Environmental criteria for fish farms based on the macrobenthos

H. Yokoyama (Environmental Management Div.)


   A quantitative survey of the macrobenthos conducted in fish farms along the coast of Kumanonada showed that the macrofauna and sediment parameters based on the macrobenthos will be of practical use as criteria for assessing fish farm environments.


[Objective]
  In 1999, "the Law to Ensure Sustainable Aquaculture Production" was established to prevent self-deterioration of aquaculture grounds. The environmental criteria used in this Law should be revised to the more appropriate criteria on the basis of the scientific data. In order to examine the applicability of the adopted criteria to fish farms, and to specify the new criteria of aquaculture environment, surveys of the bottom environments and the macrobenthos were conducted in fish farms in Kumano-nada, central Japan.
[Results]
  One of criteria used in the new Law is based on the Omori-Takeoka theory in which the peak of benthic oxygen uptake (BOU) against the loaded organic matter is regarded as an indicator of the maximum phase in the process of biological remineralization. In the present study, the peak of BOU was not  found in the observed gradient of acid volatile sulfides (AVS-S) in the sediment accompanied with increasing loaded organic matter (Fig. 1). This finding may be explained by the possible variation of biological BOU in its immediate response to the change of dissolved oxygen in the overlying, near-sediment-surface water.
  A quantitative survey of the macrobenthos was conducted in 22 fish farms with the collaboration of the Owase Fisheries Laboratory, Fisheries Research Division, Mie Prefectural Science and Technology Promotion Center. The biomass in summer peaked in sediments containing 1.2 mg/g of total nitrogen, where aerobic mineralization of the loaded organic matter is supposed to occur (Fig. 2). Animals sere scarcely found in sediments with AVS-S > 1.7mg/g, suggesting this as a critical condition for the aquaculture environment (Fig. 3).
  An index "ED",  which shows the topographic situation of the sampling site, was devised. Six assemblages were recognized by cluster analysis. These assemblages were classified into three groups in the gradients of ED and fish production, i.e., a group with high density and high diversity (A-D), a group characterized by an impoverished fauna (E), and an azoic site group (F), which respectively indicate healthy conditions, cautionary conditions, and critical conditions (Fig. 4). Thus, the macrofauna and sediment parameters based on the macrobenthos proposed in the present study will be of practical use as criteria for assessing fish farm environments.
 
[Publications]
1) Yokoyama, H. (2000). Environmental quality criteria for aquaculture farms in Japanese coastal areas-a new policy and its potential problems. Bull. Natl. Res. Inst. Aquacult., 29:123-134.
2) Yokoyama, H., A. Nishimura and M. Inoue (2000). Macroinvertebrates as biological indicators to assess the influence of aquaculture on the coastal environment. European Aquaculture Society Special Publication No. 28 (Abstracts of contributions presented at the International Conference AQUA 2000), p.762.
3) Yokoyama, H., Sakami, T. (in press). Examination of the benthic oxygen uptake rate as an environmental criterion for fish farms in Gokasho Bay. Nippon Suisan Gakkaishi.

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