protected areas’ Application of principles to Australia’s South West Marine Region.
November 2009 Allen Consulting Group (Report to the Conservation Council of Western Australia)
Spillover is generated by the build-up over time in the ‘no-take’ marine reserve of size of
individuals, numbers and overall biomass of exploited species, and in some cases species
diversity. Juvenile or adult fish or invertebrates will cross reserve boundaries and be
available to be caught outside reserves. The extent of movement distance will increase
depending on the extent of fishing across the margins – the well-known phenomenon of
‘fishing the line’ experienced adjacent to New Zealand marine reserves such as Leigh,
Cathedral Cove, Kapiti and Kokomohua. More problematic to prove is the extent and value
to fisheries of eggs, larvae and small juveniles which may be carried by currents out of
reserves to the potential benefit of wider marine areas.
There is evidence that ecological benefits of some (but not all) reserves have spilled over to
neighbouring harvested areas through increased catch per unit effort and increased
population size, as well as harvests of larger and often more highly valued fish (4). Studies
(5) have demonstrated increases in the catch per unit effort of target species in adjacent
non-reserve areas after the creation of a protected area.
A 2004 study (6) demonstrated that the hypothesised “spillover effect” and “recruitment
effect” can be observed at the edges of marine reserves. The recruitment effect—i.e. the
dispersal of larvae and juveniles from marine reserves to surrounding fisheries—was
confirmed in later studies, one of which was conducted on a reserve network in Northwest
Mexico. The surveys (7) indicated that the protection from marine reserves resulted in a
three-fold increase in the density of the larvae of commercially valued molluscs at the
reserve edges.
Some good case studies are recorded in a report (8) for the New South Wales Marine Parks
Authority:
‘Spillover’ refers to the movement of adults and juveniles from no-take zones into
neighbouring fished areas, and the extent to which this occurs is dependent on the size of
the zones and habitat configuration within them, and the abundance and mobility of the
species. Such movements can lead to increased abundance adjacent to no-take zones, and
often fishers change their attitude over time regarding marine parks as they experience
improved fishing in these areas. For example:
• In the Red Sea mean catch per unit effort of targeted fish species increased by about twothirds within fished areas adjacent to no-take zones after 5 years of protection.
• Within 5 years of the creation of a network of sanctuary zones around the Caribbean
island of St. Lucia, catch by fishers increased between 46 and 90%, depending on the gear
they used.
4
Gell, Fiona.R. & Callum M. Roberts. 2003. Benefits beyond boundaries: the fishery effects of marine reserves.
Trends in Ecology and Evolution 18(9):448–455.
5
Beukers-Stewart B, et al 2005, ‘Benefits of closed area protection for a population of scallops’, Marine
Ecology Progress Series, Vol. 298, pp.189–204
6
Russ, G. R., Alcala, A. C., Maypa, A. P., Calumpong, H. P., & White, A. T. (2004). Marine reserve benefits local
fisheries. Ecological Applications,14(2),597–606.
7
Cudney-Bueno, R., Lavin, M. L., Marinone, S. G., Raimondi, P. T., & Shaw, W. W. (2009). Rapid effects of
marine reserves via larval dispersal.PLoSONE,4(1).
8
Marine Parks Authority 2008, ‘A review of benefits of marine protected areas and related zoning
considerations.’ Marine Parks Authority Secretariat Web: www.mpa.nsw.gov.au
• Since 1985 all new Florida trophy records for black and red drum (Sciaenops ocellatus and
Pogonias cromis) have been won for fish caught adjacent to a sanctuary zone near Cape
Canaveral.
• Adjacent to a sanctuary zone around part of Apo Island (Philippines) the biomass of
surgeonfish (Naso vlamingii) over time increased by a factor of 40 outside but close to the
reserve boundaries (200 to 250 m), but not at greater distances (250 to 500 m). Hook- andline catch per unit effort for surgeonfish was 45 times higher within 200 m of the reserve
boundary than for all other fishing grounds combined.
• In the Moreton Bay Marine Park, mud crabs (Scylla serrata) were twice as common in
sanctuary zones than in fished areas, and were also larger. Tagging work showed that some
of these crabs “spilled over” into fished areas.
• Similar movements from sanctuary zones into fished areas were found for mud crabs in
the Solitary Islands Marine Park, with fishers often targeting zone boundaries’
Closer to home, at Taputeranga Marine Reserve on the Wellington South Coast, research
has been carried out on blue cod. This species is known to be relatively sedentary,
establishing and strongly defending territories on the seabed. They are voracious feeders
often being the first species caught when baited hooks are lowered to the bottom in any
new fishing spot. This perhaps goes a long way to explain why they are so easily fished out
by recreational anglers from certain localities!
These results are very relevant to marine reserves with blue cod, showing positive results
not only for an increase in size of individual fish and in numbers only 5 years after the
establishment of the marine reserve, but also in movement of relatively territorial fish
outside of the reserve.
While it can be understood that commercial fishers may want more proof of real value to
them from spillover there can be confidence that a marine reserve will have a positive
effect, not only in providing a benchmark of recovered habitat to assist fisheries
management, but also as a source of legally catchable fish stock over time for the benefit of
recreational and customary fishers.
Crayfish may be inclined to wander out of marine
reserves. Photo D. Stent
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. 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.
Blue cod can be more territorial within a
home range Photo D. Stent
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, who habitually fish “the
margins” outside reserves, with good results.