Humpback Whale Interpolation of Sightings-per-Unit-Effort (SPUE) in the Southern Gulf of Maine
- OVERVIEW: This feature dataset contains combined cetacean sightings from the Manomet Bird Observatory (MBO) and from the North Atlantic Right Whale Consortium (NARWC) databases binned in total (i.e., all seasons/months) for the years 1970-2005. The spatial extent of the records included in these feature classes span the southern Gulf of Maine and are bounded by the meridians: -71.00 W and -67.00 W and by the parallels 43.50 N and 41.00 N. Only records from dedicated aerial surveys and platforms-of-opportunity, which met pre-defined criteria, were used in our calculations. In total, these data included 653,725 km of survey track, 16 species and 34,589 cetacean observations in the years 1970-2005. EFFORT CORRECTION (SPUE): In order to minimize bias from the uneven allocation of survey effort in both time and space, we used the sightings-per-unit-effort (SPUE) algorithm. This method produced an index of relative density by quantifying the number of individual cetaceans per unit length of track line within user defined temporal and spatial units. SPUE allows comparisons between discrete spatial units and temporal subsets within the study area. The factor of 1,000 was included to avoid very small decimal SPUE values. SPUE = 1,000 x (n/e) n = number of individuals e = km of surveyed trackline CETACEAN SIGHTINGS: The territorial waters of the United States support a wide diversity of cetaceans (approximately 60 species), with many areas considered critical habitat for endangered cetaceans. The Gulf of Maine region including Georges Bank is regularly utilized by approximately thirteen species of cetacean, mainly for feeding. Sixteen cetacean species were recorded in the MBO and NARWC databases, but not all of them were binned and analyzed. The Stellwagen Bank National Marine Sanctuary chose seven species and two groups on which to focus. These species and groups are listed below: By cetacean species: Atlantic White-Sided Dolphin (Lagenorhynchus acutus) Fin (Finback) Whale (Balaenoptera physalus) Humpback Whales (Megaptera novaengliae) Minke Whale (Balaenoptera acutorostrata) Northern (Black) Right Whales (Eubalaena glacialis) Pilot Whale (Globicephala melaena) Sei Whale (Balaenoptera borealis) By cetacean group: Dolphin/porpoise group: Atlantic White-Sided Dolphin (Lagenorhynchus acutus) Bottlenose Dolphin (Tursiops truncatus) Common (Saddleback) Dolphin (Delphinus delphis) Harbor Porpoise (Phocoena phocoena) Gray Grampus (Risso's) Dolphin (Grampus griseus) Unidentified Dolphin or Porpoise Unidentified Lagenorhynchus Unidentified Stenella White-Beaked Dolphin (Lagenorhynchus albirostris) Baleen whale (Mysticeti) group: Blue Whale (Balaenoptera musculus) Fin Whale (Balaenoptera physalus) Humpback Whale (Megaptera novaengliae) Minke Whale (Balaenoptera acutorostrata) Northern Right Whale (Eubalaena glacialis) Sei Whale (Balaenoptera borealis) Unidentified Balaenoptera Unidentified Fin or Sei Whale Unidentified Rorqual By richness and diversity indice: Species Richness (R) Shannon-Wiener Diversity (H) Evenness Indices (Eh) Simpson Diversity (D) Evenness Indices (Ed) INTERPOLATING CETACEAN SIGHTINGS: Cetaceans are highly mobile animals with complex and continuous patterns of movement. In order to better convey this continuity, we interpolated the binned marine mammal relative abundance values to produce a conterminous surface. Specifically, the SPUE values for each 5 x 5 minute grid cell centroid were interpolated spatially using an Inverse Weighting Distance (IDW) algorithm found in ESRI's Geostatistical Analyst Extension. The resulting interpolated surfaces were classified into quantiles (based on the interpolated values of the all season surface), and exported as filled contour polygon shapefiles. FILE NAMING CONVENTION: The naming convention each polygon feature class includes the common name of the group or species and time period for which it was binned. The name: AtlanticWhiteSidedDolphin_Bin_Total for example, would indicate that this feature class encompasses Atlantic White-Sided Dolphin sightings binned in total (i.e., it includes all season/months).
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