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.

Atlantic menhaden (Brevoortia tyrannus) support the largest fishery by volume on the United States East Coast, while also playing an important role as a forage species. Managers’ and stakeholders’ increasing concerns about the impact of Atlantic menhaden harvest on ecosystem processes led to an evolution in the assessment and management of this species from a purely single-species approach to an ecosystem approach. The first coastwide stock assessment of Atlantic menhaden for management used a single-species virtual population analysis (VPA). Subsequent assessments used a forward projecting statistical catch-at-age framework that incorporated estimates of predation mortality from a multispecies VPA while analytical efforts continued toward the development of ecosystem models and explicit ecological reference points (ERPs) for Atlantic menhaden. As an interim step while ecosystem models were being developed, a series of ad hoc measures to preserve Atlantic menhaden biomass for predators were used by managers. In August 2020, the Atlantic States Marine Fisheries Commission formally adopted an ecological modeling framework as a tool to set reference points and harvest limits for the Atlantic menhaden that considers their role as a forage fish. This is the first example of a quantitative ecosystem approach to setting reference points on the United States Atlantic Coast and it represents a significant advance for forage fish management. This case study reviews the history of Atlantic menhaden stock assessments and management, outlines the progress on the current implementation of ERPs for this species, and highlights future research and management needs to improve and expand ecosystem-based fisheries management.

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Managers, stakeholders, and scientists recognize the need for collaborative, transparent, integrated approaches to complex resource management issues, and frameworks to address these complex issues are developing. Through the course of 2019, the Mid-Atlantic Fishery Management Council developed a conceptual model of ecosystem linkages and risks for summer flounder, a species of recreational and commercial fisheries importance. The proximal aim of the model was to develop a list of integrated management questions that could be refined and addressed through a future quantitative management strategy evaluation. As such, this conceptual model served as a scoping tool. However, the true value of the conceptual model lays elsewhere: familiarizing resource managers historically focused on single-species management with the potential utility of an ecosystem approach to management. This paper details the goals and development of the conceptual model and situates this process in the broader context of best practices for collaborative open science and scientific reproducibility. Further, it highlights a successful path by which the shift towards ecosystem-based management can be actuated.

Fish populations with broad age distributions are expected to have higher reproductive capacity than age-truncated populations because of the disproportionate contributions of older fish. Harvest slot limits, an expected means of ameliorating age truncation, are modeled for Tautog Tautoga onitis in an overfished population subunit that is experiencing overfishing. Tautog, currently managed with a 40-cm minimum size limit (MSL), is a candidate species for slots because it is relatively long-lived and slow-growing, with low discard mortality. We evaluated changes in biomass and abundance at age relative to management with the current MSL regulations using a forward population simulation model for four slots: 35-45 cm (small-wide), 38-42 cm (small-narrow), 40-50 cm (large-wide), and 43-47 cm (largenarrow), inclusive of lower and upper length limits. Angler behavioral responses were evaluated at 0, 10, and 20% noncompliance with the upper slot limit. The biomass and number of fish removed were reduced with harvest slot limit management relative to the MSL, but because the harvest was redirected to smaller fish the reduction in numbers removed was not as large as the reduction in biomass removed. Slot limits broadened the age structure within 10 years by reducing fishing mortality on extant fish. Median spawning stock biomass (SSB) recovered more quickly in three of the slots than with MSL regulation (3-6 years to reach SSB associated with a fishing mortality that yields 30% spawners per recruit as compared to 9 years with MSL management). We concluded that harvest slot limits can