Abstract
In situ characterization of krill morphometry, behaviour and orientation is not yet routinely feasible, yet is critical to understanding swarm characteristics. A first step is to measure individual and aggregation behaviour. We report on successful use of a robust, low-cost underwater stereo video camera system to observe live Antarctic krill (Euphausia superba) in aquaria. The application of photogrammetry techniques allows animal length, orientation and three-dimensional position to be calculated from stereo video camera observations. Initially, we tested the efficacy of the stereo system by observing synthetic targets of known length and orientation to obtain estimates of measurement error. We found that on average the stereo camera system underestimated length by 0.6 mm and vertical tilt angle by +0.34°(head up), but that photogrammetric measurements of 100 randomly selected krill lengths were not significantly different from measurements of 100 randomly caught krill measured physically. During our investigation, we analysed three krill behavioural metrics: swimming speed, tortuosity, and vertical orientation under three behavioural states (undisturbed, feeding, and escape). We found that swim speed and tortuosity significantly increased when animals were feeding or exhibiting an escape response, but vertical orientation was not significantly different across states. Our investigation demonstrates that low-cost stereo video cameras can produce precise measurements that can be used for monitoring krill behaviour and population structure.
Highlights
Stereo cameras are increasingly utilized to conduct insitu observations of fish in demersal and mid-water systems for non-extractive monitoring purposes [1,2]
We report on successful use of a robust, low-cost underwater stereo video camera system to observe live Antarctic krill (Euphausia superba) in aquaria
We demonstrated that a simple, economical underwater stereo camera system can successfully record krill morphometrics and behaviour in situ with repeatable and robust measurements
Summary
Stereo cameras are increasingly utilized to conduct insitu observations of fish in demersal and mid-water systems for non-extractive monitoring purposes [1,2]. While cameras have recently been used to monitor the behaviour of Antarctic krill (Euphausia superba; hereafter krill), underwater stereo systems have been large and unsuitable for use in aquaria [4] or in the field with one exception [5]. Stereo cameras afford the opportunity to observe both krill length and orientation and potentially improve the accuracy of in situ krill biomass estimates. Published field photographic measures of krill have so far been limited to mono systems, with one notable exception [5], and stereo cameras have been mounted in air vertically above aquaria to successfully monitor krill behaviour e.g. Kawaguchi et al [4] showed that stereo systems could successfully extract quantitative metrics, such as krill speed Their system was limited to behaviour visible from the surface and so of limited utility in situ. Our research objectives were two-fold: 1) assess the potential contribution of the USCS to krill biomass estimates and 2) extract krill behaviour metrics to determine behaviour state
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