Title
Effects of Alteration to Catchments and Streams on Freshwater Fish Communities of Vanua Levu, Fiji
Author(s)
Jupiter, S.; Jenkins, A.; Koto, K.; Ah Tong, J.; Bwebe, T.; Cakacaka, A.; Dulunaqio, S.; Fox, M.; Kuritani, L.; Mario, S.; Naisilisili, N.; Nand, Y.; Tukana, A.; Weeks, R.; Yakub, N.
Published
2012
Abstract
In October and November 2010, staff from the Wildlife Conservation Society, Wetlands International‐Oceania, Department of Fisheries and Department of Forestry conducted riparian and stream surveys at 32 small stream sites in Wainunu, Kubulau, Macuata and Sasa districts of Bua and Macuata provinces on the island of Vanua Levu. The sites were chosen in areas of greater or less than 50% sub‐catchment forest cover and with intact or degraded riparian zones to assess the impact of catchment and stream alteration on in‐stream freshwater fish communities. We set out to address the question: “How does the size and composition of the riparian forest buffer strip in varying overall catchment cover conditions influence fish abundance, diversity, and water quality in the adjacent river?”
We found that the tree community size structure of the riparian zone may only have marginal influence on in‐stream fish abundance. The factors that were most strongly related to fish presence/absence and abundance were: sub‐catchment forest cover; conductivity; and the presence of downstream overhanging culverts.
Our prior research indicated that fish community composition is substantially affected when catchment forest cover falls below 50%. These findings were confirmed in our present study. This is likely due to increased sediment erosion from the adjacent lands into streambeds, which can impact feeding, breeding and resting habitat of Fiji’s native fish. Our present survey found elevated conductivity at the most degraded sites, which can be related to concentrations of suspended sediment and dissolved organic material.
Secondly, we found reduced species richness and fish abundance at sites upstream from overhanging culverts, even in locations with high cover of primary forest and intact riparian zones. Overhanging culverts block upstream migrations of fish, and a large proportion of Fiji’s freshwater fish fauna make obligate migrations from the upper or mid‐reach of streams to the sea at some phase in their life cycles. Many species that were absent from the fish assemblages upstream from overhanging culverts are those with importance for subsistence or livelihoods for inland communities. Thus, there is a pressing need to think about improved culvert design to allow for safe fish passage.
From our research, we have developed two important rule of thumb recommendations to guide local communities to manage their freshwater systems. First, communities should aspire to protect waterways in sub‐catchments with greater than 50% forest cover. It is much easier and more cost‐effective to protect existing intact landscapes than to attempt to restore them. Secondly, communities should preferentially prioritize freshwater streams for protection that are clear of downstream overhanging culverts. We have been using these guidelines to assist communities throughout Vanua Levu to designate or expand terrestrial and freshwater protected areas.
Full Citation
Jupiter S, Jenkins A, Koto K, Ah Tong J, Bwebe T, Cakacaka A, Dulunaqio S, Fox M, Kuritani L, Mario S, Naisilisili N, Nand Y, Tukana A, Weeks R, Yakub N (2012). Effects of Alteration to Catchment and Streams on Freshwater Fish Communities of Vanua Levu, Fiji. Suva, Fiji: Wildlife Conservation Society, Fiji, 1-17.
Access Full Text
Back
DMX4082300000