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Abstract

Analytical stock assessment models are routinely used in fisheries management. These models can estimate spawning stock biomass, recruitment, catch levels, and biological reference points for the sustainable use of commercially exploited fish stocks.

The data requirements for analytical models vary depending on the model type, but generally include information on age composition, maturity, recruitment and the relationship between spawning biomass and recruitment, natural mortality, fishing mortality, growth parameters, catch and effort, fishery-independent indices, gear selectivity, and length–weight relationships. A particularly limiting factor for applying these models to national stocks is the lack of detailed knowledge on catch composition (length, age, selectivity) and the absence of long time series of such data.

In this report, we present the development of an analytical assessment model for pikeperch in Lake Hjälmaren. The stock is of high importance to both commercial and recreational fisheries, and therefore many of the necessary data components have been collected over the years through various Sammanfattning Summary monitoring and research programs. Some input datasets show conflicting trends, which means the results should be interpreted with caution.

According to the model, the pikeperch stock in Hjälmaren is currently in decline, with decreasing spawning stock biomass and some signs of a weakened age structure. Nevertheless, the stock appears to have recovery potential, supported by the presence of a few stronger year classes that will soon enter the fishery. Management goals with associated biological reference points have not yet been established by managers. A test using recommended reference points from other stocks (F40%, B40%; Mace, 1994), suggest that the stock is currently above B40%, despite the recent decline in spawning stock biomass.

Although the model can provide a valuable baseline for future management of pikeperch in Lake Hjälmaren, it is important to apply the results cautiously due to the data limitations and uncertainty. Key priorities to improve the model include quantifying recent CPUE index for the commercial fishery, adding recreational catches and expanding biological monitoring of the stock. Until more and better data have been collected and the model produces more reliable estimates, we recommend that assessments of the Hjälmaren pikeperch stock continue to follow the current standard applied in Fiskbarometern (SLUs current system for assessing the status of commercial fish stocks).

Keywords

stock assessment; analytical stock model; biological status

Published in

Aqua notes
2025, number: 2025:31
Publisher: Department of Aquatic Resources, Swedish University of Agricultural Sciences

SLU Authors

Associated SLU-program

Lakes and watercourses
Use of FOMA data

UKÄ Subject classification

Ecology
Fish and Wildlife Management

Publication identifier

  • DOI: https://doi.org/10.54612/a.107qi8rvfh
  • eISBN: 978-91-8124-157-0

Permanent link to this page (URI)

https://res.slu.se/id/publ/145349