The Challenge of Observing Behavior in the Deep Green

Observing animal behavior underwater presents several challenges not faced by those in the terrestrial world.  For bird-watchers, all you really need is patience and a good set of binoculars. Any decent sized sea cliff in the UK will attract a horde of twitchers, cameras and lenses at the ready, who can blissfully watch birds taking off, landing, feeding their chicks, and arguing over nesting spots.  Similarly, back-garden bird watchers may have to contend with shyer species more likely to take off when noticed, but a diversity of feeders and nest sites (and an absence of cats) can reliably guarantee that some bird behavior will be seen.

Underwater, the biggest challenge is time... depending upon your equipment and depth you may have anything between ten minutes and two hours to observe as much as you can.  Finding fish or other sea life that are doing anything interesting (e.g., not simply swimming or resting) becomes a race against time with your air supply the limiting factor.  Diving a wreck, or a site known for a given species can up the odds significantly, but for some of the more interesting animals, it all comes down to luck.

Unless you are using a rebreather, you are also noisy as hell under water and likely to disturb or scare off the animals you are trying to observe.  Take a look at the octopus and the seal in the prior two videos... both animals are well aware of me, and neither is particularly happy that I'm around.  The octopus is fleeing from me and sees me as a predator.  The seal is taking a more wait-and-see attitude, but is clearly not comfortable being cornered by two divers.  There is no sound on either video, but if I had left the sound in, you would hear the very loud sound of my breathing and exhaling through my respirator. Rebreather divers have an advantage here, as they are virtually soundless, and they are the equipment of choice for professional underwater photographers for this reason... ...but with a cost of roughly £5,000 for the kit and training, this presents a substanial barrier to entry.

Finally, its gets dark underwater, particularly in the UK, and its easy to miss a lot of what is going on around you.  The seal and octopus videos were taken off the NE coast of England at around 10 meters... visibility is still good.  This below is more typical:




Note how much darker everything is outside of the beam of the torch... (also the noise I'm making!)  That means that a school of fish can be 10 meters away from you, just at the edge of your visibility, and deliberately avoiding this noisy invader of the deep!  Quite a few times I have seen interesting shadows swimming at the edge of my vision, or just glimpsed something disappearing into a crevice, meters away from me but too far to see clearly in the murk.

A well stocked table

The mediterranean isn't known for its diversity of life... you won't find the vast array of colorful fish that inhabit the reefs of the Red Sea, nor will you see the complex habitats of the North Atlantic kelp forests.  Much of the inshore western mediterranean is composed of vast lawns of sea grass interspersed with rocks and the occasional wreck, and supports a limited range of sea life.  The med has undergone several cycles of drying out, and the sea life within it represent the descendents of a relatively recent recolonization over the last 5 million years.

One advantage of this reduced diversity is that when you are in the med, rather than being distracted by a variety of fish, you can pay more attention to what they are actually doing.  One interesting behavior I noted was of clusters of seabream and wrasse feeding on the rocks... the smaller Rainbow Wrasse and Ornate Wrasse would hover around the larger seabream  and Ocellated Wrasse, letting them do the heavy lifting of tearing chunks of algae and encrustations off the rocks, before diving at the debris cloud to grab any interesting food morsels that were shaken free.

You can see some of this behavior in the first half of the clip below, where off to the right several small wrasse are diving through one such cloud of debris, from where a seabream has pulled away some of the encrustations.  Near the end of the clip is a different behavior - a watchful Painted Comber assessing my intentions before deciding that discretion is the better part of valour and fleeing into a nearby cranny.



For those interested in which fish is which, the two larger fish in the above photos are the White Seabream (oval with one tail spot) and Two-Banded Seabream (oval with two stripes), while the Ocellated Wrasse is the large wrasse with a small spot near the tail. There are two species of smaller wrasse in the photos and movies - the wrasse with a red stripe interrupted by a black bar is a male Mediterranean Rainbow Wrasse, while the female of the species has the dark upper body and light colored underside.  The orange wrasse with the light bands and black spot near its back is an Ornate Wrasse.