MMS Low Altitude Survey for Mammals, Southern California Bight 1975-1978

Original provider: Minerals Management Service Dataset credits: Minerals Management Service Abstract: This dataset is from the marine mammal and seabird surveys of the southern California Bight studies: Southern California Bight low aerial [Mammals] study code: SM, Contract number: AA550-CT7-36, Principal investigators: K. S. Norris and B. J. Le Boeuf, University of California, Santa Cruz, and G. L. Hunt, University of California, Irvine. Time period: May 1975 through March 1978 Study area: The Southern California Bight, from Point Conception to the United States-Mexico boundary and offshore to the 2,000 m isobath. Methodology: Aerial and ship surveys were conducted along pre-established transects designed to systematically sample marine mammal and seabird abundance in all waters of the study area. Aerial surveys were conducted at two altitudes (200 ft and about 750-1,000 ft ASL) alternating at 2-3 week intervals. Seabirds and pinnipeds were recorded only on the low-altitude surveys which predominantly sampled along eight lines of latitude, separated by 25 nm, and connecting lines of longitude. High-altitude surveys sampled cetacean abundance along 15 Loran lines oriented northeast-southwest and separated by 12-15 nm. On low-altitude surveys, seabirds were counted only within a 50 m corridor on the shaded side of the aircraft. Marine mammals were counted in an unbounded corridor on one side of the aircraft on low-altitude surveys and both sides of the aircraft on high-altitude surveys. A clinometer or marks on the wing-strut were used to estimate the declination, and the measurement or estimate later used to calculate probability density functions of frequency with right-angle distance. Ships were used for surveys of inshore waters along standard (i.e., predetermined and replicate) transects and for search, catch, and tagging/tracking of small cetaceans. The standard ship transect cruises sampled abundance of seabirds and marine mammals over banks, basins, and ridges in waters inshore of the Patton Escarpment (the shelf break). Seabirds and marine mammals were counted on both sides of the cruise track and distance estimated or measured with a range-finder. Catch cruises attempted to find and remain with schools of common dolphin and other small cetaceans; therefore, data on sightings from these cruises cannot be used as samples of animal abundance. The Southern California Bight Study also included ground and aerial censuses of pinniped and seabird colonies, and special studies of productivity, mortality rates, and foraging range. Databases produced: 1) sightings of seabirds and marine mammals on 24 low-altitude aerial surveys, 2) sightings of cetaceans on 35 high-altitude aerial surveys, 3) sightings of seabirds and marine mammals on 29 ship transect surveys, and 4) sightings of cetaceans on 34 catch cruises. Included in this database are the following: High Altitude Mammal Observations: 75,489 km of effort, 695 sightings of 68,557 individual animals Low Altitude Mammal Observations: 37,843 km of effort, 1,320 sightings of 15,070 individual animals Low Altitude Bird Observations: 35,445 km of effort, 7,950 sightings of 63,359 individual animals Ship Observations: 17,903 km of effort, 23,519 sightings of 181,287 individual animals Purpose: Objectives of the study were to characterize the marine mammal and seabird fauna of the Southern California Bight, estimate abundance of species, describe the distribution, determine the timing and routes of migrations and movements, and document seasonal changes in numbers or patterns of habitat-use. In addition, studies were conducted to determine the size and status of breeding colonies of seabirds and pinnipeds, their productivity, and trends in growth. Supplemental information: This dataset includes Low Altitude Mammal Observations (37,843 km of effort, 1,320 sightings of 15,070 individual animals) from the database described in the abstract. Low Altitude Bird Observations are available in MMS Low Altitude Survey for Seabirds, Southern California Bight 1975-1978