Wednesday, October 27, 2010

Georges Bank Krill - Take 2

Gareth here. Today we sail on our second of two cruises to Georges Bank, where we will again be studying the large aggregations of krill that we saw on our last trip out there, and the interaction of these aggregations with higher predators. The reason for having two cruises is that the first one was timed so that it would fall immediately before the herring started to spawn. In early fall the herring mill around in these deep waters just off Georges where we saw so much krill last cruise. Herring are a dominant krill predator, but at that time of year their minds aren't on food as they're getting set to spawn in the shallower waters of Georges Bank. This means that in our first cruise we could study the krill in low predation conditions.

Dissecting a herring caught during our first Georges Bank cruise to see what was in its stomach (Photo: Peter Wiebe)

Our second cruise is timed to occur after the herring have mostly finished spawning (hopefully!). Once they spawn, the herring start to feed, munching down on all the krill found in this region. So during this next cruise we'll be studying the krill's behavior in high predation conditions. This is what we refer to as a 'natural experiment.' In a laboratory setting, it's easy to conduct experiments where conditions (tank temperature, for instance) are manipulated to produce different experimental treatments. In ocean-going fieldwork it's hard to do proper experiments (e.g., it's hard to manipulate the temperature of Georges Bank) and so we look for these natural experiments where conditions vary in a way that we can capitalize upon.

Map of Georges Bank and the Gulf of Maine (NOAA-USGS). The red rectangle shows the area where we worked on our last cruise, and where we'll be starting out again this time.
During this cruise we'll again be heading out to the northwestern flank of Georges Bank, where we'll again be deploying a number of different instruments to map the krill's distribution, including two kinds of echosounders (multi-frequency and broadband), a video system, and a plankton net, as well as observers to keep track of higher predators. Our science party is made up of an 8-person zooplankton team (Gareth Lawson, Peter Wiebe, Cindy Sellers, Phil Alatalo, Wu-Jung Lee, Nick Woods, and Nick Nidzieko from WHOI, Kaylyn Becker, recently of the Gulf of Maine Research Institute) and a 3-person top predator observing team (Reny Tyson from Duke, Kelly Kleister from the Whale and Dolphin Conservation Society, and Tim White from the City University of New York).

Stay tuned for more updates from the fogs of Georges Bank!

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