Assessment of Pelagic Food Webs in Mendums Pond, NH

This study focused on the relationship between plankton in Mendums Pond, NH. A grazing experiment was conducted to determine the effect of zooplankton on the phytoplankton population. The phytoplankton were largely composed of net plankton (75 %) and this fraction was dominated by cyanobacteria (84.5 %) even though this was a slightly acidic system. Data indicated that the mean body length of zooplankton increased with depth. The average body length of Daphnia ranged from 1.4 mm in the epilimnion to 1.9 mm in the hypolimnion. Copepods followed a similar trend increasing in average body length from 0.85 mm to 0.95 mm. The high numbers of cyanobacteria and copepods resulted in a 17.92 % day-1 grazing rate indicating that almost 18 % of the total lake water was filtered every day by the zooplankton. This also suggests that the phytoplankton are reproducing at a higher rate than they are being consumed by grazers. This may raise concerns about the future diversity of the food web as cyanobacteria reproduce and become more dominant in this system

Individual- and Population-Level Effects of Temperature and Hypoxia on Two Demersal Fishes in Chesapeake Bay

Anthropogenically-induced climate change has resulted in increases in water temperature and the frequency and severity of hypoxic events in coastal areas worldwide. Temperature and hypoxia affect fishes\u27 energetics which can, in turn, be reflected in changes in reproductive success and shifts in spatial distributions. in an effort to quantify these changes in Atlantic croaker (Micropogonias undulatus) and spot (Leiostomus xanthurus) in Chesapeake Bay. I: (1) estimated standard and maximum metabolic rates and hypoxia tolerances at five temperatures (10, 15, 20, 25 and 30°C) using intermittent-flow respirometry, (2) examined the effects of hypoxia exposure on metrics of reproductive potential and, (3) developed an individual-based, dynamic-seascape model of Atlantic croaker and spot based on data from the respirometry trials, The first set of experiments showed that metabolic scope (i.e., the difference between standard and maximum metabolic rates, and within which all aerobic metabolic processes must operate) increased with increasing temperature in both species between 10 and 20°C, but plateaued above 25°C in Atlantic croaker and above 20°C in spot. Except at 10°C, the metabolic scope of Atlantic croaker was less than that of spot at all temperatures. in contrast to previous studies with Atlantic croaker from the Gulf of Mexico, the relative expression of hypoxia-inducible factors and metrics of reproduction (gonadosomatic index, most-advanced oocyte stage, and proportion of atretic oocytes) did not differ between Atlantic croaker captured under normoxic and hypoxic conditions in Chesapeake Bay. Simulations of the movements and distribution of Atlantic croaker and spot using individual-based models suggested that these species would occupy areas with warmer and better-oxygenated water than indicated by trawl survey observations from 1988-2014. Additionally, simulations indicated that a greater proportion of Atlantic croaker and spot in the Virginia waters of Chesapeake Bay would occupy the lower portion of Chesapeake Bay than indicated by capture rates from the trawl survey. My research suggests Atlantic croaker and spot are well-adapted to the environmental conditions of Chesapeake Bay during summer and are likely not affected by the frequent hypoxic episodes occurring in the subestuaries of the lower Chesapeake Bay. The apparent larger effect of elevated temperature on the metabolic scope of spot may provide them a greater capacity for movement, growth, and reproduction in warmer conditions and thus, a competitive advantage over Atlantic croaker as water temperatures continue to rise due to anthropogenically-induced climate change. My results indicate that intermittent exposure to hypoxic conditions is unlikely to negatively affect the reproductive potential of Atlantic croaker. Additional research, however, is necessary to better understand how this intermittent hypoxia exposure affects the endocrine pathways controlling reproduction. Finally, although climate-change science frequently focuses on the effects of rising coastal water temperature, and fisheries science and management on the effects on fish distributions, the results of my individual-based models suggest that predicting the effects of anthropogenically-induced climate change should not focus on temperature alone, as this may not be the most important driver of changes in fish distribution. More specifically, other factors such as time-area specific hypoxic events, prey availability, and predator avoidance likely contribute to the spatial distributions of these species in Chesapeake Bay

Post-Release Mortality of School-Size Atlantic Bluefin Tuna (Thunnus thynnus) in the U.S Recreational Troll Fishery

Atlantic bluefin tuna Thunnus thynnus (ABFT) support commercial and recreational fisheries throughout the North Atlantic Ocean. Due to heavy fishing pressure over the course of several decades, the eastern and western stocks of ABFT were overfished and the current biomass of the western stock is estimated to be approximately 19% of the biomass necessary for maximum sustainable yield. Despite a variety of management measures, including the implementation of minimum sizes and reductions of the total allowable catch (TAC) and country-specific quotas, little change was observed in the status of the western stock. The U.S. commercial and recreational ABFT fisheries are managed by the National Marine Fisheries Service (NMFS), which distributes the U.S. quota among domestic fisheries by gear type. The U.S. recreational fishery, which has historically targeted small or “school-size” (69-119cm) ABFT, is managed by open seasons, a minimum size, and bag limits (the number of ABFT allowed to be landed per vessel per day). Over the past 20 years, bag limits have been severely reduced due to decreased annual quotas, increasing the number of ABFT released each year, mostly within the school-size category. It is important, for the management of ABFT, to account for all sources of fishing mortality and the large number of releases in the recreational fishery each year could be a significant source of mortality. However, there is very little information available to assess post-release mortality of school-size ABFT in the U.S. recreational fishery. In this study, twenty pop-up satellite archival tags (PSATs) were deployed to estimate the post-release mortality of school-size ABFT captured under normal fishing conditions in the recreational fishery. PSATs recorded pressure (depth), temperature, and light data and were deployed on school-size ABFT caught using trolling methods. These tags were programmed to record data approximately every five minutes for a 31-day deployment. Nineteen tags (95%) reported to the satellites of the ARGOS system and approximately 85% (range: 34-100%) of all archived data were transmitted from each tag. Depth and temperature profiles were used to infer the survival of all 19 individuals whose tags reported (mortality=0% 95% CI=0%, 10%). Data from these tags were also used to investigate the short-term habitat utilization of school-size ABFT. During June to October, these fish spent the majority of their time in the upper 40m of the water column and at temperatures between 18 and 24oC.Individuals were more likely to make vertical excursions to depths exceeding 30m during the day than at night

Short-Term Habitat Use of Juvenile Atlantic Bluefin Tuna

Bluefin Tuna Thunnus thynnus are highly sought after in commercial and recreational fisheries along the East Coast of North America. To appropriately assess and manage Atlantic Bluefin Tuna (ABT), it is necessary to understand their habitat use during multiple ontogenetic stages. We tagged 17 juvenile ABT in the northwest Atlantic Ocean with pop-up satellite archival tags (PSATs) to determine environmental factors that may affect habitat use. The PSATs were deployed off the coast of Massachusetts in August and September 2012. A generalized linear mixed model was applied to determine factors affecting the mean depth occupied by fish, and beta regression was used to understand factors affecting the proportion of time spent below the thermocline. Thermocline depth significantly affected the mean depth occupied by juvenile ABT and the proportion of time they spent below the thermocline. Time period (dawn, day, dusk, and night) also significantly affected the mean depth occupied by juvenile ABT. Additionally, the time period x lunar illumination interaction had a significant effect on the proportion of time spent below the thermocline. This study is the first to demonstrate that environmental factors such as thermocline depth, time period, and lunar illumination can significantly impact vertical habitat use by juvenile ABT and demonstrates the utility of generalized linear mixed models for investigating fish habitat use

YEAR-ROUND DETERMINATION OF METHANE (CH4) SOURCES AND SINKS IN ARCTIC LAKES USING CONTINUOUS AND AUTONOMOUS SAMPLING

Methane (CH4) is a potent greenhouse gas and its concentration has been increasing in the atmosphere. While natural emissions from inland water bodies are known to be important, there is large uncertainty in the amount of methane released from lakes to the atmosphere, especially from Northern latitudes. Part of this is due to limited sampling in these systems during dynamic periods, such as ice-over and ice-melt. To better understand these temporal dynamics, I used autonomous, continuous samplers (OsmoSamplers) to collect lake water year-round over two years (2015-2017). Lake water was collected at a fine temporal resolution to provide time-integrated (~1 week) samples from multiple Arctic lakes within the Mackenzie Delta. The Mackenzie Delta is a lake-rich, productive environment that is expected to be a significant source of methane to the atmosphere. Lakes spanning the central delta and outer delta were sampled for methane concentration and stable carbon isotope ratio (δ13C-CH4) changes, ion concentrations, and water column characteristics were measured with continuous sensor data (temperature, water pressure, conductivity, light, and dissolved oxygen). These unique time-series datasets show lakes exhibit a close coupling of dissolved oxygen, and other electron acceptors, with the timing of methane increasing during ice-cover. The increase in methane concentrations is primarily from diffusion out of sediments and possibly water-column methanogenesis. One lake in the outer delta exhibited thermogenic gas bubble dissolution that contributed to under-ice methane concentration increases. Following ice-melt, lake depth appears to impact methane release to the atmosphere. Shallower lakes exhibit rapid fluxes followed by significant microbial methanotrophy. Deeper lakes in the central delta are connected to groundwater, though it does not appear groundwater transports methane. This is the first study of dissolved methane and gas bubble 14C-age in the Mackenzie Delta and shows that dissolved methane is produced primarily from modern carbon sources, such as macrophyte biomass and terrestrial material, but some methane transported in gas bubbles is significantly older, with seeps in the outer delta rapidly releasing radiocarbon-dead, thermogenic methane. This study demonstrates the importance of multi-lake studies particularly with fine scale temporal sampling to understand methane processes in seasonally ice-covered lakes

The effect of photoperiod on milk production and prolactin in Holstein dairy cows

Fourteen multiparous Holstein cows were paired by stage of lactation and previous years milk yield and 14 Holstein first-calf heifers were paired by stage of lactation. One member of each pair was assigned to a 24L:OD or a 18L:6D photoperiod for 16 wk during winter 1981 (Experiment 1). A similar experiment comparing natural photoperiod (9-12 h light/day) and 18L:6D was conducted for 9 wk during winter 1982 (Experiment 2) in which 24 Holstein cows and 22 Holstein first-calf heifers were paired and assigned to groups as in the first experiment. Animals were housed in a free stall barn open on 2 sides. High pressure sodium vapor lamps provided light intensity at cow eye level of 254 26 lux during the day and 132 9 lux at night. In Experiment 1, concentration of serum prolactin (PRL) in response to thyrotropin releasing hormone (TRH)(33 μg/100 kg BW) was measured in 5 animals from each group. Prolactin response to TRH or saline was tested in 10 animals in each group in Experiment 2. Photoperiod had no effect on 4% fat corrected milk (FCM) in either age group in Experiment 1 although cows in the 18L:6D group averaged 2% higher monthly persistency in 4% FCM over the 12 wk that milk composition was monitered. Cows in the 18L:6D group averaged 5% higher monthly persistency in 4% FCM in Experiment 2 as compared to cows exposed to a natural photoperiod. Persistency in heifers was unaffected by photoperiod in this experiment. Basal concentration of serum PRL was not affected by either age or photoperiod in Experiment 1 (21.3±3.3 ng/ml). Peak concentration of serum PRL after TRH injection was not affected by photoperiod in the heifer group but cows exposed to 18L:6D had significantly higher concentrations of serum PRL after TRH injection than cows exposed to 24L:0D (560±133 vs. 229±54 ng/ml). Basal concentration of serum PRL in Experiment 2 was similar in TRH- and saline-injected animals (26.3±3.1 ng/ml) but was lower in cows than in heifers (17.1±2.0 vs. 35.5±5.0 ng/ml). Saline injection did not elicit a PRL increase nor were there any differences in concentration of serum PRL due to either photoperiod or age after TRH stimulation in Experiment 2. Weight gain of cows did not differ due to photoperiod in Experiment 1 although heifers exposed to 24L:0D gained more weight than those exposed to 18L:6D. Cows in Experiment 2 gained significantly more weight when exposed to 18L:6D. No difference in weight gain due to photoperiod was observed for heifers in Experiment 2. We conclude that milk yield in mature cows can be increased by using supplemental lighting during winter months when compared to natural photoperiod. No differences between 18L:6D and 24L:0D were observed. Prolactin does not appear to be involved in the mechanism of action of photoperiods stimulation of milk yield. Cost analysis of the above data reveal a $16.06 return on each dollar invested for supplemental lighting. The additional income realized through supplemental lighting may allow the dairyman to reduce herd size and operating costs

Investment Opportunities Forecasting: Extending the Grammar of a GP-based Tool

In this paper we present a new version of a GP financial forecasting tool, called EDDIE 8. The novelty of this version is that it allows the GP to search in the space of indicators, instead of using pre-specified ones. We compare EDDIE 8 with its predecessor, EDDIE 7, and find that new and improved solutions can be found. Analysis also shows that, on average, EDDIE 8's best tree performs better than the one of EDDIE 7. The above allows us to characterize EDDIE 8 as a valuable forecasting tool

Comparative Performance of Three Length-Based Mortality Estimators

Length‐based methods provide alternatives for estimating the instantaneous total mortality rate (Z) in exploited marine populations when data are not available for age‐based methods. We compared the performance of three equilibrium length‐based methods: the length‐converted catch curve (LCCC), the Beverton–Holt equation (BHE), and the length‐based spawning potential ratio (LB‐SPR) method. The LCCC and BHE are two historically common procedures that use length as a proxy for age. From a truncated length‐frequency distribution of fully selected animals, the LCCC estimates Z with a regression of the logarithm of catch at length by the midpoint of the length‐bins, while the BHE estimates Z as a function of the mean length. The LB‐SPR method is a likelihood‐based population dynamics model, which—unlike the LCCC and BHE—does not require data truncation. Using Monte Carlo simulations across a range of scenarios with varying mortality and life history characteristics, our study showed that neither the LCCC nor the BHE was uniformly superior in terms of bias or root mean square error across simulations, but these estimators performed better than LB‐SPR, which had the largest bias in most cases. Generally, if the ratio of natural mortality (M) to the von Bertalanffy growth rate parameter (K) is low, then the BHE is most preferred, although there is likely to be high bias and low precision. If M/K is high, then the LCCC and BHE performed better and similarly to each other. Differences in performance among commonly used truncation methods for the LCCC and BHE were small. The LB‐SPR method did not perform as well as the classical methods but may still be of interest because it provides estimates of a logistic selectivity curve. The M/K ratio provided the most contrast in the performance of the three methods, suggesting that it should be considered for predicting the likely performance of length‐based mortality estimators

Characterizing the Preferences and Values of US Recreational Atlantic Bluefin Tuna Anglers

The Atlantic Bluefin Tuna Thunnus thynnus is the target of a recreational fishery along the U.S. East Coast that is thought to be of considerable economic value. In some years, recreational landings have exceeded the sector’s annual subquota due to changes in fish availability, limited predictability of angler effort, and difficulties in realtime monitoring of catch. Understanding the drivers of angler behavior is critical for predicting how effort and harvest may vary as a function of changing fish availability, regulations, or costs. To investigate angler decision making, preferences, and values, we surveyed private recreational anglers from Maine to North Carolina and employed discrete choice experiments to determine how regulatory and nonregulatory trip-specific variables influence trip-taking behavior. A latent class-ranked log it model identified two distinct classes of anglers who exhibited differing preferences in regard to the importance of nonconsumptive aspects of Bluefin Tuna fishing (e.g., catch and release). Income and recent Bluefin Tuna targeting were the primary determinants of class membership, and higher-income anglers who had targeted Bluefin Tuna in the past 5 years were significantly more likely to be in the class that derives substantive benefits from nonconsumptive angling activities. An annual consumer surplus exceeding US$14 million was estimated for the 2015 fishery. We considered potential angler welfare impacts of possible management changes (compensating surplus) and identified a large amount of latent effort currently present in the fishery in the form of consumptive-oriented anglers. As a result, liberalization of harvest regulations could potentially lead to a large influx of effort into the fishery, which could impede the ability of managers to maintain harvest levels within prescribed limits