Researchers from multiple consortia within the Gulf of Mexico Research Initiative (GoMRI) have proposed a new approach for monitoring the populations of whales and dolphin that live in the offshore waters of the Gulf. The new program would be based on using a network of underwater recorders to listen for the sounds they produce and then turning sound detections into population numbers using advanced, newly-developed analytical methods.
The current best method for monitoring offshore populations is to count animals at the surface from ships or airplanes. While this is effective, it is expensive because the Gulf is big, the animals are at low density and they only spend a fraction of their time at the surface – so it takes a lot of effort to get a big enough sample size. Using sound makes sense for many species because sound travels very well underwater (much better than in air) while light does not, so whales and dolphins have evolved to use sounds to communicate with each other and find food (through echolocation). The sounds they produce can readily be picked up on underwater microphones deployed on recording units that can be deployed from ships. These units sink to the bottom, record sounds for several months and then return to the surface on command for servicing and replacement. After processing, the recorded sounds can be turned into an estimate of population size for each species. Lots of other information has to go into these calculations, but the researchers think that it will still be more effective to monitor this way, at least for some species, than through the surface-counting method.
The proposal for a new monitoring program arose from a GoMRI synthesis workshop on “Marine Mammal Population Modeling and Monitoring” held Oct 31-Nov 2 2018 in Washington DC. The workshop brought together researchers from four consortia to pool their findings and discuss new directions. The passive acoustic monitoring proposal is contained in a “white paper” (short research document) published this week, which was authored by all participants, led by Len Thomas from the CARMMHA consortium and David Mellinger from LADC-GEMM. Len said “I’m really excited about the potential for this new program, if we can find a way to take it forward. Passive acoustic population monitoring is a really new field, with lots of potential for getting good population numbers for hard-to-survey species like sperm whales, beaked whales and Brydes whales. Some studies have already taken place in the Gulf and so we can build on them. The next step is to form a working group to come up with a concrete survey design, and so some pilot studies. Hopefully, in a few years, we’ll be in a much better position to be able to say what is happening to our whale and dolphin populations over time, and throughout the Gulf.”