Shark numbers plummet more than 70 pct, extinction likely for some species

New research shows global shark and ray numbers have declined by more than 70 percent in the past 50 years, which is likely to lead to the extinction of some species.

And experts warn a lack of information about New Zealand oceanic shark populations is making it difficult to assess how well they are doing.

The research, published in the journal Nature last week with input from NIWA, found populations in the Pacific Ocean decreased steeply before 1990 then declined at a slower rate.

The global decline is mostly attributed to a huge increase in fishing since 1970, with half the world's 31 oceanic shark species now listed as endangered or critically endangered by the International Union for Conservation of Nature (IUCN).

The Nature paper warns urgent action is needed to prevent shark population collapses and "myriad negative consequences for associated economic and ecological systems".

NIWA fisheries scientist Dr Brit Finucci says New Zealand waters are home to about 113 shark species and their relatives.

"New Zealand not only has globally threatened oceanic species but also some globally highly threatened deep-water species as well. We know these species are very susceptible to population declines because of their biology," Dr Finucci says.

While most of our species aren't considered threatened here, Dr Finucci says there is a rapidly growing body of research linking shark movements to environmental changes.

"We don't have that information for New Zealand, and this is something we should start investigating. It is very hard to assess the status of many sharks in our waters because we don't have shark-specific monitoring programmes."

Some data is opportunistically collected either by other research surveys or reported by commercial fishers and fisheries observers.

"For some species, we have noted possible declines in recent years, but we are unsure if these trends are a real decline in abundance, a change in the fishery, or a change in animal behaviour," Dr Finucci says.

"NIWA has taken on a wide variety of shark research projects in the past including indicator analyses and stock assessments - these are important for monitoring shark populations.

"However, in order to do this modelling work, and do it well, we still need a lot of fundamental research of species' biology and ecology."

This includes mapping habitats, particularly nursery areas and pupping grounds, and determining movement patterns.

"Sharks have been part of our oceans for millions of years and if they disappear it is likely to be noticed in ways we haven't yet measured."