Assessing Shrimp (Pandalus Borealis) from Arnarfjordur (NW-Iceland) Using a Stock Production Model

Catch Per Unit Effort (CPUE) data and survey biomass indices of Arnarfjordur shrimp stock (Pandalus borealis) were used as tuning series for a surplus production model fitted using three different types of software. The three software, namely MS Excel, ASPIC, and R, all fitted the data in a similar way and gave roughly the same parameter estimates. The intrinsic growth rate, r, was estimated in the range of 0.91744 to 1.11, the catchability coefficient, q, ranged from 0.000088 to 0.000128, and the carrying capacity, K, ranged from 3162 t to 5790 t for the CPUE tuning series. For the survey tuning series, r was 0.408 to 0.629, q was 0.95 to 1.47, and K was 5512 t to 6350 t. It is observed that many of the model assumptions in the SPM are violated in this analysis. Apart from various limitations and violation of assumptions, the most important violations are the assumption that there are no species interactions that affect the abundance and productivity of the shrimp stock and the assumption of constant catchability. Though model assumptions are not met with the Arnarfjordur shrimp fishery, the survey tuning series is less violated in the model assumptions and fairly reasonably estimates the stock compared to that of the CPUE. It was found that the average estimation of MSY, BMSY, and FMSY were 776 t, 2977 t, and 0.18 respectively for the survey tuning series, and 1109 t, 2195 t, and 0.51 respectively for the CPUE tuning series. Besides, relative fishing mortality and relative biomass were inversely related, and the scenario was different between the two data series. From a management reference point of view, the survey tuning series provided more reasonable estimations for all three software platforms than the CPUE tuning series. The interaction of relative fishing mortality over relative biomass for the survey tuning series is relatively more realistic based on empirical observation where fishing intensity, predation by cod, and the effect of physical parameters on the shrimp stock were revealed by many researchers.