| Ledge state | Urchin abundance | Quality and price | Dominant harvesting strategies | Nature and value of fishermen’s knowledge about state. |
| a. Barrens |
High. Initial absence of harvesting. |
Low. | Unselective. |
Broad-scale, long-term, widely known,
but of little competitive value. |
|
Harvesting causes a transition to
conveyor belt state Kelp starts to grow back, urchin roe content increases, few predators |
||||
| ↓ | ↓ | ↓ | ↓ | ↓ |
| b. Conveyor belt |
Medium. Sufficient numbers of urchins left to balance kelp growth. |
High. | Moderately selective (harvesting from feedline). | Ledge specific, short-term, tightly guarded, competitively valuable. |
|
Heavy, continuous harvesting
creates transition to kelp-dominated
state Predators abundant, little or no urchin survival post-settlement |
||||
| ↓ | ↓ | ↓ | ↓ | ↓ |
|
c. Kelp-dominated |
Absent or very low. | No fishing. | No fishing. | Broad-scale, long-term, widely known, but of little competitive value. |