Janet A. Nye

Slow adaptation in the face of rapid warming leads to collapse of the Gulf of Maine cod fishery.

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. Warming waters prevented cod recovery in the North Atlantic. Double jeopardy In the best of worlds, exploited fish stocks are monitored so that harvest quotas protect the reproductive ability of the population. Climate change is likely to complicate this process substantially. Pershing et al. found that cod stocks declined continuously during intense warming in the North Atlantic. Fisheries quotas, even though they were responsibly set and followed by fishers, decreased the reproductive rate. Thus, managing fisheries in a warming world is going to be increasingly problematic. Science, this issue p. 809

Silver hake tracks changes in Northwest Atlantic circulation

Recent studies documenting shifts in spatial distribution of many organisms in response to a warming climate highlight the need to understand the mechanisms underlying species distribution at large spatial scales. Here we present one noteworthy example of remote oceanographic processes governing the spatial distribution of adult silver hake, Merluccius bilinearis, a commercially important fish in the Northeast US shelf region. Changes in spatial distribution of silver hake over the last 40 years are highly correlated with the position of the Gulf Stream. These changes in distribution are in direct response to local changes in bottom temperature on the continental shelf that are responding to the same large scale circulation change affecting the Gulf Stream path, namely changes in the Atlantic meridional overturning circulation (AMOC). If the AMOC weakens, as is suggested by global climate models, silver hake distribution will remain in a poleward position, the extent to which could be forecast at both decadal and multidecadal scales.

Incorporating Climate Science in Applications of the U.S. Endangered Species Act for Aquatic Species

Aquatic species are threatened by climate change but have received comparatively less attention than terrestrial species. We gleaned key strategies for scientists and managers seeking to address climate change in aquatic conservation planning from the literature and existing knowledge. We address 3 categories of conservation effort that rely on scientific analysis and have particular application under the U.S. Endangered Species Act (ESA): assessment of overall risk to a species; long-term recovery planning; and evaluation of effects of specific actions or perturbations. Fewer data are available for aquatic species to support these analyses, and climate effects on aquatic systems are poorly characterized. Thus, we recommend scientists conducting analyses supporting ESA decisions develop a conceptual model that links climate, habitat, ecosystem, and species response to changing conditions and use this model to organize analyses and future research. We recommend that current climate conditions are not appropriate for projections used in ESA analyses and that long-term projections of climate-change effects provide temporal context as a species-wide assessment provides spatial context. In these projections, climate change should not be discounted solely because the magnitude of projected change at a particular time is uncertain when directionality of climate change is clear. Identifying likely future habitat at the species scale will indicate key refuges and potential range shifts. However, the risks and benefits associated with errors in modeling future habitat are not equivalent. The ESA offers mechanisms for increasing the overall resilience and resistance of species to climate changes, including establishing recovery goals requiring increased genetic and phenotypic diversity, specifying critical habitat in areas not currently occupied but likely to become important, and using adaptive management. Incorporación de las Ciencias Climáticas en las Aplicaciones del Acta Estadunidense de Especies en Peligro para Especies Acuáticas.

Choosing and using climate-change scenarios for ecological-impact assessments and conservation decisions.

Increased concern over climate change is demonstrated by the many efforts to assess climate effects and develop adaptation strategies. Scientists, resource managers, and decision makers are increasingly expected to use climate information, but they struggle with its uncertainty. With the current proliferation of climate simulations and downscaling methods, scientifically credible strategies for selecting a subset for analysis and decision making are needed. Drawing on a rich literature in climate science and impact assessment and on experience working with natural resource scientists and decision makers, we devised guidelines for choosing climate-change scenarios for ecological impact assessment that recognize irreducible uncertainty in climate projections and address common misconceptions about this uncertainty. This approach involves identifying primary local climate drivers by climate sensitivity of the biological system of interest; determining appropriate sources of information for future changes in those drivers; considering how well processes controlling local climate are spatially resolved; and selecting scenarios based on considering observed emission trends, relative importance of natural climate variability, and risk tolerance and time horizon of the associated decision. The most appropriate scenarios for a particular analysis will not necessarily be the most appropriate for another due to differences in local climate drivers, biophysical linkages to climate, decision characteristics, and how well a model simulates the climate parameters and processes of interest. Given these complexities, we recommend interaction among climate scientists, natural and physical scientists, and decision makers throughout the process of choosing and using climate-change scenarios for ecological impact assessment. Selección y Uso de Escenarios de Cambio Climático para Estudios de Impacto Ecológico y Decisiones de Conservación.

Response to Comments on “Slow adaptation in the face of rapid warming leads to collapse of the Gulf of Maine cod fishery”

Palmer et al. and Swain et al. suggest that our “extra mortality” time series is spurious. In response, we show that including temperature-dependent mortality improves abundance estimates and that warming waters reduce growth rates in Gulf of Maine cod. Far from being spurious, temperature effects on this stock are clear, and continuing to ignore them puts the stock in jeopardy.

Reproductive Characteristics of Weakfish in Delaware Bay: Implications for Management

Abstract We quantified size and age at maturity, batch fecundity, spawning frequency, and annual fecundity for weakfish Cynoscion regalis in Delaware Bay in 1999 and 2000. Information about these critical characteristics are needed for stock assessment models, which have never been assessed in Delaware Bay nor anywhere in the range of the weakfish since 1991–1992, when abundance was very low. Stock size increased from 1991–1992 to 1999–2000, but size at maturity was 168 ± 4.1 mm (mean ± SE) and did not appear to increase with stock size. Ninety-seven percent of age-1 fish were mature, but they arrived later to the estuary, had lower batch fecundity, and spawned less frequently than did older fish. The annual fecundity of fish age 2–6 was at least 30 times as great as that of age-1 fish. Batch fecundity was similar between Chesapeake Bay and Delaware Bay in the same year once corrected for fish size. The relationships of batch fecundity to both female weight and length were statistically equal between the ...

Effects of spring onset and summer duration on fish species distribution and biomass along the Northeast United States continental shelf

Studies documenting distributional shifts of fishes typically rely on time series of annual sampling events with fixed seasonal timing and limited temporal range. Meanwhile, as temperatures along the Northeast continental shelf have increased, the seasonal cycle also shifted towards earlier spring warming and longer summers. Seasonal migrations of fish and macroinvertebrates on the continental shelf in the Northeast US are thought to be primarily controlled by temperature and as such likely follow the temperature phenology of the shelf. This study sought to determine whether apparent changes in fish biomass and distributions are linked to spring warming phenology and/or duration of summer, the effective growing season for most species. We hypothesized that the earlier spring thermal transition would occur earlier and would cause centers of biomass to be more poleward during the spring survey. We also expected lengthening summers, primarily a function of later fall cooling, to cause centers of biomass in the fall survey to be more poleward and for biomass on the shelf to be greater within and following longer growing seasons. We did not detect a strong effect of the timing of the spring thermal transition in sea surface temperature on the distribution or abundance for most of the 43 fish stocks that we examined. However, later fall cooling and longer summers had a strong effect on both abundance and biomass of many fish stocks. These findings suggest that more focus should be placed on the length of the growing season and population-level processes that result in distributional shifts and changes in abundance.