The power of science – mackerel stock in good shape
By Ian Gatt, chairman of the Scottish Pelagic Sustainability Group
Fisheries science and the calculation of stock sizes of individual species – or Spawning Stock Biomass as it is known – is an incredibly complex process, but absolutely vital in ensuring that we can manage our fisheries by setting catch limits and other practical control measures aimed at ensuring sustainability of stocks and the fisheries that depend upon them.
No more so than with Northeast Atlantic mackerel, our most valuable stock, and which has been the subject of much scientific debate in recent months. It all began when the NE Atlantic mackerel assessment was released last October by the International Council for the Exploration of the Sea (ICES), which estimated a downward trend in Spawning Stock Biomass (SSB), placing it below a reference point that indicates management action should be taken to reduce fishing pressure.
Reaching this reference point was the trigger that resulted in the decision to suspend the Marine Stewardship Council (MSC) ecolabel certification for the fishery, which is an independent endorsement that the fishery is being responsibly and sustainably managed.
But there was a problem. ICES – the scientific body that evaluates stock status and provides catch advice – was uncertain whether the assessment accurately reflected what was happening with the stock, which could be due to issues with data inputs and the way the assessment model handles the data. Fishermen were also doubtful about the veracity of the assessment, given that they were seeing an abundance of mackerel on the fishing grounds.
In particular, ICES noted that the way the mackerel tagging data is treated by the stock assessment model can change the estimate of the stock size considerably. Another factor that may have contributed to the 2018 assessment is that estimates for the number of young fish due to enter the fishery (recruitment) had not been quantified for 2016 and 2017, due to the data being unavailable at the time of the assessment.
As a result, ICES instigated an inter-benchmark process that brought the scientific community together to investigate these issues, and which reported back at the start of April this year. Their conclusion was that there were flaws in assessment, resulting in the stock size being revised up from the original 2.35m tonnes to 4.16m tonnes – a 77% increase. ICES is also undertaking a special scientific workshop in May which will strategically examine what improvements can be made to the information needed to assess changes in the mackerel stock, and to enable improved scientific advice in the future.
Naturally, Scottish mackerel fishers welcome this news, not least because they are committed to sustainable and responsible fishing and want stocks to be as healthy as possible. But what I think is especially positive is how the fishing industry, both in Scotland and Europe, is collaborating with ICES by using inputs from our own independent scientists to provide as much data as possible.
The tide has now turned on the days when fishermen and marine scientists showed little engagement with one another. Now, the mackerel and herring sector is investing considerable resources into marine science to enhance our knowledge of stocks that will help make informed management decisions. We recognise that financial resources are limited for respected bodies such as ICES and Marine Scotland and it is only right that our fishing industry contributes to the process.
Our own marine scientist, Dr Steven Mackinson, has played a key role in this process and is involved in several ICES working groups and is also co-ordinating a number of scientific surveys and projects using Scottish mackerel and herring fishing vessels as research platforms. The ultimate objective of these is to provide additional data from the fishing fleet that can be used in scientific assessments and research on changes in the marine environment.
With more knowledge of the size of stocks such as mackerel, we can continue to harvest a valuable and nutritious resource that helps ensure the world’s food security whilst at the same protecting our precious marine ecosystem.
Hopefully, this new reassessment of the NE Atlantic stock will now pave the way for the lifting of the suspension of Marine Stewardship Council (MSC) ecolabel certification of the fishery in the near future. There is already a joint ICES approved management strategy in place for the fishery between the EU, Norway and the Faroes, and we would urge Iceland and Greenland to become part of this process, too. As a responsible industry, we are committed to the long term sustainability of the mackerel stock and ensuring we have in place effective management measures to achieve this.
But with the stock in robust shape, the good news for the consumer is that people can continue to eat Scottish caught mackerel – whether fresh, smoked or tinned – safe in the knowledge that it is being harvested from a healthy and sustainable source.