How can I write an effective five-paragraph position paper in the position of a stakeholder?

You don't say in your question which stakeholder you have chosen to represent in your paper, but given that the provided newspaper article by Fidelia Andy is written on behalf of the Yakama Nation's Fish and Wildlife Committee, let's assume that this is our stakeholder. We are arguing, then, to "restore balance and common sense," with our primary aim being aligned with Andy's: to address all impacts to threatened and endangered salmon runs and recalibrate the ecosystem so that it does not privilege sea lions over other endangered species, particularly salmon.

If we are going to put ourselves in our key stakeholder's position, the first thing we need to do is identify some key points in support of this position. We can get a few of these from this article, as Andy is making an argument in defense of her position and therefore lays out several significant points. These are:



The California sea lion population is "exploding," which is threatening endangered salmon.


The Marine Mammal Protection Act and the Endangered Species act are increasingly at odds with one another.


Sea lions have been federally protected for thirty-six years. This federal protection has achieved its original goal of increasing the sea lion population, but has had consequences on other species which were unanticipated.


Marine mammal experts say that these "unnatural" conditions will be exploited by an aggressive subgroup of sea lions until they are stopped. The sea lions are taking advantage of the fish ladder and its entrance at Bonneville Dam to prey on salmon.


At one time, before there were dams, the ecosystem functioned perfectly without this imbalance. Dams have upset the natural balance and that is why we now need to take action against "impacts" to endangered salmon—in this case, the sea lions.



This gives us a good starting point for further research. The question asks you to cite at least three sources and to provide evidence to back up any important claims. So, based upon these points from Andy's article, we might want to research:



Actual numbers and statistics on the California sea lion population, its growth rate, and the comparative growth rate of salmon. Here is a recent journal article which states that the sea lion population has tripled: https://onlinelibrary.wiley.com/doi/full/10.1002/jwmg.21405


Some figures to back up the claim that the salmon population and recovery efforts in defense of it have actually been hampered by the growing sea lion population, as the stakeholder claims. Here is a recent journal article whose findings support this: https://www.documentcloud.org/documents/4254787-Chasco-Et-Al.html


Evidence that sea lions are taking advantage of the fish ladder at Bonneville Dam—this is a key causal claim in defense of the stakeholder's argument, so we will need some hard evidence to support it. Here is a news article about this issue, which cites a federal report: https://www.opb.org/news/article/sea-lions-continue-salmon-feast-at-bonneville-dam/



Now that we have our three sources—although, of course, you may find others—we should be able to begin constructing the essay using the points above. In a five-paragraph essay, the first paragraph should be your introduction, setting out what position you are going to take and the gist of what you will argue. The final paragraph will be your conclusion, which draws your argument together and solidifies your points. This leaves us three body paragraphs in which you make your stakeholder's key points, putting yourself in the mindset of your stakeholder.

I have identified above three of the strongest arguments in favor of your stakeholder's position, for which there is supporting evidence from other sources. If you take a point as the basis for your three body paragraphs, this should help you get started.