Public Release: 


University of Washington


Recording how many fish are caught is one important requirement to measure the well-being of a fish stock -- if scientists know the number of fish taken from the ocean, they can adjust management of that fishery to keep it from being overfished. Missing catch data, however, are rampant, causing concern that fisheries around the world are overfished.

A new study by University of Washington scientists finds that in many cases, this isn't true. Specifically, misreporting caught fish doesn't always translate to overfishing. The study was published online in September in the journal Fish and Fisheries.

"While quantifying total catch is important for understanding how much is removed from the system, it is possible to manage sustainably even if we don't know those numbers," said lead author Merrill Rudd, a UW doctoral student in aquatic and fishery sciences. "This paper shows there are some situations where, just because there is unreported catch, it doesn't mean we are overfishing."



In other words, the catch reporting trends -- not the specific numbers of fish caught -- are the most critical elements to consider when trying to understand a fishery's overall status, the authors said.

"It turns out that if you know what the trend is in a fish population, it doesn't matter as much if you don't know the catch numbers perfectly," said Trevor Branch, senior author and a UW associate professor of aquatic and fishery sciences. "Now we think we know better what impact unreported catch has on fishery status."

A massive effort is underway through the University of British Columbia's Sea Around Us initiative to reconstruct the catch data for fisheries worldwide. It's clear from this work that misreporting at a constant rate happens frequently in fisheries around the world. The UW study connects with the reconstruction efforts by showing that many of these fish populations can still be well managed despite management being based on models using misreported catches.

Misreporting can happen at the dock, on the boat and in processing plants -- and many fish aren't counted due to illegal fishing, sport fishing or discarded fish.



"It might not be wise to allocate all of the monitoring funds toward understanding what the total catch is because you might be able to manage sustainably without that information," Rudd said. "Instead, if you could get a handle on the trends in each fishery, that might be a better use of funds."


"My initial reaction was, 'oh my goodness, we have been overfishing this whole time. When we model this, the fishery will be in a much worse state,'" Branch said.


"A takeaway of this study is to not be so alarmist when there are missing data, and instead understand the processes of how the data are used," Rudd said. "Catch data don't exist in a vacuum. To determine how the world's fisheries are doing, you must consider the catch data with any other information available to make the management decisions."


The study was funded by the National Science Foundation IGERT Program on Ocean Change.

For more information, contact Rudd at and Branch at

Related paper:
