Shipping stocks are going up -- but what's holding them up? Image source: Getty Images.

What happened

Shipping stocks are going haywire. Yesterday, shares of dry bulk shipper DryShips (DRYS) jumped 70%. They're still locked as of 11 a.m. EST (but expected to jump as soon as trading resumes). Meanwhile, as of 11 a.m., shares of Seanergy Maritime Holdings (SHIP -1.06%) have already leapt 61.5%, and Eagle Bulk Shipping (EGLE -0.64%) -- already a strong gainer -- tacked on 13.1%.

Tiny Globus Maritime Ltd (GLBS -0.45%) saw its shares more than triple overnight, up more than 240%!

So what

At first glance, all of this kind of makes sense. After all, ever since Donald Trump became president-elect, the Baltic Dry Index (BDI) -- which reflects relative pricing strength that dry bulk shippers are able to charge for shipping goods across the ocean -- has been climbing. At today's new high of 1,084, it's up 19% from pre-election levels.

Indeed, the BDI was climbing even before Trump won the election, and has gained 30% over the past two weeks. So even if you count yourself among the Trump skeptics and entertain doubts about the man's ability to grow the economy, shipping rates were rising even when we were all expecting another Clinton administration -- and that's great news for shippers like DryShips, Seanergy, Eagle Bulk, and Globus Maritime.

Now what

All this being said, there's more than just excitement over good news going on here. In fact, I'd venture to say that some investors may be veering into irrational-exuberance territory. Case in point: One of the strongest gainers today was Diana Containerships (PSHG -3.09%), up 250%. As you may have guessed from the name, Diana Containerships doesn't do dry bulk shipping at all. (It ships, well, containers).

Such good news on the BDI may justify price jumps in the stocks of DryShips, Eagle Bulk, and all the others -- but it shouldn't affect the fortunes of Diana Containerships stock. Rather, that stock should track the numbers on a more appropriate scorecard, such as the Ningbo Containerised Freight Index. And what do we find on the Ningbo? Shipping rates are still down across the board -- down 6.3% over the past week for China-Europe routes, down as much as 5% to the Mediterranean, and down more than 20% on Mideast shipments!

So what does this mean for investors? Logical as the recent stock-price spikes may appear at first glance, given the gains on the BDI, these spikes are completely out of proportion to the gains on the dry bulk shipping index itself -- and momentum plays like this one can unwind as rapidly as they form. Exuberance is beginning to bleed over into sectors having little or nothing to do with the catalyst that sparked the rally in the first place, and this gives us additional reason for caution.

Caveat investor. Exciting as the ride has been so far, it may not end well.