Geology topics

Kristin A. Connelly

Publications and source records attributed to Kristin A. Connelly.

6 recordsLinked to original sources

USGS2021

Resource use among top-level piscivores in a temperate reservoir: Implications for a threatened coldwater specialist

Evaluations of resource use among native piscivores in natural lakes have consistently documented significant partitioning that supports coexistence. Partitioning may be less prominent in reservoirs where water-level fluctuations can compress habitat and trophic diversity, but studies are lacking. Stable isotopes and bioenergetic models were used to quantify trophic interactions within a native piscivore assemblage inhabiting a temperate irrigation reservoir and explore implications for coexistence with a focus on threatened bull trout ( Salvelinus confluentus ). As hypothesised, adult bull trout exhibited the greatest degree of trophic specialisation by consuming mostly coldwater pelagic forage fish, which were consumed seasonally by the more abundant burbot ( Lota lota ) and northern pikeminnow ( Ptychocheilus oregonensis ). Numerous trophic niche overlap probabilities exceeded 70%, were as high as 93% and greatest between bull trout and burbot. Bioenergetics simulations demonstrated the high seasonal consumption capacity of burbot relative to northern pikeminnow. As a result, threefold to fourfold fewer burbot were required to consume the annual productivity of coldwater prey important for bull trout, particularly in the absence of small-bodied mesothermic or eurythermal fish as a buffer. Collectively, our analysis elucidated relatively strong trophic niche overlap among similarly sized piscivores, the importance of maintaining a diverse forage fish community for promoting coexistence and the greatest potential for competitive interactions between adult bull trout and burbot if key prey were limited or less diverse. More studies in regulated systems are needed to test for consistent patterns and identify mechanisms that limit or promote coexistence amid growing human-induced environmental change and demands on freshwater.

Washington↗

USGS2020

Variable prey consumption leads to distinct regional differences in Chinook salmon growth during the early marine critical period

Growth during the early marine critical period is positively associated with survival and recruitment for Pacific salmon Oncorhynchus spp., so it is important to understand how certain foraging strategies may bolster growth in estuarine and marine environments. To elucidate how spatiotemporal and demographic differences in diet contribute to growth rate variability, we analyzed stomach contents in tandem with morphometric and hormonal indices of growth for subyearling Chinook salmon O. tshawytscha captured in Puget Sound, Washington, USA. Regional dietary patterns indicated that fish caught in northern Puget Sound ate insects in the estuarine and nearshore habitats, followed by decapod larvae, euphausiids, or forage fish in the offshore zone. In southern Puget Sound, fish ate insects in the estuary but were more likely to eat mysids and other crustaceans in the nearshore zone. In the marine habitats adjacent to the San Juan Islands, subyearlings ate forage fish, and their stomachs were as much as 1.4 to 3 times fuller than salmon captured in other regions. Scale-derived growth rates and insulin-like growth factor-1 levels showed distinct growth advantages for San Juan Islands fish which were strongly associated with the early adoption of piscivory. However, consumption of larger crustaceans such as mysids and euphausiids was also associated with greater relative growth regardless of where individuals were captured. These findings highlight how spatiotemporal differences in prey quantity, prey profitability, and individual foraging strategies result in variable growth rates among salmon populations. Specifically, they emphasize the role of piscivory in promoting early marine growth for out-migrating Chinook salmon.

Washington↗

USGS2018

Trophic compression of lake food webs under hydrologic disturbance

The need to protect biostructure is increasingly recognized, yet empirical studies of how human exploits affect ecological networks are rare. Studying the effects of variation in human disturbance intensity from decades past can help us understand and anticipate ecosystem change under alleviated or amplified disturbance over decades to come. Here, we use stable isotopes and an innovative analytical approach to compare the food webs of two akin lake ecosystems subject to disparate water use regimes, a pervasive, yet unappreciated stressor. We show that intensive water use (persistent, early season, rapid lake‐level drawdown) can compress trophic diversity by 46%, necessitating reorganization of biostructural elements configuring lake food webs. Compression occurred over the δ 13 C axis indicating erosion of basal trophic diversity, but food chain length remained intact over the period and intensity of disturbance examined. This study demonstrates the potential for water use, like other disturbances (warming, eutrophication, and invasive species), to mute opportunity for benthic‐pelagic coupling and benefits to lake food webs and the inherent capacity of lake ecosystems to adapt to stress. Trophically compressed lakes may be less able to adapt to intensified water use.

Ecosphere↗

USGS2018

Size, growth, and size‐selective mortality of subyearling Chinook Salmon during early marine residence in Puget Sound

In marine ecosystems, survival can be heavily influenced by size‐selective mortality during juvenile life stages. Understanding how and when size‐selective mortality operates on a population can reveal underlying growth dynamics and size‐selective ecological processes affecting the population and thus can be used to guide conservation efforts. For subyearling Chinook Salmon Oncorhynchus tshawytscha in Puget Sound, previous research reported a strong positive relationship between marine survival and body mass during midsummer in epipelagic habitats within Puget Sound, suggesting that early marine growth drives survival. However, a fine‐scale analysis of size‐selective mortality is needed to identify specific critical growth periods and habitats. The objectives of this study were to (1) describe occupancy patterns across estuarine delta, nearshore marine, and offshore epipelagic habitats in Puget Sound; (2) describe changes in FL and weight observed across habitats and time; (3) evaluate evidence for size‐selective mortality; and (4) illustrate how marine survival of the stocks studied may be affected by variation in July weight. In 2014 and 2015, we sampled FLs, weights, and scales from seven hatchery‐origin and two natural‐origin stocks of subyearling Chinook Salmon captured every 2 weeks during out‐migration and rearing in estuary, nearshore, and offshore habitats within Puget Sound. Natural‐origin stocks had more protracted habitat occupancy patterns than hatchery‐origin stocks and were smaller than hatchery‐origin stocks in both years. Regardless of origin, subyearlings were longer and heavier and grew faster in offshore habitats compared to estuary and nearshore habitats. For all stocks, we found little evidence of size‐selective mortality among habitats in Puget Sound. These patterns were consistent in both years. Finally, the weights of subyearlings sampled during July in the offshore habitat predicted Puget Sound‐wide marine survival rates of 0.4% for 2014 and 2.0% for 2015, with stock‐specific predictions ranging from 0.18% to 11.70%.

Washington↗

USGS2016

Trophic feasibility of reintroducing anadromous salmonids in three reservoirs on the north fork Lewis River, Washington: Prey supply and consumption demand of resident fishes

The reintroduction of anadromous salmonids in reservoirs is being proposed with increasing frequency, requiring baseline studies to evaluate feasibility and estimate the capacity of reservoir food webs to support reintroduced populations. Using three reservoirs on the north fork Lewis River as a case study, we demonstrate a method to determine juvenile salmonid smolt rearing capacities for lakes and reservoirs. To determine if the Lewis River reservoirs can support reintroduced populations of juvenile stream-type Chinook Salmon Oncorhynchus tshawytscha , we evaluated the monthly production of daphnia Daphnia spp. (the primary zooplankton consumed by resident salmonids in the system) and used bioenergetics to model the consumption demand of resident fishes in each reservoir. To estimate the surplus of Daphnia prey available for reintroduced salmonids, we assumed a maximum sustainable exploitation rate and accounted for the consumption demand of resident fishes. The number of smolts that could have been supported was estimated by dividing any surplus Daphnia production by the simulated consumption demand of an individual Chinook Salmon fry rearing in the reservoir to successful smolt size. In all three reservoirs, densities of Daphnia were highest in the epilimnion, but warm epilimnetic temperatures and the vertical distribution of planktivores suggested that access to abundant epilimnetic prey was limited. By comparing accessible prey supply and demand on a monthly basis, we were able to identify potential prey supply bottlenecks that could limit smolt production and growth. These results demonstrate that a bioenergetics approach can be a valuable method of examining constraints on lake and reservoir rearing capacity, such as thermal structure and temporal food supply. This method enables numerical estimation of rearing capacity, which is a useful metric for managers evaluating the feasibility of reintroducing Pacific salmon Oncorhynchus spp. in lentic systems.

Washington↗

USGS2016

Predation by Northern Pikeminnow and tiger muskellunge on juvenile salmonids in a high–head reservoir: Implications for anadromous fish reintroductions

The feasibility of reintroducing anadromous salmonids into reservoirs above high-head dams is affected by the suitability of the reservoir habitat for rearing and the interactions of the resident fish with introduced fish. We evaluated the predation risk to anadromous salmonids considered for reintroduction in Merwin Reservoir on the North Fork Lewis River in Washington State for two reservoir use-scenarios: year-round rearing and smolt migration. We characterized the role of the primary predators, Northern Pikeminnow Ptychocheilus oregonensis and tiger muskellunge (Northern Pike Esox lucius × Muskellunge E. masquinongy ), by using stable isotopes and stomach content analysis, quantified seasonal, per capita predation using bioenergetics modeling, and evaluated the size and age structures of the populations. We then combined these inputs to estimate predation rates of size-structured population units. Northern Pikeminnow of FL ≥ 300 mm were highly cannibalistic and exhibited modest, seasonal, per capita predation on salmonids, but they were disproportionately much less abundant than smaller, less piscivorous, conspecifics. The annual predation on kokanee Oncorhynchus nerka (in biomass) by a size-structured unit of 1,000 Northern Pikeminnow having a FL ≥ 300 mm was analogous to 16,000–40,000 age-0 spring Chinook Salmon O. tshawytscha rearing year-round, or 400–1,000 age-1 smolts migrating April–June. The per capita consumption of salmonids by Northern Pikeminnow having a FL ≥ 200 mm was relatively low, due in large part to spatial segregation during the summer and the skewed size distribution of the predator population. Tiger muskellunge fed heavily on Northern Pikeminnow, other nonsalmonids, and minimally on salmonids. In addition to cannibalism within the Northern Pikeminnow population, predation by tiger muskellunge likely contributed to the low recruitment of larger (more piscivorous) Northern Pikeminnow, thereby decreasing the risk of predation to salmonids. This study highlights the importance of evaluating trophic interactions within reservoirs slated for reintroduction with anadromous salmonids, as they can be functional migration corridors and may offer profitable juvenile-rearing habitats despite hosting abundant predator populations.

Washington↗