Date of Award

Fall 12-2021

Level of Access Assigned by Author

Open-Access Thesis

Degree Name

Master of Science (MS)


Marine Biology


Yong Chen

Second Committee Member

Bai Li

Third Committee Member

Amalia Harrington

Additional Committee Members

Damian Brady


The stock assessment of American lobster (Homarus americanus) plays an important role in managing the fishery in the Gulf of Maine (GOM). Various fishery-dependent and fishery-independent data are required in the stock assessment to estimate key fisheries parameters that define the population dynamics of American lobster. In the 2015 benchmark stock assessment, ventless trap survey (VTS) data were included for the first time to provide information about the sublegal lobster (carapace length < 83 mm) dynamics. However, the effectiveness of VTS data in monitoring sublegal lobsters has not been evaluated and we have little information on whether the VTS sampling design can capture sublegal lobster dynamics. The primary goal of this thesis research was to evaluate and determine whether the data collected from the Maine VTS provide robust estimation of design-based sublegal lobsters abundance index in the inshore GOM. To achieve this goal, I (1) estimated and evaluated variations in catch rates derived, respectively, from the first, second, and third ventless trap per site; 2) predicted sublegal lobster population at a high spatial resolution using generalized additive models (GAMs); (3) sampled the simulated sublegal lobster population following the sampling protocol used in the VTS program to derive a simulated VTS abundance index; and 4) compared the simulated VTS abundance index with the

predicted population abundance index in the simulated sublegal lobster population. The spatial scale of the study was defined by the National Marine Fisheries Service (NMFS) statistical areas in Maine, areas 511, 512, and 513. The lobster data used to develop the GAMs were from the Maine-New Hampshire Inshore Bottom Trawl Survey (BTS) from years 2006-2016. The VTS data from 2006-2016 were sourced as the observed VTS abundance index. VTS catch rate per trap was considered during the step of sampling the simulated sublegal lobster population using the VTS sampling protocol, and the predictive variables considered included depth and temperature. This study showed that there were no significant differences in abundance, sex ratio, and size composition of the juvenile lobsters caught by the three traps in a trawl used in a VTS and that the correlation between abundance indices from subsampling scenarios and corresponding observed abundance indices were all greater than 0.99. I conclude that the VTS provides a robust estimation of sublegal American lobster abundance index in the inshore GOM.