The Effect of Temperature on the Development, Growth and Survival of Atlantic Cod (Gadus morhua) During Early Life-Histories

For poikilothennic animals, and in particular those that inhabit aquatic habitats, temperature has a significant effect on all life processes. The purpose of this research was to investigate the contribution of temperature on embryonic development and survival and its effect on vital rates. Of particular interest was what aspect(s) of egg and larval life-histories are most affected by temperature and what consequence temperature effects may have on cumulative mortality. Three batches of Atlantic cod (Gadus morhua) eggs were acquired from a Newfoundland source of adult broodstock held at 4555°C. The eggs were divided andacclimated to four constant temperature regimes at approximately 2,4,8 and 12°C. Observations on development, growth and survival were made approximately every 4 degree days (mean temperature X number of days). Measurements taken included development stage for egg and yolk-sac period larvae, standard length of larvae, yolk-sac area, and the mortality of eggs and larvae. The analysis of size and development stage at hatch shows that the two measures are correlated. During the yolk-sac period, development-based changes in length largely eliminated any early differences in size. There was no relationship between size at hatch and the incidence of first-feeding larvae, but there was a dome-shaped relationship between temperature and the incidence of first-feeding. Relationships between the environmental temperature and rates of mortality, growth, development and yolk-sac absorption were constructed. Data were collected from two synchronized experiments. Experiment 1 was designed to evaluate the effects of temperature on the development of eggs and then on the growth of larvae. While collecting development and growth information, the yolk-sac size, feeding incidence and the condition of larvae were also noted. Experiment 2 was set up to evaluate the effects of temperature on the mortality of eggs and larvae. Temperature affected egg development and mortality, and larval growth, yolk-absorption, feeding and larval mortality, all known as vital rates. Increasing temperature exponentially decreased the time it took to reach the point at which feeding is initiated. The post yolk-sac growth for all temperatures resulted in a log-normal relationship. From the growth-temperature relationship, the maximum slope, where the growth rate per degree is maximized, and a temperature where growth per day was maximized was calculated. The predicted temperature of maximum growth rate was 7.g°C, and the predicted temperature the growth rate per degree was maximized was 4.2 C. A linear regression model best described the rate of yolk reduction across the different temperatures. The mean survival time during the egg stage showed an exponential decrease with temperature. The mean survival time for larvae resulted in a log-normal model, again with decreasing survival times with increasing temperature. The results are discussed in reference to normal temperature effects, which cause increasing vital rates with increasing temperature, and negative temperature effects, which changes the relative metabolic cost at different temperatures. Negative effects begin to dominate outside a optimal range of temperatures between 4-8°C. The temperature of maximum growth rate per degree is suggested as the optimal temperature for growth for larval cod in the field

Determining Environmental Drivers of Fish Community Structure along the Coast of Maine

The work presented here was conceived to determine whether structure in marine communities could be related to multiple scaled environmental parameters, as seen in lake and stream systems. Four datasets collected from 2001 to 2005 were used. The datasets ranged from local scale tidepool and estuarine surveys, to more regional intertidal/subtidal surveys and conclude using a coast-wide trawl survey. Initially, a bootstrap program for running principal component analysis (PCA) was developed and tested for utility with additional information from Pearson correlation coefficients. The bootstrap-PC A program was capable of determining confidence limits for correlations amongst species. The results from analysis of the survey data suggest that factors influencing tidepool species assemblages were embedded in patterns of vertical zonation horizontal gradients in sediment type (wave energy). Patterns became more structured from spring to late summer and associations amongst tidepool variables shifted from physical-algal associations to invertebrate-fish associations. The analysis of an estuarine dataset suggested estuarine assemblages reflect an interaction between topography and the location of culverts as restrictions to tidal flow, and the resulting differences in the impoundment of water. Patterns offish assemblages, in a regional survey sampling the intertidal/subtidal zone, was structured and related to potential wave energy at two scales. The first scale was local potential wave energy which related a specific site and the morphology/behavior of species capable of occupying the space. The second scale was regional and related to patterns of immigration and extinction mediated by energy acting as a barrier to certain species. When a coast-wide trawl survey was analyzed, structure in fish populations along the coast correlated to oceanographic differences observed between eastern and western Maine. Temperature, longitude and their interaction were related to patterns in biological structure in the survey data. When seen as a whole, the results demonstrate that structure is present in the distribution of species at all scales. Fisheries management initiatives would do well to understand the scales that are relevant to their mandate

Ecological and Management Implications of Climate Change Induced Shifts in the Phenology of Alewife (Alosa pseudoharengus)

Climate change is causing species to shift their phenology, or the timing of recurring life events such as migration and reproduction, in variable and complex ways. This can potentially result in mismatches or asynchronies in food and habitat resources that negatively impact individual fitness, population dynamics, and ecosystem function. This project seeks to improve our understanding of shifts in the timing of seasonal migration and spawning of adult anadromous alewife, Alosa psuedoherengus in seven natal stream systems within the state of Massachusetts: Acushnet, Agawam, Herring, Jones, Nemasket, Stoney Brook, and Town Brook Rivers. Initial analyses examined if and how the direction and magnitude of annual spawning run initiation, peak and end dates have shifted over recent decades. Preliminary results suggest that changes in alewife migration timing are not consistent across runs within Massachusetts. Trends from an overall analysis of all sites show a shift of earlier timing in run initiation dates and a shift towards later run end dates. Ongoing work seeks to evaluate the extent of estuarine habitat availability around each of the seven run sites; this will be accomplished by measuring the area of continuous wetland habitat downstream from alewife spawning ponds. Additionally, shifts in the timing of alewife migration in relation to environmental conditions such as river and sea surface temperature, river flow and winter conditions will be evaluated. Project results will help managers assess the vulnerability of alewife and other coastal species to the interactive effects of environmental and anthropogenic stressors influencing their populations across the region

Contrasting fishing effort reduction and habitat connectivity as management strategies to promote alewife (\u3cem\u3eAlosa pseudoharengus\u3c/em\u3e) recovery using an ecosystem model

Small pelagics, or forage fish, link lower and higher trophic levels in marine food webs. Recently, attention has been given to the management of forage fish, including anadromous river herring (Alewife Alosa pseudoharengus, blueback herring A. aestivalis) and American shad (A. sapidissima) due to their current depleted status and historically important ecological and economic roles. Little is known about the impact of changes in their biomass on marine food webs and what management practices will promote their recovery. Estimated historical riverine productivity was utilized to evaluate potential ecosystem impacts of the increasing river to ocean connectivity to resemble 19th-century conditions. The Ecopath with Ecosim modeling framework was used to simulate management strategies, focused on anadromous forage fish, by creating scenarios of fisheries reduction (mixed fishery effort reduction) and river to ocean habitat connectivity (75% of historical connectivity achieved). Sixty-year simulations covered the entire time series including a 36-year forecast period to evaluate the ecosystem impacts of management strategies. Results suggest nonlinear relationships and large changes in biomass flows from forage fish to upper trophic levels in the Gulf of Maine ecosystem. Increases in biomass were observed for pelagic sharks, demersal piscivores, and species of conservation concern such as pinnipeds and seabirds, although overall results were strongly influenced by indirect trophic effects. Promoting anadromous forage fish recovery through increased connectivity resulted in the redundancy of marine ecosystem niches that would increase resilience to climate, fisheries, and other perturbations. This study highlights the value of employing ecosystem models for testing management scenarios to contrast different approaches to recover anadromous forage fish towards its former ecological prominence

Interspecific and Local Variation in Tern Chick Diets Across Nesting Colonies in the Gulf of Maine

The Gulf of Maine, USA is home to four colonial co-nesting tern species: Least Tern (Sternula antillarum), Common Tern (Sterna hirundo), Arctic Tern (Sterna paradisaea), and the federally endangered Roseate Tern (Sterna dougallii). Over three decades of visual observations of chick provisioning were compiled for a comparative dietary study in the region, including the first detailed descriptions of Least and Roseate Tern chick diets. Three prey groups comprised the majority of chick diets among tern species between 1986–2017: hake (Urophycis spp. or Enchelyopus cimbrius) 28–37% frequency of occurrence (FO), sand lance (Ammodytes americanus or A. dubius) 8–22% FO, and herring (Clupea spp. or Alosa spp.) 3–30% FO. Dietary contributions varied across species and islands. At two inshore colonies, Common Tern diets contained higher amounts of sand lance (30–42% FO), while offshore islands contained lesser amounts (5–9% FO). Overall dietary diversity (H′) was similar between Common (H′ = 1.57) and Arctic Terns (H′ = 1.74) and notably lower in Roseate (H′ = 1.24) and Least Terns (H′ = 1.37), whose diets were primarily piscivorous. The degree of dietary plasticity and general feeding ecology provided by baseline dietary information can inform holistic assessments of risk to ongoing and future disturbances from fishing and climate change

Identification of supraoptimal temperatures in juvenile blueback herring (\u3cem\u3eAlosa aestivalis\u3c/em\u3e) using survival, growth rate and scaled energy reserves

For young fishes, growth of somatic tissues and energy reserves are critical steps for survival and progressing to subsequent life stages. When thermal regimes become supraoptimal, routine metabolic rates increase and leave less energy for young fish to maintain fitness-based activities and, in the case of anadromous fishes, less energy to prepare for emigration to coastal habitats. Thus, understanding how energy allocation strategies are affected by thermal regimes in young anadromous fish will help to inform climate-ready management of vulnerable species and their habitat. Blueback herring (Alosa aestivalis) are an anadromous fish species that remain at historically low population levels and are undergoing southern edge-range contraction, possibly due to climate change. We examined the effects of temperature (21°C, 24°C, 27°C, 30°C, 33°C) on survival, growth rate and energy reserves of juveniles collected from the mid-geographic range of the species. We identified a strong negative relationship between temperature and growth rate, resulting in smaller juveniles at high temperatures. We observed reduced survival at both 21°C and 33°C, increased fat and lean mass-at-length at high temperatures, but no difference in energy density. Juveniles were both smaller and contained greater scaled energy reserves at higher temperatures, indicating growth in length is more sensitive to temperature than growth of energy reserves. Currently, mid-geographic range juvenile blueback herring populations may be well suited for local thermal regimes, but continued warming could decrease survival and growth rates. Blueback herring populations may benefit from mitigation actions that maximize juvenile energy resources by increasing the availability of cold refugia and food-rich habitats, as well as reducing other stressors such as hypoxic zones

A Novel Framework to Predict Relative Habitat Selection in Aquatic Systems: Applying Machine Learning and Resource Selection Functions to Acoustic Telemetry Data From Multiple Shark Species

Resource selection functions (RSFs) have been widely applied to animal tracking data to examine relative habitat selection and to help guide management and conservation strategies. While readily used in terrestrial ecology, RSFs have yet to be extensively used within marine systems. As acoustic telemetry continues to be a pervasive approach within marine environments, incorporation of RSFs can provide new insights to help prioritize habitat protection and restoration to meet conservation goals. To overcome statistical hurdles and achieve high prediction accuracy, machine learning algorithms could be paired with RSFs to predict relative habitat selection for a species within and even outside the monitoring range of acoustic receiver arrays, making this a valuable tool for marine ecologists and resource managers. Here, we apply RSFs using machine learning to an acoustic telemetry dataset of four shark species to explore and predict species-specific habitat selection within a marine protected area. In addition, we also apply this RSF-machine learning approach to investigate predator-prey relationships by comparing and averaging tiger shark relative selection values with the relative selection values derived for eight potential prey-species. We provide methodological considerations along with a framework and flexible approach to apply RSFs with machine learning algorithms to acoustic telemetry data and suggest marine ecologists and resource managers consider adopting such tools to help guide both conservation an

Tambora and the Mackerel Year: Phenology and Fisheries During an Extreme Climate Event

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

Global Plastic Pollution Observation System to Aid Policy

Plastic pollution has become one of the most pressing environmental challenges and has received commensurate widespread attention. Although it is a top priority for policymakers and scientists alike, the knowledge required to guide decisions, implement mitigation actions, and assess their outcomes remains inadequate. We argue that an integrated, global monitoring system for plastic pollution is needed to provide comprehensive, harmonized data for environmental, societal, and economic assessments. The initial focus on marine ecosystems has been expanded here to include atmospheric transport and terrestrial and freshwater ecosystems. An earth-system-level plastic observation system is proposed as a hub for collecting and assessing the scale and impacts of plastic pollution across a wide array of particle sizes and ecosystems including air, land, water, and biota and to monitor progress toward ameliorating this problem. The proposed observation system strives to integrate new information and to identify pollution hotspots (i.e., production facilities, cities, roads, ports, etc.) and expands monitoring from marine environments to encompass all ecosystem types. Eventually, such a system will deliver knowledge to support public policy and corporate contributions to the relevant United Nations (UN) Sustainable Development Goals (SDGs)