Anchor Graveyard

Visited an island off Travera which used to be a fishing base for the annual tuna run. This was at it heyday in the 1800's with 30,000 tuna being caught at its peak. It stopped in the early 1960's and the last count was 1400. The fish came through this area and the 'season' was just 10-14 days.
How did we let it get to that? I couldn't see any info to say if the numbers coming through had increased now.
These anchors were to hold the nets down that trapped the tuna.