No abstract

We investigated patterns of grass pickerel (Esox americanus vermiculatus Lesueur, 1846) distribution in three watersheds in Ontario, Canada, using site- and reach-scale habitat variables and fish community assemblage data to determine why this species occurs sporadically throughout watersheds despite abundant seemingly suitable, but unoccupied, habitat. Habitat and fish community data were collected using conventional field sampling methods, and reach-scale habitat data were compiled with the aid of a geographic information system. We found that occupied sites had lower baseflow indices and reach slopes but higher conductivity and agricultural land uses than unoccupied sites. More grass pickerel were detected when conductivity, channel cover, and wetlands in the floodplain were highest and bank slopes lowest; this is consistent with habitat preferences described elsewhere in its range. Habitat features at the site scale appeared more important than reach-scale features suggesting that grass pickerel may be using small habitat patches. This study identifies habitat elements important to grass pickerel and offers insights into management implications.

Age assessment was conducted on the at-risk grass pickerel (Esox americanus vermiculatus Lesueur, 1846) in southern Ontario, Canada (the northern edge of the species’ range), to better understand population dynamics. Cleithral age assessment revealed different age distributions between two sample years; the first year characterized by old, large individuals and the second year characterized by mostly young of the year. Back-calculated lengths at age were used to develop the von Bertalanffy growth relationships and estimates of ultimate length. Growth rates were substantially faster in the second year, when fewer and smaller individuals were present, suggesting density-dependent effects on growth. A pseudoannulus in the cleithrum, common to this species, was shown by sequential sampling to form in early July at 70% to 80% of the first growth zone and to occur more frequently in slow-growing fish and strong year classes than in faster-growing individuals and weaker year classes. Mortality rates of females were high (26%–46%) relative to other studies and probably resulted from greater abundance of individuals. Compared with cleithra, scale ages after age 1 were consistently underestimated. Calculated length at cleithral age intervals overlapped minimally, suggesting length could be used as a proxy for assessing age of this species in Ontario to avoid lethal sampling.

Sampling method decisions are critical for the effective monitoring and management of fisheries. Deploying the most effective sampling methodologies is particularly important when responding to new invasive species, where early

Eleven Flathead Catfish (Pylodictis olivaris), representing at least five age classes, were collected between 2016 and 2018 in the lower Thames River, Ontario, Canada. The capture of two juveniles (total lengths 78 mm and 82 mm), the first records of juveniles in Canada, is a strong indication that reproduction has occurred. Previous records were thought to be individuals that dispersed from known populations in American waters of Lake Erie. Flathead Catfish is currently designated as data deficient by the Committee on the Status of Endangered Wildlife in Canada. These new findings may provide sufficient data to reconsider the conservation status of this species.