Nikki Durkan: The sound of…fishes! June 17, 2015

NOAA Teacher at Sea
Nikki Durkan
Aboard NOAA Ship Oscar Dyson
June 11 – 30, 2015

Mission: Midwater Assessment Conservation Survey
Geographical area of cruise: Gulf of Alaska
Date: Wednesday, June 17, 2015

Weather Data from the Bridge:
Wind speed (knots):  13.47
Sea Temp (deg C):  8.55
Air Temp (deg C):  9

Science and Technology Log

The sound of fishes.

What are we doing here off the coast of the Aleutian Islands? Listening…sort of.  We are collecting data used to estimate biomass (total amount of living matter in a given habitat) and to project population estimates for the Walleye Pollock Gadus chalcogrammus fishery.

Transects we fish are the lines somewhat perpendicular to the islands.

Transects we fish are perpendicular to the islands.

How do we do this? In order to understand the instruments we are utilizing, I’ll attempt a simple but not completely accurate analogy: if I bounce a basketball on a cement driveway – it could bounce back with enough energy to hit me in the face (I’m not saying this has happened to me); however, if instead, I bounce the ball down onto a grassy lawn, the ball will barely bounce back up.   Different materials reflect energy back with different frequencies and the picture this information translates to on a computer monitor is called an echogram:

Red - seafloor Bluish dots above - fishes!

Red – seafloor
Bluish dots above – fishes!

The Oscar Dyson has several scientific echosounders (EK60, EK80, and ME70) with transducers attached to our hull that send out energy at various frequencies. As we travel along the transects (mostly perpendicular to the island chain) we are collecting these acoustic data. The fish species produce a different pattern on the echogram and the swimbladder (full of air) makes them show up clearly; scientists have been studying the Walleye Pollock for a while now and have a pretty good idea of what Walleye Pollock “look” like on an echogram.  Sometimes the scientists observe an echogram that they are not certain about or want to verify characteristics such as length, weight, and age for an area – this means we get to fish!


Me learning to measure the length of a Pollock.  Photo Credit:  Patrick Ressler

Me learning to measure the length of a ~3 yr Pollock. Photo Credit: Patrick Ressler

Personal Log

The process began with a bit of dancing to Macklemore and Gangnam Style (thanks, Alyssa Pourmonir for providing the playlist!).  Music makes every task more enjoyable! I learned how to sex a fish and cut its skull open to pull out the otoliths (calcium carbonate structures located behind the brain that can be used to estimate age and growth rate) – more on this process to come! Given that I spent the majority of my childhood as a vegetarian and maintained aspirations of becoming a veterinarian and saving the lives of animals, today was a gigantic step in another direction. I could not help but feel remorse as I sliced into the bellies of the fish and splayed them open to reveal the ovaries or testis.  As a newbie, I was quite a bit slower than my coworkers, but after about 30 fish, I started to hesitate less often and verify the gonads more quickly. If any of you have spent time fishing with me, you’ll know that I enjoy the chase, but avoid handling the fish once they are on board, I’ve even been known to utter an impulsive “uh oh” when I catch a fish. I am pretty sure that after this trip, I’ll be comfortable filleting…no guarantees on my casting skills.

We unintentionally caught a salmon shark but the crew was able to return it safely!

We unintentionally caught a salmon shark but the crew was able to return it to the ocean safely!

Did you know?  Killer whales are the most widely distributed marine mammal and live in matriarchal societies.  I’ve been enjoying watching these whales from the bridge!


Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s