For some fish species environmental conditions,
especially temperature, play a large role in
their life histories. My background is with
American shad, an anadromous fish whose spawning
run is intricatley tied to river temperatures.
Speaking generally, during early springs the shad
spawning run take place earlier. For some other
species whose spawning runs may have a larger
genetic component (some Pacific salmons), an
earlier spring may not affect the timing of the
spawning run, but may influence survival of young of the year fish.
This is general (there are of course exceptions),
but I hope this is helpful in some way.
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Well (as they say) it all depends - on the resources available for them,
the predators around etc.. It may be that getting a head start will be a
good thing, and they will be bigger and have a leg up (or fin or whatever)
over the species that breed later.
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I'm going out tomorrow to sample mottled sculpin in southwest Michigan
and this will be my 4 or 5th year of data so I'll let you know what I
see. If you get lots of answers I'd love to see a summary.
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River herring (common name blue-back herring and alewife, anadromous Alosa
species) have been spotted already far upstream and that is early for RI.
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Along with colleagues I have been studying
phenology in fishes of the Rio Grande as part of
my dissertation research. We are comparing timing
of fish spawning for years 2008 2010 with an
unpublished dataset from 1995. While this time
span is probably too short to see any effects of
climate change, these years did happen to be
quite different with respect to flow regime
1995 had a very high spring flood pulse from
water you sent us down from the Rocky Mountains.
Conversely, 2008 2010 all had much weaker
spring flood pulses, which is likely going to
become the new norm if snowpack continues to
decrease from climate change. River discharge has
interesting effects on fish spawning, because for
some species it delays when they can start
reproducing (nest guarding species, for example),
whereas other species have pelagic eggs that
require high flows and turbidity. We found that
in the drier years (2008 2010), all species
shifted spawning earlier relative to 1995.
However, species that typically spawn early only
advanced spawning a few days in the dry years,
while later spawning species advanced
reproduction much more. The net result is that in
drier years there is much more among-species
overlap in reproductive seasonality. Because
larvae of these species have highly overlapping
dietary and habitat preferences, one could
imagine that this has the potential to increase
competition and affect reproductive success of
particular species. Getting back to the original
question, the effects of climate change are
not-necessarily restricted to temperature change.
Discharge can also play a major role in
reproductive phenology in riverine fishes. Sorry
for such a long answer! I would be happy to hear
if you get additional responses.
