MMS High Altitude Survey 1980-1983

Original provider:
Minerals Management Service

Dataset credits:
Minerals Management Service

Abstract:
This dataset is from the marine mammal and seabird surveys of central and northern California studies: Central/northern California - high aerial [Cetaceans] study Code: CH, Contract number: 14-12-0001-29090, Principal investigator: Thomas P. Dohl, Center for Marine Studies, University of California, Santa Cruz

Study area: Shelf, slope, and offshore waters to a distance of 100 nm off the California coast from Point Conception to the California-Oregon boundary.

Methodology: Offshore transect surveys were flown twice-monthly at two different altitudes (200 ft and about 750-1,000 ft ASL) along approximately 40 east-west transect lines extending an average of 60 nm offshore. The transects sampled on a given survey were selected randomly from a set of 92 standard (predetermined) lines spaced at intervals of 5' of latitude. Standard transects provided systematic coverage of shelf, slope, and offshore waters in the study area. Sightings of seabirds, pinnipeds, and sea otters were recorded only on low-altitude surveys. Sightings of cetaceans and turtles were recorded on both low- and high-altitude surveys. Seabird sightings were recorded only on the shaded side of the aircraft within a strip transect of 50 m width. Marine mammal and turtle sightings were recorded within an unbounded corridor on both high- and low-altitude surveys, but only the shaded side of the aircraft was searched on the low-altitude surveys. Cross-legs connecting standard transects were searched only on high-altitude surveys. Offshore cross-legs were searched on both sides of the aircraft, while only the nearshore side was searched on cross-legs along the coast. Declination angle was measured and noted for each marine mammal/turtle sightings and later used to calculate a probability density function of frequency with right-angle sighting distance. Navigation was by Loran and VLF-Omega.

Databases produced: Three databases of sightings at sea were produced by these studies (data on numbers of seabirds and pinnipeds on land were also collected but are not addressed in the present study). These include: 1) sightings of cetaceans and turtles recorded on 36 high-altitude aerial surveys, 2) sightings of cetaceans, pinnipeds, sea otters, and turtles recorded on 36 low-altitude aerial surveys, and 3) sightings of seabirds on 36 low-altitude aerial surveys. Each sighting database is accompanied by files providing the search effort on transect and environmental characteristics of the waters surveyed (e.g., sea surface temperature).