Image copyright Getty Images Image caption Digital technology is providing scientists with a more detailed understanding of the structure of fish populations

Electronic tag data is revealing complex behaviour in fish populations, raising questions about current fisheries management policies.

The technology shows that populations contain sub-groups with different migratory behaviour, according to US fish expert Prof David Secor.

He said that this insight casts doubt on the effectiveness of fisheries' geographic boundaries.

Prof Secor outlined his findings at a science conference in Denmark.

"We've had this view that we manage fisheries based on boundaries," explained Prof Secor, from the Chesapeake Biological Laboratory at the University of Maryland Center for Environmental Science.

"This is important because we have to regulate jurisdictional fisheries and we have to know how many fish are harvested so we can make sure that not too many fish are caught."

Counting the uncountable

But auditing fishing in this way, he added, means placing fish populations within those regulatory boundaries.

"Our new discoveries are really challenging the idea that populations of marine fish species fit nicely into those boundaries," Prof Secor said.

"Firstly, populations actually have structure. This structure contains sub-groups that have different seasonal migration behaviours."

He compared this to bird species, studied on land, which often have both "resident" and "migratory" groups within the same population. "We are beginning to see this, with digital age discoveries, in fish populations; there are resident and migratory groups."

The improved understanding of the complex and dynamic population patterns was emerging as a result of advances in technology that allowed researchers to electronically tag fish and monitor the movement and migration of individuals, he told BBC News.

Prof Secor shared his research at the International Council for the Exploration of the Sea (Ices) Annual Science Conference 2015, which is being held this week in Copenhagen.

Ices is a global organisation, with a network of more than 4,000 scientists from 20 member nations, that "develops science and advice to support the sustainable use of the oceans".

Each year, Ices provides scientific data and information to EU fisheries ministers as they meet to set annual catch quotas. However, the political gathering is often criticised for failing to fully take into account the scientific advice.

Stable seas

However, Prof Secor was hopeful that advances in the scientific understanding of life patterns beneath the waves could help deliver sustainable marine stewardship.

"What this suggests is a possible opportunity to build stability by conserving this kind of structure in populations. This structure can actually help buffer the population against future change, such as climate change," he observed.

He added that the data also revealed the importance of an age structure within fish populations. Many species take many years to reach sexual maturity and removing too many mature individuals disrupts the population's ability to renew itself.

Prof Secor said: "Age structure is important in terms of allowing the ongoing production of populations. It is very hard to build it back into populations once it has been removed."

UN data suggests that global fish consumption has doubled in the past five decades and it is a trend that is set to continue, as the world's human population continues to expand and become increasingly urbanised.

Against this backdrop of increasing demand, there is a need for effective, sustainable fisheries management in order to satisfy the world's growing appetite for the fruits of the sea.

The Ices Annual Science Conference runs until Friday.