Workshop on Baltic Salmon Management Plan (WKBALTSALMP)
This report contains the output of the International Council for the Exploration of the Seas (ICES) workshop on evaluating a draft Baltic salmon management plan (WKBaltSalMP). The main aim was to provide scientifically based responses to a special request received from the European Commission (EC; see EU request on evaluation of a draft multiannual plan for the Baltic salmon stock and the fisheries exploiting the stock). The process included two meetings attended by scientific experts, national managers and stakeholder representatives.
As requested, information on river size and estimated potential productivity was compiled and updated following consultation with national experts within ICES WGBAST (Baltic Salmon and Trout Assessment Working Group). Existing and alternative reference points for assessment of stock status and fishing opportunities were also examined. The group concluded that the currently used targets (50% and 75% of the potential smolt production capacity, PSPC) are inconsistent with the overall objective in the draft plan of achieving maximum sustainable yield (MSY). As a precautionary reference point Rlim was evaluated, defined as the lowest level of smolt production from which the stock would be expected to recover to its specific MSY-level (RMSY) in one salmon generation, if all fishing was completely closed.
Simulations developed specifically for the workshop allowed evaluation of requested recovery rates of individual wild salmon stocks under alternative commercial fishing scenarios. The simulations examined commercial harvest rates ranging from 0 to 0.9 (encompassing rates that gives maximum yield in the commercial sea fisheries, located between 0.2 and 0.3; Figure 5.1.1), with additional values examined below 0.1 to better illustrate impacts on less productive river stocks.
Neither the EC request nor the draft multiannual plan specify criteria for when (i.e. with what probability) a target has been reached. Therefore, stock-specific tables with simulation-based probabilities of smolt production being above alternative targets for each fishing scenario are presented. These analyses only included river stocks currently assessed analytically by ICES. For remaining stocks, such river specific probabilities could not be determined.
For river stocks not assessed analytically, correlative analyses between total estimated sea survival and recruitment over generations were performed. These results indicate that sea survival seem to play an important role in the development also for these stocks, similar to for those currently included in the ICES model.
A simplified stable-state population dynamics model was constructed to study trade-offs between mixed (sea) and stock-specific (river) fisheries in terms of achievable catches and proportions of stocks above/below reference points. This analysis illustrated that when the mixed fishery harvest rate is low all river stocks can achieve MSY, whereas when this harvest rate increases, smaller (less resilient) stocks fall below this target. That some smaller stocks fall below MSY (or even goes towards extinction) does not make a noticeable difference to the total yield. Hence, there exists an inbuilt conflict between overall production aims and protection of weak stocks that can only be resolved if mixed-stock sea fisheries for Baltic salmon are kept at a low level.
The report also contains requested comments on the draft management plan. The workshop identified that the draft has a strict focus on commercial sea fisheries, although the relative importance of recreational fisheries for Baltic salmon has increased significantly over time. The current two management units for EU commercial fisheries (subdivisions 22 to 31 and Subdivision 32) are further maintained in the draft, whereas evidence has accumulated that salmon are mi-grating between these areas more than previously recognized. The draft finally does not address management of hatchery-reared Baltic salmon more than marginally, despite large ongoing releases for various purposes in most countries.
Published under the auspices of the following ICES Steering Group or Committee