Franz J. Mueter

Relationships between coastal ocean conditions and survival rates of northeast Pacific salmon at multiple lags

Abstract We tested the hypothesis that survival rates from spawners to recruits in Pacific salmon Oncorhynchus spp. are primarily related to coastal ocean conditions during migration to the sea and soon after. We correlated measures of survival rate in units of log e (recruits/spawner) for 110 stocks of pink salmon O. gorbuscha, chum salmon O. keta, and sockeye salmon O. nerka with regional-scale indices of coastal sea surface temperature, sea surface salinity, and upwelling as well as with a large-scale index of ocean climate. We examined correlations by month and at multiple lags spanning the periods of spawning, freshwater residence, and early ocean residence of salmon. Survival rates of all three salmon species were related to ocean temperatures just prior to, during, and after out-migration, which are indicative of the early marine conditions experienced by juvenile salmon. This is consistent with the hypothesis that the early marine period is critical to the survival of juvenile salmon. However, sur...

Spatial Match-Mismatch between Juvenile Fish and Prey Provides a Mechanism for Recruitment Variability across Contrasting Climate Conditions in the Eastern Bering Sea

Understanding mechanisms behind variability in early life survival of marine fishes through modeling efforts can improve predictive capabilities for recruitment success under changing climate conditions. Walleye pollock (Theragra chalcogramma) support the largest single-species commercial fishery in the United States and represent an ecologically important component of the Bering Sea ecosystem. Variability in walleye pollock growth and survival is structured in part by climate-driven bottom-up control of zooplankton composition. We used two modeling approaches, informed by observations, to understand the roles of prey quality, prey composition, and water temperature on juvenile walleye pollock growth: (1) a bioenergetics model that included local predator and prey energy densities, and (2) an individual-based model that included a mechanistic feeding component dependent on larval development and behavior, local prey densities and size, and physical oceanographic conditions. Prey composition in late-summer shifted from predominantly smaller copepod species in the warmer 2005 season to larger species in the cooler 2010 season, reflecting differences in zooplankton composition between years. In 2010, the main prey of juvenile walleye pollock were more abundant, had greater biomass, and higher mean energy density, resulting in better growth conditions. Moreover, spatial patterns in prey composition and water temperature lead to areas of enhanced growth, or growth ‘hot spots’, for juvenile walleye pollock and survival may be enhanced when fish overlap with these areas. This study provides evidence that a spatial mismatch between juvenile walleye pollock and growth ‘hot spots’ in 2005 contributed to poor recruitment while a higher degree of overlap in 2010 resulted in improved recruitment. Our results indicate that climate-driven changes in prey quality and composition can impact growth of juvenile walleye pollock, potentially severely affecting recruitment variability.

Reassessing regime shifts in the North Pacific: incremental climate change and commercial fishing are necessary for explaining decadal‐scale biological variability

In areas of the North Pacific that are largely free of overfishing, climate regime shifts - abrupt changes in modes of low-frequency climate variability - are seen as the dominant drivers of decadal-scale ecological variability. We assessed the ability of leading modes of climate variability [Pacific Decadal Oscillation (PDO), North Pacific Gyre Oscillation (NPGO), Arctic Oscillation (AO), Pacific-North American Pattern (PNA), North Pacific Index (NPI), El Niño-Southern Oscillation (ENSO)] to explain decadal-scale (1965-2008) patterns of climatic and biological variability across two North Pacific ecosystems (Gulf of Alaska and Bering Sea). Our response variables were the first principle component (PC1) of four regional climate parameters [sea surface temperature (SST), sea level pressure (SLP), freshwater input, ice cover], and PCs 1-2 of 36 biological time series [production or abundance for populations of salmon (Oncorhynchus spp.), groundfish, herring (Clupea pallasii), shrimp, and jellyfish]. We found that the climate modes alone could not explain ecological variability in the study region. Both linear models (for climate PC1) and generalized additive models (for biology PC1-2) invoking only the climate modes produced residuals with significant temporal trends, indicating that the models failed to capture coherent patterns of ecological variability. However, when the residual climate trend and a time series of commercial fishery catches were used as additional candidate variables, resulting models of biology PC1-2 satisfied assumptions of independent residuals and out-performed models constructed from the climate modes alone in terms of predictive power. As measured by effect size and Akaike weights, the residual climate trend was the most important variable for explaining biology PC1 variability, and commercial catch the most important variable for biology PC2. Patterns of climate sensitivity and exploitation history for taxa strongly associated with biology PC1-2 suggest plausible mechanistic explanations for these modeling results. Our findings suggest that, even in the absence of overfishing and in areas strongly influenced by internal climate variability, climate regime shift effects can only be understood in the context of other ecosystem perturbations.

Killer whale depredation and associated costs to Alaskan sablefish, Pacific halibut and Greenland turbot longliners.

Killer whale (Orcinus orca) depredation (whales stealing or damaging fish caught on fishing gear) adversely impacts demersal longline fisheries for sablefish (Anoplopoma fimbria), Pacific halibut (Hippoglossus stenolepis) and Greenland turbot (Reinhardtius hippoglossoides) in the Bering Sea, Aleutian Islands and Western Gulf of Alaska. These interactions increase direct costs and opportunity costs associated with catching fish and reduce the profitability of longline fishing in western Alaska. This study synthesizes National Marine Fisheries Service observer data, National Marine Fisheries Service sablefish longline survey and fishermen-collected depredation data to: 1) estimate the frequency of killer whale depredation on longline fisheries in Alaska; 2) estimate depredation-related catch per unit effort reductions; and 3) assess direct costs and opportunity costs incurred by longliners in western Alaska as a result of killer whale interactions. The percentage of commercial fishery sets affected by killer whales was highest in the Bering Sea fisheries for: sablefish (21.4%), Greenland turbot (9.9%), and Pacific halibut (6.9%). Average catch per unit effort reductions on depredated sets ranged from 35.1–69.3% for the observed longline fleet in all three management areas from 1998–2012 (p<0.001). To compensate for depredation, fishermen set additional gear to catch the same amount of fish, and this increased fuel costs by an additional 82% per depredated set (average

The ecology of gadid fishes in the circumpolar Arctic with a special emphasis on the polar cod (Boreogadus saida)

433 additional fuel per depredated set). In a separate analysis with six longline vessels in 2011and 2012, killer whale depredation avoidance measures resulted in an average additional cost of

Vertical Movements of Juvenile Sablefish in Coastal Southeast Alaska

494 per depredated vessel-day for fuel and crew food. Opportunity costs of time lost by fishermen averaged

Distinction of saffron cod (Eleginus gracilis) from several other gadid species by using microsatellite markers

522 per additional vessel-day on the grounds. This assessment of killer whale depredation costs represents the most extensive economic evaluation of this issue in Alaska to date and will help longline fishermen and managers consider the costs and benefits of depredation avoidance and alternative policy solutions.

Climate impacts on eastern Bering Sea foodwebs: a synthesis of new data and an assessment of the Oscillating Control Hypothesis

In high-Arctic marine ecosystems, the gadids Boreogadus saida (Lepechin, 1774) and Arctogadus glacialis, hereafter referred to as polar cod and Arctic cod, as respective European common names, are foundation species that make up important links between lower and higher trophic levels of the food web (Bradstreet et al. 1986; Christiansen et al. 2012; Hop and Gjosaeter 2013). Other Arctic gadids considered here are the saffron cod [Eleginus gracilis (Tilesius, 1810)], which is endemic to the Pacific Arctic but extends into boreal waters as far south as Japan (Mecklenburg et al. 2002), and its Atlantic sister species, the navaga [Eleginus navaga (Walbaum, 1792)], which is limited to European Arctic and subarctic waters of the Barents, White and Kara seas (Cohen et al. 1990). There is a strong imbalance in the scientific literature regarding these species—a search for the words ‘‘Boreogadus’’ in Google Scholar (April 2016) resulted in 4010 hits, compared to only 522 hits for ‘‘Arctogadus,’’ reflecting a greater emphasis on the more abundant polar cod. The genus ‘‘Eleginus’’ resulted in 1480 hits (E. gracilis: 1070; E. navaga: 408), reflecting the importance of saffron cod as a subsistence resource in parts of the North Pacific. While research on B. saida has a long history, particularly in Russia (Andriyashev 1954; Rass 1968; Ponomarenko 2000; Boitsov et al. 2013), interest in Arctic marine ecosystems has grown in recent years as summer sea ice cover has diminished and water temperatures have increased (Wang and Overland 2009). Arctic gadids, in particular polar cod, have been a focal point for studies of climate impacts (Fortier et al. 2006; Benoit et al. 2008; Bouchard and Fortier 2008; Renaud et al. 2012) and pollution impacts (Christiansen and George 1995; Nahrgang et al. 2010; Dussauze et al. 2014; Geraudie et al. 2014; Andersen et al. 2015). Yet, our current understanding of these important Arctic species is surprisingly fragmented and inconclusive, leaving major gaps in knowledge that prevent a holistic understanding of the interaction between these species and their environment. This special issue contains a collection of manuscripts from an international workshop on the ecology of circumpolar Arctic gadids. The workshop was convened during the Ecosystem Studies of the Subarctic and Arctic Seas (ESSAS) Annual Science Meeting, 8–9 April 2014, in Copenhagen, Denmark. Four of the papers in this collection take a comparative approach across species: Bouchard et al. (2016) compare the early life history of polar cod and Arctic cod, Laurel et al. (2016) contrast the growth rates of four gadids in the North Pacific under different temperatures, Kunz et al. (2016) compare growth of polar cod and Atlantic cod (Gadus morhua) under different temperatures and CO2 levels, and McNicholl et al. (2015) compare diets of two potential competitors, polar cod and capelin (Mallotus villosus). A single paper focuses on saffron cod, specifically their trophic dynamics as inferred from several trophic biomarkers (Copeman et al. 2016). The remaining This article belongs to the special issue on the ‘‘Ecology of Arctic Gadids,’’ coordinated by Franz Mueter, Jasmine Nahrgang, John Nelson and Jorgen Berge.

Opposite effects of ocean temperature on survival rates of 120 stocks of Pacific salmon (Oncorhynchus spp.) in northern and southern areas

AbstractDiel vertical migration is commonly associated with pelagic fish species, but demersal fishes may also undertake vertical movements while managing foraging tradeoffs during their vulnerable juvenile stage. We examined fine-scale vertical movements of age-0 juvenile Sablefish Anoplopoma fimbria to better understand behavioral patterns that may affect their survival in nearshore habitats. Thirteen juvenile Sablefish (mean FL = 241.9 mm) were implanted with acoustic transmitters and were monitored by use of two acoustic receivers from October 5 to November 14, 2003, within St. John Baptist Bay, Baranof Island, Alaska. The six fish that remained within range of the receivers spent the majority of their time near the bottom but made periodic vertical excursions. Generalized linear mixed-effects models were used to determine the relationships between excursion frequency and the tidal stage and diel period. For all Sablefish, variation in excursion frequency was related to date and diel period, with the ...

Climate change in the southeastern Bering Sea: impacts on pollock stocks and implications for the oscillating control hypothesis

The views and opinions expressed or implied in this article are those of the author (or authors) and do not necessarily reflect the position of the National Marine Fisheries Service, NOAA. Abstract—Nine microsatellite loci isolated in saffron cod (Eleginus gracilis) have potential applications for population genetics. Polymerase chain reaction products of samples of E. gracilis from northwestern Alaska amplified reliably, produced only one or two microsatellite bands, and had no apparent homozygote excess. A collection of E. gracilis sampled in the Gulf of Alaska (GOA) near Kodiak Island did not amplify reliably at one locus, and allele frequency profiles clustered distinctly (with principal component analysis [PCA]) from the northwestern Alaska collection. Northwestern Alaska and GOA E. gracilis collections were genetically different (on the basis of a standardized genetic differentiation measure [G′ST]=0.313, chord distance [Dchord]=0.078, P<0.0001) and differed in expected average heterozygosities at shared loci (0.859 and 0.689, respectively). We tested the microsatellite primers on other gadid species endemic to the northern Pacific Ocean, Bering Sea, and Arctic Ocean for cross-species amplification. Not all loci amplified reliably in navaga (E. nawaga), Pacific tomcod (Microgadus proximus), Arctic cod (Boreogadus saida), Pacific cod (Gadus macrocephalus), or walleye pollock (G. chalcogrammus). Reliable loci varied in microsatellite size profiles and produced distinct PCA clusters and accurate genotype assignments that allowed accurate species identification. The identifications support previous morphological and genetically determined systematic classifications and distinguished the geographically separated collections of E. gracilis. The saffron cod (Eleginus gracilis) is a gadid fish distributed from the northern Gulf of Alaska (GOA), around the Pacific Rim into the Sea of Okhotsk, and into the Arctic Ocean abutting the North Pacific Ocean (Cohen et al., 1990; Mecklenburg et al., 2016). Mature fish, which generally exceed 20 cm in fork length (FL) and may grow to more than 50 cm FL, are eaten by indigenous Alaskans and in Asia and have potential for commercial harvest in North America (Cohen et al., 1990; NPFMC1; Love et al.2).