Freshwater Fish Assemblages Vary Across Sites Within an Oil Palm Plantation in East Kalimantan, Indonesia

Abstrak

Graphical Abstract Highlight Research 1. Freshwater habitats within the oil palm plantation landscape retained 51 fish taxa from 16 families and six orders. 2. Fish assemblage structure varied markedly among the nine sampling sites. 3. Water depth was the environmental variable most consistently associated with fish assemblage attributes. 4. Local habitat heterogeneity should be maintained to support freshwater fish diversity in oil palm plantation landscapes. Abstract Freshwater fish assemblages within operational oil palm plantations remain poorly characterized, particularly their variation across environmentally heterogeneous aquatic habitats. This study assessed fish diversity, assemblage composition, and local environmental conditions at nine freshwater sites (eight streams and one swamp) within a single operational plantation landscape in East Kalimantan, Indonesia. Using an observational field survey, fish were sampled once per site in May 2022 with habitat-dependent fishing gears. Diversity indices, individual-based rarefaction, ordination, and exploratory correlations were used to describe site-level patterns. The survey recorded 932 individuals representing 51 taxa, 16 families, and six orders, including two Near Threatened and eight Bornean-restricted taxa. Richness ranged from six to 25 taxa, with the highest values at MES01 (25), REA11 (24), and REA7 (20). REA7 also had the highest Shannon diversity (2.485), while rarefaction indicated that high richness at these sites was not attributable solely to catch size. Water depth was positively correlated with observed abundance (Spearman’s ρ = 0.817, p = 0.007) and negatively correlated with evenness (ρ = −0.717, p = 0.030). Non-metric multidimensional scaling revealed spatial variation in assemblage composition (stress = 0.093), whereas the constrained environmental model was not statistically significant (p = 0.115). These results document substantially heterogeneous freshwater fish assemblages within the sampled plantation, with depth-related associations remaining exploratory. Unequal gear deployment, unadjusted multiple testing, and single-occasion sampling limit interpretation of environmental drivers and wider generalization. Repeated seasonal surveys with standardized sampling effort are needed to establish whether these site-specific patterns persist and inform freshwater habitat conservation.

Kata kunci

• Water depth
• Fish assemblages
• Oil palm plantation
• Habitat heterogeneity
• Species richness