My research interests include freshwater fish ecology, conservation and management. Some of the tools I have used answer research questions include biotelemetry, fish aging, stable isotopes and citizen science. Below are a few of the major research themes I have been apart of, resulting publications, associated blog posts and other links for more information.
My research has been primarily conducted through Dr. Christopher Somers wildlife ecology and genetics research lab at the University of Regina. For more information on Dr. Somers’ program you can visit his website by clicking here.
THEME 1: USING STABLE ISOTOPES TO UNDERSTAND FISH POPULATION STRUCTURE AND SUBDIVISION
Stable isotopes are food web based markers which provide temporally and spatially integrated insights into fish resource use. Collaborators and myself use these markers to assess aspects of niche, population structure and subdivision of freshwater fish populations based on recent resource use. This approach provides a unique, ecological basis for subdivision that is distinct but complementary to other approaches (e.g., genetics, tag-recapture). We have used this approach to test hypotheses about potentially local populations as well as to describe broad lake-wide stock structure. The population and niche level divisions we identify can, and have been used, to address fisheries management questions. Published papers within this theme are listed below, with associated abstracts (summary of the study). If you do not have access to these articles feel free to contact me for a copy.
- Eberts, R.L., B., Wissel, G.L., Simpson, S.S., Crawford, W., Stott, R.H., Hanner, R.G., Manzon, J.Y., Wilson, D.R., Boreham, and C.M., Somers. 2017. Isotopic structure of Lake Whitefish in Lake Huron: evidence for regional and local populations based on resource use. North American Journal of Fisheries Management, 37(1): 133-148. URL: http://www.tandfonline.com/doi/full/10.1080/02755947.2016.1245225.
Abstract: 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 (δ13C) and nitrogen (δ15N), 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) across Lake Huron. We found large isotopic variation among fish from different sites (ranges: δ13C = 10.2‰, δ15N = 5.5‰) and variable niche size and levels of overlap (standard ellipse area = 1.0–4.3‰2). Lake Huron contained spawning phase fish from four major isotopic clusters largely defined by extensive variation in δ13C, and the isotopic composition of fish sampled was spatially structured both within and between lake basins. Based on cluster compositions, we identified six putative regional groups, some of which represented sites of high diversity (three to four clusters) and others with less (one to two clusters). Analysis of isotopic values from Lake Whitefish collected from summer feeding locations and baseline prey items showed similar isotopic variation and established spatial linkage between spawning-phase and summer fish. Our results show that summer feeding location contributes strongly to the isotopic structure we observed in spawning-phase fish. One of the regional groups we identified in northern Georgian Bay is highly distinct based on isotopic composition and possibly ecologically unique within Lake Huron. Our findings are congruent with several previous studies using different markers (genetics, mark–recapture), and we conclude that current management units are generally too small and numerous to reflect the population structure of Lake Whitefish in Lake Huron.
- Eberts, R., Manzon, R.G., Wilson, J.Y., Boreham, D.R., and Somers, C.M. 2016. Consistent differential resource use by sympatric Lake (Coregonus clupeaformis) and Round Whitefish (Prosopium cylindraceum) in Lake Huron: A multi-time scale isotopic niche analysis.Canadian Journal of Fisheries and Aquatic Sciences, 73(7): 1072-1080. URL: http://www.nrcresearchpress.com/doi/abs/10.1139/cjfas-2015-0324#.WRZ-NbzyuRs.
Abstract: 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.
- Butt, J.C.,Eberts, R.L. and Somers, C.M. 2017. Sympatric walleye (Sander vitreus) and sauger ( canadensis) in large reservoirs: variable isotopic niche size and overlap across multiple time scales. Fisheries Management and Ecology, Early View. URL: http://onlinelibrary.wiley.com/wol1/doi/10.1111/fme.12227/abstract.
Abstract: Walleye Sander vitreus and sauger Sander canadensis may occupy similar niches in sympatric populations, but their long-term resource use is poorly studied. Multi-tissue (liver, muscle, and bone) isotopic niche analyses were used to compare resource use by these species in two large reservoirs in Saskatchewan, Canada. Population isotopic niches were larger for sauger (1.73 – 3.60 ‰2) than walleye (0.51 – 2.61 ‰2) in Lake Diefenbaker, but opposite in Tobin Lake (sauger = 0.54 – 2.57 ‰2; walleye = 1.30 – 2.94 ‰2). Analyses of population overlap suggest that these species co-exist via niche partitioning, but partitioning was more pronounced in Lake Diefenbaker (overlap = 6-38%; Tobin Lake overlap = 18-62%). The size of individual niches and levels of intra- and inter-specific overlap among individual fish also varied with reservoir. This study shows that walleye and sauger use different resources across different time scales, but the degree of partitioning can vary markedly with environment.
THEME 2: Post Catch-and-release behaviour of freshwater sportfish
I am interested in what freshwater sportfish do after recreational catch-and-release. Collaborators and I use tag-and-recapture and acoustic telemetry study designs to document behaviours after release and try to determine what factors influence these responses. We work on a variety of species (including Walleye, Sauger, Northern Pike, Common Carp, Burbot) in Saskatchewan (Canada) waterbodies. We use post active tracking (manual tracking) and passive tracking (remote array) techniques.
For more information on this ongoing research you can check out my previous blogs about this work, visit Dr. Chris Somers’ home page on this research, and our interactive facebook page. We use this facebook page to share research updates and conduct citizen science, as anglers can report recaptured fish tags through this platform.
THEME 3: Barotrauma RELIef in freshwater sportfish
Barotrauma can cause significant immediate and delayed post catch-and-release mortality. It can also cause sublethal behavioural impairments, and ultimately negatively impacts fish welfare. One strategy to reducing the impact of barotrauma is to use one of various barotrauma relief methods to aid release. However, these methods have not been tested in many freshwater sportfish (largely marine studies), and little attention has been given to their sublethal impacts. My goal is to better understand the effectiveness of various barotrauma relief methods (venting, recompression or descending, fin-weights) for Walleye (Sander vitreus) suffering from barotrauma. Do these methods have long-term benefits or are there potential harms? Above all, I suggest deep-water fishing be avoided when possible to reduce the incidence of barotrauma.
In addition to the paper listed below you can read more about barotrauma in one of my earlier blogs by clicking here.
- Eberts, R.L.and Somers, C.M. 2017. Venting and descending provide equivocal benefits for catch-and-release survival: study design influences effectiveness more than barotrauma relief method. North American Journal of Fisheries Management, 37(3): 612-623. URL: http://www.tandfonline.com/doi/abs/10.1080/02755947.2017.1307292.
Abstract: 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