Shark attack - Streamline English book. Use past tense or presense tense

Question

'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!

Answer 1

Especially in conversation, people often tell a story, or part of it, in the present tense, to give a sense of immediacy. Analysts of its use in conversation have argued that it serves to "foreground" an event, i.e. signalling that one event is particularly important, relative to others.

The tense can shift to the present and then just as swiftly back again:

I was in a fight last night. I was in Joe's Bar, minding my own business, when all at once there's a guy yelling "Limey pantywaist!" in my face. He hauls off and aims a punch at me. I see he's had a few to drink, so I stick out my foot to trip him up and over he goes. The cops came and said he didn't like English accents and had been in trouble before.

In writing it can be called the 'dramatic present', 'historical present', or 'narrative present':

If the funeral had been yesterday, I could not recollect it better. The very air of the best parlour, when I went in at the door, the bright condition of the fire, the shining of the wine in the decanters, the patterns of the glasses and plates, the faint sweet smell of cake, the odour of Miss Murdstone’s dress, and our black clothes. Mr. Chillip is in the room, and comes to speak to me.

"And how is Master David?" he says, kindly.

I cannot tell him very well. I give him my hand, which he holds in his. — Charles Dickens, David Copperfield, Chapter IX

https://en.wikipedia.org/wiki/Historical_present

Answer 2

You're correct. The author mixed his tense.

It's sloppy writing, but tends to happen more with people relating their own story, especially in such an emotional situation. Notice the violent parts tend to slide back into present tense? It's like he's reliving the experience as he's writing it.