conditions at a given latitude will match those usual farther equatorward so eastern
tropical Pacific and subtropical offshore species displaced poleward will reproduce
and their young will grow. They never produce the typical biomass of these eastern
boundary currents. However, a single season of normal conditions completely
reverses the situation to subpolar faunas with higher biomass. Stocks are partly rebuilt
by transport, partly by growth and reproduction along the way. The response of
plankton occurs on the same time scales as the El Niño cycle without lasting effects.
(^) Effects on nekton are partly parallel to those of plankton, partly longer lasting,
depending upon behavior. During strong El Niño events, subtropical fish like
yellowfin tuna with a usual northern limit south of San Diego move northward
following the warming, generating landings at Oregon ports. Subtropical species like
Mola mola, the ocean sunfish, are seen off British Columbia or even Alaska (Pearcy
& Schoener 1987). When colder conditions resume, they disappear. Whether these
fish die or move south as conditions cool is uncertain, but a return swim is very likely.
Coastal anadromous fish like salmon and steelhead trout remain mostly in their usual
migratory patterns during El Niños. Smolts of both chinook and coho salmon entering
the ocean from coastal rivers between northern California and British Columbia
during El Niño conditions suffer strong reductions in survival and growth due to the
warmth and low plankton availability.
(^) Effects of El Niño on long-lived, relatively sessile fishes like the rockfish of the
shelf (Sebastes spp.) are short-term losses in growth potential. It is certain that most
older fish weather through El Niño periods, in fact they must do it many times during
lives spanning multiple decades. Recruitment from larval stages can be reduced by
warmth and starvation, or possibly favored by unusual retention of larvae inshore
(Yoklavich et al. 1996). Of course, survival of such fish populations never depends
upon successful reproduction in every year. Effects on long-lived benthos are similar,
they survive but growth slows. For example, red abalone tagged at about 3 years of
age (50–100 mm diameter) around Santa Rosa Island in the Southern California Bight
grew by 37 mm at age 5 years in the 1978–1980 normal interval. In the 1981–1983
interval with a strong El Niño, they grew only 30 mm, a modest but significant effect
(Haaker et al. 1998). There was no measurable difference in mortality rate. Again,
relatively sessile animals like red abalone that live 25+ years must be adapted to
survive multiple El Niños. Farmed oysters in Washington state showed record lows in
the ratio of meat to shell volume during the 1982–1983 El Niño (Schoener & Tufts
1987), exacerbating a longer-term decline in body condition initiated in 1976
coincident with the general shift to warmer conditions. Effects on short-lived and
infaunal benthos are little studied.
(^) At the top of the food chain, both seabirds and marine mammals suffer very large
mortality during strong El Niños. Persistent counting of dead birds along Oregon
beaches shows sharp increases in mortality during warm, low-production periods.