By Dr. Jeff Drazen, Professor, University of Hawaiʻi at Mānoa
May 25, 2018
In most parks we visit, there are signs that make it clear you should NOT feed the wildlife. And for good reason, it habituates them to people, changes their normal behaviors, and squirrels and raccoons weren’t designed to live on Cheetos.
So you might be surprised that we are feeding the deep-sea wildlife in the middle of the Pacific Ocean. We use camera systems designed to sink to the seafloor, free of the ship, with a parcel of food (dead fish) in view. These baited cameras attract all sorts of fishes, large shrimp, and other animals right to where we want them. These are the top predators and scavengers of the deep and we are delivering a source of natural food right to them. Our cameras can be used to identify, count, and measure the animals attracted.
It’s fair to ask why we don’t use the remotely operated vehicle (ROV) to study top predators. We do, but ROVs provide an incomplete picture because the amount of large fishes and shrimps are low, so you might pilot the ROV along the seafloor for quite a while before ever seeing one. Also, the organisms are mobile, so they can move away from the noisy and brightly lit ROV before we have the chance to observe them. Fortunately, in a low-food environment such as the deep ocean, most top predators are scavengers, too. We feed them to lure them directly in front of our cameras. The platform we deploy the cameras on is quiet and we only turn on the lights and film every few minutes so disturbance to the animals is minimized.
Our goal is to find out which scavengers live in the vast Clarion-Clipperton Zone (CCZ), where manganese nodule mining is likely to occur in the next decade. The area is huge and it is likely that the community varies across the region and perhaps it includes species only found there. This matters because the mining activities will cover enormous areas. Mobile animals may be able to avoid the mining machines, but the habitat for fishes and other top predators may be destroyed. Several no-mining zones (called Areas of Particular Environmental Interest or APEIs) have been established in the CCZ by the International Seabed Authority to protect habitat and communities. We are surveying several of these areas to understand exactly what they are protecting.
So far, we have deployed our baited cameras to the seafloor in APEI 7, which is just north of the equator and at the western end of the CCZ. On the abyssal plain at ~4,800 meters, we found rattail fishes, a few large red shrimp, and white blunt-snouted cusk eels.
Rattail fish and white cusk eels on the abyssal plain in APEI 7 (4,800 meters depth). Video courtesy of the DeepCCZ expedition. Download (mp4, 3.4 MB).
We expected to find these animals as they appeared in the eastern end of the CCZ; however, we were amazed by the large numbers of rattails. This APEI is close to the equator where upwelling of nutrient-rich water creates very productive surface waters and ultimately a higher food supply to the deep seafloor. This could explain why this region has so many rattails.
We have also dropped our baited cameras to a seamount that stretches from the abyssal seafloor up to about 3,000 meters depth. This is still at abyssal depths, and some animals found on the plain might be found there also. However, our first deployment found a very different community of scavengers dominated by cutthroat eels that reached amazing numbers (perhaps as many as 50 visible at once – see the video below). We need to evaluate the generality of this finding and are waiting to recall our system from its latest seamount deployment.
A swarm of cutthroat eels on the top of a seamount in APEI 7 (3,200 meters depth). Video courtesy of the DeepCCZ expedition. Download (mp4, 7.9 MB).
Top predators, feeding on diverse prey in the food web, often are affected by the sum of all types of natural and anthropogenic (human-caused) changes to the environment. Thus, changes in the numbers or behavior of polar bears in the Artic or spotted owls in the forests of the Pacific Northwest have been bellwethers for ecosystem health across whole regions. By feeding the wildlife (natural food and in small amounts), we are learning a great deal about the communities of top predators in the CCZ before mining occurs. Perhaps these top predators will help us understand ecosystem health in the APEIs and across the CCZ.
