Cetacean Monitoring Systems
Project planning generally includes some of the following steps and more (e.g. staffing, costs, data archiving):
You are welcome to contact us to discuss your plans, and here are notes on Frequently Asked Questions.
How many PODs do we need?
Assessing the response of cetaceans to a fishery pinger: use a cycling pinger to provide ON/OFF periods for comparison and monitor the effect with two or more C-PODs in a line from the pinger. The pinger will be recorded by the closest POD(s) so that ON/OFF periods are available to apply to the remainder.
Environmental Impact Assessments: see EIAs.
Comparison of sites regarding cetacean use: Highly seasonal patterns of use are commonly seen so a 1 year study is a minimum time period with one or two PODs per site. The differences to be detected are likely to be very large, so less data (fewer PODs) are required than in trend/population studies (see below).
Trends in density of animals/population: These require the largest numbers of loggers because the difference to be measured is very small. The number of loggers will be determined by the level of precision required, the likely detection rate, and the heterogeneity of the habitat – if that is high a greater variance between detection rates at monitoring sites is likely to make confidence intervals wider.
What operational statistic should we use?
C-PODs don't count animals, they measure the time for which animals are detectable. If animals moved rapidly around a large area, loggers would record more encounters than if they moved slowly, so encounter rates are not measures of density, but time present (TP) – the sum of train durations is, and will remain more or less constant at likely rates of movement.
Counting click trains, as a form of cue counting, introduces a behavioural element (rate of head movement) that is unwanted if the aim is to measure density of animals.
The percentage of detection positive minutes, DPM, has proved to be a stable and well-behaved statistic that is now widely used. The time period of one minute can be raised with some benefit provided it does not often exceed 30% and is always below 60%. This measure still includes some behavioural element that needs to be considered.
So for density or habitat use the choice is between DPM and TP. At present we would recommend TP for porpoises and narrow-band high frequency (NBHF) species and DPM for the rest.
Behavioural metrics are not yet well defined, although it is clear from a number of studies that faster click rates are indicative of feeding activity.
How should the PODs be moored?
Do we need to calibrate our new C-PODs?
No. Earlier versions of T-PODs were completely un-calibrated and users were advised that they should be calibrated. Further, their hydrophones were more vulnerable to hard impacts. C-PODs are tightly calibrated (standardised) during manufacture and are extremely robust.
How long will the PODs run?
In many projects it is a good plan to service C-PODs at shorter intervals than the maximum possible in order to avoid loss of data if a POD is lost. Where loss is unlikely to occur, 4 months is expected with good quality D-cells and over 5 months is usual, with some projects seeing over 200 days.
Heavy memory use in sites with high levels of substrate transport noise can limit deployments to 2.5 months.
It takes most users three or four days to become familiar with the software, setting-up and handling of C-PODs, with further learning time for data analysis.