NEFSC Aerial Survey - Summer 1998

Keywords: Observation, Occurrence,Marine Animal Survey,Marine Biology,Marine mammals,Sea turtles,Aircraft,Visual Sighting, Occurrence
Temporal coverage: 1998/1998

Original provider:
NOAA Northeast Fisheries Science Center (NEFSC)

Dataset credits:
NOAA Northeast Fisheries Science Center (NEFSC)


Abstract:
Platform: NOAA 57 Twin Otter Aircraft 
Dates: July 18 - August 21 1998
Location: Inshore areas from 38 deg north latitude on the United States east coast to Cape Breton Island, Nova Scotia, Canada 

This aerial survey was flown in conjunction with shipboard surveys being conducted during the same time frame. The R/V Abel-J was chartered to conduct line transect surveys offshore from 38 deg N offshore from approximately 40 fathoms to the Gulf Stream, and north to the Northeast Channel east of Georges Bank. The aerial survey covered all inshore areas from the beach to the 40 fathom boundary of the shipboard survey and extended east to Cape Breton Island, Nova Scotia, Canada. 

The survey was flown using line transect methodology. There were three observers at all times, left bubble window, right bubble window and one observer looking straight down in a belly window position. There were four observer positions, left, right, belly, and on break. Observers rotated positions on the half hour unless the end of a trackline would fall within 5-10 minutes of the half hour interval. A fifth person was the designated recorder and remained at the recording station throughout the flight. 

The observers reported sightings of all marine mammals, fish, and boats encountered. The marine mammals were identified to species and their angle of inclination (when perpendicular to the aircraft) was measured with an electronic protractor. Angles above 60 deg were recorded with 10° intervals marked on the bubble. The observers scanned from the horizon to the trackline, concentrating their effort from 2 miles inward. The belly window observer was limited to a 28 deg view on both sides of the trackline and these sightings were recorded as the degrees right or left. 

Weather conditions were recorded at the beginning of each transect and whenever conditions changed during the transect. Conditions recorded include: cloud cover (% cover), Beaufort sea state (recorded in tenths), observer glare (none, slight, moderate, severe), and overall quality of sighting conditions (excellent, good, moderate, fair, poor). Observer positions were recorded at each rotation. 

Surface water temperature was recorded using an infra-red temperature sensor in the belly of the aircraft and recorded with time every minute. The computers used for sightings data and for the sea surface temperature were synchronized with the GPS for time.

The survey was flown at an altitude of 600 feet and at 110 knots over the water. All animals seen within two miles of the trackline were identified to species and counted  (aircraft broke from survey effort in cases of uncertain identity). Unidentified animals beyond two miles from the trackline were not examined for species identification. 

The survey flew either east/west or north/south tracklines with ten mile spacing. These tracklines were planned to cross lines of bathymetry rather than follow them. Survey conditions required Beaufort sea state 3 or less, some small sections of tracklines were conducted up to Beaufort 4, however only if conditions were known to improve to survey conditions on 80% or more of the entire days flight. 

Flights were planned to center on 1200 hours (noon) to minimize glare for the observers, on some occasions flights were begun earlier or later to minimize sea state, fog conditions or wind. Flights were aborted when observer viewing quality dropped below Fair for two or more observers. Flight duration depended on the aircraft load conditions and transect lengths. On days when the flight would return to the same airport and personal luggage was not transported additional fuel could be carried and survey days of 6 hours were possible. On days when transiting to a new location, flight duration was limited to approximately 5 hours. Some flights were purposely shorter than the maximum when the transect lengths prohibited another full line to be flown. The aerial survey was comprised of eighteen flight days over the survey period, with nearly 11,000 nautical miles of transect lines flown. Three days were aborted early
due to weather and observer quality issues and those lines repeated on following survey days. 

Approximately 79% of the survey was flown in Beaufort 2.0 or less and only 5% in Beaufort 3.1 - 4.0. There were thousands of recorded sightings over the survey and from these there were a total of 4,802 individuals of marine mammals, comprising 17 species. Additionally we counted 315 turtles from three species (loggerhead, leatherback and Kemp's ridleys), and over 5,000 fish, rays and sharks from nine species groups. Sightings of boats, fishing gear, and debris have not been summarized here but are available in the database for interested parties.

Purpose:
Estimate abundance for as many species as possible.

Supplemental information:
3/8/06: Data correction - sightings of humpback whale were mistakenly linked to Balaenidae (180531) and are now linked to <i>Megaptera novaeangliae</i> (180530).