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These pages are still under construction. |
Classification
where does it fit in the classification tree ?
this will be a gliffy diagram only
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Indicator
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summary
Summary of indicator structure and function
| Indicator | Attribute | Purpose | If restricted to taxa, list which ones | Ecosystem applicability | Robustness or variability | Management objective/direction | Stakeholder/Public acceptability | Reference(s) | wiki page status | ||
|---|---|---|---|---|---|---|---|---|---|---|---|
| To measure biomass trend over time | Species-based | Decreasing | Resource Potential | Widely accepted | |||||||
| what is it? | Pick one or more of the following:
| Demonstrable (D) or Aspirational (A) based on Observations, speculation, or association | Pick one of the following:
| Identified capability | Biological classification level | Response variable | Drivers | Robustness | |||
| Temporal variability of total biomass | Tropic shifts; community structure | fisheries | Should be applicable to all ecosystems | Demonstrable | Community; Ecosystem | Species-based; trophodynamics | Trophodynamics | Potentially medium to high |
Examples of how the indicators is used for ecosystem management and ecosystem status and trends
| Indicator examples | Current status and trends | Management objective/direction | Stakeholder/Public acceptability | |||
|---|---|---|---|---|---|---|
| Examples of how the indicator is used. | Pick one of the following: |
| where can this indicator be used? all over or just locally ie:
| what error level or variability is there? robustness rating of low, medium or high for each indicator | Pick one of the following:
| Pick one of the following:
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Pick one of the following:
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Attribute
Definition
"Total biomass of surveyed species is a conservative property of an ecosystem; as species are fished and their biomass reduced, other species increase in abundance and “replace” these species in the foodweb. With the removal of top predators lower trophic levels can be expected to increase. Thus changes in total biomass can be reflective of changes in ecosystem productivity." (methods details page of http://www.indiseas.org/).
Data required
Category of indicator
size-based, species-based, trophodynamics or environmental
others????/
environmental drivers are are most likely related to total system biomass and biomass of specific biological groups variables, (Fu et al 2012).
trophodynamic drivers are most relevant to the mean trophic level of community and the demersal-to-pelagic biomass ratio (Fu et al 2012).
Direction of change (Reference points, trajectories or directions for indicator)
Definition and/or background
The following is from Fulton et al (2004a) -
Total biomass variability is a measure for comparing the variability of total biomass of a community (CVt) with the biomass variability of individual species (CVi) in that community. The ratio of CVt to CVi can be used as an indicator for detecting unstable communities (Blanchard and Boucher 2001). The biological basis for the index is that in an unstressed “healthy” community the coefficient of variation of the total fish community biomass should be lower than the coefficient of variation of individual species biomass. This is because energy limitations are regulated by the interactions between competing species, or between predators and prey (particularly in temperate systems where food chains are simpler). Thus, an extreme low in one species should be compensated for by a high in another species and so while the individual species are highly variable the sum of their biomasses is fairly steady. As a result, the coefficient of variation (CVt) of the total biomass is lower than the coefficient of variation of species biomass (CVi) in a stable system. In a system that is fished, the removal of biomass by fisheries may move the system to a point where the variation of species is more independent, as the species are no longer energy limited and the influence of interactions between species are not as strong, and as a result the overall variation can increase. Consequently, the coefficient of variation (CVt) of the total biomass is not necessarily lower than the coefficient of variation of species biomass (CVi) in such a perturbed state (Blanchard and Boucher 2001).
The index is calculated as follows:
need to add equation 5.2
where CVi is the coefficient of variation for species i, σi is the standard deviation and x (need to have a line over the top of the x) is the mean of the measured variable (biomass landings, CPUE and biomass) for species i. CVt is the sum of all the CVi.
This approach (of comparing CVt and CVi) was initially developed for examining fish assemblages, and it has been used as a broad indicator of fisheries impact on demersal fish communities (Duplisea et al. 1997, Blanchard and Boucher 2001). However, other ecosystem components (e.g. invertebrates; plankton, seagrass, algae) could also be used, but this suggestion has yet to be tested. In addition to its role as an indicator of community structure, the tracking of the coefficients of variation through time could also be a useful indicator of stock and trophic status, as a change in the evenness of fluctuations in biomass may reflect a shift from large, stable k-selected species to more variable r-selected species.
Attribute
Tropic shifts, community structure
Purpose
fisheries, birds and mammals
Taxa
Data required
The following is from Fulton et al 2004a -
- Biomass (wet weight) of species caught (target and non-target)
- CPUE (and effort)
Ecosystem applicability
The following if from Fulton et al (2004a) -
Should be applicable to all ecosystems, and has been applied to comparisons of fish communities in the Bay of Biscay and Gulf of Lions (Blanchard and Boucher 2001).
Identified capability
Biological classification level
Response variable
Drivers
Is there any additional information that would be of interest in regards to ecological drivers?
If not can leave this section blank and just fill in the table instead.
Robustness
The following is from Fulton et al 2004a -
Potentially medium to high: The main limitations relate to the use of CPUE data, which can be highly variable and inconsistent. As a result, accurate data on total biomass may not be recorded. Moreover, market forces, rather than just the ecological effects of fishing, can influence the catches (so catch shifts to planktivores from piscivores without a concomitant shift in the underlying system). It is also worth remembering that if a species goes extinct its CVi will be zero and any fluctuation in overall biomass will be greater than it. Thus, to be truly robust, this indicator requires testing on data sets derived from research surveys that are not linked to effort, and/or from data collected in unfished reference areas. It could also be useful to examine time series data of target species (which tend to be large piscivores), as this could give a measure of the total biomass variability over time in established fisheries and provide a snapshot of how the higher trophic levels, which regulate the energy flow, have varied. Lastly, estimating variability can require a lot of data, especially if it is to be separated from time trends in the data sets used (Rochet and Trenkel 2003).
Current status and trends
what was it like in an undisturbed/unexploited system?
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which way is the indicator showing a population is going in? decreasing or increasing ??
Robustness and Certainty
“Biomass” was not used to characterise the ecosystem state since survey data does not provide absolute estimates of biomass and thus is not comparable between species or ecosystems (due to differences in species catchability and surveys).
what error level or variability is there?
what factors contribute to variability?
is there were could include discussion about type I and II errors...or are we talking statistical errors in calculating the indicator? or both?
Management strategies and/or objectives
Resource Potential
Widely Accepted by stakeholders
Associated links
Indicators for the Seas - http://www.indiseas.org
People
Not sure if I want this here yet...who would I actually link to?? scientist? mangers? both?
References
Methods details page http://www.indiseas.org/, accessed 20/08/2012.
Background reading
Other references that would be useful to read in regard to the indicator referred to on this page.
Management strategies and/or objectives
define a standard set of management objectives?? ie from Indiseas
- Conservations biodiversity
- Ecosystem stability and resistance to perturbations
- ecosystem structure and functioning
- resource potential
has it been used in a management strategy? if so how?
relationship to management strategies/ objectives
Stakeholder/public acceptability
Acceptability with stakeholders
- by all stakeholder
- by the public
- understandable to the stakeholders
Associated links
Hyperlinks to organisations, databases, webportals, and ID books, that are associated with this indicator, if appropriate.
References
Fulton, E.A., Smith, A.D.M., Webb, H., and Slater, J. (2004a) Ecological indicators for the impacts of fishing on non-target species, communities and ecosystems: Review of potential indicators. AFMA Final Research Report, report Number R99/1546.
References that Fulton et al uses for this indicator:
Blanchard, F., and J. Boucher. 2001. Temporal variability of total biomass in harvested communities of demersal fishes. Fisheries Research 49: pp 283-93.
Duplisea, D. E., S. R. Kerr, and L. M. Dickie. 1997. Demersal fish biomass size spectra on the Scotian Shelf, Canada: species replacement at the shelfwide scale. Canadian Journal of Fisheries and Aquatic Sciences 54: pp 1725-35.
Rochet, M.-J., and V. M. Trenkel. 2003. Which community indicators can measure the impact of fishing? a review and proposals. Canadian Journal of Fisheries and Aquatic Science 60: pp 86-99.
Background reading
Fulton, E.A., Fuller,M., Smith, A.D.M., and Punt, A. (2004) Ecological indicators of the ecosystem effects of fishing: Final report. AFMA Final Research Report, report Number R99/1546.
Possible references for updating this indicator
Citation
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