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We propose an extension of the N-mixture model that enables the estimation of abundances of multiple species as well as the correlations between them. Our novel multi-species N-mixture model (MNM) is the first to address the estimation of both positive and negative inter-species correlations, which allows us to assess the influence of the abundance of one species on another. We provide extensions that permit the analysis of data with excess of zero counts, and relax the assumption that populations are closed through the incorporation of an autoregressive term in the abundance. Our approach provides a method of quantifying the strength of association between species' population sizes and is of practical use to population and conservation ecologists. We evaluate the performance of the proposed models through simulation experiments in order to examine the accuracy of both model estimates and coverage rates. The results show that the MNM models produce accurate estimates of abundance, inter-species correlations and detection probabilities at a range of sample sizes. The MNM models are applied to avian point data collected as part of the North American Breeding Bird Survey between 2010 and 2019. The results reveal an increase in Bald Eagle abundance in south-eastern Alaska in the decade examined. [ABSTRACT FROM AUTHOR]

Total mercury concentrations ([THg]) exceed thresholds of concern in some Steller sea lion (Eumetopias jubatus) tissues from certain portions of the Aleutian Islands, Alaska. We applied compound-specific stable isotope analyses of both carbon and nitrogen in amino acids from fish muscle tissue to quantify the proportional contributions of primary production sources and trophic positions of eight prey species (n = 474 total) that are part of Steller sea lion diets. Previous THg analyses of fish muscle, coupled with monomethylmercury analyses of a subset of samples, substantiated previous findings that fishes from the west of Amchitka Pass, a discrete oceanographic boundary of the Aleutian Archipelago, have higher muscle Hg concentrations relative to fishes from the east. The δ 13 C values of essential amino acids (EAAs) in fish muscle demonstrated that although most fishes obtained their EAAs primarily from algae, some species varied in the extent to which they relied on this EAA source. The δ 15 N values of phenylalanine (0.9 to 7.8 ‰), an indicator of the isotopic baseline of a food web, varied widely within and among fish species. Trophic position estimates, accounting for this baseline variation, were higher from the west relative to the east of the pass for some fish species. Trophic magnification slopes using baseline-corrected trophic position estimates indicated similar rates of Hg biomagnification to the east and west of Amchitka Pass. Multiple linear regression models revealed that trophic position was the most important driver of fish muscle [THg] with less variation explained by other parameters. Thus, higher trophic positions but not the rate of Hg biomagnification to the west of Amchitka Pass may play a role in the regional differences in both fish and Steller sea lion [THg]. Although, differences in Hg contamination and uptake at the base of the east and west food webs could not be excluded., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have influenced the work reported in this paper., (Copyright © 2023 Elsevier B.V. All rights reserved.)