Aquatic Environment and Biodiversity Annual Review 2012

iogenic areas.
Scallop dredge.
Tasman &
Golden Bays.
Bottom trawl,
scallop &
oyster dredge
Graveyard
complex
“seamounts”,
northern
Chatham Rise.
Orange roughy
bottom trawl.
AEBAR 2012: Benthic impacts
analysis dredge fishing intensity was more important than substrate type for
many taxonomic groups. Sponges seemed most affected by scallop
dredging, and samples taken in an area once rich in sponges had
few species in 1999. This area had probably been intensively
dredged for scallops. Analysis of historical samples of scallop
survey bycatch showed a marked decline in sponge species
richness between 1996 and 1998.
In 2006, significant differences were identified among areas within
which fishing was or was not allowed. Species contributing to these
differences included those identified as being most vulnerable to
the effects of fishing. These differences could not be attributed
specifically to fishing because of interactions with environmental
gradients and uncertainty over the history of fishing. No significant
change between 1999 and 2006 was identified.
In 2010, analysis of both epifaunal and infaunal community data
identified change since 2006, and significant depth, habitat and
fishing effects. The combined fishing effects accounted for 15 –
30% of the total variance (about half of the explained variance).
Individual species responses to fishing were examined, and those
identified as most sensitive to fishing in this analysis had
previously been categorised as sensitive on the basis of life history
characteristics within the 2006 study.
Observational,
gradient
analysis
Observational,
multiple
analyses
A gradient analysis was adopted to investigate the importance of
the different factors affecting epifaunal and infaunal communities
in Tasman and Golden Bays. Fishing was consistently identified as
an important factor in explaining variance in community structure,
with recent trawl and scallop effort being more important than
other fishing terms. Important environmental variables included
maximum current speed, maximum wave height, depth, % mud,
and salinity. Fishing accounted for 31–50% of the explained
variance in epifaunal and infaunal community composition, species
richness, and Shannon-Weiner diversity. Overall, models explained
30–54% of variance, and additional spatial patterns identified in the
analysis explained a further 5–16% of variance.
From surveys in 2001 and 2006, substrate diversity and the amount
of intact coral matrix were lower on fished seamounts. Conversely,
the proportions of bedrock and coral rubble were higher. No
change in the megafaunal assemblage consistent with recovery
over 5–10 years on seamounts where trawling had ceased. Some
taxa had significantly higher abundance in later surveys. This may
be because of their resistance to the direct effects of trawling, their
protection in natural refuges, or because these taxa represent the
earliest stages of seamount recolonisation.
181
Tuck et al.
2009
Tuck & Hewitt
2012
Tuck et al.
2011
Clark et al.
2010a&b
Williams et al.
2011
An expert based assessment of 65 threats to 62 marine habitats from saltmarsh to the abyss
(MacDiarmid et al. 2012) concluded that only 7 of the 20 most important threats to New Zealand
marine habitats were directly related to human activities within the marine environment. The most
important of these was bottom trawling (ranked third equal most important), but invasive species,
coastal engineering, and aquaculture were also ranked highly. However, the two top threats, five of
the top six threats, and over half of the 26 top threats stemmed largely or completely from human
activities external to the marine environment (the most important being ocean acidification, rising sea
temperatures, and sedimentation resulting from changes in land-use). The assessment suggested that
the number and severity of threats to marine habitats declines with depth, particularly deeper than
about 50 m. Shallow coastal habitats face up to 52 non-trivial threats whereas most deep water
habitats are threatened by fewer than five. Coastal and estuarine reef, sand, and mud habitats were
considered to be the most threatened habitats whereas slope and deep water habitats were among the
least threatened.