Abstract
Pop-up satellite archival tags (PSATs) have recently been applied in attempts to follow the oceanic spawning migration of the European eel. PSATs are quite large, and in all likelihood their hydraulic drag constitutes an additional cost during swimming, which remains to be quantified, as does the potential implication for successful migration. Silver eels (LT = 598.6±29 mm SD, N = 9) were subjected to swimming trials in a Steffensen-type swim tunnel at increasing speeds of 0.3–0.9 body lengths s−1, first without and subsequently with, a scaled down PSAT dummy attached. The tag significantly increased oxygen consumption (MO2) during swimming and elevated minimum cost of transport (COTmin) by 26%. Standard (SMR) and active metabolic rate (AMR) as well as metabolic scope remained unaffected, suggesting that the observed effects were caused by increased drag. Optimal swimming speed (U opt) was unchanged, whereas critical swimming speed (U crit) decreased significantly. Swimming with a PSAT altered swimming kinematics as verified by significant changes to tail beat frequency (f), body wave speed (v) and Strouhal number (St). The results demonstrate that energy expenditure, swimming performance and efficiency all are significantly affected in migrating eels with external tags.
Highlights
The European eel (Anguilla anguilla) is common in waters of Western Europe
There were no significant differences in standard metabolic rate (SMR), active metabolic rate (AMRcrit) or metabolic scope between trials
This study demonstrates that attaching a pop-up satellite archival tags (PSATs) dummy to European eels, results in an increased oxygen uptake during swimming, an increased cost of transport, and a decreased swimming efficiency and performance
Summary
The European eel (Anguilla anguilla) is common in waters of Western Europe. The spawning site of this species is believed to be the Sargasso Sea since this is where the smallest eel larvae have been found [1,2,3], but so far neither spawning adults nor eggs have been found in the Sargasso Sea to confirm this. The nutritional status of individuals at the onset of migration may play a role, in that many eels apparently do not have the minimum fat content required to fuel the journey [5,6,7,8]. Further insights into this part of the European eels reproduction cycle, are very valuable for future management of the species both with regards to conservation and successful breeding programs in aquaculture. Migrating European eel are much smaller than other species traditionally used in PSAT studies, and it is possible that the hydrodynamic resistance of the tag is a barrier to successful migration
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