Roberts, K. N. (2022) The structure and dynamics of fish isotopic and trophic niches in natural lakes and constructed fisheries offsets in the Alberta Oil Sands.

Thesis Title: The structure and dynamics of fish isotopic and trophic niches in natural lakes and constructed fisheries offsets in the Alberta Oil Sands.

Author: Karling Roberts

Abstract

Habitat offsets, where damages to natural ecosystems caused by socio-economic development projects are compensated for by the construction or restoration of ecosystems, can contribute to biological conservation when implemented properly. But, large uncertainties remain surrounding our ability to construct ecosystems that offer high quality habitat and sustainably provide desired ecosystem functions and services. Trophic structure and dynamics sustain ecosystem stability and function by limiting competition between consumers and alleviating prey species from damaging levels of predation. The application of food web theory has improved outcomes in ecological restoration and conservation, and has the potential to do the same for habitat offsetting. In this thesis I present one way trophic structure and seasonal trophic dynamics of an offset can be assessed, and examine how stable isotope analysis can be improved for use on sensitive species and in multi-season studies.

In the Alberta oil sands, unavoidable destruction of fish habitat from open-pit mining is offset with the construction of small lakes on or near mine sites. To investigate trophic structure in constructed offsets, I sampled the first offset lake constructed in the Alberta oil sands, Horizon Lake, and eight natural lakes for comparison. I measured stable carbon and nitrogen isotope ratios in the tissues of fish, and used these values to estimate metrics of trophic structure. I found that, despite the unique fish assemblage found in the offset lake, its trophic structure metrics are within the range of variation detected in natural lakes. The offset lake was most similar in terms of habitat to natural lakes that are relatively small and deep, but its trophic structure was more similar to large lakes with diverse fish assemblages. We recommend trophic structure continue to be examined in these and other offsets to further our understanding of their potentially unique ecology.

Seasonal variation in environmental conditions and resource availability may play an underappreciated role in the maintenance of biodiversity, especially in ecosystems that experience drastic seasonal changes. High-latitude and high-altitude aquatic ecosystems switch between an open water state in the summer and an ice covered state in the winter. This large environmental change is associated with reduced primary and secondary productivity, but it is not clear how consumers such as fishes respond. To address this knowledge gap, I examined the trophic dynamics of fish populations in three natural lakes and one constructed offset habitat. I used stable isotope analysis and stomach content analysis to assess if fish were 1) maintaining the same diet across seasons, 2) changing their diet seasonally, or 3) going dormant seasonally. We found that fishes most commonly change their diet between seasons in the three natural lakes and the offset. But, there was also evidence of diet maintenance and seasonal dormancy. Flexible foraging and a diversity of seasonal trophic responses among fish populations are likely contributing to the maintenance of biodiversity within these ecosystems. Evidence of winter activity by fishes in the offset is promising, and suggests the habitat is fulfilling its role as an over-wintering habitat for fishes.  

Stable isotope analysis is an important ecological method with many applications, but it often requires lethal sampling to obtain tissue samples. In addition, most stable isotope research is performed in the summer, leaving a gap in our understanding of whether isotope data collected in different seasons can be interpreted using the same methods. To address this, I investigated how lethal (muscle) and non-lethal (fin) tissues differ in their stable carbon and nitrogen isotope ratios, and whether inter-tissue differences change with season. I found that muscle and fin differ consistently in carbon and nitrogen stable isotope ratios, but whether season affects this relationship is species- and isotope-dependent. We recommend accounting for differences in tissue types whenever possible, and accounting for season of capture when research questions are highly sensitive to variation in isotope ratios.

Overall, this thesis demonstrates how ecological study of constructed offsets can advance our understanding of human modified ecosystems, basic ecological principles, and ecological methods. As offsetting grows as a practice across Canada and around the world, using these large-scale projects to further these objectives is imperative for improving the practice of offsetting and represents an enormous opportunity for advancing ecological research. 

Bazan, S. (2021) Tubifex habitat analysis to assess whirling disease risk in Alberta, Canada.

Thesis Title: Tubifex habitat analysis to assess whirling disease risk in Alberta, Canada.

Author: Sergio Bazan

Abstract

During July 2021, 30 sampling sites at Bow River Watershed and 6 sampling sites at Crowsnest River were visited to perform tubifex relative abundance counts and the collection of environmental conditions associated to each site, such as stream characteristics, water physicochemical parameters, sediment composition and quality. Relative abundance of tubifex worms at Crowsnest River was significatively higher than any Hydrologic Unit 8 (HUC8) of Bow River Watershed except for Jumpingpound Creek (p-value 0.372). Higher relative abundance of tubifex worms were found in Jumpingpound Creek and Highwood River within Bow River watershed, but the difference with the other HUC8 was not statistically significant. The land use analysis results show higher relative abundance of tubifex worms around urban and farmland areas. However, the differences between all land use categories were not statistically significant (p-value 0.515), The same results were found for Silt-Clay type of sediments over of Granular sediments with no statistically significant difference (p-value 0.543). A multivariable linear model of tubifex relative abundance for the study area was built. The adjusted r-squared value was (R 2 = 0.1755). The variables included in the model were: the water pH, the wetted width, the stream velocity, the estimated flow, and the sediment classification. However, the assumption of linearity and homogeneity of variances were not meet by the proposed linear model.

Congratulations to Karling Roberts and Taylor Lund for their paper which was “Highly Commended” for the FSBI Huntingford Medal!

Congratulations to Karling Roberts and Taylor Lund, whose paper (citation below) was listed as one of two papers Highly Commended for FSBI Huntingford Medal!

  • Roberts, K.N., Lund, T., Hayden, B. and S. Poesch (2022) Season and species influence stable isotope ratios between lethally and non-lethally sampled tissues in freshwater fish. Journal of Fish Biology 100(1): 229-241. (link

Dutra, M.C.F., Pereyra, P.E.R., Hallwass, G., Poesch, M.S. and R.A.M. Silvano. (2023). Fishers’ knowledge on trophic ecology and of the tropical ‘super fish’ Plagioscion squamosissimus in two Brazilian Amazonian rivers. Neotropical Ichthyology 21(1): e220041.

Abstract:

Fishers’ local ecological knowledge (LEK) can provide new data on fish trophic ecology. The pescada (Plagioscion squamosissimus) is among the most caught fishes in small-scale fisheries in the Brazilian Amazon. Our main goal was to evaluate the abundance, size, relevance to small-scale fisheries and trophic ecology (diet and feeding interactions) of P. squamosissimus in the Tapajós and Tocantins rivers, in the Brazilian Amazon, utilizing  data from fishers’ LEK and fish sampling. We hypothesized a higher abundance, size and more prey and predators cited by fishers of P. squamosissimus in the more pristine Tapajós River. We interviewed 61 and 33 fishers and sampled fish in nine and five sites in the Tapajós and Tocantins Rivers, respectively, in 2018. The comparison between fishers’ citations and fish sampled indicated a higher relevance of P. squamosissimus to fishers in the Tapajós River, where this fish had an average larger size and where the interviewed fishers mentioned more food items of P. squamosissimus. These results show that P. squamosissimus is a generalist fish, that is resilient to fishing and environmental pressures, as well as being important to fisheries and food security, and that LEK can provide useful insights to fisheries managers. Keywords: Offsetting; Conservation policy; Biodiversity market; Preservation.

Citation: Dutra, M.C.F., Pereyra, P.E.R., Hallwass, G., Poesch, M.S. and R.A.M. Silvano. (2023). Fishers’ knowledge on trophic ecology and of the tropical ‘super fish’ Plagioscion squamosissimus in two Brazilian Amazonian rivers. Neotropical Ichthyology 21(1):e220041.

Also Read:

Pereyra, P.E.R, Hallwas, G., Poesch, M.S. and R. Silvano (2021) ‘Taking fishers’ knowledge to the lab’: an interdisciplinary approach to understand fish trophic relationships in the Brazilian Amazon. Frontiers in Ecology and Evolution.

*Lab members: Mark Poesch. Check out opportunities in the lab!