Genomic population structure of Grass Pickerel (Esox americanus vermiculatus) in Canada: management guidance for an at-risk fish at its northern range limit

Movement of an imperiled esocid fish in an agricultural drain

“…Variance in the stationary and mobile population proportions between sites was better explained by habitat variables than the number of immigrations or emigrations between sites. The distribution of Grass Pickerel movement distances showed a long-tail distribution, implying high intraspecific movement variation among the studied Grass Pickerel, which may have implications for gene flow among both historical and contemporary Grass Pickerel populations [ 50 ]. Low frequency of movements over 5 km and low frequency of movements downstream from Beaver Creek to Black Creek are indicative of difficult movement conditions between the Beaver Creek agricultural drain and other neighboring habitats.…”

“…Among these ecological functions are the location of refugia during adverse conditions, colonization of new or reconnected habitat, effective feeding and predation avoidance, and maintaining metapopulation dynamics and gene flow among neighboring populations. Recent work on Grass Pickerel landscape genetics has shown limited to no gene flow over relatively short stream distances [ 50 ]. We have shown that a few Grass Pickerel may move relatively long distances (although none > 14 km), yet most tagged Grass Pickerel were stationary and fragmented riverscapes may prevent these long-distance movements from resulting in gene flow—consistent with the results of Lujan et al [ 50 ].…”

“…Recent work on Grass Pickerel landscape genetics has shown limited to no gene flow over relatively short stream distances [ 50 ]. We have shown that a few Grass Pickerel may move relatively long distances (although none > 14 km), yet most tagged Grass Pickerel were stationary and fragmented riverscapes may prevent these long-distance movements from resulting in gene flow—consistent with the results of Lujan et al [ 50 ]. If limited movement and, hence, gene flow, is similar in other Grass Pickerel populations throughout southern Ontario, there are a few key considerations for the conservation of the species.…”

“…Some of the stream reaches with the highest recorded local abundances of Grass Pickerel are agricultural drains that mirror the shallow slopes, vegetated channels with ample floodplain habitat, and high-conductivity (i.e., clay-rich) substrate characteristics of naturally occurring wetland and stream Grass Pickerel habitat [ 9 ]. Its Canadian range consists of four disjunct populations that likely originated from a single Pleistocene refugium, but are now geographically and genetically distinct, with contemporary gene flow between populations unlikely [ 50 , 51 ]. Further, a recent analysis of Niagara Peninsula (Ontario) subpopulations suggests that even geographically close subpopulations (< 30 river km) have limited gene flow, perhaps due to habitat barriers to functional movement [ 50 ].…”

“…Its Canadian range consists of four disjunct populations that likely originated from a single Pleistocene refugium, but are now geographically and genetically distinct, with contemporary gene flow between populations unlikely [ 50 , 51 ]. Further, a recent analysis of Niagara Peninsula (Ontario) subpopulations suggests that even geographically close subpopulations (< 30 river km) have limited gene flow, perhaps due to habitat barriers to functional movement [ 50 ].…”