Uso de combustibles

As previously described, the SASI approach disaggregates fishing effort by gear type, and classifies habitat into ten types based on two energy levels and five substrate types, with a suite of geological and biological structural features inferred to each habitat type. With respect to a feature-gear-substrate-energy combination, ‘vulnerability’

represents the extent to which the effects of fishing gear on a feature are adverse. ‘Vulnerability’ is defined as the combination of how susceptible the feature is to a gear effect and how quickly it can recover following the fishing impact. Specifically, susceptibility is defined as the percentage of total habitat features encountered by fishing gear during a hypothetical single pass fishing event that have their functional value reduced, and recovery is defined as the time in years that would be required for the functional value of that unit of habitat to be restored. Functional value is intended to indicate the usefulness of that feature in its intact form to a fish species requiring shelter. This relative usefulness as shelter can be extended to the prey of managed species as well, which provides indirect benefits to the managed species. However, because functional value is difficult to assess directly, and will vary for each managed species using the feature for shelter, feature removal or damage is used as a proxy for reduction in functional value. Results such as percent reduction of a geological or biological feature are common in the gear impacts literature.

In order to make the susceptibility and recovery information work as a set of model parameters, the susceptibility and recovery of each feature-gear-substrate-energy combination is scored on a 0-3 scale as described in Table 20. The scaling process eliminated any differentiation in units (i.e. percent change for susceptibility vs. time for recovery). The scale is also intended to compare the magnitidue of susceptibility and recovery values, since susceptibility and recovery are closely related. Quantitative susceptibility percentages in Table 20 indicate the proportion of features in the path of the gear likely to be modified to the point that they no longer provide the same

functional value. Recovery does not necessarily mean a restoration of the exact same features, but that after recovery the habitat would have the same functional value. Table 20 – Susceptibility and recovery values

Code Quantitative definition of susceptibility Quantitative definition of recovery

0 _{0 – 10%} < 1 year

2 25 - 50% 2 – 5 years

3 > 50% > 5 years

Each matrix shown in the following sections includes the features present in that particular substrate and energy environment, gear effects related to that gear type and feature combination, susceptibility and recovery for each feature, and the literature deemed relevant to assigning S and R for a particular feature and gear combination. Susceptibility and recovery are scored based on information found in the scientific literature, to the extent possible, combined with professional judgment where research results are lacking or inconsistent. To direct PDT members to the appropriate research during the evaluation process, studies are assigned to matrix cells using the literature review database. For this purpose, the set of studies used to inform a particular susceptibility or recovery value is defined fairly narrowly. In some cases, studies from the literature review beyond those listed in a given matrix cell are used as well. For example, otter trawl studies are used to inform some of the scallop dredge scores. Also, for a given scored interaction in the matrix, some studies listed may have informed the score more than other studies. Details regarding the justification for each S or R score, with numbered references, are condensed into separate tables.

In some cases, the fields from the database do not align perfectly with cells in the matrices. This is because the database fields were developed and coded somewhat earlier in the process, while the matrices were still being refined. In particular, mud, sand, and muddy sand were coded during the literature review, but only mud and sand are used to define the model grid and thus only mud and sand matrices are developed. When studies were assigned to matrix cells, those coded as muddy sand went into both the mud and sand matrices, leaving the analyst to determine whether the study was most appropriately applied to one, the other, or both.

In cases where no studies are available to inform a particular S or R value, the analyst relied on the gear and feature descriptions combined with their professional judgment. In some cases, studies that considered another gear type, or were conducted in a

different habitat type (either a different substrate, energy regime, or both) are considered.

All feature-substrate-gear-energy combinations are evaluated with the exception of hydraulic dredges, which are scored for sand and granule-pebble substrates only as they are unable to fish in other substrates (Table 21).

Table 21 – Matrices evaluated. Each substrate-type matrix included both energy environments and all associated features.

Gear type Mud Sand Granule-

pebble Cobble Boulder

All trawl gears X X x X X

Scallop dredge X X X X X

Hydraulic dredge - X X - -

Longline X X X X X

Gillnet X X X X X

Trap X X X X X

Susceptibility and recovery scoring was discussed at five Plan Development Team (PDT) meetings between January and August 2009. These group discussions ensured that each team member had the same understanding of what was meant by susceptibility and recovery, and understood the assumptions underlying the assessment. During this period, matrices were evaluated in three iterations. Before the March 2009 Science and Statistical Committee (SSC) review, geological features were scored for the otter trawl and scallop dredge matrices by all team members. Before the May PDT meeting,

geological and biological features were scored for all mobile gears by all team members. Before the August PDT meeting, geological, biological, and some prey features were scored for all gears, with a subset of team members scoring each matrix. At the August meeting and in subsequent weeks, the PDT divided into small groups of 3-4 members each to evaluate each gear type in detail. Individual members submitted matrices to the group, including justification for each score, and the sub-teams developed consensus scores for each feature. Once consensus was reached for each gear type, the matrices were considered more holistically and scores were compared across gear types to ensure consistency. This final consideration of values continued through March 2010. During this period, the following “rules” for matrix evaluation were developed.

1. Susceptibility was evaluated for the entire swath of seabed affected by the gear during one tow.

In most cases, a feature is small in comparison with the path of the gear. In the case of larger features, (e.g. sand waves), or gears with narrower footprints (e.g. fixed gears), impacts to the portion of the feature in the path of the gear are evaluated.

2. Susceptibility was generally assumed to be similar for both high and low energy areas and therefore a single score was given for both, but recovery was assumed to vary such that separate high and low energy scores could be assigned as appropriate.

Note that in the matrices below, separate high and low energy susceptibility scores are shown to indicate more clearly which features are inferred to which substrate-energy combinations.

3. Susceptibility to and recovery from all trawl gear impacts were considered in one matrix, even though the gears were separated for the purposes of realized area swept and adverse impact modeling.

SASI identifies four trawl gear subtypes (generic, shrimp, squid, raised footrope), but matrices for each type are not completed, for the following reasons. First, literature support for disaggregated shrimp, squid, and raised footrope matrices is limited, as indicated in Table 16. Second, because the contact indices and gear component

dimensions vary by gear type, the gears can be distinguished in the model outputs even if susceptibility and recovery scores are the same.

4. The intention of the susceptibility scoring was to consider loss or damage of features in the path of the gear for the portion of the gear that was actually in contact with the seabed, allowing the contact index to account for any reduction in area swept.

However, given that the matrices are based on the results of research that uses actual fishing gears, with varying levels of contact with the seabed, it is difficult to avoid double counting seabed contact in the model, in that the level of gear contact affects the S scores and then may be further accounted for in the area swept models described in section 6.0.

5. Although gear components were modeled separately to estimate area swept, for each gear type, all components were considered together when evaluating susceptibility.

A primary reason for this is that the literature generally does not disaggregate gear effects by component. However, analysts considered the relative contribution of each gear component to area swept when evaluating the matrices.

6. The matrix evaluations consider a hypothetical single pass, with no baseline state of the seabed or features assumed.

Generally, areas within the SASI model domain as well as study sites in the fishing impacts literature have been subject to repeated fishing disturbance for many years. The single pass approach makes the results of some studies more difficult to apply to the scoring of susceptibility and recovery. While there are a number of studies among the 97 evaluated that examine habitat impacts at this level, many do not. It can be argued that such experimental impact studies are simply not practicable at ‘relevant’ temporal and spatial scales (Tillin et al. 2006, Hinz et al. 2009), but comparative studies also have drawbacks. Comparative studies can be somewhat difficult to evaluate and extrapolate because the scale of fishing disturbance may vary widely between studies, and is often vaguely quantified as high or low (Hinz et al 2009). More generally, a challenge

inherent to evaluating the result of the fishing impacts literature is the lack of true control sites and the confounding of natural variations that predispose an area to trawling in comparison with a nearby area with the actual effects of trawling on seabed features (Tillin et al. 2006, Hinz et al. 2009).

7. Recovery rates of features assume the absence of additional fishing pressure. As a final note regarding the methods used in the matrix-based assessment, it is possible that given the same methods, feature definitions, gear type definitions, and literature to draw from that a different group of experts might score susceptibility and recovery differently. As noted above, an iterative, team-based approach to scoring is used. The matrix evaluations are inherently qualitative, so there is no ‘right’ answer. The goal is to have internal consistency between team members in their approaches, and to ensure consistency across substrates and gear types in the final values. The scores are being used to estimate the relative impacts of various fishing gears on different types of seafloor features, so in this sense, internal consistency in scoring is more important than the actual scores.