The FAO guidelines note (paragraph 45) that, “where site-specific information is lacking, other information that is relevant to inferring the likely presence of vulnerable populations, communities and habitats should be used”. For much of the SPRFMO Area, data on seabed biodiversity and benthic community composition are not available. Ancillary information on biologically important physical factors will therefore need to be used to predict likelihood and suitability of areas for supporting VMEs. These physical factors should also be used to stratify the evaluation of likelihood of an activity having significant adverse impacts, and to evaluate whether proposed management and mitigation measures will provide adequate protection and prevent significant adverse impacts on VMEs which may occur within each stratum. The most important physical factors, and recommended stratification by these factors, are listed below:
Biogeographic Zone: Reflecting oceanographic conditions (water masses) in large ocean areas, such as the Southwest Pacific Ocean.
Proximity / Connectivity: Being the distance between underwater topographic features (such as seamounts), and the relationship of seamount direction to current flow. These affect the abilities of fauna to disperse and colonize adjacent seamounts. The range indicating a separate feature has been proposed as 100km - 200km and Clark (2008).
Close (<100km separation) and Distant (> 100km separation) are recommended as appropriate strata for precautionary conservation in the central Pacific region.
Summit Depth / Seabed Depth Range: Depth is a major determinant of species composition, particularly on deep-sea seamount features with high elevation. Elevation above the abyssal plain (which typically lies at ~4000m deep in the South Pacific Ocean) is also a relative measure of seamount size. The following depth strata are recommended for the purposes of evaluating likelihood of impacts and adequacy of protection measures (modified from those recommended by Clark (2008) to divide strata at 2,000m, the current maximum trawlable depth):
0 - 200 m - This stratum represents the protrusion of a seabed feature into the photic zone.
201 - 800m - This stratum represents the depth distribution range of the scattering layer, composed of vertically migrating animals, and the impact of these on the fauna that exists on seamount summits. 800m is the upper bathyal split proposed by Zezina (1997).
801 - 2,000 m - This stratum covers part of the 800 - 3,500m depth band recognized as the lower bathyal biogeographic zone, as assigned by Zezina (1997) based on a global evaluation of brachiopods. The lower bathyal zone has been divided at 2,000m for the purpose of designing representative closures in the bottom trawl footprint.
> 2,000m - This is the stratum below current trawling technology, and currently beyond impact by deepwater trawling.
Seabed Topography: Seabed topography is an indicator of seabed geology, and therefore of substratum suitability for supporting VME species. FAO (2008) specifically recognizes the following as being features that potentially support species, groups or communities which may contribute to forming VMEs:
Submerged edges and slopes; summits and flanks of seamounts, guyots, banks, knolls, and hills; canyons, trenches and hydrothermal vents.
(FAO 2008, Clark 2008, Penney et al. in press)
4.5Significant Adverse Impacts
The assessment of impacts of bottom fishing activities on benthic ecosystems consists of two separate and distinct components: i) whether such activities will have adverse impacts on actual VMEs; and ii) whether such impacts will be ‘significant’. The definition of ‘significance’ of impacts is the most difficult of these two components to determine, and there are widely differing views, and relatively little international guidance, on what would constitute a significant impact. The FAO deep-sea guidelines (FAO 2008) attempt to provide some guidance on this:
17. Significant adverse impacts are those that compromise ecosystem integrity (i.e. ecosystem structure or function) in a manner that: (i) impairs the ability of affected populations to replace themselves; (ii) degrades the long-term natural productivity of habitats; or (iii) causes, on more than a temporary basis, significant loss of species richness, habitat or community types. Impacts should be evaluated individually, in combination and cumulatively.
18. When determining the scale and significance of an impact, the following six factors should be considered:
i. the intensity or severity of the impact at the specific site being affected;
ii. the spatial extent of the impact relative to the availability of the habitat type affected;
iii. the sensitivity/vulnerability of the ecosystem to the impact;
v. the extent to which ecosystem functions may be altered by the impact; and
vi. the timing and duration of the impact relative to the period in which a species needs the habitat during one or more of its life-history stages.
19. Temporary impacts are those that are limited in duration and that allow the particular ecosystem to recover over an acceptable time frame. Such time frames should be decided on a case-by-case basis and should be in the order of 5-20 years, taking into account the specific features of the populations and ecosystems.
20. In determining whether an impact is temporary, both the duration and the frequency at which an impact is repeated should be considered. If the interval between the expected disturbance of a habitat is shorter than the recovery time, the impact should be considered more than temporary. In circumstances of limited information, States and RFMO/As should apply the precautionary approach in their determinations regarding the nature and duration of impacts.
When evaluating the potential significance of adverse impacts of bottom fishing activities in the SPRFMO Area, the above factors should all be considered when determining how to measure significance of any potential impact, and in then evaluating those impacts. However, the above factors are not adequate in themselves to actually measure significance of impacts, and need to be interpreted and used to develop specific measures of significance for each impact. Each bottom fishery impact assessment conducted will need to detail how the above factors were used to develop a definition of ‘significance’ for the purposes of the assessment, and what actual measures of significance were used to measure the impact of the fisheries concerned.
The significance of fishing impacts should be evaluated as a function of the total amount of effort, spatial footprint per unit of effort, and the actual impact within the spatial footprint per unit effort (Sharp et al. 2008). These factors should be detailed in fishing plans and descriptions of the gear to be used, and quantitatively estimated. Remaining components needed to evaluate significance of impact are the likelihood of interaction per fishing event (which is a function of the distribution of vulnerable species or communities relative to the fishery footprint) and the ecological consequence of a given impact (which depends on the distribution, density, and recovery potential of the organisms in question). These latter factors are highly difficult to measure for deepwater fisheries, but assessments will need to include some estimation of likelihood of interaction and ecological consequences. This information may need to be inferred from studies in other areas.
Cumulative or recurring impacts magnify the ecological consequence of an impact on organisms which have low recovery rates. If the frequency of impact is shorter than the recovery period of the species and biogenic habitats concerned, recovery can be negligible. Assessments need to specifically consider the rate of impact (on a temporal and geographical scale) in relation to rates of recovery of taxa likely to occur in impacted areas, and to evaluate the likely cumulative nature of impacts