First, troule-shoot the problem you now have as Freddy mentioned above.
If you determine that the pump is indeed shot, remove it and bring it to your local West Marine or your favorite marine supply store. They will have either a Jabsco or Shurflo of a similar type. Get the highest pressure model they have....your gonna want to be able to easily blast all that Tuna blood off your deck.
I've used both makes over the years and lean towards the Jabsco, mainly because they have easy to use quick disconnect fittings for the hoses, and supply a new trigger hose handle and filter strainer in the box with the new pump.
I have a shurflo pump (blaster) on my Islander.Plenty of pressure.Usually the problem is the switch on the pump. You can replace this switch yourself. If the pump is not working , open up the switch and jump it out.If the pump then works replace switch.If the pump doesn't work you probably need new pump. If you need new pump check prices on line. West Marine will match any price except e-bay.
You can also pry the lid off closest to the bench seat.It is under there.You will have to go under the bench seat to fully remove it.you will end up with a soar chest, but it's cheaper than having someone else do it. It helps to have a second pair of hands.