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Final Technical Report: - Southwest Fisheries Science Center - NOAA

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4.3 Model Scale: Resolution and Extent<br />

4.3.1 Resolution<br />

Selecting an Appropriate Resolution for ETP Cetacean-Habitat Models<br />

We found that resolution did not affect the functional form of habitat relationships<br />

or maps of predicted densities and that inter-annual habitat variability had a greater<br />

impact on the predictive power of the habitat models than resolution. The absence of<br />

scale dependence in these models suggests that the resolutions evaluated (2 to 120 km)<br />

occur within a single domain of scale, which is defined as a range of resolutions over<br />

which ecological patterns do not vary (Wiens 1989). Results of our analyses have<br />

already been published (Redfern et al. 2008) and are therefore not repeated in detail here.<br />

A transect segment length of approximately 10 km was used for the ETP models.<br />

Selecting an Appropriate Resolution for CCE Cetacean-Habitat Models<br />

We summarized dolphin and oceanographic data in 2, 10, 20, 40, 60, and 120 km<br />

segments along the transect lines. We selected four species which represented a broad<br />

range of habitat preferences: striped dolphin, short-beaked common dolphin, Risso’s<br />

dolphin, and northern right whale dolphin. Over 15,000 km of sampling data (Fig. 15)<br />

collected by the <strong>Southwest</strong> <strong>Fisheries</strong> <strong>Science</strong> <strong>Center</strong> (<strong>NOAA</strong> <strong>Fisheries</strong>) were used in the<br />

analyses. The data were collected from two comparable research vessels from late July<br />

until early December in 1991, 1993, 1996, and 2001. Data collection procedures are<br />

reported elsewhere (Kinzey et al. 2000, Barlow et al. 2001, Fiedler and Philbrick 2002).<br />

Encounter rate and group size models were built at each resolution for the four species<br />

considered in our analyses; methods followed those published in Redfern et al. (2008).<br />

The total number of segments and number of dolphin sightings are presented in Table 12.<br />

Habitat variables used in our analyses include surface temperature and salinity, the<br />

natural logarithm of surface chlorophyll concentration, thermocline depth and strength,<br />

seafloor depth, an estimate of temperature fronts defined as the difference between the<br />

minimum and maximum temperatures on a segment, and Beaufort sea state, which was<br />

used to account for the difficulty of detecting dolphins at higher Beaufort sea states<br />

(Barlow et al. 2001).<br />

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