126
C. F. HICKLING
New estuarine environments can be the result of movements and
changes in the level of the land. Estuaries may be drowned river
valleys in which subsequent silt deposition proceeds apace. Again, the
land may slowly tilt and so become submerged. Taiwan, for example,
is tilting to the east-ward so that the flat land on the west coast is
slowly rising (Lin, 1968). Over the centuries, the present salt flats on
the west coast, on which there are important brackish-water fish farming industries, will rise above sea level to the point where they will
become free of salt and fit for agricultural use, while new accretions of
land to seaward will be reclaimed for fish farming.
I n the northern Adriatic, vast engineering works were undertaken
by the Romans, and, later, by the Venetian Republic, to prevent the
silting up of the lagoon which protected the city from her foes and
carried her sea-borne commerce. These works also resulted in marsh
and lagoon formations which are now the sites for a large fish farming
industry (Fig. 11, p. 183).
3. Tidal conditions
Some movement of sea water, due to changes of level, is important
in brackish-water fish farms. On non-tidal seas such as the Black Sea,
there are seasonal changes of level due to evaporation, and both
seasonal and longer term changes of level due t o the wind. These
changes may exceed one metre in the Black Sea (Ilin, 1954), and be
sufficient to cause currents to flow into and out of the limans through
their natural or artificial channels t o the sea. I n the northern Adriatic
there is a natural tide which may exceed 110 cm, though the tidal
amplitude becomes much less in the more southerly Adriatic. Such
small changes of level are not enough t o allow for a complete drainage
of the ponds or limans, and this must be a factor in their modest rate
of production per unit area.
Where the estuary is truly tidal and has more constant and regular
changes of water level, these can be used to fill fishponds ; to top them
up as may be required in order to replace water lost by evaporation
and seepage during the growth of the fish crop; to empty them as
needed in order to sort out, count, or harvest the crop ; and to expose
them to sun and wind and tillage.
The inflowing water carries with it nutrients, silt, and detritus,
which fertilize the pond and by frequent changes of water keeps the
salinity under control. Therefore, it is of the first importance that
estuarine fishponds should have an assured supply of sea water (Schuster, 1952; de Angelis, 1960), so care must be taken that they are
planned with due consideration of tidal data at the site. Schuster
C. F. HICKLING
New estuarine environments can be the result of movements and
changes in the level of the land. Estuaries may be drowned river
valleys in which subsequent silt deposition proceeds apace. Again, the
land may slowly tilt and so become submerged. Taiwan, for example,
is tilting to the east-ward so that the flat land on the west coast is
slowly rising (Lin, 1968). Over the centuries, the present salt flats on
the west coast, on which there are important brackish-water fish farming industries, will rise above sea level to the point where they will
become free of salt and fit for agricultural use, while new accretions of
land to seaward will be reclaimed for fish farming.
I n the northern Adriatic, vast engineering works were undertaken
by the Romans, and, later, by the Venetian Republic, to prevent the
silting up of the lagoon which protected the city from her foes and
carried her sea-borne commerce. These works also resulted in marsh
and lagoon formations which are now the sites for a large fish farming
industry (Fig. 11, p. 183).
3. Tidal conditions
Some movement of sea water, due to changes of level, is important
in brackish-water fish farms. On non-tidal seas such as the Black Sea,
there are seasonal changes of level due to evaporation, and both
seasonal and longer term changes of level due t o the wind. These
changes may exceed one metre in the Black Sea (Ilin, 1954), and be
sufficient to cause currents to flow into and out of the limans through
their natural or artificial channels t o the sea. I n the northern Adriatic
there is a natural tide which may exceed 110 cm, though the tidal
amplitude becomes much less in the more southerly Adriatic. Such
small changes of level are not enough t o allow for a complete drainage
of the ponds or limans, and this must be a factor in their modest rate
of production per unit area.
Where the estuary is truly tidal and has more constant and regular
changes of water level, these can be used to fill fishponds ; to top them
up as may be required in order to replace water lost by evaporation
and seepage during the growth of the fish crop; to empty them as
needed in order to sort out, count, or harvest the crop ; and to expose
them to sun and wind and tillage.
The inflowing water carries with it nutrients, silt, and detritus,
which fertilize the pond and by frequent changes of water keeps the
salinity under control. Therefore, it is of the first importance that
estuarine fishponds should have an assured supply of sea water (Schuster, 1952; de Angelis, 1960), so care must be taken that they are
planned with due consideration of tidal data at the site. Schuster