July 17, 2007 — One of the first ever detailed studies on deep water lantern sharks, so named for their ability to glow in the dark, has found they are in danger of extinction.
Recent studies have linked declines in shark populations to the collapse of entire marine ecosystems. The loss of lantern sharks could devastate other ocean life globally, as many lantern sharks have wide ranges.
Researchers focused on one species in particular, the smooth lantern shark, commonly caught as by-catch in Portuguese trawling and longline fisheries. Since the bioluminescent shark has little commercial value, the fishermen usually just discard it.
"What we now know is that this species has a vulnerable life cycle characterized by slow growth rates, low fecundity and late maturity," lead author Rui Coelho told Discovery News.
"When fisheries mortality increases, the populations start to decline and cannot compensate for this," added Coelho, a shark researcher at the University of Algarve, Portugal.
He and colleague Karim Erzini analyzed 614 by-catch sharks over a two-year period. Their measurements showed the species grows anywhere from 5 to 19 inches long.
The sharks have special light-producing organs, called photophores, mostly found on their sides.
"These photophores may be used to allow individuals to escape from predators, approach prey without the sharks being detected or for species recognition, such as during the mating season," explained Coelho.
The scientists developed a unique way to determine the age of the sharks: The inner portions of their spines grow continuously. By counting growth bands in this spinal area, similar to counting tree rings, the researchers could estimate each shark's age.
Their findings have been accepted for publication in the journal Fisheries Research.
The oldest male they found was 13 years old, while the oldest females were 17 years old.
Eggs found within females numbered, on average, 10.44. Since this shark's reproductive cycle may last as long as three years, the birthrate is extremely low when compared to most other animals and fishes. The researchers also noticed that many females miscarried — likely due to stress — when they became by-catch.
