Morgan H. Bond

Phenotype flexibility in wild fish: Dolly Varden regulate assimilative capacity to capitalize on annual pulsed subsidies

1. Large digestive organs increase rates of energy gain when food is plentiful but are costly to maintain and increase rates of energy loss when food is scarce. The physiological adaptations to this trade-off differ depending on the scale and predictability of variation in food abundance. 2. Currently, there is little understanding of how animals balance trade-offs between the cost and capacity of the digestive system in response to resource pulses: rare, ephemeral periods of resource superabundance. We investigated the physiological and behavioural tactics of the fish Dolly Varden (Salvelinus malma) that rear in watersheds with low in situ productivity, but experience annual resource pulses from the spawning migrations of Pacific salmon. The eggs of Pacific salmon provide high-energy food for Dolly Varden. 3. Dolly Varden sampled 6 weeks prior to the resource pulse exhibited atrophy of the stomach, pyloric caeca, intestine and liver. Throughout the portion of the growing season prior to the resource pulse, fish exhibited empty stomachs, low indices of energy condition and muscle isotope signatures reflecting the previous resource pulse. 4. During the resource pulse, Dolly Varden exhibited large digestive machinery, gorged on salmon eggs and rapidly stored energy in fat reserves, somatic growth and gonad development. Dolly Varden appeared to achieve nearly their entire annual energy surplus during the ∼ 5-week period when sockeye salmon spawn. 5. Digestive flexibility provides Dolly Varden the energy efficiency required to survive and reproduce when resource abundance is concentrated into an annual pulse that is predictable, yet highly ephemeral. Although fish are known to incur extremely variable energy budgets, our study is one of the first to document digestive flexibility in wild fish. Our study emphasizes that fish can rely heavily on rare, high-magnitude foraging opportunities. Human actions that attenuate spikes in food abundance may have stronger than anticipated effects on consumer energy budgets.

Should I Stay or Should I Go? The Influence of Genetic Origin on Emigration Behavior and Physiology of Resident and Anadromous Juvenile Oncorhynchus mykiss

Abstract We investigated the interaction among genetically identified origin, behavioral tendency to emigrate, and Na+, K+-ATPase enzyme activity in recently diverged subpopulations of resident (above-barrier) rainbow trout Oncorhynchus mykiss and steelhead (anadromous rainbow trout) in Scott Creek, California. Genetic assignment tests found that the frequency of resident and anadromous origin fish varied by sampling location within the watershed. Individuals immediately below barriers assigned to both above-barrier (37%) and anadromous (63%) subpopulations, and distinct differences in size and age were observed. However, the majority of downstream migration behavior occurred in fish of anadromous ancestry, which represented 97% of the fish sampled as outmigrating smolts. Nonmigratory fish of both life history types and origins typically had low Na+, K+-ATPase activity levels throughout most of the year, but significantly elevated levels were observed in individuals from both groups during the spring smol...

Assessing Avian Predation on Juvenile Salmonids using Passive Integrated Transponder Tag Recoveries and Mark–Recapture Methods

Abstract Many populations of coho salmon Oncorhynchus kisutch and steelhead O. mykiss are listed under the U.S. Endangered Species Act. Until recently, the role of avian predation in limiting recovery of coho salmon and steelhead in central California coastal watersheds has been overlooked. We used recoveries of passive integrated transponder (PIT) tags from Ano Nuevo Island (ANI), a breeding site for several species of piscivorous seabirds, to estimate predation rates on juvenile salmonids and identify susceptible life stages and species responsible for predation. A total of 34,485 PIT tags were deployed in coho salmon and steelhead in six watersheds in San Mateo and Santa Cruz counties. Tags were deposited on ANI by predators after ingestion of tagged fish. Because tags were not removed from the island and were detected on multiple sampling occasions, we were able to use mark–recapture models to generate a corrected minimum predation estimate. We used POPAN, a variation of the Jolly–Seber model, to gene...

Is isolation by adaptation driving genetic divergence among proximate Dolly Varden char populations

Numerous studies of population genetics in salmonids and other anadromous fishes have revealed that population structure is generally organized into geographic hierarchies (isolation by distance), but significant structure can exist in proximate populations due to varying selective pressures (isolation by adaptation). In Chignik Lakes, Alaska, anadromous Dolly Varden char (Salvelinus malma) spawn in nearly all accessible streams throughout the watershed, including those draining directly to an estuary, Chignik Lagoon, into larger rivers, and into lakes. Collections of Dolly Varden fry from 13 streams throughout the system revealed low levels of population structure among streams emptying into freshwater. However, much stronger genetic differentiation was detected between streams emptying into freshwater and streams flowing directly into estuarine environments. This fine-scale reproductive isolation without any physical barriers to migration is likely driven by differences in selection pressures across freshwater and estuarine environments. Estuary tributaries had fewer larger, older juveniles, suggesting an alternative life history of smolting and migration to the marine environment at a much smaller size than occurs in the other populations. Therefore, genetic data were consistent with a scenario where isolation by adaptation occurs between populations of Dolly Varden in the study system, and ecological data suggest that this isolation may partially be a result of a novel Dolly Varden life history of seawater tolerance at a smaller size than previously recognized.

Combined Effects of Barge Transportation, River Environment, and Rearing Location on Straying and Migration of Adult Snake River Fall-Run Chinook Salmon

AbstractHoming and straying in salmon have been extensively studied, yet it has proven difficult to disentangle the biotic and abiotic factors that influence straying. In the Columbia River basin, some juvenile salmon are collected at dams and transported downstream to increase survival during seaward migration, and as returning adults they experience a range of environmental conditions as they ascend the river. We examined 8 years of PIT tag detection data for hatchery-reared, fall-run Chinook Salmon Oncorhynchus tshawytscha released in the Snake River to evaluate the combined effects of juvenile barging, rearing and release locations, and environmental conditions on adult migration speed and straying below and above the Columbia River–Snake River confluence. Straying to the upper Columbia River was 10–19 times more likely among adults that were barged as juveniles from Snake River dams than among adults that were in-river migrants or that were transported from McNary Dam (below the confluence) as juveni...

Re-awakening dormant life history variation: stable isotopes indicate anadromy in bull trout following dam removal on the Elwha River, Washington

Migratory species take advantage of multiple habitats during their life cycle to optimize growth, survival, and reproduction. However, migration also makes them vulnerable to habitat degradation and exploitation in each habitat, and loss of connection between habitats. Partially migratory species (i.e., migration is facultative rather than obligate) can persist after loss of connectivity and may then resume migration after the habitats are reconnected. We analyzed stable isotopes of carbon and nitrogen to investigate the possible use of marine habitats for foraging by bull trout, Salvelinus confluentus, in years immediately after removal of impassable hydroelectric dams on the Elwha River, Washington State, USA. Juveniles in the Elwha River estuary were similar in δ15N and δ13C values to those in the estuary of the free-flowing Dungeness River nearby, and the values of fish from the estuaries were higher than those of juveniles collected in the river, consistent with use of marine food sources. Adult bull trout collected in each of the rivers had values indicating extensive reliance on marine prey - similar to those of adult Pacific salmon that had spent several years at sea. Taken together, these data demonstrate that the Elwha River bull trout, almost entirely landlocked for a century, are rapidly resuming anadromy and that the marine prey contribute substantially to their trophic ecology and likely their growth. More broadly, the results reveal the importance of connectivity for migratory fishes, their ability to resume anadromy once the connection between habitats is restored, and the population resilience that partial migration provides for them.

Can dietary reliance on Pacific salmon eggs create otolith Sr/Ca signatures that mimic anadromy in resident salmonids?

Many aspects of the ecology, growth, life history, and population dynamics of fishes differ between anadromous populations and those residing exclusively in freshwater habitats. Analysis of the elemental composition of otoliths (ear stones) is commonly used to indicate the migration history of individuals, relying on the differences in ambient concentrations of calcium, strontium, and barium and their subsequent incorporation into calcified structures. Dietary contribution to otolith chemistry is often overlooked, but in this study we report results consistent with the possibility that reliance on food resources derived from the ocean via Pacific salmon can produce otolith Sr/Ca ratios suggesting anadromy in freshwater resident fish. Dolly Varden, Salvelinus malma, from the Iliamna River, Alaska feed very heavily on eggs and other tissues from sockeye salmon, Oncorhynchus nerka, and their otoliths had Sr/Ca ratios typical of fish making seasonal migrations to marine waters but the Ba/Ca ratios were consistent with residence in fresh water. Water samples from the river provided no indication that the elevated Sr concentrations came from the river. A simulation of otolith chemistry resulting from Sr incorporation from both water and diet across a range of published values in salmonids indicates that a diet of salmon eggs and tissues can produce marine Sr/Ca ratios while fish remain in fresh water. Without experimental evidence such as a controlled diet study these results are suggestive but not conclusive. Nevertheless, they send a cautionary note that in some cases heavy reliance on marine-derived food sources might affect otolith microchemistry, creating an appearance of anadromy in fish that did not leave fresh water.

Use of egg size differences in anadromous (sockeye salmon) and non-anadromous (kokanee) forms of Oncorhynchus nerka to infer ancestral origins of a landlocked population

Life history traits reflect interactions between evolutionary lineage and environmental conditions. Translocations of populations to new environments, and changes in their natal environment, provide insights into the factors controlling life history. For example, the trade-off between egg size and egg number is a well-studied adaptation in fishes, and especially salmon and trout. We used existing and new data on this tradeoff in anadromous sockeye salmon, Oncorhynchus nerka, and the non-anadromous form of the species (kokanee), to investigate the likely origin of a population of uncertain ancestry, land-locked for a century above an impassable dam. Native kokanee have smaller eggs than do the larger-bodied anadromous sockeye salmon. However, the land-locked population in Lake Sutherland, in the Elwha River system, Washington, USA had much larger eggs for their body size than any other kokanee population, similar only to the land-locked descendants of anadromous sockeye salmon in New Zealand. After evaluating and rejecting a series of competing explanations for the unusually large eggs, we infer that the population was mostly likely of anadromous origin, retaining the ancestral tendency to produce large eggs, despite the sacrifice in fecundity that is necessitated by the limited female energy resources. This study revealed the utility of life history traits for studying the ancestral origins of a population for which molecular genetic tools were not informative. Worldwide, many populations have been transplanted or exposed to new conditions, affording similar opportunities to investigate phenotypic plasticity and evolutionary adaptations.

Use of Stable Isotopes and Otolith Micro-Chemistry to Evaluate Migration in Male Chinook Salmon, Oncorhynchus tshawytscha, from an Alaskan River

Abstract In salmonid fishes, males display much more variation in age and size at maturity than females, including a greater proportion of non-anadromous individuals, and those spending fewer years at sea than females. The life history of Chinook salmon is especially variable among Pacific salmon species, including non-anadromous (precocious parr) and early maturing anadromous males (jacks) but these have been studied primarily in populations towards the central and southern part of their range. In this study we investigated reports of small and putatively non-anadromous male Chinook salmon in Lake Creek, Alaska, using otolith microchemistry and stable isotopes. Small males (ca. 300–350 mm fork length) displayed otolith Sr:Ca ratios and &dgr;15N values consistent with anadromy; indeed, the &dgr;15N values of these “mini-jacks” that had spent a year at sea and larger jacks (ca. 500 mm) were more enriched than those of the larger, older conspecifics. Thus the multiple alternative anadromous male life history patterns reported in southern populations (and often associated with rapid pre-smolt growth in hatcheries) are present in more northerly wild populations of Chinook salmon as well. Moreover, variation in stable isotopes indicated differences in marine distribution related to age (with younger fish closer to the coast), and otolith microchemistry suggested that some of the young males may have moved to low salinity water during their period of marine residence.