Incorporating Environmental Variability Into Assessment and Management of American Lobster (Homarus americanus)

The American lobster (Homarus americanus) support one of the most valuable fisheries in the United States. A growing body of literature recognizes the importance of environmental variables in regulating this species’ biogeography and population dynamics. However, the current lobster stock assessment and management do not explicitly consider the impact of environmental variables such as water temperature and assumes spatiotemporal variabilities in the lobster environment as random background noises. Furthermore, while climate-induced changes in marine ecosystems continue to impact the productivity of lobster fisheries, studies that model lobster response to altered environmental conditions associated with climate change are lacking. As such, evaluating changes in lobster biogeography and population dynamics, as well as explicitly incorporating quantified lobster response to altered environmental conditions into the specie’s stock assessment will be critical for effective lobster fisheries management in a changing environment. This dissertation research developed a modeling framework to assess and incorporate environmental variability in assessment and management of American lobster stocks in the Gulf of Maine, Georges Bank, and southern New England. This modeling framework consists of: 1) a qualitative bioclimate envelope model to quantify the spatiotemporal variability in availability of suitable lobster habitat; 2) a statistical climate-niche model to quantify spatiotemporal variability of lobster distribution; and 3) a process-based population size-structured assessment model to incorporate the effect of environmental variable such as water temperature in lobster population dynamics. The developed modeling framework was used to predict climate-driven changes in lobster habitat suitability and distribution, as well as to determine whether incorporating the environmental effects can better inform historical recruitment especially for years when recruitment was very low or very high. The first component of the framework provides a qualitative bioclimate envelope model to evaluate the spatiotemporal variability of suitable lobster habitat based on four environmental variables (bottom temperature, bottom salinity, depth, and bottom substrate type. The bioclimate envelope model was applied to lobsters in Long Island Sound and inshore Gulf of Maine waters. In the Long Island Sound, an examination of the temporal change in annual median habitat suitability values identified possible time blocks when habitat conditions were extremely poor and revealed a statistically significant decreasing trend in availability of suitable habitat for juveniles during spring from 1978 to 2012. In the Gulf of Maine, a statistically significant increasing trend in habitat suitability was observed for both sexes and stages (juvenile and adult) during the spring (April–June), but not during the fall (September–November). The second component of the framework provides a statistical niche model to quantify the effects of environmental variables on lobster abundance and distribution. The statistical niche model was used to estimate spatiotemporal variation of lobster shell disease in Long Island Sound, and to quantify environmental effects on season, sex- and size-specific lobster distributions in the Gulf of Maine. In the Long Island Sound, the statistical niche model found that spatial distribution of shell disease prevalence was strongly influenced by the interactive latitude and longitude effects, which possibly indicates a geographic origin of shell disease. In the Gulf of Maine, the statistical niche model indicated that bottom temperature and salinity impact on lobster distribution were more pronounced during spring, and predicted significantly higher lobster abundance under a warm climatology scenario. The third component of the framework provides a size-structured population model that can incorporate the environmental effects to inform recruitment dynamics. The size-structured population model was applied to the Gulf of Maine/Georges Bank lobster stock, where climate-driven habitat suitability for lobster recruitments was used to inform the recruitment index. The performance of this assessment model is evaluated by comparing relevant assessment outputs such as recruitment, annual fishing mortality, and magnitude of retrospective biases. The assessment model with an environment-explicit recruitment function estimated higher recruitment and lower fishing mortality in the early 2000s and late 2010s. Retrospective patterns were also reduced when the environmentally-driven recruitment model was used. This dissertation research is novel as it provides the comprehensive framework that can quantify impacts of environmental variability on lobster biogeography and population dynamics at high spatial and temporal scales. The modeling approaches developed in this study facilitate the need to invoke assumptions of environment at non-equilibrium and demonstrate the importance of considering environmental variability in the assessment and management of the lobster fisheries. This dissertation is dedicated to increase the breadth of knowledge about the dynamics of lobster populations and ecosystems and renders a novel first step towards sustainable management of this species given the expected changes in the Northwest Atlantic ecosystem

Contrasting patterns in the occurrence and biomass centers of gravity among fish and macroinvertebrates in a continental shelf ecosystem

The distribution of a group of fish and macroinvertebrates (n = 52) resident in the US Northeast Shelf large marine ecosystem were characterized with species distribution models (SDM), which in turn were used to estimate occurrence and biomass center of gravity (COG). The SDMs were fit using random forest machine learning and were informed with a range of physical and biological variables. The estimated probability of occurrence and biomass from the models provided the weightings to determine depth, distance to the coast, and along-shelf distance COG. The COGs of occupancy and biomass habitat tended to be separated by distances averaging 50 km, which approximates half of the minor axis of the subject ecosystem. During the study period (1978–2018), the biomass COG has tended to shift to further offshore positions whereas occupancy habitat has stayed at a regular spacing from the coastline. Both habitat types have shifted their along-shelf distances, indicating a general movement to higher latitude or to the Northeast for this ecosystem. However, biomass tended to occur at lower latitudes in the spring and higher latitude in the fall in a response to seasonal conditions. Distribution of habitat in relation to depth reveals a divergence in response with occupancy habitat shallowing over time and biomass habitat distributing in progressively deeper water. These results suggest that climate forced change in distribution will differentially affect occurrence and biomass of marine taxa, which will likely affect the organization of ecosystems and the manner in which human populations utilize marine resources.publishedVersio

Influencia de factores ambientales sobre potas oceánicas (Cephalopoda: Ommastrephidae) explotadas comercialmente: un enfoque para la gestión de stocks

Ommastrephid squids are short-lived ecological opportunists and their recruitment is largely driven by the surrounding environment. While recent studies suggest that recruitment variability in several squid species can be partially explained by environmental variability derived from synoptic oceanographic data, assessment of ommastrephid stocks using environmental variability is rare. In thisstudy, we modified asurplus production model to incorporate environmental variability into the assessment of threeommastrephid squids (Ommastrephes bartramii in the northwest Pacific, Illex argentinus in the southwest Atlantic and Dosidicus gigas in the southwest Pacific). We assumed that the key environmental variables—suitable sea surface temperature on spawning grounds during the spawning seasons and feeding grounds during the feeding seasons—have effects on the carrying capacity and the instantaneous population growth rate, respectively, in the surplus production model. For each squid stock, the assessment model with environmental variability had the highest fitting accuracy and the lowest mean squared error and coefficient of variation, and the management reference points based on the optimal model were more precautionary. This study advances our understanding of the interactions between the environment and ommastrephid squid population dynamics and can therefore improve the management of these commercially valuable stocks with a short life cycle.Los miembros de la familia Ommastrephidae (potas) son cefalópodos de vida breve y oportunistas ecológicos, estando sus reclutamientos profundamente influidos por el ambiente circundante. Aunque algunos estudios recientes sugirieron que la variabilidad del reclutamiento en varias especies de esta familia podría explicarse parcialmente por la variabilidad ambiental derivada de datos oceanográficos sinópticos, la gestión de los stocks de omastréfidos empleando factores medioambientales es muy poco frecuente. En el presente trabajo, se ha modificado un modelo de producción generalizada incorporando en él factores ambientales con objeto de ofrecer una herramienta para la gestión y manejo de tres pesquerías: la de Ommastrephes bartramii en el Pacífico Noroeste, la Illex argentinus en el Atlántico sudoeste y la de Dosidicus gigas en el Pacífico sudoeste. Se asumió que los factores ambientales clave: una apropiada temperatura superficial en las áreas de puesta durante las épocas de freza y en las áreas de alimentación durante las estaciones de nutrición, tenían efectos sobre la capacidad de carga y el crecimiento instantáneo de la tasa de crecimiento de la población, respectivamente, en el modelo de producción generalizada. Para el stock de cada especie, el modelo de gestión con las variables ambientales mostró el mayor y más preciso ajuste y el menor error cuadrático y coeficiente de variación; además, los puntos de referencia de manejo basados en el modelo optimizado fueron los más precautorios. El presente estudio significa un avance en nuestro conocimiento sobre las interacciones entre el ambiente y la dinámica de las poblaciones de especies de esta familia de cefalópodos, lo que puede mejorar la gestión de estos stocks de especies de vida breve, cuya importancia comercial es muy grande

Leading Effects in Hadroproductions of Lambda_c and D From Constituent Quark-Diquark Cascade Picture

We discuss the hadroproductions of Lambda_c, Lambda_c bar, D and D bar in the framework of the constituent quark-diquark cascade model taking into account the valence quark annihilation. The spectra of Lambda_c and Lambda_c bar in pA, Sigma^-A and pi^-A collisions are well explained by the model using the values of parameters used in hadroproductions of D and D bar. It is shown that the role of valence diquark in the incident baryon is important for D bar productions as well as for Lambda_c production.Comment: 11 pages, 5 figures, v2:some explanations added, references added, typos corrected, v3: top margin change

コウセイシ カスケード モデル ニヨル KP オヨビ πP ショウトツ ニオケル チャーム ハドロン ノ セイセイ

We investigate the meson, baryon and anti-baryon productions in Kp and πp collisions in terms of the constituent cascade model which includes charm flavour. We compare our predicted spectra of charmed hadrons with the experimental data. Our model sugests the different leading particle effects on D mesons between π^+ and π^- beams