Research Document 2023/075
2019 Framework Assessment of American Lobster (Homarus americanus) in LFA 34–38
By Cook, A.M., Hubley, P.B., Howse, V., and Denton, C.
Abstract
The inshore commercial fishery for American Lobster (Homarus americanus) has been active for over 150 years in Lobster Fishing Areas (LFAs) 34–38. These areas cumulatively cover 34,000 km2 from southwestern Nova Scotia, north to the Bay of Fundy and along the New Brunswick coast to the Canadian-United States border. The fishery is active throughout the LFAs with both inshore and offshore components.
Lobster stocks in LFAs 34-38 have a long history of assessments which are conducted almost annually. The last framework for assessing Lobster in LFAs 34-38 occurred in 2013 with separate assessment documents for LFA 34 and LFAs 35-38. The most recent stock assessments for LFA 34 use landings, the Inshore Lobster Trawl Survey (ILTS) catch rate index, and raw commercial catch rates as primary indicators of stock status.
LFAs 35-38 were assessed as one unit with a single set of primary stock status indicators. These indicators include landings, raw commercial catch rates, and total abundance from the Fisheries and Oceans Canada (DFO) summer Research Vessel (RV) survey.
In this stock assessment framework the stock status indicators were re-examined and their methodologies for estimation evaluated. Background on the available data sources and analyses were described. The code to perform all analyses is available on a GitHub repository. This framework will provide information on ecological and environmental indicators, incrementally moving toward applying an ecosystem approach to stock assessments. Indicators will be estimated for each LFA separately. It was recognized that there are likely connections between LFAs and similar processes impacting production; however, each LFA is managed separately with unique conservation measures adopted.
There are three groups of indicators in this document, primary, secondary, and contextual. The primary indicators will be used to define stock status, and reference points will be developed. Secondary indicators are those in which time-series trends will be updated and displayed in subsequent stock status reports; however, no reference points will be developed for these indicators. The contextual indicators will be included in stock assessments, and will be infrequently updated.
LFA 34
In LFA 34, the time-series trends in abundance (or biomass) of several size classes of Lobster were examined across multiple surveys. From each of these surveys, two time trends were often identified using Dynamic Factor Analysis (DFA), showing a dramatic increase in recent years. This increase was also observed in the commercial catch rates as well as the total landings. Given relatively constant effort in this fishery, it has long been presumed that landings are proportional to total abundance. There was supporting evidence from the indicators of distribution and patchiness which suggest that the LFA 34 Lobster are more evenly distributed across a much broader range of habitats than previously reported.
The commercial biomass index and the relative fishing mortality (relF) indicators from the bottom trawl surveys were suggested as Primary Indicators with reference points developed based on changes in productivity. Secondary Indicators include landings, commercial catch rates, and recruitment indices.
LFA 35-38
Although LFAs 35, 36, and 38 were assessed separately, a common approach to providing stock assessment advice was proposed. Each LFA has fishery independent data collections, however none have a sufficient data density (or spatial coverage) to be used as a primary indicator of abundance. The combined LFAs 35-38 DFO summer survey series will provide Secondary Indicators to the overall Bay of Fundy area. The fisheries dependent commercial catch rate model was selected as the Primary Indicator of stock status as it provides information on the effort corrected catches in each LFA. The reference points developed for each LFA were based on the productivity changes within each area. Total landings is the longest time series of data within the LFA and as such it will remain a Secondary Indicator.
HARVEST CONTROL RULES
A simulation model was developed to explore the biological implications of different Harvest Control Rules (HCR). Simulations were conducted only for LFA 34 in this framework. This simulation model represents the first steps in developing a useful tool to describe some of the population processes across LFAs. The basis for the simulation is moult process model where moult frequency is dependent on degree days (temperature x time), as determined from an analysis of tagging data. Other inputs include area specific size of maturity, and available estimates of fishing mortality or exploitation. The simulation model tracks a Lobster cohort from late juvenile to adult stages through moulting, reproduction, fishing, and natural mortality. The outputs include total landings (numbers and weight) and egg production, and are used to determine the biological impacts of the type and relative magnitude of the HCRs such as changes in Minimum Legal Size (MLS), change in the duration of the fishing season, protection of a window size of Lobsters, and protection of Lobsters above a maximum size.
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