Research Document 2020/017
2018 Framework Assessment of American Lobster (Homarus americanus) in LFA 27–33
By Cook, A.M., Hubley, P.B., Denton, C., and Howse, V.
Abstract
The American Lobster fisheries in Lobster Fishing Areas (LFAs) 27–33 have been active for more than 100 years, with variable levels of productivity throughout that time. The current Lobster stocks in LFA 27–33 are supporting some of the highest landings on record for the region. All of these fisheries are effort controlled, with a limited number of licenses per LFA, trap limits per license, defined season lengths and minimum legal retainable sizes.
The last framework assessment for these fisheries was conducted in 2011 (Tremblay et al. 2011) and thoroughly reviewed the data sources, provided some options for preforming stock assessment and directions moving forward. During that framework it was determined that fishery landings was the best proxy for Lobster abundance from the available information and that it should be the primary indicator of stock status with defined reference points (Tremblay et al. 2012). The risks associated with relying on landings as a proxy for abundance were noted. Subsequent stock assessments and stock status updates have focussed on the changes in landings, Fishermen and Scientists Research Society (FSRS) recruitment traps and commercial trap catch rates to provide stock status information to resource managers. The focus of the current framework was to continue the work of the previous stock assessment framework, include additional analysis and data to determine the best approach for providing stock assessment advice given our available data streams.
In this framework, all LFAs were examined separately, despite suggestions of linkages between LFAs through direct movement and similarity of population processes. This choice was made as each LFA is managed separately and several possess unique conservation measures which may impact observed trends in indicators.
The current data to assess LFA 27–33 Lobster stocks include landings, commercial catch rates, FSRS recruitment trap surveys, Port and At-Sea sampling. Each of these data sources provides information on the Lobster in sampled areas; however most of our extended time series comes from fishery dependent data sources and therefore largely reflect removals from the LFAs rather than the Lobster population. The FSRS recruitment traps and At-Sea samples provide a broader depiction of the Lobster in the region.
A range of indicators were either updated or developed based on these data sources. The indicators represented biological status (e.g. median and maximum size, proportion large Lobster, proportion of berried females, proportion of new recruits in the fishery, reproductive potential), abundance or biomass (e.g., landings, commercial catch rates, FSRS recruitment trap catch rates) and exploitation (cohort analysis or change in ratio). These indicators were separated into primary, secondary and contextual categories.
Primary indicators define stock status, through comparing time series trends to reference points. The proposed primary indicator of biomass was commercial catch rates. The proposed primary fishing pressure indicator was the exploitation indices estimated through Continuous Change in Ratio (CCIR). Commercial catch rates was suggested as a better index of biomass than landings as using landings makes the strong assumption effective effort will be constant through time. This assumption may be presently true, but changes in management measures, if for example, stock status falls into the cautious zone, or if fishing operations are altered, will affect the continuity of the landings time series. There is currently no removal reference for any Fisheries and Oceans Canada (DFO) Maritimes Region LFA, however, the time series of estimates of exploitation from the CCIR provided robust estimates which can serve as the basis for adopting a removal reference.
Secondary indicators will represent important time series trends which will be tracked individually, but no reference points defined. The proposed secondary indicators will be landings, fishing effort and the FSRS recruitment trap recruit and legal catch rate series. The remainder of the indicators will remain contextual with broad patterns tracked over time.
Methods to estimate by-catch through effort proration were provided with examples from LFA 27, 31B and 32 where up to date data was readily available.
A simulation model was developed to explore the biological implications of different Harvest Control Rules (HCR). Example simulations were conducted for several LFAs and HCR. 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 as determined from an analysis of tagging data. Other inputs include area specific size at maturity and CCIR exploitation rates. 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 Sizes (MLS), change in the duration of the fishing season, protection of a window size of Lobster and protection of Lobster above a maximum size.
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