Case Study: Ecological corridors in ecological networks
This case study is part of the IUCN Guidelines for conserving connectivity through ecological networks and corridors illustrating initiatives around the world that are working toward maintaining, enhancing, and restoring ecological connectivity. See all case studies here.
Grassroots reserves have strong benefit for river ecosystems in the Salween River Basin
By Aaron A. Koning, Cornell University
Key lesson
Recognition and enforcement of river reserves by the local communities, which benefit local fisheries and enhance the health of the river system, is a significant first step to increasing in-stream connectivity in the Mae Ngao River in Thailand.
Context and challenge
In many low-income countries, people depend highly on inland fisheries for daily nutrition, creating strong incentives to access the resource regardless of regulations. Even in protected areas that contain human populations, hunting bans rarely extend in practice to fish. While national fishery regulations and guidelines exist in Thailand, in remote areas such as the Mae Ngao River, enforcement is difficult and rare. Due to their linear nature and the dependence of many sectors upon rivers and their waters, it is a challenge to create ecological corridors covering entire river basins or even individual rivers.
Approach
Throughout Southeast Asia, in response to perceived declines in fish populations, concerns for continued resource security, and encroachment from outsiders using illegal fishing gear (e.g. electric shocking), small no-take reserves on rivers have been created by local communities, established by non-governmental organisations or imposed by national governments. These small reserves are effectively the only management action for these intensive-harvest fisheries. In tributaries of the Salween River in north-western Thailand, ecological networks of small riverine reserves continue to grow, particularly among fishery-dependent communities where overharvest is common.
Figure 1. Ecological network of no-take reserves on the rivers in the Mae Ngao River Basin in north-western Thailand © Aaron A. Koning
Examples of ecological corridors
One such ecological network is located in the Mae Ngao River Basin of north-western Thailand, which encompasses 1,000 km2 and over 8,000 people among more than 70 villages (Figure 1). Over 25 years ago, the first community- created reserve was established following a meeting with a local NGO, which suggested creating small areas closed to fishing as a conservation measure. Initially, only one community took this action, but the practice has slowly spread since to include more than 50 others, which largely act independently and are unsupported by government or other outside entities. Communities individually determine reserve locations, sizes and penalties for non-compliance, which range from the equivalent of 15 USD to over 300 USD. Inside reserves, all harvest activities are prohibited, including harvest of snails and other aquatic invertebrates, which otherwise are commonly eaten, particularly during the extended dry season (November–May). Outside of reserves, harvest effort is high, using a variety of methods (e.g. gill nets, lines, traps, hand spears). Fishing effort often extends from the borders of the reserve for hundreds of meters both upstream and downstream, creating a gauntlet of nets and hooks for fish moving outside of protected areas. Several neighbouring communities have added additional regulations outside reserves, notably banning the use of diving masks in collecting snails and spearfishing. Spearfishing, particularly in the dry season when water temperatures are warm, the water is clear, and local schools are on break, is thought to have a large impact on populations of fish of all sizes.
Figure 2. In no-take reserves, large schools of fish can be seen from the riverbank. © Aaron A. Koning
Results
There is no broader strategic planning among communities regarding the creation of reserves. In fact, there is a general lack of recognition even among community members of the number of reserves in existence throughout the Mae Ngao River Basin. Nevertheless, there are now 52 reserves that, basin-wide, cover 2% of all perennially flowing water, and form a network of protected areas within the larger river network. This network has been entirely created and enforced by individual communities.
However, intense fishing effort forms a large barrier to connectivity between and among reserves. Viewed at more local scales, though, individual reserves are typically long enough to connect habitats within the river network, including pools that are critical refugia for many species during dry season. In the rainy season, when river levels increase by up to 5 m from dry-season lows, fishing effort goes down and systemwide connectivity goes up, giving fish the opportunity to move for breeding.
Because of the disparity in harvest effort between reserves and other areas, the effects of the conservation action can be seen even from the river bank, where large schools of fish become points of interest for tourists and travellers in the area (Figure 2).
A comparison of 23 of these small reserves with adjacent fished areas showed gains in fish species richness, density and biomass commensurate with reported gains from marine reserves (Koning, 2018; 2019). Specifically, richness increased in reserves relative to fished areas by 27% and density by 124%, and biomass was 23 times higher on average. Although benefits were often observed only three to five years after a reserve was established, gains were sustained through time.
Community members regularly harvest large fish outside of reserves and credit fish movement out of reserves for such catches. It remains unclear whether reserves are sufficiently large to maintain populations over the long term and whether there is regular movement among reserves that would transfer critical genetic diversity among potentially isolated sub-populations. Given the seasonal fluctuations in the river, though, it seems likely that fish movement occurs during the rainy season.
The extent to which these small reserves are able to benefit local fish populations is all the more remarkable given that communities have largely acted independently without a broader coordination of effort. Next steps for this reserve network would be to work with communities, informed by the surveys conducted previously and the body of reserve design theory that has been developed for marine systems, to attempt to optimise reserves individually and collectively for maximum conservation and fishery benefits.