A California university study suggests that current approaches to rebuild fisheries based on maximizing harvest and stock size are insufficient, and more rigorous and computationally intensive approaches could facilitate conservation planning and resource management.
The University of California Berkeley research team analyzed decision-making processes for setting fish harvest quotas and estimated biomass, catch and profit for 109 fisheries through 2050. They concluded that current methods fail to rebuild many fish stocks, achieving a 55 percent recovery rate on average, while methods borrowed from robotics reached 85 percent global fish stock recovery by 2050, and increased economic returns.
Many fisheries that have been historically over-exploited are now considered to be rebuilding, with hope that current best practices could ensure the recovery of most overfished species by mid-century.
The results from the UC Berkeley research team, which included Milad Memarzaden and Carl Boettiger, appeared online in the Proceedings of the National Academy of Sciences.
The analysis suggests this optimism may be premature, as current projections typically assume managers can have perfect measurements of current stock sizes.
The research demonstrates how such an assumption can undermine rebuilding efforts under current best practices and even drive unintentional stock declines.
“I’ve never really thought about it nor am I very familiar with the field of robotics but there is nothing prescriptive in our management to preclude innovative analytic tools that could be employed to best estimate time frames to rebuild,” said Diana Stram, plan coordinator for the North Pacific Fishery Management Council in Anchorage, Alaska.
“For stocks such as groundfish where we may have better information and understanding of recruitment we can do a fairly good job of projecting stock status, but for stocks with highly variable or very low levels of recruitment such as some crab stocks at low levels of abundance, we are really dependent on estimation of random recruitment into the future to estimate rebuilding times,” she said.
Memarzaden noted that his understanding is that salmon management in the Pacific Northwest is based on a constant escapement approach, while commercial marine fisheries are managed using constant-mortality targets.
Maximum sustainable yield (MSY) is the maximum average annual catch that can be removed from a stock over an indefinite period under prevailing environmental conditions. As defined this way, MSY makes no allowance for environmental variability.
Fisheries scientists worked out MSY in the 1950s, and almost two decades later they discovered more dynamic strategies of which the most profitable was a so called “bang-bang strategy,” Boettiger said. In short, if the stock size is 150 percent of the biomass calculated by the MSY, increase the allowable harvest to get that biomass down or if 50 percent below the MSY, halt fishing.
The research team noted that many fisheries that have been historically over-exploited are now considered to be rebuilding, supported by the hope that current best practices could ensure the recovery of most overfished species by mid-century. They suggest by borrowing novel decision methods from the field of robotics that stock rebuilding can be achieved in the face of measurement and environmental uncertainty, while also achieving higher economic returns than expected under current approaches.
The complete study is available at EurekAlert, a publication of the American Association for the Advancement of Science, is online https://www.eurekalert.org/file/jrnls/pnas/pdfs/pnas.201902657.pdf