(DRAFT) - Taxonomy
Species tuna, bluefin
Species Id M010510
Date 26 AUG 96
TAXONOMY
NAME - tuna, bluefin
OTHER COMMON NAMES - Bluefin tuna, tuna, bluefin, tunny, common tuny, horse mackerel, great albacore, giant tuna and shortfinned tuna
ELEMENT CODE -
CATEGORY - Fish
PHYLUM AND SUBPHYLUM - Chordata, Vertebrata
CLASS AND SUBCLASS - Teleostomi,
ORDER AND SUBORDER - Perciformes,
FAMILY AND SUBFAMILY - Scombridae,
GENUS AND SUBGENUS - Thunnus,
SPECIES AND SSP - thynnus,
SCIENTIFIC NAME - Thunnus thynnus
AUTHORITY - Linnaeus, 1758
TAXONOMY REFERENCES - 258 and 1717
COMMENTS ON TAXONOMY -
A relatively large family of pelagic marine fishes occurring in tropical,
subtropical, and temperate waters of the world's oceans. Most are powerful
and active swimmers and many undertake considerable migrations; some form
large schools.
Four genera (Auxis, Euthunnus, Katsuwonus, and Thunnus) have a
countercurrent heat-exchanger system, a modification of the vascular system,
enabling them to maintain a body temperature higher than the temperature of
the surrounding water, i.e., they are warm blooded.
Predatory fishes, the scombrids feed in schools on small fishes and squids;
smaller species may be planktivorous.
The family is of great commercial and recreational importance. Commercial
fisheries may involve long-distance, high-seas operations using large modern
and efficient vessels, locally directed fisheries (mackerel), or artisanal
fisheries as in many parts of the tropics. A variety of gear is employed
such as purse seines, gill nets, trap nets, seines, and hook-and-line. The
world catch fluctuates annually between 4 and 6 million tonnes.
Fifteen genera with 49 species; 7 genera with 12 species reported from the
Canadian Atlantic area during summer months. Most enter Canadian waters
after warming has occurred and feed on the abundant food fishes such as
herring. Spawning usually occurs far to the south.*258*
Taxonomy - 1 (DRAFT) - Status
Species tuna, bluefin
Species Id M010510
Date 26 AUG 96
STATUS
Coded Status
Game (Consumptive Recreational)
Commercial
Existing, FMP exists
Commercial/consumption
See Comments
REFERENCES FOR STATUS - 258
COMMENTS ON STATUS -
The bluefin tuna has been sought by man for food for over 2000 yr at least,
especially in the Mediterranean where it was well known and admired because
of its size, predictability, and power. Unfortunately heavy exploitation
has taken its toll and bluefin stocks are seriously threatened. The
establishment of the International Commission for the Conservation of
Atlantic Tunas (ICCAT) will, it is hoped, curb overexploitation. Also,
Japanese biologists have been developing an aquaculture program which
involves rearing bluefin from egg to market size. Their progress to date
has been encouraging.
The bluefin tuna became known in eastern Canada primarily as a game or sport
fish, sparked by the establishment of the International Tuna Cup Matches at
Wedgeport, NS in the late 1930's. Large tuna do not frequent waters off
Nova Scotia as they once did. For some years Newfoundland waters were their
choice, but in recent years the scene has shifted to the Gulf of St.
Lawrence waters of Prince Edward Island, New Brunswick, and Nova Scotia.
The current all-tackle world angling record for bluefin tuna, 679.0 kg was
for a fish caught off Auld Cove, in the Strait of Canso, Gulf of St.
Lawrence, Nova Scotia, in 1979.
A unique fishery for bluefin tuna was conducted for many years in St.
Margarets Bay, NS. Here the large, giant tuna, over 136 kg, were caught in
trap nets during summer and transferred to live holding pens where they were
fed for fatttening. When the fat content of the tissue reached the level
desired fish were butchered, dressed (headed and gutted) and shipped by
refrigerated transport and air to arrive in Japan within 72 h for used in
the Japanese raw fish (sashimi or sushi) market. The St. Margarets Bay
fishery has declined markedly in recent years.
The catch of bluefin tuna in the North Atlantic is governed by ICCAT. The
1985 Canadian quota for bluefin tuna was 573 t or 1521 fish, of which only
329 fish were caught.
Commercially, bluefin tuna are caught in traps, on longlines, or by purse
seine. The flesh is eaten raw, fresh or canned. North Americans are most
familiar with the canned product. In North America bluefin tuna are seldom
canned, and then oly those less than 25 kg in weight.*258*
Status - 1 (DRAFT) - Distribution
Species tuna, bluefin
Species Id M010510
Date 26 AUG 96
DISTRIBUTION
Distribution - 1 HABITAT ASSOCIATIONS
HABITAT - MARINE
REFERENCES FOR HABITAT - 258
LAND USE -
Water
Bays and Estuaries
REFERENCES FOR LAND USE - 258
COMMENTS ON HABITAT ASSOCIATIONS -
The bluefin tun is the largest member of the mackerel-like fishes (family
Scombridae). It moves northward into Canadian waters in summer and
southward again in late fall. Those entering Canadian waters may be
'giants', over 136.0 kg, or rarely 'jumpers', weighing 22.7-68.0 kg.
'Jumpers' arrived late in August, left in October, and occurred only in the
southern part of the Canadian region. 'Giants' arrive in June and stay
until October or later. They occur over the continental shelf, off
Newfoundland, and in the Gulf of St. Lawrence, at depths of 27-183 m, often
in schools of less than 50 fish, seeking food among the schools of herring,
capelin, mackerel, or squid. Using a countercurrent heat-exchange system,
the bluefin can maintain muscle temperatures 10-15 C above the temperature
of the surrounding water. The ability to elevate the body temperature
enables this warmwater species to invade cool northern waters and take
advantage of the abundance of food found there. The body fat thus
accumulated provides the energy for the extensive migrations undertaken by
bluefin tunas. They not only move from the waters off Florida and the Gulf
of Mexico northward as far as Newfoundland and the Gulf of St. Lawrence and
return, but large and small ones also undertake transatlantic migrations.
Adults tagged off the Bahamas were recaptured 4 mo later off Norway, a
distance of at least 6779 km.*258*
ANIMAL/PLANT SPECIES ASSOCIATIONS -
Predation and Competition: Adult bluefin have few enemies other than man but
a few do fall prey to killer whales (Orcinus orca) and mako sharks. Pilot
whales (Globicephala melaena) were also noted as predators. The mortality
on young tuna, however, must be high for they live in surface layers, where
they are vulnerable to other pelagic predators and seabirds. Hooked bluefin
are often attacked and eaten by mako sharks.*258*
Parasites and disease: Few parasites have been reported from bluefin tuna
caught in Canadian waters. However, bluefin from the Gulf of St. Lawrence
landed on Prince Edward Island in 1983 and examined by W.E. Hogans contained
some parasites previously unrecorded from bluefin tuna, while others may
represent incidental infections received from prey species. The parasites
found were Hirundinella ventricosa, Hysterothylacium adunca,
Hysterothylacium incurum, Hysterothylacium reliquens, Anisakis simplex,
Genitocotyle atlantica, Derogenes varicans, and Rhapidascaris camura. The
trematode, Hirundinella ventricosa, was reported from the stomach. Recently
the parasitic copepod Caligus coryphaenae was reported from bluefin tuna
caught in the Gulf of St. Lawrence off Prince Edward Island. The rate of
infection was high, 73.3 percent, and averaged 13.5 parasites per fish.
In a study of copepod parasites of scombroid fishes throughout their range,
C. coryphaenae and six additional species of copepods, including Pennella
sp. were listed.*258*
Habitat Associations - 1 (DRAFT) - Food Habits
Species tuna, bluefin
Species Id M010510
Date 26 AUG 96
FOOD HABITS
TROPHIC LEVEL -
CARNIVORE
REFERENCES FOR TROPHIC LEVEL - 258
LIFESTAGE FOOD FOOD PART
Important Squid, Octopus Not Specified
General Fish Not Specified
General Clupeiformes Not Specified
General Crustaceans Not Specified
General See Comments; Food
REFERENCES FOR GENERAL FOOD - 258
REFERENCES FOR IMPORTANT FOOD - 258
COMMENTS ON FOOD -
Tuna are voracious and active predators and require a great deal of food,
yet the stomach is relatively small so they must eat frequently. In
Canadian waters both pelagic and bottom fishes are eaten, including capelin,
saury, herring, mackerel, latern fishes, and barracudinas, as well as silver
hake and white hake. It was found that squid are the most important food of
Newfoundland tuna (Conception Bay), with capelin and saury next in
importance. Euphausiids are also eaten.
Bluefin maintain their viscera at an elevated temperature of 10-15 C above
water temperature, thus increasing the rate of digestion and the rate of
food intake. The high food intake enables them to accumulate body fat which
provides the energy for the extensive migrations they undertake.*258*
Food Habits - 1 (DRAFT) - Environment Associations
Species tuna, bluefin
Species Id M010510
Date 26 AUG 96
ENVIRONMENTAL ASSOCIATIONS
Environment Associations - 1 (DRAFT) - Life History
Species tuna, bluefin
Species Id M010510
Date 26 AUG 96
LIFE HISTORY
Description: Body stout but efficiently streamlined, fusiform, little
compressed greatest depth below middle of first dorsal fin, body then
tapering to a slender caudal peduncle with a strong median keel, smaller
keel above and below it, posteriorly. Head conical; snout pointed; mouth
terminal, lower jaw slightly projecting, one series of small conical teeth
in each jaw; eye relatively small. Gill rakers 24-43 on first arch. Fins;
dorsals, 2, first of 14 spines, first two spines longest, whole fin
depressible in groove, second dorsal, of 1 spine, 13 rays, narrowly
separated from first doral and slightly higher tahn first dorsal, not
depressible, followed by 9 finlets; caudal widely forked, lunate, firm;
anal, 1 spine, 12 rays, same size and shape as second dorsal, followed by 8
or 9 finlets; pelvics small, thoracic, ventral, under pectorals, fold into
a depression thus increasing streamlining; pectorals, 30-36 rays, short, not
reaching interspace between first and second dorsal fins. Scales cover
body, those in pectoral region forming an obscure corselet. Lateral line
complete. Ventral surface of liver striated. Vertebrae 39 (18 precaudal +
21 caudal). Size: to a large size in Canadian waters, usually about 270 cm
FL and 400 kg or more. Color: dorsal surface dark blue to black shading to
lighter blue on the sides and silvery gray below, lower flanks and abdomen
sometimes with faint, colorless transverse lines and rows of dots only
visible when fish is very fresh; first dorsal fin yellowish, sometimes
bluish; second finlets yellowish, edged with black; median caudal keel black
on adults.
Reproduction: Bluefin tuna do not reproduce in Canadian waters. The two
major spawning grounds in the western Atlantic are the Straits of Florida
and the Gulf of Mexico; less important spawning areas may also exist.
Spawning occurs during April, May, and June in subsurface waters. Females
of 270-300 kg may produce upwards of 60 million eggs in a spawning season.
Fertilized eggs are small, usually 0.9-1.1 mm in diameter, buoyant,
spherical, transparent, and have a single oil globule. At temperatures of
24.9-29.5 C in the Straits of Florida, hatching occurs in a few days.*258*
Growth: Young bluefin hatch when 2-3 mm long; the yolk sac is absorbed at 4
mm. Early growth is rapid. Recent work on aging larvae using otolith
microstructure has enabled biologists to estimate daily growth increments.
In general, males tend to grow larger and are therefore heavier than
females, while females appear to live longer than males. Males and females
of the same length weigh about the same.
The large bluefin tune (giants) that enter Canadian waters in early summer
to feed remain for 5 mo of the year or more, and gain weight rapidly at
about 8.5-10 percent of their body weight per month before leaving in late
fall. This rapid increase in weight-length relationships is great. Large
bluefins taken off Newfoundland in mid-August at a fork length of 229 cm
weighed 204 kg; at 224 cm, 232 kg; and at 259 cm, 273 kg.
Bluefins may reach a maximum age of 38 yr. The all-tackle world angling
record was 679 kg for a fish caught off Cape Breton, NS, in October 1979.
Vertebral centra and fin-ray sections have been used for aging but otoliths
are considered most reliable at present.*258*
LIFE HISTORY CODES -
Breeding Spawning Season: April
Breeding/Spawning Season: May
Life History - 1 (DRAFT) - Life History
Species tuna, bluefin
Species Id M010510
Date 26 AUG 96
LIFE HISTORY CODES -
Breeding/Spawning Season: June
Gestation/Incubation Period: 1-2 days
REFERENCES FOR LIFE HISTORY- 258
Life History - 2 (DRAFT) - Management Practices
Species tuna, bluefin
Species Id M010510
Date 26 AUG 96
MANAGEMENT PRACTICES
Management Practices - 1 (DRAFT) - References
Species tuna, bluefin
Species Id M010510
Date 26 AUG 96
References
258 * Scott, W.B., M.G. Scott. 1988. Atlantic Fishes of Canada.
Canadian Bulletin of Fisheries and Aquatic Sciences (219) (ed.).
University of Toronto Press Toronto, Canada:731.
References - 1