Final Technical Report: - Southwest Fisheries Science Center - NOAA
Final Technical Report: - Southwest Fisheries Science Center - NOAA
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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