Assessing the health of data-limited fisheries

About

With natural resources like forests and reservoirs, it is generally a straightforward process to determine the quality and condition of the resource in question: you can observe the health and coverage of trees and the level of water in a reservoir. For fisheries, it is not quite so simple - how can you assess something that you can’t fully observe? In the past, researchers and managers only knew the condition of a small fraction of the world’s fisheries - the large, valuable fisheries for which we have ample data. However, these well-studied fisheries represent only a few hundred of the world’s 10,000+ fisheries, meaning our view of the overall health of global fisheries has been skewed: more than 70% of the world’s total catch comes from unassessed fisheries.

In order to make more informed decisions on how to sustainably manage them, emLab Ocean & Fisheries researchers developed an innovative method for assessing the health of the world's data-limited stocks.

Approach

We coupled the compilation of existing stock assessments to an extensive database of characteristics of each unassessed fishery, such as time series of catch and fishery development and species’ life history traits. Building on fishery science, our method assumes that the status of a population is a function of its life-history traits and harvest history, and the manner in which these variables collectively affect fishery status is consistent across species with similar characteristics.

To predict the status of unassessed fisheries, we compiled a companion database of 7721 marine fisheries from the UN FAO landings database. This database determines the finest resolution for analysis—species caught by a country within an FAO region. After focusing exclusively on finfish and aggregating across countries for highly mobile species, our final data set contains 1793 distinct unassessed marine fisheries from around the world, comprising
23% of global landings. For each unassessed fishery, we applied the most data-rich model possible, yielding time-series estimates of stock status for each fishery

This approach does not produce precise estimates for individual fisheries, and therefore is not a substitute for formal assessment, but it does provide a method for estimating the status of collections (including the global status) of previously unassessed stocks.

Key Findings

Our findings indicate that biomass levels in the majority of unassessed fisheries are low, confirming our initial hypothesis that unassessed fisheries are in poor condition. At the time of our analysis in 2012, about 18% of unassessed stocks were collapsed. On the other hand, assessed stocks showed signs of ongoing recovery and stabilization at sustainable levels, a trend that is consistent regardless of the country that manages them. And while management institutions play a key role in determining the condition of fisheries, the biological characteristics of the target species can also render a fishery vulnerable to overfishing. For example, we found that many struggling fisheries target species with a specific set of life history traits, such as slow growth, late maturation, and large body sizes.

While our findings raise concerns about the status of global fish stocks, we also identified opportunities for improving fishery yields and conservation outcomes for many of the world’s most depleted fisheries. These improvements could be achieved in part by implementing innovative fishery reforms, such as data-limited stock assessments and rights-based fishery management. Our results suggest that significant food security and conservation benefits could be achieved if overfished stocks were rebuilt to sustainable levels: more than 60% of unassessed stocks would provide increased sustainable catches, and the average in-water biomass levels would increase by more than 50%. Most importantly, our results demonstrate that fisheries in regions or countries dominated by small-scale operations stand to achieve the greatest benefits, a promising finding for sustaining food security and vibrant coastal economies worldwide.

Partners

This effort was a collaboration with Dr. Ray Hilborn at the University of Washington, completed with support from the Waitt Foundation, the Walton Family Foundation, the Gordon and Betty Moore Foundation, the David & Lucile Packard Foundation, and the Oak Foundation.