Fished for their meat and liver oil, many remarkable deep-water sharks and rays now face extinction

By Brittany Finucci, National Institute of Water and Atmospheric Research, Cassandra Rigby, James Cook University

The deep ocean, beyond 200 metres of depth, is the largest and one of the most complex environments on the planet. It covers 84% of the world’s ocean area and 98% of its volume – and it is home to a great diversity of species.

Yet it remains among the least studied places on Earth, with no comprehensive assessments of the state of deep-water biodiversity and no policy-relevant indicators to guide the taking of species targeted by fisheries.

This also applies specifically to deep-water sharks and rays, even though these species make up nearly half of the recognised diversity of all cartilaginous fishes (sharks, rays, and chimaeras) we know today.

Our research highlights how our growing impact on the deep ocean raises the threat to these species.

Using the International Union for Conservation of Nature Red List of Threatened Species, we show that the number of threatened deep-water sharks and rays has more than doubled between 1980 and 2005, following the emergence and expansion of deep-water fishing.

We estimate one in seven species (14%) are threatened with extinction.

Fishing for meat and oil

Deep-water sharks and rays are in a group of marine vertebrates that are most sensitive to overexploitation. This is because of their long lifespans (possibly up to 450 years for the Greenland shark, Somniosus microcephalus) and low reproduction rate (only 12 pups in a lifetime for the gulper shark, Centrophorus granulosus).

These biological characteristics make them similar to formerly exploited, and now highly protected, marine mammals.

The Greenland shark and the leafscale gulper shark (Centrophorus squamosus), for example, have population growth rates comparable to the sperm whale (Physeter macrocephalus) and the walrus (Odobenus rosmarus), respectively. Despite their known inherent vulnerability, there are very few species-specific management actions for deep-water sharks.

Our research shows that overfishing is the primary threat to deep-water sharks and rays.

Read Full Story https://theconversation.com/fished-for-their-meat-and-liver-oil-many-remarkable-deep-water-sharks-and-rays-now-face-extinction-224230