Seaweed Reproduction and Harvest Rebound in Southcentral Alaska: Implications for Wild Stock Management

In Alaska, interest in harvesting seaweeds for personal use is growing and information on potential impacts of this activity on sustainability of wild populations is lacking. This study provides information on reproductive timing and size, standing crop, and harvest rebound of three commonly harvested seaweeds in Southcentral Alaska: the rockweed, Fucus distichus; the sugar kelp, Saccharina latissima; and the bull kelp, Nereocystis luetkeana. From March through October 2018, seaweeds were surveyed for reproductive status and harvested to determine how much biomass was available. From the harvests, individuals were measured to determine the size when they first become reproductive. Harvested plots were re-harvested to determine biomass regrowth after 2, 4, and 6 months. Fucus and Nereocystis were broadly reproductive over the summer, while Saccharina was not. The presence of reproductive Fucus and Nereocystis throughout the summer could buffer the impacts of late season harvesting. Depending on the species (e.g., Fucus), individuals that became reproductive at a larger size were associated with lower density and lower biomass areas with slower recovery. The amount of biomass available for harvest and the amount that regrew following a harvest were temporally variable but had spatial differences that were consistent throughout the summer. Regrowth following harvesting for all three species was generally low after only 2 months, but the amount of biomass after 6 months post-harvesting was sometimes comparable to non-harvested areas. This study demonstrated that to varying extents, seaweed harvesting may be sustainable if timing of reproduction, available biomass, and regrowth are all considered.