The Unintended Catch: Population Declines in Greater Scaup due to Fishery Bycatch

This post belongs to a series written by students in the Conservation Biology course BSC4052 at the University of South Florida. This course provides an overview of major themes in conservation practice and related applied problems in biology, including: population ecology in the context of conservation, patterns of diversity, valuing diversity, threats to diversity, management actions and strategies for preserving diversity.

Athena Varvarezis is a senior at the University of South Florida studying Marine Biology. Growing up in Pennsylvania, she loved the wildlife in her backyard as much as the wildlife shown in television documentaries. Athena has always wanted to protect and preserve the nature she adored growing up for future generations, and that is what she plans to do post-graduation.

Article: Marchowski D, Jankowiak Ł, ŁAwicki Ł, Wysocki D, Chylarecki P. 2020. Fishery bycatch is among the most important threats to the European population of Greater Scaup Aythya marila. Bird Conservation International:1-18. DOI:10.1017/s0959270919000492.

Our Outdoor Neighbors

The Greater Scaup is a wide-ranging species of benthivorous diving duck. This is a type of aquatic bird that dives underwater to find food, such as mollusks, insects, and aquatic plants. Aquatic birds such these not only have an important ecological role, they are also indicator species, species that can be used to infer the condition of their environment (Lehikoinen et al. 2016; Marchowski et al. 2020). As such, The Greater Scaup, can be used to infer threats to other species that live in the same area. Currently, it is faced with serious long-term population declines due to habitat degradation, toxins, climate change, and fishing activities. If no measures are taken, this species will be at risk of extinction.

“Ducks on water” by Jean Beaufort shows two male Greater Scaup swimming. Source:

As demand for fish increases, so does the amount of bycatch. Fishing bycatch occurs when non-target species are caught in the process of fishing. This has been a problem for many wild species, including several species of diving ducks (Marchowski et al. 2020). Dominik Marchowski and colleagues recently conducted a study investigating the relative importance of fishing bycatch in the decline of a European population of Greater Scaup. This study is crucial to improve regulations and decrease mortality for this species and other diving ducks.

The Greater Scaup

Female Greater Scaup. Source: Pixabay

There are a few different subspecies of the Greater Scaup. For this study, research was done on the European populations that migrate mainly from Russia in the summer to Northwest Europe in the winter. This population is at especially high risk from fishing bycatch as it migrates to the southern Baltic Sea at the same time that fisheries using gillnets are active (Marchowski et al. 2020). The research team carried out multiple analyses using available data from previous studies on Greater Scaup abundance to create several models of population growth and estimate the direct impact fisheries will impose. Researchers had three main objectives: 1) to assess the extent of the impact bycatch has had on the Greater Scaup population in recent years;  2) predict future changes in population size and assess whether this population will be able to function long-term given mortality associated with bycatch; and 3) create a mathematical model to predict bycatch mortality based on estimates of vulnerability to bycatch and on area affected by bycatch This will allow future assessments of changes in bycatch mortality without extensive surveillance of the habitat.

Show Me the Dataset

The scientists found that fishery bycatch was responsible for significant population declines and confirmed to be the major contributor to the mortality of the Greater Scaup in Northwest Europe. Analyses focused on Greater Scaup populations in the counties where this species would fly to during winter; this includes Poland, Germany, the Netherlands, and Denmark. Of those, sites in Germany and Poland constituted the highest amount of bycatch, ranging between 86-97% of the total bycatch calculated. High mortality rates like these are non-sustainable. Within 30 years, the population is expected to drop by 57%, which will then label the Greater Scaup as ‘endangered’; fishery bycatch will have been responsible for over half of those deaths.

What Comes Next?

While the data collected makes the future look grim, this information can be used to prevent further population declines of Greater Scaup and other aquatic bird species. Restricting fishing gear such as gillnets in areas where Greater Scaup migrate and instead using bird-safe fishing gear will reduce bycatch, benefiting this species and other diving ducks that inhabit this area (Marchowski et al. 2020). Due to the Greater Scaups role as an indicator species, better protection for just this species can assist in conservation efforts for other species in the Baltic Sea. This study brought to light the extent of damage done by bycatch and therefore gives us the opportunity to correct our actions before it is too late. The Greater Scaup is only one of many aquatic birds facing extinction due to fisheries. Enforcing fishing rules in the Baltic Sea can set better expectations for similar fisheries around the world and help preserve the biodiversity of all aquatic birds.


Lehikoinen A, Rintala J, Lammi E, Poysa H. 2016. Habitat-specific population trajectories in boreal waterbirds: alarming trends and bioindicators for wetlands. Animal Conservation:88. DOI: 10.1111/acv.12226.

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Jeannie Wilkening

Jeannie Wilkening

I am currently a PhD student in Environmental Engineering at UC Berkeley where my research focuses on ecohydrology, which means I look at interactions between ecosystems and the water cycle. Before coming to Berkeley, I did my undergraduate in Chemical Engineering at University of Arizona and an MPhil in Earth Sciences at University of Cambridge, where my research focused on biogeochemical cycling in salt marshes. When I'm not in the lab, I enjoy knitting, hiking, watching too much Netflix, and asking strangers if I can pet their dog. Twitter: @jvwilkening

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