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Redd counts are commonly applied to estimate spawning population size for salmonids and allow for broad spatial and temporal coverage in monitoring efforts. However, the utility of redd counts may be compromised by observation error, particularly with respect to superimposition, where later arriving spawners construct redds overlapping existing redds. Here, we provide a mechanistic evaluation of the effects of superimposition on the error structure and biological significance of redd count data for Yellowstone cutthroat trout (Oncorhynchus clarkii bouvieri) spawning within tributaries to the Snake River, Wyoming. We used a Bayesian framework to parse observation error into distinct components and found low detection of redd clusters (i.e., areas of superimposition) was offset by overestimates of the number of redds per cluster, such that observed counts accurately reflected census redd abundance. However, a saturating relationship between redd counts and spawner abundance indicated that counts is best interpreted as effective reproductive effort rather than spawner abundance. Our results provide a mechanistic understanding of redd count data that can be used to assess their application and interpretation for monitoring. Key words: trout, superimposition, redd counts, observation error, monitoring, Bayesian model, Introduction Understanding population status and trends is critical for effectively managing and conserving species of recreational, commercial, or ecological value (e.g., Hilborn et al. 2020). Conservation targets for vulnerable and [...]

Retention forestry can help achieve multiple objectives in production forests, but its effectiveness is often low due to high mortality of the trees retained. We assessed the potential of improving tree survival in a low-level retention system in mixed forests by comparing the retention of multiple species of solitary trees (dispersed retention) and two approaches to aggregated retention. We annually monitored 58 dispersed-retention sites (since 2001) and 21 aggregated-retention sites (since 2013) in Estonia. Eight-year total mortality was 45% for solitary trees (and 1%-4% annually thereafter) but only 8% for tree groups; special planning for wind protection provided little further reduction. These estimates do not include dieback-affected Fraxinus excelsior L. that had distinct mortality dynamics independent of the retention pattern. Ulmus spp. also died frequently within the groups due to a dieback disease. Mixed-species tree groups enabled partial retention of Picea abies (L.) H. Karst that has extremely poor survival when retained solitarily. Likely, ecological costs of aggregated retention include some loss of microhabitat quality of individual trees. An optimal retention strategy could combine tree groups (maximizing wind protection and patch integrity) and individual trees (maximizing tree-scale biodiversity qualities), which collectively would also spread the risks of diverse mortality agents. Key words: ash dieback, mixed forest, spatial planning, tree mortality, variable retention, 1. Introduction Partial retention of forest structure at harvests is a flexible approach for addressing ecological sustainability in forest management (Lindenmayer et al. 2012). The mission of such a retention [...]

Throughout all oceans, aggregations of zooplankton and ichthyoplankton appear as horizontal sound scattering layers (SSLs) when detected with active acoustic techniques. Quantifying the composition and density of these layers is prone to sampling biases. We conducted a net and trawl survey of the epipelagic fauna in northern Norway (70[degrees] N) in June 2018 while an autonomous surface vehicle equipped with a broadband echosounder (283-383 kHz) surveyed the same region. Densities from the autonomous hydroacoustic survey were calculated using forward estimates from the relative density from the net and trawl, and inversion estimates with statistical data-fitting. All four methods (net, trawl, acoustic forward and inverse methods) identified that copepods dominated the epipelagic SSL, while pteropods, amphipods and fish larvae were present in low densities. The density estimates calculated with the inverse method were higher for mobile zooplankton, such as euphausiid larvae, than with the other methods. We concluded that the inverse method applied to broadband autonomous acoustic surveys can improve density estimates of epipelagic organisms by diminishing avoidance biases and increasing the spatio-temporal resolution of ship-based surveys. Key words: broadband acoustics, inversion, machine learning, autonomous surface vehicle, zooplankton, Introduction Pelagic zooplankton and ichthyoplankton form dense horizontal aggregations throughout all oceans and represent an easily accessible food source for higher trophic levels. In the North Atlantic, these organisms funnel [...]

Large, tabular icebergs known as 'ice islands' frequently transit the eastern Canadian Arctic and sub-Arctic after breaking away from ice tongues in northern Greenland. Here, we mine the Canadian Ice Island Drift, Deterioration and Detection (CI2D3) Database to contribute a descriptive assessment of the drift and grounding locations of Petermann ice islands (PII) following calving events at the Petermann Glacier in 2008, 2010, and 2012. We also use the CI2D3 Database to demonstrate how gridded bathymetry products can be improved using observations of ice island grounding and knowledge of ice island thickness. We find that most PII fragments followed a common southbound drift route directed by outflow from the Arctic Ocean and the dominant Baffin and Labrador Currents, which are strongest along the steep continental shelf break. Smaller ice islands were more prone to drift into the deeper waters of central Baffin Bay. As previously noted by northern community members, ice islands were also observed to drift into many adjacent sounds, channels, inlets, and straits. PIIs often grounded on shoals in Kane Basin, to the east of Coburg Island, and along the southeast coast of Baffin Island. Potential inaccuracies in two gridded bathymetry products were located in Jones Sound, near Coburg Island, and along the east coast of Baffin Island. Our approach to identifying these potential inaccuracies is shown to be sensitive to the estimate of ice island keel depth. Overall, this work provides synthesized observations of ice island occurrence and grounding as well as an approach to improving bathymetry products in a resource-rich marine region where traffic and industry operations are increasing. Key words: ice islands; icebergs; ice hazards; risk assessment; Canadian Arctic; Greenland; Petermann Glacier; Newfoundland and Labrador; bathymetry; currents Des icebergs tubulaires de grande taille, appeles << iles de glace >> transitent souvent dans l'est de l'Arctique canadien et dans la region subarctique apres s'etre detaches de langues glaciaires du nord du Groenland. Ici, nous depouillons la base de donnees canadienne sur la derive, la deterioration et la detection des iles de glace (CI2D3) afin d'aboutir a une evaluation descriptive des lieux de derive et d'echouement des iles de glace de Petermann (PII) a la suite d'evenements de velage du glacier Petermann survenus en 2008, 2010 et 2012. Nous nous servons egalement de la base de donnees CI2D3 pour montrer comment les produits bathymetriques peuvent etre ameliores au moyen d'observations de l'echouement des iles de glace et de connaissances sur l'epaisseur des iles de glace. Nous avons constate que la plupart des fragments de PII suivaient une route de derive commune vers le sud dirigee par le debit sortant de l'ocean Arctique et les courants dominants de Baffin et du Labrador, courants qui sont a leur plus fort le long du rebord abrupt du plateau continental. Les iles de glace plus petites etaient plus susceptibles de deriver dans les eaux plus profondes du centre de la baie de Baffin. Comme des membres de communautes nordiques l'ont deja fait remarquer, il y a egalement eu des observations d'iles de glace a la derive dans de nombreux detroits, traits, chenaux et canaux. Les PII se sont souvent echoues sur les hauts-fonds du bassin Kane, a l'est de l'ile Coburg, et le long de la cote sud-est de l'ile de Baffin. Les inexactitudes potentielles de deux produits bathymetriques quadrilles se trouvaient dans le detroit de Jones, pres de l'ile Coburg, et le long de la cote est de l'ile de Baffin. Il s'avere que la methode que nous avons adoptee pour determiner ces inexactitudes potentielles est sensible a l'estimation de la profondeur des quilles des iles de glace. Dans l'ensemble, cette etude a permis d'obtenir des observations synthetisees de l'occurrence et de l'echouement des iles de glace ainsi qu'une methode visant a ameliorer les produits bathymetriques dans une region marine riche en ressources oU la circulation et les activites industrielles sont en voie d'augmentation. Mots cles: iles de glace; icebergs; dangers lies a la glace; evaluation des risques; Arctique canadien; Groenland; glacier Petermann; Terre-Neuve-et-Labrador; bathymetrie; courants Traduit pour la revue Arctic par Nicole Giguere. [phrase omitted], INTRODUCTION Ice shelves and ice tongues, which extend from glaciers or are affixed to land, can calve large, tabular icebergs that are referred to as 'ice islands' in the Arctic [...]