Description
Yellowfin tuna is an abundant tropical tuna, found throughout
the warmer reaches of the Atlantic, Pacific and Indian oceans.
Yellowfin tuna are considered a single species in all oceans.
However, the relationships between distinct seasonal aggregations
of yellowfin within ocean basins are not well described. In the
western Atlantic Ocean, fisheries have developed to target aggregations
of yellowfin tuna in the Gulf of Mexico, Caribbean Sea, and along
the Continental Shelf and slope waters from Hatteras to Cape Cod.
Much larger harvests occur at fishing grounds in the east Atlantic.
Yellowfin are exposed to fisheries in Massachusetts only off the
south side of Cape Cod, where seasonal warming and Gulf Stream
influences allow yellowfin to range over the Continental Shelf
to forage during the summer.
Like the other tunas, yellowfin are well known for their physical
beauty and powerful swimming. The similar appearance of tunas
can lead to some confusion over identification. The bluefin, albacore,
yellowfin, and bigeye tuna all have a streamline, "football"
shape with darker coloration dorsally and silvery colors on the
side. In the yellowfin, the dorsal surface is dark blue and can
appear brownish when in the water. True to name, the yellowfin
can have much yellow in their fins and shiny, golden yellow along
their sides. Coloration alone won't allow you to separate these
tunas. A key feature to use at sea is the length of the pectoral
fin. The yellowfin pectoral fin reaches the beginning of the second
dorsal fin. The albacore pectoral fin always goes beyond the start
of the second dorsal and the bluefin pectoral fin never reaches
the second dorsal fin. The combination of color and pectoral fin
size should suffice in most cases, although in small yellowfin,
a combination of the above and gill raker counts (27-33) and presence
of a smooth liver may be needed for a positive identification.
Another thing to keep in mind is that only bluefin tuna occur
in the Gulf of Maine.
Yellowfin tuna are even faster growing than bluefin tuna, but
do not reach the large size of their giant cousin. The all-tackle
record is a 388 lb. yellowfin tuna caught in Mexico in 1977. On
the east coast, yellowfin tuna over 200 lbs. are uncommon. After
one year of life, yellowfin are 8-10 pounds. Age-2 yellowfin are
about 35 lbs. and age-3 about 75 pounds. A four year old yellowfin
averages about 130 lbs. which is a little less than twice that
expected of age-4 bluefin tuna. Most of the yellowfin we see on
the Continental Shelf each summer are similar in size and typically
age-2 or age-3. For reasons not well understood, age-1 are not
common and absent in most years on the east coast. Age 4-6 yellowfin
have become less common in recent years, a likely response to
fishing mortality.
Habits
Similar to bluefin tuna, yellowfin tuna's circulatory system
acts to retain metabolic heat. This warms their bodies above ambient
temperature and allows them to process food and transport oxygen
more efficiently. Their ability to stay warm does not match the
near warm-blooded bluefin tuna, and as a result, their migration
range is more limited by water temperature. The bulk of the population
is found at oceanic habitats within 20º latitude of the equator
and typically in waters at least 64 ºF. Water temperatures
of 68 ºF or higher are often associated with higher catch
rates. Their sensitivity to cooler temperatures also limits vertical
movements to the relatively thin layer between the thermocline
and surface.
While most of the Atlantic yellowfin tuna population is found
not too far from the equator, the warm Gulf Stream allows fish
to stray north on the west side of the ocean. There appears to
be some allegiance among yellowfin tuna in the western North Atlantic
Ocean, although there is not enough genetic or migration data
to suggest there is a separate stock. During the winter, an aggregation
of yellowfin tuna can be found associated with the Gulf Stream
running off Cape Hatteras and east of the Continental Shelf slope
for several hundred miles. With the warming of summer, some of
these fish seem to slip west of the Gulf Stream to forage in the
canyons of the Continental Shelf slope and during the warmest
months fan out over the shelf to forage along water temperature
edges. We actually know little about how these fish interact with
yellowfin found in the Caribbean Sea, Gulf of Mexico and east
Atlantic. We do know that water temperature limits their progress
north. No yellowfin have been caught on the Continental Shelf
above Nantucket Shoals and the slope canyons off of Georges Bank
and Nova Scotia mark the northern limit off the shelf.
The recent colonization of yellowfin tuna to the Continental
Shelf south of New England in the 1970s and accumulating evidence
of the influence of global warming on marine habitats raises an
enticing question for scientists and anglers to consider as we
begin the 21st century. Will yellowfin tuna make the turn around
Cape Cod and soon become a seasonal predator in the Gulf of Maine?
It has not been documented so far. Nantucket Shoals and the Great
South Channel act as a thermal barrier and typical summer Gulf
of Maine water temperatures are thought to be too cool for yellowfin.
But, they come close enough now to enter the Gulf on a day-trip
and would like the food. And it would certainly be a welcome visit.
Yellowfin tuna have been exploited at high levels for decades
in the Atlantic Ocean, however, the harvest appears to be near
sustainable yields. Some of this good fortune may come from their
prolific biology. Yellowfin tuna grow very fast and reach sexual
maturity at age-2 or age-3. Age-2 and age-3 yellowfin can produce
several million eggs, and a yellowfin reaching age-4 can produce
over eight million eggs and has a narrowing list of predators.
This natural history provides good opportunity for successful
year classes to come along. The primary spawning grounds in the
Atlantic is thought to be the Gulf of Guinea and some spawning
occurs in the Gulf of Mexico. Yellowfin cohorts tend to stick
together, with tight size ranges found in schools. The age-2 and
age-3 yellowfin we see spilling over the Continental Shelf each
season are seeking large concentrations of pelagic prey; and typically
feed on sand lance, squid, mackerel, and butterfish.
Management
Fisheries for yellowfin tuna in the western North Atlantic
Ocean have developed fairly recently. The first recorded catch
in the western North Atlantic Ocean came in 1949. From 1949 to
1956, a federal research vessel caught five yellowfin while trolling
off the edge of the Continental Shelf. Japanese longline fleets
began targeting yellowfin in the Atlantic in 1955, primarily off
of South America. Commercial harvest in the U.S. began with purse
seine catches in the 1960s, followed by longline activity in the
1970s. Purse seine have been remained sporadic, occasionally reaching
1,000 mt, while the longline fishery developed into the primary
harvesting sector for yellowfin tuna in the west Atlantic. Recreational
catches of yellowfin tuna began in the 1970s as rod and reel fishermen
began picking up yellowfin on the Continental Shelf while targeting
other pelagics. Yellowfin tuna soon became a principal target
for offshore recreational fleets on the east coast. The rise in
importance of yellowfin tuna to east coast fisheries is dramatic.
In the 1950s and 1960s, yellowfin tuna was nearly unknown to longline
and rod and reel fisheries on the east coast, and since the mid-1980s
it has become the dominant tuna species in terms of landings and
has generated tremendous economic benefits. As important as yellowfin
catches are to the U.S., they are greatly exceeded by the Atlantic-wide
harvest of which the U.S. contributes less than five percent.
Yellowfin tuna in the Atlantic Ocean are managed by the International
Commission for the Conservation of Altantic Tunas (ICCAT). Yellowfin
tuna fisheries under ICCAT do not presently have the detailed
country-based quota systems found for Atlantic bluefin tuna. Stock
assessments to date have determined that yellowfin tuna are fully
exploited in the Atlantic with harvest levels near maximum sustainable
yield. Yellowfin tuna management in the Atlantic has primarily
been limited to attempts to cap fishing mortality with minimum
sizes and restrictions to fishing practices. Despite the determination
that Atlantic yellowfin tuna are not overfished, concerns are
growing over increasing catches, especially by longline fleets
that are making unregulated harvests in the Atlantic outside the
authority of ICCAT. The National Marine Fisheries Service is responsible
to implement ICCAT regulations and manage domestic fisheries for
yellowfin tuna. A minimum size of 27 inches (curved fork length)
is currently in place for all U.S. Atlantic fisheries. For permit
requirements and regulations contact NMFS at http://www.nmfspermits.com
or (888)-872-8862.
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Recreational Fishery Regulations
Both the recreational and commercial fisheries for yellowfin
tuna are regulated by the National Marine Fisheries Service
(NMFS). Click here
for more information, or call 1-888-USA-TUNA.
Angling and Handling
Tips
Yellowfin tuna are one of the most challenging species
to catch with a rod and reel off the coast of Massachusetts.
Their large size and high capacity for exercise can result in
broken tackle if you are poorly prepared. Yellowfin are usually
targeted along the Continental Shelf south of Martha's Vineyard
where seasonal conditions create an exciting fishery for pelagic
tunas, sharks and marlin. Boats typically need to run offshore
at least 20 miles to find the right temperature edges for attracting
yellowfin tuna. Trolling and chumming are the primary methods
used by anglers. Trolling involves creating a flashy presentation
of multiple lures trolled in the boat wake while moving along
at 7-8 nautical miles per hour. Single hook lures with plastic
skirts are a common offering and chains or spreader bars of
lures are an option to increase the visual attraction. Green
is a popular color for yellowfin tuna. The idea is to have a
pattern of lures that splash, wiggle and sparkle enough to trick
the fish into thinking it is attacking a group of agitated baitfish.
Chumming involves introducing a baited hook to yellowfin tuna
while the boat is drifting or anchored. Cut pieces of butterfish
or silver hake are common baits, and small pieces of the bait
are deliberately tossed in the water around the baited hook
to attract tuna.
Both methods use similar tackle. Since yellowfin
typically range between 30-80 pounds in this fishery, you most
often see high quality 30, 50, or 80 pound-class reels and rods
and line used. Yellowfin that exceed 100 pounds are matched
well with the 80 pound class gear. Lighter tackle can be used
and is gaining popularity, but you better have time on your
hands if you want to land a 150 lb. yellowfin tuna with 30 pound
class tackle.
Once hooked, rods are taken from rod holders and transferred
to the angler wearing a gimbal belt and/or back harness. This
sets up a "stand-up" fish fighting technique that
can quickly fatigue the inexperienced angler faced with a large
tuna. The excitement generated in the cockpit as multiple yellowfin
tuna strike and rip line off the reels has to be a highlight
of sportfishing opportunities off the coast of Massachusetts.
Tunas were built to get away, and are not that
great at playing hurt. If you plan to release your catch, keep
the fish in the water if possible while you carefully remove
the hook. Avoid bruising or cutting the tuna during boatside
handling If the tuna is fatigued, swim the fish along for a
few minutes while the boat is in gear to allow the fish to "catch
its breath" (release carbon dioxide and make up oxygen
debt). If you plan to boat the tuna, then bleed and chill the
fish as soon as possible. Fresh yellowfin is a delight to eat
and a 40 pound fish can feed plenty of people. Yellowfin eaten
raw doesn't have the premier reputation of bluefin tuna sashimi,
but don't pass it up if you like sashimi. And marinated yellowfin
steaks on the grill are thought by some to be best among the
large pelagics.
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Commercial Fishery Regulations
Both the recreational and commercial fisheries for Yellowfin
tuna are regulated by the National Marine Fisheries Service.
Click here for more
information, or call 1-888-USA-TUNA.
