Document Type

Internship Report

Publication Date

Fall 2015

Abstract

With the challenges and costs associated with conducting surveys to estimate cetacean abundance, recent efforts have considered the use of opportunistic sighting and stranding data to estimate stocks. This study compared sightings reported by members of the public (n = 6934) and stranding data (n = 458) using both spatial and temporal analyses for ten species of cetaceans in the inside waters of the state of Washington from January 1995 through June 2015. The main goal of the project was to see where sightings and strandings overlapped and examine potential influences in cases of disagreement in order to evaluate the value of opportunistic data in determining cetacean abundance. The species with enough sightings and stranding data to support spatial and temporal analysis of sufficient power were gray whales (Eschrichtius robustus), harbor porpoises (Phocoena phocoena), and Dall’s porpoises (Phocoenoides dalli). Gray whales represented the largest sample size for sightings and exhibited the strongest positive relationship between sightings and strandings both spatially and annually. Harbor porpoises represented the largest strandings dataset and there was a positive relationship between strandings and sightings annually, but little to no relationship spatially. For Dall’s porpoises, the opposite was observed. When comparing the data seasonally, no significant trends were observed. Other species such as humpback whales (Megaptera novaengliae) and minke whales (Balaenoptera acutorostrata) were sighted regularly but had few to no documented strandings. Fin whales (Balaenoptera physalus), on the other hand, were associated with several stranding records, although not regularly sighted, as a result of ship strikes and subsequent transport of the carcass. These results suggest that opportunistic sighting and stranding data can be utilized to estimate the abundance of some cetacean species, but not without inherent limitations.

Comments

Department: MBF

MPS Track: MMS

Location: Cascadia Research collective

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