Date of Award

Summer 8-18-2023

Level of Access Assigned by Author

Open-Access Thesis

Degree Name

Master of Science (MS)

Department

Civil Engineering

Advisor

Kimberly Huguenard

Second Committee Member

Lauren Ross

Third Committee Member

Damian Brady

Abstract

Understanding the linkage between hydrodynamics, biofouling and shellfish growth enables Maine aquaculture farmers to optimize their net profit. This thesis focuses on lantern-net based Atlantic Sea Scallop farming, which is a relatively new industry in Maine with excellent economic potential. This study characterized and quantified the hydrodynamics, biofouling, and shellfish growth along a scallop longline at the Darling Marine Center experimental aquaculture farm from July-Oct 2021. Its purpose was to investigate farm-wide associations of water, scallops and biofoulants that can be applied by aquaculture farmers to improve cultivation methods and act as foundational work for future research. Hydrodynamics were quantified with monthly tidal surveys with an underway Acoustic Doppler Current Profiler (ADCP) and a vertical profile and incident current angles from a moored ADCP near to the longline. Methods to measure in-water weights of biofouling on lantern nets were developed and applied on a monthly time scale, and scallop heights and weights were also recorded in parallel. Velocities local to the farm generally showed flow reduction in space and over time in the farm layer as lantern net mass and solidity increased due to biofouling and scallop growth, while flows accelerated underneath the farm- a phenomenon that occurred due to conservation of mass. The effects of friction imposed by the farm structure (inclusive of biofouling and scallops) upon the ambient hydrodynamics, were directly quantified as tidal asymmetries (ratio of D4/D2 tidal energy bands) and as normalized magnitudes of the after-farm velocities. Accumulated biofouling weight and scallop weight were shown to have a significant, linear relationship that varied throughout the water column on both the tidal asymmetries and normalized magnitudes, controlling for oceanographic conditions. The northern half of the longline (farthest into Lowes Cove) presented lower velocity magnitudes throughout the tidal cycle (≤1 cm/s) than did the southern half (≥1cm/s), and it also demonstrated lower shellfish growth but higher biofouling settlement and accumulation than the southern half. The orientation of ambient current relative to the longline (incident angles) and farm wake generation were examined to determine if farm orientation was a factor in this reduction in velocity moving northwards up the longline. It was discovered that the Darling Marine Center aquaculture farm was in its own wake for 65% of flood tide velocities. This likely effected shellfish growth negatively and biofouling accumulation positively, as downstream nets would experience decreased flow speed inside the wake of upstream nets. Further study is recommended to determine if rotating the farm would be beneficial to cultivation goals. This study demonstrated that the connection of hydrodynamics, shellfish growth, and biofouling in semi-sheltered lantern net farms is quantifiable and statistically significant. Findings underscore the importance of knowledge about incident current angles in farm siting and mooring orientation decisions, as well as providing foundational information on how biofouling, scallop cultivation, and local flow interact.

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