1990

1
1990s (Big Changes)

• Off California In 1992, Russian survey ship
  Novodrutsk discovers abundant sardines beyond 200
  miles!
• Sardines decline in Peru, disappear in Japan
• But continue to increase in California Current
  (Offshore!)
• Suddenly increase in South Africa
• 1988 recognized as a regime shift in some systems
  but not others (puzzling)

2
1990s (Regimes become Mainstream)

• Interdecadal variability and regimes become
  popular and acceptable
• Beyond ENSO, identification of PDO, NAO
• Roemmich and McGowan (1995) describe declining
  trend in CalCOFI zooplankton
• Tendency to misidentify partial cycles (not
  publishable) as global change (popular and easily
  publishable)

3
Late 1990s(Environmental Fishery Models)

• Environmentally-explicit sardine models become
  feasible
• Previously, abundance and environment were
  confounded
• Post-shift data provide contrast
• Fishery and environmental effects can now be
  distinguished
• California sardines (Jacobson and MacCall 1995)
• Japanese sardines (Wada and Jacobson 1998)

4
California SardinesFishery vs. Environment

• In 1995, Jacobson and MacCall produced
  temperature-dependent sardine reproduction curves
• A sardine produces twice the recruits in
  favorable times
• During very cold periods, no level of fishing is
  sustainable
• Fishing must be severely restricted

5
California SardinesFishery vs. Environment

• Between 1950 and 1965 fishing rate was 36/yr
• The fishery caught 928,000 tons, during which
  time the resource declined by 777,000 tons
• Only 16 of the catch was sustainable
• 84 of the catch was mined from the resource
• Some of the decline would have happened without
  fishing
• This was severe overfishing
• The resulting depletion retarded the subsequent
  recovery
• An approximate sustainable fishing rate was
• 16 x 36 6 per year

6
Japanese SardinesA Clear Regime Shift

• In 1998, Wada and Jacobson showed what happens
  demographically under favorable and unfavorable
  conditions
• In Japan, sardines produce 20 times more recruits
  when conditions are favorable!
• Shifts are sudden

7
But how does it happen?

• Numerous recent attempts at synthesis
• SCOR WG98, McFarlane et al., Chavez et al.
• 20 years since Kawasaki, and still no answer
• The key paradox It remains unclear why sardines
  increase off Japan when local waters cool and
  become more productive, whereas they increase off
  California and Peru when those regions warm and
  become less productive (Chavez et al. 2003)
• A new hypothesis was proposed at Bakuns
  2001Honolulu workshop Its the flow!

8
The Flow HypothesisPhysical Aspects

• Retention of larvae is a major problem for fishes
  living in boundary currents
• Larval/juvenile development time is a rigid
  constraint
• Conditions of high flow rate result in high loss
  of offshore-spawned larvae
• Conditions of low flow rate allow use of the
  offshore regions for reproduction
• Larvae are able to gain swimming capability
  before being lost from the system

9
The Flow HypothesisFeeding and Fecundity

• The nature and role of offshore feeding
  conditions needs study
• In the CC, northward migrating sardines gain
  access to rich food supplies (Parrish hypothesis)
• A recent sardine landed in Oregon had 27 oil
  content
• Oil translates directly to fecundity in clupeoids
  due to indeterminate high frequency spawning
• Warmer northern water also avoids lower thermal
  limits
• Possible mesoscale, frontal effects on food
  supplies associated with flow conditions

10
2000
11
1939

• Now the early surveys make more sense!
• ca. 200,000 sq miles of habitat become available
  for sardines
• Older fish tend to live farther north (upstream)
  during low-flow periods
• The 1950s collapse southward was also due to the
  loss of northern offshore habitat, not just
  fishing