Abstract
Efforts to protect and restore tropical wetlands impacted by feral pigs
(Sus scrofa) in northern Australia have more recently included exclusion
fences, an abatement response proposing fences improve wetland condition
by protecting habitat for fish production and water quality. Here we
tested: 1) whether the fish assemblage are similar in wetlands with and
without fences; and 2) whether specific environmental processes
influence fish composition differently between fenced and unfenced
wetlands. Twenty-one floodplain and riverine wetlands in the Archer
River catchment (Queensland) were surveyed during post-wet (June-August)
and late-dry season (November-December) in 2016, 2017 and 2018, using a
fyke soaked overnight (~14-15hrs). A total of 6,353 fish
representing twenty-six species from 15 families were captured. There
were no multivariate differences in fish assemblages between seasons,
years and for fenced and unfenced wetlands (PERMANOVA, Pseudo-F
<0.58, P<0.68). Late-dry season fish were
considerably smaller compared to post-wet season: a strategy presumably
to maximise rapid disposal following rain. At each wetland a calibrated
Hydrolab was deployed (between 2-4 days, with 20min logging) in the
epilimnion (0.2m), and revealed distinct diel water quality cycling of
temperature, dissolved oxygen and pH (conductivity represented
freshwater wetlands) which was more obvious in the late-dry season
survey, because of extreme summer conditions. Water quality varied among
wetlands, in terms of the daily amplitude, and extent of daily
photosynthesis recovery, which highlights the need to consider local
site conditions rather than applying general assumptions around water
quality conditions for these types of wetlands examined here. Though
many fish access (fenced and unfenced) wetlands during wet season
connection, the seasonal effect of reduced water level conditions seems
to be more over-improvised compared to whether fences are installed or
not, as wetlands supported few, juvenile, or no fish species because
they had dried completed regardless of whether fences were present or
not.