The bigger they are, the faster they fall, implications of size selective fishing on the spawning stock of Pandalus borealis in the Svartnes basin, (Balsfjord, northern Norway) as relates to size, age, growth, and abundance

Abstract

The Svartnes basin stock of Pandalus borealis Krøyer, 1838 was investigated in the east Atlantic boreal zone of Balsfjord (northern Norway). The scope of the study spanned 12 years (March 2010 - October 2021), including two periods; prior to January 2017, with no commercial shrimp fishing; and after 2017, with commercial shrimp fishing. The study sought to determine the effects induced by size selective commercial shrimp fishing practices on the Svartnes basin stock dynamics of P. borealis, as relates to size (carapace length), age (years), growth (growth performance index), and abundance (sampled catch). There were no discernible indices of change between year classes of P. borealis with respect to age and growth during the study. More time is required to fully observe the development of year classes beginning in and after 2017. Catch per unit effort exhibited a notable decrease following the onset of commercial shrimp fishing, as did the number of females retained in each sample trawl haul. The carapace length of females within the 95th percentile of the spawning stock, depicted a significant decreasing trend (F= 19.1, n= 19, p< 0.001). A reduction in carapace length of large females indicates the size selective effects of fishing pressures exerted by the commercial shrimp fishery. The development of the Svartnes basin stock of P. borealis should continue to be monitored over time, in response to the fishery. Increased understanding of changes in the stock dynamics as induced by external pressures, will help to further improve management practices, and protect the identity of individual stocks.