Are persuasion skills necessary to negotiate a salary?

It will be very hard to convince anyone in anything without!

Sure it is. it's all about plus other techniques.

definitely!! since if the other party have it he will persuade you to give him what he needs :) 

You are in the driving seat if you bare well qualified and have experience. Then you need to prove to them that you will become an indispensable part of the company..

However if you are at or near entry level, you could use your soft skills to persuade the interviewer to set a slightly higher pay package by convincing him that you are hoping to develop yourself with the company.

yes just show your abilities and value that how you best fit for this job and than negotiate on the salary

Not necessary but listen to there offer and respond when needed

Obviously If you are applying for a sales job other depends on the situation

Yes, its necessary to convince the employer that you are worth that salary expected by you.