Namibia plans to stop oil and gas companies from carrying out off-shore exploration for part of the year, to protect the fishing industry, a senior official said Monday.

Amid concerns that seismic surveys may be disrupting the migratory routes of tuna, senior fisheries ministry official Anna Erastus told AFP such tests would now only take place from May to September.

“This arrangement is to be communicated to the companies that are issued with such licences by the ministry of mines,” said Erastus.

Brazilian oil firms HRT and Petrobras, as well as Spain’s Repsol have exploration licenses in Namibia.

Offshore exploration began in Namibia in the late 1960’s and resulted in major gas finds, though little in the way of oil. But technological advances mean there are now high hopes that Namibia can become a crude producer on a similar scale to neighbouring Angola, Africa’s second-biggest producer after Nigeria. A rush of companies are now carrying out seismic testing in the southern Atlantic, which involves bouncing sound waves off undersea rock formations to detect deposits.

But there are fears these activities may be responsible for a decline in the tuna haul, from 1,800 tonnes last year to about 650 tonnes so far this year. Output in 2011 was 4,000 tonnes. Namibia’s fishing industry is worth around 5 billion rand ($500m) a year.

Erastus said that as a first step the ministry has decided to delay a proposed seismic survey for oil and gas due to take place in the Orange River Basin in February. She did not name the company involved.

Namibian officials are also in talks with neighbouring South Africa, which Windhoek wants to adopt similar restrictions.

“The issue is further complicated by the fact that the same company is also proposing to undertake a February survey in South African waters, just across the Namibia-South Africa border,” Erastus said. “This is in the direct path of tuna migrating from South African to Namibian waters.”

Apart from the unspecified upcoming survey, there are about four wells that are expected to be drilled in 2014.

A task force has also recommended further research to establish the effects of noise pollution on the fish, explore alternative methods of conducting seismic surveys and satellite tagging of tuna to identify migratory routes.

Namibia’s cabinet in September placed a 16-month moratorium on marine phosphate mining, pending an assessment on its impact for fishing.