More on the Factors that Limit the Abundance of Pacific Salmon (Oncorhynchus spp., Family Salmonidae) during the Ocean Phase of Their Life History

Шунтов, В. П.; Темных, О. С.; Naydenko, S. V.

doi:10.1134/s106307401907006x

“…Declines in the growth of all salmon species across most of their range are the most commonly observed effect of density dependence, including hatchery production (Bigler et al, 1996; Oke et al, 2020). Though not included in our analyses because it did not explicitly evaluate hatchery fish and in contrast to most results, Shuntov et al (2019, 2020) argued that competition for prey at sea is minimal because prey biomass is exceptional and because salmon consume a small fraction of the available prey. However, this assessment cannot explain the density‐dependent biennial patterns observed in Pacific salmon metrics (growth, abundance, productivity, maturation) in response to the biennial abundances of highly abundant pink salmon (Ruggerone et al, in press; Ruggerone & Connors, 2015; Ruggerone & Nielsen, 2004), of which many are hatchery fish (Ruggerone & Irvine, 2018).…”

Section: Resultsmentioning

confidence: 99%

“…Declines in the growth of all salmon species across most of their range are the most commonly observed effect of density dependence, including hatchery production (Bigler et al, 1996;Oke et al, 2020). Though not included in our analyses because it did not explicitly evaluate hatchery fish and in contrast to most results, Shuntov et al (2019Shuntov et al ( , 2020 argued that competition for prey at sea is minimal because prey biomass is exceptional and because salmon consume a small fraction of the available prey.…”

Section: Hatchery Effects In Oceanmentioning

confidence: 99%

A global synthesis of peer‐reviewed research on the effects of hatchery salmonids on wild salmonids

McMillan

¹

,

Morrison²,

Chambers

³

et al. 2023

Fisheries Management Eco

22

2

0

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Hatcheries have long produced salmonids for fisheries and mitigation, though their widespread use is increasingly controversial because of potential impacts to wild salmonids. We conducted a global literature search of peer‐reviewed publications (1970–2021) evaluating how hatchery salmonids affected wild salmonids, developed a publicly available database, and synthesized results. Two hundred six publications met our search criteria, with 83% reporting adverse/minimally adverse effects on wild salmonids. Adverse genetic effects on diversity were most common, followed by effects on productivity and abundance via ecological and genetic processes. Few publications (3%) reported beneficial hatchery effects on wild salmonids, nearly all from intensive recovery programs used to bolster highly depleted wild populations. Our review suggests hatcheries commonly have adverse impacts on wild salmonids in freshwater and marine environments. Future research on less studied effects—such as epigenetics—could improve knowledge and management of the full extent of hatchery impacts.

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“…Besides competition for shared prey, alternative explanations for the negative link between pink salmon abundance and sockeye salmon size include more complex effects via the food web that manifest as changes in growth opportunity for sockeye salmon or spatial–temporal avoidance of competitor species that restricts access to resources, all of which are based upon direct or indirect ecological interactions between the two species. However, some studies have indicated that food availability in the ocean may not be a limiting factor and that interspecific competition between salmon species may not be strong [ 46 ]. While conclusive experimental evidence for a phenomenon that plays out the scale of the North Pacific Ocean is not possible to obtain, (i) similar relationships have been reported between sockeye salmon, pink salmon and SST in other regions [ 47 , 48 ], (ii) we were unable to identify convincing alternative mechanisms to explain these negative relationships between body size and salmon abundances that do not involve direct or indirect ecological interactions within and between the two species, and (iii) the correlations between salmon abundances and sockeye salmon body size are strong [ 49 ].…”

Section: Discussionmentioning

confidence: 99%

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

Ohlberger

¹

,

Cline

²

,

Schindler

³

et al. 2023

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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.

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“…Most salmon research is focused on freshwater and coastal environments, despite most salmon stocks spending the majority of their lives in the open ocean of the North Pacific where they gain the majority of their body mass feeding on marine resources (Beamish, 2018; Shuntov & Temnykh, 2011; Startsev & Rassadnikov, 1997). Inside this “black box,” Pacific salmon face a myriad of poorly understood challenges to their survival, from finding prey to avoiding competitors, predators, and disease, resulting in large and sometimes unexpected temporal shifts in marine survival (Holtby et al, 1990; Kendall et al, 2017; Radchenko, 2012; Shuntov et al, 2019).…”

Section: Introductionmentioning

confidence: 99%

“…Most salmon research is focused on freshwater and coastal environments, despite most salmon stocks spending the majority of their lives in the open ocean of the North Pacific where they gain the majority of their body mass feeding on marine resources (Beamish, 2018; Shuntov & Temnykh, 2011; Startsev & Rassadnikov, 1997). Inside this “black box,” Pacific salmon face a myriad of poorly understood challenges to their survival, from finding prey to avoiding competitors, predators, and disease, resulting in large and sometimes unexpected temporal shifts in marine survival (Holtby et al, 1990; Kendall et al, 2017; Radchenko, 2012; Shuntov et al, 2019). The winter months in particular, when limited prey availability might critically impact survival of first ocean‐winter juvenile and subadult salmon, are the least understood, despite strong potential for impact on stock performance (Beamish & Mahnken, 2001; Ishida et al, 2000; Nagasawa, 2000; Naydenko et al, 2016; Shuntov et al, 2017).…”

Section: Introductionmentioning

confidence: 99%