2.5. Review and analysis of call detections

Daily presence of all call types for each of the four species was summarized into weekly bins and plotted across the spatial extent of the passive acoustic recorders (regions 1–11) over (a) the entire time series (2004–2014); and (b) the time series split between 2004 to 2010 and 2011 to 2014. This split was the same as used for the analysis of NARW acoustic presence in Davis et al. (2017), which was based on the timing of the marked climatological shifts in the Gulf of Maine (Record et al., 2019) and multiple species' distribution changes in the western North Atlantic Ocean (Pershing, Mills, Dayton, Franklin, & Kennedy, 2018). Only regions with acoustic occurrence in both time periods were compared.

We ran a generalized linear model (GLM) in R 3.4.1 (R Core Team, 2017), using the libraries MASS (Venables & Ripley, 2002), car (Fox & Weisburg, 2011), and phia (De Rosario‐Martinez, 2015) to test whether the annual occurrence of each species across regions differed over the two time periods. In this analysis, we defined the number of days per year (summed across all recorders for each region) with detected species‐specific vocalizations as the dependent variable, and defined time periods (2004–2010; 2011–2014) and regions as independent variables, with their interaction effects included in the model. A GLM with a Poisson distribution with log‐link was run given that the detection data were counts, accounting for zero‐inflated, discrete data. Within each year and region, the number of recording days was multiplied by the duty‐cycle to correct for non‐continuous data. As recording effort (the number of days during which recorders were present) varied across time and region, we included the log of the number of days during which recorders were present plus 1 (because for some time*region cells, there were no recorders present) as an offset in the model. This procedure resulted in the following model structure:

Lastly, results from these analyses were compared to the NARW's daily presence data from Davis et al. (2017) to compare the seasonal presence of five baleen whale species.