ABSTRACT Daily ring counts in young-of-the-year fishes are important for estimating important vital rates, such as growth, mortality, and timing of hatch. To accurately estimate some of these rates, the timing of the first daily ring must be estimated accurately. Variation in the timing of the first daily ring can be attributed to many factors, including biology of the species and experience of laboratory personnel. The amount of variation and the degree of differences, however, have not been quantified, hindering the utility of daily ring information to provide accurate estimates of spawning and hatching times. We conducted a review of studies for freshwater fishes in the continental United States to quantify variation in daily ring validation studies as it relates to timing of the first ring. We found 40 studies representing 12 orders, 15 families, and 35 species. Most studies investigated rings in the sagittae, although the lapilli and asterisci were also used for a few species. Variation in the timing of the first ring formation was evident, but not consistent among otolith types or groups of fishes. The first daily ring in sagittae varied from 31 d before hatch to 150 d after hatch. First daily ring formation in lapilli was consistent within families but formed before hatch in some families of fish and after hatch in other families. The first daily ring in asterisci were near universally formed after hatch, with the exception of one species of sturgeon (family Acipenseridae). Only three of the nine species where replicate studies existed were found to exhibit consistent first ring formation timing. Such findings suggest that differences among laboratories and personnel may play a larger role than differences among species or populations when inconsistent first ring formation timing results occur. For most species, error surrounding differences in timing formation is about 1 week, except for Salmoniformes, where error was up to a 150-d difference. Incorporating species biology along with uncertainty in temporal estimates based on otolith chronology would aid interpretation of results in field situations.

ABSTRACT Every spring, many postspawn steelhead kelts (hereafter, “kelts”) migrate downstream through the Columbia River basin, but few return to spawn again. Here, we synthesize research on the physiology of the postspawn period conducted for a project implementing reconditioning of female kelts as a restoration method. By the kelt stage, lipid stores were depleted, leaving muscle protein as the main energy source. During the ∼10-week recovery period after spawning, heavy mortality occurred, and growth rates were minimal or negative. Survival through this period depended on the ability to maintain osmotic homeostasis and access remaining lipid stores. Plasma levels of estradiol and vitellogenin diverged between consecutive and skip spawning kelts beginning at 20 weeks postspawn, enabling screening of fish for reproductive status prior to release. Consecutive spawners consistently grew faster than skip spawners during the 10 weeks after spawning, suggesting that a positive energy balance during this period promotes ovarian recrudescence. Treatments to control parasites and pathogens were required to maximize survival. Spawn timing was similar between first time spawners and reconditioned kelts. Egg production increased at the second spawning. We found no support for a hypothesized trade-off between reproductive investment in initial vs. future reproduction in reconditioned kelts.

Abstract Translocation of adult salmon is an expanding management tactic, especially in rivers with impassable dams. Understanding the productivity of translocated adults compared to donor populations and contribution to subsequent adult returns (i.e., via cohort replacement rate [CRR]) is critical to evaluating the efficacy of translocation programs. However, empirical CRR estimates are difficult to generate due to life history (LH) complexity, including spatiotemporal diversity created by translocation protocols and diverse juvenile rearing habitats. We built a CRR model for spring-run Chinook Salmon Oncorhynchus tshawytscha in Oregon’s North Santiam River, where two large dams lack fish passage facilities. The model estimates relative replacement metrics for two adult groups: below-dam spawners and above-dam spawners translocated into historical upstream habitat. It also tracks the relative contributions of 13 distinct juvenile phenotypes (i.e., “LH pathways”): 3 produced by the below-dams group and 10 from the above-dams group that includes reservoir-rearing pathways. The fractional CRR of LH pathways varied by >60-fold, with higher CRR for less common spring yearling smolt LHs. Simulated management scenarios indicated low likelihood of replacement of the original adult cohort. The approach provides a framework for evaluating trade-offs and feedbacks among intraspecific diversity, management actions, and LH pathway composition in spatially structured migratory populations.

ABSTRACT Across western North America, juvenile salmon and other migratory fish are killed in irrigation systems, which has population-level impacts for species at risk. How to reduce or prevent these deaths is an important policy issue. Federal policy in the United States requires that fish be screened from water withdrawn from rivers containing salmon and prescribes screen designs in irrigation canals to return fish to the river. A recently published study demonstrated that juvenile salmon survival was 10–37% lower for fish that entered a diversion channel and were screened and returned to the river compared to fish that remained in the river and were passed over a diversion dam. An independent study demonstrated that hydraulic patterns at in-river screening structures can allow most fish to bypass the water withdrawal and remain in the river, whereas screens in irrigation canals stressfully concentrate the fish before sending them back to the river, where they are especially vulnerable to predation. Present policies favoring in-canal screening warrant re-examination to include in-river screening methods that can increase fish survival by keeping them in the river.