Aquaculture 2022

February 28 - March 4, 2022

San Diego, California

APPROACHES TO MONITORING AND MANAGING MARINE LIFE INTERACTIONS WITH OPEN-OCEAN AQUACULTURE FACILITIES: RESULTS OF A WORKSHOP AND ENGINEERING MEASUREMENTS

 

 Ann E. Bowles*, Mark Drawbridge, Pamela K. Yochem, Paul Dobbins, James Kohl, Daniel Codd, and Diane Windham

 

Hubbs-SeaWorld Research Institute

2595 Ingraham Street

San Diego, CA  92109

abowles@hswri.org

 



To date, p rotected marine vertebrates  have rarely been injured or killed during physical interactions with aquaculture gear.   Although  the evidence for this observation is  compelling when compared with  observed effects of fisheries, concerns persist because it is not backed by a substantial body of scientific research or modeling.   In 2019, under funding from the NOAA Saltonstall -Kennedy grant program, we conducted a workshop on the science and engineering of interactions between marine vertebrates and open-ocean aquaculture facilities.   The workshop focused on evidence of injuries and mortalities;  practices adopted by farms to  collect observations  and minimize interactio ns;  design and engineering of aquaculture gear ;  and physics and physical models of the behavior of lines and cages . 

E vidence presented during the  workshop and since supports the rarity  of entanglement and injury , amounting to fewer than 25 incidents  involving protected species over the last four decades .  Biologist p articipants noted that  this count does  not include the effects of  permitted  lethal  takes on  seals and sea lions after depredation attempts.  They also described gaps in effort to collect data.  D etailed observations of actual interactions are still very limited and  forensic approaches are rarely applied to incidents .  There is also substantial granularity in the information  available  on abundance and movements of species of concern .  Farmers, including two successful West Coast  finfish operations, described best practices for eliminating gaps, which included ongoing documentation and maintenance procedures.  Both farmers and engineers pointed to significant differences between aquaculture and fishing gear, foremost in the tension applied to all types of lines.   Engineers described ongoing efforts to model the behavior of aquaculture gear under the influence of waves and currents, and the dynamics of entanglement .  To date models of entanglement have focused only on fishing gear. 

 Line tension is hypothesized as an important factor in takes.  It is simplest to study in line-based operations (e.g., bivalves) .  W e made  initial physical measurements  of  a sample of line types  used in  both  aquaculture and  fisheries.  We included samples of line (10 – 13 mm [3/8” to &fraq12;”] nominal diameter ) weathered by a macroalgae grower for  up to  5 years.  Based on measurements of elasticity as tension was applied, weathering made the lines stiffer but less resistant to strain .   A  preliminary finite element model describing deflection  as  transverse force  was applied ( e.g., when an animal contacts a line) showed that even modest tension had a more important effect on line displacement than elasticity.   In summary, both  the  workshop and feasibility measurements emphasized the value of obtaining  detailed,  direct measurements of marine life interactions with aquaculture gear.