Expedition to Tierra del Fuego – January 30, 2003
After a brief team meeting Carmen, Alexandra, Olivia and Humphrey held an impromptu discussion on sampling invertebrate populations on Bahia Lomas (mussels, clams and marine worms). Carmen’s project will be the first systematic survey of marine invertebrates of the bay and the southermost on the continent. The study will have two main goals. The first is to determine what species occur in the bay and in what concentrations, and second to determine what species of invertebrates red knots and hudsonian godwit feed upon.
It’s a messy business sampling invertebrates. The team slogged through the intertidal mud, collecting samples along a 2 km transect even while an approaching cold front lumbered into our area with a light cold drizzle. They discovered clams and worms living in an amazing variety of habitats spread throughout what appears to most observers as one homogenous tidal flat. The two main areas are defined by spring and neap tides
The moon creates the ocean’s tides, but here on the bay it not only causes the twice daily cycle known to all but an extraordinary monthly cycle as well. The full moon tide, or spring tide, can increase the normal tide of 8 meters (26 feet) to 10.5 m (33 ft) all within a few days. These highest high tides, which occur on every full and new moon, flood hundreds of square kilometers of mud 6-8 days each month. The absence of slope means the advancing tide inundates areas not normally flooded. These infrequently inundated flats are much different than those flooded by the normal twice-daily tide. On their first day Carmen’s team found the latter was sandy with abundant clams, the former muddy with abundant worms. For shorebirds this means that white rumped sandpipers and godwits prefer the mud and red knots the sand. It also means that the infrequently flooded areas make good roosting sites until the spring tide floods the mud flat and forces them into inland areas.
Later in the day we fought a 30-knot wind sweeping the tidal flats to erect 20 mist nets in these roosting sites. With the tide still far below that of last year (9.1 m as compared to 10.5 m) we cannot expect any decent opportunities to cannon net for a few days, if at all. Instead, we set several lines of mist nets. Capturing birds in mist nets requireds dark and calm so their use is limited to those nights of calm winds, no moon and high tide, a rare event in Bahia Lomas. At least we can avoid the solar radiation from the massive hole in the atmosphere above us.
We set the nets in two lines extended out onto the mudflat perpendicular to the shore in an area where the high tide would flood under the net but not touch the bottom of the net. Shorebirds will only fly over water so the nets must be set in advance of the tide. Tonight we’ll give it a try if the wind subsides.
Larry Niles 2/1/03