'I had swum about 13 miles and I was about a mile and a half out when suddenly something came straight up out of the water, knocking me off my surfboard and into the air.
'I didn't know it was a shark until I surfaced again. Then I saw this big fish swimming around with my surfboard in its mouth.
'I could see its long grey dorsal fin and I thought, "Oh, my God, it's a Great White Shark." The next thought was, "Nobody gets this close to a Great White and lives to tell the tale."
'You just don't know what you're going to do in a situation like mine. I saw the shark coming towards me with my surfboard in its jaws. I grabbed the tail of the surfboard and climbed back on it. I don't know why. Then I was afraid that if the shark let go of the board he'd go for me.
'I got on my knees on the tail of the board, trying to keep my balance because all the time he's shaking the board - trying to get me off it.
Question: A man who had been attacked by a shark told about it. I dont understand why in the first sentence, they use "got on" is in past tense, but then "trying" and "he's shaking..." are in presense tense. The actions are in the past so I think they must be "tried" and ", tried to keep my balance....all the time he shaked...-tried"
Please help me to explain why they use present tense!