Archive for January 2016

Sharks We Need To Protect – Blacktip Reef Shark

Blacktip Reef Shark (Carcharhinus melanopterus)

IUCN STATUS: Near Threatened
You don’t have to feed them; just tap the water, and they come racing toward you. We know that working with models is never easy, but these sharks are eager to pose – finding the right pose is another question altogether. Blacktip sharks are one of the most common shark species found inshore off the coast of Florida. Although the majority of shark bites in Florida are likely attributable to this species, there has never been a fatal attack credited to this species in this region.

DID YOU KNOW? Blacktip reef sharks have a home range of around .21 square mile, among the smallest of any shark species

Blacktip SharkFast Facts About Sharks


Sharks are vulnerable to fishing pressure because they:

  • Grow slowly

  • Take many years to mature (12 to 18 years in some species)

  • Often reproduce only every other year

  • Have few young per brood (only 2 pups in some species)

  • Have specific requirements for nursery areas (bays and estuaries)

  • Are caught in many types of fishing gear (hook and line, gillnet, trawl)

  • Sharks have adaptations allowing them to be apex predators including:

  • Teeth that are replaced throughout their life

  • Sensitive smell receptors

  • Eyes that adapt quickly to low light levels

  • Lateral line receptors that sense movement in the water

  • Electroreceptors that detect electrical fields due to the presence of prey

5-spd-year-of-shark-blacktipreefshark

Habitat  –  The blacktip shark inhabits inshore and offshore waters, but is not a truly pelagic species. They are often seen nearshore around river mouths, bays, mangrove swamps, and in other estuaries, though they do not penetrate far into freshwater. They can be found offshore and over deep waters near coral reef dropoffs, but primarily stay in the upper 100 feet (30 m) of the water column. This species, there has never been a fatal attack credited to this species in the east coast/western Atlantic region. This shark inhabits shallow coastal waters and estuaries and offshore surface waters. Blacktip sharks use shallow inshore waters from South Carolina to Texas as nursery areas for their pups in spring and summer. They can be found in groups as young or adults feeding in shallow water.

Geographical Distribution  –  Blacktip sharks are cosmopolitan in tropical to subtropical coastal, shelf, and island waters. In the Atlantic during their seasonal migration they range from Nova Scotia to Brazil, but their center of abundance is in the Gulf of Mexico and Caribbean Sea. Off the east coast of the United States blacktip sharks range from New England to Mexico but are most commonly found between North Carolina and Texas, especially in spring and summer. They occur throughout the Mediterranean and along the central West coast of Africa. In the Pacific they range from Southern California to Peru, including the Sea of Cortez. They occur at the Galapagos Islands, Hawaii, Tahiti, and other South Pacific Islands, to the North coast of Australia. In the Indian Ocean they range from South Africa and Madagascar up to the Red Sea, Persian Gulf, throughout India’s coast, and east to the coast of China.

Size, Age, and Growth  –  The maximum reported length of the blacktip shark is 8.4 feet (255 cm). Size at birth is 15-28 inches (38-72 cm). Average adult size is around 4.9 feet (150 cm), weighing about 40 lbs. (18 kg). This species is a relatively fast growing shark, maturity is 4-5 years for males, and 6-7 years for females. The maximum age of blacktips is thought to be at least 12 years.  In waters off the southeastern U.S., the length at maturity is 4.8 feet (145 cm) total length (TL) for males corresponding to a weight of approximately 43 pounds (19.5 kg) and 5.2 feet (156 cm) TL for females corresponding to a weight of approximately 55 pounds (25 kg) (source: Castro 1996).

Food Habits –  The blacktip shark primarily feeds on small schooling fishes such as herring, sardines, menhaden, mullet, and anchovies, but also eats many other bony fishes including catfishes, groupers, jacks, snook, porgies, grunts, croakers, flatfishes, triggerfish, and porcupine fish. They are also known to consume some elasmobranch species including dogfish, sharpnose sharks, young dusky sharks, skates, and stingrays. Crustaceans and squids are also occasionally taken.

Blacktips, as well as their close relative the spinner shark, are known to breach out of the water while feeding, sometimes spinning up to three or four times around their axis. This behavior is thought to facilitate the sharks’ predatory success while feeding on schools of fish near the surface. The sharks vertically attack the school at high speed, snapping at the fish as they pass through it. The momentum then carries them through the ocean’s surface.

Reproduction –  Development in the blacktip is viviparous, meaning they give birth to live, free-swimming young like others in the carcharhinid family. Males reach sexual maturity between 4.4 and 5.9 feet (135-180 cm). Females reach maturity at 3.9-6.3 feet (120-190 cm). Gestation last 10-12 months, and they give birth in late spring and early summer to 1-10 pups. Females give birth in inshore estuarine nursery grounds where the young remain for the first years of their lives.

Predators –  Adult blacktip sharks do not have any common natural predators. Like other members of this shark family, however, the young are likely to be at risk from larger sharks.BlackTip 1

It’s a sobering statistic: Up to 25 percent of the world’s sharks and rays are threatened with extinction, according to the IUCN Shark Specialist Group (SSG). Using the IUCN Red List of Threatened Species criteria, the SSG says that of the 1,041 species assessed, 107 rays and 74 sharks are classified as threatened.

Because they grow slowly and produce few young, both sharks and rays are susceptible to overexploitation — including overfishing from targeted fishing, bycatch and finning. Thanks largely to compelling arguments from the diving community, we’re making progress to ensure that these animals receive the conservation attention they desperately need. While our work in recent years represents terrific progress, the IUCN study reminds us that these threatened species, and closely related ones — such as guitarfish, sawfish, skates and stingrays — also need our attention.

“Significant policy strides have been made over the past two decades, but effective shark and ray conservation requires a dramatic acceleration in pace as well as an expansion of scope to include all shapes and sizes of these exceptional species,” says Sonja Fordham, IUCN SSG deputy chair
and president of the Washington, D.C.-based Shark Advocates International, a project of the Ocean Foundation.

Healthy shark and ray populations are priceless. Project AWARE and other conservation agencies work every day to make strong arguments for change, but we need your help. Let’s truly make this the year of the shark — together.

Want to get involved with shark conservation? Visit the Project AWARE website and find out how you can make a difference – http://www.projectaware.org/

via 10 Sharks We Need To Protect | Sport Diver.

Posted Sunday, 31 January 2016 by Culebra Snorkeling and Dive Center in Culebra Posts & Reviews

Cruises to Culebra from Puerto Rico | Best Caribbean Cruises | Islands

Old San Juan, the historic district of Puerto Rico’s biggest city, is a mecca for cruise ships. And why not? The port’s location and availability of non-stop flights from major U.S. markets make it a great jumping-off point for ships exploring the heart of the Caribbean. Here are seven great cruise itineraries that either begin or include a stop in Puerto Rico.

puerto-rico-cruise-windstar
Courtesy of Windstar Cruises
via Cruises to Puerto Rico | Best Caribbean Cruises | Islands.

See 5 bright planets at once! | EarthSky.org

First time we can see 5 planets at once since 2005. All 5 are up before dawn. The moon is now sweeping past the planets and can help you identify them.

The last time we saw all five visible planets together was from about December 15, 2004, to January 15, 2005, over a decade ago.

By bright or visible planet, we mean any planet in our own solar system that’s easily viewed without an optical aid and that has been watched by our ancestors since time immemorial.

See photos of the 5 planets, from the EarthSky community

In their outward order from the sun, the five bright planets are Mercury, Venus, Mars, Jupiter and Saturn. These planets are easily seen in our sky because they are relatively nearby. Their disks reflect sunlight and shine with a steadier light than the distant, twinkling stars.

You can catch most of these planets long before dawn. Jupiter rises first, in the evening hours, followed by Mars after midnight and then Saturn, Venus and Mercury. Click here for recommended almanacs that will help you find when each planet rises into your sky for any given date.

Distances from the sun of planets in our solar system, expressed in A.U.  Graph via planetsforkids.org

Distances from the sun of planets in our solar system, expressed in A.U. Graph via planetsforkids.org

Relative distances of the planets to the sun. These distances are expressed in astronomical units (AUs, or sun-Earth units):

Mercury: 0.387 AU
Venus: 0.723 AU
Earth: 1.000 AU
Mars: 1.524 AU
Jupiter: 5.203 AU
Saturn: 9.529 AU
Uranus: 19.19 AU
Neptune: 30.06 AU

When will we see all five planets together again? We’ve had a number of people ask us when the next presentation of the five visible planets in the same sky will take place. It will be possible to view all five in the evening sky – very briefly – from about August 13 to 19, 2016.

There’s a huge caveat, however. Right now, all five planets are strung out across the early morning sky in an easy-to-see way (well, Mercury is the tough one, so close to the sunrise, but keep watching … it’ll get easier). In August, Mercury and Venus will be sitting low in the west at dusk and not that easy to catch from northerly latitudes.

The Southern Hemisphere definitely has the big advantage for spotting all five planets in the August, 2016, evening sky.

Bottom line: All five bright planets – Mercury, Venus, Mars, Jupiter and Saturn – will appear together in the morning sky from about January 20 to February 20, 2016. That hasn’t happened since 2005. The moon is sweeping past the planets, beginning with Jupiter on the night of January 27, 2016. Then Mars on the morning of February 1. Then Saturn, Venus, Mercury!

Source: See 5 bright planets at once! | EarthSky.org

Posted Sunday, 31 January 2016 by Culebra Snorkeling and Dive Center in Culebra Posts & Reviews

How to Select the Perfect Dive Fins

Fin

When it comes to scuba diving gear, there are numerous benefits to finding the perfect pair of fins: maximum thrust, increased comfort, less leg strain and way more fun. But with the wide selection of styles on the market, where should divers begin their search? The following tips should help you narrow your choices. In the end, the toughest part is picking just one.

GETTING THE RIGHT FIT
The most important factor in choosing fins is getting the proper fit. Here’s how to measure the best fit for both full-foot and open heel fins.
**
Full-Foot Fins**
To test the fit of full-foot fins, put your weight on the ball of your foot, as if from a runner’s starting position, and try to step out of it. If it comes off, it’s too big.
**
Open-Heel Fins**
To test the fit of open heel fins, sit down with the fin on and try to wiggle your foot back and forth and up and down. The fins should move as one with the foot without slipping.

PADDLE FINS VS. SPLIT FINS
The difference between paddle fins and split fins is basically a matter of kicking style.

How Paddle Fins Work
Paddle fins work best with a traditional, longer scissors kick.
* Simple Physics: Paddle fins act as a natural extension of the human leg, giving our feet — which are not designed to create efficient thrust in water — much-needed assistance.
* Blade Designs: The main difference between paddle fins are in the size, shape and construction of the blade.
* For Best Performance: Use a long, smooth flutter kick, and consider alternating with a frog kick to share the load with other muscle groups.

How Split Fins Work
Split fins work best with a shallow and rapid flutter kick.
* Propeller Effect: The technology for this type of fin is based on each side of the split blade twisting independently to create lift that translates into greater thrust.
* Decreased Resistance: The design is meant to reduce leg and ankle strain, because the split blade operates more efficiently with less drag during the up and down strokes.
* For Best Performance: With split fins, use a slightly shallower and more rapid flutter kick.

via How to Select the Perfect Dive Fins | Sport Diver.
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