Joint ICES/NAFO/NAMMCO Working Group on Harp and Hooded Seals (WGHARP)

The main objective of the working group was to review recent surveys of Greenland Sea harp and hooded seal pup production and examine harvest scenarios for these populations as well as harp seals in the White Sea. No new survey to estimate pup production of Barents Sea/White Sea harp seals was completed. No new survey information was available for the Northwest Atlantic.

The 2022 Greenland Sea aerial survey images were analyzed manually and with the aid of automatic detection methodology (deep learning). For assessment purposes, this report only refers to the manual counts. Correction factors based on staging surveys were applied according to established methodology. The 2022 Greenland Sea harp seal pup production estimate for harp seals was 92,769 (CV = 20.2%), which is significantly higher than the 2018 estimate but similar to that based on the 2012 survey. The hooded seal pup production estimate for 2022 was 13,509 (CV=12.9%), slightly but not significantly higher than the 2018 estimate.

Subsequent to the recent benchmark meeting, model development indicated that the model estimates of adult population size for the Greenland Sea population of harp seals is highly sensitive to the standard deviation on the prior for initial population size. The WG therefore concluded that the current version of the assessment model could not be used to explore harvest scenarios based on estimates of current or projected total population size. Moreover, given the fact that the estimate of current total population size is unreliable, it also did not allow for robust calculation of Potential Biological removals (PBR). Tentatively, two different approaches are presented that might be used to inform sustainable harvest levels until the model has been further improved and reviewed: 1) an adaptive management approach based on population trends and 2) PBR based on a conservative population estimate that is a simple scaling of the observed levels of pup production, based on plausible values of adult:pup ratios.

The Greenland Sea hooded seal population shows continued decline, and remains below the Lower Reference Limit despite no hunting since 2007.

In a recent review of the status of the Northwest Atlantic harp seal population, model fit to aerial survey estimates of pup production and annual reproductive rates was poor compared to previous assessments indicating underlying problems relating to model assumptions and/or structure. A new hierarchical Bayesian state-space model was fitted to the same data on pup production, annual fecundity, human removals, and environmental conditions used in the previous assessment to produce annual estimates of pup production and total abundance from 1952 - 2019. Data on age structure based upon random samples were also included, and the process model incorporated environmental stochasticity and several other improvements. The new model estimates were similar to the previous model through 1990 but then diverged, indicating that the population peaked in 1997 at 6.6 million animals, almost a decade earlier than modelled in previous assessments. After a period of decline due to high catches and poor ice conditions, the new model provides an abundance estimate of 4.7 (95% Credibility Interval (CI) 3.7-5.7 ) million in 2019, compared to an estimate of 7.6 (95% CI 6.6-8.8) million in the last assessment. The lower estimates of recent abundance reflect higher and more variable juvenile mortality after 2000 due to a combination of density-dependent and density-independent factors operating on juvenile survival. The new model also suggests a decline in equilibrium abundance (K) levels from 7.6 (95% CI=7.4 to 7.8) million Northwest Atlantic harp seals prior to 2000 to 6.8 (95% CI=6.7 to 6.9) million animals post-2000.