Can Marine reserves have beneficial effects on surrounding, unprotected fished areas?

As consumers, we are very dependent on the ocean and the rich resources it has to offer. But these resources are under threat through over fishing and the affects this has on habitats. Whole species are known to be decreasing in population at a dramatic rate. This could lead to extinction of species, disruption to the food chain and destruction to habitats. Over fishing not only affects the environment, but can cause many social and economic problems, such as a lack of a main food source and loss of livelihood. Marine reserves provide restricted fishing or no take rules, to certain areas of the ocean. This helps prevent or slow the depletion of various organisms and populations. It also allows habitats under threat, regenerate, helping populations further. A controversial theory surrounding this subject, suggests that Marine reserves not only benefits the protected area, but surrounding unprotected, fished areas.

Many of our seas are feeling the human effect of over fishing, with both commercial and non-commercial fishing leading to a decrease in fish populations through out our oceans. Over fishing not only affects the species in question, but has a knock on effect through out the ecosystem, by disrupting the food chain. Many of the techniques used in commercial fishing, such as trawling, damages marine habitats and leads to discarding of fish that are caught as a by-product. The UN Food and Agriculture Organization found that around 80% of fisheries in the world are depleted or fully to over exploited. Depleted stocks are resulting in the loss of $50 Billion to fishing vessels. The UN Food and Agriculture Organization also found that there would be no change in catch yield if half of the worlds fishing vessels were to be taken out of use.  An example of severe over fishing was seen in Newfoundland in 1992, where Atlantic cod populations plummeted and lead to not only the collapse of an ecosystem, but of thousands of people’s livelihoods. To this day, cod populations have not recovered to their original abundance. Another example of this was observed in a study in the North Sea, where it was found Atlantic cod populations were severely depleted or on the verge of extinction (1).

However measures are being taken to help reverse the effects or at least discourage over fishing. Marine Reserves are present throughout the world, with legal protection, where fishing is banned and areas are protected from development. These actions have proved successful in many reserves at increasing density, biomass, size and diversity of organisms. One study carried out in California found all four of these biological measures were significantly higher inside Marine reserves than outside (2). Marine reserves also help increase larval biomass, as organisms are able to spawn in a much safer habitat, free from destruction, from fishing methods such as trawling.

The theory that Marine reserves can benefit fisheries and unprotected areas has been seen to be controversial, yet there are many studies that it is in fact the case.

Thus possibly providing solutions to growing problem of over fishing and depletion. The theory suggests that the high abundance of fish and larvae produced within protected areas benefit surrounding areas and fisheries through over spilling into the areas. A study carried out off the coast of Apo Island, Philippines, observed biomass of Carangidae (jacks) and Acanthuridae (surgeonfish). It was found biomass of these two species tripled inside no-take Marine reserves and increased significantly in areas outside of the reserve. Estimates predicted that population of both jacks and surgeonfish, inside and outside the reserve, had increased dramatically after the set up of the reserve in 1981 (3).  This increase can be hugely beneficial to local fisheries and fisherman, as both species were important providers of food and income.

A second study supporting this theory was carried out in St. Lucia and Florida. In St. Lucia, were several reserves were established. After the set up of these reserves, the number of fish caught, outside the reserves, was observed. The results showed there was a significant increase in fish caught, ranging from 46 to 90%. The equipment used to catch the fish determined these figures. This is a huge increase and provides strong evidence to support the theory that Marine reserve can benefit fisheries (4). The study not only suggests that reserves can increase yield, but also size of fish. The second half of the study took place in Florida, showing the Merritt Island Wildlife Refuge contributed to the introduction of record sized fish in near by fisheries (4).

Marine reserves have not only been beneficial to fish communities. A programme was set up in 1997, in Ucunivanua village, Fiji, to help the depletion of the Anadara clam. Locals had seen the decline in the clam, which was their main fisheries species and approached the University of the South Pacific. Through protection programmes involving banning mangrove cutting, banning on fishing of certain fish species and obtaining incomes from other areas besides fishing, the Anadara species thrived. After 3 years of protection, the Anadara clam population had increased by thirteen times inside the reserve and by five times outside of the reserve (5). A second census after a period of 5 years, clam population inside the reserve had increased further, by nineteen times and by seven times outside the reserves. Locals were also observing that the time to catch a single clam had halved (5). It was also observed that the size of clams inside the reserve had increased and species known to have left the area, such as stingrays were returning. Not only did this benefit the Anadara clam, but educated locals in finding sustainable ways to fish in their area and helped bring back a major part of their income.

Protected areas allow organism populations to reproduce with out disruption from fishing or damage to the organisms’ habitat, meaning large quantities of larvae can be produced. The movement of larvae, from Marine reserves to other areas is known as larval export, this spill over can be beneficial to these surrounding areas, as it provides an import of larvae, that could counter balance or slow down the depletion of populations of various organisms. One study found that the increase in recruitment of larval export, from Marine reserves to surrounding areas was greater than the decrease of recruitment from over fishing (6). In this case, suggesting that marine reserves could be used as important tool to solving the problems caused by over fishing.

However, it could be viewed that reserves are only fuelling the problem of over fishing, by producing and encouraging larger populations and large larval export, that could later be fished outside of the reserves. Thus over fishing could go on at the same rate, as much of the fish caught will be replaced through overspill and larval export. This can be seen in cases, where productivity has increased both inside and outside reserves, but to a much higher degree inside the reserve as fish are being caught on a large scale outside the reserve.

By viewing evidence from various studies, it seems clear that marine reserves have huge benefits to surrounding areas and fisheries. With studies showing increases in fish population, size, diversity and biomass, as a result of reserves, both inside and outside reserves. Yet with marine organisms being in such high demand, it may not be enough to reverse the damage of over fishing. But it cannot be doubted that marine reserves have a positive effect, providing a protected habitat, encouraging growth and increasing population sizes, both inside and outside protected areas.


(1) ScienceDirect – Fisheries Research : Modelling recruitment and abundance of Atlantic cod, Gadus morhua, in the eastern Skagerrak–Kattegat (North Sea): evidence of severe depletion due to a prolonged period of high fishing pressure. [Accessed November 14, 2010].

(2) The impact of marine reserves: Do reserves work and does reserve size matter? Available at: [Accessed November 14, 2010].

(3) ESA Online Journals – MARINE RESERVE BENEFITS LOCAL FISHERIES. Available at: [Accessed November 14, 2010].

(4) Effects of Marine Reserves on Adjacent Fisheries — Roberts et al. 294 (5548): 1920 — Science. Available at: [Accessed November 14, 2010].

(5) ScienceDirect – Trends in Ecology & Evolution : Benefits beyond boundaries: the fishery effects of marine reserves. [Accessed November 14, 2010].

(6) Detecting larval export from marine reserves — PNAS. Available at: [Accessed November 14, 2010].

13 years ago

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