PACIFIC BLUEFIN TUNA – TROLL CAUGHT Thunnus orientalis ...

PACIFIC BLUEFIN TUNA – TROLL CAUGHT
Thunnus orientalis
Sometimes known as Bluefin Tuna, Northern Bluefin, Kuro maguro
SUMMARY
Pacific Bluefin Tuna are commonly caught by troll fishing, which has very low levels of bycatch
and causes no habitat damage. They are typically found in the North Pacific, and can travel huge
distances from their spawning grounds in the western Pacific to the eastern Pacific. Pacific
Bluefin Tuna are fished for by many countries including Japan, U.S., and Mexico, and they are
prized on the sashimi market. Due to high demand and market value, fishing pressure is too high
and Pacific Bluefin Tuna are uncommon. Chef Barton Seaver cautions: “Bluefin is the king of
the sea. It is the fattiest, richest fish in the ocean. Bluefin's unique flavor contributes to its great
appeal. However, we have eaten our way through this species' ranks and have forfeited our
ability to consume this fish. It is a taste that may be lost for many generations to come, maybe
forever. However, in most preparations, Bluefin can be substituted by pole-caught Yellowfin
tuna which, although not quite as elegant, is a great eating experience. For preparations such as
grilled tuna, try to seek out Albacore or even the tuna cousin, Wahoo.”
Criterion Points Final Score Color
Life History 1.75 2.40 - 4.00
Abundance 0.50 1.60 - 2.39
Habitat Quality and Fishing Gear Impacts 3.25 0.00 - 1.59
Management 1.50
Bycatch 3.50
Final Score 2.10
Color

LIFE HISTORY
Core Points (only one selection allowed)
If a value for intrinsic rate of increase („r‟) is known, assign the score below based on this value.
If no r-value is available, assign the score below for the correct age at 50% maturity for females
if specified, or for the correct value of growth rate ('k'). If no estimates of r, age at 50% maturity,
or k are available, assign the score below based on maximum age.
1.00 Intrinsic rate of increase 10 years; OR growth rate
30 years.
2.00 Intrinsic rate of increase = 0.05-0.15; OR age at 50% maturity = 5-10 years; OR a
growth rate = 0.16–0.30; OR maximum age = 11-30 years.
Sexual maturity begins at 150 cm or 5 years of age in the Pacific Ocean, while in the Sea
of Japan maturity occurs at a younger age of 3 years or 120 cm (Tanaka 2006). Growth
rates (k) of Pacific Bluefin Tuna Pacific Bluefin Tuna have been estimated to range from
0.104 to 0.195 and maximum ages have been estimated to be 26 years (Yukinawa and
Yabuta 1967, Shimose et al. 2008, and Shimose et al. 2009). Pacific Bluefin Tuna can
reach a maximum size of 300 cm and weight of 450 kg. (Fishbase 2009).
3.00 Intrinsic rate of increase >0.16; OR age at 50% maturity = 1-5 years; OR growth rate
>0.30; OR maximum age

-0.25 Species has a strategy for sexual development that makes it especially vulnerable to
fishing pressure (e.g., age at 50% maturity >20 years; sequential hermaphrodites;
extremely low fecundity).
-0.25 Species has a small or restricted range (e.g., endemism; numerous evolutionarily
significant units; restricted to one coastline; e.g., American lobster; striped bass; endemic
reef fishes).
-0.25 Species exhibits high natural population variability driven by broad-scale
environmental change (e.g. El Nino; decadal oscillations).
Studies to determine the effect of global warming on Pacific Bluefin Tuna distributions
have been started but the trends are difficult to interpret (Yamada et al. 2009). Pacific
Bluefin Tuna spawn in waters around 26º C and prefer water around 18ºC during their
migrations, which appear to be influenced by prey abundance and ocean currents
(Inageke et al. 2001). Fluctuations of peak recruitments in the 1950‟s and 1970‟s
corresponded with weak Aleutian Low, warm sea surface temperatures (SST) in the
central North Pacific and spawning areas (ISC 2008). Significant correlations between
Pacific Bluefin Tuna recruitment and Pacific Decadal Oscillation have been noted (ISC
2008). Data also shows that high recruitment occurs during periods of high temperatures
in spawning areas (ISC 2008).
+0.25 Species does not have special behaviors that increase ease or population consequences of
capture OR has special behaviors that make it less vulnerable to fishing pressure (e.g.,
species is widely dispersed during spawning).
+0.25 Species has a strategy for sexual development that makes it especially resilient to fishing
pressure (e.g., age at 50% maturity

ABUNDANCE
Core Points (only one selection allowed)
Compared to natural or un-fished level, the species population is:
1.00 Low: Abundance or biomass is 125% of BMSY or similar proxy.
Points of Adjustment (multiple selections allowed)
-0.25 The population is declining over a generational time scale (as indicated by biomass
estimates or standardized CPUE).
Standardized catch per unit effort (CPUE) for longline fisheries indicated that abundance
increased during the early to late 1990‟s (Yamada et al. 2009). Abundances have
fluctuated since the peaks in the late 1990‟s but appear to have decreased in recent years
(Yamada et al. 2009). Standardized CPUE indices are difficult to interpret for this species
because of changes in gear configurations and fishing grounds over time (ISC 2008). The
longline CPUE is thought to be a good representative of the trends in abundance for adult
Pacific Bluefin Tuna (ISC 2008). Peaks in abundance occurred in the 1960‟s, 1970‟s,
early 1990‟s and 2000 but have since gradually declined (ISC 2008).

-0.25 Age, size or sex distribution is skewed relative to the natural condition (e.g.,
truncated size/age structure or anomalous sex distribution).
The size of Pacific Bluefin Tunas caught depends on the individual fisheries targeting
them (Yamada et al. 2009). Trolling vessels in the western and central Pacific Ocean
catch juvenile Pacific Bluefin Tuna (15-30 cm) from July through October (IATTC
2008). From November through April larger (35-60 cm) juvenile Pacific Bluefin Tuna
are taken by trolling (IATTC 2008). Overall the majority of Pacific Bluefin Tuna caught
are considered „small‟ (Yamada et al. 2009). Sex to size ratio is also skewed, with a
higher proportion of females less than 160 cm (ISC 2008).
-0.25 Species is listed as "overfished" OR species is listed as "depleted", "endangered",
or "threatened" by recognized national or international bodies.
The results of the latest population assessment indicate that current fishing mortality is
too high (ISC 2009) but Pacific Bluefin Tuna are not considered overfished.
-0.25 Current levels of abundance are likely to jeopardize the availability of food for other
species or cause substantial change in the structure of the associated food web.
+0.25 The population is increasing over a generational time scale (as indicated by biomass
estimates or standardized CPUE).
+0.25 Age, size or sex distribution is functionally normal.
+0.25 Species is close to virgin biomass.
+0.25 Current levels of abundance provide adequate food for other predators or are not
known to affect the structure of the associated food web.
It is not known if current levels of Pacific Bluefin Tuna abundance will affect the
associated food web. We have not added or subtracted points due to this lack of
knowledge.
0.50 Points for Abundance

HABITAT QUALITY AND FISHING GEAR IMPACTS
Core Points (only one selection allowed)
Select the option that most accurately describes the effect of the fishing method upon the habitat
that it affects
1.00 The fishing method causes great damage to physical and biogenic habitats (e.g., cyanide;
blasting; bottom trawling; dredging).
2.00 The fishing method does moderate damage to physical and biogenic habitats (e.g., bottom
gillnets; traps and pots; bottom longlines).
3.00 The fishing method does little damage to physical or biogenic habitats (e.g., hand
picking; hand raking; hook and line; pelagic long lines; mid-water trawl or gillnet;
purse seines).
Most Pacific Bluefin Tuna are caught using purse seines, longlines and troll gear, with
some fish also caught by pole and line, set and drift nets (Yamada et al. 2009, and ISC
2008). Japanese trolling vessels catch about 25% or 3,000-5,000 mt (per year) of the total
Japanese catch of Pacific Bluefin Tuna (Yamada et al. 2009). Trolling does very little
damage to the physical habitat (Chupenpagdee et al. 2003).
Points of Adjustment (multiple selections allowed)
-0.25 Habitat for this species is so compromised from non-fishery impacts that the ability of the
habitat to support this species is substantially reduced (e.g., dams; pollution; coastal
development).
-0.25 Critical habitat areas (e.g., spawning areas) for this species are not protected by
management using time/area closures, marine reserves, etc.
Time area closures are not in place in the spawning grounds of Pacific Bluefin Tunas.
-0.25 No efforts are being made to minimize damage from existing gear types OR new or
modified gear is increasing habitat damage (e.g., fitting trawls with roller rigs or
rockhopping gear; more robust gear for deep-sea fisheries).
-0.25 If gear impacts are substantial, resilience of affected habitats is very slow (e.g., deep
water corals; rocky bottoms).
+0.25 Habitat for this species remains robust and viable and is capable of supporting this
species.
Oceanic habitat is likely healthy enough to support Bluefin Tuna populations.

+0.25 Critical habitat areas (e.g., spawning areas) for this species are protected by management
using time/area closures, marine reserves, etc.
+0.25 Gear innovations are being implemented over a majority of the fishing area to
minimize damage from gear types OR no innovations necessary because gear effects
are minimal.
Habitat effects of trolling for Pacific Bluefin Tuna are minimal.
+0.25 If gear impacts are substantial, resilience of affected habitats is fast (e.g., mud or sandy
bottoms) OR gear effects are minimal.
3.25 Points for Habitat Quality and Fishing Gear Impacts
MANAGEMENT
Core Points (only one selection allowed)
Select the option that most accurately describes the current management of the fisheries of this
species.
1.00 Regulations are ineffective (e.g., illegal fishing or overfishing is occurring) OR the
fishery is unregulated (i.e., no control rules are in effect).
2.00 Management measures are in place over a major portion over the species' range but
implementation has not met conservation goals OR management measures are in
place but have not been in place long enough to determine if they are likely to
achieve conservation and sustainability goals.
Pacific Bluefin Tuna are managed by the West and Central Pacific Fishery Commission
(WCPFC) and the Inter-American Tropical Tuna Commission (IATTC). Population
assessments are completed by the International Scientific Committee for tuna and tunalike
species in the North Pacific Ocean (ISC).
The WCPFC introduced several new management efforts for Pacific Bluefin Tuna after
the 2008 population assessment (WCPFC 2008), such as fishing effort north of 20° N
shall not increase from current levels and increasing the data collection system (WCPFC
2008). Previously enacted management efforts include vessel monitoring systems
(WCPFC 2007) and observer programs (WCPFC 2007b). The IATTC has not
implemented any conservation measured aimed at Pacific Bluefin Tuna.

3.00 Substantial management measures are in place over a large portion of the species range
and have demonstrated success in achieving conservation and sustainability goals.
Points of Adjustment (multiple selections allowed)
-0.25 There is inadequate scientific monitoring of stock status, catch or fishing effort.
Uncertainty within the population assessment process for Pacific Bluefin Tuna is caused
by a need for additional biological information such as size patterns, and growth and
maturity rates, as well as enhanced collection of detailed data from many small-scale
fisheries (Miyake et al. 2004). Additionally, there are problems associated with catch and
effort estimates for several fisheries (Yamada et al. 2009).
-0.25 Management does not explicitly address fishery effects on habitat, food webs, and
ecosystems.
-0.25 This species is overfished and no recovery plan or an ineffective recovery plan is in
place.
Although not considered overfished, abundance of Pacific Bluefin Tuna is very low and
recovery plans do not appear to be effective.
-0.25 Management has failed to reduce excess capacity in this fishery or implements
subsidies that result in excess capacity in this fishery.
Reductions in capacity in other fisheries, such as the purse seine fisheries, are needed to
increase the abundance of large tuna species like Pacific Bluefin Tuna (Miyake 2005).
+0.25 There is adequate scientific monitoring, analysis and interpretation of stock status, catch
and fishing effort.
+0.25 Management explicitly and effectively addresses fishery effects on habitat, food
webs, and ecosystems.
The Inter-American Tropical Tuna Commission and West Pacific Fishery Management
Council address fishery effects on ecosystem components such as trophic interactions and
the physical environment (IATTC 2008, and WPFMC 2008).
+0.25 This species is overfished and there is a recovery plan (including benchmarks, timetables
and methods to evaluate success) in place that is showing signs of success OR recovery
plan is not needed.

+0.25 Management has taken action to control excess capacity or reduce subsidies that result in
excess capacity OR no measures are necessary because fishery is not overcapitalized.
1.50 Points for Management
BYCATCH
Core Points (only one selection allowed)
Select the option that most accurately describes the current level of bycatch and the
consequences that result from fishing this species. The term, "bycatch" used in this document
excludes incidental catch of a species for which an adequate management framework exists. The
terms, "endangered, threatened, or protected," used in this document refer to species status that is
determined by national legislation such as the U.S. Endangered Species Act, the U.S. Marine
Mammal Protection Act (or another nation's equivalent), the IUCN Red List, or a credible
scientific body such as the American Fisheries Society.
1.00 Bycatch in this fishery is high (>100% of targeted landings), OR regularly includes a
"threatened, endangered or protected species."
2.00 Bycatch in this fishery is moderate (10-99% of targeted landings) AND does not
regularly include "threatened, endangered or protected species" OR level of bycatch is
unknown.
3.00 Bycatch in this fishery is low (

-0.25 Bycatch of this species (e.g., undersize individuals) in other fisheries is high OR bycatch
of this species in other fisheries inhibits its recovery, and no measures are being taken to
reduce it.
-0.25 The continued removal of the bycatch species contributes to its decline.
+0.25 Measures taken over a major portion of the species range have been shown to
reduce bycatch of "threatened, endangered, or protected species" or bycatch rates
are no longer deemed to affect the abundance of the "protected" bycatch species
OR no measures needed because fishery is highly selective (e.g., harpoon; spear).
Troll fisheries are very selective and have very low bycatch of „threatened, endangered or
protected‟ species. The Inter-American Tropical Tuna Commission (IATTC) has several
measures in place to reduce bycatch that include industry education and observer
programs (IATTC 2008).
+0.25 There is bycatch of targeted (e.g., undersize individuals) or non-targeted species in
this fishery and measures (e.g., gear modifications) have been implemented that
have been shown to reduce bycatch over a large portion of the species range OR no
measures are needed because fishery is highly selective (e.g., harpoon; spear).
Bycatch in the Pacific Bluefin Tuna fishery is very low (IATTC personal communication
2009).
+0.25 Bycatch of this species in other fisheries is low OR bycatch of this species in other
fisheries inhibits its recovery, but effective measures are being taken to reduce it over a
large portion of the range.
+0.25 The continued removal of the bycatch species in the targeted fishery has had or will
likely have little or no impact on populations of the bycatch species OR there are no
significant bycatch concerns because the fishery is highly selective (e.g., harpoon; spear).
3.50 Points for Bycatch

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