A report has just been published that examines the possible link between a number of naturally occurring climatic phenomenon and the rise, collapse and return of Atlantic Bluefin Tuna (subsequently referred to as ‘bluefin’) to the Nordic fishery over the last century.
More broadly it argues that these factors are largely responsible for wider substantial shifts in the geographical range of bluefin, and they should be incorporated into the factors considered as part of the stock management process.
The paper ‘Atlantic Multidecadal Oscillations drive the basin-scale distribution of Atlantic bluefin tuna’ argues that the phenomenon – abbreviated to AMO — is largely responsible for this shift in range, and that will potentially also create negative conditions for the Spawning of bluefin in the Mediterranean influencing their abundance in future years.
That data suggests multiple distinct phases of ‘warm’ and ‘cold’ phases since 1634. Most recently it claims a ‘warm’ period from 1925-1960, followed by a ‘cool’ period from 1960 to 1996
The central thesis is that we have been in a ‘warm’ period of the AMO since 1996, characterised by higher average temperatures in the north east of the Atlantic, and that this has historically been accompanied by a large shift in the geographical distribution of bluefin towards these areas.
We welcome any considered contribution to our understanding of this vulnerable species, and there are some very interesting points raised by this study.
The Bluefin Tuna UK campaign has a number of highly qualified marine scientists amongst its supporters and we have drawn upon their feedback in this article.
In light of that, we feel it is appropriate for us to make a number of observations about the the report and in particular, some of the opinions subsequently expressed by one of the authors, Dr Richard Kirby. Those opinions go well beyond those of the paper itself and are not in our view validated by its content. Attempting to inappropriately extrapolate from this study that Recreational angling for Atlantic bluefin in UK waters would be a mistake is unjustified, ill-founded and appears to reflect a different agenda to that of the paper itself.
Indeed, if this pattern of increasing numbers of bluefin present in UK waters continues, it in our view argues more strongly in favour of our proposal to establish a licensed, live release recreational fishery accompanied by a substantial research program that could help teach us much more about the reasons for this change in distribution.
In this article we wanted to raise those concerns, and in a number of follow up articles we will additionally address some of the ill-considered specific observations about bluefin made by Dr Kirby.
Having looked into the methodology surrounding the stock assessments data, there are some questions. The authors combined ICCAT data from 1950-2011 with historical data from 1634-1959 trap data to produce an abundance index for the whole period and used a simple non-parametric test to justify this.
The authors are simply not comparing the same thing. Whilst the ICCAT Stock Spawning Biomass calculation incorporates the fishing effort exerted in order to produce the metric the trap data has no such correction.
The reliance upon data from as far back as 384 years ago and modelling relationships from such data is clearly questionable. Even the data from 1880 to the 1920s on the sea surface temperatures illustrating the AMO shows massive year to year variations in temperatures. It is only since about 1930 that there appears consistency in that data and the patterns it implies.
Only ‘half’ of the picture:
The authors state ‘Our analysis therefore suggests that bluefin tuna occurrence in the North Atlantic is controlled by a northeastern/southwestern “seesaw” of habitat suitability so that long-term local fluctuations in bluefin tuna abundance may reflect changes in spatial distribution rather than changes in the size of eastern and western populations’.
They go on to state that ‘we have shown that the AMO is an important determinant of the bluefin tuna’s spatial distribution and regional abundance in the North Atlantic and that recent recovery of the eastern stock may reflect the current positive AMO phase’.
There are two problems with this observation.
The authors do not include any assessment of the western Atlantic stock that could confirm this phenomenon, even over the recent, shorter ‘post industrial fishing’ era for which data would be available.
Furthermore, the authors state whilst ‘current changes in abundance occurring in the eastern region may relate to 90% of Atlantic Bluefin tuna populations’….that the two stocks ‘were assumed to be approximately the same order of magnitude in the 1970’s until the Western stock collapsed’.
This is factually incorrect.
Exhaustive ICCAT data clearly show in the early 1970s that stock was around 50,000 tonnes, against over 300,000 tonnes in the EA/Med. The authors then use the assumption that the eastern stock comprised an unproven 50% of the population over a 400 year period….. Such an assumption undermines the integrity of the analysis when claiming a substantial shift from the western Stock to the eastern stock as a function of the AMO.
Mediterranean spawning risks:
In the press release accompanying publication of the report Dr Robin Faillettaz, a co-author states that ‘the most positive phases of the AMO also have a detrimental effect upon recruitment in the Mediterranean Sea, which is currently the most important spawning ground, and that will affect adult abundance a few years later’.
One problem with this claim is that we are already 23 years into the ‘warm’ phase and no such impact has been determined by multiple detailed stock assessments by the the huge science team of the Governing body ICCAT.
In fact, their comprehensive analysis shows that since 2011 there has been a substantial INCREASE in the Spawning Stock Biomass in the Mediterranean/East Atlantic.
The report itself is much more cautious on this issue. They conclude that the impact of the AMO upon the Mediterranean is lower than elsewhere. The report actually emphasises a broader issue of rising sea temperatures globally as a risk to spawning if they continue, and in the short term have possibly improved spawning conditions. In any event, the report also concludes that when this phenomenon allegedly occurred in the main western spawning ground, the Gulf of Mexico, bluefin responded by establishing additional spawning areas further north.
Our biggest concerns however are with regard to the observations made by Dr Kirby in the press release accompanying the publication of the report.
He makes a number of statements that are ill-founded and completely unrelated to the content of the report.
His assertion that the mortality rate of bluefin in recreational fisheries is ’17-40%’ is very selective and misleading. There are multiple studies undertaken with conditions consistent with that of the fishery we are proposing that consistently show a mortality rate of less than 5%. We have published a detailed rebutall of this misleading assertion on our websites.
We should mention that catch and release angling is a much used in scientific research, in multiple tagging programs, including recent ones supported and funded by the WWF and the UK’s own research program that got underway in 10/2018 in Cornwall.
He talks about creating a “safe space” for “UK Bluefin”.
That is flawed thinking. These very same fish will still be heavily targeted by Japanese, Spanish and French fleets on their way to and from these waters. Norway’s quota was just doubled and Denmark is now applying for a Commercial quota. The idea of a ‘safe space’ in our waters may make him feel warm and fuzzy inside but does nothing for the future fortunes of Atlantic bluefin.
Time to move away from failed, Commercial fishing exploitation of Bluefin….
We are surprised that Dr Kirby is so concerned about a request for a selective, licensed live release fishery that is asking for 0.05% of the total quota for Atlantic bluefin, just 20 tonnes out of soon to be 38,350…. Even the reference to recreational fishing within the report is surprising when in the three largest quota holders, Spain, France and Italy, only allocate 1-2% of their quota to recreational anglers.
Of much greater concern should be the continued dominance of huge commercial fishing operators browbeating ICCAT into quota’s that push the boundaries of the scientific recommendations.
It may suggest that there is a different, anti-angling agenda behind Dr Kirby’s assertions.
We are now apparently 23 years into what could be a 30-40 year ‘warm’ cycle. Should it persists then the shift of Atlantic bluefin into northern Atlantic (including UK) waters could continue for many years to come and even intensify.
We need more information on Atlantic bluefin, ongoing — simple as that. Every ICCAT Stock assessment bemoans the quality of the data they have. Much of the most valuable data that is obtained, helping our understanding of their status comes from research gathered by, you guessed it, anglers!
Our proposal for a ‘world-leading’ live release recreational fishery working alongside marine scientists would aid the conservation of bluefin tuna through angling’s unique ability to catch fish for scientific purposes and return them unharmed.
Instead of opposing our proposals for a revolutionary, sustainable approach to management of bluefin, Dr Kirby should see that the kind of model we are proposing is not only a valuable potential contributor to the data, but is the most forward looking way of managing this vulnerable species.
If we can prove that here in UK waters, we may well be able to change the way other countries manage ‘their’ bluefin. That’s the way to help ensure a stable, sustainable future for Atlantic bluefin tuna.