Sawdust ingestion by the tropical shad (Tenualosa macrura, Teleostei : Clupeidae): implications for conservation and fisheries

Tenualosa macrura is the main target species of a gillnet fishery in the co astal waters of the Bengkalis region, Indonesia, where it has a strong cult ural significance. However, in recent decades, the fishery has declined mar kedly. The stomach contents of 1255 fish were dominated by sawdust (by weig ht), and only 36% of the diet comprised planktonic Crustacea. Carbon isotop e analyses showed that the delta C-13 signature of this sawdust matched the delta C-13 signature of old-growth hardwood timber. Plankton samples from the waters where these fish were caught had high concentrations of sawdust, and 25 sawmills were mapped along the banks of waterways that drained into these coastal waters. Sawdust has no, or very little nutritional value for T. macrura or other species of planktivorous fish, and can only have a neg ative impact on their health and survival. However, the impact would depend on how much of its life cycle is spent in these coastal waters. We calcula te that T. macrura spends between 2.2 and 33% of its adult life in these sa wdust-rich waters. Although overfishing may be the main cause of the declin e in this fishery, we propose that sawdust pollution may also contribute si gnificantly, threatening the survival of this and possibly other planktivor ous fishes in this region. (C) 2000 Elsevier Science Ltd. All rights reserv ed.