Fisheries Oceanography

SST anomalies off Peru coastline

ENSO impacts on pelagic fishes: variable catch reductions (Peru)

A. Bertrand

0

4

8

12

1950 1960 1970 1980 1990

Cat

ch (M

. ton

s)

El Nino

(Yánez et al. 1992)

Spatio-temporal scales of effects on peruvian pelagic fisheries

A. Bertrand

Time

Space

DecadeInter-annualMonth Season YearDay

Ocean

Local

Regional

Basin Stock condition before ENSO

Adapted reproduction

Fishery pressure

Local Upwelling

ENSO strength and duration

Inter-decadal regime

Large scale forcing

Small scale forcing

Pacific Decadal Oscillations

ENSO and pelagic fisheries: regime shift

Chavez et al. 2003

ClupeidaeAmerican shadAlosa sapidissima

Engraulidaebaelama anchovyThryssa baelama

(Chavez et al. 2002)

A. Bertrand

(Chavez et al. 2002)

A. Bertrand

Pacific Decadal OscillationWarm Phase Cool Phase

Wintertime Wind (arrows) and Sea SurfaceTemp (colors)- Affect the N. Pacific, with secondary signatures in the tropics (opposite for ENSO)

Pacific Decadal Oscillation(PCA of N. Pacific SST)

20-30 year duration

A. BertrandChavez et al 2003

A. BertrandChavez et al 2003

Humans as Top Predator

Prod

uctio

n (

mill

ion

tonn

es)

50

100

1800 1840 1880 1920 1960 2000Year

EE

Zs C

laim

s

Global Trend in Landings

(Pauly et al., 2002)

Non-registered catches

Expansion of fisheries

A. Bertrand

(Pauly et al., 2002)

Non-registered catches

Expansion of fisheries

A. Bertrand

Trawling

Humans as “engineer species”

• Trawling disrupts sea bottom……

• Trawling ecosystem effects:– Decrease of spatial complexity– Decrease of target and bycatch

species– Increase of scavenger species– Overall loss of biodiversity (macro-

organism level)

Trawled Un-trawled

Trawled AreaUn-trawled Area

(bottom sonar images)

Trawling Impact

Bycatch of unwanted species

Turtle Excluder Device (TED)

Trawling frequency by german vessels between 1993 & 1996

(Rijnsdorp 1997)

P. Cury

Marine Protected

AreasNo Trawling Area

Gulf of Maine

Gillnetting

Bycatch of unwanted species

(Pauly et al., 2002)

Non-registered catches

Expansion of fisheries

A. Bertrand

Purse seining

Schooling behavior

Bycatch of unwanted species

(Pauly et al., 2002)

Non-registered catches

Expansion of fisheries

A. Bertrand

Longlining

Bycatch of unwanted species

(Pauly et al., 2002)

Non-registered catches

Expansion of fisheries

A. BertrandWhy steady increase?

Catches per 100 hooks (Japanese fleet)1952

1964

1958

1980

Myers & Worm, 2003

Shark Populations NE Atlantic

Baum et al. 2003

Fishing Down the Food Web

Fishery induced changes in world fish composition

Compensation in exploited fish communities

(Tropical Atlantic)

Myers & Worm, 2003

● Blue Marlin△ Sailfish○ Swordfish

Compensation in exploited fish communities

(Southern Grand Banks)

Myers & Worm, 2003

● Codfishes (Gadidae)○ Flatfishes (Pleuronectidae)

Seafood consumption (US)