By Brett Glencross
A landmark study by Fulton and colleagues, analysing decades of data from the highly complex Gulf of Thailand fishery, underlines that ecosystems are not static. They are deeply dynamic, with constantly shifting baselines where both annual variability and humanity’s impacts change the very rules of the game. For decades, marine fisheries management has relied on calculating the exact ‘Maximum Sustainable Yield’ (MSY) for cod, tuna or snapper. While many of the large fisheries (e.g., Anchoveta or Blue whiting) might be close to single-species fisheries, most fish are caught as part of a mix of species, though gear type has a big impact on this too.
When we overfish top predators, the ecosystem doesn’t just become an emptier version of its former self; it restructures entirely. Prey species, like small-pelagics and fast-growing invertebrates explode in the absence of those predators. This altered ecosystem subsequently creates a new baseline with entirely different productivity rates. In such a situation the traditional, single-species MSY calculations for these waters suddenly become completely untethered from reality because the biological reality itself has been altered.
To solve this, the authors advocate for aggregate production models, looking at the ecosystem’s total biomass and yield rather than getting bogged down in the impossible task of tracking dozens of individual species. It is a pragmatic, elegant shift toward Ecosystem-Based Fisheries Management (EBFM).
This is where the paper’s true power lies. It exposes fisheries management not as a purely mathematical exercise but as a series of profound ethical and societal trade-offs. If your goal is focussed on maximising local employment and food volume, you will manage the ecosystem to favour high-yielding, low-value species. If your goal is maximum economic revenue, you will manage it for high-value predators, requiring completely different gear and far fewer boats. Or if you want to manage it for maximum biodiversity and abundance (an often-quoted environmental goal), you choose a different strategy again. Ultimately, there is no single solution, just various trade-offs.
Importantly though, the study provides an interesting observation. It notes that multispecies yield curves tend to be flatter than single-species ones. This means we can actively choose to dial back fishing pressure to protect vulnerable, slow-growing species without triggering a catastrophic drop in total catch. Fulton and her co-authors have provided a robust roadmap for a mature, aggregate approach to marine management. However, now the ball is now firmly in the court of government, policymakers and society. I guess those trade-offs never end…
