Measuring the population size of animals that live so deep in the ocean provides many challenges. Various techniques are used in our research. Traditionally trawl surveys have provided estimates of the health of populations. This involves randomly trawling a net along the bottom within an area in which the species are known to occur. The results of this are used as a representative sample of the fish populations and multiplied up to provide an estimate of the overall population.
More recent techniques involve the use of acoustic technology.
Sound waves are emitted by a towed acoustic transmitter. These waves travel down through the water column and bounce back off any fish or other animals within the beam. A large school makes a large echo of sound to the acoustic receiver. It's fascinating to observe the behaviour of many of the fish, how far off the bottom they are and at what angle they are swimming. It has been a real privilege to see some of these deepwater fish and associated benthic animals.