A 1995 study found in \cite…

A 1995 study found in \cite{diana2006increasing} indicated that less than one quarter of the total mortality of the perch fish population was due to anglers and cormorants. The study found that cormorants caused less than 6.4% of perch mortality. They conclude that control measures weren’t necessary at the time of the study. The study also mentioned the cormorants fed heavily during the April to May period. This suggests shrinking the hunting period to focus this period could have the desired effects of reducing fish mortality by cormorants, while keeping a sustainable population of cormorants.

\cite{ fielder2008examination} analyzed the literature and found the yellow perch population decrease in the 1970s to early 1980s was due to recreational fishing exploitation, not cormorants. In 1995, the population decrease of yellow perch was due to breeding reasons, most likely do to environmental factors such as water temperature and water levels. This study does suggest the cormorants had the strongest impact on yellow perch populations, but they weren’t the only factors. This suggests that the fishermen’s’ concern of the population decrease of yellow perch may not be entirely due to the cormorant population.

\cite{fielder2010response} found that a decrease in cormorant population was correlated with an increase in yellow perch population. They also state that there are many other factors that affect the yellow perch population, including commercial fishing. It isn’t only the cormorants’ fault.
They estimate 1000 cormorants and 500 nests in the Les Cheneaux Islands location to be sustainable. However, if 50 cormorants could be killed by a hunter each day, then in 20 days a single hunter could destroy the sustainable cormorant population, or 20 hunters in a day. That isn’t sustainable, even if the population was overpopulated initially. Decreasing the number of cormorants that can be killed by an individual would be better for sustainability.

\cite{ ostman2013estimating } found in its studies that cormorants do affect the catch rates of fishermen, however it isn’t as substantial as some may think. Fish have to be a certain size to catch with a net, and cormorants eat smaller fish. Cormorants were found to eat 13-34% of perch of size ready to be caught by nets. In other words, approximately 70% of fish cormorants eat aren’t affecting fisherman’s catch rate during that season.

\cite{ ostman2012cormorant } has found that a large cormorant population does decrease the population yellow perch, but have little effect on other types of fish. Therefore, the general decrease of fish species population cannot be completely attributed to cormorants.

It is also worth mentioning that hunting during nesting season isn’t a sustainable practice. Other birds that nest with cormorants will get scared and leave their nests, decreasing the population of non-cormorants as a result. Without the period of breading peacefully, the cormorant population will crash and possibly become endangered. From a touristic point of view, gunshots will be heard nearly year-long and people relax by lakes, and other cormorant-filled locations.

@article{diana2006increasing,
title={Do increasing cormorant populations threaten sportfishes in the Great Lakes? A case study in Lake Huron},
author={Diana, James S and Maruca, Susan and Low, Bobbi},
journal={Journal of Great Lakes Research},
volume={32},
number={2},
pages={306--320},
year={2006},
publisher={BioOne}
}
@article{fielder2008examination,
title={Examination of factors contributing to the decline of the yellow perch population and fishery in Les Cheneaux Islands, Lake Huron, with emphasis on the role of double-crested cormorants},
author={Fielder, David G},
journal={Journal of Great Lakes Research},
volume={34},
number={3},
pages={506--523},
year={2008},
publisher={BioOne}
}

@article{fielder2010response,
title={Response of yellow perch in Les Cheneaux Islands, Lake Huron to declining numbers of double-crested cormorants stemming from control activities},
author={Fielder, David G},
journal={Journal of Great Lakes Research},
volume={36},
number={2},
pages={207--214},
year={2010},
publisher={Elsevier}
}

@article{ostman2013estimating,
title={Estimating competition between wildlife and humans--a case of cormorants and coastal fisheries in the Baltic Sea},
author={{\"O}stman, {\"O}rjan and Bostr{\"o}m, Maria K and Bergstr{\"o}m, Ulf and Andersson, Jan and Lunneryd, Sven-Gunnar},
journal={PLoS One},
volume={8},
number={12},
pages={e83763},
year={2013},
publisher={Public Library of Science}
}
@article{ostman2012cormorant,
title={Do cormorant colonies affect local fish communities in the Baltic Sea?},
author={{\"O}stman, {\"O}rjan and Bergenius, Mikaela and Bostr{\"o}m, Maria Kristina and Lunneryd, Sven-Gunnar},
journal={Canadian Journal of Fisheries and Aquatic Sciences},
volume={69},
number={6},
pages={1047--1055},
year={2012},
publisher={NRC Research Press}
}