Geology topics

Daniel Schindler

Publications and source records attributed to Daniel Schindler.

4 recordsLinked to original sources

USGS2023

Spatial and temporal variation of large wood in a coastal river

Large wood (LW) is a critical habitat-forming feature in rivers, but our understanding of its spatial and temporal dynamics remains incomplete due to its historical removal from waterways. Few studies have the necessary spatial and temporal extent and resolution to assess wood dynamics over long time periods or in response to flood disturbance. We used an exceptional dataset from 65 km of a free-flowing coastal river in Oregon, USA, to characterize LW dynamics over a 12-year period (1989–2000). Our objectives were to assess the spatial dynamics of LW over multiple spatial scales and characterize changes in these patterns in response to a major flood in November 1996. Higher LW densities were found in the tributaries, and higher temporal variation of density existed in the main stem. Within years and among reaches, LW density varied by 2 to 3 orders of magnitude across the river. Patterns of LW accumulation across the river were not comparably different when considered at spatial resolutions < 6 km. A large flood in 1996 homogenized the wood distribution across the system, particularly at fine spatial scales (that is, 1.5–0.1 km scales), but considerable heterogeneity was reestablished within 2–3 years post disturbance. At the habitat unit scale, LW tended to accumulate in locations with narrow channel widths, and to a lesser extent, in shallow reaches. These data highlight the dynamic nature of the natural wood regime in coastal rivers that is produced by continuous recruitment and transport through the system.

Oregon↗

USGS2023

Declines in body size of sockeye salmon associated with increased competition in the ocean

Declining body sizes have been documented for several species of Pacific salmon; however, whether size declines are caused mainly by ocean warming or other ecological factors, and whether they result primarily from trends in age at maturation or changing growth rates remain poorly understood. We quantified changes in mean body size and contributions from shifting size-at-age and age structure of mature sockeye salmon returning to Bristol Bay, Alaska, over the past 60 years. Mean length declined by 3%, corresponding to a 10% decline in mean body mass, since the early 1960s, though much of this decline occurred since the early 2000s. Changes in size-at-age were the dominant cause of body size declines and were more consistent than trends in age structure among the major rivers that flow into Bristol Bay. Annual variation in size-at-age was largely explained by competition among Bristol Bay sockeye salmon and interspecific competition with other salmon in the North Pacific Ocean. Warm winters were associated with better growth of sockeye salmon, whereas warm summers were associated with reduced growth. Our findings point to competition at sea as the main driver of sockeye salmon size declines, and emphasize the trade-off between fish abundance and body size.

Alaska↗

USGS2023

Divergent responses of western Alaska salmon to a changing climate

Headlines Western Alaska salmon abundance reached historic extremes during 2021-22, with record lows for Chinook and chum salmon (81% and 92% below the 30-year mean, respectively) and record highs for sockeye salmon (98% above the 30-year mean). Salmon are maturing at smaller sizes. Since the 1970s, for example, Yukon River Chinook salmon have decreased an estimated 6% in mean adult body length and 15% in fecundity, likely exacerbating population declines. Salmon population declines have led to fishery closures, worsened user conflicts, and had profound cultural and food security impacts in Indigenous communities that have been tied to salmon for millennia. Changes in abundance and size are associated with climatic changes in freshwater and marine ecosystems and competition in the ocean. Changes in predators, food supply, and disease are also likely important drivers.

Alaska↗

USGS2016

Evaluating early-warning indicators of critical transitions in natural aquatic ecosystems

Ecosystems can show sudden and persistent changes in state despite only incremental changes in drivers. Such critical transitions are difficult to predict, because the state of the system often shows little change before the transition. Early-warning indicators (EWIs) are hypothesized to signal the loss of system resilience and have been shown to precede critical transitions in theoretical models, paleo-climate time series, and in laboratory as well as whole lake experiments. The generalizability of EWIs for detecting critical transitions in empirical time series of natural aquatic ecosystems remains largely untested, however. Here we assessed four commonly used EWIs on long-term datasets of five freshwater ecosystems that have experienced sudden, persistent transitions and for which the relevant ecological mechanisms and drivers are well understood. These case studies were categorized by three mechanisms that can generate critical transitions between alternative states: competition, trophic cascade, and intraguild predation. Although EWIs could be detected in most of the case studies, agreement among the four indicators was low. In some cases, EWIs were detected considerably ahead of the transition. Nonetheless, our results show that at present, EWIs do not provide reliable and consistent signals of impending critical transitions despite using some of the best routinely monitored freshwater ecosystems. Our analysis strongly suggests that a priori knowledge of the underlying mechanisms driving ecosystem transitions is necessary to identify relevant state variables for successfully monitoring EWIs.

Proceedings of the National Academy of Sciences of↗