Abstract
Telemetry studies on aquatic animals often use external tags to monitor migration patterns and help to inform conservation effort. However, external tags are known to impair swimming energetics dramatically in a variety of species, including the endangered European eel. Due to their high swimming efficiency, anguilliform swimmers are very susceptibility for added drag. Using an integration of swimming physiology, behaviour and kinematics, we investigated the effect of additional drag and site of externally attached tags on swimming mode and costs. The results show a significant effect of a) attachment site and b) drag on multiple energetic parameters, such as Cost Of Transport (COT), critical swimming speed (Ucrit) and optimal swimming speed (Uopt), possibly due to changes in swimming kinematics. Attachment at 0.125 bl from the tip of the snout is a better choice than at the Centre Of Mass (0.35 bl), as it is the case in current telemetry studies. Quantification of added drag effect on COT and Ucrit show a (limited) correlation, suggesting that the Ucrit test can be used for evaluating external tags for telemetry studies until a certain threshold value. Uopt is not affected by added drag, validating previous findings of telemetry studies. The integrative methodology and the evaluation tool presented here can be used for the design of new studies using external telemetry tags, and the (re-) evaluation of relevant studies on anguilliform swimmers.
Highlights
Telemetry studies on aquatic animals often use external tags to monitor temporal and spatial movements and answer ecological questions
Surgery and handling Eels were completely unresponsive under anaesthesia, and subsequently responded well to anaesthesia, surgery, attachment of the dummies, and handling, with no mortalities and no infections observed over the entire course of the experiments (2.5 months)
The Strouhal number was significantly higher for site B compared to site A (p,0.05, N = 8; table 2). These results indicate an effect of the attachment site on both energetic and kinematic parameters, with site B being more disadvantageous than site A
Summary
Telemetry studies on aquatic animals often use external tags to monitor temporal and spatial movements and answer ecological questions. Dieffenbachii [9], A. japonica [10], various tropical eels [11]) including the critically endangered [12] European eel (A. anguilla, [13]) In this species, it has been shown that PSATs increase the Cost Of Transport (COT) up to 3-fold [14,15] and possibly impair escape manoeuvres from predators [16]. Compared to other aquatic animals, eels have an extremely high swimming efficiency [17,18,19,20], up to six times higher than rainbow trout [21] and some 1.3–1.4 times the values for other species [22] This high swimming efficiency is possibly based on a combination of low drag and high thrust of the anguilliform swimming mode [23], making them susceptible to added drag
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