The Cadrin Lab

at UMass Dartmouth - SMAST

Category: Defense Announcements (page 1 of 2)

Doctoral Proposal Defense – Parth Sastry

October 9, 2025 / / 0 Comments
EAS Doctoral Proposal Defense
by Parth Sastry
Date:  Thursday, November 6, 2025
Time: 1:00pm
Topic:  Mesoscale Eddies and Tracer Transports Into the Eastern Tropical Pacific Oxygen Deficient Zone
Location:  SMAST East 101-103
                           Meeting ID: 959 4416 7939
Passcode: 222984
Abstract:     
Oxygen deficient zones (ODZs) are biogeochemically relevant regions of interest, characterized by very low to undetectable oxygen concentrations within the water column. They are found in all the world’s oceans, with the largest being in the eastern tropical Pacific (ETP). In conjunction, the region is home to a rich mesoscale eddy field, assumed to be associated with frequent wind jet events over the Gulf of Tehuantepec along with instabilities in the larger circulation. These wind events drive upwelling over the ocean, causing cold, dense, nutrient-rich waters to be oxygenated, potentially
being a significant source of oxygen into the ODZ.
A landmark study in 2015 by Cole et al. utilized information from Argo profiles – analyzing salinity anomalies – to obtain estimates of horizontal eddy di!usivities throughout the global ocean. These estimates help us account for smaller scale mixing processes a!ecting tracers in models, including oxygen. In the first part of the thesis, we improve upon this previous study by deriving a method to obtain a lower bound for horizontal eddy di!usivity via analyzing profiles within mesoscale eddies utilizing our knowledge of the eddy tracks to constrain observed salinity anomalies to a purely local-stirring induced anomaly. Hence, our analysis accounts for advective contributions to these anomalies and shows a reduction compared to di!usivities in the previous study. We still observe an elevated band of di!usivities along the “eddy alley” in the ETP – of the order of 5 → 103 m2s→1 – showcasing agreement with estimates from other studies that parameterize di!usivities. However, this estimate is still higher than what is used in common global climate models – leading them to potentially underestimate the oxygen flux into the ODZ.
Coastal waters in the region are more oxygenated than waters further out in the open ocean. Mixing of local climatological oxygen gradients by mesoscale eddies is one component of oxygen transport into the ODZ, which we quantify in the second chapter via our obtained di!usivity estimates. The aforementioned upwelling events are another source of oxygen. They oxygenate cold, dense water which then subducts into the ODZ. We propose to examine the statistics and nature of upwelling events via sea surface temperature maps from reanalysis products to quantify the amount of oxygen that gets transported cross-shelf as a consequence of these events. This analysis could examine whether wind-driven upwelling is a significant source of oxygen for the deeper waters of the ODZ. We also examine and diagnose particular upwelling events with models like HYCOM, to quantify the fraction of oxygenated water that gets advected to the ODZ, compared to along the coast – giving us better estimates of net oxygen transport. We seek to answer three key questions in this chapter – 1) How significant are upwelling events compared to local stirring in cross-shelf oxygen transport into the ODZ?, 2) Do high-resolution ocean models capture upwelling events as an oxygen source in the region? and 3) How do model computations of net oxygen transport compare with our estimates?
The mesoscale eddies observed in this region have a statistically significant relationship with the Tehuantepecer, a mountain-gap wind travelling through the Chivela pass and passing over the Gulf of Tehuantepec, that can often reach storm intensities. Our aim for the final part of the thesis is to investigate, via a hierarchy of increasingly complex ocean models in the Julia software package ClimaOcean, the generation and evolution mechanism of these eddies. A previous study utilizing the Regional Ocean Modeling System (ROMS) to model the region, showed that the predominant source of eddy kinetic energy (EKE) in the region are instabilities of the mean seasonal circulations and not transient wind work. This conclusion was drawn purely from a EKE budget analysis and did not analyze the generation mechanism of these eddies. We wish to examine, via process studies, what local processes drive eddy generation and whether they can explain observed asymmetries among anticyclones/cyclones in stability and size.
ADVISOR(s):  Dr. Amit Tandon, Department of Estuarine and Ocean Sciences, SMAST
                                                          (atandon@umassd.edu)
COMMITTEE MEMBERS:  Dr. Mark Altabet, Dept. of Estuarine and Ocean Sciences, SMAST
                                                           Dr. Geoffrey Cowles, Dept. of Fisheries Oceanography, SMAST
                                                           Dr. Eric D’Asaro, Applied Physics Laboratory, University of Washington
NOTE: All EAS Students are ENCOURAGED to attend.
                        Contact abedard1@umassd.edu for any questions.

DEOS PhD Dissertation Proposal Defense: Most Israt Jahan Mili

August 7, 2025 / / 0 Comments

“Development and application of a hyperspectral absorption-based primary productivity algorithm in the northern Gulf of Mexico”

By: Most Israt Jahan Mili

 

Advisor
Steven Lohrenz (Professor, SMAST / Estuarine and Ocean Sciences, UMassD)

 

Committee Members
Miles Sundermeyer (Professor, SMAST / Estuarine and Ocean Sciences, UMassD)
Mark Altabet (Professor /Chairperson, SMAST / Estuarine and Ocean Sciences, UMassD)
Juanita Urban-Rich (Associate Professor, School for the Environment, UMass Boston)
Geoffrey Cowles (Associate Professor, SMAST / Fisheries Oceanography, UMassD)

Tuesday August 12, 2025
11:00 AM
SMAST East 101-103
836 S. Rodney French Blvd, New Bedford
and via Zoom

Abstract:

Ocean primary production (PP) by phytoplankton forms the basis of the marine food web and is a critical component of the global carbon cycle. The northern Gulf of Mexico (nGOM) is a region of high biological productivity largely influenced by the nutrient input from the Mississippi and Atchafalaya rivers. High productivity has also been linked to recurrent hypoxia in this region. Ship-based in situ measurements of PP are limited in temporal and spatial coverage. Bio-optical models of PP enable the extrapolation or estimation of PP over more extended temporal and spatial scales. Such models have been based on in situ measurements of bio-optical properties as well as satellite observations, or combinations thereof.
Categories of models include wavelength-integrated vs wavelength-resolved, depth-integrated vs depth-resolved, chlorophyll-based vs phytoplankton absorption-based and carbon-based models. Wavelength-resolved models are more computationally intensive but provide a more accurate representation of the light field. Absorption-based models have the advantage of more directly characterizing light absorption by phytoplankton in contrast to chlorophyll-based models. Existing global PP models are primarily tuned for open ocean conditions and do not necessarily perform well on regional scales, such as the nGOM.
The optically complex nature of the river-influenced nGOM necessitates the use of a regionally tuned optical algorithm for the estimation of PP. Given this background, the first objective of this work was to describe and develop a regionally tuned, hyperspectral, wavelength-resolved, absorption-based PP algorithm for the nGOM, termed the wavelength-resolved model (WRM). Using in situ observations of photosynthesis-irradiance (P–E) in combination with vertical profiles of diffuse attenuation, we applied the WRM to the estimation of PP in major water mass types in the region. Average water column-integrated primary production (IPP) was 0.408 mol C m-2 d-1 and  ranged between 0.094 – 1.574 mol C m-2 d-1, with the lowest values observed in the outer and the highest in the mid-shelf region. The performance of the WRM was also evaluated in comparison to a conventional wavelength-integrated model (WIM), which is a chlorophyll-based model using wavelength-integrated photosynthetically active radiation (PAR) as input. Preliminary results revealed that the WRM yielded slightly higher IPP values compared to the conventional PAR-based WIM model, particularly at offshore stations. There was a slight negative bias in the WIM estimates of IPP as compared to the WRM with a mean bias error (MBE) of -0.08 mol C m-2 d-1 (0.96 g C m-2 d-1) and a p-value of 5.87 × 10-5 for a two-sided t-test. Furthermore, a modified version of the WRM, termed the wavelength-resolved model estimate (WRME), was developed to facilitate the application of the hyperspectral, absorption-based algorithm to satellite-derived hyperspectral ocean color observations.

The second objective of this study will be the adaptation of the algorithm to hyperspectral satellite ocean color observations such as those from the recently launched Plankton, Aerosol, Cloud, Ocean Ecosystem (PACE) satellite mission and its hyperspectral Ocean Color Instrument (OCI) sensor. Additional future hyperspectral missions, such as the Geosynchronous Littoral Imaging and Monitoring Radiometer (GLIMR), will further enhance this capability. This will enable the observation of PP across broader spatial and temporal scales in the nGOM.  We will also examine the vertical structure of phytoplankton absorption, using relationships between chlorophyll fluorescence and in situ measurements of phytoplankton absorption to assess the influence of vertical structure in IPP estimates.

Finally, the third objective will be to characterize the observed patterns in satellite-derived IPP in relationship to in situ measured biogeochemical (nutrients, pCO2) and physicochemical properties in the region and more broadly, to major circulation features in the nGOM.

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https://umassd.zoom.us/j/95009717853

Meeting ID: 950 0971 7853

Passcode: 404584

DFO PhD Dissertation Proposal Defense: Drake Ssempijja

August 7, 2025 / / 0 Comments

“Understanding Abandoned, Lost, and Otherwise Discarded Fishing Gear as a Source of Plastic Pollution in Inland Fisheries”

By: Drake Ssempijja

 

Advisor
Dr. Pingguo He (UMass Dartmouth)

 

Committee Members
Dr. Steve Cadrin (UMass Dartmouth), Dr. Chris Rillahan (UMass Dartmouth), and Dr. Paul Winger (Memorial University of Newfoundland)

Monday August 25, 2025
1:00 PM
SMAST East 101-103
836 S. Rodney French Blvd, New Bedford
and via Zoom

Abstract:

Abandoned, lost, and otherwise discarded fishing gear (ALDFG) is a problem that is increasingly of concern to global fisheries resources and the aquatic environment, with nearly 2% of all fishing gear used in marine fisheries lost to the ocean annually. This has negative impacts on the aquatic ecosystem, which includes but not limited to ghostfishing mortality to commercial, recreational, and protected species, degradation of sensitive benthic habitats, negative impact on recreational use of beaches and shorelines when drifting ashore and hazard to navigation when floating inside shipping lanes and coastal areas. Most of the research on the status, extent and solutions to the ALDFG challenge have been done in the marine fisheries of the developed world, with very few studies in inland fisheries. The objectives of this research are to improve the understanding of the status, extent and management of ALDFG by providing evidence-based ALDFG estimates, drivers and current management regimes to aid in developing mitigation strategies specific to inland fisheries. The proposed thesis will include: 1) an in-depth global account of the state of ALDFG in inland fisheries in the last 50 years through a systematic review and analysis; 2) estimates of gear loss, understanding of the drivers and analysis of available ALDFG management strategies for gillnet and longline fisheries in Lake Victoria, East Africa;  3) use of a gap analysis framework methodology to assess the robustness of existing policy environment and legislative arrangements concerning the management of ALDFG in Lake Victoria at the regional and riparian country level in order to identify gaps and provide recommendations for improved management; and 4) development of a comparative analysis of the transboundary management of ALDFG in Lake Victoria and the American Great Lakes to advance understanding of cross-jurisdictional ALDFG management in inland fisheries. The thesis will be a pioneering work on ALDFG and fishery-related plastic pollution in inland waters.

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https://umassd.zoom.us/j/99192100393

Meeting ID: 991 9210 0393

Passcode: 838266

DFO MSc Defense: Kevin Bennett

August 7, 2025 / / 0 Comments

“Development of a Field Computer/Camera System for Living Marine Resource Monitoring and Application to Improve the Understanding and Assessment of River Herring Migrations”

By: Kevin Robert Bennett

Advisor
Dr. Pingguo He (UMass Dartmouth)

 

Committee Members
Dr. Christopher Rillahan (UMass Dartmouth) and Dr. Robert Vincent (MIT Sea Grant)

Thursday August 21, 2025
1:00 PM
SMAST East 101-103
836 S. Rodney French Blvd, New Bedford
and via Zoom

Abstract:

This thesis describes an underwater video camera and a solar-powered single-board computer system designed and assembled with commercially available components to monitor living marine resources in their habitats. The system can directly observe and record migrating river herring, a collective name for Alewife (Alosa pseudoharengus) and Blueback Herring (Alosa aestivalis). River herring populations are depleted relative to historic levels due to decades of habitat loss and overexploitation; harvest is now widely prohibited. River herring in select river systems are monitored by human observers, and some have electronic counting systems. However, current fish-counting technologies are phasing out, and developing additional fish enumeration methodologies is a high priority. Video recording systems made with commercially available components are accessible, relatively low-cost, and offer standardization of equipment and data between users. Electronic video monitoring systems are also easily replicable and suitable for species such as river herring. To monitor and record the annual spring migration of spawning river herring in New England rivers, I created and deployed multiple solar-powered computers paired with underwater cameras. These systems are designed to operate in remote locations and record videos of migrating fish, which can then be reviewed to produce spawning population count estimates. Video monitoring systems are also useful for comparing fish stocks before and after restoration efforts and fish passage installations. This portable, solar-powered, single-board computer system is intended to be an economical, robust, and modular field computer system that can be easily customized to fit user needs. A video surveillance system provides observation coverage for the times of the day when human observers are not present; recorded fish migrations improve population estimates through more complete monitoring of the event. This system can also support upgrades and future expansion; a temperature probe can be installed alongside the camera. Recent developments in edge computing technology offer the potential for in-situ object recognition through on-board image processing. Natural resource managers can leverage a combination of consumer technologies to monitor ecosystems and make effective decisions.

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https://umassd.zoom.us/j/91540616096

Meeting ID: 915 4061 6096

Passcode: 068189

Dissertation Defense: Siddhant Kerhalkar

July 10, 2025 / / 0 Comments

Department of Estuarine and Ocean Sciences

PhD Dissertation Defense 

“Salinity Stratification and Lateral Variability in the Northern Indian Ocean: From Calm Diurnal Cycles to Cyclone-Induced Recovery”

By: Siddhant Kerhalkar

Advisor
Amit Tandon
Commonwealth Professor, Department of Estuarine and Ocean Sciences
UMass Dartmouth

Committee Members

Miles A Sundermeyer

Professor, Department of Estuarine and Ocean Sciences

UMass Dartmouth

Steven Lohrenz

Professor, Department of Estuarine and Ocean Sciences

UMass Dartmouth

J. Thomas Farrar
Senior Scientist, Physical Oceanography Department
Woods Hole Oceanographic Institution, Woods Hole, MA, USA

Kenneth Hughes
Senior Lecturer, School of Science
University of Waikato, Hamilton, New Zealand


Monday July 28, 2025
2:00 PM
SMAST East 101-103
836 S. Rodney French Blvd, New Bedford
and via Zoom

 

Abstract:

Monsoons over the Indian subcontinent deliver copious seasonal rainfall from June to November, yet their inherent Monsoon Intra-seasonal Oscillations (MISOs) remain poorly predicted. Errors in MISO predictions significantly affects regional and global weather forecasts. Improving MISO predictability requires a deeper understanding of ocean-atmosphere coupling and improved representation of upper-ocean stratification within the Northern Indian Ocean (NIO), particularly at mesoscale and submesoscale length scales. This thesis investigates upper-ocean variability at these scales under two key meteorological regimes preceding MISO onset: calm, clear-sky conditions and tropical cyclone events.

 

Chapters 2 and 3 of this thesis examine the spatial inhomogeneity in sea surface temperature (SST) evolution over diurnal and intra-seasonal timescales, respectively. Both chapters focus on how unique freshwater-driven salinity stratification contributes to this variability, utilizing remote sensing, in-situ observations, and 1-D modeling.

 

Chapter 2 reveals that while satellites show diurnal SST amplitude differences of O(1oC) over 100 km, in-situ observations capture finer-scale and more extreme variability. The upper ocean’s response to diurnal heating is inhomogeneous at over mesoscale and smaller lengths (< 100 km), particularly on days with Diurnal Warm Layer (DWL) presence compared to non-DWL days. Observations and complementary 1-D model simulations demonstrate that lateral differences in salinity stratification can account for up to 0.2oC differences in diurnal SST magnitudes for shallow mixed layer scenarios (< 8 m). Salinity stratification also modifies vertical DWL evolution at scales comparable to initial mixed layer depth.

 

Chapter 3 extends this analysis to intra-seasonal timescales, demonstrating a nuanced role for salinity stratification in modulating spatial variability in SST evolution. Depending on the surface forcing and water clarity, enhanced salinity stratification can either increase or decrease surface warming, thereby driving spatial differences in SST of O(0.5oC) over 14-21 days. Higher daily mean net heat flux and turbid water conditions lead to stronger warming and density enhancement in salinity fronts, whereas lower heat flux may suppress warming, leading to density compensation. An analytical threshold daily mean heat flux (Qcross) is derived to predict when stratification leads to stronger warming. This threshold typically falls between 103-130 Wm-2 in tropical open-ocean contexts, varying with initial and forcing conditions. These findings highlight a crucial interplay between salinity stratification, surface fluxes, and bio-optical feedbacks in shaping intraseasonal SST evolution and its spatial variability.

 

Chapter 4 presents rare in-situ observations of the upper ocean following Cyclone Biparjoy in the NIO. The post-cyclone wake, nearly 30 km wide, exhibited asymmetric buoyancy gradients and vertical structures of temperature, salinity, and velocity at its edges. This asymmetry reflects the influence of submesoscale processes like Ekman Buoyancy Fluxes and Mixed Layer Eddies, with downfront (upfront) orientation relative to southwesterly monsoon winds at the edges of the wake. These unique observations highlight how interactions between monsoon winds and underlying three-dimensional submesoscale processes, in conjunction with surface heating, accelerate the recovery of a slow-moving cyclone wake.

 

Collectively, the findings from this thesis highlight the dynamic nature of upper-ocean variability under contrasting meteorological conditions and offer physical insights that can guide improvements in MISO forecasting.

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https://umassd.zoom.us/j/92441261277

Meeting ID: 924 4126 1277

Passcode: 0109

DEOS PhD Defense: Elizabeth Emily Ells

June 30, 2025 / / 0 Comments

“Quantifying Nitrogen Removal via Natural and Engineered Remediation Strategies for Southeastern Massachusetts Estuaries”

By: Elizabeth Emily Ells

Advisors
Dr. Micheline Labrie (UMass Dartmouth)

Dr. Miles Sundermeyer (UMass Dartmouth)

Committee Members
Dr. Mark Altabet (UMass Dartmouth), Dr. David Schlezinger (UMass Dartmouth), and Dr. Craig Taylor (WHOI)

Tuesday July 15, 2025
11:00 AM
SMAST West 204
706 S. Rodney French Blvd, New Bedford
and via Zoom

Abstract:

Anthropogenic nitrogen (N) enrichment has degraded water quality and ecosystem function in southeastern Massachusetts (MA) estuaries and globally. In coastal communities like Cape Cod, nitrate from septic systems enters groundwater and discharges into estuaries, serving as a primary source of N pollution. This has prompted municipalities to explore innovative, cost-effective strategies to reduce N loading and restore impaired estuaries. This dissertation focused on in-transit and in-estuarine approaches for N reduction that rely on microbial conversion of nitrate to dinitrogen gas. Specifically, this dissertation evaluated: oyster-associated denitrification, macrophyte-associated denitrification, and surface-water permeable reactive barriers (PRBs).

Chapter One quantified denitrification associated with Eastern oysters (Crassostrea virginica) using aquaculture oysters collected from three temperate estuaries. Significant denitrification rates were measured in association with both live oysters and empty shells. In Lonnie’s Pond (Orleans, MA), these rates contributed an estimated 12 kg N2-N annually to the N removal budget based on a standardized deployment of 225 kg dry tissue weight. N removal via oyster-associated denitrification was comparable to oyster-enhanced sediment denitrification and made up almost half of the N removed through harvest. Thus, oyster-associated denitrification represents a potentially significant pathway that should be included in future N removal budgets.

Chapter Two evaluated macrophyte-associated denitrification through a case study of Mill Pond (Falmouth, MA), a temperate freshwater pond characterized by dense macrophyte growth and seasonal anoxia. The pond naturally attenuates N, reducing loading to the downstream Green Pond estuary. Previous research indicated that 50% of incoming N was attenuated within Mill Pond; however, known freshwater attenuation pathways (e.g. sediment burial and denitrification, and plant assimilation) failed to fully account for observed N losses. This study showed that macrophyte-associated denitrification accounted for an attenuation of 818 ± 80 kg N annually, resolving 67% of the previously unexplained N attenuation. This research suggests that macrophyte-associated denitrification is a dominant N removal process within this eutrophic freshwater pond, contributing to a 14% reduction in the potential watershed load entering Green Pond.

Chapter Three examined surface-water PRBs as an innovative N reduction approach for agricultural freshwater flow-through systems. These carbon-based treatment barriers were evaluated in laboratory column and flume experiments and deployed in the channels of two cranberry bogs in southeastern MA. Results from column and flume experiments and field deployments were synthesized in a conceptual model to evaluate the underlying factors (e.g., PRB design parameters, and biological and physical timescales) which combined to produce the observed measurements. Results indicated that surface-water PRB success depends on the co-occurrence of labile carbon, sustained anoxic conditions and sufficient flushing to support measurable nitrate reduction.

Collectively, this dissertation quantified N removal using three natural and engineered N reduction strategies currently being applied or considered in southeastern MA. Chapter One added empirical data necessary to determine the potential efficacy of oyster-associated denitrification and for integrating it into an existing oyster N attenuation budget. Chapter Two refined the N budgets in a eutrophic freshwater pond, and established macrophyte-associated denitrification as an important N removal pathway. Chapter Three developed and evaluated a retrofitted approach to the traditional PRB to treat agricultural waters prior to their discharge into coastal ecosystems; however, effectiveness in the field was limited by hydraulic interactions with the PRB. Together this work offers municipalities new low-cost and innovative tools to manage their N loads to reach compliance with total maximum daily loads prior to discharge in coastal estuaries, particularly when combined with other attenuation methods.

https://umassd.zoom.us/j/92396171223

Meeting ID: 923 9617 1223

Passcode: 482554

DFO Defense: Alison Frey

May 19, 2025 / / 0 Comments

Department of Fisheries Oceanography

“The Spawning Dynamics and Biology of Cod in Southern New England Offshore Wind Energy Areas”

By:

Alison Frey

Advisor

Steven X. Cadrin (UMass Dartmouth)

Committee Members

Kevin Stokesbury (UMass Dartmouth), Lauran Brewster (UMass Dartmouth), and Greg DeCelles (Ørsted)

Thursday June 5, 2025

1:00 PM

SMAST East 101-103

836 S. Rodney French Blvd, New Bedford

and via Zoom

Abstract:

Atlantic cod (Gadus morhua) supported a robust fishery through most of the 20th century, but due to overfishing and environmental change, stocks collapsed in the 1990s, and populations remain below target biomass levels. Successful spawning and recruitment are critical for stock rebuilding, but spawning is a sensitive period within the lifecycle of cod and is vulnerable to anthropogenic activities. The most southern cod stock off Southern New England is currently assessed to be overfished with overfishing occurring. Offshore wind energy development is occurring on a known spawning ground, Cox Ledge, which is designated as Essential Fish Habitat and a Habitat Area of Particular Concern, and may have impacts on cod reproduction. To characterize impacts of offshore wind development on spawning of Southern New England cod, data on habitat use and spawning dynamics were collected via acoustic telemetry to compare pre-construction and post-construction residency to the spawning ground (chapter 1). Environmental drivers of cod presence on Cox Ledge will be assessed with generalized linear models (chapter 2), and biological sampling will be used to estimate size at maturity to inform the data-moderate Southern New England stock assessment (chapter 3). This proposed work will aid in effective assessment and management of fisheries and offshore wind interactions with vulnerable living marine resources.

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Topic: Ali Frey Thesis Defense

Time: Jun 5, 2025 12:00 Eastern Time (US and Canada)

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https://umassd.zoom.us/j/94363529761

 

Meeting ID: 943 6352 9761

Passcode: 595695

 

DFO Defense: Angelia Miller

May 19, 2025 / / 0 Comments

Department of Fisheries Oceanography

“Impacts to stock abundance indices due to offshore wind development-driven changes to fishery-independent survey effort”

By:

Angelia Miller

Advisor

Dr. Gavin Fay (University of Massachusetts Dartmouth)

Committee Members

Dr. Steven X. Cadrin (University of Massachusetts Dartmouth), and Dr. Catherine Foley (NOAA NEFSC)

Tuesday May 20th, 2025

1:30 PM

SMAST East 101-103

836 S. Rodney French Blvd, New Bedford

and via Zoom

Abstract:

Offshore wind energy development is occurring throughout the Northeast Large Marine Ecosystem and will interact with many marine use sectors, including fisheries. Wind areas overlap spatially with the footprint of the National Marine Fisheries Service (NMFS) Northeast Fisheries Science Center (NEFSC) multispecies bottom trawl survey, which has been conducted since the 1960s, and whose data are relied upon for the assessment and management of many fisheries stocks in the Northeast U.S. This fishery-independent survey is confronted by potential preclusion of trawl sampling efforts due to the spatial conflict arising from offshore wind energy development. My thesis aims to quantify the impacts of preclusion to monitoring and operations and understand changes to species distributions and abundances within wind areas, which could jointly affect downstream data products, such as stock abundance indices, and fisheries management advice. The first phase of my study serves as a proxy for expected losses for comparison to my species distribution modeling and suggests that, when accounting for reduced trawl samples, annual estimates of relative abundance are lower than those calculated when including all samples. Additionally, when compared to a random, null model of effort reduction, preclusion of wind areas resulted in lower abundance estimates. Applying summer flounder (Paralichthys dentatus) and Atlantic mackerel (Scomber scombrus) as two case study species, I fit a spatiotemporal generalized linear mixed effects model (GLMM), generate simulated survey data, and calculate indices of abundance and population trends to compare survey outcomes with and without trawl samples inside proposed wind development areas in the second phase of my study. I employed the species distribution operating model to examine changes in fish density under assumed changes in species productivity, and to survey catch rates, as a function of offshore wind development. I found that the loss of samples inside wind areas has a substantial impact on estimates of abundance indices and population trends. This study contributes directly to implementation of the Federal Survey Mitigation Strategy for the Northeast U.S. Region (Action 3.2.2) as a part of the Survey Simulation Evaluation and Experimentation Project, which aims to assess potential impacts to the bottom trawl survey operations and data products and identify mitigation strategies to maintain data integrity. Furthermore, this study contributes to the current knowledge surrounding the impacts that offshore wind energy development can have on fishery-independent surveys, which globally is scarce.

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https://umassd.zoom.us/j/92249874120

Meeting ID: 922 4987 4120

Passcode: 747985

DFO Defense: Nicholas M. Calabrese

May 12, 2025 / / 0 Comments

Department of Fisheries Oceanography

“LOOK BUT DON’T TOUCH: MINIMALLY INVASIVE TRAWL SURVEY TECHNOLOGY”

By:

Nicholas M. Calabrese

Advisor

Kevin Stokesbury (UMass Dartmouth)

Committee Members

Steven X. Cadrin (UMass Dartmouth), Pingguo He (UMass Dartmouth), Michael J.W. Stokesbury (Acadia University), and Anna Mercer (NOAA Federal)

Wednesday May 28th, 2025

1:00 PM

SMAST East 101-103

836 S. Rodney French Blvd, New Bedford

and via Zoom

Abstract:

The School for Marine Science and Technology (SMAST) video trawl survey employs cameras mounted in the open codend of a trawl to identify and numerate groundfish. This minimally invasive survey technology has been used for semi-annual surveys of Atlantic Cod (Gadus morhua) in the Western Gulf of Maine since 2020. Accurate estimates of absolute abundance from the video trawl survey required estimates of catchability, efficiency, and fish length. This project aimed to address these requirements through three experiments and evaluate sampling methodology in a fourth experiment. First, a passive integrated transponder (PIT) tag detection system was developed, tested, and installed in the codend of the net. The custom-designed PIT tag detection system achieved an efficiency of 79%, with detection rates influenced by tag orientation and group size. Then, a mark-recapture experiment to estimate the efficiency and catchability of Atlantic cod was conducted using this system. A Petersen mark-recapture model, based on 1,094 tagged fish and six recaptures, accounting for both discard mortality and reader efficiency, yielded a doorspread efficiency of 12% and a catchability coefficient of 0.0024 per hour of towing. Next, the accuracy of length measurements derived from an off-the-shelf stereoscopic camera mounted within the trawl was assessed. This camera produced inaccurate length measurements, however, these findings helped inform the design of a custom imaging system. Finally, optical data from the survey were used to evaluate the effects of sampling design, tow duration, and sampling intensity on the variance of population estimates through a novel analytical approach. Stratified random sampling produced more precise biomass estimates than simple random sampling. In addition, CPUE mean, and variance increased with shorter tow durations. A 30-minute tow duration minimized within-tow variability and yielded the most precise abundance estimates, although this analysis lacked factors such as fish size and logistical constraints. Collectively, this research advances fisheries-independent survey methodology by addressing key limitations of new approaches.

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https://umassd.zoom.us/j/92695694559

Meeting ID: 926 9569 4559

Passcode: 106409

 

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For additional information, please contact Callie Rumbut at c.rumbut@umassd.edu

DFO Thesis Defense Announcement: Sean Boisvert

April 22, 2025 / / 0 Comments

Department of Fisheries Oceanography

“A Numerical Investigation of Size-Selectivity in a Modified Scallop Dredge”

By:

Sean Boisvert

Advisor

Geoffrey Cowles (University of Massachusetts Dartmouth)

Committee Members

Pingguo He (University of Massachusetts Dartmouth), and Douglas Zemeckis (Rutgers University)

Thursday May 8th, 2025

2:00 PM

SMAST East 101-103

836 S. Rodney French Blvd, New Bedford

and via Zoom

Abstract:

The US Atlantic sea scallop (Placopecten magellanicus) fishery, one of the most economically significant in the country, faces challenges related to unintentional capture of undersized scallops and other non-target species. Minimizing retention of bycatch and small scallops can result in economic gain and healthier populations. To address these issues, a modified scallop dredge was developed by Atlantic Cape Fisheries, LLC and features a modified cutting bar with a foreface angle that can be adjusted to a range of angles relative to the seabed to improve the size-selective sorting process. This study complements field research conducted using paired trawls of the modified dredge and standard turtle deflector dredge (TDD) by investigating the underlying hydrodynamic effects of different cutting bar angles and tow speeds on scallop escapement. A coupled computational fluid dynamics (CFD) and particle tracking model approach is used to analyze these effects. The unsteady viscous flowfield is computed with the FUN3D CFD flow solver using an unstructured body-fitted mesh to resolve the boundary layer on the dredge frame. The resulting time-dependent velocity field is used to drive simulations of the trajectories of scallops using a dynamical particle tracking scheme implemented in MATLAB. This model quantifies escape probabilities and other metrics such as shedding frequency, vertical particle velocities, average time to reach the twine top, average height achieved, and average particle trajectories. Simulations were conducted for multiple cutting bar angles, tow speeds, and scallop sizes to assess the modified dredge’s effectiveness compared to the standard TDD. We examined scallop trajectories across 26 size bins (30-160 mm shell height) for nine cutting bar angles (15°-75°) and the standard TDD at a nominal tow speed of 2.5 ms-1 (~5 knots), with additional experiments at 2 ms-1 (~4 knots) and 3 ms-1 (~6 knots) for three angles (30°, 45°, 60°). In total, 468 numerical experiments tracked 15 million particles, requiring approximately 50 hours of computational walltime. Results show that shedding frequency decreased as cutting bar angle increased. The 15° and 30° angle cutting bar angle yielded the highest escape probabilities, particularly for smaller scallops, exceeding the TDD by up to 40%. Higher angles (60°-75°) produced intermittent high vertical velocities but led to lower escape probabilities, attributed to less frequent eddy formation. Scallops released near the cutting bar (0.1 m above seabed, 0.4 m downstream) had the highest escape probabilities. Tow speed had a positive effect on escape probability, especially for the TDD configuration. This study bridges the gap between field trials and the fundamental understanding of scallop sorting mechanisms in the dredge’s wake. The findings of this research have important implications for the design and testing of modified fishing gear. The use of CFD modeling, as evidenced in this study, presents a valid, cost-effective alternative to traditional at-sea gear testing, allowing for extensive design exploration and optimization in a controlled and computationally efficient manner.

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For additional information, please contact Callie Rumbut at c.rumbut@umassd.edu
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