Environmental Engineering Reference
In-Depth Information
Basin all year round. Furthermore, the fish community has diversified into one
that incorporates benthic species that, prior to oxygenation, could not have
survived the anoxic conditions in these deeper parts of the water column.
Recent netting data have revealed roach, perch, bream, chub and gudgeon
(Gobio gobio), and a survey in 2004 revealed a marked shift in species compos-
ition, with gudgeon dominating within the oxygenated region. The continued
dominance of this species throughout the Turning Basin is significant as
previous surveys undertaken between 1998 and 2000 (Nash et al.
2003
) recorded
extremely low numbers of gudgeon. Gudgeon are known to show plasticity in
their habitat requirements, though they are described as being 'largely a fish of
running water and only occasionally occurring in lakes . . . its oxygen require-
ments are similar to those of grayling and bullhead' (Maitland & Campbell
1992
). Clearly this benthic species is taking advantage of the improved condi-
tions in the Turning Basin attributable to the summer oxygenation scheme.
Despite the enhanced oxygen levels in the Turning Basin, the depth and lack
of spawning habitat renders this area unsuitable for reproduction and rearing
of juvenile fish to sustain the current population. However length frequency
calculations on roach data from 2007 showed a comparatively wide range of
lengths in the upper MSC compared to the lower sections of the Canal, having
between three and five age cohorts (APEM
2008a
). A distinct 0
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age class in the
area shows recent recruitment and suggests spawning activity is present either
within the Canal or in its feeder streams. Indeed results from electric fishing
undertaken in the River Irwell in 2005 revealed important nursery areas for
juvenile fish in the shallower margins immediately downstream of the
entrance to Wilburn Street Basin 2.5 km from the Turning Basin (APEM
2005
).
Over 300 predominantly juvenile fish were caught, including chub, gudgeon,
perch, roach and stickleback. It is suggested that, as these fish age, they will
move downstream in search of new habitats and thus help sustain the fish
populations in the oxygenated Turning Basin. The presence of juvenile fish also
highlights the importance of generic water quality improvements within the
catchment in helping to sustain and, in the future, enhance these nursery
areas. Investments by United Utilities in tandem with catchment management
research by the Mersey Basin Campaign are gradually resulting in tangible
water quality improvements through reduced BOD, suspended solids, ammo-
nia and nutrient concentrations (APEM
2006a
).
Crucially, the MSC has been designated under the Freshwater Fisheries
Directive (FFD) (78/659/EEC) as a cyprinid fishery from the River Irwell near
Salford University to the freshwater limit of the Canal at Latchford Locks
(22 km of the MSC). Despite the infrastructure investments and scientific
research described above, the quality of water in the MSC does not currently
meet the EC FFD standards, which was the impetus behind a recent intensive
study undertaken by APEM (APEM
2008a
). Results from fish sonar surveys
