Nansen’s reversing bottle Nansen bottles, invented by the Norwegian oceanographer Fridtjof Nansen, are cylindrical containers that sample sea temperature and salinity. The bottle, more precisely a metal or plastic cylinder, is lowered on a cable into the ocean, and when it has reached the required depth, a brass weight called a "messenger" is dropped down the cable. When the weight reaches the bottle, the impact tips the bottle upside down and trips a spring-loaded valve at the end, trapping the water sample inside. The bottle and sample are then retrieved by hauling in the cable.
Peterson’s grab Device is used by aquatic and marine biologists. Since 1930 the Petersen grab has been used in fresh water for collecting macroscopic fauna in sand, gravel, marl, clay or clay combinations. If used in salt water, it must be painted for protection. Since it has been widely used over 6 decades, it is ideal for comparing samples with data collected previously by a Petersen grab. Vent holes permit water to flow through while the grab is being lowered, minimizing diagonal movement as well as reducing the frontal shock wave generated by descent. Jaws close clamshell fashion
Dredges Similar to a beam trawl, a dredge consists of a rugged triangular steel frame and tooth-bearing bar, behind which a mat of linked steel rings is secured. A heavy netting cover joins the sides and back of this mat to form a bag in which the catch is retained. Shellfish are raked out of sand or gravel and swept into the bag. Several dredges are towed together from a tow bar and larger vessels generally tow two bars, one from each side of the vessel. In suction dredges and hydraulic dredges, water is shot into sediments and displaced shellfish are collected in a mesh bag (hydraulic) or sucked to the surface through a pipe (suction).
Scallop Dredge Scallop dredging involves using a dredge that consists of a metal frame with spring-loaded teeth to which a chain-mesh bag is attached. The dredge is towed over seabed habitats, where the teeth rake the seabed disturbing the scallops. This gear is extremely robust and can be used over much harder grounds than traditional trawls. As a consequence, scallop dredges can severely damage other seabed organisms and habitats.
Clamshell bucket dredge The clamshell bucket dredge, also known as the grab dredge, is the most commonly used mechanical dredge. the world over. This dredge may consist simply of a crane mounted on a spud barge, although most bucket dredges have a crane/barge system specifically designed and constructed for dredging. A bucket dredge is operated similarly to a land-based crane and bucket. The crane operator drops the bucket through the water column, allowing it to sink into the sediment on contact. The loaded bucket is then lifted, causing the jaws to close, and raised through the water column. Once above the water surface, the operator swings the bucket over the receiving container (usually a barge) and lowers the bucket to release its load. The bucket dredge usually leaves an irregular, cratered sediment surface (Herbich and Brahme 1991).
Other dredges Dredge and power shovel : Dredges There are two types of dredge: the mechanically operated and hydraulically operated. Mechanical dredges, which are similar to land-based excavating machines, were the first to be developed and can be classified as dipper, grapple, or ladder dredges.