Benchmark Workshop on Selected Deep-Sea Fisheries Stocks (WKBDEEP)

The objective of this benchmark process was to propose and evaluate assessment methods and the data upon which they depend for the three stocks: Greater silver smelt in Division 5a and Subarea 14 (aru.27.5a14), Blue ling in Division 5a and Subarea 14 (bli.27.5a14), and Black scabbard fish in subareas 1, 2, 4-8, 10, and 14, and divisions 3.a, 9.a, and 12.b (bsf.27.nea). Greater silver smelt was previously assessed using Gadget (category 1) whereas blue ling and black scabbard fish using data limited methods (category 3).

Landings, discards, survey data, and commercial catch and effort data for all stocks were extensively reviewed and collated during the data workshop. For all stocks, revisions were made to the data preparations and methodology behind the derivation of the stock biomass indices, stock and catch weights, maturity data and natural mortality. All the terms of reference were covered during the data workshop and an agreement was reached on the data for to use for an assessment, projections, and reference points of each stock reviewed.

This was the first benchmark workshop for blue ling, while black scabbard fish and greater silver smelt were last benchmarked in 2013 and 2019 respectively. For all three stocks, considerable changes were made to the input data and assessment method, and consequently for reference points. For blue ling an age—length assessment model (Gadget) was developed, synthesizing available knowledge and data on the population dynamics. For greater silver smelt, SAM was proposed as an assessment method. The proposed assessment method for black scabbard fish is based on data limited methods (category 3). Sensitivity runs were conducted to investigate the sensitivity to key assumptions and the workshop reviewed and agreed on the final assessment method configuration.

The workshop further reviewed and agreed on the methods used to calculate reference points and forecasts and on the proposed reference points for blue ling and greater silver smelt.