There are MANY more conclusive studies that I can cite, but methinks you might get the gist of the matter from these:
Competing tradeoffs between increasing marine mammal predation and fisheries harvest of Chinook salmon
Abstract
Many marine mammal predators, particularly pinnipeds, have increased in abundance in recent decades, generating new challenges for balancing human uses with recovery goals via ecosystem-based management. We used a spatio-temporal bioenergetics model of the Northeast Pacific Ocean to quantify how predation by three species of pinnipeds and killer whales (Orcinus orca) on Chinook salmon (Oncorhynchus tshawytscha) has changed since the 1970s along the west coast of North America, and compare these estimates to salmon fisheries. We find that from 1975 to 2015, biomass of Chinook salmon consumed by pinnipeds and killer whales increased from 6,100 to 15,200 metric tons (from 5 to 31.5 million individual salmon). Though there is variation across the regions in our model, overall, killer whales consume the largest biomass of Chinook salmon, but harbor seals (Phoca vitulina) consume the largest number of individuals. The decrease in adult Chinook salmon harvest from 1975-2015 was 16,400 to 9,600 metric tons.
Thus, Chinook salmon removals (harvest + consumption) increased in the past 40 years despite catch reductions by fisheries, due to consumption by recovering pinnipeds and endangered killer whales. Long-term management strategies for Chinook salmon will need to consider potential conflicts between rebounding predators or endangered predators and prey.
https://pubmed.ncbi.nlm.nih.gov/29158502/
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Wild Chinook salmon productivity is negatively related to seal density and not related to hatchery releases in the Pacific Northwest
Abstract
Predation risk and competition among conspecifics significantly affect survival of juvenile salmon, but are rarely incorporated into models that predict recruitment in salmon populations. Using densities of harbour seals (Phoca vitulina) and numbers of hatchery-released Chinook salmon (Oncorhynchus tshawytscha) smolts as covariates in spatially structured Bayesian hierarchical stock–recruitment models, we found significant negative correlations between seal densities and productivity of Chinook salmon for 14 of 20 wild Chinook populations in the Pacific Northwest. Changes in numbers of seals since the 1970s were associated with a 74% decrease (95% CI: −85%, −64%) in maximum sustainable yield in Chinook stocks. In contrast, hatchery releases were significantly correlated with Chinook productivity in only one of 20 populations. Our findings are consistent with recent research on predator diets and bioenergetics modeling that suggest there is a relationship between harbour seal predation on juvenile Chinook and reduced marine survival in parts of the eastern Pacific. Forecasting, assessment, and recovery efforts for salmon populations of high conservation concern should thus consider including biotic factors, particularly predator–prey interactions.
https://cdnsciencepub.com/doi/abs/10...jfas-2017-0481
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Salmon-Seal Interactions - Impact of Seals on Salmon
During the Salish Sea Marine Survival Project, four key hypotheses were assessed:
An increase in the abundance of predators has led to higher juvenile salmon/steelhead mortality.
Certain predators specialize in consuming juvenile Coho, Chinook and steelhead, and the number of predators that specialize has increased.
Predation rates have increased due to large pulses juvenile salmon/steelhead entering the marine environment.
The probability of being detected/targeted by predators may decrease with an increase abundance of alternative prey e.g herring, hake, anchovy etc.
https://www.marinescience.ca/salmon-...ons/log-booms/
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Harbor seal diet in northern Puget Sound: implications for the recovery of depressed fish stocks
ABSTRACT
Recovery of severely declining resource stocks often leads to enforced quotas or reduced human access to those resources. Predators, however, do not recognize such restrictions and may be attracted to areas of increased prey abundances where human extraction is being limited. Such targeting by predators may reduce or retard the potential recovery of depressed stocks. In the San Juan Islands, northern Puget Sound, USA, marine reserves were implemented to recover depressed fish populations. We examine the role of harbor seals Phoca vitulina in the San Juan Islands food web. We describe the temporal and spatial variability in their diet, emphasizing species for which reserves were established (rockfish Sebastes spp.) and other important depressed stocks, including salmon Oncorhynchus spp. and Pacific herring Clupea pallasii. During winter and spring, seals primarily consumed Pacific herring, Pacific sand lance Ammodytes hexapterus, northern anchovy Engraulis mordax, and walleye pollock Theragra chalcogramma. During summer/fall, adult salmonids composed >50% of the diet and were particularly important in odd-numbered calendar years, when pink salmon O. gorbuscha spawn. Rockfish were not a primary prey species at any time of the year, suggesting that the abundance of alternative prey species may reduce predation pressure and provide a critical buffer to rockfish predation. The importance of considering increased visitation by marine predators to areas where potential prey are enhanced through restrictions on human extractions should be considered when modeling the efficacy of quotas and reduced access areas, such as marine reserves.
https://www.int-res.com/abstracts/meps/v464/p257-271
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Has Steller Sea Lion Predation Impacted Survival of Fraser River Sockeye Salmon?
Abstract
The commercially, recreationally, and culturally important Fraser River Sockeye Salmon Oncorhynchus nerka has experienced a productivity decline over the past 3 decades, which—along with greater temporal variation in annual abundance (i.e., cyclic dominance)—may at least partly be due to Steller sea lion Eumetopias jubatus (SSL) predation on returning adult salmon. This assumes that SSLs residing around northern Vancouver Island (British Columbia, Canada) target Sockeye Salmon for just a few weeks during the peak of their run. It is a reasonable enough assumption to warrant immediate priority for field research on SSL behavior and diets during the migration period. We evaluated the plausibility of the assumption with a variety of approaches ranging from simple estimates of maximum SSL consumption to partitioning of observed marine mortality rates and analysis of SSL foraging behavior to show that SSLs could have caused the decline in productivity and abundance of Fraser River Sockeye Salmon.
https://afspubs.onlinelibrary.wiley....1002/fsh.10488
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Competing tradeoffs between increasing marine mammal predation and fisheries harvest of Chinook salmon
Many marine mammal predators, particularly pinnipeds, have increased in abundance in recent decades, generating new challenges for balancing human uses with recovery goals via ecosystem-based management. We used a spatio-temporal bioenergetics model of the Northeast Pacific Ocean to quantify how predation by three species of pinnipeds and killer whales (Orcinus orca) on Chinook salmon (Oncorhynchus tshawytscha) has changed since the 1970s along the west coast of North America, and compare these estimates to salmon fisheries. We find that from 1975 to 2015, biomass of Chinook salmon consumed by pinnipeds and killer whales increased from 6,100 to 15,200 metric tons (from 5 to 31.5 million individual salmon). Though there is variation across the regions in our model, overall, killer whales consume the largest biomass of Chinook salmon, but harbor seals (Phoca vitulina) consume the largest number of individuals. The decrease in adult Chinook salmon harvest from 1975–2015 was 16,400 to 9,600 metric tons. Thus, Chinook salmon removals (harvest + consumption) increased in the past 40 years despite catch reductions by fisheries, due to consumption by recovering pinnipeds and endangered killer whales. Long-term management strategies for Chinook salmon will need to consider potential conflicts between rebounding predators or endangered predators and prey.
https://www.nature.com/articles/s41598-017-14984-8
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Estimates of Chinook salmon consumption in Washington State inland waters by four marine mammal predators from 1970 – 2015
Abstract
Conflicts can arise when the recovery of one protected species limits the recovery of another through competition or predation. The recovery of many marine mammal populations on the west coast of the United States (U.S.) has been viewed as a success; however, within Puget Sound in Washington State (U.S.) the increased abundance of three protected pinniped species may be adversely affecting the recovery of threatened Chinook salmon (Oncoryhnchus tshawytchsa) and endangered killer whales (Orcinus orca) within the region. Between 1970 and 2015, we estimate the annual biomass of Chinook salmon consumed by pinnipeds has increased from 68 to 625 metric tons. Converting juvenile Chinook salmon into adult equivalents, we found that by 2015 pinnipeds consumed double that of resident killer whales, and six times greater than the combined commercial and recreational catches. We demonstrate the importance of interspecific interactions when evaluating species recovery. As more protected species respond positively to recovery efforts, managers should attempt to evaluate trade-offs between these recovery efforts and the unintended ecosystem consequences of predation and competition on other protected species.
https://tspace.library.utoronto.ca/b...-2016-0203.pdf
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Harbour seals target juvenile salmon of conservation concern
Abstract
Knowing the species and life stages of prey that predators consume is important for understanding the impacts that predation may have on prey populations, but traditional methods for determining diets often cannot provide sufficient detail. We combined data from two methods of scat analysis (DNA metabarcoding and morphological prey ID) to quantify the species and life stages of salmon (Oncorhynchus spp.) consumed by harbour seals (Phoca vitulina) in the Strait of Georgia, Canada, where juvenile Chinook (Oncorhynchus tshawytscha) and coho (Oncorhynchus kisutch) salmon survival is poor. Harbour seals primarily consumed adult salmon of lesser conservation concern in the fall (August–November): chum (Oncorhynchus keta: 18.4%), pink (Oncorhynchus gorbuscha: 12.6%), sockeye (Oncorhynchus nerka: 7.4%), Chinook (7.1%), and coho (1.8%). However, the opposite species trend occurred during the spring when seals preferred juvenile salmon of greater conservation concern (April–July): coho (2.9%), Chinook (2.9%), sockeye (2.5%), pink (1.4%), and chum (0.8%) — percentages that can equate to many individuals consumed. Our data suggest that harbour seals select juveniles of salmon species that out-migrate at ages >1 year and provide evidence of a potential causal relationship between harbour seal predation and juvenile salmon survival trends.
https://mmru.ubc.ca/wp-content/pdfs/...et_al_2017.pdf
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EVALUATION OF PINNIPED PREDATION ON ADULT SALMONIDS AND OTHER FISH IN THE BONNEVILLE DAM TAILRACE, 2021
EXECUTIVE SUMMARY
California sea lions (CSL; Zalophus californianus) and Steller sea lions (SSL; Eumetopias jubatus) aggregate at the base of Bonneville Dam where they feed on Pacific salmon, steelhead (Oncorhynchus spp.), and White Sturgeon (Acipenser transmontanus), some of which are listed as threatened or endangered under the Endangered Species Act (ESA). The Federal Columbia River Power System 2020 Biological Opinion continued the requirement for the U.S. Army Corps of Engineers to monitor the seasonal presence, abundance, and predation activities of sea lions at Bonneville Dam. Here we report these data for the 2020-2021 season. Per requirements of National Oceanic Atmospheric Administration, we monitor and report data for the fall and winter period of 2020 and the traditional spring period of 2021. Abundance was monitored daily, while predation sampling started when there were ≥ 20 pinnipeds in the tailrace of Bonneville Dam.
The first pinnipeds returned to Bonneville in mid-July 2020. Between 3 August – 31 December 2020 we recorded an average of 29.6 ± S.D. 13.3 SSLs each day. CSLs were not observed during this period. Fish predation monitoring began on 16 August 2020 when abundance was consistently ≥ 20 pinnipeds. Predation sampling during the fall period was variable and occurred in Powerhouse 1 and Powerhouse 2 at differing times from 16 August to 8 December 2020. One week of sampling in September was completely missed due to wildfire smoke. Fall predation sampling ended due to increasing cases of COVID-19. Note: total predation at Bonneville Dam during this time is likely higher than these estimates due to predation in other tailraces. Predation estimates for this period are seen in the table below.
Monitoring continued during the traditional spring season (January – May) despite the COVID-19 pandemic. Predation sampling started on 4 April 2021, when we were close to the 20-animal trigger and concluded when pinnipeds were nearly absent from the dam on 18 May. Abundance was monitored daily, an average of 10.9 ±
S.D. 16.7 SSLs and 1.5 ± S.D. 2.3 CSLs were observed each day during the spring period.
https://pweb.crohms.org/tmt/document...l%20Report.pdf
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Declining patterns of Pacific Northwest steelhead trout (Oncorhynchus mykiss) adult abundance and smolt survival in the ocean
Recent research in inland seas, including Puget Sound and Georgia Basin, suggests that pinnipeds such as harbor seals (Phoca vitulina) contribute to the mortality of migrating smolts, including steelhead (Berejikian et al. 2016) and other salmon (Thomas 2015). Puget Sound steelhead experience high levels of mortality in the Sound during their migration to the ocean despite relatively short migration distances, mortality rates that could not be sustained and have any adults return to spawn (Moore et al. 2010b, 2015).
https://cdnsciencepub.com/doi/full/1...6#.W7D_yNhKhsM
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Salish Sea Marine Survival Project: Predation
This team assessed the impact of seals on salmonids in Cowichan Bay by counting the number of predators in the Cowichan Bay, quantifying predation events from visual observations, and determining diets from morphological and genetic analysis of fecal samples. Data collected for 2012-2014 provides the following estimates of the percentage of chinook and coho juveniles lost to seal predation in the Strait of Georgia:
-Chinook: Mean = 40% (95% CI: 32-45%)
-Coho: Mean = 47% (95% CI: 44-52%)
https://marinesurvivalproject.com/re...ist/predation/
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Decline of Interior Fraser Steelhead
Robert Bison Biologist Province of BC
Hypothetical factors considered to have good a priori reasons
for expecting a potential affect on productivity:
• Predation by pinnipeds on returning adults
• Predation by harbour seals on out-migrating smolts
• Competition with salmon in the ocean
• Ocean conditions
https://ufawu-unifor.org/wp-content/...or-Murdoch.pdf
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Role of pinniped predation in recent B.C. fish stock collapses - Dr. Carl Walters (UBC)
https://www.youtube.com/watch?v=4ZF_0npi8M0
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Seals/Sea Lions and Fish Stock Collapses - Dr. Carl Walters (UBC)
https://www.youtube.com/watch?v=01Rdm0m8xic
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Evaluating a proposal by the Pacific Balance Pinnipeds Society for seal harvesting - UBC
https://www.youtube.com/watch?v=7FBrBK_FRBk
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Webinar: Impacts of Pinniped Predation on BC Salmon - Dr. Carl Walters
On Thursday, October 28, 2021, Dr. Carl J. Walters, Professor Emeritus at UBC; from the Institute for the Oceans and Fisheries, UBC, presented on the Impacts of Pinniped Predation on BC Salmon. In his presentation, he discussed the following topics:
· Seals and sea lions are far more abundant today than they have been for the last several millennia, when First Nations harvesting kept them down
· They are consuming more fish than all the commercial fisheries (and aquaculture) combined
· In the Georgia Strait, seals have had particularly severe impacts on early marine survival rates of chinook and coho salmon, reducing abundances of larger fish by 80%
· We are not certain that seal reductions in the Georgia Strait would mean more fish available, because other stress factors like disease might be making the juvenile salmon more vunerable and could kill them even if seals were not
· It would be a major management experiment to reduce seal numbers to see if survival rates do improve, but the benefits of this experiment far outweigh possible costs
https://bcwf.bc.ca/impacts-of-pinnip...-on-bc-salmon/
Pacific balance pinniped society important notice
Linear Mode
