By Max Campbell
Collecting accurate data about catch and bycatch in fisheries is of great importance for managing fish stocks and preventing overfishing into the future.
Currently, most available catch data comes from reported catch from vessel logbooks. This data has obvious limitations including: ease of reporting, lack of expertise in identifying catch, and conflicts of interest. These limitations could lead to biased catch and bycatch records.
Trained onboard human observers can address many of the potential biases in the catch recorded on fishing vessels, however, they are expensive and limited in supply. Instead, electronic monitoring (EM) offers a an opportunity to collect more accurate catch data on these fishing vessels.
In our paper (Brown et al. 2021 Marine Policy) we used a combination of logbook, human observers, and EM data from Palau, Federated States of Micronesia and the Republic of the Marshall Islands longline fishing vessels, to investigate differences among these methods. Further, we also describing complex patterns found catch and bycatch using advanced statistical methods.
We worked with The Nature Conservancy, who over a number of years have been helping these nations pilot electronic monitoring of their fisheries.
Dealing with catch data collected multiple methods in a multi-country setting has its challenges. This project required a great deal of care when processing the data, which was overcome by multiple researchers in our team performing detailed interrogations of the data.
We found that the retained catch reported in logbooks was up to three times lower than the retained catch reported by human observers and EM, and there was a lower species diversity reported in logbooks. Concerningly, we also found many discards were usually not reported in logbooks (including several threatened species such as several marine turtles).
Further, analysis of EM data revealed some previously undocumented correlations among several key catch and bycatch species in the fishery, that were likely induced by specific fishing practices (like use of certain types of bait).
We found that EM and Observer catch records were comparable, thus, EM may provide a suitable alternative to human observers. Where EM data seemed to provide a much more comprehensive representation of species composition and a more accurate catch data than the logbook records.