As I am now living and working as a dive instructor here in the Cayman islands I decided to do a piece on the sharks that can be found here.
Sharks of the Cayman Islands
We are lucky enough here in the Cayman Islands to have a variety of shark species, some of which reside here full time and some of which are transient – passing by on migratory routes seasonally.
In this section we have split sharks into two groups. The first group entitled Coastal Sharks covers most of the species you will find in shallow (<200ft / <60m) water around Cayman’s coral reef systems, mangroves, turtle grass beds and sand flats. The second group titled Pelagic Sharks covers those species that predominantly reside in deep open water.
The International Union for Conservation of Nature (IUCN) “Red List” conservational status section for each species (http://www.iucnredlist.org/) is very informative
Coastal Sharks
Nurse Shark (Ginglymostoma cirratum)
| IUCN Conservation Status (Red List): Data Deficient (Globally), Least Concern (Central America & Caribbean). |
| Population Trend: Unknown |
| Life Span: unknown but thought to be around 25 years |
| Max Length: ~14ft (430cm) |
| Reproduction: Ovoviviparous |
| Gestation Period: 5-6 months |
| Litter Size: 20-30 |
| Size at Birth: ~ 12 inches (31cm) |
| Mating Cycle: Every 2 years |
Nurse Sharks are found in tropical and subtropical waters at depths of less than 240ft (73m). They are relatively docile and are highly resident with strong site fidelity preferring specific resting areas. They will return to the same site each day, although an individual may have several favourite spots. Nurse Sharks are one of a number of species of shark that have strong muscles by which they actively pump water over their gills. This allows them to rest while still able to respire. They are mainly active at night, preying on lobsters, molluscs and small fish. Nurse Sharks have very small teeth, the size of large grains of sand; they feed primarily by sucking prey into their mouths. Nurse Sharks vary in colouration from a dark grey to yellow brown and their skin has a very rough texture, more so than most sharks species. This species if often mistaken for Lemon Sharks due to similarities in body sharp and colouration.
| The main similarities between Nurse Sharks and Lemon Sharks are: |
| 1. Similar colouration: dark grey to yellow brown. |
| 2. Dorsal fin size: the first and second dorsal fin on both Nurse and Lemon Sharks are very similar in size; in most shark species the second dorsal fin is much smaller than the first. |
| 3. Dorsal fin position: the first dorsal fin on Nurse and Lemon Sharks is set quite far back, giving them both similar profiles when seen from the side. |
| The main differences between Nurse Sharks and Lemon Sharks are: |
| 1. The shape of the eyes: Nurse Sharks eyes tend to look much more “bug-like” than the more “feline” looking eyes of the Lemon Shark. |
| 2. Daytime behaviour: Nurse Sharks will generally be resting during the day while Lemon Sharks are active. |
| 3. Visible teeth: Nurse Shark teeth are very small and are too small to see at a casual glance, while Lemon Shark teeth may be visible as they are fairly large. |
Lemon Shark (Negaprion brevirostris)
| IUCN Conservation Status (Red List): Near Threatened (Globally) |
| Population Trend: Unknown |
| Life Span: ~ 25 years |
| Max Length: ~11ft (340cm) |
| Reproduction: Viviparous |
| Gestation Period: 12 months |
| Litter Size: 4-17 |
| Size at Birth: ~ 20 inches (31cm) |
| Mating Cycle: Every 2 years |
Lemon sharks are named for their yellow brown colouring. They give birth in shallow mangrove estuaries. As juveniles, they live in small groups feeding on small fish, crustaceans, molluscs, cephalopods (octopus & squid) and worms. For the first three years of their lives Lemon Sharks live in small, well defined territories (~820ftsq-1 / 250msq-1) which they patrol. On reaching maturity they move offshore (~ 5ft / 1.5m, ~13 years old), where their diet changes to larger fish, small sharks, rays, lobsters and crabs. Lemon Sharks are among the few shark species that are tolerant of relatively high water temperatures, low salinity and low oxygen concentration that come from living in shallow coastal waters.
Caribbean Reef Shark (Carcharhinus perezi)
| IUCN Conservation Status (Red List): Near Threatened (Globally) |
| Population Trend: Decreasing |
| Life Span: 25 years |
| Max Length: historically up to ~9ft (2.8m), but now ~7ft (2.2m) due to fishing pressure. |
| Reproduction: Viviparous |
| Gestation Period: 12 months |
| Litter Size: 4-6 |
| Size at Birth: ~ 29 inches / 74cm |
| Mating Cycle: Every 2 years |
Caribbean Reef Sharks are found only in the Caribbean, Gulf of Mexico and Western Atlantic Ocean and as the name suggests, they prefer shallow coral reef environments, particularly at reef drop-offs and the outer reef wall. As with most sharks, this species is more active at night than during the day, and feed mainly on a wide variety of reef fish and cephalopods (octopus and squid).
The Caribbean Reef Shark was nicknamed the “sleeping shark” as it is one of the few requiem sharks that can rest on the sea bed while still respiring. It is one of the largest predators in coral reef systems making it an apex predator in this habitat. As such the Caribbean Reef Shark holds top-down control, meaning its presence affects the composition of the reef community through predation and mediation of the numbers of other reef species. Recent studies have shown that the removal of Caribbean Reef Sharks from the reef environment leads to the degradation and eventual smothering of the coral reef by algae. This action is facilitated by the initial boost in smaller predatory species, such as grouper and snapper, which then remove the herbivorous species, such as parrot fish, from the reef. This is followed by a decline in grouper and snapper as their prey source becomes depleted. Caribbean Reef Sharks are valuable to the tourism industry: in the Bahamas the economic value of one live reef shark was found to be in the hundreds of thousands of dollars each year.
Caribbean Reef Sharks can be confused with a number of other species from this family including, blacktip, bull, silky, dusky and spinner sharks. The only shark in this list common in Cayman is the blacktip shark and some of the differences used to distinguish them are:
| 1. Interdorsal ridge: Caribbean Reef Shark has a small ridge that runs between the first and second dorsal fin on its back, Blacktip Sharks do not have an interdorsal ridge. |
| 2. Snout shape: Blacktip Sharks have a pointed, triangular looking snout, Caribbean Reef Shark has a rounded blunt snout. |
| 3. Size: Caribbean Reef Sharks will grow up to 3ft / 0.9m longer than Blacktip Sharks tend to be more rotund. |
Blacktip Shark (Carcharhinus limbatus)
| IUCN Conservation Status (Red List): Near Threatened (Globally) |
| Population Trend: Unknown |
| Max Length: ~5.5ft (1.7m) |
| Life Span: at least 12 years |
| Reproduction: Viviparous |
| Gestation Period: 11-12 months |
| Litter Size: 1-10 |
| Size at Birth: 22-24 inches / 56-61cm |
| Mating Cycle: Every 2 years |
Blacktip Sharks are found in tropical and subtropical shallow coastal waters. The females give birth in the same nursery sites they were born in themselves and the pups spend the first three months of their lives in these nurseries, feeding on small fish and cephalopods (octopus and squid). As adults Blacktip Sharks are mainly piscivores (feed on fish) and tend to be segregated groups by both age and sex. While they are known to be very timid sharks wary of humans, but they are also very fast and energetic. They are one of the few shark species that make spectacular spinning leaps out of the water whilst feeding on schooling fish.
Blacktip Sharks are named for the black tips or edges on their pectoral, pelvic and dorsal fins. However many other shark species can be mis-identified as Blacktip Sharks as many other requiem sharks also have dark tips on their fins.
Pelagic Sharks
Tiger Shark (Gladeocerdo cuvier)
| IUCN Conservation Status (Red List): Near Threatened (Globally) |
| Population Trend: Unknown |
| Max Length: ~18-20ft (5.5->6.0m) |
| Life Span: 20-50 years |
| Reproduction: Ovoviviparous |
| Gestation Period: 16 months |
| Litter Size: 10-80 |
| Size at Birth: 20-35 inches / 50-89cm |
| Mating Cycle: Every 2 years |
Tiger Sharks are found in most tropical and subtropical oceans, in both coastal waters and pelagic (open) water and feed largely on rays and turtles. The deepest known sighting of a Tiger Shark was in the Cayman trench at just shy of 900ft (274m).
Genetic analyses have shown that populations from the Atlantic and Pacific regions are significantly dissimilar, suggesting that there is no sexual mixing between these populations. On the contrary, genetic analyses have also shown there is complete mixing within these two groups.
Tiger Sharks are generally slow swimming, and along with their colour and stripe – spot patterning, they depend on being undetected by their prey species. Their reputation as being dangerous is often exaggerated, the name alone invites fear. Interaction with divers, however, has shown time and again that they have little interest in humans, although wild animals should be treated with respect at all times and never provoked.
Great Hammerhead Shark (Sphyma mokarran)
| IUCN Conservation Status (Red List): Endangered (Globally). |
| Population Trend: Decreasing |
| Max Length: ~18-20ft (6.0m) |
| Life Span: 20-30 years |
| Reproduction: Viviparous |
| Gestation Period: 11 months |
| Litter Size: up to ~50 pups |
| Size at Birth: 23-27 inches / 58-69cm |
| Mating Cycle: Every 2 years |
Great Hammerhead Sharks can be found in pelagic and coastal systems and can be seen in very shallow water where they forage and give birth. This species is reported to have suffered a dramatic decline of more than 80% in the past 25 years.
The largest of all known hammerhead species, the Great Hammerhead is known to be a nomadic animal, seldom travelling in groups more than two. The distinctive characteristics that set it apart from other hammerhead species are its size and girth, and the extremely tall dorsal fin (sometimes up to 39inches / 1.0m). There are several considered ideas on the reason of the “hammer” or cephalofoil head. Firstly, they use their head to pin the rays that they feed on to the ground, where they can then take selective bites from the ray wings. Secondly, the array of electro-pores or ampullae of Lorenzini combined with the large width of the head is thought to allow for global position triangulation using the earth’s magnetosphere, aiding their navigation of the oceans with stunning accuracy. They also scan the sea bed using their electro-sensitive pores much like using a metal detector, picking up electrical rhythms of buried prey animals.
Interestingly when Hammerhead pups are born their head is quite soft and malleablefor an easier birthing with the head hardening shortly after birth.
Oceanic White Tip Shark (Carcharhinus longimanus)
| IUCN Conservation Status (Red List): Vulnerable (globally), Critically Endangered (Gulf of Mexico). |
| Population Trend: Decreasing |
| Max Length: ~13ft (4.0m) |
| Life Span: unknown but thought to be around 25 years |
| Reproduction: Viviparous |
| Gestation Period: 10-12 months |
| Litter Size: 1-15 |
| Size at Birth: 23-25 inches / 58-64cm |
| Mating Cycle: Every 2 years |
Oceanic White Tip Sharks are amongst the most wide ranging of shark species in tropical, subtropical and warm temperate oceans, often at the surface over water of a depth of >650ft / 198m. They are a slow moving species that is active both day and night.
Historically this species was frequently sighted, often following large container ships or fishing boats. However over the past fifty years, world fisheries have drastically reduced their populations. In the Gulf of Mexico, Oceanic White Tip Sharks have declined drastically by 99.3%.
The Oceanic White Tip Shark is epipelagic, living predominantly in the upper 660ft / 200m of the open ocean. In this environment the habitat is uniform with very few places for prey species to hide except among floating debris and weed. Bait fish (fry and spats of pelagic and coastal fish species) accumulate in these hides,bringing in larger fish species such as Mahi Mahi (Dolphin Fish), which makes up a large portion of Oceanic White Tip Sharks diet and are patrolled by these sharks.
Like many shark species the Oceanic White Tip Sharks segregates by age and sex, but they are one of the few shark species whose nurseries appear to be oceanic and pelagic. Notably larger individuals are caught at greater depths than smaller individuals and the species is found in greater concentrations with increasing distance from land mass.
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