Migration and abundance of bigeye tuna (Thunnus obesus) inferred from catch rates and their relation to

variations in the ocean environment.

PFRP Meeting, Honolulu, 9-11 December , 2003

Pat Hyder, Keith Bigelow, Jeff Polovina, Mike Seki, Bo Qiu, Pierre Flament and Rusty Brainard

Acknowledgements: Sibert, Itano, Musyl, Gunn, Hampton, Brill

Annual spatial bigeye CPUE distributionHawaii based long line (Hawaiian waters to 35 N to Palmyra waters to 0 N)

CPUE (= fish/hook) α abundance (& catchability)If ∆ca << ∆ab then cpue ~α abun

It also depends on uniformity of effort cov. and type – data filtered > 10 HBF

Jan/Feb Mar/Apr May/Jun

Sep/Oct180 E 220 E

0 N

40 N

Jul/Aug Nov/Dec

Bigeye inter-annual and annual fish, hook and CPUE variationInter-annual variation Annual Variation

Increasing effortMarked reduction in CPUE following high catches during the 1997-98 ENSO period

fish

hooks

cpue

Time (years from 1990)Marked annual cycle for the full Hawaiian region with a maximum towards the end of the annual cycle

fish

hooks

cpue

Time proportion of the annual cycle

Bigeye CPUE centre of mass(Σ(cpue*lat. or lon.)/Σ(cpue)~ mean position)

fish

hooks

cpue

fish

hooks

cpue

CO

M L

atitu

deC

OM

latit

ude

CO

M L

atitu

de

CO

M la

titud

eC

OM

latit

ude

CO

M L

atitu

de

Time (years from 1.11990) Time (proportion of the annual cycle)

Bigeye CPUE and temp. (10 & 100m) var. at various latitudes(Temp from JPL ECCO model – note little seasonal T variation >100m)

CPUE

Temp

CPUE

Palmyra - Equatorial (2.5-10 N)Irregular thermal/CPUE cycleHigh catches associated with the period after ENSO upwelling

Hawaii – Sub-tropics (20-25 N) Seasonal thermal/CPUE cycleHigh CPUE associated with preferred thermal range (23-26 C) at end of annual cycle

Northern sub-tropics (30-35 N)Marked seasonal thermal/CPUE cycle. Significant CPUE only in third quarter when temp reaches preferred range

Years from 1.1.1990

Temp

CPUE

Temp

Month/ColorJ/F=greenM/A=redM/J=yellowJ/A=cyanS/O=blueN/D=magenta

Latitudinal bigeye CPUE and temperature (10m) bi-monthly variation (JPL ECCO model)

CPUE ~ continuous despite effort changes.Area under the CPUE curve ~ consistent during the year & represents total stock.Migration >>(A) Mar/Apr (red) - max CPUE southward. (B) Sep/Oct (blue) - max CPUE northward. >> region of maximum CPUE migrates N/S with the region of preferred thermal range (indicated with stars on thermal trace and below)

Pref T range (23 to 26) migrates N/S.

Time (prop. year)

hooks

fish

cpue

temp

Latitude0 N 40 NLa

titud

e0 N

40 N

Physiological reason for bigeye upper layer thermal preference(23-26oC water preferred to warm blood between dives?)

CPUE comparison with temp. indicates a preference for upper layer of 22<T<28oC which agrees with archival tag data (22-26oC) since fish depth not known for CPUE.

Exception is in subtropics where the fish appear to remain for short period longer than expected from surface temperature to feed at sub tropical convergence front.

Bigeye tuna have unique systems for diving to preserve heat (counter current vascular system), as well as to preserve oxygen and for low light eye adaption. They remain in the warm upper layer at night and return to this layer briefly between dives during the day (in a yo-yo type of behavior). May require specific temp range?

Upper layer temperature (9m) (JPL ECCO Model)

CPU

E

22I

28I

DiveCycle

Therm.Pref.

After Bigelow et al, 2002 and Musyl et al, 3003

Mesoscale variability in bigeye CPUE

Grouped Images CPUE, Chlorophyll (Seawifs), thermal and SSH (Aviso) & SSH slope.- Apparent concentration in/near high chlorophyll cyclonic eddies (upwelling).- Mesoscale CPUE variations due to abundance and catchability variations analysis is in progress. Not simple as effort is not uniform, uncertainty in line location (~ 40 km), and environ. effects on catchability (shear, pycnocline depth) may be significant but vary on the same scales as larger changes in abundance.

Weekly Sequences

Example: Late Dec 1997

Thermal conc. as 23oC isotherm moves south withseason.

Pacific-wide bigeye CPUE center of mass motionsor migrations (Japanese and SPC all fleet (A.F.) data)

Northern hemi. (blue) Southern hemi. (red) Both hemi (green)

CO

M L

atitu

de

Hawaii

Pacific (SPC AF)

Pacific (Japan)

Time (proportion of year)

Seasonal migrations in theory should be reflected in Pacific wide COM variations since reversal in both season and direction away from the equator result in in phase N-S motion in both hemispheres. However, Pacific-wide averaging will remove asymmetry in the migration cycle since it averages together opposing seasons in the two hemispheres.

Although Pacific wide analysis may indicate migration, to reduce errors care needs to be taken to select a suitable region for the analysis where effort exceeds a minimum level over the whole region. Where inter-stock differences exist analysis region may also be selected to include a single stock.

Pacific bigeye CPUE center of mass motion or migration(SPC all fleet data – Northern hemisphere – 100-290 E)

May/Jun (blue) - max south Nov/Dec (mag) - max north

Bigeye >>Significant N-S migrationNon-significant E-W migration

‘o’s represent mean location of CPUE COM for each monthError bars are stan. dev. of 30 annual values

Bigeye conventional tag data(suggestive not conclusive – more data required in sub tropics)

Southern hemispherePacific, SPC data (Hampton, Gunn, Williams)

Northern hemisphereHawaii Local, Seamounts(Itano, Holland)

We present the sub-tropical releases as equatorial tags do not appear to indicate seasonality .

Filtered to remove fish which traveled less than 3 degrees or 1 month (and represents a small proportion of the tags).

Latitudinal CPUE COM migration for various pelagic species (SPC A.F. data – Northern hemisphere Pacific)

Time (proportion of year)

Albacore (red)Yellow Tuna (green)Bigeye Tuna (blue)Striped Marlin (yellow)’Blue Marlin (cyan)Black marlin (magenta)Sword fish (black)

Month of max N-S Migrations======================

Spec North SouthAlba Nov JunYell N/A N/ABige Oct MayStri Jun DecBlue (Jun) (Dec)Blac (Jun) (Dec)Swo Oct May Time proportion of year

CO

M L

atitu

de

Significant N-S migrations are apparent for bigeye, albacore, swordfish and marlin (opposite phase) for Pacific-wide stock.Significant E-W migration is observed for yellowfin (E-Jun W-Dec) & albacore

Conclusions• Changes in CPUE associated with ocean abundance variations

appear to be larger than variations in catchability. Hence, CPUE is a parameter which can be used to indicate and quantify abundance.

• A bigeye thermally driven migration is evident which agrees withtheir known preference for 23-26 C water. This results in significant seasonal changes in both the Pacific-wide CPUE (particularly in the sub-tropical waters) and total catch of Hawaiian long line bigeye fishery.

• CPUE center of mass appears to be a useful parameter to highlight migration. However, care needs to be taken to select a suitable region for the analysis where effort exceeds a minimum level.

• Pacific-wide data suggest significant migrations may occur for various pelagic species.

• Assessment of mesoscale variability in CPUE due to changes in both abundance and catchability with satellite derived parameters (temp, chlor., currents) is in progress.

• More archival and conventional tag data is needed in the sub tropical waters to confirm derived migrations, and determine latitudinal variation in depth/thermal preference.

Bigeye – Japanese and all fleet Pacific

Other species SPC - includes albacore, yellowfin, bigeye, marlin (str/blue/blck), sword

Striped marlinAlbacore

Seasonal surface temperature and high catch locations

Seasonal surface chlorophyll and high catch locations

Spatial bigeye CPUE (Japanese long line) spatial distribution

Spatial bigeye (SPC all fleet data) spatial distribution

Spatial albacore (SPC all fleet data) spatial distribution

Yellow fin tuna (SPC A.F. data) spatial distribution

Sword fish (SPC A.F. data) spatial distribution

Striped marlin (SPC A.F. data) spatial distribution

Yellowfin Tuna COM –SPC all fleet data(30S to 30 N 100 to 210 E)

Albacore COM – SPC all fleet data(10 to 50 N and 140 to 240 E)

Striped marlin – SPC all fleet data(0 to 40 N 180-260 E)

Sword fish – SPC all fleet data(15-45 N and 120 to 220 E)