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McGowan C.P.,U.S. Geological Survey | McGowan C.P.,North Carolina State University | Smith D.R.,U.S. Geological Survey | Sweka J.A.,U.S. Fish and Wildlife Service | And 8 more authors.
Natural Resource Modeling

Adaptive management requires that predictive models be explicit and transparent to improve decisions by comparing management actions, directing further research and monitoring, and facilitating learning. The rufa subspecies of red knots (Calidris canutus rufa), which has recently exhibited steep population declines, relies on horseshoe crab (Limulus polyphemus) eggs as their primary food source during stopover in Delaware Bay during spring migration. We present a model with two different parameterizations for use in the adaptive management of horseshoe crab harvests in the Delaware Bay that links red knot mass gain, annual survival, and fecundity to horseshoe crab dynamics. The models reflect prevailing hypotheses regarding ecological links between these two species. When reported crab harvest from 1998 to 2008 was applied, projections corresponded to the observed red knot population abundances depending on strengths of the demographic relationship between these species. We compared different simulated horseshoe crab harvest strategies to evaluate whether, given this model, horseshoe crab harvest management can affect red knot conservation and found that restricting harvest can benefit red knot populations. Our model is the first to explicitly and quantitatively link these two species and will be used within an adaptive management framework to manage the Delaware Bay system and learn more about the specific nature of the linkage between the two species. © 2011 Wiley Periodicals, Inc. Source

McGowan C.P.,U.S. Geological Survey | Smith D.R.,U.S. Geological Survey | Nichols J.D.,U.S. Geological Survey | Lyons J.E.,U.S. Fish and Wildlife Service | And 4 more authors.
Biological Conservation

Decision analytic approaches have been widely recommended as well suited to solving disputed and ecologically complex natural resource management problems with multiple objectives and high uncertainty. However, the difference between theory and practice is substantial, as there are very few actual resource management programs that represent formal applications of decision analysis. We applied the process of structured decision making to Atlantic horseshoe crab harvest decisions in the Delaware Bay region to develop a multispecies adaptive management (AM) plan, which is currently being implemented. Horseshoe crab harvest has been a controversial management issue since the late 1990s. A largely unregulated horseshoe crab harvest caused a decline in crab spawning abundance. That decline coincided with a major decline in migratory shorebird populations that consume horseshoe crab eggs on the sandy beaches of Delaware Bay during spring migration. Our approach incorporated multiple stakeholders, including fishery and shorebird conservation advocates, to account for diverse management objectives and varied opinions on ecosystem function. Through consensus building, we devised an objective statement and quantitative objective function to evaluate alternative crab harvest policies. We developed a set of competing ecological models accounting for the leading hypotheses on the interaction between shorebirds and horseshoe crabs. The models were initially weighted based on stakeholder confidence in these hypotheses, but weights will be adjusted based on monitoring and Bayesian model weight updating. These models were used together to predict the effects of management actions on the crab and shorebird populations. Finally, we used a dynamic optimization routine to identify the state dependent optimal harvest policy for horseshoe crabs, given the possible actions, the stated objectives and our competing hypotheses about system function. The AM plan was reviewed, accepted and implemented by the Atlantic States Marine Fisheries Commission in 2012 and 2013. While disagreements among stakeholders persist, structured decision making enabled unprecedented progress towards a transparent and consensus driven management plan for crabs and shorebirds in Delaware Bay. © 2015 Published by Elsevier Ltd. Source

Heck K.L.,Dauphin Island Sea Laboratory | Heck K.L.,University of South Alabama | Fodrie F.J.,University of North Carolina at Chapel Hill | Madsen S.,Atlantic States Marine Fisheries Commission | And 2 more authors.
Marine Ecology Progress Series

Temperatures are rising in most temperate and polar environments, and a welldocumented effect of this change is a poleward range shift by a wide variety of terrestrial and aquatic species. In the northern Gulf of Mexico (GOM), an increasing number of tropical species have recently become established among the extant warm-temperate fauna. These include a diversity of tropical fishes, manatees, green turtles, warm-water corals, and black mangroves. The impact of these species may be profound, primarily because temperate species are restricted from shifting northward by the North American land mass. Thus, as tropical species expand northward in the GOM, they must interact with the extant species and potentially compete for essential resources or become prey for each other. Here we focus on tropical immigrants capable of transforming the vast and highly productive seagrass systems of the northern GOM, emphasizing herbivorous parrotfishes and comparing their impact with endemic seagrass-resident fishes. Increased numbers of these herbivores (plus green turtles and manatees) would likely shift detritus-based food webs in seagrass meadows to webs dominated by direct consumption of seagrasses. We provide estimates of some expected consumption rates and effects of these tropically associated seagrass herbivores and predict that the consequences of the increased tropicalization of northern GOM seagrass meadows will be: substantially reduced standing crops and structural complexity of seagrass meadows; increased energy flux through grazing food webs; and a greatly reduced nursery role that will result in much smaller adult populations of those finfish and shellfish species that rely on seagrasses as nurseries. © Inter-Research 2015. Source

Lynch P.D.,National Oceanic and Atmospheric Administration | Nye J.A.,State University of New York at Stony Brook | Hare J.A.,National Oceanic and Atmospheric Administration | Stock C.A.,National Oceanic and Atmospheric Administration | And 4 more authors.
ICES Journal of Marine Science

The term river herring collectively refers to alewife (Alosa pseudoharengus) and blueback herring (A. aestivalis), two anadromous fishes distributed along the east coast of North America. Historically, river herring spawning migrations supported important fisheries, and their spawning runs continue to be of cultural significance to many coastal communities. Recently, substantial declines in spawning run size prompted a petition to consider river herring for listing under the Endangered Species Act (ESA). The ESA status review process requires an evaluation of a species' response to multiple stressors, including climate change. For anadromous species that utilize a range of habitats throughout their life cycle, the response to a changing global climate is inherently complex and likely varies regionally. River herring occupy marine habitat for most of their lives, and we demonstrate that their relative abundance in the ocean has been increasing in recent years. We project potential effects of ocean warming along the US Atlantic coast on river herring in two seasons (spring and fall), and two future periods (2020-2060 and 2060-2100) by linking species distribution models to projected temperature changes from global climate models. Our analyses indicate that climate change will likely result in reductions in total suitable habitat across the study region, which will alter the marine distribution of river herring. We also project that density will likely decrease for both species in fall, but may increase in spring. Finally, we demonstrate that river herring may have increased sensitivity to climate change under a low abundance scenario. This result could be an important consideration for resource managers when planning for climate change because establishing effective conservation efforts in the near term may improve population resiliency and provide lasting benefits to river herring populations. © 2014 Published by Oxford University Press on behalf of International Council for the Exploration of the Sea. Source

Nesslage G.M.,Atlantic States Marine Fisheries Commission | Wilberg M.J.,Post University
North American Journal of Fisheries Management

Single-species surplus production models are often used to assess multispecies assemblages in data-poor situations where catch and effort data are insufficient to perform individual species assessments. We examined the performance of single-species surplus production models applied to aggregated multispecies assemblages and explored the incorporation of time-varying parameters to improve model estimates. We simulated the dynamics of three species with different intrinsic growth rates and survey catchabilities over 50 years in the presence of fishing and a single fishery independent survey. Schaefer surplus production models with and without time-varying growth rate and catchability were fitted to simulated data. We then compared the ability of each model to accurately estimate multispecies maximum sustainable yield and terminal year biomass and to accurately reflect overall trends in individual component stocks. All models produced biased estimates, but the accuracy of multispecies assemblage maximum sustainable yield was improved with the incorporation of time-varying parameters. The terminal biomass of the assemblage was best estimated by a basic production model in two of three scenarios. Multispecies assemblage trends were not reflective of all individual component species, resulting in situations in which some species were overexploited and others underexploited. Although the incorporation of time-varying parameters improved the accuracy of some estimates in this application, the direction and magnitude of bias may not be predictable unless the relative differences in growth rate and catchability among species in the assemblage are known. If single-species surplus production models are the only viable option for modeling assemblages, precautionary reference points should be adopted. Scaling the level of precaution to the range of growth rates among species in the assemblage is recommended. © American Fisheries Society 2012. Source

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