484
D. H. CUSHING:
high band in the equatorial region. The Bay of Bengal and the eastern tropical ocean again
appear to be relatively rich, but not as rich as during the period of the SW monsoon.
In the NE monsoon, the total production throughout the ocean is about 1.3 . 10 8 tons
wet weight and during the SW monsoon 2.0'10 8 tons wet weight. So the total annual
tertiary production is 3.3 .10 8 tons wet weight. By far the greater proportion of this
quantity lies in the open ocean and is part of the oceanic ecosystem, most of which is
inaccessible to exploitation by fishermen. However, in the upwelling areas another form
of ecosystem is found. Off southern Arabia, for example, there might be an annual
production of 4 - 5 . 10 6 tons.
4. Tuna Production
The tuna stock before exploitation is given as kg per 100 hooks nighc\ by 10°
squares, throughout the ocean in Fig. 6. The main point is that more tuna are found in
the western half 6f the ocean and that most are found to the east and SE of Madagascar.
From the distribution of tertiary production, the higher densities in the equatorial region
might be expected, taking into account the possibility that the classification of data by
squares may be a little coarse. However, the productive area east and SE of Madagascar
is unexpected and there is little production there at the primary, secondary and tertiary
levels. The catches by weight in that area were predominantly of yellowfin tuna; the
explanation of the concentration remains obscure.
Attempts were made to transform the total weight of tuna stock into production units
in gC m -2. Those needing estimates of the catchability of the hooks and the migration
speeds failed through lack of information.
5. Transfer Coefficients
Ecological efficiency is defined as the ratio of yield in one trophic level to that in the
one below (SLOBODKIN, 1961). If yield is a constant fraction of production, then the ratio
in production is an estimate of ecological efficiency. This ratio I have called a transfer
coefficient, to distinguish it from the stricter term ecological efficiency. The transfer
coefficient was calculated as the ratio of gC m- 2 180 day-l in secondary production
to that in primary production; the values range from about 2% to about 34%.
In Fig. 7 the transfer coefficients are plotted against the primary production as gC m- 2
180 day-l in both monsoons. The open circles show the points for the SW monsoon
and the triangles those for the NE monsoon. The black circles are averages for intervals
on the abscissa and a curve has been fitted by eye to the average points. The mean transfer
coefficient for the whole ocean for both monsoons is very close to 10%, which is near
the value found by SLOBODKIN in his experimental Daphnia populations. The highest
transfer coefficient obtained with chickens is about 40%. For animals which have to
search for food, perhaps survive for periods of time on less than a maximum ration, and
which have to devote perhaps 15% of body weight or more to reproduction, the transfer
coefficient must be considerably less than 40%. If half of any increment to adult body
weight must be devoted to reproduction and if half must be devoted to energy spent on
searching, then the 40% is reduced to 10%. But as STEELE (1965) has pointed out, if
much of the biomass is composed of non-reproducing juveniles a higher transfer coefficient is sometimes possible, up to 25%. In this case the secondary production comprises
a number of generations. The simplest way of looking at the problem is to consider the
gonad weight as a proportion of the body weight. From generation to generation the first
D. H. CUSHING:
high band in the equatorial region. The Bay of Bengal and the eastern tropical ocean again
appear to be relatively rich, but not as rich as during the period of the SW monsoon.
In the NE monsoon, the total production throughout the ocean is about 1.3 . 10 8 tons
wet weight and during the SW monsoon 2.0'10 8 tons wet weight. So the total annual
tertiary production is 3.3 .10 8 tons wet weight. By far the greater proportion of this
quantity lies in the open ocean and is part of the oceanic ecosystem, most of which is
inaccessible to exploitation by fishermen. However, in the upwelling areas another form
of ecosystem is found. Off southern Arabia, for example, there might be an annual
production of 4 - 5 . 10 6 tons.
4. Tuna Production
The tuna stock before exploitation is given as kg per 100 hooks nighc\ by 10°
squares, throughout the ocean in Fig. 6. The main point is that more tuna are found in
the western half 6f the ocean and that most are found to the east and SE of Madagascar.
From the distribution of tertiary production, the higher densities in the equatorial region
might be expected, taking into account the possibility that the classification of data by
squares may be a little coarse. However, the productive area east and SE of Madagascar
is unexpected and there is little production there at the primary, secondary and tertiary
levels. The catches by weight in that area were predominantly of yellowfin tuna; the
explanation of the concentration remains obscure.
Attempts were made to transform the total weight of tuna stock into production units
in gC m -2. Those needing estimates of the catchability of the hooks and the migration
speeds failed through lack of information.
5. Transfer Coefficients
Ecological efficiency is defined as the ratio of yield in one trophic level to that in the
one below (SLOBODKIN, 1961). If yield is a constant fraction of production, then the ratio
in production is an estimate of ecological efficiency. This ratio I have called a transfer
coefficient, to distinguish it from the stricter term ecological efficiency. The transfer
coefficient was calculated as the ratio of gC m- 2 180 day-l in secondary production
to that in primary production; the values range from about 2% to about 34%.
In Fig. 7 the transfer coefficients are plotted against the primary production as gC m- 2
180 day-l in both monsoons. The open circles show the points for the SW monsoon
and the triangles those for the NE monsoon. The black circles are averages for intervals
on the abscissa and a curve has been fitted by eye to the average points. The mean transfer
coefficient for the whole ocean for both monsoons is very close to 10%, which is near
the value found by SLOBODKIN in his experimental Daphnia populations. The highest
transfer coefficient obtained with chickens is about 40%. For animals which have to
search for food, perhaps survive for periods of time on less than a maximum ration, and
which have to devote perhaps 15% of body weight or more to reproduction, the transfer
coefficient must be considerably less than 40%. If half of any increment to adult body
weight must be devoted to reproduction and if half must be devoted to energy spent on
searching, then the 40% is reduced to 10%. But as STEELE (1965) has pointed out, if
much of the biomass is composed of non-reproducing juveniles a higher transfer coefficient is sometimes possible, up to 25%. In this case the secondary production comprises
a number of generations. The simplest way of looking at the problem is to consider the
gonad weight as a proportion of the body weight. From generation to generation the first