Mice problem. Advice needed please.

swingaloo

We have a garage at the bottom of the garden which was built back in the 1970s. It's perfectly functional but due to the way it was built it is not mice proof and its not possible to make it so. It has always been used for storage for lawn mowers, bikes, shelving for paint etc.

My husband and his mate love fishing and until recently all the fishing equipment was stored by his mate as his garage was sealed all round. now he has moved house and cant store it so it has been put in our garage. However our garage has gaps between the roof and the panels the side are made of, its waterproof as the roof overhangs but it also has gaps under the doors as the ground is uneven and it backs onto an allotment.
Since putting the fishing stuff in there we have had loads of mice. We found they had bitten through one of the bags and made a nest inside. Clearly the fishy smell has attracted them (though it does nothing for me!) and despite removing everything to clear it all out, power washing the floor and making sure the tackle bags have been put in large plastic lidded boxes we cannot get rid of the mice. They are now all over the garden, we can sit and watch then coming from under the door running around then scooting back under. They can also get through gaps between the panels in certain places.
I cant use poison as we have a dog and despite not liking them taking over the garden I would like a nice way to get risk of them if there is such a thing. Im aware that they breed in large numbers so it will only get worse. My worry now is that they may get braver and come up the steps to the house and I have double doors leading from the kitchen to the garden which I like to be able to leave open during good weather.

I also enjoy feeding the birds and have managed to get many varieties into the garden but now Ive stopped doing that as the birds drop seed, suet, fruit etc which just feeds the mice.

I really need advice on the easiest way to stop the increase in numbers, at first I could sit on the bench and just see the odd one, now I can watch 7 or 8 all running round between my plants. I know that I will never have a mouse free zone living close to a allotments and having a garden but we have been in the house 4 years now and this is the first time I have seen any, especially during the daytime. I think it has to be the fishing tackle that is attracting them and we have tried all ways to store it but the smell from it is still there.  
Ive been told to use poison, traps, trap cages, things that make a high pitched sound which they dont like but I would like to hear advice from someone who has maybe had the same problem.
Thanks for reading.

Bookworm105

use shotgun

JGB1955

Get a pest control expert in.

Runner_Duck

From what I've read, clearing up where they were before eradicating the problem is one of the worst things you can do, it just causes the mice to scatter. You might want to consider metal bins for the bait.  Having said that there is no 'nice' way to deal with this number of mice.  You need an expert.