Extinction risk and overfishing: Reconciling conservation and fisheries perspectives on the status of marine fish populations

Background/Question/Methods

Anthropogenic disturbances are ubiquitous in the world's oceans, but their impacts on marine species are hotly debated. A longstanding and unresolved aspect of this debate is the relevance of IUCN Red List evaluations to marine fishes. Here, in a step towards resolving this debate, we systematically evaluate the status of marine fishes using both conservation (threatened or not) and fisheries (above or below reference points) metrics, compare alignment between these metrics by using a ‘hits, misses, false alarms’ framework, and diagnose why discrepancies arise between them.

Results/Conclusions

Whereas only 13.5% of Red Listed marine fishes (n=2952) are considered threatened, 21% of exploited marine fish populations with stock assessments (n=166) currently are below their lower (riskier) reference points and 40% are below their higher (more conservative) ones. Were these populations to be evaluated by Red List Criteria (A1), 29.5% would currently considered to be threatened with extinction. These conservation and fisheries metrics aligned well (70.5% to 80.7%, depending on the references points and time periods examined). Although false alarms, where sustainably fished populations were categorized by the Red List (A1) criterion as threatened, were common (27.7%) during populations' period of greatest decline, there were few for the current statuses of populations, especially when populations were benchmarked against more conservative reference points (6.6%). Moreover, egregious errors (where populations were categorized at opposite extremes of the fisheries and conservation metrics) were rare. Misalignment is heavily influenced by differences in the metrics used by the IUCN Red List and fisheries science to evaluate whether a population is in trouble. The Red List A1 criterion is triggered when declines exceed 50% over the longer of ten years or three generations, while fisheries reference points are tied to population productivity not rates of change, and may not be triggered until populations are less than 15% of unfished biomass. This mathematical disconnect makes many populations prone to false alarms during the fishing down phase of fishery development. Conversely, populations at low biomass and with long exploitation histories can be susceptible to misses due to decline rates being below IUCN triggering thresholds. Together, these analyses indicate that conservation and fisheries scientists agree on the statuses of exploited marine fishes in most cases, and that differences stem from the exploitation history of the population and the conflicting triggers between the two approaches.