Scientists have a new ally helping them explore the ocean’s seabeds–sea lions. A team in Australia recruited endangered Australian sea lions (Neophoca cinerea) to carry video cameras down to this little explored region of the ocean. The videos helped the team identify some previously unmapped sea lion habitats in the benthic zone–or the lowest ecological zone in a body of water. The pinniped-assisted findings are described in a study published August 7 in the journal Frontiers in Marine Science.
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Deep dives
Our knowledge of the sandy and rocky bottom of the seas is quite patchy. Dives with remotely operated underwater vehicles (ROVs) like Alvin or Jason Jr. from Woods Hole Oceanographic Institution can be costly and logistically prohibitive. The vehicles are expensive and require certain weather conditions to dive. It is also simply difficult for humans to get to deep and remote offshore habitats even with high-tech submersibles.
“Using animal-borne video and movement data from a benthic predator is a really effective way of mapping diverse benthic habitats across large areas of the seabed,” Nathan Angelakis, a study co-author and PhD student with The University of Adelaide and the South Australian Research and Development Institute, said in a statement. “These data are useful both for mapping critical habitats for an endangered species such as the Australian sea lion, and more broadly, for mapping unexplored areas of the seabed.”
In the study, eight adult female Australian sea lions from the Olive Island and Seal Bay colonies were equipped with small and light-weight cameras. The team glued the cameras and tracking instruments on small pieces of neoprene–the material that most wetsuits are made of–that were then attached to the sea lions’ fur. In total, the filming and tracking equipment weighed less than 1 percent of the sea lions’ body weight. This prevented additional drag and allowed them to move without restriction. The sea lions took recordings over two to three days.
“We deployed the instruments on adult females so we could recover the equipment a few days later when they returned to land to nurse their pups,” said Angelakis. “We used satellite-linked GPS loggers on the sea lions, which meant we could track their position in real-time and knew when they had returned to the colony.”
How to predict a habitat
In total, the team gathered 89 hours of animal-borne video. The researchers identified six benthic habitats: macroalgae reef, macroalgae meadow, bare sand, sponge/sand, invertebrate reefs, and invertebrate boulders.
Back on dry land, the team used machine learning models to predict the large habitat areas across the continental shelf of southern Australia. They did this by incorporating data on oceanographic and environmental factors collected over 21 years into the models. These factors may be important drivers of the structure and distribution of these habitats.
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“The sea lions from both locations covered quite broad areas around the colonies. In our calculations, we kept the area in which we predicted habitats small to maximize the precision of our predictions,” Angelakis said. “This allowed us to model benthic habitats across more than 5,000 square km [1,930 square miles] of the continental shelf.”
Sea lion vision
The Sea lion cams also filmed different habitats than in some of the previously mapped regions of South Australia. The pinnipeds may not use or swim through certain habitats or have a preference for some areas over others. The researchers also point out that some of the regions may have been missed.
However, the footage still fills in some knowledge gaps about the seabeds, while providing critical information about endangered marine species. Marine populations declined by more than 60 percent over the past 40 years. This method can also be used to survey and assess other marine species of interest that the sea lions caught on camera.
According to the team, assessing a marine environment from a predator’s perspective instead of a human’s can improve our understanding of the benthic environment and develop a more complete map of the seabed.