7 research outputs found
Fishery collapse, recovery, and the cryptic decline of wild salmon on a major California river
Fall-run Chinook salmon (Oncorhynchus tshawytscha) from the SacramentoâSan Joaquin River system form the backbone of Californiaâs salmon fishery and are heavily subsidized through hatchery production. Identifying temporal trends in the relative contribution of hatchery- versus wild-spawned salmon is vital for assessing the status and resiliency of wild salmon populations. Here, we reconstructed the proportion of hatchery fish on natural spawning grounds in the Feather River, a major tributary to the Sacramento River, using strontium isotope (87Sr/86Sr) ratios of otoliths collected during carcass surveys from 2002 to 2010. Our results show that prior to the 2007â2008 salmon stock collapse, 55%â67% of in-river spawners were of hatchery origin; however, hatchery contributions increased drastically (89%) in 2010 following the collapse. Data from a recent hatchery marking program corroborate our results, showing that hatchery fish continued to dominate (âŒ90%) in 2011â2012. Though the rebound in abundance of salmon in the Feather River suggests recovery of the stock postcollapse, our otolith chemistry data document a persistent decline of wild spawners, likely leading to the erosion of locally adapted Feather River salmon populations
âWe Used to Say Rats Fell from the Sky After a Flood:â Temporary Recovery of Muskrat Following Ice Jams in the Peace-Athabasca Delta
Elders and Indigenous land users in the Peace-Athabasca Delta (PAD) have observed a dramatic decline in the relative abundance of muskrat in recent decades (~1935â2014). The main explanation for the decline has been reduction in suitable habitat as a result of decades with reduced frequency of ice-jam flooding on the Peace River. Under favourable conditions, ice jams can cause flooding of perched basins within the PAD that would otherwise receive no recharge from floodwaters. To examine whether abundance of muskrat in the PAD is driven by flooding, we tested the predictions that the density of muskrat (estimated by winter counts of houses) (1) was inversely related to the number of years since major ice jam floods and (2) increased with water depth. An ongoing collaborative monitoring program initiated in 2011, combined with analysis of data from past surveys (1973â2015), allowed Indigenous land users and scientists to document a 10 to 100-fold increase in the density of muskrat houses in 24 basins, over the two years following ice-jam flood events in the PAD. During 1973â2015, in the periods between major floods, density of houses dropped by approximately 79% for every year after a significant flood. In 27 basins surveyed from 2011 to 2015, density of muskrat houses increased by two orders of magnitude in the two years following a flood in the spring of 2014. Density of muskrat houses had a non-linear relationship with estimated depth of water at the time of fall freeze-up; the highest densities of muskrat houses were in basins with about 60 â 250 cm of water at the time of freeze-up. The depth of snow at the time of surveys did not have a strong relationship with the density of muskrat houses. However, few houses were counted in basins with more than 20 cm of snow, likely because deeper snow made it more difficult to conduct surveys and spot houses. Factors other than an increase in the depth of water at fall freeze-up may provide the mechanisms by which flooding affects muskrat. Density of muskrat houses is clearly tied to ice-jam flooding in the PAD. However, the local mechanisms by which floods affect muskrat are best understood by Indigenous land users and remain poorly understood by Western science. Indigenous peoples continue to regard muskrat as an indicator of ecological and cultural health of the PAD. This study highlights the value of consistent ecological monitoring that includes Indigenous knowledge.Les aĂźnĂ©s et les utilisateurs des terres autochtones du delta des riviĂšres de la Paix et Athabasca ont observĂ© une baisse draconienne de lâabondance du rat musquĂ© au cours des derniĂšres dĂ©cennies (~1935-2014). La principale explication du dĂ©clin est la diminution dâabris convenables, et ce, en raison de plusieurs dĂ©cennies marquĂ©es par la frĂ©quence rĂ©duite dâinondations causĂ©es par des embĂącles dans la riviĂšre de la Paix. Dans des conditions favorables, les embĂącles peuvent causer lâinondation des bassins perchĂ©s au sein du delta des riviĂšres de la Paix et Athabasca qui autrement ne recevraient pas de recharge des eaux de crue. Afin dâexaminer si lâabondance du rat musquĂ© dans le delta des riviĂšres de la Paix et Athabasca est favorisĂ©e par les inondations, nous avons testĂ© des prĂ©visions selon lesquelles la densitĂ© du rat musquĂ© (estimĂ©e par le nombre dâabris en hiver) 1) Ă©tait inversement liĂ©e au nombre dâannĂ©es depuis les derniĂšres importantes inondations causĂ©es par des embĂącles et 2) augmentait avec la profondeur de lâeau. Un programme collaboratif de suivi continu lancĂ© en 2011, combinĂ© Ă lâanalyse de donnĂ©es des relevĂ©s antĂ©rieurs (1973-2015), a permis aux utilisateurs des terres autochtones et aux scientifiques de multiplier de 10 Ă 100 fois la densitĂ© dâabris du rat musquĂ© dans 24 bassins, au cours des deux annĂ©es suivant des Ă©vĂ©nementsdâinondation causĂ©s par des embĂącles dans le delta des riviĂšres de la Paix et Athabasca. Entre 1973 et 2015, durant les pĂ©riodes se situant entre les inondations importantes, la densitĂ© dâabris a diminuĂ© dâenviron 79 % chaque annĂ©e suivant une inondation importante. Dans 27 bassins sondĂ©s entre 2011 et 2015, la densitĂ© dâabris du rat musquĂ© a augmentĂ© de deux ordres de grandeur au cours des deux annĂ©es ayant suivi une inondation survenue au printemps de 2014. La densitĂ© dâabris du rat musquĂ© avait une relation non linĂ©aire avec la profondeur de lâeau estimĂ©e au moment de la prise des glaces en automne; les plus fortes densitĂ©s dâabris du rat musquĂ© se trouvaient dans les bassins ayant de 60 Ă 250 cm dâeau au moment de la prise des glaces. La profondeur de la neige au moment des relevĂ©s nâavait pas de relation solide avec la densitĂ© dâabris du rat musquĂ©. Cependant, nous avons comptĂ© peu dâabris dans les bassins comptant plus de 20 cm de neige, probablement parce quâil Ă©tait plus difficile dâeffectuer des relevĂ©s et de trouver les abris dans la neige plus Ă©paisse. Des facteurs autres que lâaugmentation de la profondeur de lâeau au moment de la prise des glaces en automne pourraient fournir les mĂ©canismes par lesquels les inondations se rĂ©percutent sur les rats musquĂ©s. La densitĂ© dâabris du rat musquĂ© est manifestement liĂ©e aux inondations causĂ©es par des embĂącles dans le delta des riviĂšres de la Paix et Athabasca. Toutefois, les utilisateurs des terres autochtones comprennent mieux les mĂ©canismes locaux par lesquels les inondations se rĂ©percutent sur les rats musquĂ©s, tandis quâils demeurent mal compris par la science occidentale. Les peuples autochtones continuent de considĂ©rer le rat musquĂ© comme un indicateur de la santĂ© Ă©cologique et culturelle du delta des riviĂšres de la Paix et Athabasca. Cette Ă©tude fait ressortir la valeur dâun suivi Ă©cologique constant qui tient compte des connaissances autochtones
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Considerations for the Development of a Juvenile Production Estimate for Central Valley Spring-Run Chinook Salmon
Effective species management depends on accurate estimates of population size. There are, however, no estimates of annual juvenile production for Central Valley spring-run Chinook Salmon (âspring runâ), a highly imperiled species in California, making it difficult to evaluate population status and effectively manage key issues such as entrainment of this species at water diversions. In recognition of this critical information gap, we initiated an effort to develop a juvenile production estimate (JPE) for spring run, defined here as an annual forecast of the number of juvenile Central Valley spring-run Chinook Salmon that enter the SacramentoâSan Joaquin Delta (âDeltaâ) from the Sacramento Valley. This metric would allow for a more robust scientific assessment of the population, which is needed to effectively manage water to reduce effects on spring run, a key condition of state permit requirements. To help guide this effort, we organized a workshop for stake-holders, managers, and scientists to review some of the key aspects of spring-run biology, examine the management and conservation importance of a JPE, identify knowledge gaps, introduce new tools, and discuss alternative approaches to forecasting the number of spring run emigrating from the Sacramento River drainage and into the Delta. This paper summarizes the spring-run biology, monitoring, and emergent methods for assessment considered at the workshop, as well as the guiding concepts identified by workshop participants necessary to develop a JPE for spring-run Chinook Salmon