140
C. F. HICKLING
The second condition for success will be the maximum amount of
automation, in view of the very high cost of labour in this as in other
countries. Carlin states that the feeding of the young salmon in Sweden
is highly automated.
But the intensive rearing of fish in cages, pounds or rafts makes no
use of the natural fertility of the estuary, and their food represents the
production of large areas external to the estuary. Rejected food, and
the waste-products and excretions of the caged fish, will contribute to
the fertility rather than draw from it.
B. The fertility of estuaries
1. Natural fertility
The great natural fertility of estuaries was emphasized in two
symposia held in America in 1966 and 1968, by the American Fisheries
Society (1966) and the American Association for the Advancement of
Science (ed. G. H. Lauff, 1967) respectively.
For example, Chesapeake Bay is estimated to produce at a rate of
80 lblacrelannum, and the Sea of Azov is equally productive. Zenkevitch (1963) quotes the very high figure of 100 kg/hectare/annum as the
rate of commercial production of fish in the Siwash liman ; but this may
refer to the liman used as a mullet farm. If the southern North Sea may
be regarded as an estuary, as Korringa (1967) does, and as it was in very
recent time, then in 1948 it gave a crop of fish of 52 kglhectare as compared with 26 kg/hectare for the rest of the North Sea (Kalle, 1953).
Korringa (1967) states that in terms of crop per unit area the
estuaries are much richer than the sea in food resources.
2. Benthic production
An interesting point about this estuarine fertility is that, unlike
the open sea or lakes, where plankton is the prime producer, in estuaries
the plankton plays a minor role, while the benthos is the dominant
primary producer. Lackey (1967), for example, found that in estuaries
benthic diatoms far outnumbered planktonic diatoms, and in most
cases formed a large percentage of the organisms present. I n the
Italian valli, de Angelis (1960) states that “ the physico-chemical
characteristics of lagoon water and variations in these, produce a
biological medium which is rich in benthos and which has an intense
bottom life, yet is generally poor in plankton.” Ilin (1954) states that
most of the natural fertility of the Black Sea limans is due to organogenic material accumulated on the bottom silt. To quote Hedgpeth
(1967-8) “it is a functionof the comparatively shallow depth of estuaries
C. F. HICKLING
The second condition for success will be the maximum amount of
automation, in view of the very high cost of labour in this as in other
countries. Carlin states that the feeding of the young salmon in Sweden
is highly automated.
But the intensive rearing of fish in cages, pounds or rafts makes no
use of the natural fertility of the estuary, and their food represents the
production of large areas external to the estuary. Rejected food, and
the waste-products and excretions of the caged fish, will contribute to
the fertility rather than draw from it.
B. The fertility of estuaries
1. Natural fertility
The great natural fertility of estuaries was emphasized in two
symposia held in America in 1966 and 1968, by the American Fisheries
Society (1966) and the American Association for the Advancement of
Science (ed. G. H. Lauff, 1967) respectively.
For example, Chesapeake Bay is estimated to produce at a rate of
80 lblacrelannum, and the Sea of Azov is equally productive. Zenkevitch (1963) quotes the very high figure of 100 kg/hectare/annum as the
rate of commercial production of fish in the Siwash liman ; but this may
refer to the liman used as a mullet farm. If the southern North Sea may
be regarded as an estuary, as Korringa (1967) does, and as it was in very
recent time, then in 1948 it gave a crop of fish of 52 kglhectare as compared with 26 kg/hectare for the rest of the North Sea (Kalle, 1953).
Korringa (1967) states that in terms of crop per unit area the
estuaries are much richer than the sea in food resources.
2. Benthic production
An interesting point about this estuarine fertility is that, unlike
the open sea or lakes, where plankton is the prime producer, in estuaries
the plankton plays a minor role, while the benthos is the dominant
primary producer. Lackey (1967), for example, found that in estuaries
benthic diatoms far outnumbered planktonic diatoms, and in most
cases formed a large percentage of the organisms present. I n the
Italian valli, de Angelis (1960) states that “ the physico-chemical
characteristics of lagoon water and variations in these, produce a
biological medium which is rich in benthos and which has an intense
bottom life, yet is generally poor in plankton.” Ilin (1954) states that
most of the natural fertility of the Black Sea limans is due to organogenic material accumulated on the bottom silt. To quote Hedgpeth
(1967-8) “it is a functionof the comparatively shallow depth of estuaries