HUMPACS West

Europa's NOT Drunk!

You may have noticed that Europa has been bouncing around a bit more than it did on HUMPACS East. Well don’t worry…it’s intentional!

The general path that Europa is following goes along 20oN latitude.

The reason that it is not going in a straight line is because there are numerous seamounts and guyots (aka tablemounts) that we are having it navigate over on it’s way to the Mariana Trench.

Seamounts are basically underwater mountains that are at least 1,000m tall. They do not actually reach the ocean’s surface. Guyots are seamounts that did, at one time, rise above the ocean’s surface, but then eroded away, flattened out, and eventually sunk back down underwater.

Why does all of this matter?

Well, since Europa is basically a very small fish in a very big pond, we need to strategically look for these humpback whales. Even though most of the time the tops of these seamounts and guyots can be found many hundreds, if not thousands, of meters below the ocean’s surface, they are actually great producers of marine ecosystems. That makes us think that we might have a better shot at stumbling upon some humpbacks in those areas, as opposed to simply out in the middle of an even deeper ocean.

There has been some research to support the statement that humpbacks seem to frequent seamounts and guyots, though the exact reason why hasn’t been determined.

The leading theories are that the landmarks serve as resting and/or feeding areas, points for navigation, and even meeting grounds (source: PubMed Central®).

Maybe they’re sharing different versions of their song? At the end of the day, we don’t really know why…yet!

If you’d like to dive a little deeper into the science and evolution of a seamount, check out our blog post Mountains in the Deep Sea.

Figure 1: Europa’s path on a nautical chart. Europa is currently traveling from East to West, and navigating over many different seamounts and guyots. (Depths are in meters).

Figure 1: Europa’s path on a nautical chart. Europa is currently traveling from East to West, and navigating over many different seamounts and guyots. (Depths are in meters).

 
Figure 2: Zoomed in image to show more detailed depths of the Horizon Tablemount that Europa traveled over Jan 16-19, 2019.

Figure 2: Zoomed in image to show more detailed depths of the Horizon Tablemount that Europa traveled over Jan 16-19, 2019.

Figure 3: Europa circling a particular seamount. We will have Europa do this from time to time to search a little more for humpbacks in areas we suspect them to be.

Figure 3: Europa circling a particular seamount. We will have Europa do this from time to time to search a little more for humpbacks in areas we suspect them to be.

If you check out the HUMPACS page, you’ll notice that from January 16-19 Europa was cruising over the Horizon Tablemount. In another two or three weeks, Europa should be traveling around the HIG Guyot. This particular guyot is of note to us here in Hawaii because it was actually discovered about 37 years ago by the “Kana Keoki” research vessel, and named after the Hawaiian Institute of Geophysics (source: Marineregions.org).

So, for those of you that were wondering, and dare we say concerned, about Europa’s up and down path…worry no more! Europa is doing exactly what we want it to do, and we’re collecting lots of great data that we look forward to sharing later on.

Until then, keep checking in and watching Europa as it makes it’s way West across the Pacific Ocean.

Also, check out our live audio stream of the humpback whales that are swimming around Puako, HI right now!

Aloha!



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Can You Hear Me Now?

When we were preparing for the first leg of HUMPACS, referred to as HUMPACS East, we found ourselves faced with a tough decision when it came to how the hydrophone should be mounted.

“Do we hang the hydrophone, or try to hard mount it as close to the sub as possible?”

When doing hydrophone operations just outside of Puako, Hawaii, we have found that you get the best audio if you hang the hydrophone at least 30 feet below the sub. This, obviously, is due to the fact that we’re basically decoupling the hydrophone from the sub. We also are able to pick up more sounds when we’re deeper.

Hearing that, you might wonder why we decided to hard mount the hydrophone during HUMPACS East.

Well, what we have also learned through years of experience monitoring the gliders off the coast of the Big Island is that when we have a hydrophone hanging, ocean currents become a much larger problem.

There are different currents at different depths, and so even though the glider (float, sub and hydrophone) are all relatively in vertical alignment, each part of them is getting pushed and pulled by a different current.

In Hawaii, it’s not that big of a deal for us because we keep the gliders in a relatively small area the majority of the time, and we can go rescue the glider if we really need to.

When sending it across the Pacific Ocean, it’s a different story. There are no rescue missions. It just has to work!

For that reason, we decided to keep the hydrophone hard mounted directly to the sub, with no separation or “acoustic isolation”. We knew that the background noise (flow noise, wing springs and rudder) would be very loud. However, we confirmed that even with all this loud background noise we would be able to detect humpback whales, as we did a proof of concept with humpbacks singing off Puako before sending it east. All this was worth it to know that the hydrophone would be very safe. After all, we’d never made this trek before, (no one had for that matter), so we didn’t know what kind of abuse it might encounter. Sharks, rubbish, wear and tear, getting tangled up by the umbilical. These were all big concerns, and, at the time, we needed to play it as safe as possible.

HUMPACS East  Copper Hydrophone Mount

HUMPACS East

Copper Hydrophone Mount

All these concerns continued to stand true with HUMPACS West. We still agreed that the unknowns about drifting were too much of a risk, so we mounted it close, but not hard mounted.

Since we did not encounter any drift that could have entangled the hydrophone, nor any shark bites, for HUMPACS West, we decided to see what the minimum distance was that we could drop the hydrophone and achieve higher quality audio. We still needed to keep the hydrophone safe, but we wanted more vibration isolation between the sub and the hydrophone itself.

After testing many different materials and changing up the distance of which we dropped the hydrophone below the sub we came to the conclusion that a three inch drop using EPDM Fiberglass Reinforced rubber sheets to mount was the way to go. It improved our audio and also kept the hydrophone safe at the same time. As an additional safety measure, we added a deflector bar to the bottom of the sub to help prevent shark bites and entanglement on the hydrophone.

HUMPACS West  EPDM Fiberglass Reinforced Hydrophone Mount

HUMPACS West

EPDM Fiberglass Reinforced Hydrophone Mount

Take a look at the two spectrograms below and see the difference in noise levels. HUMPACS West is exponentially more quiet than HUMPACS East. There is also almost a complete elimination of the 650Hz and 975Hz harmonics from the rudder module. This, alone, is a very improved piece of the puzzle, as the primary range that we listen and view the humpbacks’ song is in that <1KHz range.

HUMPACS West Spectrogram

HUMPACS West Spectrogram

HUMPACS East Spectrogram

HUMPACS East Spectrogram

As you can see, HUMPACS West is much more quiet as far as background noise goes. What’s that do for us? Well, if the background noise is less, then it becomes substantially easier to detect humpback whales (and other species). This improvement should greatly improve our post processing efforts, and is more efficient at detecting as many humpbacks as possible.

Currently, Europa is a little over 700nm (nautical miles) west of the Big Island of Hawaii. Follow its journey on the HUMPACS page!

Aloha!


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We're Back!

Europa is back in the water on her second mission to listen for humpback whales, just in time for the Holidays. Last year, Europa successfully completed the East Leg (from Hawaii to the Baja California Seamount Province and back), and now she will swim to the Mariana Trench and back (the West Leg). Biologists have wondered if there is an undiscovered distribution of humpback whales among the seamounts between these areas. Since the East Leg was successful, we hope Europa’s journey west will be triumphant. You can track Europa’s path on our website. Stay tuned for more updates!

Wishing you a Happy Holiday and a Joyful New Year!


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