Expedition
Log
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Brenda L.
Norcross
Herring in the Prince
William Sound Ecosystem
Although it is not popular,
closing the herring fishery in Prince William Sound now will
make for a better fishery in the future. The current
population of herring in Prince William Sound is at
historical low levels. Herring is not only important to
commercial fisheries, which were closed 1993 -1996 and 1999
- 2001, but also to the numerous marine mammals, birds and
fishes that rely on herring as food. To increase the herring
population more juveniles have to be produced. The research
my colleagues and I have done shows that many factors affect
how many baby herring will survive.
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erring babies
and juveniles. Note dime for comparison.
Click
image for a larger
view.
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These factors affect all life
stages. If more adult herring spawn, more eggs will be laid.
More eggs will survive is there are few storms, small waves,
and few birds eating the eggs. Baby herring that are
physically or genetically damaged will not survive. Water
currents that keep the baby herring in Prince William Sound
and move them to nursery areas in bays are good for
survival. To survive, herring juveniles must avoid being
eaten by other fish and birds as they grow from August
through October. In addition, during that time, they must
have a lot to eat, because they need lots of stored food to
survive over winter. A warm winter is bad for herring
survival because metabolism is high and they use up their
stored food too quickly. Not only do all these factors
affect the survival of herring until they are one year old,
but the effects are not the same in all parts of Prince
William Sound.
There is a range of survivals
expected at each of these life stages. I looked at the high
and low extremes of possible survival for each stage to
calculate possible survival of herring to age one year. My
estimates show that for every one million herring eggs that
are laid, the range of survivors is between one and 6,500.
It takes approximately 40 to 100 adult herring to produce
those one million eggs. The same amount of eggs are not laid
every year, so how many juveniles survive depends on the
number which were laid. As a high example, in 1988
approximately four trillion eggs were deposited. That number
of eggs should yield between 4.5 million and 25 billion
juveniles. As a low example, in 1997 two trillion eggs were
deposited, yielding approximately 2.4 million to 13 billion
juveniles. The extremes of outstanding or failed survival
are quite rare.
A minimum amount of spawning
fish is needed to guarantee the continued existence of
herring in Prince William Sound. If the estimated amount of
herring falls below the minimum herring needed, the
commercial herring fishery is closed. That is what happened
in 1993 - 1996 and again 1999 - 2001. Many herring juveniles
survived in 1988, but very few have survived since then. The
Exxon Valdez oil spill killed baby herring in 1989.
It also badly affected their food and spawning.
Additionally, the oil spill lowered the resistance of
herring to disease. Many fish became diseased and died in
1993. Without more fish surviving to take their place, the
amount of herring stayed at low levels and the fisheries
stayed closed. Again in 1999, disease was killing the
herring, and again, there are few fish alive the following
years. Though the cause of the disease in 1999 was not
related to oil, the impact was the same, the commercial
fisheries were closed for several years. The herring
industry used to be valued at between six and 11 million
dollars per year in Prince William Sound. For the last three
years, the value has been zero. This has had a profound
impact on the economy of the region.
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Balls of
herring juveniles in bays in Prince William
Sound.
Click
image for a larger
view.
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Humans cannot change the
environmental factors. Closing the fishery to protect the
number of spawning adults is the only part of the ecosystem
that humans can control. Though it is not a guarantee of how
many juveniles will survive, it does increase the odds of
survival. More herring need to survive to support the
commercial fishery as well as to support all the animals
that depend on them for food. Closing the fishery now will
be good for both the fishery and the ecosystem in the
future.
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