DOI: 10.5061/dryad.hmgqnk9h2
title: Endothermy makes fishes faster but does not expand their thermal niche

description: 1. Regional endothermy has evolved several times in marine fishes, and two
 competing hypotheses are generally proposed to explain the evolutionary
 drivers behind this trait: thermal niche expansion and elevated cruising
 speeds. Evidence to support either hypothesis is equivocal, and the
 ecological advantages conferred by endothermy in fishes remain debated. 2.
 By compiling published biologging data and collecting precise speed
 measurements from free-swimming fishes in the wild, we directly test
 whether endothermic fishes encounter broader temperature ranges, swim
 faster, or both. Our analyses avoid several complications associated with
 earlier tests of these hypotheses, as we use precise measurements of the
 thermal experience and speed of individual fish. 3.
 Phylogenetically-informed analyses of 89 studies reporting temperature
 ranges encountered by tagged fishes reveal that endotherms do not
 encounter broader temperature ranges than their ectothermic counterparts.
 In contrast, speed measurements from 45 individuals (16 species, of which
 4 were regional endotherms) show that endothermic fishes cruise ~ 1.6
 times faster than ectotherms, after accounting for the influence of body
 temperature and body mass on speed. 4. Our study shows that regionally
 endothermic fishes – those with the ability to conserve metabolically
 derived heat through vascular countercurrent heat exchangers and elevate
 the temperature of internal tissues – swim at elevated cruising speeds,
 although not as fast as previously thought. Contrary to previous studies
 of endothermy’s role in thermal niche expansion, our results suggest the
 significance of endothermy in fishes lies in the advantages it confers to
 swimming performance rather than facilitating occupation of broader
 thermal niches. Given speed’s major influence on metabolic rate, our
 updated speed estimates imply endotherms have lower routine energy
 requirements than current estimates. 5. Our findings shed light on the
 evolutionary drivers of regional endothermy in fishes and question the
 view that the trait confers resilience to climate change through broader
 thermal tolerance than that of ectotherms.
description: <strong>Two datasets were collected for this study: (1)
 thermal niche expansion dataset & (2) elevated cruising speeds
 dataset. </strong> <strong>(1) Data
 collation: Thermal niche expansion dataset</strong>
 Data collection for this study consisted of an extensive
 literature review of peer-reviewed published sources. Library and
 electronic database searches were carried out across multiple platforms,
 such as JSTOR, Web of Science, ScienceDirect, Research Gate, among others.
 Title searchers and keywords included ‘biologging’, ‘thermoregulation’,
 ‘endothermy’, ‘regional endothermy’ ‘tagging’, ‘shark(s)’, ‘teleost(s)’,
 ‘ectothermic’, ‘internal temperature’, ‘body temperature’, ‘thermal
 ecology’, ‘thermal niche expansion’, ‘elevated cruising speeds’ and/or
 ‘shark tagging’. In addition, studies cited in papers found during these
 searches, but not identified directly by the search, were also included.
 Papers for this study were chosen based on a number of selection criteria:
 (1) species tagged (e.g. marine species only), (2) tag type (e.g. Pop-up
 Archival Tag; PAT), (3) location of animal at time of tagging (e.g. only
 wild fishes in their natural habitat were utilised), (4) frequency of data
 collection/recording, (5) duration of recording, (6) type of publication
 (e.g. peer-reviewed journal articles only), (7) recorded parameters (e.g.
 depth, ambient temperature, internal temperature), and (8) availability
 and reliability of the data (e.g. robustness of methodologies and
 technologies used). We chose several data parameters to extract during
 this review: species common name, species scientific name,
 thermoregulatory ability, tag type, body size, number of individuals,
 ambient and body temperature (min., max., mean, 10% upper and lower
 percentiles), recording duration, depth (min., max., mean, 10% upper and
 lower percentiles) and latitude (if available).  
 <strong>(2) Speed measurements: Elevated cruising speeds
 dataset</strong> We confined our data collection
 to speed propellers of the same type, from the same manufacturer, to
 directly collect precise speed measurements of fishes free-swimming in the
 wild, whilst simultaneously recording the ambient temperature, along with
 several other parameters. We captured fish by drum
 lines, long lines, or by angling. Biologging packages were fitted to
 dorsal or pectoral fins of each animal, which was then immediately
 released; associated methods detailed further in published sources
 (Watanabe et al., 2019a, Watanabe et al., 2019b, Huveneers et al., 2018,
 Papastamatiou et al., 2018, Watanabe et al., 2015, Nakamura et al., 2011).
 Biologging packages varied slightly among species but all packages
 included accelerometers (recording tri-axial acceleration at 25Hz and
 depth at 1Hz; Techno-Smart AGM-1), temperature loggers (recording ambient
 temperature at 1Hz) and propeller-based speed sensors (all manufactured by
 Little Leonardo Corp.) of similar models (PD3GT logger, maximum dimensions
 115 x 21mm, 60g in air; W1000-PD3GT logger, 22 x 123 mm, 90 g in air; and
 ORI400/1300-PD3GT logger, 16 mm × 74 mm, 37 g in air), measuring speed in
 m s-1 (accuracy of 0.03 – 0.05m s-1), recording at 1Hz (Payne, N. L.,
 Iosilevskii, G. et al., 2016, Nakamura et al., 2011, Watanabe et al.,
 2015). To enable retrieval, tag packages also included a VHF transmitter
 (Advanced Telemetry Systems, MM100), satellite position only tag (Wildlife
 Computers Model 258; ARGOS enabled) and a time-release mechanism. Once
 detached from the animal, packages floated to the surface as they were
 constructed of a positively buoyant material (Diab Syntactic ©
 non-compressible foam). Packages were then located using the ARGOS system
 and a VHF receiver and retrieved from the ocean surface by
 boat. 
 <strong>References</strong>
 Huveneers, C., Watanabe, Y., Payne, N. & Semmens, J.
 (2018). Interacting with wildlife tourism increases activity of white
 sharks. Conservation Physiology, 6. Nakamura, I.,
 Watanabe, Y., Papastamatiou, Y., Sato, K. & Meyer, C. (2011).
 Yo-yo vertical movements suggest a foraging strategy for tiger sharks
 Galeocerdo cuvier. Marine Ecology Progress Series, 424, 237-246.
 Papastamatiou, Y. P., Watanabe, Y. Y., Demšar, U., Leos-Barajas,
 V., Bradley, D., Langrock, R., Weng, K., Lowe, C. G., Friedlander, A. M.
 & Caselle, J. E. 2018. Activity seascapes highlight central place
 foraging strategies in marine predators that never stop swimming. Movement
 Ecology, 6, 9. Payne, N. L., Iosilevskii, G., Barnett,
 A., Fischer, C., Graham, R. T., Gleiss, A. C. & Watanabe, Y. Y.
 (2016). Great hammerhead sharks swim on their side to reduce transport
 costs. Nature Communications, 7, 12289. Watanabe, Y.
 Y., Goldman, K. J., Caselle, J. E., Chapman, D. D. &
 Papastamatiou, Y. P. (2015). Comparative analyses of animal-tracking data
 reveal ecological significance of endothermy in fishes. Proceedings of the
 National Academy of Sciences, 112, 6104-6109. Watanabe,
 Y. Y., Payne, N., Semmens, J., Fox, A. & Huveneers, C. (2019a).
 Hunting behaviour of white sharks recorded by animal-borne accelerometers
 and cameras. Marine Ecology Progress Series, 621, 221-227.
 Watanabe, Y. Y., Payne, N. L., Semmens, J. M., Fox, A. &
 Huveneers, C. (2019b). Swimming strategies and energetics of endothermic
 white sharks during foraging. The Journal of Experimental Biology, 222,
 jeb185603.