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Snorkel surveys are frequently used to monitor stream-dwelling fish. Inferring local abundance from snorkel surveys is complicated by two primary factors: variable fish detection probabilities and the relative abundance of fish in habitat types below the recommended minimum depth for snorkeling. We examine these factors across three salmonid species (Oncorhynchus spp.), 4 years, and 113 location-years in Oregon coastal streams. We calibrate snorkel counts to mark-recapture estimates and develop mathematically explicit expressions that convert a new snorkel count into a probability density of abundance for streams containing mixed habitat types that were and were not snorkeled. Snorkelers detected 63%, 47%, and 39% of juvenile coho salmon (Oncorhynchus kitsutch), steelhead trout (Oncorhynchus mykiss), and cutthroat trout (Oncorhynchus clarkii clarkia) estimated by mark-recapture, respectively, but uncertainty within and among sampling units was high. Further, analytics developed here can be used to infer abundance and uncertainty for habitat types that were not snorkeled. Our quantification of uncertainty arising from using snorkel counts as a proxy for abundance will help managers balance biological risks with available resources. [ABSTRACT FROM AUTHOR]

Courter et al. (2022) address one of the most complicated and disputed topics in fisheries management--the effects of hatchery-origin fish on natural-origin fish. I contend that Courter et al. misinterpret [...]

To purchase or authenticate to the full-text of this article, please visit this link: http://dx.doi.org/10.1111/j.1523-1739.2007.00766.x Byline: MATTHEW R. FALCY ([dagger]*), CRISTIAN F. ESTADES ([dagger]) Keywords: corridor; patch size; population model; population size; spatially explicit simulation Abstract: Abstract: The establishment of biological corridors between two otherwise isolated habitat patches is a common yet contentious strategy for conserving populations in fragmented landscapes. We compared the effectiveness of corridors with the effectiveness of an alternate conservation strategy, the enlargement of existing habitat patches. We used a spatially explicit population model that simulated population size in two kinds of patches. One patch had a corridor that connected it to a larger 'source' patch and the other patch was unconnected and enlarged at the periphery by an area the same size as the corridor. Patch isolation, corridor width, patch size, and the probability that individuals would cross the border from habitat to matrix were varied independently. In general, population size was greater in enlarged patches than in connected patches when patches were relatively large and isolated. Corridor width and the probability of crossing the border from habitat to matrix did not affect the relative benefit of corridors versus patch enlargement. Although biological corridors may mitigate potential effects of inbreeding depression at long time scales, our results suggest that they are not always the best method of conserving fragmented populations. Abstract (Spanish): La Efectividad de los Corredores en Relacion con la Ampliacion de Parches de Habitat Resumen: El establecimiento de corredores biologicos entre dos parches de habitat aislados es una estrategia comun, pero discutible, para la conservacion de poblaciones en paisajes fragmentados. Comparamos la efectividad de los corredores con la efectividad de de una estrategia de conservacion alternativa, la ampliacion de los parches de habitat existentes. Utilizamos un modelo poblacional espacialmente explicito que simulaba el tamano de la poblacion en dos tipos de parches. Un parche tenia un corredor que lo conectaba a un parche 'fuente' mas grande y el otro parche estaba desconectado y fue ampliado en la periferia con una superficie equivalente a la del corredor. El asilamiento del parche, la anchura del corredor y la probabilidad de que los individuos cruzaran el limite entre el habitat y la matriz fueron variados independientemente. En general, el tamano poblacional fue mayor en los parches ampliados que en los conectados cuando los parches eran relativamente grandes y aislados. La anchura del corredor y la probabilidad de cruzar el limite entre el habitat y la matriz no afectaron al beneficio relativo de los corredores versus la ampliacion de parches. Aunque los corredores biologicos pueden mitigar los efectos potenciales de la depresion por endogamia en escalas de tiempo largas, nuestros resultados sugieren que no siempre son el mejor metodo para la conservacion de poblaciones fragmentadas. Author Affiliation: ([dagger])Departamento de Manejo de Recursos Forestales, Universidad de Chile, Casilla 9206, Santiago, Chile Article History: Paper submitted June 22, 2006; revised manuscript accepted May 3, 2007. Article note: (*) Current address: Ecology, Evolution, and Organismal Biology, 253 Bessey Hall, Iowa State University, Ames, IA 50011, U.S.A., email mfalcy@iastate.edu