Those of us who fish, hunt or trap are well aware of what bag limits are: it’s how many of a species of fish or bird or animal we may legally kill.
We also are subject to rules that tell us how many of each species we can have in our possession at one time.
Those numbers are not arbitrary. The state determines what they should be to maintain healthy populations of whatever is being fished, hunted or trapped, and they can change from year to year.
Biologists can figure out approximately how many fish are being caught in a season and about how many anglers are out on Moosehead, but they don’t know the real impact because they don’t know how densely populated certain areas of the lake are with each species.
That will change for at least lake trout or togue, since the biologists have new nets for trapnetting them in deeper waters so they can tag them. Lake trout have become overpopulated in the past, and the state increased the bag limit to get them under control.
“The tagging study will really help us estimate the rate of exploitation from angling,” said Tim Obrey, Moosehead regional biologist with the Maine Department of Inland Fisheries and Wildlife.
That will be good information that helps them in the future. But how are bag limits determined now? It turns out that it’s complicated and scientific.
Here is the explanation offered by Obrey in his own words in his latest Moosehead Lake fishing report. The term “harvest” refers to being caught for food or trophy:
From time to time, we report information about how many fish are harvested or how many fish we would like to see harvested, and occasionally we are asked how exactly we come up with those numbers.
It’s a great question. It involves a fair amount of work, but it is one of the most important indices we use, especially on Moosehead Lake.
I liken harvest information to a store owner keeping track of inventory. It is essential to manage your business. You need to know what you have on your shelves and how much of it goes out the door.
With species like deer and moose, we require hunters to check their harvest. That’s relatively easy to do if you’re harvesting one or two critters and have a check station in nearly every town. Fish are a different situation. They don’t have UPC labels and it’s up to the fisheries biologists to check your fish.
We need two pieces of information to estimate harvest: The number of anglers (and hours) that fished on a lake in a given season and the rate at which anglers harvested fish.
To estimate angler use, we usually contract with the Maine Warden Service to fly a plane over a selected number of lakes several times a week to count the number of parties fishing at any given hour of the day. We also can count anglers by snowmobile on smaller waters.
We know that there are only a percentage of anglers out fishing. For example, if our angler surveys show that 80 percent of all parties are fishing at 10 a.m., then we can expand that aerial angler count by 20 percent to estimate total parties for the day.
The number of parties is then expanded by the average number of anglers per party to determine total anglers for the day. That number is expanded again by the number of hours each angler fishes to estimate total hours of fishing.
The second part of the harvest equation is the rate of harvest. When we are interviewing anglers either on the ice or at access sites, we ask them how long they fished and what they caught. From this information we can calculate the average number of fish harvested per hour.
So now we can combine the number of fish harvested per hour and the total estimated number of hours anglers fished to generate an estimate of fish harvested.
We see changes in catch rates over the length of the season, so we usually generate these estimates for each month, then combine them for the season.
For example, brook trout fishing is best in January and fades by March, so it would be less accurate to use the January catch data for March anglers.
It is a fairly expensive proposition to generate a use and harvest estimate on our larger bodies of water. It costs several thousand dollars for the aerial angler counts each season for this region.
We also must have an adequate sample size from our angler interviews.
On Moosehead Lake, it takes at least three staff to cover the lake during the winter months. We have just three permanent staff and can sometimes hire a temporary staff member, but that doesn’t leave much wiggle room to work on other lakes in this region, which has just more than 250,000 acres of standing water.
