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Indicator summary

 Summary of indicator structure and function

Examples of how the indicators is used for ecosystem management and ecosystem status and trends

Definition and/or background

The following is from Fulton et al 2004a -

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It is noteworthy that pressures on the system other than fishing can affect the indicator. The ratio can also respond to changes (increase or decreases) in nutrient levels. Increases in nutrient levels can result from pollution or impacts of bottom fishing gear (which can mobilise nutrients from benthic sediments) and declines can be due to changed hydrodynamics or from impact mitigation schemes. An increase in nutrients will generally result in an increase of planktivores, whilst a decrease will result in a decline. As an example of both effects, when the Aswan dam was constructed in the Nile (Egypt), nutrient inputs into the Mediterranean declined causing an initial significant decline in sardines (pelagics) and a subsequent change in the P:D ratio. The ratio increased again when enriched drainage water reached the system many years later. (Caddy 2000). Both effects are illustrated in Figure 51.5.

Image Added

Figure 5.51: The ratio of pelagic to demersal landings off the Nile Delta prior to and after the construction of the Aswan Dam. The rise in pelagics appears to be linked to enriched drainage water from the Delta (after Caddy 2000). need to add figure 5.5(Figure provided by Fulton et al 2004a).

Piscivore/planktivore (PS/ZP) ratio

This indicator is very similar to the P:D ratio, except that it records the ratio of the biomass (or harvests) of piscivores to that of zooplanktivores, rather than planktivores to demersals. As with the P:D ratio, trends in this indicator are more useful than strict values and it is also susceptible to changes in market demand, capture technology (particularly if based on landings data rather than fishery independent data) and changes in environmental conditions (e.g. nutrient levels) (Caddy and Garibaldi 2000). 

Attribute

tropic structure

Purpose

fisheries

Taxa

Data required

The following is from Fulton et al 2004a -

• Biomass and/or landings of demersal (or piscivorous) and pelagic species
• Diet composition (so can classify groups based on diet into piscivore, zooplanktivore, zoobenthivore and herbivore etc)

Ecosystem applicability

The following is from Fulton et al 2004a -

Investigated for mostly temperate shelf to coastal inshore regions and some tropical reefs in Northern and Southern hemispheres (Fulton unpub, Caddy 2000). Not as established for tropical lagoonal systems or deepwater slope regions, though some work based on FAO data has incorporated deepwater sites (Caddy and Garibaldi 2000).

Identified capability

Biological classification level

Response variable

Drivers

Robustness

The following is from Fulton et al 2004a -

Potentially medium to high: If the ratio is based on catch statistics alone, P:D and PS/ZP can be confounded by changes in targeting. Moreover, changes in productivity (which are often due to changes in nutrient levels) can also affect the system and these indicators. However, if based on fisheries independent data then they are potentially useful indicators of the overall trophic structure of the system.

Current status and trends

The following is from Fulton et al 2004a -

In a meta-study of pelagic:demersal (P:D) biomass ratios from 270 coastal marine systems around the world (mostly from North America, Europe and Australasia) the P:D ratio for the entire system, not just the harvested components, was found to be consistently around the 0.15 – 0.3 level (Fulton unpub). Similarly, in a study concentrating on Port Phillip Bay, Victoria, the P:D ratio was 0.26 (Fulton unpub). These studies potentially provide some reference points for using the P:D indicator. If the ratio of small pelagics begins to increase beyond these sorts of levels, then ecosystem impacts are indicated. However, if the indicator is based on landings rather than fisheries independent biomass data the ratio may be much higher even in “healthy” systems. Thus, trends in the ratio are more informative than strict values.

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

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.

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Xu, F.L., R.W. Dawson, S. Tao, J. Cao, and B.G. Li. 2001. A method for lake ecosystem health assessment: an Ecological Modeling Method (EMM) and its application. Hydrobiologia 443: 159-175.

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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