Modeling the processes affecting larval haddock (Melanogrammus aeglefinus) survival on Georges Bank

Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution February 2011The ultimate goal of early life studies of fish over the past century has been to better understand recruitment variability. Recruitment is the single most important natural event controlling year-class strength and biomass in fish populations. As evident in Georges Bank haddock, Melanogrammus aeglefinus, there is a strong relationship between recruitment success and processes occurring during the planktonic larval stage. Spatially explicit coupled biological-physical individual-based models are ideal for studying the processes of feeding, growth, and predation during the larval stage. This thesis sought new insights into the mechanisms controlling the recruitment process in fish populations by using recent advances in biological-physical modeling methods together with laboratory and field data sets. Interactions between feeding, metabolism and growth, vertical behavior, advection, predation, and the oceanic environment of larval haddock were quantitatively investigated using individual-based models. A mechanistic feeding model illustrated that species-specific behavioral characteristics of copepod prey are critically important in determining food availability to the haddock larvae. Experiments conducted with a one-dimensional vertical behavior model suggested that larval haddock should focus on avoiding visual predation when they are small and vulnerable and food is readily available. Coupled hydrodynamics, concentration-based copepod species, and individual-based larval haddock models demonstrated that the increased egg hatching rates and lower predation rates on larvae in 1998 contributed to its larger year-class. Additionally, results from these coupled models imply that losses to predation may be responsible for interannual variability in recruitment and larval survival. The findings of this thesis can be used to better manage the haddock population on Georges Bank by providing insights into how changes in the physical and biological environment of haddock affect their survival and recruitment, and more generally about the processes significant for larval fish survival.Financial support was provided by a WHOI Watson Fellowship, a WHOI Coastal Ocean Institute Student Research Proposal Award, and GLOBEC grants NA17RJ1223 (NOAA) and OCE0815838 (NSF)

Demersal fish biomass declines with temperature across productive shelf seas

Aim: Theory predicts fish community biomass to decline with increasing temperature due to higher metabolic losses resulting in less efficient energy transfer in warm-water food webs. However, whether these metabolic predictions explain observed macroecological patterns in fish community biomass is virtually unknown. Here, we test these predictions by examining the variation in demersal fish biomass across productive shelf regions. Location: Twenty one continental shelf regions in the North Atlantic and Northeast Pacific. Time Period: 1980-2015. Methods: We compiled high-resolution bottom trawl survey data of fish biomass containing 166,000 unique tows and corrected biomass for differences in sampling area and trawl gear catchability. We examined whether relationships between net primary production and demersal fish community biomass are mediated by temperature, food-web structure and the level of fishing exploitation, as well as the choice of spatial scale of the analysis. Subsequently, we examined if temperature explains regional changes in fish biomass over time under recent warming. Results: We find that biomass per km2 varies 40-fold across regions and is highest in cold waters and areas with low fishing exploitation. We find no evidence that temperature change has impacted biomass within marine regions over the time period considered. The biomass variation is best explained by an elementary trophodynamic model that accounts for temperature-dependent trophic efficiency. Main Conclusions: Our study supports the hypothesis that temperature is a main driver of large-scale cross-regional variation in fish community biomass. The cross-regional pattern suggests that long-term impacts of warming will be negative on biomass. These results provide an empirical basis for predicting future changes in fish community biomass and its associated services for human wellbeing that is food provisioning, under global climate change

Potential impacts of climate change on agriculture and fisheries production in 72 tropical coastal communities

Climate change is expected to profoundly affect key food production sectors, including fisheries and agriculture. However, the potential impacts of climate change on these sectors are rarely considered jointly, especially below national scales, which can mask substantial variability in how communities will be affected. Here, we combine socioeconomic surveys of 3,008 households and intersectoral multi-model simulation outputs to conduct a sub-national analysis of the potential impacts of climate change on fisheries and agriculture in 72 coastal communities across five Indo-Pacific countries (Indonesia, Madagascar, Papua New Guinea, Philippines, and Tanzania). Our study reveals three key findings: First, overall potential losses to fisheries are higher than potential losses to agriculture. Second, while most locations (> 2/3) will experience potential losses to both fisheries and agriculture simultaneously, climate change mitigation could reduce the proportion of places facing that double burden. Third, potential impacts are more likely in communities with lower socioeconomic status

Scenario set-up and forcing data for impact model evaluation and impact attribution within the third round of the Inter-Sectoral Model Intercomparison Project (ISIMIP3a)

This paper describes the rationale and the protocol of the first component of the third simulation round of the Inter-Sectoral Impact Model Intercomparison Project (ISIMIP3a, www.isimip.org) and the associated set of climate-related and direct human forcing data (CRF and DHF, respectively). The observation-based climate-related forcings for the first time include high-resolution observational climate forcings derived by orographic downscaling, monthly to hourly coastal water levels, and wind fields associated with historical tropical cyclones. The DHFs include land use patterns, population densities, information about water and agricultural management, and fishing intensities. The ISIMIP3a impact model simulations driven by these observation-based climate-related and direct human forcings are designed to test to what degree the impact models can explain observed changes in natural and human systems. In a second set of ISIMIP3a experiments the participating impact models are forced by the same DHFs but a counterfactual set of atmospheric forcings and coastal water levels where observed trends have been removed. These experiments are designed to allow for the attribution of observed changes in natural, human and managed systems to climate change, rising CH4 and CO2 concentrations, and sea level rise according to the definition of the Working Group II contribution to the IPCC AR6

Modelling the sources of mortality for larval haddock on Georges Bank and their effects on behavior

Fish larvae have the ability to change their vertical position in the water column and thusly cannot be treated as passive particles in coupled biological-physical individualbased models (IBMs). The vertical variability of light, turbulence, temperature, prey, predators, and horizontal currents in the ocean affects the survival of larval fish through effects on feeding, growth, advection, and predation mortality. A dynamic model of the vertical position of larval fish in response to individual state and environmental conditions is needed for use in three-dimensional IBMs. A 1-dimensional model was constructed of an idealized water column representative of spring conditions on the southern flank of Georges Bank. The water column was used to test six behavioral rules of individuals parameterized as larval haddock (Melanogrammus aeglefinus) under different conditions of prey and turbulence stratification. Our objectives were to determine how behaviors based on different state and environmental variables affect depth distribution and mortality, and which behaviors produce a vertical distribution most similar to observations. Individuals applying behaviors associated with feeding had distributions comparable to observations and the highest survival. The use of behaviors derived from a trade-off between gut fullness and visual predation led to distributions unlike observations and high starvation mortality of the largest larval size class. Results suggest that larvae should make their vertical behavior decisions based on the risk of starvation rather than predation. A realistic model of larval haddock vertical position could be developed using only behaviors related to its prey distribution and foraging success