Similajau National Park: Protected Landscape and Geographic Context in Bintulu Division

Similajau National Park is particularly known for its exceptional hornbill diversity, with eight species recorded including the rhinoceros hornbill and black hornbill. The park also hosts seasonal green sea turtle nesting at Turtle Beach from March to September, and dolphin populations are regularly observed in the coastal waters between March and September. The park contains a higher concentration of tongkat ali trees than any other national park in Sarawak, making it botanically distinctive. Its combination of accessible coastal rainforest, wildlife viewing opportunities, and relatively compact trail system makes it a notable destination within Sarawak's protected area network.

Similajau National Park was first established in 1976 as a protected coastal area in Bintulu Division. The initial park boundary encompassed approximately 70.64 square kilometers, extending from the Sungai Likau area in the south to the Sungai Similajau in the north along a 30-kilometer coastal stretch. On February 17, 2000, a significant expansion added 19.32 square kilometers to the park, increasing its total area to 89.96 square kilometers. This expansion reflected the growing recognition of the park's ecological value and the need to protect additional coastal and forest habitat. The park operates under the management authority of Sarawak Forestry and maintains an official website for visitor information. The park has historically been referred to as both Similajau and Samalaju National Park, with the latter name appearing in some official and published sources.

Similajau National Park occupies a distinctive coastal position along the South China Sea, where the landscape transitions from sandy beaches and rocky shores through mangrove zones into lowland rainforest. The park's terrain is relatively flat near the coast but rises gently into rolling hills inland, supporting the mixed dipterocarp and kerangas forest types. Rocky outcrops such as Batu Anchau and Batu Mandi punctuate the landscape, with the latter visible only during low tide approximately four kilometers offshore. The park contains several watercourse features including the Likau River, which supports crocodilian populations, and the Sebubong River with its natural swimming pool accessible by boat. The coastline features distinct beach areas including Golden Beach and Turtle Beach, where seasonal turtle nesting occurs. The Selunsur Rapids provide another notable water feature, most visible after heavy rainfall.

The vegetation of Similajau National Park comprises three principal forest types that reflect the park's ecological diversity. Beach vegetation dominates the immediate coastal fringe, while kerangas heath forests characterize the more nutrient-poor soils of the park's interior. Mixed dipterocarp forest, typical of lowland Borneo, occupies the remaining areas and contains the park's tallest trees. The park is botanically notable for its population of tongkat ali, a slender tree reaching heights of up to 15 meters that produces clusters of red fruits maturing to black. This species occurs more abundantly in Similajau than in any other Sarawak national park. The bintangor tree is another significant species found in both hill and swamp forest areas within the park. The park supports mangrove forest along certain sections, particularly along the education trail where a 450-meter plank walk provides visitor access through this specialized coastal ecosystem.

Similajau National Park supports a diverse fauna population across its terrestrial and marine environments. Twenty-four mammal species have been recorded within the park, including several primate species such as gibbons, Raffles' banded langurs, and long-tailed macaques. The bird population is particularly significant, with 185 species identified including eight hornbill species representing all major hornbill types found in Sarawak, including the prominent rhinoceros hornbill and black hornbill. Migratory water birds including Storm's stork pass through the park seasonally. Marine wildlife is abundant in the adjacent waters, with five dolphin species regularly observed: Irrawaddy dolphin, bottlenose dolphin, Indo-Pacific humpback dolphin, finless porpoise, and pantropical spotted dolphin. These dolphins can be seen from the park shore in groups of four or more during the early morning from March through September. Green sea turtles come ashore to nest at Turtle Beach during the same March to September period. The Likau River is home to both false gharial and saltwater crocodile species. The horseshoe crab appears along the shores during the breeding season from early May to October, often in pairs, with Sagor catfishes feeding on their eggs.

Similajau National Park functions as an important protected area within Sarawak's coastal zone, preserving lowland forest ecosystems that have faced significant conversion pressure across Malaysian Borneo. The park's designation as IUCN Category II reflects its primary purpose of protecting natural ecosystems while allowing for compatible recreational use. The protection of the coastal strip, including beach, mangrove, and forest habitats, ensures continuity of habitat for species that depend on both terrestrial and marine environments. The dolphin populations represent a particular conservation concern, as these marine mammals require healthy ocean conditions and are sensitive to coastal development and maritime traffic. The seasonal turtle nesting beaches receive protection during the breeding season, helping to maintain nesting success for green sea turtles. The presence of eight hornbill species indicates the park provides suitable foraging and nesting habitat for these ecologically important birds, which serve as seed dispersers in tropical forests.

Similajau National Park exists within the broader context of Sarawak's coastal communities and indigenous land-use traditions. The park area falls within the Bintulu Division, a region with a mix of Malay coastal communities and indigenous Bornean peoples. The river systems flowing through the park, including Sungai Likau and Sungai Similajau, have historically supported local fishing and transportation activities. The park's name derives from the Similajau River, which forms its northern boundary. While the park itself is managed as a protected area under state forestry authority, surrounding lands may continue to be used for traditional activities by local communities. The park provides educational opportunities through its nature trails, with the education trail specifically designed to teach visitors about local tree species, supporting environmental awareness and cultural understanding of the region's natural heritage.

Similajau National Park offers several standout features that distinguish it within Sarawak's protected area network. The Golden Beach provides a scenic coastal destination accessible by hiking or boat along the 9.8-kilometer main trail. Turtle Beach I and II host seasonal green sea turtle nesting from March to September, offering wildlife observation opportunities during this period. The dolphin populations are reliably observable from the shore during the first half of the year, with groups regularly seen from the park in early morning hours. The eight hornbill species present make the park exceptional for birdwatching enthusiasts. The Batu Anchau black rock formation at the end of a 2.1-kilometer trail provides a distinctive geological landmark. The Sebubong Pool offers a natural swimming area in the river, accessible only by boat. The variety of trail options, ranging from the mangrove education trail to longer hikes to the beach and rock formations, provides diverse visitor experiences.

The optimal time to visit Similajau National Park depends on the experiences sought. For dolphin watching, the period from March to September offers the best odds of observing these marine mammals, with early morning visits providing the highest likelihood of sightings. Green sea turtle nesting at Turtle Beach occurs during the same March to September window, making this the ideal period for turtle-related wildlife observation. The dry season from early May to October brings horseshoe crabs to the shore for breeding, creating a unique opportunity to observe this ancient species. The monsoon season from November to March brings heavier rainfall to the region, which can affect trail conditions and accessibility. However, the Selunsur Rapids are most impressive after rainfall, so those interested in this feature may prefer the wetter months. Overall, the March to September period represents the most wildlife-rich season for the park.