www.searchmesh.net
Author(s):
Report on applicability of the SACFOR scale for
recording relative abundances of colonial organisms
in beam trawl samples
Matthew Curtis (cefas), Roger Coggan (Cefas)
Document owner:
Roger Coggan ([email protected])
Reviewed by:
N/A
Workgroup:
Metadata Working group
MESH action:
Actions 2 & 3
Version:
2.0
Title:
Date published:
Language:
TG0511 Cefas03_Applying SACFOR report.pdf
English
Number of pages:
5
Summary:
The utility of the SACFOR scale of relative abundance
was tested as a substitute for ‘Presence/Absence’
records of colonial taxa captured in a series of 2-metre
beam trawl samples used in habitat mapping surveys. It
was concluded that the SACFOR scale was not
applicable in this instance due to the variability in size of
catch and the subjectivity involved in applying the scale.
Reference/citation:
N/A.
Keywords:
SACFOR, relative abundance, beam trawl
File name:
Bookmarks:
Related
information:
www.searchmesh.net
Change history
Version:
Date:
Change:
2.0
30/03/07
Report placed in MESH project wrapper
1.0
01/11/05
Original report presented at Project Meeting, Belfast,
2005
www.searchmesh.net
Report on applicability of the SACFOR scale for recording relative
abundances of colonial organisms in beam trawl samples
Matthew Curtis & Roger Coggan
Cefas cruise CEND 9/05. MESH Cruise Ref:07-05-01
Methods
Three long-term monitoring sites in the North Sea were sampled with a 2-metre beam trawl. The
trawl was towed over a nominal distance of 100 metres at ~1 knot. The samples were
processed on board, following standard Cefas procedures. This includes the identification and
enumeration of all individual organisms (i.e. those that can be counted). Colonial organism were
identified and recorded as ‘Present’.
2-metre beam trawl and example of catch
Tests were made to see if the ‘presence/absence’ record for colonial organisms could be
improved by applying a scale of relative abundance (SACFOR – Superabundant, Abundant,
Common, Frequent, Occasional, Rare) widely used in quadrat-style sampling in littoral surveys.
www.searchmesh.net
After identification the colonial taxa were placed into separate piles on a white tray so that their
relative abundance could be estimated. This was achieved by comparing the quantity of each
colonial animal with the quantity of the rest of the current and previous beam trawl samples.
Results
The table below presents the result recorded when applying the SACFOR scale of the
Station
Replicate
Taxon
Flustra foliacea
Hydrallmania falcata
Abietinaria abietina
Vesicularia spinosa
Obelia sp.
Sertularia sp.
Bougainvillia sp
Alcyonidium diaphinum
NMMP 466
A
B
C
NMMP 484
A
B
NMMP 536
A
B
C
F
R
R
O
R
R
R
R
R
R
R
R
R
R
R
F
R
R
R
R
R
O
R
R
O
R
O
F
F
F
O
R
R
R
R
R
R
R
Key: Superabundant, Abundant, Common, Frequent, Occasional, Rare
Sample volumes were low (generally <10 litres) and variable. This made it difficult to apply the
scale uniformly (equitably) across different samples. For example, the assessment of Obela sp.
across all the catches ranged from Rare to Frequent. However, it was considered that the initial
assessment of rarity in samples B & C from site NMMP 466 was greatly influence by the very
low sample volume. Had the trawl been towed for twice as long, the catch might have been
bigger and the subjective assessment may have been given as ‘Frequent’.
Conclusion
The application of the SACFOR scale requires that the observer has quite some considerable
prior experience processing trawl catches, through which they have developed a personal
(subjective) appreciation of the two extremes of the scale (Superabundant and Rare). The scale
can not easily be applied in an equitable manner by inexperienced personnel.
As the scale is subjective, it is likely that different observers would relative abundance
categories to taxa from the same catch (i.e. observer A will assign the category ‘Rare’ where
observer B would assign the category ‘Occasional’.
It is concluded that the SACFOR scale is not suitable for the assessment of relative abundance
for colonial taxa sampled by beam trawls.
Recommendations
We consider that the recording of biomass would be one solution to assessing relative
abundance, as this can be compared directly with biomass of taxa that can be properly
enumerated.
www.searchmesh.net
An alternative would be to assess relative abundance using a log scale, which may be far easier
for inexperience personnel to apply. We suggest the following: if there are <=10 colonies then
record the actual number of colonies, otherwise estimate the number of colonies using a log
scale (101, 102, 103) and note the results on the log-sheet using words (tens, hundreds,
thousands) to avoid confusion with truly numeric data.