We’ve known for a long time that Atlantic bluefin tuna
migrations are complex, with fish spawned into the Mediterranean Sea traveling
into North American waters, while fish spawned off North America were thought
to cross the ocean to swim off European shores.
Now, thanks to a
recent paper published by a team of scientists led by Dr. Barbara A. Block of Stanford
University’s Department of Biology and Department of Oceans, we also know that the
bluefins’ sojourns to the western Atlantic may be particularly important to tuna
stocks’ health.
“Ensuring the future of Atlantic bluefin tuna,” which
appeared in the April 20, 2026 volume of the Proceedings of the National
Academy of Sciences, reviews three decades of archival, satellite, and
acoustic tagging data, and advises
“that exploitation of Med-spawning fish, particularly on the
spawning grounds, may impact all fisheries in the North Atlantic basin through
their extensive distributional range,”
and also that
“Shifting selectivity to older year classes releases juvenile
bluefin from the Med to the higher productivity of the North Atlantic, where
they experience multiple years of growth and lower fishing mortality before
returning to their spawning grounds.”
“Management of this internationally shared resource requires high
quality scientific information—and this work provides one example of that. This research addresses one of the primary
sources of uncertainty surrounding the amount of mixing and movement occurring
between these two stocks. This is a critical
piece of information needed to inform sustainable yield advice.”
The cross-ocean movements of Atlantic bluefin have long been
an issue for not only scientists and fisheries managers, but anglers and
commercial fishermen as well; there has always been the questions of whether restrictive
regulations constraining harvest of the western stock might be frustrated when
tuna cross into the eastern Atlantic, where more permissive management measures
prevail, and whether the relatively small United States quota makes sense in
the face of the far higher quotas awarded to nations that fish in the
Mediterranean and eastern Atlantic.
The new paper answers those questions, noting that
“electronic tagging results for adolescent and mature fish
indicate that the Med stock subsidizes the North American fisheries and,
importantly, exploitation of Med spawning fish, particularly on the Med
spawning grounds, impacts all [Atlantic bluefin tuna] fisheries in the North
Atlantic.”
As NMFS explains,
“The results show that many bluefin tuna move from eastern
Atlantic and Mediterranean waters to the western Atlantic to forage and
grow. These fish often remain in the
west for several years before returning to the Mediterranean Sea or spawning in
the Slope Sea. Tagging also demonstrated
that adult fish tagged in the U.S. and Canadian waters move back to the
Mediterranean to spawn and often return the following year to the western Atlantic
to forage along the U.S. eastern seaboard.
Importantly, bluefin tuna that originated in the western Atlantic, however,
tend to stay west of the 45oW management line.”
The reason that eastern stock bluefin often migrate into
western Atlantic waters appears to be food, with NMFS suggesting that
“Tuna are likely heading west to find and feed on vital prey
such as Atlantic mackerel, Atlantic herring, and menhaden, which are abundant
in U.S. and Canadian waters.”
But regardless of why many of the eastern stock bluefin move
west, the movements of the eastern and western stocks make it clear that
management measures intended to protect the western stock bluefin are not
compromised by significant numbers of those fish traveling to eastern Atlantic water. However, the many eastern stock bluefin that
enter the western Atlantic also receive such measures’ protection, to the
benefit of both North American fishermen and the bluefin themselves.
The paper notes that the eastern stock is thought to be
about 10 times as large as the western stock, although there is substantial
uncertainty surrounding that number, and that the total allowable catch for the
eastern stock is 40,570 metric tons, compared to just 2,726 metric tons for the
western stock. Fishing activity in the eastern
Atlantic was and is also much more intense, with the paper stating that
“From 1990 to the mid-2000s, estimated fishing mortality F
was, adjusting for underreporting, typically 0.15 to 0.20 [or, very approximately, 15%
of the population removed each year] for eastern juveniles (ages 2 to 5)
and 0.3 to 0.4 [roughly
25 to 35 percent annual removals] for large individuals 9age 10+),
concentrated primarily in the Med. This
period of heightened catch did not occur in the west…or north…, meaning that
migrating to the West or North Atlantic provided eastern [Atlantic bluefin
tuna] with relative safety from fishing mortality for almost 20 [years]. [citations omitted]”
It thus advised that
“In the Med, shifting selectivity of fishing to older ages in
recent years and reducing [total allowable catch] not only controlled
overfishing but created, in effect, an escapement management regime…that
allowed migrating eastern [Atlantic bluefin tuna] juveniles and subadults to
enjoy a longer, safer, and more productive juvenile growth period than those
remaining in the Med. Effectively, an
unknown number of Med juveniles were able to ‘escape’ selection at an early
age, forage, and reach maturity in the North Atlantic. We hypothesize that this led to higher
spawning contribution per recruit, higher overall abundance, and greater
fishery yields, with the lower exploitation rates of North American fisheries
providing a release from fishing mortality…
[citations omitted]”
But it wasn’t only the eastern stock that benefited.
“[F]or the western stock, as the supply of eastern [Atlantic
bluefin tuna] increased the relatively static western area [total allowable
catch] exerted decreasing mortality upon the western stock. After years of relative stasis, the western-only
larval and [longline fishery] catch indices in the Gulf [of Mexico] now show
substantial increases indicating that growth of the western stock may have only
responded due to managing fishing mortality of the eastern stock… [citations omitted]”
The management measures adopted for the western stock three
decades ago proved to be a conservation success story for the entire Atlantic bluefin
tuna population. As NMFS observed,
“The major conservation and management measures taken by ICCAT,
combined with shifting catches to larger fish, resulted in a dramatic
turnaround of the stock. Reducing
fishing mortality to sustainable levels allowed several year classes of fish to
survive, grow, and leave the Mediterranean to seek the productive feeding
grounds of the North Atlantic. This escapement
from Mediterranean spawning areas to wider Atlantic waters with stricter
harvest measures allows bluefin tuna to live longer, grow larger, and
contribute more offspring to the population.
This emphasizes the importance of managing fishing mortality in areas of
high vulnerability such as spawning aggregations…
“Whether the current Atlantic bluefin fishery total allowable
catch remains sustainable in the face of a rapidly changing ocean and
increasing human demand remains uncertain.
What is certain is the return on investment for state-of-the-art
science.
“U.S. anglers have been frustrated in recent years by strict
harvest measures for bluefin, but the science confirms that these measures are
effective. Our conservation efforts are
having huge impacts—not just for the United States, but across the Atlantic. Anecdotal evidence supports this, with
anglers along the U.S. East Coast catching more and larger bluefin than in the
past 30 years. The stock recovery is
such that ICCAT adopted higher total allowable catch for the western stock…”
Yet, among all of those positive comments and unqualified
support for good fisheries science lurks a substantial amount of irony.
Nor is it completely clear where the notion came from,
although
a recent article that appeared in The Fisherman magazine might make one
suspect that it arose somewhere within the recreational fishing industry. That article read, in part,
“There is no doubt that there is a booming recreational and
for-hire fishery in the Mediterranean and Eastern Atlantic waters with little
catch data being submitted for too many years now. Earlier this year the [European Union]
implemented new mandatory, daily electronic data reporting requirements for
marine recreational fisheries targeting certain species, including
bluefin. However, other nations that are
not part of the EU but are part of European and African continents are
reporting little if any recreational catch, despite landings occurring. There is still a glaring disconnect.”
The article fails to mention that the only two non-EU countries
in the Eastern Atlantic are Norway,
which has a national recreational quota of a whopping 10 metric tons—fewer bluefin
than anglers killed off the southeastern United States during the first two weeks
of 2026—and the United
Kingdom, where the recreational quota is a still-tiny 20 mt. There are more non-EU
nations bordering on the Mediterranean Sea, but they include states such as Albania,
Bosnia and Herzegovina, Serbia, and Montenegro, none of which are known as
recreational fishing powerhouses, and none of which have any recreational quota
at all.
So, the argument that the United States is justified in not counting
its recreational landings against its quota because some non-EU nations might be
doing the same thing falls pretty flat.
Yet the article goes on.
“The ICCAT Eastern Atlantic/Mediterranean management requires
that recreational catch be reported and assigned to one’s quota. The U.S. has argued that a parallel requirement
does not exist for the Western Atlantic contracting parties in Western bluefin
management Recommendation 22-10. As a
result—and because of the lack of recreational catch recreational catch
reporting for many years now by the Eastern Atlantic/Mediterranean contracting
parties—the U.S. notified ICCAT in January 2026 that it is exploring continuing
to meet its requirement to report our recreational catch but not count it
against the US quota…
“Not surprisingly, this proposal has been heavily criticized by
our friends across the pond. It should
be noted that our recreational quota is negligible in comparison to the Western
and Eastern Atlantic/Mediterranean bluefin quotas that are dominated by commercial
quota allocations.”
Once again, we see arguments of dubious merit.
“An annual [total allowable catch], inclusive of dead
discards, of 3,081.6 [metric tons] is established for 2026, 2027, and 2028…If
the total catch in the western area exceeds 3,081.6 t in any
year, it shall constitute an exceptional circumstance… [emphasis added]”
To argue that “total catch” included dead discards, but
excluded recreational landings, would be ludicrous.
In addition, Recommendation 25-05 is generally sector neutral;
while it mentions recreational fisheries twice, it only mentions commercial
fisheries once. The natural counter to
the argument that the Recommendation doesn’t explicitly require including recreational
landings in the quota is that it doesn’t explicitly require including
commercial landings, either. The only
explicit references are to “total catch” and “dead discards.” Yet the mandatory counting of commercial
landings against the quota is assumed.
But the ultimate argument for counting recreational landings
against the U.S. quota is that it would be in the long-term interests of United
States fishermen to do so. As the new
research indicates, the restrictive management measures in place in the western
Atlantic benefited both the eastern and western bluefin stocks. Placing greater fishing pressure on fish in
the western Atlantic now, by omitting recreational landings from the United State’
quota and so increasing the western kill, could only risk reversing three
decades of progress.
In the end, “Ensuring the future of Atlantic bluefin tuna” is
a very valuable bit of research. NMFS
was completely justified in calling it “state-of-the-art science.”
But the thing about state-of-the-art science is that, while
it is a good thing in and of itself, it is far more valuable if it is actually
put to use. NMFS shouldn’t just issue
press releases hailing the paper. It
should put the paper’s findings to practical use, and continue to cooperate
with the ICCAT management scheme that made the western Atlantic a valuable sanctuary
for bluefin tuna for the past 30 or more years.