TUNA TALES

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TUNA TALES
TUNA I A Fishery Management Case
Study Yellowfin Tuna and Dolphins in the
Eastern Tropical Pacific TUNA II The Worlds
Tuna Fisheries
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General Comments About Tuna Tuna are neither warm
blooded nor cold blooded. Their circulatory
system allows them to maintain their body
temperature higher than their surroundings, but
they cannot maintain a constant body
temperature. The principal factors limiting the
distribution of tuna are temperature and oxygen
concentration. Because of their high metabolic
rates, tuna are voracious predators. Daily food
consumption can be as high as 25-30 of their
body weight. Tuna are known to undertake very
long migrations. Migrations across entire ocean
basins are not unusual. To some extent tuna may
use ocean currents to guide them on these
migrations, but they also appear to have a
geomagnetic sense. Skipjack, yellowfin, and
bigeye tuna are generally considered to be
tropical tunas. Albacore and bluefin tuna are
found in more temperate latitudes
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Some big picture items to think about
Tuna enjoy Warm Water Lots of Oxygen Lots
of Food
The eastern sides of ocean basins have Shallow
Thermocline Shallow Oxygen Zone Nutrient-Rich
Upwelling Zones
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Some big picture items to think about
Tuna enjoy Warm Water Lots of Oxygen Lots
of Food
The eastern sides of ocean basins have Shallow
Thermocline Shallow Oxygen Zone Nutrient-Rich
Upwelling Zones
Along the west coasts of continents tuna can be
found In Higher Concentrations In Shallower
Water Closer to Shore For Easier Fishing
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Commercial catches of skipjack, yellowfin,
bigeye, and albacore tuna
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Skipjack tuna
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Skipjack information Virtually the entire catch
occurs in the Pacific (70) and Indian (24)
oceans. The western Pacific accounts for 50 of
the catch. Skipjack are the smallest of the
commercially important tunas and have the largest
surface-to-volume ratio. This makes
thermoregulation more difficult for skipjack than
the other tuna species. Temperature range is
20-30oC. Skipjack are also unique among the
tunas in that the adults have no swim bladder.
Hence they must expend more energy in routine
swimming.
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Skipjack information Skipjack have a definite
tendency to school, and most skipjack are caught
with purse seines. FADs have been a major
impetus to the skipjack fishery in the western
Pacific. Diet includes clupeids, crustaceans,
and mollusks, but may also include other
skipjack. Peaks in foraging occur around dawn
and dusk. Predators on skipjack tuna include
sharks, billfish, wahoo, yellowfin tuna, and, in
the case of small skipjack, even seabirds.
Spawning occurs throughout the year in tropical
latitudes but is confined to the summer months at
higher latitudes. Major market for skipjack tuna
is canned tuna light-meat tuna.
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Management Western Pacific - Convention on the
Conservation and Management of Highly Migratory
Fish Stocks in the Western and Central Pacific
Ocean. First meeting of the group in December
2004. Indian Ocean - Indian Ocean Tuna
Commission (IOTC). Agreement came into force in
March 1997. Member nations who object to a
decision by the IOTC are not bound by it.
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Yellowfin tuna
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Yellowfin information Geographical distribution,
temperature range, and spawning behavior very
similar to skipjack. Tend to associate with
dolphins more than any other species. Yellowfin
have a keen sense of smell dolphins have none.
However, dolphins can track prey using ultrasonic
echolocation. Pacific (67) and Indian Ocean
(22) account for most of the catch. Much of the
fishing is done with purse seines. Canned tuna
(light tuna) is again the primary market.
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Bigeye tuna
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Bigeye information Similar in appearance to
yellowfin, but swim at greater depths and have a
higher fat content. Catch distributed as
follows Pacific (50), Indian (30), Atlantic
(20). Small bigeye are caught as bycatch of
purse seining for skipjack and yellowfin. The
larger and more valuable bigeye are taken with
long lines. The meat of bigeye tuna turns light
grey and sometimes darkish after cooking or
grilling, a characteristic that makes it less
suited for canning than skipjack, yellowfin, or
albacore tuna. By far the most popular market
forms for bigeye tuna are fresh fillets (sashimi)
and fresh whole fish. The principal market is
Japan, where bigeye sashimi is in high
demand. The principal fishing nations are Japan
and Taiwan.
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Not a great deal is known about the ecology of
bigeye tuna, and scientists do not agree on
whether the stocks are being fully exploited.
The bycatch of bigeye associated with the
skipjack and yellowfin fisheries is a concern,
since the fish in question are not sexually
mature.
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Albacore tuna
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Albacore information Albacore is a temperate
water fish, and stocks in the northern and
southern hemisphere are disjoint. In the
northeastern Pacific, for example, albacore are
not found in water with a temperature greater
than 19oC. The principal fishing areas are the
western and central Pacific, which together
account for 58 of the catch. Almost all
albacore are caught either with pole-and-line,
surface trolling, or long lines. There is no
purse seine fishery for albacore. The principal
market for albacore is canned tuna. Albacore is
the only canned tuna marketed as white tuna.
Due to its unusual bone structure and the soft
consistency of its meat, albacore cannot be
filleted. As in the case of bigeye, Japan and
Taiwan dominate the catch.
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Bluefin tuna
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Bluefin tuna being readied for auction at Tokyos
Tsukiji Fish Market.
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Commercial catches of bluefin tuna species
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Atlantic bluefin information Atlantic bluefin
are found only in the North Atlantic and
Mediterranean and Black Sea. Bluefin in the
South Atlantic are southern bluefin. Atlantic
bluefin are the largest of the tunas, with
weights up to 680 kg and a lifespan up to 30
years. The fishery for Atlantic bluefin goes
back literally thousands of years. There are two
spawning areas, one in the Gulf of Mexico between
mid-April and mid-June, and the second in the
Mediterranean and Adriatic Seas from June through
August. There is controversy over whether the
stocks should be considered separate or not.
Tagging studies have shown that the tuna
definitely make trans-Atlantic migrations. Atlant
ic bluefin dive to depths of as much as 1,000
meters and feed on fish such as mackerel, herring
whiting, and squid.
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The commercial value of Atlantic bluefin prior to
1970 was about 0.10 per kg. Increasing demand
for giant bluefin to supply the Japanese sushi
and sashimi markets changed this picture
dramatically. With the development of air freight
in the early 1970s, giant Atlantic bluefin were
being caught and immediately shipped to Japan,
where they were sold for more than 2 per kg. n.
b., Current prices are 20-70 per
kilogram. Management International Commission
for the Conservation of Atlantic Tunas (ICCAT)
formed in 1969. Western Atlantic stock of
bluefin tuna continued to decline, and in 1981
ICCAT set a quota of 1,160 tonnes for the western
Atlantic. This is based on the assumption by
ICCAT that there were two separate stocks
western and eastern Atlantic.
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The commercial value of Atlantic bluefin prior to
1970 was about 0.10 per kg. Increasing demand
for giant bluefin to supply the Japanese sushi
and sashimi markets changed this picture
dramatically. With the development of air freight
in the early 1970s, giant Atlantic bluefin were
being caught and immediately shipped to Japan,
where they were sold for more than 2 per kg. n.
b., Current prices are 20-70 per
kilogram. Management International Commission
for the Conservation of Atlantic Tunas (ICCAT)
formed in 1969. Western Atlantic stock of
bluefin tuna continued to decline, and in 1981
ICCAT set a quota of 1,160 tonnes for the western
Atlantic. This is based on the assumption by
ICCAT that there were two separate stocks
western and eastern Atlantic.
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Since 1982 the annual catches of bluefin tuna
from the western Atlantic have fluctuated around
an average of about 2,200 tonnes. During the
same time catches of bluefin in the eastern
Atlantic and Mediterranean increased to roughly
40,000 tonnes, with most of the catch coming from
the Mediterranean Sea. By the early 1990s the
western Atlantic bluefin stock had declined by
about a factor of 10 from its level in 1975, and
by 1993 the eastern Atlantic population was
estimated to be only 13 of its size in 1970.
Efforts by several countries (Sweden, Kenya) to
list the western Atlantic bluefin population in
Appendix I of the Convention on International
Trade in Endangered Species (CITES). Proposals
withdrawn as result of pressure from
Japan. About 65 of the catch currently comes
from the Mediterranean. Atlantic bluefin are
taken using pole-and-line, surface trolling, and
long lines.
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Restrictions on fishing have apparently stopped
the decline of the western Atlantic bluefin stock
in recent years. However, the stock is either
not recovering or is recovering very slowly. At
its 1998 meeting, ICCAT adopted a rebuilding
program for the western stock with a goal of
reaching the maximum sustainable yield in 20
years. The total allowable catch (TAC) in the
western Atlantic is currently 2,700 tonnes, with
about 55 of that quota being allocated to the
United States. In the Mediterranean, about 30
of the catches in 1993 were below the minimum
size limit, an indication that the nations
involved in the fishery were not adhering to
ICCAT recommendations. Scientific evidence
indicates that the catch in the eastern
Atlantic/Mediterranean must be reduced to no more
than 25,000 tonnes before the stock can begin
rebuilding. The reported catch in the eastern
Atlantic/Mediterranean in 2002 was a little less
than 33,000 tonnes.
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Pacific bluefin information The Pacific bluefin
fishery is the only unregulated bluefin fishery
in the world. Japan currently accounts for
about 64 of the catch, virtually all of which is
taken in the northwest Pacific. Taiwan (west
central Pacific and northwest Pacific) and Mexico
(east central Pacific), account for the remainder
of the catch. Unlike the Atlantic bluefin, there
is clearly only one stock of Pacific bluefin
tuna. Adults are known to spawn between the
Philippines and southern Japan and in the Sea of
Japan during the spring and summer. Tagging
studies indicate that some Pacific bluefin remain
in the western Pacific for their entire lives.
Others migrate to the eastern Pacific, mostly
during the first and second years of life, and
remain there for 1-2 years.
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Pacific bluefin are caught on a variety of gear,
and some are taken as bycatch of longlines
targeting tropical tuna. The fish caught using
surface gear are often juveniles, i.e., sexually
immature. Almost all Pacific bluefin taken in
the eastern Pacific are sexually immature.
Japanese catch Pacific bluefin less than one year
old by trolling. The fish are 15-30 cm in
length. Theoretical studies indicate that yield
per recruit would be maximized if Pacific bluefin
were not recruited to the fishery until age 3-5.
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Southern bluefin information Southern bluefin
are the most overexploited of the bluefin
tuna. There is only one known breeding ground,
in the Indian Ocean southeast of Java, Indonesia.
Juveniles migrate down the west coast of
Australia. They may spend the first few summers
of their life in surface waters off the south
coast of Australia, but during the winter they
move into deeper, temperate oceanic waters. The
fishery is dominated by Japan and Australia. As
is the case with other bluefin species, surface
gear takes many sexually immature fish.
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Since about 1990 a fishery has developed off the
coast of South Australia for juvenile fish that
are transferred to floating enclosures and
fattened to increase their market value.
Initially these farmed fish were caught with
pole-and-line, but they are now taken with purse
seines. The fish are transferred to floating
pens, which are towed to Port Lincoln (South
Australia). From there the tuna are transferred
to moored farm pens. In recent years 60-70 of
the global catch of southern bluefin tuna has
been longlined. The recruitment of young fish
declined substantially after 1980, and fisheries
biologists agree that the stock has been the
victim of recruitment overfishing since that
time. Current estimates indicate that the
spawning stock biomass is roughly 7-15 of the
level in 1960 (when substantial reductions had
already occurred). Recognizing that the southern
bluefin stock was in trouble, Japan, Australia,
and New Zealand set informal catch quotas from
1989 to 1993, with Australia allocated 5,265
tonnes, Japan 6,065 tonnes, and New Zealand 420
tonnes. The three countries signed an
international convention in 1993 called the
Commission for the Conservation of Southern
Bluefin Tuna (CCSBT) After 1994, the catch
quotas were allocated by the CCSBT.
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South Korea and Taiwan joined the CCSBT in 2001
and 2002, respectively, and Indonesia has become
a cooperating non-member. Under current
management there is no evidence that the spawning
stock is recovering. The initial goal of the
CCSBT was to rebuild the spawning stock to the
1980 level by 2010, but that target has now been
pushed back to 2020. However, Australian and New
Zealand scientists give the CCSBT little chance
of achieving that goal and feel that further
reductions in the catch quotas will be needed to
give the stock a chance to recover. The long
time to reach sexual maturity makes this species
particularly vulnerable to overfishing.
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Tuna Management Persepctives
I. Species II. Oceans III. Nations
http//www.intfish.net/
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Management Western Pacific - Convention on the
Conservation and Management of Highly Migratory
Fish Stocks in the Western and Central Pacific
Ocean. First meeting of the group in December,
2004. Indian Ocean - Indian Ocean Tuna
Commission (IOTC). Agreement came into force in
March 1997. Member nations who object to a
decision by the IOTC are not bound by it.
Eastern Pacific Inter-American Tropical Tuna
Commission (IATTC). Originally (1950) USA and
Costa Rica. Now 12 nations. Principal focus is
yellowfin tuna.
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Geographical area under the purview of the
Convention on the Conservation and Management of
Highly Migratory Fish Stocks in the Western and
Central Pacific Ocean.
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Management IATTC and CYRA Inter-American
Tropical Tuna Commission (IATTC). Formed in 1950
by USA and Costa Rica. Now includes 12
countries. Purview is eastern tropical Pacific
to 140o west longitude. Management has been
almost entirely concerned with yellowfin
tuna. Commissions Yellowfin Regulatory Area
(CYRA) is de facto where the ITTAC is regulating
tuna catches
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Geographical extent of the CYRA.
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International Commission for the Conservation of
Atlantic Tunas (ICCAT). ICCAT established as a
result of a meeting between Brazil, Japan, South
Korea, and the United States in 1966. One of
the constraints limiting the effectiveness of the
ICCAT is the fact that it can only make
recommendations. It has no direct powers of
enforcement, and as noted in the case of Atlantic
bluefin, ICCAT recommendations are not always
followed by the contracting parties. ICCAT
studies indicate that there is no prospect for
significant increases in tuna catches. In the
case of albacore, for example, the recommended
total allowable catch for 2004 is 63,700 tonnes,
which is virtually identical to the average
annual catch of albacore from 1998 through
2002. Atlantic bluefin have clearly been
overexploited.
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Tuna catches in the Atlantic Ocean
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Indian Ocean Tuna Commission (IOTC). Agreement
entered into force in 1997. Currently 23 member
nations. Conservation and management measures
binding on members of the IOTC must be adopted by
a two-thirds majority of members present and
voting. However, individual members objecting to
a decision are not bound by it.
Tuna catches in the Indian Ocean
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Commission for the Conservation of Southern
Bluefin Tuna (CCSBT). Went into force in
1994. Despite management, the stock does not
seem to be recovering. Problem with catch of
sexually immature fish. Convention on the
Conservation and Management of Highly Migratory
Fish Stocks in the Western and Central Pacific
Ocean Entered into force on June 19, 2004.
First meeting is December 2004. Japan and the
United States have not ratified the Convention.
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A Tuna Management Case Study Good Idea, Poor
Execution, and a Little Bit of Luck
Goal of management has been to keep catch per
unit effort above 2.7 tonnes per fishing day and
to base a given years quota largely on whether
the preceding years quota resulted in an
increase or decrease in the CPUE. Problems
associated with projecting the time when the
quota would be reached has often resulted in
catches exceeding quotas. Poor judgement used in
adjusting quotas. Regime shift favoring
yellowfin tuna seems to have occurred in
1983-1985. There were very good recruitment
years in 1998-2000.
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Goal of management has been to keep catch per
unit effort above 2.7 tonnes per fishing day and
to base a given years quota largely on whether
the preceding years quota resulted in an
increase or decrease in the CPUE.
Catch (tonnes)
2.7 tonnes of catch
1 day of effort
(Days)
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Record of catch per unit effort and spawning
stock biomass of yellowfin tuna in the CYRA.
(Note that the y-axes dont go to zero)
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Record of catch per unit effort and spawning
stock biomass of yellowfin tuna in the CYRA.
(Note that the y-axes dont go to zero)
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A Tuna Management Case Study Good Idea, Poor
Execution, and a Little Bit of Luck
A Pacific Basin Regime Shift and some following
good recruitment years did more good than the
management efforts in this case. Think what
would have happened to this fishery had the
regime shift not been a beneficial one!