Lake Restoration with KOPEL
The oxbow lakes of the Lower Kinabatangan Floodplain make up a rare type of aquatic habitat and are critical breeding areas for many freshwater fish species. Many of these lakes are deemed exceedingly high conservation value due to their rarity and the ecological significance they provide.
Unfortunately, due to rapid sedimentation and the incursion of alien invasive species the Kinabatangan’s oxbow lakes and the aquatic diversity within them, are under severe threat. Lakes that have been completely covered by a mat of invasive water weeds can lose up to 95% of their aquatic diversity, this includes the knock-on impacts to many endangered or vulnerable species such as aquatic dependent bird and mammal species.
The Tungog Lake is one such example. This lake is a special type of Oxbow Lake because it is not part of any broader catchment – hence there is no tributaries running into or out of the Tungog Lake. This means, for the most part, the Tungog Lake is a totally closed aquatic ecosystem, and only connects to the Kinabatangan River in exceedingly highwater events, such as during the annual wet season. This means the Tungog Lake remains mostly clear of sediment from the main river and is thus very deep and surprisingly clear. Estimates suggest the lake is more than 1,000 years old.
Prior to the year 2001, the Tungog Lake was revered by local people and is a site of much mystery and legend. There are numerous historical stories associated with the Tungog Lake. Previously, the site was frequented by local fishermen for specific high value fish species such as the Marbled Goby (Oxyeleotris marmorata) and the famous sport fish Pelian (Tor Tambroides) among many other fish species. Fishing in the Tungog Lake has always been exceedingly small scale due to a combination of factors; namely the large crocodiles that frequent the lake, and the difficulty accessing this location by boat.
A major threat to the Tungog Lake began with the floods of 2001, when the flood borne water weed Salvinia molesta was introduced into the lake. Salvinia is an alien invasive species that can double its size rapidly within days and has no natural predators in the local ecosystem. This means it grows completely unchecked. After its introduction, the Salvinia rapidly spread across the Tungog Lake, covering it completely in a thick mat of weed by the end of 2003. Sadly, before this time, no one paid much attention to these weeds. These weeds were previously only found in drains and in rare cases local fishponds. After realising the disaster unfolding on the Tungog Lake, KOPEL began the gruelling work of removing this devastating weed species in the year 2004.
Salvinia and other aquatic water weeds are one of the foremost threats to the aquatic ecosystems in the Kinabatangan. The impacts of these weeds include the physical blockage of sunlight for the aquatic species, and a spiralling decline of dissolved oxygen that provides life to all aquatic organisms. Salvinia coverage can bring about a decline in aquatic diversity, and the acceleration of infilling. This impacts to the wider food web, depleting fish stocks, displacing birds and mammals, and likewise displacing local fishermen to ever shrinking locations, and hence exacerbates overfishing.
KOPEL’s laboured for three long years, removing the Salvinia weed from the Tungog Lake. Initially KOPEL scooped the weed manually, then later a locally designed method using small boats was used. KOPEL’s ecotourism and volunteers played a major part in this process, and KOPEL eventually cleared the Tungog Lake of Salvinia by early 2007. Subsequently KOPEL maintained the Salvinia regrowth with proceeds from ecotourism activities until 2013 when tourism and much of KOPEL’s activities were shut down for six months due to the Tanduo Crisis. During this shut down period, and in the absence of monthly removal of Salvinia regrowth, the Salvinia weed made a dramatic comeback, regrowing over one third of the lake surface.
Due to travel bans to the east coast of Sabah, and lack of revenue streams, KOPEL struggled to make any headway with the Salvinia weed on the Tungog Lake. The ongoing struggle inspired a rethink of the costly and labour-intensive approaches. New approaches were sought to reduce the carbon footprint of this work and support the transition to a more ecologically sustainable approach, for example, utilising biological control. The long-term goal was shifted to reduce the need for manual labour and costly boats, and hence free-up these resources for other critical conservation work. Subsequently and after a further four long years of work with Sabah State Government Agencies, the biological control Cytobagous salviniae was finally released at Tungog Lake in October 2018.
In parallel, and through the support of volunteers and ecotourists, KOPEL continues to employ the manual and semi mechanical methods to keep the weeds from completely covering the lake. Now more than two years after release of the biological control there has been some noticeable impact on the Salvinia. In parallel, the KOPEL team has also removed more than 50% of the weed through physical labour. Unfortunately, there is still a long way to go, and KOPEL welcomes all forms of support, most notably those ecotourists willing to volunteer and help this initiative achieve its goal to rid the lake of the invasive water weed Salvinia.
To get involved in KOPEL’s Salvinia removal and lake restoration efforts read more here
For more technical reports read more here
For more information on getting involved in KOPEL’s lake restoration initiative, volunteering or setting up a school or university program with KOPEL please feel free to contact KOPEL Office at +6089551070 or visit our Contact page.