Julius found out that the Greenland shark mates for 100 years

Greenland shark, researcher Julius Nielsen Arctic Hub Greenland Research Greenlandic Institute of Natural Research, University of Copenhagen

A shark that reaches sexual maturity after its 100 years’ birthday, raises concern within fishery administrations. Julius Nielsen, however, do not think that the frequent bycatch of the old shark necessarily is a problem.


By Signe Ravn-Højgaard


Although Julius Nielsen does not brag about it, he has achieved what many researchers do not even dare dream about. In 2016 his research results reached the front page of Science – one of the most renowned scientific journals. The research was subsequently mentioned in newspapers around the globe.


Julius Nielsen along with colleagues from the Greenlandic Institute of Natural Research, University of Copenhagen and other collaborating institutions had discovered that the Greenland shark is much older than assumed. They found out that it can turn several hundred years old – in many cases up to 400 years! Although the age cannot be determined precisely, it is evident that the shark can become very old.


The team of researchers also found out that the female sharks are more than 100 years old before they reach sexual maturity.

This new knowledge has given rise to concerns in international fishery organizations, as the Greenland shark is a frequent bycatch in trawling and longlining fisheries in Greenland and elsewhere in the North Atlantic. And the research results may indicate that the shark is vulnerable: if the mating sharks die in bycatch, it will take many years before we get a new generation of sharks. For this reason, if too many sharks are caught involuntarily certain types of fisheries can risk losing their sustainability certificates.

“It might turn 100 years before it reaches sexual maturity, but it can have kids for more than 100 years. ” Julius Nielsen.


More knowledge

However, although it seems logical that an animal for whom it takes a 100 year to reach mating age, is vulnerable to bycatch, according to Julius Nielsen, the concern may very well rest on wrong assumptions.


He believes that more knowledge about the Greenlandic shark can improve regulation of the catch. Hopefully, more research can lead to less concern and less restrictions of bycatch in places where there is no reason for it. On the other hand, the research can also point to areas where we need to be extra careful, for example because big old mating sharks live here.


The fishermen also need to learn how to handle sharks caught in bycatch the right way.


Julius Nielsen explains: “If handled with care a Greenland shark in bycatch is not the same as a dead shark. That argument can become important when the impact of bycatch on the shark population is assessed.”


”I believe that if we knew everything about the biology of the Greenland shark, we would be less concerned about it. It might seem logical that because it is difficult for the Greenland shark to mate and accordingly have few kids, however I believe they have a ton of offspring!” says Julius Nielsen and adds: “It might turn 100 years before it reaches sexual maturity, but it can have kids for more than 100 years. The fact that every year hundreds and maybe thousands of big sharks are caught might indicate that they have a lot of kids. There is something in their biology is less worrying than when it comes to normal fish. And we need to find out what that is,” Julius Nielsen says.


Therefore, Julius Nielsen continues his research in the Greenland shark. And there is a lot we still do not know about the animal.

In fact, a baby shark has only been caught very few times and that was far south by the deep-water Mid Atlantic Ridge. In such areas there is hardly any commercial fishery nor research fishery and thus we do not know much about the animals living in this area.


Baby sharks by mail

For this reason, Julius Nielsen was very excited when a fisherman from a commercial trawler in Greenland sent him an email about the two baby sharks caught as bycatch on his ship along with a big Greenland shark. The fisherman believed that the babies might be newborns from the big Greenland shark. So, the baby sharks were frozen and sent to Julius Nielsen and the Zoological Museum in Copenhagen. When they arrived at the laboratory in Copenhagen, it became clear that they unfortunately were not Greenland shark babies, but a similar species.


”That was a shame as it would really have been sensational, if this was in fact newborn baby sharks. That has never been found in Greenland before. In fact, we don’t even know if the Greenland shark mate in Greenland at all. Indeed, we don’t even know where it mates at all,” explains Julius Nielsen and stresses that he was still glad that the fisherman sent him the sharks.

His research is very dependent on a good cooperation with the fishermen. More knowledge about the Greenland shark requires examinations of sharks in different sizes from different places. For this reason, Julius Nielsen has often gone out speaking to the fishermen, asking them what they have observed in their trawl.