Science Advisory Report 2021/024

Impacts of agricultural drain maintenance in Beaver Creek on Grass Pickerel (Esox americanus vermiculatus), a fish species at risk

Summary

• The Beaver Creek watershed in southwestern Ontario encompasses approximately 37.3 km² of primarily agricultural land and flows into Black Creek, a tributary to the Niagara River. Beaver Creek is classed as a municipal drain and, thus, subject to periodic drain maintenance. A large population of Grass Pickerel (Esox americanus vermiculatus), a species at risk in Canada, is found in Beaver Creek and would potentially be impacted by any drain maintenance activities undertaken in the watershed.
• The western branch of Beaver Creek was subjected to drain maintenance and reconstruction, using natural-channel principles, in the fall of 2011. This maintenance impacted 2.8 ha of fish habitat in Beaver Creek. The eastern branch of Beaver Creek was left in its naturalized state.
• To determine if there were impacts on the fish community, and specifically on the Grass Pickerel population, DFO conducted long-term monitoring of the fish community and habitat in Beaver Creek in 2009 to 2013 and in 2015.
• Two incidents of Grass Pickerel population decline were observed in Beaver Creek over the course of this study. The first occurred after the sample period in 2009 and was evidenced by reduced abundance observed during summer sampling of 2010. The second was observed after a significant drought in 2012. These declines were observed over the entire study area.
• An age-and-growth study of Grass Pickerel in Beaver Creek and Jones Creek (located in Eastern Ontario) showed Grass Pickerel in Canada were between young-of-the-year (YOY) and age 8, as determined by cleithral aging. Length-at-age estimates show that Grass Pickerel collected in Beaver Creek in 2009 had significantly slower growth rates than those collected in 2011.
• Comparison of aging structures showed that scales were not reliable for age estimation in Grass Pickerel and tended to underestimate age compared to age estimates based on cleithra. Length-at-age estimates were reliable and a strong relationship between cleithral radius and body length was observed.
• A population-genetics analysis, using tissue samples collected from across the Canadian range of Grass Pickerel was conducted to determine the species’ population structure in Canada. Preliminary results show no evidence of population structure in Grass Pickerel in Canada, thus, findings from the study of Beaver Creek should be applicable across the species’ range in Canada where habitats are similar.
• A study of the movement of Grass Pickerel in Beaver Creek using PIT tags showed that Grass Pickerel can undertake movements on the scale of drain maintenance (0.5–1.0 km), indicating potential for the species to recolonize areas following drain maintenance; however, few individuals (13.3% in 2009, 5.6% in 2010) were observed to move such distances.
• Long-distance movement (0.9 km–3.1 km) by Beaver Creek Grass Pickerel was dispersive in nature (not cyclical) and no evidence of migration was observed over the course of the movement study. Long-distance movement was undertaken by larger individuals in better condition than individuals that did not move between sites.
• Simulation modelling was conducted to determine the impact that changes in habitat quantity may have on Grass Pickerel population size in Beaver Creek, and to provide estimates of minimum viable population size (MVP) and the minimum area for population viability (MAPV). When available, data specific to Beaver Creek were used to estimate model parameters; however, relationships from the literature were necessary to estimate fecundity, mortality, and individual area requirements.
• Based on life-stage specific estimates of habitat area, calculated from 2010–2011 water-level data and a GIS-based flooded area analysis, the population model predicted that the number of adult Grass Pickerel in the main tributary is limited by the quantity of age 1+ fish habitat. YOY habitat becomes limiting when the amount of habitat available is decreased below 60,000 m². Spawning habitat was not limiting unless a large area per individual female is required for successful spawning, or if flooded habitat was reduced below 100,000 m² during the spawning period.
• The MVP required to achieve a 99% probability of persistence over 100 years with a 15% chance of catastrophe (a one-time 50% reduction in population size) per generation was 1,653 age 3+ Grass Pickerel. Maintaining a population of this size required 14,853 m² of age 1+ fish habitat, 4921 m² of YOY habitat and 7,992 m² of spawning habitat.
• Before-after-control-impact (BACI) analyses were conducted at multiple time-scales to determine the impact of drain maintenance and reconstruction activities on the habitat, Grass Pickerel abundance, and the general fish community. Significant effects were observed in the Grass Pickerel abundance and several habitat variables including: conductivity; vegetation cover; water temperature; and, water depth. Effects were most pronounced within the reconstructed section.
• Following drain maintenance and reconstruction activities, the reconstructed section of Beaver Creek was recolonized by Grass Pickerel. Grass Pickerel abundance, as measured by catch per unit effort (CPUE), was increased in the reconstructed section following maintenance and reconstruction activities. It is unknown to what extent this increase in CPUE represents movement of individuals from other locations in the creek into the reconstructed section, or increased production of Grass Pickerel in the reconstructed section.
• The creation of deeper pools likely mitigated the effects of the drought observed in 2012, insulating the Grass Pickerel population in the reconstructed section from a mortality event.
• Due to the infrequent nature of long-distance movements undertaken by Grass Pickerel, drainage activities should be undertaken outside of areas with high Grass Pickerel abundance (preferably downstream), whenever possible.
• Future drain maintenance activities in areas with Grass Pickerel populations should incorporate natural-channel design features. The reconstruction activities should strive to include the creation of deeper pool habitats that will provide low-velocity habitat and refuge during low water-level events, along with shallow areas, with little flow, where submerged aquatic macrophytes can establish. Maintenance and reconstruction activities should also strive to retain channel complexity, a functioning floodplain habitat, and connections of the floodplain to the main stream channel. These features were incorporated during reconstruction of Beaver Creek; however, it is unknown what the effects on Grass Pickerel population and habitat would have been in the absence of these natural channel design features.
• The presence and dispersal ability of a source population to recolonize the reconstructed area following in-stream works should be considered when planning future maintenance and reconstruction activities.
• Whenever opportunities are presented, future drainage projects should incorporate pre- and post-construction monitoring to increase the number of case studies available to reduce uncertainty related to the effects of these activities and to inform future management decisions regarding drain maintenance effects on at-risk fish species. Monitoring should be conducted for as long as possible prior to, and following, the drainage activities to detect changes in habitat and abundance. This study has shown that changing the amount of time that monitoring is conducted can alter the ability to detect the effects of drain maintenance and reconstruction on fish population and habitat.
• Monitoring projects should include standardized sampling effort between sites and among years, and care should be taken to implement a study design that allows for rigorous statistical analyses.

This Science Advisory Report is from the October 4-5, 2016 regional peer review meeting on Impacts of agricultural drain maintenance in Beaver Creek on Grass Pickerel (Esox americanus vermiculatus), a fish species at risk. Additional publications from this meeting will be posted on the Fisheries and Oceans Canada (DFO) Science Advisory Schedule as they become available.

Science Advisory Report 2021/024 (PDF, 386 KB)

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