Farm Findings: Seaweed Farms can be used for Marine Mammal Monitoring

Dolphins and porpoises are some of the most famous, and adored, marine creatures in the world. Besides being incredibly charismatic, they have an unparalleled ability to connect humans with the ocean. They fuel coastal tourism, get people of all ages out on the water, and are powerful ambassadors for conservation – reminding people that marine life can be social, intelligent and complex. 

We are lucky enough to have many populations of dolphins and porpoises (also referred to as “cetaceans”) in U.K. waters. Consequently, this means that we are sharing ocean resources and space with them. To be “good neighbours” to cetaceans it is crucial that we understand how they use marine areas to meet their needs. 

Through a trial study at Câr-y-Môr we found that seaweed farms are ideal locations to monitor marine mammals and, perhaps, to investigate how they respond to human activity. We deployed underwater microphones (called “hydrophones”) below different farm sites and left them to record for 2 months at a time in different seasons. This method of study is called passive acoustic monitoring – “passive” referring to our ability to leave the hydrophones recording with little oversight for long periods of time. 

The underwater recordings are then combed through for sounds made by cetaceans. The hydrophones we deployed at Câr-y-Môr have a companion computer program that automatically detects the “clicking” vocalisations dolphins and porpoises use to track down their prey. From the timing and quantity of these clicks we could estimate how long they stayed in an area, and, if they left, how long it took them to return. In the future, we may also be able to estimate how many individuals there were, and if they were hunting or socialising.

Action shot of the Acoustic Probe being deployed

Diagram showing the Acoustic Probe floating above the seabed, where it can detect cetacean clicks

Image of the Acoustic Probe after 2 months of recurring underwater

Even though the data we returned from this study was preliminary, it was exciting to see a record of cetacean activity around the seaweed farm.

Figure 1. The average residency time (left) and average return time (right) of cetaceans for each month of the study period.

Seaweed farms are ideal for this kind of work, as they are regularly monitored and often collect local data that can later be compared to cetacean activity. Weather conditions, current speeds, boat activity, and (through underwater video monitoring) even the presence of certain fish species are all useful things to know as we try to understand how dolphins and porpoises are using the area alongside humans.

Some of the farms participating in the Unlocking the Power of Seaweed project will be deploying hydrophones along with our SubCams and GrowProbes in the upcoming years, and we’re looking forward to integrating the data they collect into the bigger picture of seaweed farming and its environmental impacts.