Feature-based tracking of urethral motion in low-resolution trans-perineal ultrasound

This paper describes a novel algorithm for tracking the motion of the urethra from trans-perineal ultrasound. Our work is based on the structure-from-motion paradigm and therefore handles well structures with ill-defined and partially missing boundaries. The proposed approach is particularly well-suited for video sequences of low resolution and variable levels of blurriness introduced by anatomical motion of variable speed. Our tracking method identifies feature points on a frame by frame basis using the SURF detector/descriptor. Inter-frame correspondence is achieved using nearest-neighbor matching in the feature space. The motion is estimated using a non-linear bi-quadratic model, which adequately describes the deformable motion of the urethra. Experimental results are promising and show that our algorithm performs well when compared to manual tracking

Fish and Ships: Impacts of Boat Noise on the Singing Fish, Porichthys notatus

As anthropogenic ocean noise rises, research into its impacts on marine life is intensifying. Recent studies show concerning effects of noise on a variety of taxa, including fish. However currently lacking are in situ studies: the majority of fish studies have been lab-based, which lack the natural conditions and interconnections that put results in context. Further, the dearth of baseline information on natural fish sounds, communication and behaviours, limits predictions of noise impacts. Here I investigated the highly vocal plainfin midshipman (Porichthys notatus) in its natural habitat to determine the effects of boat noise on wild fish. Porichthys notatus uses sound to communicate during courtship and aggression, and depends on paternal care to safeguard nests in intertidal zones over several months. I first described acoustic communication features of P. notatus in situ by quantifying its vocalizations from longterm audio recordings gathered via hydrophones near a nesting site. I then characterized behaviours associated with acoustic signals by analyzing audio and video data of nest-guarding P. notatus. Finally, I determined the response of P. notatus to live motor-boat noise by examining behavioural and vocal activity of P. notatus in boat noise, ambient and control conditions. In addition to the manual analysis, I used an automated approach to determine overall movement of P. notatus under boat noise, ambient and control conditions. Findings reveal that when exposed to boat noise, fewer P. notatus predators were documented in the vicinity of P. notatus nests, while P. notatus increased overall time spent moving inside nests. Thus, noise benefits P. notatus indirectly by decreasing predator pressure, yet has direct negative impacts on P. notatus by increasing stress and metabolic costs. Such results reveal fitness consequences at both species and ecosystem scales, and indicate the importance of accounting for ecological relationships when predicting noise effects