The Impact of Multiple Nursery Areas on the Population Structure of Atlantic Menhaden, \u3ci\u3eBrevooria tyrannus\u3c/i\u3e

Understanding the population structure and patterns of connectivity in marine fishes is essential when making predictions about a species\u27 resiliency and persistence in an increasingly changing environment. The Atlantic Menhaden Brevoortia tyrannus is a clupeid that plays a critical role in the marine food web and supports one of the largest fisheries on the US East Coast. In addition to a decrease in overall numbers and spawning stock biomass, recruitment levels have remained low since the 1990s. Menhaden use numerous estuaries along the Atlantic coast for juvenile development before recruiting to the adult population and the contribution of each of these nursery grounds is currently unknown. The Chesapeake Bay is believed to contribute 69% of the total recruits, although this estimate has never been quantitatively verified and is 25 years old, predating current low recruitment levels and increased development along the coastline. This study investigated the potential of trace element (Li, Mg, Mn, Rb, Sr, Y, Ba and Pb) and stable isotope (δ 13C and δ18O) signatures in otoliths to distinguish between coast-wide nursery grounds of menhaden for 2009-2011. Using geochemical signatures specific to each year, juvenile menhaden collected from Connecticut to South Carolina were classified to regional nursery grounds at nearly 90% accuracy. The geochemical signatures were applied to adult menhaden of unknown natal origin that corresponded to these year-classes to determine which nursery is producing the most recruits to the fishable stock. The results indicate that while the Chesapeake Bay still dominates the proportion of age-1 recruits, the Bay\u27s contribution has declined by 16-65% of the earlier estimate. Additionally, an evaluation of older age classes (ages 2-4), the spawning stock, offered a more complete assessment with nearly 70% of adults originating from the Northeast and Southeast nursery grounds rather than the Mid-Atlantic as previously believed. This study successfully evaluates historical estimates of nursery contribution for menhaden, identifies regions that are currently essential for survivorship of this population, and, thus, provides critical information to future stock assessments for this species

The Path to an Ecosystem Approach for Forage Fish Management: A Case Study of Atlantic Menhaden

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

Gene content evolution in the arthropods

Arthropods comprise the largest and most diverse phylum on Earth and play vital roles in nearly every ecosystem. Their diversity stems in part from variations on a conserved body plan, resulting from and recorded in adaptive changes in the genome. Dissection of the genomic record of sequence change enables broad questions regarding genome evolution to be addressed, even across hyper-diverse taxa within arthropods. Using 76 whole genome sequences representing 21 orders spanning more than 500 million years of arthropod evolution, we document changes in gene and protein domain content and provide temporal and phylogenetic context for interpreting these innovations. We identify many novel gene families that arose early in the evolution of arthropods and during the diversification of insects into modern orders. We reveal unexpected variation in patterns of DNA methylation across arthropods and examples of gene family and protein domain evolution coincident with the appearance of notable phenotypic and physiological adaptations such as flight, metamorphosis, sociality, and chemoperception. These analyses demonstrate how large-scale comparative genomics can provide broad new insights into the genotype to phenotype map and generate testable hypotheses about the evolution of animal diversity