Life‐history and other vital rate information is important for effective species conservation by informing demographic trends and aspects of population viability. However, species‐specific information is lacking for many small‐bodied freshwater fishes, which can make it difficult to relate demographic trends to threats or recovery actions. Silver Shiner (Notropis photogenis), a small‐bodied species listed as Threatened under Canada's Species at Risk Act, lacks well‐informed age and vital rate information. We aged 254 Silver Shiner using opercular and otolith structures and determined that Silver Shiner is short‐lived, with a probable maximum age of 4. Three years of field collections (2017–2019) were used to parameterize growth models and to estimate adult (age 1–3+) mortality rates. Silver Shiner captured in urban reaches exhibited altered growth and higher mortality compared to non‐urban reaches, indicating that urbanization may have demographic impacts on the species. Results highlight the importance of detailed age and vital rate information for assessing threats and informing effective conservation approaches for imperilled fishes. Furthermore, the potential negative impact of urbanization on the growth and survival of this species highlights the urgency of better understanding the influence of urbanization on small‐bodied freshwater fishes in general.
Niche specificity can predispose species to population declines during periods of resource limitation, yet trophic niche specificity is poorly known for many small-bodied freshwater fishes. Applying a two-tiered approach involving stomach content and stable isotope analyses, we examined the diet and trophic niche of the threatened eastern sand darter (Ammocrypta pellucida (Putnam, 1863)) and co-occurring fishes in the Thames River, Ontario, Canada. As with previous studies, stomach content analysis revealed that eastern sand darter consumed a variety of benthic organisms including Chironomidae, Cladocera, Ostracoda, Oligochaeta, and Ephemeroptera; however, proportional contributions of prey groups differed based on stable isotope analysis, highlighting the potential for seasonal variation in prey consumption. Despite evidence of a generalist strategy, stable isotope analysis indicated eastern sand darter exhibited a relatively narrow trophic niche relative to co-occurring fishes. Trophic niche overlap was relatively minor between eastern sand darter and drift-feeding fishes (spotfin shiner (Cyprinella spiloptera (Cope, 1867)), emerald shiner (Notropis atherinoides Rafinesque, 1818), and buffalo sp. (genus Ictiobus Rafinesque, 1820)), but was more evident between eastern sand darter and benthic and benthopelagic fishes (johnny darter (Etheostoma nigrum Rafinesque, 1820) and blackside darter (Percina maculata (Girard, 1859))), indicating that competition with these species may be more likely during periods of prey scarcity.
The consumption of terrestrial prey by fishes highlights the functional value of terrestrial habitats, but such consumption is not well documented for many small-bodied species. We determined the diet and consumption of terrestrial prey by a threatened fish, silver shiner Notropis photogenis, using stomach content and stable isotope analyses to better understand the functional role of riparian habitat for the species. Results indicate silver shiner is a generalist drift feeder that consumes a wide range of aquatic and terrestrial prey. Both stomach content and stable isotope analyses indicated that terrestrial prey was commonly exploited and that terrestrial prey consumption was both seasonally and spatially variable. Based on stomach contents, the contribution of terrestrial prey was (average ± SD) 41.53 ± 32.35% in fall and 20.45 ± 20.45% in summer; based on stable isotopes it was 35.24 ± 4.41% in fall and 39.88 ± 12.34% in summer. During fall, when bankside terrestrial invertebrates were more abundant, silver shiner stomachs contained significantly more terrestrial prey in reaches where riparian vegetation cover was highest, indicating that intact riparian cover may facilitate access to high-quality prey. The consumption of terrestrial prey may be particularly important in fall, as it may promote increased growth and survival leading to more successful overwintering. Our findings suggest that terrestrial subsidies are ecologically valuable for silver shiner and that the protection of reaches with intact riparian habitats would likely improve conservation and recovery efforts by helping ensure access to key prey resources.
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