We’re excited to see two new papers published in Aquatic Mammals journal, furthering our knowledge of porpoise health, energetics and the effects of exposure to pile-driving noise.
As part of a larger energetics set of studies, Ron Kastelein and the SEAMARCO group have been conducting experiments to try to better understand how pile-driving noise (which occurs during offshore construction) affects harbour porpoises. In these experiments, they explored how harbour porpoise food intake, body condition and breathing rate change seasonally. The authors of the study noted:
Correlation analysis revealed that respiration rate and body mass declined with increasing water temperature and that respiration rate increased with increasing food consumption. When the porpoise’s body length was stable, his food consumption also decreased as the water temperature increased. If the data from the present study are representative of other male harbor porpoises, these results indicate that male harbor porpoises may need different amounts of food depending on the season and on whether they are growing or adult. Food consumption peaks in winter; thus, seasonality should be taken into account in energetics studies. Depending on food availability at sea, harbor porpoises may be more or less vulnerable to disturbances that decrease their foraging efficiency. With information from this longitudinal study, experts will be better informed on typical body condition patterns when considering the Interim Population Consequences of Disturbance (iPCoD) model.
Please check out the paper here.
The other paper published last week, explored the swimming speeds of a harbour porpoise exposed during a previous study. They determined:
The speed at which they swim both determines the acoustic exposure and impacts the energetic costs of a behavioral response. Therefore, information on swimming speed is important for estimating the potential impact of pile driving sounds on the hearing, the energetics, and the population dynamics of harbor porpoises. The video recordings from the Kastelein et al. (2013b) study were analyzed for swimming speed. During quiet baseline periods, the mean swimming speed of the porpoise was 4.3 km/h, and he swam a mean distance of 2.2 km in 30 min. Even at the lowest SPL tested (130 dB re 1 μPa), his mean swimming speed was significantly greater than during baseline periods. At the highest SPL (154 dB re 1 μPa), his mean swimming speed was 7.1 km/h, and he swam a mean distance of 3.6 km in 30 min. Swimming speed did not decline significantly during the 30-min test periods, and a speed of ~7 km/h appears to be sustainable for harbor porpoises.
You can check out the paper on swimming speed following pile-driving playback here. This papers have interesting implications for noise impact assessment approaches – where predictions are made over the ranges at which disturbance and potential hearing damage occur, and a range of assumptions are applied in those calculations.
More generally, given our work on the Population Consequences of Disturbance (PCoD) , we are particularly interested in these kinds of study as they provide crucial contextual ‘jigsaw pieces’ to help us better understand how disturbance affects individual animals. For example, these studies highlight that all disturbance is not equal, i.e. being disturbed at different times of year might result in different consequences to individual animals (given their improved or reduction body condition). In addition, factors like condition or breathing rate (also known as respiration rate or surfacing rate) should be considered in ‘response’ studies – as they clearly fluctuate based on this new research.
We’re excited to see what comes next from this SEAMARCO research effort!