Abstract
Tidal inlets such as the FORCE demonstration area are dynamic regions that provide important habitat for h arbor porpoise (Phocoena phocoena). Harbor porpoise use echolocation to hunt and communicate (Kastelein et al. 2002), and they are known to be very susceptible to noise disturbance (Tougaard et al. 2009). Few studies to date have focused on exposure to continuous low frequency noise sources such as that emitted by tidal turbines. The tidal dynamics inform the presence of porpoises in these areas in complex ways. Hence, long-term and ongoing monitoring of this variability has been an important component of understanding the impacts of installing tidal turbines at this site. FORCE contracted SMRU Consulting (Canada) to complete equipment calibration and click detection data analysis relating to the deployment of passive acoustic monitors (C-PODs) in support of its marine mammal environmental effects monitoring program (EEMP). The most recent EEMP-specific monitoring began on 7 June 2016 and concluded on 18 January 2017, encompassing two C-POD deployment periods with monitoring periods of 84 and 118 days respectively. The installation of the Cape Sharp Tidal Venture’s (CSTV) tidal turbine occurred on 7 November 2016, with associated vessel activity also occurring the next day.
This report firstly summarizes the dynamic temporal patterns in porpoise presence in Minas Passage 2011-2017 related to key environmental covariates, notably annual, seasonal, tidal and day vs night variability. It is important to note that temporal coverage was intermittent over this period, with only one winter-early spring period of baseline. Spring through fall data was better represented with two or three years of data collection. We then use this information to provide a statistical analysis of the distribution and activity of harbor porpoise around the FORCE demonstration area in response to the installation and operation of the turbine during the 2nd of the 2016/2017 C-POD deployments, for which data from 5 C-PODs was available.
From May 2011 through to January 2017, there have been 805 monitoring days and 2847 C-POD days, spread across 8 locations within and immediately outside the FORCE area. Overall, harbor porpoises have been detected on 98.4% of days at a median of 6 detection positive minutes per day and maximum of 44 minutes. No dolphins were detected during any of the C-POD deployments at any of the 8 C-POD locations. A statistical model using all C-POD monitoring days confirmed porpoise presence varied significantly by time of year (peak period May/June and lower secondary peak October/November), by current speed and tidal height (preference for 0-2.5 m/s ebb tides), by time of day (higher activity at night) and across the lunar cycle (affected by the position in the spring-neap tide cycle). C-POD performance (termed % time lost) also varied due to noise effects, notably due to non-biological clicks associated with sediment transfer during periods of relatively high current velocity.
During the 2nd of the 2016/2017 C-POD deployments, porpoises were detected at all five monitoring locations on each of the 45 pre-installation days (median 4 detection positive minutes per day) and on 71 of 73 (97.3%) days post-installation of the turbine (median 3 detection positive minutes per day). Consequently, there was no evidence of porpoise exclusion of the mid-range (210 – 1710 m) study area post-installation, noting that changes in the overall distribution of porpoise within the vicinity of the turbine is considered of higher importance.
A statistical model of this period tested for changes in the distribution of harbor porpoise in relation to the installation and operation of the turbine. East1, a site 210 m north of the turbine at 41 m depth, showed statistically fewer porpoise detections post installation of the turbine, whereas D1, a site 230 m northwest of the turbine at 33 m depth, on the rock shelf on which the turbine was also installed, showed no significant effect on porpoise detection rates. Both these sites had overall lower activity levels pre- and post-turbine installation, whereas the sites > 1 km west and south of the turbine had overall higher activity levels. West1, located inside the FORCE demonstration area (1,140 m from the turbine), and West2 (1,710 m away just outside of the FORCE demonstration area), both statistically declined in porpoise detections post installation, while South2 (1,690 m away, south of the FORCE demonstration area) and the deepest site at 68 m depth, had similar detections rates pre and post installation (i.e., no turbine effects). Declines in post installation detection rates were between 41-46%. The obvious and immediate drop in detections observed at East1, West1 and West2 likely represent disturbance from vessel activity, while subsequent dips observed after this period may reflect continued lunar-scale fluctuations related to lower detection performance of C-PODs during all spring tides (higher % lost time). These observations coupled with high levels of inter-annual and site variability and the very short post-installation period so far analyzed, result in the overall conclusion that further C-POD data collection is required before robust inferences can be drawn and preliminary statistical results of mid-range turbine effects at some sites can be substantiated. In particular, continued C-POD monitoring will allow for a better comparison with previous baseline data collected