Hi Sol! This seems like an awesome project! I have a few questions in response: Where were you thinking of deploying this payload and for how long? 

Regarding hydromoth recorders, there have been several concerns that have popped up in my work with deploying the them at this depth because it's a contact type hydrophone which means it utilizes the case to transmit the sound vibrations of the marine soundscape to the microphone unlike the piezo element based hydrophones. 

• At 30-60m you will likely have the case leak after an extended period of time if not immediately. The O-ring will deform at this depth, especially around the hinge of the housing. The square prism shape is not ideal for deep deployments you describe.  
• After that depth and really starting at about 50m, a major concern is synthetic implosion from the small air pocket of the hydromoth not having a pressure release valve and lithium ion batteries getting exposed to salt water. This type of reaction would cause your other instruments to probably break or fail as well. 
• You are unlikely to get a signal with a reinforced enclosure. The signal is generated via the material and geometry of the housing. The plastic will probably deform and mess with your frequency response and sound to noise ratio. If you place it against metal, it will dampen the sound quite a lot. We tried to do this, but the sensitivity is quite low with a large amount of self noise. 

• A side not: for biodiversity assessments, the hydromoth is not characterized and is highly directional, so you wouldn't be able to compare sites through your standard aocustic indices like ACI and SPL.  

  That said if you are deploying for a short time, a hydrophone like an Aquarian H1a attached through a penetrator of a blue robotics housing that contains a field recorder like a zoom recorder may be optimal for half a day and be relatively cheaper than some of the other options. You could also add another battery pack in parrallel for a longer duration. 

   

Congrats @MattyD797 and team!!! We do a lot of work in the underwater bioacoustic realm and your tool certainly seems like it would be a great instrumental addition to the community. Look forward to learning more about your project!

Liz

Hello Nadia,

A forensic genetic challenge  exists when DNA is destroyed by processes used in manufacturing of derivative animal products, preventing law enforcement in identification of protected species.  Alternative methods such as lipid profiles or isotope analysis unique to certain species may be possible but require voucher specimens that may or may not be available and methods that have not been tested or peer reviewed. Examples below:

1. derivative products made from endangered shark squalene (eg. Liver oil capsules).
2. derivative products made from lion bone and tiger bone (eg. lion bone cake and tiger wine).
   
   This is a law enforcement issue and would like to discuss possible solutions. 

Hi Sol,

I think your concern is well placed.  The pros typically tow an array of hydrophones, in its simpler configuration it looks like a long fat rubber hose containing maybe a dozen transducers feeding their electrical signals to a recording unit back on the ship.  All this is done to reduce noise from the ship, from waves crashing, and flow noise.  The multiple transducers can also be electronically tuned to be directional so that it can be "pointed" away from a noise source (like the ship).

In your position, I would just try the simplest thing that could work, then fix the problems as they arise.  It could be you may need to be dead in the water while recording.  To address surface noise (slapping waves, wind), you could mount the hydromoth low down on a spar buoy, which you tow into position.

Best of luck, it sounds like an interesting project (c:

Hydromoths are great for the price but they do not have the most streamlined housing and audio quality won't be as good as something like a SoundTrap or really any recorder with a proper hydrophone and 16-bit +DAQ system.

If you can afford it, this is an excellent SoundTrap based towed autonomous system NOAA have been using. It might work towed behind an autonomous vehicle

Alternatively, if you can have something inside the vehicle, a simple tape recorder (e.g. Tascam DR40X) and hydrophone on cable  will provide excellent sound quality. You could also use something like a Raspberry Pi with audio focussed ADC hat to record but that would require a bit more programming. Even consider a standard AudioMoth and plug a proper hydrophone into the audio jack - this would still have a 12-bit ADC but would provide better sound quality than a hydromoth (hydrophones are more omnidirectional and there's no air filled causing reflections and attenuation)

Hi Karima - Are you looking for volunteers in specific regions or fisheries?