Seabirds consume forage fish, which are keystone species in many marine ecosystems. The Junk Food Hypothesis proposes that high-lipid prey should produce better reproductive performance by seabirds. In the Gulf of Maine, changes in the forage fish community followed rapid warming post-2005 and included a decline in high-lipid Atlantic herring Clupea harengus. We studied 3 species of alcid (Atlantic puffin Fratercula arctica, razorbill Alca torda, common murre Uria aalge) over 23 yr at 3 colonies to assess changes in chick diet and its relationships with reproductive success. Puffin and razorbill chick diet changed over time; puffin diet was highly variable taxonomically, whereas razorbill diets were more consistent, showing proportional changes within fewer taxa. For puffins and razorbills, herring was replaced by sand lance Ammo dytes spp. and other taxa with lower energy density. Puffins did not require high-lipid fish to breed successfully, but diet -reproduction relationships became unpredictable following ex tremely warm winters (2013 and 2016). Razorbills and murres provisioning with low-lipid fish showed reduced chick condition and breeding success. We concluded that razorbills and murres need higher-quality diets than puffins, which more frequently exploited lower-lipid food during food shortages. However, puffin reproductive output was much more vulnerable to ocean warming owing to their longer breeding season and more varied diet. Different responses of closely-related species to changes in prey are driven by differences in chick-development strategies with clear implications for using seabirds as environmental indicators.

Ecosystem-based fishery management requires understanding of relationships between exploited fish and their predators, such as seabirds. We used exploratory regression analyses to model relationships between Atlantic herring (Clupea harengus) in the diet of seabird chicks at nine nesting colonies in the Gulf of Maine and four types of fishery-and survey-derived herring data. We found several strong relationships, which suggests spatial structuring in herring stocks and likely patterns of herring movements before they recruit into the fishery. Some types of herring data seldom used in stock assessments -notably acoustic surveys, fixed-gear landings, and mass-at-age (i.e., weight-at-age) -correlated as strongly with seabird data as more commonly used series, such as mobile-gear landings and modeled spawning stock biomass. Seabird chick diets collected at specific locations thus offer a promising means to assess the size, distribution, and abundance of juvenile herring across a broad area prior to recruitment, which is a major source of uncertainty in fisheries. Common terns (Sterna hirundo) showed the most potential as a bioindicator, correlating well and showing consistent spatial patterns with 11 of 13 fishery data series.Résumé : La gestion écosystémique des pêches nécessite une compréhension des liens entre les poissons exploités et leurs prédateurs, tels que les oiseaux marins. Nous avons utilisé des analyses de régression exploratoires pour modéliser les relations entre le hareng de l'Atlantique (Clupea harengus) dans l'alimentation de jeunes oiseaux de mer dans neuf colonies de nidification dans le golfe du Maine, et quatre types de données sur les harengs issues de la pêche et de campagnes d'évaluation. Nous avons relevé plusieurs relations marquées qui indiqueraient la présence d'une structure spatiale dans les stocks de harengs et de probables motifs de déplacement des harengs avant leur recrutement dans la pêche. Certains types de données sur les harengs rarement utilisés dans les évaluations des stocks, dont des données de relevés acoustiques, de débarquements de navires à engins fixes et de poids selon l'âge, présentent une corrélation tout aussi forte avec les données sur les oiseaux de mer que des séries plus couramment utilisées, comme les débarquements de navires à engins mobiles et la biomasse modélisée du stock reproducteur. Les régimes alimentaires des jeunes oiseaux de mer prélevés en des sites précis constituent donc une approche prometteuse pour évaluer la taille, la répartition et l'abondance des harengs juvéniles avant leur recrutement à l'échelle d'une grande région, des facteurs qui constituent une importante source d'incertitude dans les pêches. Les sternes pierregarins (Sterna hirundo) montrent le meilleur potentiel comme bioindicateur, puisqu'elles présentent une bonne corrélation et des motifs spatiaux concordants avec 11 des 13 séries de données issues de la pêche. [Traduit par la Rédaction]

Lethal control of wildlife represents an ethical concern for managers, exacerbated by a lack of replicated or controlled data for most taxa or regions. The Gulf of Maine (GOM) has a history of intensive lethal and nonlethal predator control to protect terns (Sterna spp.) from inflated populations of predatory gulls, especially herring (Larus argentatus) and great black‐backed gulls (L. marinus; large gulls). We described management strategies in the GOM, reviewed methods of nonlethal and lethal types of control, and compared the effectiveness of 3 control regimes (lethal, nonlethal‐only, and no control) using weighted means of reproductive success metrics for 4 tern species. Nonlethal‐only control is the least effective method of predator control; lethal control is consistently the most effective. Arctic terns (Sterna paradisaea) were the most susceptible to predation, whereas common terns (Sterna hirundo) were the most resilient. We concluded that targeted lethal control is necessary in the GOM to protect tern colonies from depredation and nesting exclusion by large gulls, and cannot be substituted with nonlethal control. Cessation of lethal control leads to abandonment of tern colonies within 6–7 years, but resumption of appropriately timed lethal control can lead to recolonization the same year. A combination of nonlethal and lethal methods can minimize the number of gulls taken. We recommend that any application of lethal control carefully considers the local needs of any target species and recognizes the need for spatial and temporal commitment. © 2017 The Wildlife Society.

Seabirds are considered bioindicators of bottom-up ecosystem processes, owing to seabirds’ dependence on marine prey. However, ground-nesting seabirds are susceptible to predation, which can limit their use as bioindicators. Machias Seal Island (MSI) supported the largest colony of Arctic Terns (Sterna paradisaea Pontoppidan, 1763) in the Gulf of Maine metapopulation, but prolonged breeding failure led ∼90% of terns to abandon the colony in 2006. We analyzed 12 years of food, weather, and predation data using logistic regression models to determine which had the strongest influence on breeding success. Food–weather interactions were important; under low rainfall, more euphausiids (northern krill, Meganyctiphanes norvegica (M. Sars, 1857)) in the diet increased breeding success, but euphausiids had a negative effect as rainfall became moderate or high. Predation by Herring Gulls (Larus argentatus Pontoppidan, 1763) increased following the cessation of lethal predator control; we identified a predation threshold of 25%, beyond which terns could not breed successfully. The collapse of MSI’s tern colony can be attributed entirely to gull predation. The breeding success of terns at MSI cannot be used as a bottom-up ecosystem bioindicator without accounting for predation. Managers of ground-nesting seabirds should consider predation and food as equally valid potential causes of population or reproductive declines.

Ecosystem-based fisheries management, which considers the interactions between fisheries, target species, and the physical and biological components of ecosystems, is necessary to ensure that directed fisheries avoid adverse impacts to ecosystems over the long term. The successful implementation of ecosystem-based fisheries management requires an understanding of predator-prey relationships and ways to operationalize such relationships to inform fisheries management. Here, we investigated if the diet of a generalist predator, Atlantic puffin Fratercula arctica, can be used as an indicator of the abundance of 2 commercially exploited prey species (haddock Melanogrammus aeglefinus and Acadian redfish Sebastes fasciatus) in the Gulf of Maine. Because haddock and redfish eaten by puffins are juveniles (age 0), there is potential to use their proportions and lengths in puffin diet to better understand the processes influencing haddock and redfish recruitment. By using principal component analysis to develop measures of diet across multiple puffin colonies, we show both spatial variation and large-scale patterns in the proportions and lengths of haddock and redfish in puffin diet. Spawning stock biomass was a strong predictor of haddock proportion in puffin diet and a moderate predictor of redfish proportion; however, proportions in puffin diet did not predict age-1 recruitment, suggesting that variation in recruitment is caused by processes that occur after the puffin breeding season and which affect the survival of older juveniles. Haddock length on one colony was a moderate predictor of age-1 recruitment. We conclude that puffin diet can be used as an indicator of haddock and redfish abundance.