Global warming has increased the frequency of extreme climate events, yet responses of biological and human communities are poorly understood, particularly for aquatic ecosystems and fisheries. Retrospective analysis of known outcomes may provide insights into the nature of adaptations and trajectory of subsequent conditions. We consider the 1815 eruption of the Indonesian volcano Tambora and its impact on Gulf of Maine (GoM) coastal and riparian fisheries in 1816. Applying complex adaptive systems theory with historical methods, we analyzed fish export data and contemporary climate records to disclose human and piscine responses to Tambora’s extreme weather at different spatial and temporal scales while also considering sociopolitical influences. Results identified a tipping point in GoM fisheries induced by concatenating social and biological responses to extreme weather. Abnormal daily temperatures selectively affected targeted fish species—alewives, shad, herring, and mackerel—according to their migration and spawning phenologies and temperature tolerances. First to arrive, alewives suffered the worst. Crop failure and incipient famine intensified fishing pressure, especially in heavily settled regions where dams already compromised watersheds. Insufficient alewife runs led fishers to target mackerel, the next species appearing in abundance along the coast; thus, 1816 became the “mackerel year.” Critically, the shift from riparian to marine fisheries persisted and expanded after temperatures moderated and alewives recovered. We conclude that contingent human adaptations to extraordinary weather permanently altered this complex system. Understanding how adaptive responses to extreme events can trigger unintended consequences may advance long-term planning for resilience in an uncertain future.

Data gathered by citizen scientists can help ecologists understand long-term trends and can improve the quality and quantity of data about a resource. In Maine and Massa­chusetts, numerous citizen science programs collect data on river herring, anadromous fish that migrate each spring from the ocean to spawn in rivers and lakes. In collabora­tion with state and local resource managers and academic institutions, these programs aim to protect and restore river herring, improve local watersheds, and in some cases, support commercial harvesting. To better understand how programs are run and how data are used by managers, we interviewed program coordinators and resource manag­ers. Interviews revealed that resource managers consider citizen science–generated river herring data in decision making, but that their concerns about data quality affect if and how data are used. Although not without challenges, standardizing monitoring approaches could improve data collection and use. We offer six considerations related to standardization for managers.

In the nearshore Gulf of Maine, a combination of factors (overfishing, ecosystem change, and ocean warming) is thought to govern groundfish recovery. We analyzed feeding habits of demersal predatory fish from Midcoast Maine (abundant river herring) and Passamaquoddy Bay (low river herring) in eastern Maine, using stomach content and stable isotope analyses, to determine the prevalence of river herring (alewife, Alosa pseudoharengus, and blueback herring, A. aestivalis) in nearshore (<4.5 km) groundfish diets. Invertebrates dominated all predator diets at all sites. At Midcoast sites, catch-per-unit-effort (CPUE) of Atlantic cod was higher, and fish predators showed a strong seasonal pattern in river herring consumption compared to Passamaqouddy Bay. Cod, pollock (Pollachius virens), and sculpins (Myoxocephalus octodecimspinosus and M. scorpius) from Midcoast sites tended to be enriched in δ15N relative to Passamaquoddy Bay. Contrasting fast vs. slow turnover tissue (fin vs. muscle) indicated that focal species migrated or food availability changed seasonally and Atlantic mackerel (Scomber scombrus) in Passamaquoddy Bay were assimilating into a trophically depleted food web. We posit that lack of forage fish in Passamaquoddy Bay contributed to conditions that encourage an invertebrate based diet. River herring are also an order of magnitude less abundant in Passamaquoddy Bay than at Midcoast sites, limiting the availability of this seasonal food source. River restoration may contribute to recovery of groundfish stocks nearshore by increasing the availability of high lipid, seasonally available prey.

Bycatch of mid-trophic-level anadromous fishes that connect marine and freshwater ecosystems is a growing conservation concern. Anadromous alewife (Alosa pseudoharengus) and blueback herring (Alosa aestivalis) are important components of coastal freshwater and marine food webs, but have experienced dramatic declines in the abundances of spawning adults. Freshwater-focused restoration efforts have yielded few consistent signs of recovery, raising concerns that bycatch in Northwest Atlantic commercial fisheries may be negating these conservation actions. Using data from 15 microsatellites genotyped for baseline populations and bycatch, we conducted genetic stock identification to understand how bycatch was partitioned among previously identified regional genetic stocks. We then combined this information with fishery observer data to estimate genetic stock-specific bycatch mortality for the southern New England Atlantic herring fishery (2012–2013). Bycatch overall, but especially in the Atlantic herring fishery, was disproportionately assigned to the most severely depleted genetic stocks (alewife southern New England stock — 70% of assignments; blueback herring mid-Atlantic stock — 78% of assignments). These genetic stocks overlap in the region surrounding Long Island Sound, suggesting that bycatch taken from this area in recent years may be negatively impacting recovery efforts in this region. Our study suggests that mitigating bycatch on the southern New England fishing grounds may benefit recovery efforts for alewife and blueback herring genetic stocks that have experienced the greatest declines in spawning adult abundances.

Stocking programs have been used extensively to mitigate declines in anadromous fishes, but these programs can have long-term unintended genetic consequences. Stocking can homogenize population structure, impede local adaptation, and hinder the use of genetic stock identification as a fishery management tool. Using 12 microsatellite loci, we evaluate the spatiotemporal genetic structure of 16 anadromous alewife (Alosa pseudoharengus) populations in Maine, USA, to determine whether inter-basin stocking practices have influenced population structure and the genetic diversity of the species in this region. Although, no pre-supplementation samples exist, comparative analyses of stocked and non-stocked populations show that stock transfers have influenced alewife population genetic structure. Genetic isolation by distance (IBD) was non-significant among stocked populations, but significant among non-stocked populations. However, two populations, Dresden Mills and Sewell Pond, appear to have resisted genetic homogenization despite stocking. Non-significant genic and genetic differentiations were broadly distributed among alewife populations. Hierarchical AMOVA indicated highly significant differentiation among temporal replicates within populations, and Bayesian clustering analysis revealed weak population structure. A significant correlation was observed between stocking (time and events) and pairwise \({\text{F}}_{\text{ST}}^{{\prime }}\) among alewife collections, and an analysis of IBD residuals showed a significant decline in the amount of genetic differentiation among populations as the extent of stocking activity increased. These findings call for an increased awareness of evolutionary processes and genetic consequences of restoration activities such as inter-basin stock transfers by fisheries management and conservation practitioners.

Alewife (Alosa pseudoharengus) and blueback herring (Alosa aestivalis), also known collectively as either river herring or gaspereau, are anadromous clupeid fishes that display spatiotemporal overlap during riverine spawning migrations. Both species have experienced severe population declines within portions of their ranges. Evidence that they home to their natal rivers to spawn suggests the likelihood of ecologically significant population structure, yet this hypothesis has not been rigorously tested. We examined genetic diversity, differentiation and population structure in 34 alewife and four blueback herring populations spanning a 2,500 km portion of their northern range, using 14 microsatellite loci. Significant differentiation was detected among most rivers, and eight genetically defined alewife population clusters that largely corresponded to hydrographic regions were identified. Similar population structure was seen for blueback herring. Genetic isolation by distance was not significant among alewife populations in regions that have been historically influenced by dams, and/or stock transfers, but was highly significant in two regions that have not been subject to these influences. Genetic differentiation of alewife populations was strongest in the Bay of Fundy. Bottleneck tests revealed evidence of demographic bottlenecks in all of the alewife populations. Lastly, our results indicated that hybridization between alewife and blueback herring is common.

A major challenge in conservation biology is the need to broadly prioritize conservation efforts when demographic data are limited. One method to address this challenge is to use population genetic data to define groups of populations linked by migration and then use demographic information from monitored populations to draw inferences about the status of unmonitored populations within those groups. We applied this method to anadromous alewife ( Alosa pseudoharengus ) and blueback herring ( Alosa aestivalis ), species for which long‐term demographic data are limited. Recent decades have seen dramatic declines in these species, which are an important ecological component of coastal ecosystems and once represented an important fishery resource. Results show that most populations comprise genetically distinguishable units, which are nested geographically within genetically distinct clusters or stocks. We identified three distinct stocks in alewife and four stocks in blueback herring. Analysis of available time series data for spawning adult abundance and body size indicate declines across the US ranges of both species, with the most severe declines having occurred for populations belonging to the Southern New England and the Mid‐Atlantic Stocks. While all alewife and blueback herring populations deserve conservation attention, those belonging to these genetic stocks warrant the highest conservation prioritization.

Alewife Alosa pseudoharengus is an anadromous clupeid fish of long-standing ecological and socioeconomic importance along the Atlantic coast of North America. Since the 1970s, Alewife populations have been declining throughout the species' range. A number of hypotheses have been proposed to explain the decline, but a lack of basic information on population demographics inhibits hypothesis testing. In this study, we evaluated the use of morphometric analysis to discriminate among spawning stocks of Alewives collected from 24 sites in Maine and one site in Massachusetts. We first identified 10 morphometric measurements that were not influenced by the freezing-thawing process, and then used principal component and discriminant function analyses to develop stock-structure classification models from these 10 measurements. Classification models were able to discriminate Alewives to be from Maine or the single Massachusetts site 100% of the time. In addition, classification models correctly classified pooled sampling sites from the extreme western and eastern parts of Maine with 64% accuracy. Morphometric analysis may therefore provide an easily accessible, comparatively fast, and inexpensive method to discriminate marine-captured Alewives spawned in areas separated by major biogeographic regions, large geographic distances (100s of kilometers), or both, and thus help inform questions about stock composition at these spatial scales for assessment surveys and bycatch events.

Limited information is available regarding long-term compensation in the food webs of exploited ecosystems. We compared the results of 3 studies that assessed the diets of Atlantic cod from Passamaquoddy Bay, Maine, USA, spanning 100 yr, using diet summary statistics to compare historical and modern datasets. We found that 1965 cod consumed fewer invertebrates than cod caught in 1896, but that cod caught in the period 2005 to 2008 ate diet items more similar to the 1896 fish. Large cod caught in the summer of 1965 primarily ate fish, particularly Atlantic herring, whereas few fish were found in the diets of 2005 cod. Documented changes in diet may reflect changes in technology and resource exploitation that altered the prey field available to cod over time. In the 1890s, the herring and finfish fisheries were widespread and landings were large, but other components of the food web, particularly invertebrates, were comparatively unexploited. Impacts on the benthos of Passamaquoddy Bay increased by the 1960s with the widespread use of heavy dredge and trawl gear. By 2005, most fisheries had abandoned Passamaquoddy Bay, and cod and herring were reduced in numbers. Ecosystem resilience can be seen in the return of modern cod to the 1896 diet, but compensatory dynamics in the food web appear to have favored benthic, then pelagic, and finally a 'balance' of diet constituents, but with fewer commercially important finfish in the ecosystem overall. When and where the data exist, 18th and 19th century accounts of fishery activity can be used to put modern trends in perspective.

This article documents the addition of 299 microsatellite marker loci and nine pairs of single‐nucleotide polymorphism (SNP) EPIC primers to the Molecular Ecology Resources (MER) Database. Loci were developed for the following species: Alosa pseudoharengus, Alosa aestivalis, Aphis spiraecola, Argopecten purpuratus, Coreoleuciscus splendidus, Garra gotyla, Hippodamia convergens, Linnaea borealis, Menippe mercenaria, Menippe adina, Parus major, Pinus densiflora, Portunus trituberculatus, Procontarinia mangiferae, Rhynchophorus ferrugineus, Schizothorax richardsonii, Scophthalmus rhombus, Tetraponera aethiops, Thaumetopoea pityocampa, Tuta absoluta and Ugni molinae. These loci were cross‐tested on the following species: Barilius bendelisis, Chiromantes haematocheir, Eriocheir sinensis, Eucalyptus camaldulensis, Eucalyptus cladocalix, Eucalyptus globulus, Garra litaninsis vishwanath, Garra para lissorhynchus, Guindilla trinervis, Hemigrapsus sanguineus, Luma chequen. Guayaba, Myrceugenia colchagüensis, Myrceugenia correifolia, Myrceugenia exsucca, Parasesarma plicatum, Parus major, Portunus pelagicus, Psidium guayaba, Schizothorax richardsonii, Scophthalmus maximus, Tetraponera latifrons, Thaumetopoea bonjeani, Thaumetopoea ispartensis, Thaumetopoea libanotica, Thaumetopoea pinivora, Thaumetopoea pityocampa ena clade, Thaumetopoea solitaria, Thaumetopoea wilkinsoni and Tor putitora. This article also documents the addition of nine EPIC primer pairs for Euphaea decorata, Euphaea formosa, Euphaea ornata and Euphaea yayeyamana.

SUMMARY 1. The introduction of invasive species is one of the main threats to global biodiversity, ecosystem structure and ecosystem processes. In freshwaters, invasive crayfish alter macroinvertebrate community structure and destroy macrophyte beds. There is limited knowledge on how such invasive species-driven changes affect consumers at higher trophic levels. 2. In this study, we explore how the invasive rusty crayfish Orconectes rusticus, a benthic omnivore, affects benthic macroinvertebrates, as well as the broader consequences for ecosystem-level trophic flows in terms of fish benthivory and trophic position (TP). We expected crayfish to decrease abundance of benthic macroinvertebrates, making most fish species less reliant on benthic resources. We expected crayfish specialists (e.g. Lepomis sp. and Micropterus sp.) to increase their benthic dependence. 3. In 10 northern Wisconsin lakes, we measured rusty crayfish relative abundance (catch per unit effort, CPUE), macroinvertebrate abundance, and C and N stable isotope ratios of 11 littoral fish species. We used stable isotope data and mixing models to characterise the trophic pathways supporting each fish species, and related trophic structure to crayfish relative abundance, fish body size and abiotic predictors using hierarchical Bayesian models. 4. Benthic invertebrate abundance was negatively correlated with rusty crayfish relative abundance. Fish benthivory increased with crayfish CPUE for all 11 fish species; posterior probabilities of a positive effect were >95%. TP also increased slightly with crayfish CPUE for some species, particularly smallmouth bass, largemouth bass, rock bass and Johnny darter. Moreover, both fish body size and lake abiotic variables explained variation in TP, while their effects on benthivory were small. 5. Rusty crayfish abundance explained relatively little of the overall variation in fish benthivory and TP. Although rusty crayfish appear to have strong effects on abundances of benthic macroinvertebrates, energy flow pathways and trophic niches of lentic fishes were not strongly influenced by invasive rusty crayfish.

Consensus-based research uses scientific inquiry as an unbiased tool to contrast opposing positions in resource conflicts. However, when applied inappropriately, science is more likely to polarize opposing parties. Opposing parties also may use a consensus-based research process to delay actions not in their interest. The recreational smallmouth bass (SMB) Micropterus dolomieu fishery in the St. Croix River, New Brunswick-Maine is an example of how consensus-based research failed to bring opposing sides in a natural resource conflict to a mutually agreeable resolution. Recreational fishing guides blamed high alewife Alosa pseudoharengus returns for the crash of a naturalized SMB fishery in the upper watershed and proposed an exclusion law in response. In 1995, Maine legislated that all fishways in the St. Croix River be closed to alewives, with a resulting decline from 2.6 million alewives in 1987 to 900 by 2002. Claims of insufficient data to describe alewife ecological impacts on SMB led to formation of a local, state, provincial, U.S., and Canadian stakeholders science committee charged with developing a study that would describe SMB and alewife interactions. The committee identified the question "has alewife presence contributed to poor SMB Population performance" as of primary importance to moving forward to a resolution. To test this hypothesis, SMB condition and growth, and the diet habits and diet overlap of alewives and SMB, were used as indicators of competition. Results, presented here, indicate that growth did not decline in the presence of alewives, age-0 SMB condition did not decline when alewives were present, and diet overlap between the two species was low in three of four lakes examined. Thus, the available data did not indicate that alewives caused poor SMB population performance, The project results helped break down institutional barriers between Maine natural resource agencies. However, local recreational fishermen were not satisfied with the project process or results, claiming that their interests, as represented by the state freshwater fish and game agency, were not seriously considered. They opposed and nearly defeated a bill to reintroduce alewives to the St. Croix River in 2008, again citing insufficient data to justify the action.

Trees that fall into lakes from riparian forest become habitat for aquatic organisms, and are potentially an important link between terrestrial and aquatic ecosystems. Coarse woody habitat (CWH) promotes the production of benthic invertebrate prey and offers refuge for prey fishes, which are in turn consumed by piscivorous fishes. We used a simulation model to explore responses of an aquatic food web to changes in CWH caused by lakeshore residential development and windstorm, as well as to harvest of adult piscivores. Residential development had a negative effect on fishes, and could lead to extirpation of benthivorous prey fish species. In contrast, pulsed addition of CWH following a windstorm had little effect on the aquatic food web. Our results suggest that CWH is more important as shelter for prey fishes than as a substrate for benthic invertebrate production. However, piscivore harvest can supersede the role of CWH as prey shelter, leading to piscivore collapse and prey persistence even when CWH levels are low enough to promote piscivore dominance. Thus, the effects of lakeshore residential development on fishes can be masked by angler harvest of top piscivores.

Exotic species invasions and climatic variation that occurred in north central Wisconsin provided the opportunity to contrast influences of climate and invasive species in shaping fish community dynamics in five Wisconsin lakes from 1981 to 2001. Year (passage of time) was positively correlated (r > 0.9) with invasive species. Year, invasive species, and climatic variables were the principal determinants of fish community dynamics according to redundancy analysis (RDA). The same invasive species negatively affected the same general group of species in different lakes; benthic invertivores declined in lakes invaded by crayfish, Orconectes spp., and pelagic zooplanktivores declined in lakes invaded by rainbow smelt, Osmerus mordax . Micropterus dolomieu , Pimephales notatus , and Notropis volucellus increased in abundance in lakes invaded by crayfish. When year was included in RDAs as a covariable (partial RDA), fish community changes in three lakes did not differ significantly from ordinations of Monte Carlo simulated data; for two lakes, growing season length and lake productivity were significant explanatory variables under the reduced model. The resulting shifts in the fish community might represent declines in those species that used resources similar to the invading crayfish and smelt or were eaten by the invading smelt. Subsequent community compensation might have occurred, with other species increasing in response to the declines in species affected directly by the invasive species.

We compared fish species compositions among four site types (lake, lake mouth, stream mouth, stream) along the gradient from stream to lake for 12 tributary mouths. Comparison of species richness, rarefaction species diversity, and species density all supported the same pattern: stream-mouth sites contained the highest number of species, followed by stream sites, lake-mouth sites, and lake sites, even though lake and lake-mouth sites yielded more individuals and were larger in area and volume. Principal components analysis formed three clusters of mixed sites based on similarities in dominant fish species rather than designations of lake, lake mouth, etc. Rank order assemblage tests revealed that species composition of tributary-mouth sites was similar in only one quarter of the systems sampled; other systems showed a transition from "lake" to "stream" species compositions at or near the tributary mouth. Species assemblage comparisons within site types between systems revealed low consistency in the composition of stream-mouth sites and high consistency for the other site types. We concluded that the tributary mouth fits the definition of an ecotone and speculate that the difference in hydrologic and geomorphic properties of streams and lakes played a role in the patterns that we saw on either side of the tributary mouth.