Introduction

The phenomenon of Epizootic Shell Disease (ESD) arguably destroyed commercial lobstering south of Cape Cod. Its incidence has increased north of Cape Cod in the Gulf of Maine and Georges Bank and we can ask whether it is following a similar pattern in the Gulf of Maine where it could be a major economic factor in the region for both Maine, New Hampshire, Massachusetts as well as Canada. The NOAA NE Groundfish Survey, paused in Spring 2000 due to the pandemic, was re-established in Spring 2021 and the protocol developed for surveying for ESD was carried out.

The relevant data sets from NOAA NMFS were transformed to provide appropriate input for analysis, testing the assumption of random occurence of ESD. If uniform across the Gulf of Maine and Georges Bank, it could be evaluated by a Chi Square test of the contingency tables of numbers of ESD and non-ESD lobsters observed in trawls, clustered so as to make numbers of ESD lobsters high enough within groups to allow clusters to be observed and tested if they meet the low sample number limits on testing contingency tables using Chi-Square methodality (McHugh 2013). If clustered in the available data, one could proceed to explore what was causing the clustering.

This report focuses on one season of data, Spring 2021, but could be applied retrospectively to the other three available data sets Fall 2018, Spring 2019 and Fall 2019. Application of the Chi-Square test to sequential strings of trawls from the Gulf of Maine and Georges Bank in Spring 2021 suggests ESD is clustered and Monte Carlo examinations of random collections of trawls confirm the importance of the sequential sets as capturing that clustering. This clustering has relevance in the further discussion of whether ESD should be more correctly considered enzootic or epizootic which is also related to discussion of 'areas of endemism' (Cassagranda and Lizarralde de Grosso 2013).

Methods

Data Collection

The collection of American lobster ESD data was accomplished using the protocols established in the FSCS2.0 computer directed protocol that involves protocols for all the NE Groundfish Survey organisms and includes online guides at four workstations devoted to the survey. Three of the workstations are manned each by a team of two, a cutter and a data recorder. The FSCS2.0 computer directs the protocol to be followed for each organism being worked on at a given workstation. A head workstation is occupied by the watch chief who decides how many baskets of an organism will be processed in each trawl. If a very large catch of an organism has occurred at a trawl site the watch chief will do a sub-sample of the baskets to establish which organisms are to be worked up at a team workstation. Chosen samples are then worked up and data on lobsters includes the trawl number that has metadata including all physical information about the trawl site (time, latitude, longitude, depth, and CTD (concentration, temperature, density) associated data). Within the sample each lobster has its sex, carapace length (CL), condition of legs and claws, presence of barnacles determined and state of ESD determined on a 4 point scale (0-3) (Smolowitz et al. 2005). ESD lobsters graded 1-3 were frozen for validation and measurements on land.