Using Grizzly Bears to Assess Harvest-Ecosystem Tradeoffs in Salmon Fisheries

Using grizzly bears as surrogates for “salmon ecosystem” function, the authors develop a generalizable ecosystem-based management framework that enables decision-makers to quantify ecosystem-harvest tradeoffs between wild and human recipients of natural resources like fish

Variation in spatial and temporal gradients in zooplankton spring development: the effect of climatic factors

1. We examined the temporal and spatial heterogeneity of zooplankton in lake surface waters during the spring of 3 years in Lake Washington, U.S.A., a large lake with a high production of sockeye salmon fry. 2. We show large within-season and among-year variation in the horizontal distribution of temperature, chlorophyll a concentration, and zooplankton in the lake. The main pattern, a delay in zooplankton population increase from the north- to the south-end of the lake, recurred in each year and was persistent within each spring. 3. The delay is primarily caused by the development of a temperature gradient during spring warming, as cold mountain water enters the south end of the lake, while warm water enters the north end via a river draining a nearby lake. Climate factors, such as air temperature and precipitation during winter and spring, appear to influence the extent of the delay of zooplankton increase. 4. If the climate continues to warm, the temporal disconnection in zooplankton development between lake areas immediately influenced by cold river inflow and areas that are influenced by spring warming may increase in magnitude. Thus, the different areas of the lake may not contribute equally to fish production

Oceanographic influences on patterns in North Pacific salmon abundance

We identified three dominant patterns of temporal variation (1951–2002) in the abundance of 34 stock groups of wild North American and Asian pink salmon (Oncorhynchus gorbuscha), chum salmon (Oncorhynchus keta), and sockeye salmon (Oncorhynchus nerka) that were related to patterns of oceanographic variability. We identified these patterns using three different ordination methods and found consistent patterns across these methods. Alaskan salmon dominated the most prominent pattern, which exhibited a positive abundance shift in the mid-1970s. In general, warm (cold) periods in the Gulf of Alaska and eastern Bering Sea corresponded with high (low) abundance years for these stock groups. The second abundance pattern captured differences among Asian, northern North American, and southern North American population groups and was associated with an intense, large-scale Aleutian Low. To our knowledge, this is the first analysis that identifies regional patterns of covariation in salmon abundance around the entire North Pacific Rim, and it highlights the existence of basin-wide covariations in wild salmon abundance that are associated with spatially coherent and regionally distinct patterns in North Pacific climate. </jats:p

Data from: Fertilizer legacies meet saltwater incursion: challenges and constraints for coastal plain wetland restoration

Coastal wetland restoration is an important tool for climate change adaptation and excess nutrient runoff mitigation. However, the capacity of restored coastal wetlands to provide multiple ecosystem services is limited by stressors, such as excess nutrients from upstream agricultural fields, high nutrient legacies on-site, and rising salinities downstream. The effects of these stressors are exacerbated by an accelerating hydrologic cycle, expected to cause longer droughts punctuated by more severe storms. We used seven years of surface water and six years of soil solution water chemistry from a large (440 ha) restored wetland to examine how fertilizer legacy, changes in hydrology, and drought-induced salinization affect dissolved nutrient and carbon concentrations. To better understand the recovery trajectory of the restored wetland, we also sampled an active agricultural field and two mature forested wetlands. Our results show that nitrogen (N) and phosphorus (P) concentrations in soil solution were 2–10 times higher in the restored wetland compared to two mature forested wetlands, presumably due to legacy fertilizer mobilized by reflooding. Despite elevated nutrient concentrations relative to reference wetlands, the restored wetland consistently attenuated N and P pulses delivered from an upstream farm. Even with continued loading, N and P concentrations in surface water throughout the restored wetland have decreased since the initial flooding. Our results suggest that high nutrient concentrations and export from wetlands restored on agricultural lands may be a severe but temporary problem. If field to wetland conversion is to become a more widespread method for ameliorating nutrient runoff and adapting coastal plain ecosystems to climate change, we should adopt new methods for minimizing the initial export phase of wetland restoration efforts

tower_longterm_surfacewater

File contains 7 years of surface water chemistry from the Timberlake Observatory for Wetland Restoration (TOWeR) site

An integrated population model for estimating the relative effects of natural and anthropogenic factors on a threatened population of Pacific trout

SummaryAssessing the degree to which at-risk species are regulated by density dependent versus density independent factors is often complicated by incomplete or biased information. If not addressed in an appropriate manner, errors in the data can affect estimates of population demographics, which may obfuscate the anticipated response of the population to a specific action.We developed a Bayesian integrated population model that accounts explicitly for interannual variability in the number of reproducing adults and their age structure, harvest, and environmental conditions. We apply the model to 41 years of data for a population of threatened steelhead troutOncorhynchus mykissusing freshwater flows, ocean indices, and releases of hatchery-born conspecifics as covariates.We found compelling evidence that the population is under strong density dependence, despite being well below its historical population size. In the freshwater portion of the lifecycle, we found a negative relationship between productivity (offspring per parent) and peak winter flows, and a positive relationship with summer flows. We also found a negative relationship between productivity and releases of hatchery conspecifics. In the marine portion of the lifecycle, we found a positive correlation between productivity and the North Pacific Gyre Oscillation. Furthermore, harvest rates on wild fish have been sufficiently low to ensure very little risk of overfishing.Synthesis and applications.The evidence for density dependent population regulation, combined with the substantial loss of juvenile rearing habitat in this river basin, suggests that habitat restoration could benefit this population of at-risk steelhead. Our results also imply that hatchery programs for steelhead need to be considered carefully with respect to habitat availability and recovery goals for wild steelhead. If releases of hatchery steelhead have indeed limited the production potential of wild steelhead, there are likely significant tradeoffs between providing harvest opportunities via hatchery steelhead production, and achieving wild steelhead recovery goals.</jats:p

Spatial–Temporal Dynamics of Early Feeding Demand and Food Supply for Sockeye Salmon Fry in Lake Washington

Abstract.—We compared temporal consumption rates by sockeye salmon Oncorhynchus nerka fry with food supply to evaluate how different survival and dispersal rates or additional hatchery pro-duction affected the winter carrying capacity of Lake Washington, Washington. Peak immigration of sockeye salmon fry into southern Lake Washington precedes the spring zooplankton bloom by 2–3 months. Zooplankton density, fish diet, and growth were sampled during winter and spring 2001, when a record 52.4 million fry entered the lake. Supplementary information on the distribution and dispersal of fry was collected in 2002 and 2003. We used bioenergetics modeling to estimate the temporal–spatial consumption by fry during early lake rearing. Cyclops bicuspidatus were dominant in the diet and zooplankton assemblage but declined from more than 30/L in late February and early March to fewer than 5/L during mid-March and early April. Fry ate significantly larger Cyclops than the average size in the lake; approximately 83 % of the food items in the stomachs were larger than 0.8 mm, which was the minimum food item size. Hydroacoustics and midwater trawling surveys during 2002 and 2003 suggested that fry dispersed quickly over the southern half of the lake and used depths of 0–30 m. Under the most realistic scenarios for fry dispersal, feeding, and survival, total consumption of all prey by sockeye salmon fry represented 5 % of the average monthly biomas