You compete in a very aggressive space with lots of professional muscle. The SEOs in this space are experienced, hungry, savvy and sometimes tricky. The sites that you compete against have enormous development budgets and can toss teams of people into a project. Their authors produce best-on-the-web content with first class authorship, fantastic maps, great photos and more. I could go on and on.
You don't reveal this in your post but my question is.....
What are you doing that will put you on a footing to compete with these cannibals - even in small niches?
SEO in the travel area is a "Battle of Resources".
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Some suggestions after a quick look at your site...
-- I think that your on-page optimization needs kicked up a notch. I would read the SEOmoz guide. Run the optimization tool in the rankings checker. The terms that you are gunning for based upon title tags are not even present on some of the pages that I visited. You are competing against the cannibals. Sharpen your knife!
-- What are you putting on this site that will stand apart in your niche and attract links? I see lots of short content with chest thumping. How about some real meat about your destinations? For example, you offer a Galapagos tour but I can't find much about why people would want to visit that destination... What are they going to see... what important things happened there.. why are these islands some of the most unique rocks on this planet.. Walk in the steps of Darwin and share some of his observations... the history of the place, conservation, iguanas, boobies, tortoise, flightless cormorants, tropical penguins., the unique environment... people are fascinated with volcanoes! I hope that your tour guides know about all of this stuff and are ready to sing about it. Convince me that you are the tour company that should take me. I am not convinced that you know what is there. I wanna be sure that I get my money's worth and make good use of my time. I am not convinced that you know enough about this destination to teach me anything. Tell me the story that will get my blood pumping to visit and ready to reach for my wallet!
-- Give people pages that they can link to from their FB wall and say... I AM GOING HERE! WOW! Eat your heart out!
-- What are you doing to make this site exceptionally easy to share via social media? I can't find the buttons... oh... there are a couple darked out ones waaaay down in the bottom of the footer. Nobody is looking down there... put them up high were everyone will see them and get their mouse on them quickly.
-- Don't advertise an empty forum at the top of your site. Get some action in there. Have your guides post some conversation starters. Have them invite questions. Ask a few satisfied travellers to share their experience. Visitors are going to leave if they look in there now.
-- On your chat page get CENTRAL TIME right up there with the times of operation. People don't know if your chat team is in London, Tokyo or Peoria.
-- You say that your traffic is down year-over-year. Have you looked into analytics to see if your rankings have dropped, if your long tail has fallen, where was that lost traffic coming from. Just guessing, I think that you are losing it to competitors in your niche who are aggressively building best-on-the-web content that attracts lots of heavy links and scoops long tail traffic away from other websites. Also, even small websites in your niche are building pages with substantive content that are optimized for specific keywords like finely crafted arrows.
-- Finally, your destinations each had several pages of information and when I clicked from one to another they were slow to load and did not have a consistent look and feel. I recommend a seamless format and am wondering if the big juicy photo at the top is the way to go. They are great photos but they are pushing your content way down and are not consistent from page to page.... I wondered if I was still on the right part of the site.
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I know that I poked really hard at you in my reply. But in this niche you got to go for their throats because they are already reaching for yours.
Good luck.