Comprehensive bycatch assessment in U.S. fisheries

We show an overall decline in bycatch since 2005, but highlight fisheries and gear types that may benefit from implementing novel bycatch reduction strategies.
Comprehensive bycatch assessment in U.S. fisheries

The solution to any problem, fisheries-related or otherwise, is to document its symptoms, determine how they change over time, and identify where to direct resources to obtain desired outcomes. Our group at NOAA has been working on the problem of fisheries bycatch, or the unintended catch of species that are not sold. Our desired outcome is increased fisheries sustainability by reducing the number of individuals and species that are bycaught. However, data limitations impede our ability to mitigate fishery bycatch at regional, national, and global scales. 

Where data are plentiful, it is our responsibility as scientists to enhance data accessibility and provide synthetic analyses of existing knowledge to properly guide management. To this end, we present the most comprehensive analysis and public database of fisheries bycatch in the United States, containing over 30,000 bycatch estimates for 95 US fisheries from 2010-2015.

The U.S. has long understood the necessity of collecting bycatch data to improve fisheries sustainability, and provides a global model of best practices for marine fisheries. Annually, the U.S. National Marine Fisheries Service supports nearly 1,000 independent observers who record and quantify bycatch events in dozens of federally managed fisheries. Each year this amounts to over 70,000 at-sea days for these dedicated observers.

Sustainable fisheries are an integral component of food security and economic well-being - Photo courtesy of Lee Benaka

These observations are summarized every few years in the National Bycatch Report (NBR). While the NBR is a valuable resource for determining national bycatch patterns, its format was not easy to use for a synthetic project.

Our goal with the study we published in Nature Sustainability was to present a synopsis of these hard-earned data as well as highlight which fisheries, gear types, and regions were performing well, and which had room to improve. In doing so, we compared U.S. fisheries to their international equivalents and provided a blueprint for how these data could be useful for other nations trying to optimize the management of their marine resources. Further, we wanted to facilitate use of these data by a broad swath of people, from schoolteachers to fisheries managers.

To accomplish this, we created a database by integrating raw data from the over 200 available NBR reports into a streamlined databased that allowed for synthesized analyses and insights. We further enhanced the NBR data by collating information on the conservation status of bycaught species and the quality of the bycatch estimates. To enable future use of these data, we also created a web-based application to coincide with the paper’s publication that allows these data to be queried, filtered, visualized, and downloaded.

Our findings for U.S. fisheries were encouraging. The rate of fish and invertebrate discards for all fisheries combined declined from 17% in 2005 to 10.5% in more recent years. This aligned well with the most recent measured global discard rate of 10.8%. Overall, we estimate that U.S. fisheries comprise 3.5% of discards globally. We also illustrate the relative impact of different gear types to specific taxa: gillnets disproportionally bycatch marine mammals, longlines are most detrimental for seabirds and sea turtles, and certain types of trawls (otter, bottom, and shrimp) had high bycatch of sea turtles as well as finfish and invertebrates (see figure below).

Bycatch patterns by gear type
Figure 2 from our paper illustrating that those fisheries with the highest proportion of fish and invertebrate bycatch are trawl and longline fisheries (a). Longline fisheries are also disproportionately responsible for the majority of interactions with sea turtles and seabirds (b). Marine mammals are most heavily impacted by gillnets, as shown in the MMPA Category I chart (c).

These findings provide a roadmap of where and how to target management to achieve our desired outcome of further reducing bycatch. For example, we can pinpoint fisheries where gear modifications or alternative management strategies like dynamic ocean management might be successful at mitigating bycatch. This helps ensure that managers get the most conservation return on conservation dollar spent.

While we note that bycatch is only one aspect of fisheries sustainability, it is one where we have ample data and ought to use it to the best of our ability, particularly in the United States. However, analogous data are often unavailable internationally, rendering global comparisons difficult or impossible. As a result, we hope our work encourages other nations to collect and disseminate their bycatch data to coordinate global efforts toward solving the issue of bycatch in marine fisheries.

Laysan albatross
Laysan albatross breed in the Hawaiian Islands, are found throughout the north Pacific, and are bycaught in U.S. fisheries - Photo by Matt Savoca

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