Eavesdropping on dolphins

Please welcome my next science+comics interview victim, Alexis!

Name: Alexis Rudd
Job: PhD student in Zoology at the University of Hawaii
Research: Alexis uses passive acoustic monitoring to study whales and dolphins off Hawaii

News Flash!! Whales and dolphins, a.k.a. cetaceans, hang out near the Hawaiian Islands! Okay, not a news flash at all, everyone knows that. But you may be surprised to learn that we don’t actually know much about them – what they’re doing, where they’re going, and why – especially once you get out to the deeper rougher waters further from shore. So why is it important to know about their hangout spots and behaviors? It’s because that kind of information can help us design and implement effective management and conservation strategies. Yes, cetaceans hang out near Hawaii, and we want to keep it that way!

Here’s the thing. Whales and dolphins (and loads of other animals) like to spend time where food is available. In the ocean, the big driver behind food abundance is primary productivity – phytoplankton, or plants that live in the sunlit upper layers of the ocean. And just like on land, different places in the ocean are more productive than others: some places are lush and green with plants and all the life they support, and other places are sort of like deserts – yes, animals live there, but it’s on a whole different scale. Here’s an image of productivity (actually, it’s an indicator of productivity – chlorophyll concentration, which satellites pick up by its color).

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This picture shows green where there is a lot of productivity, and blue where there’s not much. So the deepest blues show where the ocean “deserts” are. The green places tend to be where nutrients are available – things like nitrogen and phosphate (yup, same stuff that’s in fertilizers for your garden), which might run off the land, or be brought up to the surface in upwelling zones.

But – not to worry! – it’s not exactly a dead zone around Hawaii. It just means that cetaceans might need to look for an oasis sometimes. One theory is that cold, nutrient-rich water gets pulled to the surface by cyclonic (counter-clockwise) eddies, triggering a cascade of activity up the food web – a very enticing fish/squid/zooplankton buffet indeed.

To address these kinds of theories, Alexis needs to figure out whether cetaceans are indeed seeking out certain environmental and oceanographic conditions. Often, studying cetaceans means getting on a boat and looking for them visually. This works reasonably well in calm waters, but it gets pretty tough to pick out a dolphin or a whale when the water is choppy. The prevailing winds are westerlies, and they come sweeping across the Pacific from California. Calm zones form on the leeward side of the islands, but the wind speeds up as it squeezes through the gaps, creating regions of high wind and rough seas.

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Instead of looking for cetaceans visually, Alexis listens for the sounds they make. And here’s where the super creative part of her research comes in: she tags along on a tugboat that brings supplies to the different islands. Being the persistent scientist that she is, Alexis went out every two weeks for a year and a half, installing her underwater recording package (hydrophone) on the barge behind the tugboat. This setup was ideal in a lot of ways: first of all, people need their supplies all year round, so this vessel does regular trips. Second, having the hydrophone on a barge – separated from the loud tug engines – makes it easier to pick out cetacean sounds. Here’s what the basic setup looks like:

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As the tugboat moves from island to island, it provides a great acoustic “view” of a very large area – the calm leeward side of the islands and also the windier regions between the islands. So Alexis is able to get a great “big-picture” idea of what’s going on.

She’s now collected hundreds of hours (!!) of recordings, and is going through the process of checking and documenting all of the identifiable cetacean calls. She links each call up to the location where the barge was at that time so that she can gather up all the data at the end and figure out whether there are correlations between the animals’ presence and environmental or oceanographic conditions.

Alexis has an excellent and very informative blog, and I encourage you to head on over and check it out: http://bioacoustics.blogspot.com/

She also did a guest blog post over at Scientific American Blogs, where she talks about the experience of partnering with commercial shipping to do her research: Towing my weight: partnering with commercial shipping for whale and dolphin research.

By the way, this is how an ocean themed interview should be conducted:

pirate_interview

… with pirate hats all around.

Krill and other zooplankton … and sequential hermaphroditism.

Have I mentioned this before? Fin whales love to eat krill. It’s a huge part of their diet (along with other types of zooplankton, small schooling fish, and sometimes a squid or two). Since zooplankton are so important to my animal of study, I’m taking a course on marine zooplankton ecology. Understanding more about them will help me understand more about fin whales!

It’s the second week of class, and we’re already giving presentations – phew! Luckily they are fun – we were encouraged to be creative, sing songs, write haikus – so long as we included the actual science in there somewhere. Here’s mine…

People gave really great talks today – one fact in particular that I found fascinating was that there are several types of animals (zooplankton and fish, at least) who are not only hermaphroditic (crazy in itself!) but that belong to a category of hermaphrodite that is sequential – they start off life as either male or female, and then at some point they switch genders. Amazing! (here’s the wikipedia page describing sequential hermaphoroditism)

Seafloor geodesy and whales

School is totally kicking my butt this week.  Oh, finals week.  I cannot wait for Friday!

Despite the stressful aspect, watching other people’s presentations for my two classes has been really neat.  It makes me realize that I’m going to school with a lot of smarty pants.  Seafloor geodesy!  Seismic reflection and refraction!  Ice crystals, avalanches, glaciers, liquefaction, episodic tremor and slip…

Molly Moon’s and more inverse theory

It was a long day, lots of code writing.  But it was fun, because I was working on an interesting inverse problem.  Probably not that interesting to people who know lots about inverse theory, but it’s new to me, so still very cool.  Since I’m not great at writing efficient code, it was a long 6 hours before I could see any results.  But in the end I got a really pretty picture that might tell me something about using earthquake positioning techniques to locate a whale far outside a seismic network.  Well, about 15 km outside a network that covers roughly 5km x 10km of seafloor in 2km water depth.  So pretty far.

And yes.  I am a day behind in my little drawings.  At some point I will surely skip a day.  But I’m trying to keep up for as long as I can.

Oh… what’s that you say?  You want to see the results of yesterday’s work?  Alright!  It might not make sense, and there is always a chance it’s just outright incorrect.  But at the very least, those are some dramatic colors, no?  I had to scale the color values though – basically the colors are in a log scale.  So where it says 10, it actually means 10^{10}, an 8 means 10^{8}, and so on.  So yeah, those position errors way outside the network are huge.  HUGE.