Sampling Nets

1. Trawls of one form or another have been used in oceanographic research since humans first began to study the diversity of life in the oceans. In general, they are essentially large nets, akin to those used by fishermen. Today, trawls can take a wide variety of forms depending on what types of organisms are of most interest. The type of trawl used to study large shoals of adult cod, for example, is very different from that used to collect small planktonic larval cod. There are both benthic (acting much like a big skimmer along the surface of the ocean floor) as well as pelagic (down to depths as great as 3000 meters) trawls. Some trawls, such as the MOCNESS ( ) used for plankton tows, can be made to sample at different depths in series in order to study the movement of organisms up and down in the water column. Though different trawls can be extremely useful in the study of marine biodiversity, they have their limitations. Many animals have been shown to be very good at avoiding capture in trawls and other species can be easily damaged or destroyed (especially those from great depths and those that are soft-bodied, such as jellyfish) in the process. Therefore, trawls are often combined with other research tools such as VPRs, acoustics, and larger imaging equipment to optimize the data gathered. Trawls have proven themselves to be a mainstay of marine research; CoML projects use them extensively.
   
   
2. Plankton Nets, a modification on the standard trawl design, are used to quantitatively collect planktonic organisms of nearly any size, intact. Towed by a research vessel, plankton nets generally have a very long funnel shape to them that can catch a huge amount of differently sized plankton simply by changing the mesh size of the net. At the end of the funnel is a collection cylinder called a cod-end that catches all the organisms. The large amount of very small organisms caught by a plankton net can keep even a very experienced scientist busy for hours.
   
   
3. Epibenthic Sledges are instruments for collecting organisms, essentially combining a trawl and a benthic grab into one. An epibenthic sledge consists of a rectangular steel frame with a mesh net (often more than one) attached to it. This device is towed along the ocean floor, its weight scraping into the benthos collecting any organisms that live in or on the sediment as well as any in the water column just above the benthos. A video camera is often attached to the net to have an associated image. Epibenthic sledges are very good for collecting relatively mobile (but not fast swimming) animals and other benthic organisms, but can cause some injury to more delicate organisms.
   
   
4. Cod-end Aquarium is a very highly modified version of a trawl that allows for the intact, live, capture of large zooplankton and fish from great depths. It is essentially a trawl net with a large compartment at the end that can seal off at different depths, capturing the collected organisms within, and keeping them secured in the pressurized aquarium-like container. This overcomes much of the shortfalls of traditional collection techniques of deep-sea organisms, especially due to damage and destruction due to rough handling in nets and the massive pressure change from the deep. Being able to collect a live and healthy specimen for observation is a tremendous benefit to science.