Geoscience Reference
In-Depth Information
types 5 (250.9 ha), 3 (237.1 ha), and 4 (185.0
ha; Annex 2). This habitat was the predominant
vegetation form in 63% of the vegetation polygons,
a secondary co-dominant type in 22% and tertiary
co-dominant in 15%.
Habitat condition could only be determined
with confidence in 65 of the 105 assessment
units. Of these, 62 were classified as favourable
and three as inadequate (Plate 20a). Habitat
composition and structure was favourable in 54
assessment units, and inadequate in 11 units,
mainly because of invasive and transformer species
(90% of the cases) and fragmentation (10% of
cases; Plate 20b). The habitat was considered non-
vulnerable to human pressures in 15 assessment
units but vulnerable in 51, mainly because of the
presence of embankments, bank reinforcements,
water abstraction, flow regulation and point and
diffuse pollution (Plate 20c). Conservation status
was classified as favourable in 21.5% (
n
=
14) of
the assessment units, 'favourable at risk' in 57%
(
n
=
37), and inadequate in 21.5% (
n
=
14) (Plate
20d).
distribution range, respectively; the As on, Pas-
Pisue na, and Deva rivers have lost less (16.4%,
24.4% and 38.8%, respectively) (Annex 3; Figure
16.7a). These differences may be caused by large
dams (
10 m high) located in the lower courses of
the first three rivers.
All salmon populations in Cantabrian rivers
are considered vulnerable to human pressures
(Annex 3; Figure 16.7b); this is mainly the result
of point and diffuse pollution, water abstraction,
barriers to migration, habitat degradation due to
bank reinforcement, and also angling. Distribution
range was only considered favourable for the
As on, Pas-Pisue na and Deva populations, but
inadequate for the other rivers (Annex 4). The
population structure and composition indicator was
inadequate for all the salmon populations (Annex
4). Consequently, the overall conservation status
for all the salmon populations was classified as
inadequate (Table 16.2).
Discussion
Distribution and conservation status
of Atlantic salmon
During 1990-2008, 4538 adult salmon were
caught, representing an average annual catch of
229.4 salmon (SE:
±
36.4). The Pas-Pisue na and
As on River catchments contributed, on average,
40% and 24% to the annual catch totals
respectively. Numbers caught varied from 53 in
1998 to 602 in 1991 (Figure 16.6a). The 5-year
running average reached a maximum of 384.6
for the period 1990-1994 and a minimum of 128
during 2002-2006 (Figure 16.6b). Salmon were
found in 32% (
n
The criteria, rules and assumptions used in the
assessment method indicate that the conservation
status for the majority of alluvial alder-ash forest
found along the
Natura 2000
river network in
Cantabria was 'favourable-at risk' whilst that of the
salmon population was 'inadequate'.
Alder-ash conservation status
The distribution of alder-ash alluvial forest along
Cantabrian rivers is similar to its distribution
throughout northern Spain, where riparian
galleries on alluvial soils occur from almost sea
level to 700 m (Lara
et al.
, 2004). One of the
main constraints in reaching conclusions about
conservation status using our method is data
quality and in particular the availability of reliable
information at a scale relevant for the study of
riparian habitats. In most cases the detail required
is more than that appearing on 1:5000 scale maps.
Although obtaining this information is costly
and specialist botanist knowledge is required, the
results represent a valuable baseline for future
assessment
31) of the electro-fished survey
sites, but fry were only present in 20 of them
(Figure 16.1).
The potential reference length of river for salmon
was estimated at 556.6 km. Salmon have a current
distribution of 236.4 km, meaning that 57.5% of
the potential distribution has probably been lost
since the 1950s and contributed to their extinction
from six rivers (Annex 3). The Saja-Besaya, Nansa
and Miera rivers have lost an estimated 87.8%,
72.7%
=
and
42.8%
of
their
salmon
population
of
conservation
status
(Dias
et
al
.,
