Doubt and success all in the same day!

Having been a fishery scientist for almost 25 years, I've gotten used to the fact that the job can present highs and lows in the same day. Like with all jobs, sometimes things go well & sometimes not. This, to me, is the very definition of life. It all must be taken in stride.

A few things about yesterday's 1st field effort needed to be discussed so today Jean, Jean-Christophe, Orlane & I met after lunch. One problem we discussed is that our 63 micron mesh net seemingly caught no daphnia or bythotrephes, both comparatively large-bodied zooplankton. Why? Was it because few were available to be caught or did they somehow avoid the small mesh net? We decided that next time we will also collect zooplankton with a 200 micron mesh net so we can compare results. Also, we generally caught few larvae, and by the time we measured them in the afternoon, they were in poor shape. We decided that we were trawling at the same speed as past studies, and that maybe keeping the fish cooler may keep them alive longer so we can get better estimates of their length. We decided to revisit these issues after our second sampling event, scheduled for Thursday.

Before I came to France, I made a trip to Cornell Biological Field Station to visit Dr. Lars Rudstam & his student Toby Holda. They have been working on methods for masking fish from Mysis so that scattering from fish does not lead to a bias (overestimation) of Mysis biomass. Toby provided me some of his computer files & data, and I've been studying their method so I can reproduce it. Understand I respect Lars & Toby immensely! Copying is, after all, the greatest form of flattery.

Here I show four echograms collected with 70 kHz.  In the top, I've shown data > -85 decibels (dB). One can see small pelagic fish on the right-hand side. The second panel from the top is the same data, but shown at > -125 dB so it includes scattering from small-bodied organisms. In the third panel we mask out the fish and bottom (see black). In the bottom panel, we borrow data from near the fish (but with no fish) to fill in the space in the echogram occupied by the fish. And just like magic, the fish scientist has removed the fish.  It is good to close out the day on a high note!