Science Advisory Report 2019/054

Assessment of the Maritimes Region American Eel and Elver Fisheries

Summary

• Stock status is not specifically addressed in this assessment because of deficiencies in the reporting of catch and effort in eel fisheries prior to 2016 and because key fisheries-independent indices of standing stock are not expected to be updated until 2019 or later.
• The 2015 and 2016 commercial large eel fisheries were smaller than those of previous decades in terms the number of available licences, the amounts of gear under licence, and in both the number of active participants and amounts of gear associated with active licences. Total commercial landings for the 2015 (36.1 t) and 2016 (44.1 t) eel fisheries were lower by a factor of about four than the 1993 to 2004 average.
• Commercial eel fishing occurred in 47% of the 93,718 km² of available habitat (AH) in DFO Maritimes Region in 2015, and 43% in 2016.  Eels were fished within 5.6% of the total AH, 5.25% of the drainage area under hydroelectric development, and within 92% (2015) and 86% (2016) of the estimated 38,032 km² of the total AH of habitat known to contain the swimbladder parasite Anguillicoloides crassus.
• The presently inaccessible 17,014 km² area of the Saint John River drainage lying above the Mactaquac Dam and below Grand Falls represents approximately 18% of the habitat historically available to the American Eel.
• The management strategy of limiting elver fisheries to rivers that have not been fished for large eels within any of the three prior years has limited the extent of overlap between the two fishery sectors to <10% of the habitat available to eels.
• The number of rivers where authorized elver fishing activities can take place increased from 65 in 1996 to 111 by 2004, and has been frozen at that number since 2004. Elver fisheries occurred in 92 (28.5% AH), 86 (27.4% AH), and 83 (27.5% AH) rivers during 2015, 2016, and 2017, respectively. The fishery footprint of directed elver fishing is modest at the regional level.
• Total annual landings in the commercial elver fishery exhibited an overall increase with time, with the five biggest years occurring in the last six years of the time series that ends in 2017. The annual Total Allowable Catch was not achieved in any fishing year.
• The potential exists for the area subjected to directed fishing on American Eel to increase with time, either through greater participation in the eel fishery or exchange of rivers presently fished for elvers for those that are larger in drainage area.
• Continuing to minimize the spatial overlap between eel and elver fisheries is an appropriate interim conservation measure until sufficient data is acquired to assess the extent of the cumulative mortality associated with fisheries at multiple life stages.
• Currently, one fishery-independent elver abundance index is available, from the East River-Chester.  Elver run size exhibited high inter-annual variability with runs during adjacent years differing by 50% or more in some years. On average, elver runs to the East River-Chester have increased since 1990.
• Spawner per Recruit (SPR) analyses were used to define mortality reference points for all directed fisheries and hydroelectric facilities. The mortality rate that results in a 70% loss of spawning biomass relative to the population without losses from human activities (SPR30), was recommended as the limit removal reference (i.e., the maximum acceptable human-induced mortality rate). The mortality rate that results in a 50% loss of spawning biomass would be the target value (SPR50).
• The SPR analyses applied to the assumed average life-history traits of Maritimes Region eel populations give fishing mortalities (F) corresponding to SPR30 and SPR50 of  0.166 and 0.09, respectively, considering mortality from large eel fishing only.
• Mortality reference points corresponding to SPR30 and SPR50 for eels for a single downstream pass through a hydroelectric facility were F = 1.204 and F = 0.693, respectively, considering turbine mortality only.
• The fishing mortality rates for elver fisheries corresponding to SPR30 and SPR50 are 1.2 and 0.69, respectively (equal to exploitation rates of 0.70 and 0.50), considering mortality from elver fishing only.
• The assessment of current mortality relative to reference points is limited to the elver fishery because of data limitations concerning eel harvests, eel biomass, and adult eel survival following downstream transit through hydroelectric facilities.
• Direct evaluation of elver escapement past the localized East River-Chester elver fishery (years 1996-2002, 2008-2018) estimated that annual removals by elver fishing represented between 5% and 65% of the total elver run to the river. These removal rates are below the limit exploitation rate of 0.69 in all years but were above the target exploitation rate of 0.49 in 5 out of 17 years.
• Under the assumption that elver recruitment across all fished watersheds and years has been at a level equal to the median observed values for East River-Chester, the existing river-specific elver fishery quotas have in some cases exceeded either the target fishing rate at SPR50 or the maximum acceptable fishing rate defined by SPR30. The potential for over-fishing to occur appears to be highest on rivers ≤250 km² in drainage area. It may be possible to set river-specific quotas that will vary with the watershed area using an estimate of elver abundance from the single monitored site, East River-Chester, as a guide.
• The running median abundance for the East River-Chester elver recruitment index is recommended as the principle indicator of status. For stock status updates, the 3-year running mean of elver recruitment at East River-Chester would be compared to the median value over the 1996 to 2018 times series. A re-assessment earlier than the proposed 5-year assessment schedule may be warranted if the 3-year running mean of the elver recruitment index for East River-Chester falls below 2.33 kg/km².

This Science Advisory Report is from the September 5-6, 2018 Assessment of American Eel in the Maritimes Region. Additional publications from this meeting will posted on the Fisheries and Oceans Canada (DFO) Science Advisory Scheduleas they become available.