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Beginning in the 1980s, return rates of Atlantic salmon (Salmo salar) to the Penobscot River, Maine, USA, declined and have persisted at low levels. This downturn coincided with similar declines in North American and European Atlantic salmon stocks and with changes in the Northwest Atlantic ecosystem. Previous studies investigated whether early marine growth explained the declines, but results varied, with decreased growth associated with declines in European stocks but not North American stocks. In this study, we evaluate whether growth over the entire marine stage is related to Atlantic salmon marine survival. We constructed a growth time series from scales of returned Penobscot River Atlantic salmon spanning periods of varying marine survival. We used analysis of variance (ANOVA) and post hoc tests to quantify seasonal growth increment differences and principal component analysis to characterize variability among the suite of growth increments. We observed reduced growth during the second winter and second marine year starting in the 1990s, with compensatory seasonal growth relationships. These results indicate that diminished growth during late marine stages is associated with low return rates in this population. A partir des annees 1980, les taux de retour de saumons atlantiques (Salmo salar) dans le fleuve Penobscot (Maine, Etats-Unis) ont baisse pour ensuite demeurer faibles. Ce declin coincide avec des declins semblables des stocks nord-americains et europeens de saumons atlantiques et avec des changements dans l'ecosysteme de l'Atlantique Nord-Ouest. Des etudes anterieures ont tente d'etablir si la croissance en mer expliquait ces baisses, avec des resultats mitiges, dont une diminution de la croissance associee a des declins dans les stocks europeens, mais non dans les stocks nord-americains. Nous avons evalue s'il existe une relation entre la croissance durant l'ensemble de la phase marine et le taux de survie en mer du saumon atlantique. Nous avons constitue une serie chronologique de croissance a partir d'ecailles de saumons atlantiques de retour dans le fleuve Penobscot couvrant des periodes caracterisees par differents taux de survie en mer. Nous avons utilise l'analyse de variance et des tests post hocs pour quantifier la variation des increments de croissance saisonniers et l'analyse en composantes principales pour caracteriser la variabilite au sein de la serie d'increments de croissance. Nous relevons une croissance reduite durant le deuxieme hiver et la deuxieme annee en mer a partir des annees 1990, marquee par des relations de croissance saisonniere compensatoire. Ces resultats indiquent qu'une croissance reduite durant la phase marine est associee a de faibles taux de retour dans cette population. [Traduit par la Redaction], Introduction Over recent decades, declines in Atlantic salmon (Salmo salar) populations in both North America and Europe have been associated with large-scale ecosystem changes in the North Atlantic Ocean (Beaugrand [...]

The first marine circulus is the scale feature associated with marine entry and has been used to support research evaluating the relationships between size, growth, and survival for Atlantic salmon. Ambiguity in growth rates and circulus deposition during the transition from freshwater to the marine environment leads to difficulty in the correct identification of the first marine circulus. In this study, scale growth occurring after the last freshwater annulus (plus-growth) was characterized for Atlantic salmon smolts migrating out of the Narraguagus River in Maine. Plus-growth was present in over 95% of scales from smolts leaving the river and represented on average 12.2% of total freshwater growth. These findings suggest plus-growth presents a significant source of error in growth analyses, if ignored, and the characterization of this scale feature helps to inform accurate identification of marine entry for future studies. Run day was a driver of plus-growth, suggesting extended freshwater residency provides opportunity for growth prior to smolt emigration. The negative association between fork length and plus-growth suggests smaller smolts that delay migration are demonstrating compensatory growth. Cumulative air temperature was positively associated with plus-growth, suggesting warming spring temperatures driven by climate change may influence size at marine entry for smolts. [ABSTRACT FROM AUTHOR]

Fish scale microchemistry can be used to make life‐history inferences, although ecological studies examining scale composition are relatively rare. Salmon scales have an external layer of calcium phosphate hydroxyl apatite (HAP). The structure, hardness, and calcium content of this layer have been shown to vary within and between species. This variation may lead to misinterpretation of trace element profiles. This study uses backscatter scanning electron microscopy with electron dispersive spectrometry to compare scales from salmon populations and to present a more detailed analysis of scale HAP than was previously available. Our findings extend the range of salmon populations for which HAP Ca is available and confirm previous findings that the HAP Ca is relatively invariable within this species. [ABSTRACT FROM AUTHOR]

Ecosystem management requires an integrated understanding of ecological interactions. In the Gulf of Maine (GoM), trophic information pertaining to commercially important groundfishes and nearshore prey communities is lacking. We characterized nearshore communities and groundfish diets using data collected from nearshore surveys (864 bottom trawls and 3638 stomach samples of six groundfish species) conducted biannually (spring and fall) in Midcoast Maine and Penobscot Bay from 2012 to 2022. Groundfish diets were dominated by some of the most available nearshore prey (gadiform and clupeiform fishes and pandalid and crangonid shrimps). Shifts in relative prey availability over environmental gradients (e.g., depth and position along the coast), across seasons, and over years corresponded with parallel patterns in prey contributions to groundfish diets in specific predator–prey interactions. Negative trends in the relative availability and diet occurrence of signature GoM prey taxa (Northern shrimp Pandalus borealis, Atlantic herring Clupea harengus, and euphausiids) indicate that broader ecosystem changes, such as steady rises in water temperature and shifts in species distributions, are impacting nearshore trophic dynamics in the GoM. These observations provide timely information on mechanisms that underlie groundfish productivity and warrant inclusion of nearshore trophic dynamics in relevant ecosystem models. [ABSTRACT FROM AUTHOR]