A predictive model and field test of interactions between short-finned pilot whales and a pelagic longline fishery

There is increasing recognition that, to be effective, fisheries management should incorporate spatial and temporal variation in the distribution of both target and non-target species. It is particularly difficult to mitigate the bycatch of highly mobile marine mammals using static management approaches, and the development of novel adaptive strategies is critical to effectively managing their populations. In the northeast United States, interactions between short-finned pilot whales (Globicephala macrorhynchus) and a pelagic longline fishery result in the entanglement and hooking of pilot whales. Estimated mortality levels have become unsustainable in recent years, and attempts to decrease the number of interactions have been unsuccessful. We integrated data on pilot whale movements generated from satellite telemetry (n=35) and spatial data on fishing effort to better understand the spatial nature of these interactions. First, we used Generalized Additive Mixed Models (GAMMs) and k-folds cross-validation to develop spatial predictions of high risk areas for bycatch. We then evaluated the model’s ability to predict interactions using data from fisheries observers. The model performed well in predicting pilot whale occurrence, showing a mean R2 value of 0.52 and a mean AUC of the Receiver Operator Curve of 0.90 for the 10 folds, reflecting an excellent fit between training and test datasets. Predicted pilot whale occurrence was strongly correlated with interactions per unit effort for observed longline sets (Pearson’s correlation=0.79, p-value = 0.006315). Sets with observed pilot whale interactions had significantly higher predicted probabilities of pilot whale occurrence than those in which no pilot whale interactions were observed (Wilcoxon rank sum test, p=8.71 x 10-5). Our results suggest that predictive habitat models generated from telemetry data can be an effective means of forecasting times and areas with a high risk of bycatch and may be useful in developing adaptive management strategies to mitigate fisheries interactions with marine mammals.


Thorne, L., R. Baird, D. Webster, J. Stepanuk, A. Read. 2017. A predictive model and field test of interactions between short-finned pilot whales and a pelagic longline fishery. Abstract (Proceedings) 22nd Biennial on the Biology of Marine Mammals, Halifax, Nova Scotia, October 22-27, 2017.