At-sea aerial survey species observations in southern California, 1999-2002

Broad survey lines, island radial survey lines, coastal survey lines, and focal-area (Santa Barbara Channel) survey lines were surveyed during each oceanographic season: spring (May), fall (September), and winter (January) during 1999 (May and September), 2000 (January, May, September), 2001 (January May, September), and 2002 (January). Aerial survey methods follow Mason et al. (2007). Specifically, we recorded all sightings of marine animals, vessels, and floating objects from twin-engine, high wing aircraft (Partenavia P-68s, Aspen Helicopters, Oxnard, CA, or California Department of Fish and Game) along pre-determined 100-meter (50 meters per side) strip transects at 60 meters above sea level. Surveys were flown at 160 kilometers per hour, and we used a Global Positioning System (GPS) unit linked to a laptop computer that allowed us to simultaneously collect coordinates (WGS-84 map datum), sea surface temperature (SST, degrees Celcius [°C]) determined via a belly-mounted, digital infrared radiation pyrometer (Heitronics™ KT19.85; measurement interval = 1 s, response time = 3 ms, emissivity = 0.99). SST values were appended to GPS flight data based on date and time. During individual surveys, observers frequently verified strip widths using hand-held clinometers. Observations generally were discontinued when glare exceeded greater than 25% of the field-of-view or if sea state exceeded Beaufort 5 (29–38 kilometers per hour wind speed). Observations were recorded into hand-held audio recorders. The third (non-dedicated) observer assisted the pilot with navigation, monitored sensor data, and maintained the onboard computer. The third observer also recorded incidental observations of marine mammals outside transects (i.e., non-standardized effort sightings). The effort for incidental marine mammal observations is not always consistent because the third observer was sometimes required to be engaged in other activities. Observations of species or individuals identified to nearest taxon included number of individuals, time, pre-coded behaviors, flight direction, and interspecies or vessel associations. Digital recordings of observations were archived and used by observers after surveys to enter data into a customized Graphical User Interface. Observation data were proofed after transcription to ensure accuracy or to resolve inconsistencies. Species observations were linked with GPS-based tracklines generated at 1 to 3 s intervals. Based on variations in the lag-time between sightings and recordings, we estimate that observations have a nominal along-trackline spatial accuracy of 222 meters, based on a five-second lag at 160 kilometers per hour survey speed. These data are associated with the following publication: Mason, J.W., McChesney, G.J., McIver, W.R., Carter, H.R., Takekawa, J.Y., Golightly, R.T., Ackerman, J.T., Orthmeyer, D.L., Perry, W.M., Yee, J.L. and Pierson, M.O. 2007. At-sea distribution and abundance of seabirds off southern California: a 20-Year comparison. Cooper Ornithological Society, Studies in Avian Biology Vol. 33.