Research Document 2018/034
Assessment of the Offshore American Lobster (Homarus americanus) in Lobster Fishing Area (LFA) 41
By Cook, A.M., Hubley, P.B., and Denton, C.
Abstract
The Lobster Fishing Area 41 (LFA 41) offshore Lobster fishery has been active since the early 1970s and is currently the only Total Allowable Catch (TAC)-based Lobster fishery in Canada. The TAC has been set to 720 t since the mid-1980s without change, despite increases in survey biomasses. The fishery currently has 8 licenses that are owned by a single corporation and are fished from a single vessel.
This stock assessment follows the Framework Assessment of 2017 (Cook et al. 2017), applying the methods and agreed upon primary and contextual indicators from that work.
Four multispecies trawl surveys conducted by two agencies, Fisheries and Oceans Canada (DFO) and the National Marine Fisheries Service (NMFS), occur within LFA 41 and adjacent areas. Each of these surveys provides indices of biomass and abundance, size frequency, sex ratio, distribution and environmental variables. Six at-sea observed trips are conducted each year, which provide further information on by-catch profiles, and Lobster size and sex information.
Time series of a suite of standard indicators including total abundance, median and maximum size, mature and immature sex ratio, patchiness of distribution, area occupied, abundance of large females and recruit abundance were used to describe the changes in the LFA 41 Lobster stock over time. Additionally, ecosystem indices including predation, bottom water temperature, and the Atlantic Multidecadal Oscillation (AMO) were provided to describe some of the external factors that may impact Lobster productivity. All indicators were combined and ranked through a modified principle components analysis to display the coherence in indicator trends over time. Overall, patterns suggest decreasing median and maximum size of the Lobster stock over time, as well as decreasing predation pressure and increasing abundance, distribution, bottom temperature, and AMO.
Data-driven primary indicators were assessed against the proposed reference points from Cook et al. (2017) with overall stock status being in the Healthy Zone as all four surveys are above their respective Upper Stock Indicators (USIs). The LFA 41 Lobster stock has been in the Healthy Zone since 2002, and it has not been in the Cautious Zone since the time series began in 1981.
The reproductive-potential primary indicator, which has long been considered an important component of Lobster stock productivity, remains above the upper bound. This integrative measure incorporates the size distribution of the female Lobster, as well as the abundance-at-length to estimate total egg production. Although median and maximum size are decreasing, which would result in a decrease in mean individual fecundity, the increase in abundance more than offsets this reduction, resulting in the high levels of reproductive potential.
The levels of bycatch in the LFA 41 Lobster fishery have been declining in recent years and currently represent 1.4% of total landings, based on 17% observer coverage. The most frequently captured non-target species include Jonah Crab, Cusk, Atlantic Cod, Red and White Hake, and Atlantic Sea Raven. The non-retained Lobster, which includes berried, v-notched, culls (missing one or two claws), and undersized Lobsters, represent 23% of total landings. In 2016, soft-shelled and cull Lobster account for 28% and 43% respectively, which increased from 2% and 26% in 2015.
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