224
11. Horseshoe Crabs and Shorebi rds
1: TOTAL ADULT ... 2: TOTAL ADULT ... 3: TOTAL ADULT ... 4: TOTAL ADULT ... 5: TOTAL ADULT ...
1: 4000000.00
====i:==2'==='=1==2'- - - ---:
1: 2000000.00
100.00
50.00
1:
25.00
I
75.00
5
Seasons
FIGURE 11.9
rates between 0 and .20. From Figures 11.9 to 11.12, it is clear that harvesting
decreases the number of horseshoe crabs present, and thus the number of
shorebirds. However , in many cases, steady-state values can still be attained.
Sustainable levels of exploitation can be attained-where crab populations
diminish at first, but steady-state conditions eventually prevail. However, the
threshold exploitation level for either fishery is approximately Ilo/o-for
4: BIRDS
J
, 1
: 6 2- -
I 3
I
!
5: BIRDS
I
I
- 1
•
1
1
_ ._ 1 _ '- 2
3
3
2
3: BIRDS
2: BIRDS
1: BIRDS
1: 2000000.00
!
1: 1000000.00
4
5
100.00
5
50.00
Seasons
4
25.00
5
75.00
FIGURE 11.1 a
l
I