Pacific Salmon in Puget Sound: abundance, survival and body size (1970-2015)

Pacific salmon and trout (Oncorhynchus spp.) inhabiting Puget Sound marine waters have experienced both recent and long-term variability in abundance while supporting robust commercial, tribal, and sport fisheries. In recent years, numerous species-specific status reports have been completed, though formal comparisons among all five species of salmon and steelhead trout are not available. We compared spatial and temporal patterns of abundance, survival, productivity, and body size between hatchery-origin and naturally-produced adult salmon and steelhead trout returning to marine waters of Puget Sound, Washington, USA. Stock-specific total run size (of fish at the entrance to Puget Sound) was calculated for pink (O. gorbuscha), chum (O. keta), coho (O. kisutch), sockeye (O. nerka), and Chinook (O. tshawytscha) salmon for years 1970-2015 by combining estimates of escapement (spawners) with stock-specific estimates of harvest (catch) in Puget Sound marine and fresh waters. In general, trends in abundance varied by species and origin (hatchery vs naturally produced) with increased abundance, survival, and productivity associated with species exhibiting “fry” (vs. “smolt”) life history types. Overall, average weight of salmon and steelhead has decreased significantly since 1970 with the exception of coho salmon. Information presented here will allow fishery managers to evaluate recovery plans and harvest objectives as well as identify trends in abundance, survival, and productivity related to climate and life history expression

Evolution of age and length at maturation of Alaskan salmon under size-selective harvest

-Spatial and temporal trends and variation in life-history traits, including age and length at maturation, can be influenced by environmental and anthropogenic processes, including size-selective exploitation. Spawning adults in many wild Alaskan sockeye salmon populations have become shorter at a given age over the past half-century, but their age composition has not changed. These fish have been exploited by a gillnet fishery since the late 1800s that has tended to remove the larger fish. Using a rare, long-term dataset, we estimated probabilistic maturation reaction norms (PMRNs) for males and females in nine populations in two basins and correlated these changes with fishery size selection and intensity to determine whether such selection contributed to microevolutionary changes in maturation length. PMRN midpoints decreased in six of nine populations for both sexes, consistent with the harvest. These results support the hypothesis that environmental changes in the ocean (likely from competition) combined with adaptive microevolution (decreased PMRNs) have produced the observed life-history patterns. PMRNs did not decrease in all populations, and we documented differences in magnitude and consistency of size selection and exploitation rates among populations. Incorporating evolutionary considerations and tracking further changes in life-history traits can support continued sustainable exploitation and productivity in these and other exploited natural resources

Anadromy and residency in steelhead and rainbow trout (Oncorhynchus mykiss): a review of the processes and patterns

Oncorhynchus mykiss form partially migratory populations with anadromous fish that undergo marine migrations and residents that complete their life cycle in fresh water. Many populations’ anadromous components are threatened or endangered, prompting interest in understanding ecological and evolutionary processes underlying anadromy and residency. In this paper, we synthesize information to better understand genetic and environmental influences on O. mykiss life histories, identify critical knowledge gaps, and suggest next steps. Anadromy and residency appear to reflect interactions among genetics, individual condition, and environmental influences. First, an increasing body of literature suggests that anadromous and resident individuals differ in the expression of genes related to growth, smoltification, and metabolism. Second, the literature supports the conditional strategy theory, where individuals adopt a life history pattern based on their conditional status relative to genetic thresholds along with ultimate effects of size and age at maturation and iteroparity. However, except for a generally positive association between residency and high lipid content plus a large attainable size in fresh water, the effects of body size and growth are inconsistent. Thus, individuals can exhibit plasticity in variable environments. Finally, patterns in anadromy and residency among and within populations suggested a wide range of possible environmental influences at different life stages, from freshwater temperature to marine survival. Although we document a number of interesting correlations, direct tests of mechanisms are scarce and little data exist on the extent of residency and anadromy. Consequently, we identified as many data gaps as conclusions, leaving ample room for future research

A Review of Pink Salmon in the Pacific, Arctic, and Atlantic Oceans

The Northern Hemisphere Pink Salmon Expert Group Meeting was held on October 2–3, 2022 in Vancouver, Canada, immediately preceding the International Year of the Salmon (IYS) Synthesis Symposium. The rapid expansion of pink salmon was the theme for the meeting, and experts came together to discuss the current state of knowledge for pink salmon. Specific topics of focus included the range expansion into the Atlantic and Arctic oceans, trends in distribution and abundance, research and monitoring approaches, potential inter-specific interactions, mitigation efforts, and plans for future collaborations. The outcomes of the meeting were presented at the IYS Synthesis Symposium and are further disseminated through this NPAFC Technical Report. The Executive Summary section of this report provides a brief background, a condensed overview of each topic, and concludes with overarching takeaway messages that are intended to guide future collaborations.publishedVersio

A Review of Pink Salmon in the Pacific, Arctic, and Atlantic Oceans

The Northern Hemisphere Pink Salmon Expert Group Meeting was held on October 2–3, 2022 in Vancouver, Canada, immediately preceding the International Year of the Salmon (IYS) Synthesis Symposium. The rapid expansion of pink salmon was the theme for the meeting, and experts came together to discuss the current state of knowledge for pink salmon. Specific topics of focus included the range expansion into the Atlantic and Arctic oceans, trends in distribution and abundance, research and monitoring approaches, potential inter-specific interactions, mitigation efforts, and plans for future collaborations. The outcomes of the meeting were presented at the IYS Synthesis Symposium and are further disseminated through this NPAFC Technical Report. The Executive Summary section of this report provides a brief background, a condensed overview of each topic, and concludes with overarching takeaway messages that are intended to guide future collaborations.publishedVersio

Fishery Selection on Alaskan Sockeye Salmon: Are We Catching the Big Ones and Is There Potential for Evolutionary Change?

Bristol Bay, Alaska, USA, produces some of the most abundant and biologically diverse sockeye salmon (Oncorhynchus nerka) runs in the world, many of which have been heavily fished by gillnet fisheries for over 100 years. Quantification of fishery selection on age and size at maturation over long time periods is essential to understand evolutionary consequences on stock demographics and sustainable fishery management. We performed these quantifications for multiple fishing districts from 1946-2008 and evaluated how different management strategies affected fishery selection in different areas. Analyses revealed that larger than average fish were caught in most years, selection differed significantly between males and females, and patterns of selectivity differed based on harvest levels and fishing gear used. Proving evolutionary change associated with such selection is difficult, but we were able to correlate long term shifts in length at age with fishery selection across districts. We discuss how to minimize evolutionary changes in age and size at maturity due to fishery selection and conserve our valuable sockeye salmon resources

Puget Sound steelhead marine survival trends: what’s happening to our fish out there?

Steelhead trout numbers are falling dramatically in the Salish Sea and especially in Puget Sound. To better understand the patterns and put them into context, we seek to confirm the declining steelhead abundance and survival trends (both hatchery and wild fish) in Puget Sound and compare these trends with those in neighboring regions. We will first present productivity trends (specifically smolt to adult returns [SAR]) for hatchery and wild steelhead populations. We found that many coastal populations shared a pattern of declining abundance from the mid 1980s through the mid 90s, and that while many of these populations rebounded in the 2000s, Puget Sound SARs continued to decline and have generally remained below those of other regions. Second, we are performing correlative analyses on these SARs with factors potentially affecting survival including wild and hatchery steelhead smolt abundance, individual and population life-history characteristics, environmental data, and buffer prey data. We will evaluate hypotheses about spatial variation in mortality, size-selective mortality, match-mismatch, and life history variation; additional reference regarding whether and where mortality is concentrated; and account for individual or population characteristics that may differentially affect survival

Evolution of age and length at maturation of Alaskan salmon under size-selective harvest

Spatial and temporal trends and variation in life-history traits, including age and length at maturation, can be influenced by environmental and anthropogenic processes, including size-selective exploitation. Spawning adults in many wild Alaskan sockeye salmon populations have become shorter at a given age over the past half-century, but their age composition has not changed. These fish have been exploited by a gillnet fishery since the late 1800s that has tended to remove the larger fish. Using a rare, long-term dataset, we estimated probabilistic maturation reaction norms (PMRNs) for males and females in nine populations in two basins and correlated these changes with fishery size selection and intensity to determine whether such selection contributed to microevolutionary changes in maturation length. PMRN midpoints decreased in six of nine populations for both sexes, consistent with the harvest. These results support the hypothesis that environmental changes in the ocean (likely from competition) combined with adaptive microevolution (decreased PMRNs) have produced the observed life-history patterns. PMRNs did not decrease in all populations, and we documented differences in magnitude and consistency of size selection and exploitation rates among populations. Incorporating evolutionary considerations and tracking further changes in life-history traits can support continued sustainable exploitation and productivity in these and other exploited natural resources