CHANGE IN BIOLOGICAL REFERENCE POINTS UNDER DIFFERENT BIOLOGICAL, FISHERY, AND ENVIRONMENTAL FACTORS

Background. In this study, the relation between the biological reference points (BRPs) associated with Maximum Sustainable Yield (MSY) and the relevant biological, fisheries, and environmental factors were investigated. This knowledge is crucial to build the capacity for timely adaptation of management to the changes in an ecosystem. The research highlights the considerations that need to be taken into account when estimating and using BRPs in practice, and can thus lead to avoidance of overfishing. The BRPs were represented by MSY and the related spawning stock biomass (B-MSY), fishing mortality (F-MSY), and F-MSY proxies. Materials and methods. To obtain the BRPs, the method of Horbowy and Luzenczyk (2012)-that combines yield-per-recruit and spawning stock-per-recruit analyses with stock-recruitment relation models (Beverton and Holt (B&H) 1957, Ricker 1975)-was used. Data from the three biggest Baltic Sea stocks were used to test the sensitivity of BRPs to the model input data, and the influence of regime shifts or dynamics of the biological and fisheries variables on the BRPs. Results. The analyses show that an increase in maturity and weight at age generally led to an increase in BRPs. The opposite effect is observed in the case of natural mortality (stronger when the Ricker stock-recruitment (S-R) relation was used) and selectivity (proportion of the F of partially recruited age groups to the mean F of fully recruited age groups). An increase in the steepness of S-R models increases F-MSY and its proxies as well as MSY, and had a decreasing influence on B-MSY. Furthermore, the BRPs are very sensitive to the different data range divisions of the input data. Conclusion. When estimating BRPs, the time period of the input data should be selected with caution, and the appropriate time period should be based on strong biological, ecological, and environmental knowledge as, according to this study, all of these factors influence estimates of BRPs.