Today’s fish is the yellowtail snapper, or sometimes just called the yellowtail.

Physical description

Being a snapper, the yellowtail has that perfectly shaped oval “fish” body. The caudal fin is deeply forked, hinting at the swift movement of this active fish.

A yellow line marks this fish, beginning at the snout and widening down the length of the body until it covers the entire tail, hence the name.

Yellowtail snapper can grow up to 30 inches in length, although lengths of around 12 inches are probably more common in diving environments.

Geography and habitat

Yellowtail live in the western Atlantic, off the eastern coast of the U.S. all the way down to Brazil. This makes them a standard Caribbean sighting.

You’ll sometimes see them in schools, although a solitary yellowtail is not an uncommon sight. They also like to feed near the bottom.

Seafood

Yellowtail have a slightly sweet flesh, making them a popular game fish. They are classified as “Eco-OK”, which means they are fine to eat in moderation.

Further reading

Wikipedia
Florida Museum of Natural History
Environmental Defense Fund

“To really know the ocean, you have to live it.” This line from the opening narration is something every scuba diver can relate to. We spend our whole lives getting to “know” the ocean, but DisneyNature’s Oceans documentary gives us a 1 hour 25 minute taste of parts we may never see.

This documentary takes you through some fascinating images. Some things are a little familiar, but with a little twist. For instance, the film quickly shows footage of the famous sardine run off the coast of South Africa. We’ve seen it a million times, but this particular footage had a nice surprise: humpback whales! That was a new one for me.

Another example is the well-known footage of the great white shark breaching while grabbing a seal. We see something similar, but a little different. We see several clips of sharks breaching while grabbing for seals, some even missing. Basically, it’s not just re-cut footage from the BBC Planet Earth series, but entirely new scenes.

Of course, the majority of the film is comprised of things I haven’t seen. A duel between a crab and a mantis shrimp is one particular highlight. An epic battle between tens of thousands of crabs is also peculiar. Be prepared for a large variety of creatures, from huge humpbacks to the beautiful blanket octopus.

I enjoyed the movie, but if I had one complaint, it’s that the narration is a tad dull as they attempt to tie the very random footage together. The only useful thing about the narration (provided by Pierce Brosnan) is the names of the creatures you are seeing. A little more about them would’ve been appreciated at times. However, the visual quality more than makes up for it.

I also liked that it’s not heavy on the conservation side of things. Near the end they show you parts of the ocean that are polluted, and animals getting caught in nets. None of it is judging or condescending, simply stating the facts. I hope that as younger generations see footage like this at a young age, they get “brainwashed” into caring for the ocean as they get older.

Watch the trailer for some clips, or even check out the accompanying book. If you find those appealing, you’ll definitely enjoy the movie.

Any scientifically inclined divers out there? The Smithsonian Institution, National Science Foundation, and the Ocean Studies Board of the National Council is sponsoring a Research and Discoveries symposium.

The dates are May 24 and 25 in Washington, D.C., and registration appears to be free of charge.

From the website:

“50 scholars will discuss their papers on research findings from around the world on coral reefs, blue-water environments, under-ice polar habitats, temperate kelp forests and other sites of interest.”

Check it out if you’ll be in the D.C. area.

Most divers never give much thought to what their air cylinder is made of. Even so, it can affect aspects of your dive. Besides, it never hurts to know a little about the equipment you’re diving with.

Material

Cylinders are made out of two types of material: steel and aluminum (actually an aluminum alloy). Each have different properties that make it appealing for different types of construction and use.

Steel cylinders are tough, making them resistant to damage. They also tend to support higher capacities, because of their increased strength. The downside to steel is that it can rust if not properly cared for.

Aluminum cylinders are softer than steel, so they’re not as tough, although they do just fine for general use. To compensate, the walls of aluminum cylinders are thicker than for steel. For this reason, an aluminum cylinder is larger and heavier than a similar capacity steel cylinder. They also don’t handle overfilling nearly as well.

Despite this, aluminum is the dominate choice of material for cylinders in many parts of the world. The upside is that aluminum tanks are far more tolerant of corrosion from salt water. As opposed to steel cylinders, when a layer of aluminum oxide, or “rust”, forms, it acts as a barrier to prevent further oxidation. 80 cubic feet aluminum cylinders are probably the most common type encountered in tropical dive destinations.

Identification

Unless you’re into metalworking, it can be hard to distinguish between steel and aluminum tanks. It’s even worse when the cylinders are painted for enriched air diving. Fortunately, manufacturers in North America are required to stamp certain information on tanks they produce, including the type of material used.

You can find this stamp at the top, rounded part of the cylinder. It is a sequence of letters and numbers stamped into the metal, arranged into two rows.

To determine the type of metal, look in the middle of the first row. These days, you will most likely see either “3AA” or “3AL”. “3AA” is the markings for chrome-molybdenum steel, which is practically all steel cylinders made today. “3AL” is the designation for the aluminum alloy used in cylinder manufacturing.

Buoyancy

The type of cylinder you use only has one major effect on your diving: your buoyancy. Aluminum tanks are more buoyant than steel, and thus you will require more weight when diving with them. It is worth knowing what you usually dive with in order to compensate one way or the other when diving with a different cylinder.

The usual recommendation is to add about 5 lbs / 2 kg to your base weighting you get from a weighting guide to compensate for an aluminum cylinder.

Aluminum has a particularly annoying characteristic. A full steel tank is negatively buoyant. An empty steel tank is also negatively buoyant, but less so. This is why during a proper buoyancy check it is recommended to use a near-empty cylinder, or add weight to compensate. Aluminum cylinders also become more buoyant as air is consumed, but they change from being negatively buoyant to positively buoyant. This means a full aluminum cylinder will sink while an empty will float. This makes it harder to pin down a perfect weighting for the entire length of a dive.

If you’re curious, a standard steel cylinder weights about 30 lbs, while an aluminum tank weighs about 35 lbs. If aluminum tanks are heavier, then how can they be more buoyant? For the same reason they’re not as strong as steel: aluminum is less dense than steel, and thus has a lower specific weight.

I hope you learned something about cylinders today. Next time you go diving, take a quick second to identify what type of cylinder you’re using. Use this information to adjust your weighting, instead of defaulting to being overweighted. Keeping note of the tank type (when different than what you usually use) in your log book could also be useful.

Probably the biggest source of confusion during a rescue diver course is the creation of an emergency assistance plan. Students aren’t sure how much or how little to include. They aren’t sure they did it right when it doesn’t take a long time. This article is meant to clear up these problems.

First of all, I’m going to say that creating an assistance action plan should not be a terribly difficult exercise, especially in the internet age. There are a few key components that should be included along with a few optional items. Finding this information these days should be a breeze. Before we get into what exactly to include, let’s discuss the purpose of an emergency assistance plan. This should illuminate exactly what is required to construct a complete plan.

Purpose

The purpose of an assistance plan is simple: in the case of an emergency, an emergency assistance plan should assist an uninformed bystander in contacting emergency services and getting them to the location of the accident. Right away this should clue you in on what’s required. In fact, putting too much information will only slow things down during an emergency situation.

In general, there doesn’t have to be too much detail in an emergency plan. However, courses usually require plans for a specific dive site. This is probably an additional source of uncertainty. If in doubt, just ask your instructor how specific everything should be. Additionally, consult your textbook for any insights it may offer.¹ Though it never hurts to put in too much information, at least for the sake of fulfilling a course requirement.

What’s in it?

Now we know what the overall purpose of the plan is, but what exactly do we put in it? This is what everyone wants to know. After considering the purpose, we can ask some questions to discover what should be in this elusive little document.

If a diving emergency was taking place around you, what information would you need to be of some assistance? Clearly, we need some sort of contact information for the local emergency services. In particular, we want scuba-related contacts. If your diving locale has an emergency hotline dedicated to scuba emergencies, include that as well as general emergency numbers.² Look up the local Divers Alert Network (DAN) for their contact information.

This information (local EMS plus any scuba-related EMS) is the core of your emergency assistance plan. You can’t get away with less. There is, however, plenty more you could include for absolute completeness. What other information could be useful during an emergency?

Sometimes it may be faster to transport the injured yourself. For this reason, I like to include the location of the nearest hospital, possibly with a map or directions. A contact number for the emergency room is also good, to alert staff that you are on your way with an injured diver.

The location of nearby emergency equipment is also pertinent. This includes things like emergency oxygen and first aid kits. Often, EMS may take a while to arrive, costing your victim precious minutes. Being able to help in the meantime by administering oxygen or basic life support could be the difference between life and death. You may know where the oxygen tank is, but if you’re busy giving rescue breaths, you want someone else to be able to retrieve it.

Depending on where you are diving, the location of the nearest telephone may be useful. Imagine if a foreigner was responsible for contacting emergency services after an accident. They have your emergency assistance plan, but no local mobile phone. It could be when you handed them your plan you told them to use your phone, but if diving remotely this may not always be a possibility. It’s location-specific, and definitely something to think about, but not required.

My rescue instructor was fairly stringent and required that I include a script for someone to read when calling emergency services. The key parts of this script are your location (not just the dive site name, but where it actually is), and that this is a scuba diving related emergency. This bit of information could change the reaction of emergency services on the other end. For instance, they may realize that a decompression chamber is needed and avoid hospitals that aren’t equipped to handle decompression sickness, saving valuable time.

Another optional item is a map of your diving location that identifies all the important landmarks nearby, such as the emergency equipment, telephones, and even the hospital. This diagram of the dive site could be useful in an emergency, but is usually not required. If your instructor doesn’t request it, you can still include it for brownie points.

Templates

To save you some time, I created a free emergency assistance plan template. Fill out as much or as little as you (and your instructor) think is necessary, replacing the text inside the <brackets>. Delete the rest. Click the following links for the format of your choice:

iWork Pages
Word 2007 & 2008 (.docx extension)
Word 97 – 2004 (.doc extension)
Adobe PDF
Rich Text Format

My hope is that this article (and the templates) take some of the mystique out of creating an emergency assistance plan. This is something you’ll probably only have to do twice during all your training (for rescue diver and for divemaster), but it is good to know the thinking behind it’s construction and the overall purpose it serves.

Time to help me out. Is there anything critical I left out that should be in an emergency assistance plan? Let me know in the comments.

1. I can’t say for other agencies, but the PADI rescue diver manual is nearly useless for information about creating an emergency assistance plan.
2. Funny story. I did my rescue diver course in New Zealand. For my assistance plan, I wanted to include the telephone number for a local hospital. I found the hospital, looked the number up online, and put it in my plan. During the course, everyone except me noticed something wrong with the hospital’s number, +44 xxx-xxxx. Turns out the hospital was part of a UK conglomerate, and the number I found was for their main London hospital. Being a dumb American, I put the phone number with the UK country code for my New Zealand dive plan. Go me.

To be able identify and discuss fish, it is helpful to know all the types of fish fins. It makes descriptions much easier, and there really aren’t that many. Here are the eight types of fish fins:

• Dorsal fins are found on the back of the fish. There may be up to three of them. The fish uses this fin for balance in the water and sudden movements.
• Caudal fins are also known as tail fins. This is what we refer to as the fish’s tail.
• Anal fins are on the ventral (bottom) surface of the fish, behind the anus. Fish use these for stability while swimming.
• Pectoral fins are located on each side of the fish, around where the head meets the body. These are often thought of as the fish’s “arms”.
• Pelvic fins are located on each side of the fish, near it’s bottom middle. These help the fish go up and down as well as turn sharply in the water.
• Adipose fins are soft fins found between the dorsal and caudal fins, usually closer to the caudal fin.
• Caudal keels are small horizontal fins just forward the caudal fin on each side of the fish. You’ll find these on faster swimming fish.
• Finlets are small fins that look like ridges along the top and bottom of the fish, behind the dorsal and anal fins.

Click to enlarge

Of course, not all fish have every type of fin. Refer back to this page if you come across a fin you don’t know while reading our fish identification series.

It is commonly thought that fat people stay warmer in water. If you asked someone “why”, you’d probably here a joke about blubber. It’s not that simple, however.

In fact, fat does not keep you warmer underwater. It is actually muscle tissue which generates heat that keeps you warmer. Fat can’t generate heat. But again, it’s not that simple, so low body fat does not mean staying warmer.

Total body mass (muscle and fat) is more important than just proportion of body fat (although a little bit of fat tissue actually does provide a small amount of insulation). It’s hard to say anything definitive about the subject, but those with proportionately more lean muscle mass will tend to stay warmer. However, this can vary with other factors such as what temperatures you are used to as well as your metabolism.

You’ll notice that larger people do tend to stay warmer with less exposure protection. Given the above information, I believe that this is because larger people not only have more fat, but generally have more muscle underneath the fat. As I said above, it is the total body mass that is more important than the actual body fat percentage.

Don’t take this as an excuse to eat more cheesecake, though.

Project AWARE has posted a one-page PDF with 10 tips for underwater photographers.

The tips are definitely “Project AWARE”-style, in that they are meant to remind you that taking pictures comes second in priority after not hurting the aquatic environment.

Here are the 10 tips:

1. Photograph with care
2. Dive neutral
3. Resist temptation
4. Easy does it
5. Sharpen your skills
6. Be informed
7. Be an AWARE diver
8. Take only pictures, leave only bubbles
9. Share your images
10. Conserve the adventure

Check out the PDF if you’re interested and have a few minutes to spare.