Fish Identification: Leopard Shark

For the first time in our fish identification series, we're going to look at a sea creature that's not actually a fish. I think leopard sharks are awesome, and hope to come across one in a dive someday.

Physical description

[Leopard shark][]
I assume most people can tell a shark when they see one, so I'll focus on the features that make leopard sharks unique. Clearly the first distinguishing feature is the source of their name. Leopard sharks have long, slender bodies covered in dark ink stain-looking spots. Their underbelly is all white.

They have two dorsal fins. The first is about halfway along its back and the second fin, almost the same size, is close to to the caudal (tail) fin. Leopard sharks also have an anal fin on their rear underbelly. Their caudal fins have a long upper lobe which extends out much further than the lower lobe. The forward dorsal fin and pectoral fins give them their tell-tale "sharky" look.

Leopard sharks have mouths on the bottom of their heads, probably for easy consumption of bottom-dwelling food like crabs and clams. They grow to lengths of 1.2 - 1.5 m (3.9 - 4.9 ft).

Geography and habitat

The leopard shark is found along the Pacific coast of North America, as far north as Oregon all the way down to Mexico. They like muddy or flat ocean bottoms in relatively shallow water (5 m / 15 ft).

They are often found in bays or estuaries, although there have been plenty of sightings in kelp beds and rocky reefs. They usually are found relatively dormant on the ocean bottom. They are harmless to humans, but don't go harassing them.

Overfishing

Leopard shark populations were rapidly declining during the 80s due to overfishing for food and aquariums. However, regulations introduced in the 90s brought them back up to a sustainable amount. Even though I don't like the aquarium trade, it is reassuring to see regulations in place that protect threatened species through compromise and sustainable practices.

Further reading

Wikipedia
Animal bytes

[Leopard shark]: http://thedivingblog.com/uploads/2010/03/leopard_shark.jpg


BCD Overpressure Relief Valves

Overpressure relief valves are pretty much standard on today's BCDs. You can identify them as the vent-like areas, either on the shoulder and / or bottom rear of the jacket. Often they have a ball-and-string assembly attached called a "dump valve." Pulling on this will release air from the BCD through the valve. This allows the diver to vent air easily from almost any orientation underwater, without awkwardly holding their inflator hose toward the surface.

[BCD overpressure relief valve][]
As their name implies, the primary purpose of overpressure relief valves is to prevent the accidental over-inflation of BCDs. BCDs contain what are called bladders ...


Underwater Photography Links

Here's a random set of underwater photo / video links across the web.

The beautiful nature blog featured a few underwater photographs.

Amsterdam couple Cor Bosman and Julie Edwards have their photo albums online. Their photography has been featured in articles and magazine covers.

And here's a video of a clever little penguin.


Nitrox Compatible Gear

An extremely common question I see is whether or not certain gear (mainly regulators) can operate with enriched air / Nitrox. Many manufacturers even claim in their manual that Nitrox is not supported.

It is commonly accepted amongst scuba diving professionals that mixes with less than 40% oxygen are treated as air (with respect to equipment). Enriched air specialties only qualify you to use up to 40%. This means your "air-only" regulator is perfectly fine with any recreational Nitrox mix. No special assemblies or upgrades required, and your tank will not explode on your back underwater.

Interestingly, the flip side of ...


Weighting Guide

Last week we looked at how to choose a wetsuit. Today we'll cover guidelines for choosing weights. These numbers aren't set in stone, but should act as a general guide to start your proper buoyancy check. This is the first step towards perfect buoyancy control.

Naturally, if you are leaner or, um, less leaner you should adjust accordingly.

Women should add 4-5 lbs (about 2 kg) if diving in salt water, or subtract 4-5 lbs (about 2 kg) if diving in fresh water. Men should add 6-7 lbs (about 3 kg) if diving in salt water, or subtract ...


Fish Identification: Sand Diver

[Sand Diver][]
Sand divers are an interesting fish. While they can be thought of as a reef fish, you are more likely to see them beside the reef than actually on it.

Physical description

Sand divers are in the lizardfish family and share most of the same characteristics. They have longer, cylindrical shaped bodies. They range in size from 4 - 14 in (10 - 35 cm), although you may occasionally see a larger one.

Their heads resemble that of a lizard, with a wide mouth and prominent eyes. They have a fanned dorsal fin on the middle of their back, and two pectoral ...


What Wetsuit Suit Do I Wear?

It's hard to decide what exposure suit to wear. Here's a guide to help in the process, which I'll walk you through using.

To begin, find out the temperature range for the water you'll be diving in. Let's pretend I'll be diving in water that is 72-75 degrees fahrenheit. Next, we'll modify this range based on several factors:

  • Depth - Deeper water tends to be colder, so if this is a deep dive (around 30m / 100 ft), consider subtracting about 5 degrees from your temperature range. In my example, I'll be diving normal ...

Visibility for Scuba Diving

Visibility is one of the most subjective aspects of diving. Ask 10 people after a dive what they think the visibility was, and you'll get 9 different answers. The last person will spend a half hour trying to guess.

Defining

Visibility
People generally suck at estimating visibility ("viz"). Why is that? I think it comes down to a lack of common definition. I will attempt to define visibility in concrete terms.

The best place to start for this sort of thing is the dictionary. Webster's defines visibility as

The distance at which something can be seen.

We're getting ...


Bonaire Shore Diving Made Easy

Bonaire Shore Diving Made Easy
I'm going back to Bonaire in a few weeks to complete my PADI divemaster training. Along with all my gear, one thing I'll be taking is the book Bonaire Shore Diving Made Easy (BSDME).

BSDME is a small book describing 75 dive sites in Bonaire. Officially, there are 63 dive sites in Bonaire (not counting Klein), so the book more than adequately covers most diving spots. In particular, it shares the easiest entry and exit points. This can be a huge time saver for shore dives, where rocks and waves make entry and exit challenging.

BSDME also gives ...


Fish Identification: Rock Beauty

[Rock Beauty][]
Rock beauties are a common sighting on many reefs. Other names for the fish include corn sugar, coshubba, rock beasty, and yellow nanny. I haven't heard these, so stick with rock beauty and most people will know what you are talking about.

Physical description

Rock beauties are in the angelfish family, so they have the usual large-shaped, flat bodies of that species. They don't get as big as most angelfish, topping out at around 12 inches (35 cm).

Rock beauties are most easily distinguished by their color rather than their body shape. They have a bright yellow head ...