A serious obstacle to critical examination of stratification and diurnal migration of plankton has been the lack of instruments that enable the biologist to ascertain accurately the depth of his collecting net at the time of opening, fishing and closing....
Boden, Brian P., Elizabeth M. Kampa, James M. Snodgrass, and Robert F. Devereux. 1955. "A depth telerecording unit for marine biology." Journal of Marine Research 14, (2). https://elischolar.library.yale.edu/journal_of_marine_research/832