Shark diaries: November 2007

Dear Ultimate Animal Lover,

As we enter the season for the pelagic shark trips (the blue water predator trips), I thought it would be a good idea to give you a brief run down of the two main sharks we encounter on these trips.

The Blue Shark (Prionace glauca)

The blue shark is one of the most attractive and graceful of the world’s sharks. With its indigo blue colouration, it is also one of the easiest species to identify. It is often seen at the surface, particularly in higher latitudes, with its pectoral fins outspread and its first dorsal fin and upper caudal lobe out of the water.

They are mainly an open ocean shark, and are found in temperate to tropical waters world wide. They are the most wide spread of the sharks, but some stocks are seriously reduced by over fishing.

Blue sharks are great travelers and many individual sharks tagged by researchers have been discovered thousands of kilometers away, sometimes only weeks later. Little is known of their migrations. At higher latitudes populations tend to be migratory, but lower latitudes populations are mainly migrant.

The danger to divers is potentially high risk, however many encounters are organized for divers without incident. (These sharks have been blamed for feeding frenzies on survivors of ships sinking during the 2nd World War, and sailors would even claim that they would appear alongside ships when someone had died.) Blue sharks have an uncanny ability for turning up at the right place at the right time especially floating carcasses of dead whales.

Identification Checklist

• Large size
• Metallic or indigo blue upper side, bright blue sides, snowy white underside
• Slender body
• Exceptionally long, narrow, pointed pectoral fins
• First dorsal fin well behind pectorals
• Second dorsal fins about half the size of the first
• Scythe like tail
• Long conical snout
• Large round eyes centered within a white ring

Shortfin makos (Isurus oxyrinchus)

The shortfin mako shark is a sleek spindle shaped shark with a long conical snout ( very similar in appearance to the great white shark). This shark has short pectoral fins and a crescent shaped caudal (tail) fin. There is a distinct caudal keel on the caudal base. Its second dorsal fin is much smaller than the first. The teeth are slender and slightly curved with no lateral cusps, and are visible even when the mouth is closed. There is marked counter shading on this shark: dorsally it is a metallic indigo blue while ventrally it is white.

Shortfin makos are renowned for their speed and their ability to leap out of the water. In fact, there are cases when an angry Mako will jump out of the water and into the boat after it has been caught on the hook. Due to its speed and agility, this high-leaping fish is sought as game worldwide. Mako sharks have a better hydrodynamic shape than all other sharks, and this, combined with the lamnidae's typical high aerobic muscle mass, reflects in the spectacular speed and agility of both the longfin and shortfin makos

The shortfin mako is found in temperate and tropical seas worldwide. The closely related longfin mako shark, Isurus paucus, is found in the Gulf Stream or warmer offshore waters. Shortfin mako sharks live in tropical and temperate offshore waters. They are a pelagic species that occur from the surface down to depths of 150 meters (490 feet). This shark is seldom found in waters colder than 16 degrees Celsius.

The shortfin mako is found worldwide. This shark is highly migratory.
It potentially high risk, but its predominantly open ocean habitats limit contact with people.

Identification checklist

• Teeth are visible even when the mouth is closed
• Teeth are long and slender with smooth-edged cusps
• Distinct countershading, dorsally blue and ventrally white
• Moderately short pectoral fins
• Underside of the snout is white
• Lunate tail and caudal keel
• Large black eyes
  

Other shark species that have been spotted include a 13ft thin-tailed thresher shark, smooth hammer heads, great hammer heads, and oceanic white tips. These species should not be expected to be seen on a regular basis.

For more info on the Blue Water trips, please see our website.

Until next month
Best Fishes
Karen Lawrence