Bluefin Tuna and the New Moon

Barb Block from the Shogun Expedition. The wind and seas came up a bit today as we searched around for baby bluefin tuna.

A small sport fishing boat from San Diego had reported catching a handful of the collectable-sized bluefin in waters just offshore so we worked the area all day long. We had a nice stop on a small school of albacore late in the day, but found no bluefin. We think that the weather may have pushed the fish down.

But it's the phase of the new moon and we now know, from the data retrieved from more than 180 satellite tags returned to us by anglers, that the bluefin are very responsive to the moon phases: they are up closer to the surface both day and night during the new moon. In fact, when they dive, they go down to the top of the thermocline -- that's the layer of water where the temperature rapidly decreases as you go deeper -- and spend most of the day foraging between the surface and the thermocline.

That's why we’re out right now. I think we have a higher chance of encounters with the bluefin during these new moon periods. I have high hopes for Friday the 13th. The photo is Stanford graduate student Dan Madigan on his first tuna fishing trip with the team. ABOARD THE F/V SHOGUN, Off San Diego, California.