Engineering A Low-Cost Kelp Aquaculture System for Community-Scale Seaweed Farming at Nearshore Exposed Sites via User-Focused Design Process

Abstract

For over 50 years, government fishery agencies have recognized the need to transition excess fishing capacity in coastal waters to aquaculture. For the most part, investment strategies to move wild capture and harvest efforts into aquaculture have failed since the technology and capital expense for entry, such as large fish pens, was not conducive for acceptance. In contrast, low trophic level aquaculture of shellfish and seaweeds is suitable as an addition to the livelihoods of seasonal fishing communities and to those displaced by fishery closures, especially if vessels and gear can be designed around existing fishing infrastructures, thus allowing fishers to maintain engagement with their primary fishery, while augmenting income via aquaculture. In this study, an inexpensive, lightweight, and highly mobile gear for kelp seaweed farming was developed and tested over a 3-year period in southern Maine, USA. The system was different from existing kelp farming operations used in nearshore waters that use low-scope mooring lines, and heavy, deadweight anchors. Instead, a highly mobile, easy to deploy system using lightweight gear was designed for exposed conditions. The entire system fit into fish tote boxes and was loadable onto a standard pickup truck. The seaweed system had small but efficient horizontal drag embedment anchors connected to a chain catenary and pretensioned with simple subsurface flotation. The system was able to be deployed and removed in less than 4 h by a crew of three using a 10 m vessel and produced a harvest of 12.7 kg/m over an 8-month fall-winter growth period. The target group for this seaweed research and development effort were coastal fishing communities who move seasonally into non-fishing occupations in service industries, such as construction, retail, etc. An economic assessment suggests farmers would realize an 8% return on investment after3 years and $13.50/h greater income as compared to a non-farming off season job at minimum wage. This low-cost seaweed farming system for fall-winter operations fits well into a “livelihood” strategy for fishing families who must work multiple jobs in the offseason when their main fishery is unavailable.

Quantifying baseline costs and cataloging potential optimization strategies for kelp aquaculture carbon dioxide removal

“…Yields as high as 24 kg m -1 (Kim et al, 2019) and as low as 0.5 kg m -1 (Bruhn et al, 2016) have been reported from sugar kelp in northern temperate farming regions. (Stekoll et al (2021)) identified a published average of 12.5 kg m -1 , which aligns well with reported yields of 12.7 kg m -1 from a location about 87 km southwest of the case study site (St-Gelais et al, 2022). These values are derived from studies on kelp produced primarily for human food applications, in which maximum biomass yield was balanced with blade quality and fouling by epibionts.…”

Engineering design and economic analysis of offshore seaweed farm

“…These three models are made up of 14 cultivating lines of 60 meters length. According to the research of (St-Gelais et al, 2022), the peak biomass of kelp in the cultivating lines was about 12.67kg/m (±0.4kg). Hence, the kelp yield of these kelp cultivation systems produced 10642.8kg (±336kg) wet weight total over 840(60m×14) meters length of cultivation lines.…”

“…The labor costs depend on local labor rates and the expertise required for underwater construction. The man hours for the installation are estimated, as listed in Table 8 (St-Gelais et al, 2022).…”

“…However, according to the listed reviews above, except for St-Gelais et al (2022), none of the studies performed economic analysis or capital expenses assessment of their kelp farm platform taking into consideration the potential for profitability for low to middle income farmers. In addition, except for Moscicki et al (2022), most of the studies did not consider both regular (monochromatic) waves and random waves in the environmental loading scenarios of their models to prevent overprediction of expected tensions and overdesign of structure under investigation.…”

Concise review of genus Lessonia Bory

“…Kelp aquaculture has increased in the last few decades with progress made across the entire production chain, from the nursery to the post-processing of the harvest, as well as the development of new cultivation techniques and the domestication of new species (Le et al 2022;St-Gelais et al 2022). Many Lessonia species show potential for cultivation in open water and integrated with fish and mussel farms.…”