Fishery is balanced (FIB Index)

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Indicator summary

 Summary of indicator structure and function

Definition and/or background

The following is from Fulton et al 2004a -

Worldwide, fisheries have historically targeted large demersal species, including apex predators, potentially altering the trophic structure of many systems (temperate, tropical, polar). In the majority of cases, the result of this ‘fish down’ has been an unplanned shift to new fisheries, which target smaller piscivores and planktivorous species (e.g. pilchards and mackerel). The impacts of this depletion and switch in targeting can be assessed by measuring trophic status indicators such as stable radio-isotope ratios (Pauly et al. 2000) or pelagic:demersal fish ratios (Caddy 2000). Generally, a declining trend of mean trophic levels detected by these indicators provide evidence of increasing negative impacts on the ecosystems of these fisheries. However, in some instances, economic decisions have been made to target fish species at lower trophic levels (e.g. pilchards in Australia) and this can confound the findings of these kind of indicators. Ideally, what is required is an indicator that measures the status of low trophic level fisheries so that sustainability can be monitored. However, it is unlikely that any of these indicators will be free of confounding effects due to increases in system productivity due to increasing nutrient levels, or switches in targeting inspired by technology and/or economics rather than depletion (Caddy and Garibaldi 2000).

One indicator that has been proposed is the Fisheries in Balance (FIB) index. It has been proposed as an indicator of whether fisheries are balanced (Pauly et al. 2000). The index should decline only when catches do not increase as much as expected given a shift in targeting to lower trophic groups that have higher rates of production. The biological basis for the FIB index is that biological production increases by a factor of 10 for each step down in trophic level, as assimilation and wastage by predators in the higher trophic level is avoided (Pauly et al. 2000), therefore catches should increase at lower trophic levels. The FIB Index is calculated as follows:

where Y is the catch, TL the mean trophic level in the catch, TE the transfer of efficiency, i indicates the year of interest and 0 refers to any year used as a baseline (so Y₀ is the catch in the baseline year etc). (Pauly et al. 2000). Pauly et al. (2000) suggested that by following a time-series of FIB for an area it could be judged whether fishing ecologically impacts the system and so reduces the populations (and thus harvests) of species lower in the trophic web (if FIB falls it means that harvesting is occurring lower in the trophic web, but that the increase in harvest is less than the factor of 10 expected). ...

The biggest drawbacks with this indicator are related to its focus only on yield. Pauly et al. (2000) argue that what this index represents is that FIB<0 is concerning as this indicates a system which is not functioning as efficiently as it should due to the intensive fishing pressure upon it. However, it is possible that shifts in fisheries through time may end with selective harvesting, constrained by management, environment, technology or economics and this may produce catches of fish at lower trophic levels that are less than the ten-fold increase expected. Thus a healthy and sustainable fishery (for a system standpoint) can produce a FIB<0. The other drawback of this indicator is potentially more insidious. As FIB is concerned only with harvesting, it is possible for fisheries that are exploiting a very perturbed system to still produce FIB values greater than zero.

Attribute

Trophic shifts

Purpose

Fisheries

Data required

The following is from Fulton et al 2004a -

• Catch biomass of pelagic fish species
• Mean trophic level in the catch
• Time series data of catch

Ecosystem applicability

The following is from Fulton et al 2004a -

Should be applicable to all ecosystems.

Robustness

The following is from Fulton et al 2004a -

Medium: The index has potential, but it needs testing, as there is the potential for confounding or misleading messages about the true state of the system. It may be useful to apply this index in the next stage of the project on Australian databases - e.g. SEF data.

Current status and trends

The following is from Fulton et al 2004a -

As an example, Pauly et al. (2000) gave the trend in FIB from 1950 – 1997 for the north Atlantic (Figure 1). They suggested that the initial increase marked a period when the fishery expanded into new stocks and that the subsequent decline marked a decrease in the trophic level of the catch, which out stripped any increases in harvest.

Figure 1: FIB index trends for the North Atlantic (after Pauly et al. 2000). (Figure provided by Fulton et al 2004a).

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:

Caddy, J. F. 2000. Marine catchment basin effects versus impacts of fisheries on semi-enclosed seas. ICES Journal of Marine Science 57: pp 628-40.

Caddy, J. F., and L. Garibaldi. 2000. Apparent changes in the trophic composition of world marine harvests: the perspective from the FAO capture database. Ocean & Coastal Management 43: pp 615-55.

Pauly, D., V. Christensen, and C. Walters. 2000. Ecopath, Ecosim, and Ecospace as tools for evaluating ecosystem impact of fisheries. ICES Journal of Marine Science 57: pp 697-706.

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.

Citation

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Last modified on: Apr 11, 2014 15:19

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