Aquatic Environment and Biodiversity Annual Review 2012

AEBAR 2012: Benthic impacts
85–90 000 tows per year, only about 44% of which is reported on TCEPRs (virtually all other tows
are reported on TCERs)
Dredging for shellfish (oysters and scallops) is conducted in a number of specific areas that have
separate, smaller statistical reporting areas (Figure 7.10). Over the 16-year dataset, there were almost
1.5 million scallop dredge tows in the four main scallop fisheries and over 0.6 million oyster dredge
tows in the two dredge oyster fisheries . These data are collected on CELRs, usually at the spatial
scale of a scallop or oyster fishery area and the data have been summarised as the number of dredge
tows. No estimates of the area swept by these dredges have been made, but the number of reported
tows has declined markedly since the early 1990s (Figure 7.11).
Total reported trawls
160,000
140,000
120,000
100,000
80,000
60,000
40,000
20,000
-
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
2012
175
Fishing year
TCER
CELR
TCEPR
Figure 7.9: The number of trawl tows reported on Trawl Catch Effort and Processing Returns (TCEPR), Catch
Effort and Landing Returns (CELR) and Trawl Catch and Effort Return (TCER) between the 1989/90 and 2007/08
fishing years. Data for the 2011/12 year may be incomplete.
Our knowledge of the distribution of mobile bottom fishing effort within our TS and EEZ is, by
international standards, very good; since 2007/08 we have had tow-by-tow reporting of almost all
trawling with a spatial precision of about 1 nautical mile. The distribution of dredge tows for shellfish
is not reported with such high precision, but records kept by fishers in industry logbooks are often
much more detailed than the Ministry for Primary Industries standard returns, and have sometimes
been used to support spatial analyses that would not have been possible using the standard returns
(e.g., Tuck et al. 2006 for project ZBD2005/15 on the Coromandel scallop fishery and Michael et al.
2006 for project ZBD2005/04 on the Foveaux Strait oyster fishery). These studies indicate the value
of records with higher spatial precision.