I often find myself falling asleep as I edit the video footage from a long day of diving. Of course I prefer to think this has nothing to do with my advancing age. I DO appreciate that it is advancing, I just wish it wasn't doing it so fast. I dive a lot more these days than I ever could in my early years here on Catalina. There were just too many conflicting demands on my time when I taught at the old Toyon school, so multiple dives in a day were rare. Today I prefer to attribute my occasional snoozing to the fact I'm diving more frequently, and often much deeper, than I did in my youth. Such activity greatly increases the amount of excess nitrogen absorbed by my body, and this can tire even the most fit diver.
Last summer we were on the King Neptune diving at Middle or Isthmus Reef off Two Harbors. This dive site used to be among my favorite "shallow" dives because there was so much to see given the multi-level structure of the reef. Unfortunately, the highly invasive Asian alga Sargassum filicinum has become very dense on the reef top there and now crowds out much of our native algae and invertebrates. Even the fish generally seem to avoid it. This dastardly invader has also seriously impacted many other dive sites on the island's leeward coast including Sea Fan Grotto, the Empire Landing Quarry and even the Casino Point Dive Park.
Fortunately, the Sargassum is an annual, and does die off each year. Unfortunately, it leaves billions and billions of spores behind that would astound even Carl Sagan. These spores make eradication of this invader highly unlikely, since even if divers were to remove every single adult plant, the spores would permit this noxious weed to reappear each year. We will have to live with it, and undoubtedly a number of future invaders from the home waters of our trade partners.
But I digress, perhaps an indication that is indeed advancing age that is responsible for my snoozing. The focus of this column is what I found snoozing under a large ledge on the downslope of Middle Reef that day. I often dive alongside the sheltered area under such ledges, looking for critters that prefer less turbulence than encountered on the reef top. I hadn't expected to find a critter as large as this one though. What I saw was a harbor seal about my size, sleeping with its eyes closed under the ledge.
Now the Marine Mammal Protection Act prohibits interference with such critters, so I was careful not to disturb its beauty sleep. It probably had a hard night searching out blacksmith and other fish to munch on. These seals love to follow divers on night dives because their dive lights often target fish that the harbor seal can dart after for an easy meal. When you pull an all-nighter to fill your belly, it makes good sense to take a long nap in a protected area during daytime to digest your catch. Certainly no great white shark would find it here.
Since seals and sea lions are air breathers, they can't stay under water for a full eight hours of sleep as recommended by various health organizations. Heck, I rarely sleep that long either. I'm not certain of their breathhold duration underwater while in a rest state, but scientific studies have shown that when diving, harbor seals may go to a depth of 1,600 feet for as long as 35 minutes. However, their dives are usually in the 2-6 minute range. Other studies have shown harbor seals of larger size remain under longer than smaller ones, and dive duration increases as young pups grow. Seals are physically active when diving, pursuing potential food, and undoubtedly exert themselves much more on dives than when resting. As members of the true seals (Phocidae), harbor seals are believed to have higher breathhold capacity than the sea lions more frequently seen in our waters.
Unlike divers, seals and sea lions breathe surface air at normal atmospheric pressure. Divers on SCUBA breathe air supplied at pressures equal to our surrounding pressure, which varies with depth. It is this increased pressure that increases the amount of nitrogen (and oxygen, the two principal components of air) taken in by the diver's lungs. Seals are not subjected to these increased pressures, and therefore do not absorb the abnormally high levels of nitrogen that we do. My snoozin' seal was not suffering from the after effects of its dive that rendered me unconscious as I edited my video footage.
I'm getting a bit technical here, so let's return to my furry friend "sound" asleep under the ledge. I filmed it for several minutes before its eyes slowly opened. It must have recognized Dr. Bill because it quickly closed its eyes and went on dreaming about fishes... just as I dream about mermaids in my sleep. I observed it with my eyes for some time without letting my camera roll. Then it opened its eyes again and shook its head gently. Slowly the harbor seal turned around and swam away. I assumed it just needed another lungful from the surface, and moved on along the ledge to the wall at the south end of the reef. As I slowly worked my way back along the ledge, I saw that my "dive buddy" (Gary Garibaldi would be jealous if he read that) was back asleep under the ledge.
I shot a bit more footage before leaving this harbor seal to surface myself since my tank was approaching the 500 psi mark. In my experience with them in Catalina waters, these true seals are generally cautious about interacting with humans. Maybe it is because they are occasionally shot at by fishers or perhaps, like me, they are just a wee bit shy. This encounter gave me an opportunity to film one close up. It also reminded me of a dive I made with one of my students, Chris Conrad, at Long Point back in 1971.
Chris' dad, the late actor William Conrad, was a great supporter of the Toyon school, especially its biology program. He had donated the SCUBA compressor we used to fill our tanks as well as a Boston whaler Chris had used while he was a student. Chris and I went out to Long Point to dive the calm waters inside the point. During our dive, a harbor seal came up to us. It stayed with us for a bit, then dove down and picked up a sea cucumber. When it was at our depth, it released the sea cucumber. Chris and I alternated diving down to retrieve the sea cucumber, bring it back up to the harbor seal and release it for the seal to retrieve. We played catch with this very friendly marine mammal for a good portion of our dive.
Unfortunately, the only video system we had in those days (also donated by Chris' father) was a reel-to-reel deck connected to a separate camera with both requiring an electrical outlet. On top of that, it was only black-and-white and of very low resolution compared to today's high definition cameras. In those days there were no underwater housings for such a monster. Sometimes I think about how great it would be to return to those dives of yesteryear with my current high def camera and underwater housing to record some of the amazing things we saw. It would have been great to collect underwater video to provide something of a benchmark of ecological conditions back before diving really got popular and fishing activity was less intense. Hopefully my footage from today will help serve as a benchmark for the future... a good example of "shifting baselines." You do remember that column, don't you?
© 2008 Dr. Bill Bushing. Watch the "Dive Dry with Dr. Bill" underwater videos on Catalina Cable TV channel 49, 10:00 AM and 5:00 PM weekdays and on Charter Communications Cable channel 33 at 7:30 PM on Tuesdays in the Riverside/Norco area. Please help me climb out of self-imposed poverty... buy my "Munching and Mating in the Macrocystis," "Great White Sharks of Guadalupe," "Calimari Concupiscence: Mating Squid, " "Playful Pinnipeds: California Sea Lions," "Belize It or Not: Western Caribbean Invertebrates, Fish and Turtles," "Gentle Giants: Giant Sea Bass" or "Common Fish and Invertebrates of the Sea of Cortez" DVD's. Yes, take Dr. Bill home with you... we'll both be glad you did!
My furry friend snoozing and leaving to gulp some air from the surface.
This document maintained by
Dr. Bill Bushing.
Material and images © 2008 Star Thrower Educational Multimedia