3
TANE
(1967)
13:
3 -
11
AN EVALUATION OF THE THEORETICAL CAPACITY
O F A NEW Z E A L A N D H A R B O U R TO C A R R Y
A HUMAN POPULATION
B y Wilfred S h a w c r o s s *
INTRODUCTION
T h e aim of t h i s paper i s to e s t a b l i s h a l i m i t i n g factor i n the
estimate of the s i z e of a human p o p u l a t i o n s u b s i s t i n g by means of s h e l l f i s h g a t h e r i n g , under New Z e a l a n d c o n d i t i o n s . T h e r e a s o n s for s u c h a
course of i n v e s t i g a t i o n a r i s e out of the efforts of A r c h a e o l o g i s t s to c a l c u l a t e
the s i z e s of p r e h i s t o r i c p o p u l a t i o n s on the b a s i s of s u r v i v i n g food d e b r i s
on a n c i e n t settlements and these figures are important to P r e h i s t o r i a n s
because the s i z e of a community and i t s l e n g t h of o c c u p a t i o n of a l o c a t i o n
are i n d i c a t i o n s of the c u l t u r a l development of a s o c i e t y (see A s c h e r 1959,
C l a r k 1954, and T e r r e l l 1966 and S h a w c r o s s 1967 for s u c h s t u d i e s i n
A m e r i c a , Europe and New Z e a l a n d r e s p e c t i v e l y ) . In t h i s work on early
s o c i e t i e s much prominence i s g i v e n to M a n ' s e x p l o i t a t i o n of h i s environment,
but the i n s t a n c e s where some q u a n t i t a t i v e a s s e s s m e n t has b e e n obtained for
the a c t u a l v a l u e of the environment are rare, notably i n B o u r l i e r e ' s a s s e s s ment of the p o t e n t i a l of the E a s t A f r i c a n s a v a n n a h ( B o u r l i e r e 1964). T h e
reason for s u c h r e l u c t a n c e to examine the figures i s o b v i o u s , there are too
many u n k n o w n s . H o w e v e r , it seems r e a s o n a b l e to approach the q u e s t i o n by
i s o l a t i n g p a r t i c u l a r unknown factors and e x a m i n i n g them under c o n t r o l l e d
conditions.
In the present a n a l y s i s the factor to be i s o l a t e d i s the maximum
amount of food a v a i l a b l e from the e x p l o i t a t i o n of s h e l l f i s h beds i n a p a r t i c ular harbour and from t h i s it i s p o s s i b l e to c a l c u l a t e a maximum figure for
the s i z e of a human p o p u l a t i o n , a s s u m i n g that it s u b s i s t e d w h o l l y on
s u c h a food s u p p l y . In r e a l i t y there i s no e v i d e n c e for either a t o t a l s h e l l f i s h diet or a community c o n f i n e d to the r e s o u r c e s of a harbour, however, i t
i s s t i l l p o s s i b l e to draw a number of i n t e r e s t i n g c o n c l u s i o n s w h i c h w i l l be
left to the d i s c u s s i o n .
L o c a t i o n of I n v e s t i g a t i o n
Whangateau harbour, c h o s e n for t h i s study, i s s i t u a t e d on the
E a s t c o a s t of the North I s l a n d , a p p r o x i m a t e l y midway between A u c k l a n d
and Whangarei, but l y i n g j u s t south of C a p e R o d n e y and therefore o p e n i n g
into the H a u r a k i G u l f rather than d i r e c t l y i n t o the P a c i f i c O c e a n . It c o n s i s t s of one p r i n c i p a l arm, about four m i l e s l o n g by one h a l f w i d e , p a r a l l e l
to the c o a s t and separated from the s e a by a s a n d bar, a l s o about half a
mile w i d e . T h e r e are a l s o s e v e r a l l e s s e r arms w h i c h connect w i t h the main
body at the northern end and w h i c h are fed by numerous streams f l o w i n g
*
Department
of
Anthropology,
University
of
Auckland
4
land above
200 ft
mudflats
Scale
FIGURE 1
from the h i g h ground i n that quarter (see F i g . 1 ) . T h e greater part of the
harbour c o n s i s t s of s a n d b a n k s g i v i n g way to mud up the arms, i n the upper
reaches of w h i c h there are mangroves whose extent, on o b s e r v a t i o n , i s
greater than that i n d i c a t e d on the s u r v e y m a p s . A t the present time the
harbour i s a popular p l a c e for s h e l l f i s h gathering a n d i t i s evident from
numerous middens that it w a s s i m i l a r l y u s e d i n the p a s t . Furthermore
there are a number of f o r t i f i c a t i o n s l o c a t e d on p o i n t s of h i g h ground
running out into the harbour.
5
Method of Study
T h e primary o b j e c t i v e of the s t u d y was to o b t a i n an estimate of
the s i z e of the l i v i n g s h e l l f i s h p o p u l a t i o n by means of s a m p l i n g . T h e
method employed was to s e l e c t one of the s m a l l e r arms, a s s u m i n g it to be
t y p i c a l of the range of c o n d i t i o n s throughout the whole area, and to take
s a m p l e s on a grid set at regular, hundred p a c e i n t e r v a l s c o n t r o l l e d by
s i g h t i n g poles set up on the s h o r e . T h e s a m p l e s were t a k e n from a 20
centimetre square (the w i d t h of a s p a d e ) a n d washed i n a s i e v e , sorted
a c c o r d i n g to the two main s p e c i e s Chione
Amphidesma
australe
stutchburyi
( " c o c k l e " ) and
( " p i p i " ) , and s p e c i m e n s below a maximum measure-
ment of 2 c m s . , c h e c k e d a g a i n s t a gauge, were thrown out. T h i s w i l l be
referred to l a t e r . T h e s p e c i e s were then w e i g h e d a n d returned to the water
after an adequate sample had been r e t a i n e d for further a n a l y s i s , and by
t h i s method 26 s a m p l e s were t a k e n by one person during one t i d e .
T h e s e c o n d o b j e c t i v e w a s to o b t a i n v a l u e s for the amount of
e d i b l e matter i n the s h e l l f i s h . T h i s was a c h i e v e d e x p e r i m e n t a l l y by c o o k i n g and w e i g h i n g the s a m p l e s . A n effect of c o o k i n g i s to drive out water
w h i c h l e a d s to some d i f f i c u l t y i n comparing w e i g h t s , e s p e c i a l l y when
e x a m i n i n g t a b l e s of food c o m p o s i t i o n . It i s c o n s i d e r e d that probably the
best point to take i s that when the majority of the v a l v e s f i r s t start to
open, w h i c h i s after approximately A of an hour of c o o k i n g . T h e r e s u l t s
l
are o u t l i n e d i n T a b l e I.
T a b l e I. P r o p o r t i o n of meat to s h e l l f i s h by weight and effect of c o o k i n g .
Cooking
time
A hour
Uncooked
l
x
Animal
Amphidesma
Chione
k
Total
weight
Shell
weight
Meat
weight
262 gms. 181 gms.
452
286
465
297
32 gms.
52
39
8
374
24
6
230
12%
12
E s t i m a t e of S h e l l f i s h P o p u l a t i o n s
Before the commencement of t h i s s u r v e y the w r i t e r had no very
c l e a r i d e a of the d i s t r i b u t i o n of the a n i m a l s a n d for t h i s r e a s o n the r e s u l t s
of the s a m p l i n g were prepared as p o p u l a t i o n d i s t r i b u t i o n diagrams, see
P i g . 2 for Chione
and F i g . 3 for Amphidesma.
T h e p o p u l a t i o n s are s h o w n
i n terms of an estimated weight i n k i l o s per square metre and the r e l a t i v e
v a l u e s are shown by means of c o n t o u r s . It w i l l be s e e n that the
Chione
i s o v e r w h e l m i n g l y more abundant, both i n o v e r a l l d i s t r i b u t i o n , for it i s
found, i f o n l y i n s m a l l numbers and s m a l l i n d i v i d u a l s , high up the muddy
arms of the harbour, c l o s e to the t i d a l l i m i t , whereas the Amphidesma
is
l o c a t e d as an i s o l a t e d p o p u l a t i o n c l o s e to the low water and i n a s a n d y
6
In m a k i n g an estimate of e x p l o i t a b l e p o p u l a t i o n an arbitrary
l i m i t has b e e n c h o s e n of 1 k i l o per square metre, below w h i c h figure i t i s
felt that the a n i m a l s are not worth the effort of gathering. T h i s s u g g e s t s
that the upper r e a c h e s of the harbour arms and the upper t i d a l parts of the
s h o r e s s h o u l d be left out of the c a l c u l a t i o n s , though even were they to be
t a k e n into account it i s u n l i k e l y that they w o u l d m a t e r i a l l y a l t e r the r e s u l t s .
It s h o u l d a l s o be added that w h i l e the proportion of u n d e r s i z e s p e c i m e n s
i s greater i n the upper r e a c h e s they are not i n fact s u f f i c i e n t l y frequent to
be thought to alter s e r i o u s l y the f i g u r e s , that i s , there i s no l a r g e quantity
of u n d e r s i z e i n d i v i d u a l s w h i c h has been i g n o r e d .
It i s apparent that the economic part of the s h e l l f i s h p o p u l a t i o n s
i s i n some way r e l a t e d to the l e n g t h of time of t i d a l submergence or to
depth, though a d i s c u s s i o n of these factors i s outside the s c o p e of t h i s
a n a l y s i s . However, what i s relevant i s that it i s now p o s s i b l e to draw a
7
P
100
200
300
400 YDS
FIGURE 3
contour round the entire harbour i n d i c a t i n g the probable boundary of the
economic a r e a and from t h i s a v a l u e i n square metres may be c a l c u l a t e d .
T h e figure i s 6, 370, 000 square metres, w h i c h Is o b t a i n e d by c o u n t i n g the
squares i n a convenient s i z e d g r i d drawn over the p l a n of the harbour
(Monkhouse and W i l k i n s o n 1964), but i t i s r e c o g n i s e d that t h i s i s open to
some range of error for w h i c h ±5% i s e m p l o y e d .
U s i n g a s i m i l a r method i t i s p o s s i b l e to c a l c u l a t e the p r o d u c t i v ity of the sample a r e a , see T a b l e
II.
A s s u m i n g that the proportions of s h e l l f i s h i n the s a m p l e area
hold good for the whole harbour, but a l l o w i n g a ±5% error, and t a k i n g into
account the e x p e r i m e n t a l l y o b t a i n e d v a l u e s for the proportions of meat to
s h e l l i n the two s h e l l f i s h e s , for w h i c h an a d d i t i o n a l ±1% error w i l l be
g i v e n , it i s c a l c u l a t e d that the a v a i l a b l e meat i n the Whangateau harbour
would be -
8
8 X 6, 370, 000 X 227, 785
100 X
+ 6, 370, 000 X 12, 960 X 12 ± 11%
44, 951
44, 951
X
100
= 2, 802, 737 ± 11% k i l o s .
T a b l e II
M
2
Chione
P r o d u c t i v i t y of Sample A r e aAmphidesma
2
kilos
M
kilos
216
4, 325
216
648
465
13. 829
4, 212
8, 424
3, 888
36, 635
3, 888
11, 950
18. 500
6, 960
138. 200
59, 800
18, 500
44, 951
227, 785
44, 951
12, 960
E x p l o i t a t i o n by a Human P o p u l a t i o n
T h e next stage i s to convert the above figure for a v a i l a b l e meat
into u n i t s of energy w h i c h may then be d i v i d e d by a s t a n d a r d , average
human c o n s u m p t i o n rate. T h e figures u s e d are 48 c a l o r i e s per 100 grammes
for c o o k e d c o c k l e s ( M c C a n c e and Widdowson 1960) and an average c o n s u m p t i o n of some 2700 c a l o r i e s per day by an adult and moderately
active
man (Osmond and W i l s o n 1961), and b e c a u s e e a c h of these c a l c u l a t i o n s
i n v o l v e s a great d e a l of v a r i a b i l i t y , s u c h as s e a s o n a l c h a n g e s i n the s h e l l f i s h and unknown a c t i v i t y of p r e h i s t o r i c man, errors of 10% seem
reasonable.
T h e r e s u l t i s 498, 261 ± 3 1 % or between 652, 908 and 343, 592
man/days of food, or more c o n v e n i e n t l y h a l f a m i l l i o n man/days.
DISCUSSION
In a s s e s s i n g the r e a l i s m of t h i s estimate it must f i r s t be o b s e r v e d
that s e v e r a l u n l i k e l y a s s u m p t i o n s have been made. F o r example, it i s u n b e l i e v a b l e that M a o r i s h e l l f i s h gathering c o u l d have been so e f f e c t i v e as to
have extracted v i r t u a l l y 100% of the a n i m a l s from the harbour. C o l l e c t i n g
at l o w t i d e s i s an e x c e e d i n g l y l a b o r i o u s t a s k and s i e v i n g c a n o n l y be
a c c o m p l i s h e d with water. It i s l i k e l y that much of the gathering would have
taken p l a c e under water when it i s p o s s i b l e to feel the s h e l l s w i t h the
feet and to e a s i l y separate the s a n d , but at the same time it becomes far
harder to ensure thorough c o l l e c t i o n .
It i s a l s o u n n e c e s s a r y to assume that any group ever e x i s t e d on
an e n t i r e l y s h e l l f i s h diet, i n d e e d , the body of E t h n o g r a p h i c literature as
w e l l as recent A r c h a e o l o g i c a l r e s e a r c h argues a g a i n s t t h i s . On the other
hand, it i s d i f f i c u l t to e s t a b l i s h the r e l a t i v e importance of other foods,
9
e s p e c i a l l y v e g e t a b l e o n e s , for no adequate o b s e r v a t i o n s were made i n the
early days of E u r o p e a n c o n t a c t and many of t h e s e foods l e a v e no s u r v i v i n g
e v i d e n c e . However, it may be c a u t i o u s l y put forward that c u l t i v a t e d c r o p s
can never have h e l d the dominant p o s i t i o n here w h i c h they have i n more
t r o p i c a l parts of P o l y n e s i a , for s u i t a b l e c o m b i n a t i o n s of s o i l s and c l i m a t e
are not w i d e s p r e a d . T h e same r e s t r i c t i o n s are to some extent true even for
the fern root but it i s s u g g e s t e d that t h i s p l a n t i s a counterpart to the
shellfish.
A third factor w h i c h affects the c a l c u l a t i o n s i s that it i s not
entirely c l e a r whether the human body c a n extract the f u l l quota of c a l o r i e s
from s h e l l f i s h . It may be that some of the energy i n s u c h food i s o n l y obt a i n e d at the expense of expenditure of a s i m i l a r amount of effort i n the
d i g e s t i v e p r o c e s s , but to e v a l u a t e t h i s w o u l d perhaps require feeding a
person on o y s t e r s and h a r n e s s i n g him to a dynamometer.
It i s a l s o not known how the s h e l l f i s h p o p u l a t i o n s w o u l d respond
to the heavy e x p l o i t a t i o n e n v i s a g e d . A t one extreme it might e v e n l e a d to
the l o c a l e x t i n c t i o n of the a n i m a l s and t h e i r replacement by other s p e c i e s .
But it i s probable that a c e r t a i n degree of human e x p l o i t a t i o n might l e a d to
a r e s u l t b e n e f i c i a l i n human terms and it i s c e r t a i n l y true that gathering i s
going on at the present time, s o that what i s b e i n g e x a m i n e d i s not a popu l a t i o n regulated s o l e l y by " n a t u r a l " a g e n c i e s . C o n c e r n i n g the effects of
o v e r - e x p l o i t a t i o n , it was noted above that i n d i v i d u a l s below a n arbitrary
s i z e l i m i t and below an arbitrary d e n s i t y per square metre were not t a k e n
into the c a l c u l a t i o n s , because they were c o n s i d e r e d to be u n e c o n o m i c .
But there i s sound A r c h a e o l o g i c a l e v i d e n c e that the s m a l l i n d i v i d u a l s
were gathered up w i t h the larger ones ( T e r r e l l 1966: 151), i n d i c a t i n g
that no s e l e c t i o n w a s e x e r c i s e d ,
however, it seems a g a i n s t r e a s o n that
much c o l l e c t i n g w o u l d have been done i n areas w i t h very l o w y i e l d s and i t
may be s u p p o s e d that these areas w o u l d act a s r e s e r v o i r s e n s u r i n g the res t o c k i n g of the b e d s .
T h e r e a l s o a r i s e s the q u e s t i o n of the v a l i d i t y of the method of
s a m p l i n g for however c l o s e to truth the s a m p l e a r e a may be it i s far l e s s
s a t i s f a c t o r y to attempt to g e n e r a l i s e for the whole harbour from t h i s s i n g l e
arm. T h e r e might be far greater areas of mangroves, but there might a l s o be
larger beds of Amphidesma
than a n t i c i p a t e d a n d for these r e a s o n s the
present e s t i m a t e s , w i t h their a l l o w a n c e of a wide range of error, must s t a n d
u n t i l improvements are made on them.
One r e s u l t w h i c h i s s u r p r i s i n g to the P r e h i s t o r i a n whose thoughts
tend to be c o n c e r n e d w i t h l a n d a n i m a l s , i s the c o m p a r i s o n w h i c h may be
made between the marine environment, represented by the New Z e a l a n d
harbour, and the s a v a n n a h c o n d i t i o n s of E a s t A f r i c a w i t h their large
10
ungulates.
Whangateau
Albert National Park
5, 366, 594 k A m '
2 3 , 556 k / k m ( B o u r l i e r e
2
1964)
T h i s l e a v e s a s u b s t a n t i a l quantity i n favour of the c o a s t a l environment
even when a c c o u n t i s t a k e n of the higher proportion of i n e d i b l e matter i n
the s h e l l f i s h and that their meat has o n l y about one fifth of the c a l o r i f i c
v a l u e of red meat. B u t the harbour area i s s t r i c t l y l i m i t e d and though there
are numerous other harbours, both larger and s m a l l e r than t h i s one, round
the c o a s t , c l e a r l y the e x t e n s i v e n e s s of the A f r i c a n s a v a n n a h c a n n o t be
compared w i t h the r i c h e r but r e s t r i c t e d environment of the c o a s t . In c o n c l u s i o n , the estimate of the p o t e n t i a l c a p a c i t y of the Whangateau harbour
to carry a human p o p u l a t i o n g i v e s a figure of h a l f a m i l l i o n man/days of
a v a i l a b l e food, w h i c h might extend to a s much as 655, 000 man/days i f
factors of i n c r e a s e d y i e l d , higher food v a l u e and reduced human consumpt i o n are to be t a k e n into a c c o u n t . B u t i t might be more r e a l i s t i c to t h i n k of
t h i s figure i n terms of f a m i l y u n i t s of around s e v e n people e a c h . In t h i s
c a s e some fifty groups c o u l d be supported for a period of four y e a r s , by
w h i c h time regeneration would have begun, a l l o w i n g t h i s p r o c e s s to go on
indefinitely.
It s h o u l d not be s u p p o s e d that t h i s i s a d i r e c t estimate of the
r e a l p o p u l a t i o n w h i c h may have e x i s t e d at any time i n the p a s t . It c a n o n l y
be a general i n d i c a t i o n of the upper l i m i t for a p o p u l a t i o n i n the area,
u n l i k e l y ever to have been a t t a i n e d , b e c a u s e of the d i f f i c u l t y of a c h i e v i n g
s u c h e f f i c i e n t e x p l o i t a t i o n , or over - e x p l o i t a t i o n . A l t e r n a t i v e l y , it may be
even more r e a l i s t i c to see t h i s figure a s r e p r e s e n t i n g a v i r t u a l l y i n e x h a u s t i b l e food r e s e r v e to a much s m a l l e r p o p u l a t i o n , a r e s e r v e w h i c h w a s regur e g u l a r l y e x p l o i t e d i n a s m a l l way, but one to be f a l l e n back o n i n t i m e s of
poor harvest or stormy weather at s e a , a f f e c t i n g the f i s h i n g , or for other
emergencies.
T o approach the truth any c l o s e r than t h i s statement w i l l
require the other factors to be e x a m i n e d .
ACKNOWLEDGEMENTS
T h i s i n v e s t i g a t i o n was c a r r i e d out by the author w h i l e attending
a Marine E c o l o g y course h e l d at the A u c k l a n d U n i v e r s i t y Marine L a b o r a t o r y
at L e i g h , and p a r t i c u l a r thanks are due to the director, Dr W. J . B a l l a n t i n e ,
and to other members of the c o u r s e for a d v i c e and encouragement.
REFERENCES
A s c h e r . R.
1959
" A P r e h i s t o r i c P o p u l a t i o n E s t i m a t e , U s i n g Midden
A n a l y s i s and T w o P o p u l a t i o n M o d e l s . "
Journal of Anthropology.
V o l . 15: 168 -
Bourliere, F.
1964
Southwestern
178.
" O b s e r v a t i o n s on the E c o l o g y of some L a r g e A f r i c a n
M a m m a l s " i n African
Ecology and Human
Evolution
eds. F. C . H o w e l l & F . B o u r l i e r e , Methuen, L o n d o n :
43 - 54.
11
Clark, J. G . D.
1954
M c C a n c e , R . A . & 1960
Excavations
Press.
Cambridge
at Star Can.
The Composition
of Foods.
University
H . M. S. O . L o n d o n .
Widdowson, E . M .
Monkhouse, F . J .
1964
Wilkinson, H. R.
Osmond, A . &
1961
U n i v e r s i t y P a p e r b a c k s , 2nd
Tables
of Composition
of Australian
Foods.
Commonwealth Department of H e a l t h , C a n b e r r a .
W i l s o n , W.
S h a w c r o s s , W.
Maps and Diagrams.
Edition, London.
1967
" A n I n v e s t i g a t i o n of P r e h i s t o r i c D i e t and E c o n o m y
on a C o a s t a l S i t e at G a l a t e a B a y , New
to be p u b l i s h e d i n the Proceedings
Society.
Terrell, J .
1966
Zealand"
of the
Prehistoric
V o l . 33: C a m b r i d g e , E n g l a n d .
" T h e E x c a v a t i o n and A n a l y s i s of a M a o r i C o o k i n g
S i t e on P o n u i I s l a n d " , New Z e a l a n d
A s s o c i a t i o n Newsletter,
Archaeological
V o l . 9, N o . 4: 144 — 154.