Habitat Characteristics of Skipjack Tuna (Katsuwonus pelamis)in The Western North Pacific: A Remote Sensing Perspective

Robinson Mugo, Sei-Ichi Saitoh, Akira Nihira and Tadaaki Kuroyama

Fish. Oceanogr. 19:5, 382–396, 2010

Review:

Eko Susilo

Institute for Marine Research and Observation

website : www.ekosusilo.net

email : ekosusilo@kkp.go.id

Introduction

• Skipjack tuna (Katsuwonus pelamis) is a highly migratory pelagicspecies inhabiting all tropical and subtropical waters of the world’soceans

• Catches are highest from May to August off Japan by surface gearssuch as pole and line and purse seines

• Migration patterns in the western North Pacific follow a north–• Migration patterns in the western North Pacific follow a north–south seasonal cycle where the poleward movement occurs in thefall–summer season

• This migration is also influenced by ocean currents and the fishmove along prevailing currents, utilizing them as foraging habitats

• Skipjack tuna are known to associate with fronts, warm-waterstreamers and eddies during their northward migration from sub-tropical to temperate waters

The objective

• To study skipjack tuna habitat from multisensor satelliteremotely sensed environment and fishery data, using GAMsand GIS.

Migration Route

Environmental Parameter

• Skipjack tuna physiology and morphology play a major rolein determination of habitat and, by extension, distribution– Swimming– High metabolic rates– Vertical movements ; night time depths ranged from surface to

30 m, whereas day time dives often were beyond 10030 m, whereas day time dives often were beyond 100

• Temperature has been the main environmental variableused to explain skipjack tuna occurrence and abundance– Chlorophyll concentration– Ocean mesoscale variability

Data

• Skipjack tuna daily catch data (CPUE) was determined intonnes per boat day periode March to November (2004)

• Weekly and monthly MODIS – SMI– sea surface temperature (SST)

– sea surface chlorophyll (SSC)– sea surface chlorophyll (SSC)

• Sea surface height anomaly (SSHA) from AVISO

• Eddy kinetic energy (EKE)

• GAMs were constructed using the GAM function of the mgcvpackage with CPUE as the response variable and SST, SSC,SSHA and EKE as predictor variables.

Spatial distribution of skipjack tuna fishing locationsThe 20C SST and a 0.3 mg m–3 SSC contour are plotted on the respective images to emphasize

SST and SSC gradients.

Histograms ofenvironmental variables

• 20.5 to 26Csea surface

temperatures

• 0.08–0.18,

• 0.22–0.27,0.3–0.37 mg

Relativelyoligotrophic

waters 0.3–0.37 mgm3,

waters

• 0–50 cmzero to positive

anomalies

• 0–200 and700–2500 cm2s–2

low tomoderate eddykinetic energy

GAMplots

GAMs

Results for each of the 15models (model, predictorvariables used to constructit, the respective degrees offreedom, AIC, P-value andfreedom, AIC, P-value anddeviance explained)

CONCLUSIONS

• SST was the most important habitat predictor for skipjack tuna migrationin the western North Pacific, followed by SSC.

• The oligotrophic side of the Kuroshio Front and the Kuroshio Extensionwere important skipjack tuna habitat features.

• Meso-scale features such as eddies played a role in formation of skipjacktuna habitat, although that role may not be as profound as that of SST andtuna habitat, although that role may not be as profound as that of SST andSSC.

• SUGGESTION– Longer term fishery data sets, with environment data

– Higher temporal and spatial resolutions