Research in the Development of Line Transect Methods
We used line transect methods during both the aerial and shipboard surveys to estimate abundance. See Palka 1995 for a description of a line transect abundance survey. To further develop and test the data collection and analysis methods we have conducted experiments surveys and developed analytical methods which can result in less biased and more precise abundance estimates.
- In 1991 we developed and implemented the direct duplicate two-independent method to estimate the probability of detecting a group of animals on the track line (referred to as g(0)), this results in less biased abundance estimates (Palka 1995 and Palka 2005a).
- Using the 1991 and 1992 shipboard abundance survey data we showed the importance of incorporating covariates into the definition of the detection model (Palka 1996).
- Using the 1995 shipboard abundance survey data, we developed and implemented a method to account for the effects of the marine mammals either avoiding or approaching the ship before the observers on the ship can detect them (Palka and Hammond 2001).
- In 1996 we conducted an experimental survey to compare the conventional line transect methods to a newly developed adaptive line transect method. The goal of the adaptive method was to, in a statistically appropriate way, survey more in areas with higher densities of animals (Palka and Pollard 1999 and Pollard et al. 2002), thus resulting in less biased and more précised abundance estimates, especially for rare species or species that are highly spatially aggregated in large clusters.
- In 2002 we conducted a pilot aerial study to investigate the Hiby circle-back method which is a method conducted by one plane that results in estimates of g(0) for species detected during an aerial survey (Palka 2005b).
- In 2003 we conducted a shipboard study to collect dive times of Atlantic sperm whales with the ultimate goal of producing less biased sperm whale abundance estimates by correcting the abundance estimates derived from visual shipboard line transect surveys for the amount of time the sperm whales are unavailable to be detected by visual surveys (Palka and Johnson 2007).
- During several years (2004, 2007, and 2009) we collected data on the location of acoustically active marine mammals while simultaneously collecting visual line- transect data.