24Thermoregulation is presumed to be a widespread determinant of behaviour in fishes, but has not 25 often been investigated as a mechanism shaping long-distance migrations. We used acoustic 26 telemetry and animal-borne thermal loggers to test the hypothesis that seasonal migration in 27 adult walleye in Lake Erie is size-and/or sex-specific and related to behavioural

Acoustic telemetry studies have frequently prioritized linear configurations of hydrophone receivers, such as perpendicular from shorelines or across rivers, to detect the presence of tagged aquatic animals. This approach introduces unknown bias when receivers are stationed for convenience at geographic bottlenecks (e.g. at the mouth of an embayment or between islands) as opposed to deployments following a statistical sampling design. We evaluated two‐dimensional acoustic receiver arrays (grids: receivers spread uniformly across space) as an alternative approach to provide estimates of survival, movement and habitat use. Performance of variably spaced receiver grids (5–25 km spacing) was evaluated by simulating (1) animal tracks as correlated random walks (speed: 0.1–0.9 m/s; turning angle SD: 5–30°); (2) variable tag transmission intervals along each track (nominal delay: 15–300 s); and (3) probability of detection of each transmission based on logistic detection range curves (mid‐point: 200–1,500 m). From simulations, we quantified (i) time between successive detections on any receiver (detection time), (ii) time between successive detections on different receivers (transit time), and (iii) distance between successive detections on different receivers (transit distance). In the most restrictive detection range scenario (200 m), the 95th percentile of transit time was 3.2 days at 5 km, 5.7 days at 7 km and 15.2 days at 25 km grid spacing; for the 1,500 m detection range scenario, it was 0.1 days at 5 km, 0.5 days at 7 km and 10.8 days at 25 km. These values represented upper bounds on the expected maximum time that an animal could go undetected. Comparison of the simulations with pilot studies on three fishes (walleye Sander vitreus, common carp Cyprinus carpio and channel catfish Ictalurus punctatus) from two independent large lake ecosystems (lakes Erie and Winnipeg) revealed shorter detection and transit times than what simulations predicted. By spreading effort uniformly across space, grids can improve understanding of fish migration over the commonly employed receiver line approach, but at increased time cost for maintaining grids.

Cleithra are thought to accurately record age information and produce the most reliable age estimates relative to other calcified structures (e.g., scales) for long-lived species of Esocidae such as muskellunge Esox masquinongy and northern pike E. lucius. Sagittal otoliths provide the most accurate and precise age estimates for other fish species, yet sagittal otoliths have never been evaluated for age estimation of any species of Esocidae. Our objectives were to determine if: 1) sagittal otoliths provided more precise age estimates than cleithra for northern pike from two populations, and 2) sagittal otolith age estimates differed systematically from cleithrum age estimates for two populations of northern pike. Ages were estimated by three independent individuals with different experience levels from sagittal otoliths and cleithra collected from 66 northern pike (32–101 cm total length) from Devils Lake, North Dakota and 45 northern pike (27–52 cm total length) from Cable Lake, Wisconsin. Cleithrum age estimates were more precise than those from sagittal otoliths for northern pike from Devils Lake, and were similar to sagittal otolith age estimates for northern pike from Cable Lake. Sagittal otolith age estimates were similar to cleithrum age estimates for northern pike from Devils Lake, but were dissimilar for northern pike from Cable Lake. We recommend using cleithra for estimating age of northern pike given that no specialized equipment is required for processing and age estimation. However, other studies are needed to further investigate the use of sagittal otoliths to estimate age of northern pike.

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