Several studies have documented fish populations changing in response to long-term warming. Over the past decade, sea surface temperatures in the Gulf of Maine increased faster than 99% of the global ocean. The warming, which was related to a northward shift in the Gulf Stream and to changes in the Atlantic Multidecadal Oscillation and Pacific Decadal Oscillation, led to reduced recruitment and increased mortality in the region's Atlantic cod (Gadus morhua) stock. Failure to recognize the impact of warming on cod contributed to overfishing. Recovery of this fishery depends on sound management, but the size of the stock depends on future temperature conditions. The experience in the Gulf of Maine highlights the need to incorporate environmental factors into resource management.

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BackgroundHumans have reduced the abundance of many large marine vertebrates, including whales, large fish, and sharks, to only a small percentage of their pre-exploitation levels. Industrial fishing and whaling also tended to preferentially harvest the largest species and largest individuals within a population. We consider the consequences of removing these animals on the ocean's ability to store carbon.Methodology/Principal FindingsBecause body size is critical to our arguments, our analysis focuses on populations of baleen whales. Using reconstructions of pre-whaling and modern abundances, we consider the impact of whaling on the amount of carbon stored in living whales and on the amount of carbon exported to the deep sea by sinking whale carcasses. Populations of large baleen whales now store 9.1×106 tons less carbon than before whaling. Some of the lost storage has been offset by increases in smaller competitors; however, due to the relative metabolic efficiency of larger organisms, a shift toward smaller animals could decrease the total community biomass by 30% or more. Because of their large size and few predators, whales and other large marine vertebrates can efficiently export carbon from the surface waters to the deep sea. We estimate that rebuilding whale populations would remove 1.6×105 tons of carbon each year through sinking whale carcasses.Conclusions/SignificanceEven though fish and whales are only a small portion of the ocean's overall biomass, fishing and whaling have altered the ocean's ability to store and sequester carbon. Although these changes are small relative to the total ocean carbon sink, rebuilding populations of fish and whales would be comparable to other carbon management schemes, including ocean iron fertilization.

Large variations in the activity and scaling patterns of enzymes involved in anaerobic metabolism exist and appear to be related to species differences in the locomotory habits of fish. Here, we show how the scaling of muscle lactate dehydrogenase (LDH) activity is highly variable in fish, not only among species, but also among populations of yellow perch (Perca flavescens) and lake trout (Salvelinus namaycush) exhibiting large differences in the scaling of fish activity costs. These differences in LDH scaling properties were significantly related to differences in diet ontogeny. Scaling coefficients and adjusted R2 values of LDH versus body size relationships were both threefold higher in fish that do not make important diet shifts among planktivory, benthivory, and piscivory than in those that do. We argue that fish activity and related glycolytic potential are reset to lower values whenever fish are able to switch diet to larger prey while growing; we implicate the burst component of foraging (mostly attacks) as being responsible for changes in activity costs. Our results suggest that anaerobic power requirements in fish are highly plastic and adapted to local and recent food web conditions. We discuss these findings in relation to optimal foraging theory and the energetic basis of prey-size selection.

Very little is known about the consequence of human activities on the flow of energy through natural ecosystems. Here, we present a trophic-based approach to describing energy relationships in pollutant-disturbed lakes, emphasizing the importance of prey diversity in maintaining energy transfer to growing fish. Both diet and community analysis indicated that the food web leading to yellow perch (Perca flavescens) in metal-polluted lakes was extremely simplified compared with reference lakes. Through the application of an in situ marker for fish activity costs (muscle lactate dehydrogenase activity) and through bioenergetic modelling, we show how this has severe consequences on the efficiency of energy transfer to perch from their prey; premature energetic bottlenecks (zero conversion efficiency) occur when successively larger prey types are not available to growing perch. These observations provide a much needed ecological and physiological framework for assessing how energy transfer can be affected in polluted systems. Our approach need not be limited therein but should be applicable to any aquatic system where food web structure is variable and (or) disrupted.Résumé : Très peu est connu au sujet de la conséquence des activités humaines sur le transfert énergétique dans les écosystèmes. Cette étude présente une nouvelle approche pour décrire des relations énergétiques dans les lacs pollués, soulignant l'importance d'une diversité de proies pour la croissance des poissons. Les analyses de contenus stomacaux et de la communauté ont indiqué que la base de nourriture disponible aux perchaudes (Perca flavescens) provenant de lacs pollués par les métaux lourds a été extrêmement simplifiée comparativement aux lacs références. Par l'application d'un indicateur enzymatique pour les coûts d'activité (natation) chez les poissons, et par l'application d'un modèle bioénergétique, cette étude démontre que ceci a des conséquences graves sur l'efficacité du transfert énergétique de proies aux perchaudes; des entonnoirs énergétiques (aucune croissance) se produisent quand des proies de différentes tailles ne sont pas disponibles successivement aux perchaudes en croissance. Ces observations fournissent un cadre écologique et physiologique important pour évaluer comment le transfert énergétique peut être affecté dans les systèmes pollués. Cette approche n'a pas besoin d'être limitée spécifiquement aux systèmes pollués, mais pourrait être aussi appliquée à tous systèmes aquatiques où la chaîne alimentaire est variable et (ou) dérangée. Rapid communication / Communication rapide 5