Descending fish to depths of neutral buoyancy is a promising, less‐invasive alternative to swim bladder venting for relieving barotrauma and reducing mortality in sport fish. However, we lack a broad perspective on the relative benefits of these two approaches. We reviewed the most up‐to‐date literature to evaluate the effectiveness of venting compared to descending treatments. Mean relative risk (RR) based on 76 published comparisons (51 marine, 25 freshwater; 18 genera, 28 species) showed that venting (2.0 ± 4.7 [mean ± SD]) and descending (1.6 ± 1.4) both had positive effects on survival (RR ≥ 1.1). However, RR was generally small and statistically indistinguishable between treatments, providing no strong support for the use of one method over the other. Modeling of factors affecting RR showed that the study design variable “assessment method” was the only important factor affecting RR, having a larger influence on survival than habitat, capture depth, or treatment type (venting versus descending). Biotelemetry and ex situ methods produced significantly higher estimates of RR than other assessments. Our review suggests that the two major approaches to barotrauma relief do not differentially influence survival outcomes and that study design may be an important source of bias. Consequently, we recommend that managers consider barotrauma relief options carefully on a case‐by‐case basis, and we encourage additional research on sublethal endpoints in addition to mortality.Received November 29, 2016; accepted March 9, 2017 Published online May 4, 2017

Barotrauma causes stress and impairment in fish and can cause mortality after catch and release. Relief of barotrauma symptoms is necessary to reduce mortality, but we currently know little about sublethal effects associated with relief methods. Here, we assess the condition and behavior of tournament-caught Walleye Sander vitreus with barotrauma by using three popular relief methods: 1) swim bladder venting, 2) deep-water release (descending), and 3) livewell reorientation with fin weights. In a short-term ex situ experiment, 50% of untreated fish with barotrauma did not recover sufficiently to be released after 20 h. Fin weighting immediately improved condition by enabling fish to regain correct orientation; however, only 53% of fin-weighted fish recovered sufficiently to be released. All vented fish were negatively buoyant, but 73% were releasable after the holding period. In a concurrent in situ study, acoustic telemetry showed that Walleye without barotrauma (controls) made variable postrelease movements (total distance: 5.1–27.6 km), descended fish behaved similarly to controls (4.7–28.6 km), and vented fish made the shortest movements (2.6–16.7 km). However, there were no statistically significant differences in distance metrics among groups. Control and descended fish used larger areas and volumes of the lake than vented fish. Descended fish also used significantly deeper depths than vented fish, and control fish were intermediate in the depth used. Telemetry did not indicate mortality of any fish in the in situ study. Our data suggest that without treatment, mortality of Walleye with barotrauma could be as high as 50%. Fin weighting is not an effective catch-and-release aid for Walleye with moderate-to-severe barotrauma, and swim bladder venting may alter short-term, postrelease movements and habitat use. The consequences of these short-term changes to Walleye behavior from a fisheries management perspective are unclear. Eliminating catch-and-release angling in deep water is the best means of managing barotrauma in Walleye. If deep-water angling cannot be avoided, we recommend noninvasive descending over venting.

Lake Whitefish Coregonus clupeaformis is the most commercially valuable species in Lake Huron. The fishery for this species has historically been managed based on 25 management units (17 in Canada, 8 in the USA). However, congruence between the contemporary population structure of Lake Whitefish and management units is poorly understood. We used stable isotopes of carbon (δ 13 C) and nitrogen (δ 15 N), food web markers that reflect patterns in resource use (i.e., prey, location, habitat), to assess the population structure of spawning-phase Lake Whitefish collected from 32 sites (1,474 fish)

Lake (Coregonus clupeaformis) and round (Prosopium cylindraceum) whitefish are sympatric benthivores in Lake Huron that are thought to coexist via niche partitioning. However, little is known about long-term resource use and niche overlap across different temporal scales. We used a multiyear (2010–2012) and multi-tissue (liver, muscle, and bone layers) isotopic niche analysis to characterize and compare resource use by lake and round whitefish across several time scales. Lake whitefish consistently used more diverse, 13C-depleted (mean δ13C = −21.9‰) and 15N-enriched (mean δ15N = +9.3‰) resources than round whitefish (mean δ13C = −18.2‰; mean δ15N = +8.3‰). Niche overlap occurred only in liver, representing the spawning period, while niche segregation was highest in juvenile life stages. Individuals of both species made variable resource shifts among time periods, suggesting that spawning aggregations are composed of individuals representing a variety of feeding strategies and locations. Our study confirms that differential resource use is an important strategy for these fish as adults and demonstrates life-long niche partitioning beginning before age-2.

Walleye Sander vitreus is a popular species for catch-and-release angling tournaments in North America, but we currently know little about the postrelease behavior of this species and the congeneric Sauger S. canadensis. We used radiotelemetry and acoustic telemetry to track Walleyes (n = 101) and Saugers (n = 19) for 7 d after release at tournaments in Saskatchewan. Our objectives were to provide a description of postrelease movements, and examine the influence of handling variables and stress scores on movement. Walleyes made highly variable movements over 7 d, and total dispersal ranged from less than 100 m to over 28 km from the release point. Path lengths-the cumulative distance between start and end points-were considerably longer than straight-line dispersal. Walleyes made larger movements than Saugers, with average total dispersal values of 6.1 ± 6.9 km (mean ± SD) and 1.3 ± 1.8 km, respectively. Multivariate modeling revealed that species and tournament were the only important factors affecting movement. Fish size (TL), capture depth, distance transported, and time spent in a live well were not consistently important predictors of postrelease movement. Walleyes and Saugers moved much smaller distances when they had poor outcomes for the reflex action mortality predictor (RAMP) test, but RAMP scores in general did not explain a significant proportion of the variance in any fish movement metric. Swim scores at the time of release, an alternative metric of stress, also did not explain a significant proportion of variance in fish movement. Our results show intriguing variance in the behavioral response of individual Walleyes and Saugers to catch and release at tournaments, but do not identify causal factors.