Home' Fish and Game : September 2016 Contents 60
FOR EXAMPLE, ONE STUDY SHOWED THAT
70% of 23 introduced plant species in
Australia exhibited significant morphological
change in the century since their introduction. Many
species doubled or halved in crucial traits such as
plant height and leaf area.
For American science historian Matt Chew, these
findings suggest that understandings of biodiversity
that fixate on “intact” ecosystems or “pure” species
may ultimately “conflict with the facts of evolution”.
Indeed, some argue that introduced species
create almost ideal conditions for evolutionary
diversification. This occurs both in the species
themselves and among the native species they come
to interact with through competition, predation
and, in some cases, hybridisation. While some
existing native species may be driven to extinction
in the process, the introduced species also change
and ultimately diverge from their parent species
in response to their novel circumstances and
What is more, these new (native?) organisms
may be some of the most likely to succeed in a
rapidly changing world. For example, in the United
Kingdom native Spartina maritima – a species of
chordgrass – has hybridised with the introduced
S. alterniflora leading to the evolution of a new,
reproductively isolated species, S. anglica. This new
species occupies bare tidal mudflats which were not
ecologically compatible with either parent species.
There should be little doubt that, just as our
ecosystems in New Zealand are changing in
response to the thousands of species we have
introduced, the species within those systems are
changing too. Kiwi salmonids (and I use ‘Kiwi’
deliberately) are changing in response to the local
conditions of this country. It may be too soon to
recognise new species, but at the very least we
should begin to appreciate and investigate the ways
in which these populations differ from their parent
populations. The fact that humans had a hand in the
matter is no sensible impediment to that.
Historically, changes in trout morphology, when
not toward bigger sizes or more enthusiastic fighting
abilities, have often been deemed an expression of
poor condition in New Zealand. More often than not,
‘healthy’ fish are those that are seen to look most
like their ancestral progenitors – but on steroids.
Fish that do not show those characteristics tend to
be selected against by fisheries managers. However,
in many rivers and lakes, smaller and currently less
preferable fish for anglers may actually be more
suited to the local environmental conditions.
While perhaps not closely resembling their
ancestors, they are the best suited for what is in
front of them.
While not suggesting that all waterways should
be managed in this way, it is worth considering
whether the salmonids in many lakes and rivers in
New Zealand should be respected for the adaptations
they are developing over and above those their
ancestors brought to the table (to ring an admittedly
awful pun in this context). Many will recall that, for
a time, our now world-renowned brown trout had
fallen out of favour with anglers in New Zealand
and it was only after fisheries managers highlighted
their unique qualities that they rose to prominence
as sports fish. Could the unique adaptations of other,
sometimes smaller and less pugnacious, populations
of wild trout and salmon be celebrated for their
similarly unique characteristics?
New Zealanders often like to highlight and
enumerate the long evolutionary histories of our
ecosystems and the species within them, with a
particular emphasis on our Gondwanan heritage.
However, many of New Zealand’s freshwater
ecosystems are in fact not terribly longstanding, let
alone Gondwanan. Rotorua, for example, hosts some
of our most cherished lakes, but falls within one of
the most geologically active areas in the world.
All of the Rotorua lakes are volcanic in origin,
being the remnants of magma chambers that
collapsed to form calderas and subsequently flooded.
The largest, Lake Rotorua, formed in this way only
some 240,000 years ago. Later, nearby eruptions,
such as the Hatepe eruption in 180 AD and those of
Mount Tarawera in 1315 and 1886, would have had
enormous impacts on the ecosystems of these lakes.
Our introduction of salmonids to these areas, and
the changes it has since precipitated, thus need to
be considered in light of the area’s deeply turbulent
As environments in New Zealand, and elsewhere,
are increasingly influenced in every way by
humanity, suggestions that evolution must be limited
to non-human processes and protracted timeframes
are becoming progressively unsupportable. Clearly,
we’re part of nature and that nature is, and for the
most part always has been, in a constant state of
flux. Unlike many conservationists, fish and game
advocates have a long history of recognising and
embracing their relationships with nature and the
constant changes those entail.
New Zealand’s trout and salmon species are here
to stay and every year they are evolving to become
more a part of the unique fabric of this country, both
culturally and genetically. Let’s recognise this and
celebrate our wildlife, both new and old, in all its
wonderful diversity and nuance.
TROUT AND SALMON HAVE BECOME A TREASURED FORM
OF NEW ZEALAND BIODIVERSITY
SALMON IN THE RAKAIA CATCHMENT WILL HAVE DEVELOPED
TRAITS DIFFERENT TO THOSE IN NEARBY RIVER SYSTEMS
NEW ZEALAND SALMON ARE DISTINCTLY DIFFERENT FROM THEIR PARENT STOCK
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