Why did the abolones have to be guarded? What igneous method did Karana use to accomplish this?

The abalones needed to be guards from the seagulls.

From the text:

In one morning, if the meat was left unguarded, they could fly off with a month's harvest.

At first, whenever I went to the spring or to the beach, I left Rontu behind to chase them off, but he did not like this and
howled all the time I was gone. Finally I tied strings to some of the abalone shells and hung them from poles. The insides of the shells are bright and catch the sun and they turn one way and another in the wind. After that I had little trouble with the gulls.