What information is collected from taking scale samples?

Scale samples of Steelhead provide a non-lethal way of determining the age and life history of the sampled fish. The life history traits extracted from the scales include: the number of years as parr, number of years as smolt, age at maturity, number of spawning events, total number of lake years and total age. The life history information provides insights into year class strength, recruitment, exploitation rate (harvest and angling mortality) and size-at-age information for each river that is sampled. Scale samples can also allow for insights into feeding habits of Steelhead using stable isotope analysis.

What information is collected from marking fish (‘clipping fins’)?

Marking animals is a very common, non-lethal tool used to get a population estimate (i.e. how many animals are in a certain area). In fisheries, a common way of marking fish is by clipping a fin. For our purposes, marking adult Steelhead allows us to generate population estimates for streams by using a mark-recapture method (Peterson estimate).

Removing a small piece of caudal fin tissue has also been used to evaluate Steelhead genetics along the North Shore.

Why can’t you mark fish every few years instead of every year?

The formula to generate a population estimate requires that fish be marked in successive years. Furthermore, it takes 2 successive years of marking fish to get 1 estimate, 3 successive years of marking to get 2 estimates etc., therefore the more years that you are able to mark fish for, the better understanding fisheries managers will be able to get regarding the size and health of the population. This information can then be used by fisheries managers to help make informed decisions by applying adaptive management, such as what was seen on the Neebing/McIntyre Rivers in 1999.

Why are population estimates important?

Population estimates generated by marking fish as part of the Co-operative Angler Program provide quantitative data which can be used by fishery managers to make informed management decision regarding. Without the data collected by the Co-operative Angler Program, fisheries managers would have far less data to make informed decision regarding Steelhead management. In some cases, qualitative data alone may be misleading regarding the overall health of a population. For example, Portage Creek currently shows all the signs of a healthy population (good levels of recruitment, varied age classes etc.), however, based on the population estimates we can show that the population has decreased 90% over the last 12 years.

What information is collected from tagging fish?

The primary purpose of tagging adult Steelhead is to monitor movement patterns. When a Steelhead is tagged the hope is that the tagged fish will be caught again, and the number will be reported by the angler. By having a unique identification number (tag) on the fish, we are then able to infer some details about that fish’s movement.

For example: Bob tags a Steelhead while fishing on River A in the spring of 2020. The tag is numbered 12345. The following spring Bill catches a tagged Steelhead with the number 12345 on River B. Bill knows that Bob tags Steelhead, so he tells Bob that he caught a Steelhead with the number 12345 on it in River B. Bob can then infer that the Steelhead he tagged has likely spawned in a different river than where it was born. This is referred to as ‘straying’.

Based on information collected from tag returns, it appears as though approximately 2% of Steelhead along the North Shore stray between streams. Straying is a good thing as it promotes genetic diversity between rivers, and acts as a buffer if something happens to a portion of the adults in a particular river. Ultimately, straying is what lead to Steelhead being present in nearly all Lake Superior tributaries.

A second benefit of tagging is age validation. Steelhead are aged by reading the growth patterns on scales. However, as Steelhead age the growth lessens over time which can make distinguishing the annuli difficult. By scale sampling previously tagged Steelhead, we can validate the age of the fish by double checking that the age we got by reading the scale matches with the age that was previously determined.

For example: Bobs tagged a Steelhead on River A in 2014. The tag number was 23456. From the scale sample, Bob determined that the fish was 3 years old when he caught it in 2014. Bob catches the same Steelhead in River A with the tag 23456 in 2021. Bob takes another scale sample from the fish. Bobs ages the Steelhead which proves rather difficult as the edges of the scales are worn down due to the fish being old, and the annuli are close together as growth has slowed down tremendously. Despite this, Bob determines from the scales that the fish is 10 years old. Although he isn’t certain on the fish’s age from the scale alone, the tag has validated Bob’s aging.

Why can’t you just use tags to mark fish?

The biggest drawback to just using tags to mark fish are tag losses. Tag losses occur when a tag detaches from a tagged fish. This can happen for many reasons such as: anglers accidentally removing a tag when trying to read the numbers, anglers removing a tag on purpose, or the tag simply coming out of the fish. The issue with tag losses in a mark-recapture study is that fish that were marked (with a tag only) may lose the tag and be recaptured in subsequent years. This would result in an over-estimate of the population which could influence fisheries management to lessen restrictions and lead to over-fishing.

For example:

Bob samples and marks 100 Steelhead in River A using tags in 2018. In 2019 Bob returns to River A and catches 80 Steelhead. Of the 80 Steelhead Bob caught in 2019, 6 of them were tagged from the previous year. After taking scale samples from each of those 80 fish and aging them, Bob determined that in 2019 the repeat spawning rate was 50% (this means that of the 80 Steelhead that Bob caught in 2019, 50% of them were present in the spawning population in 2018, 0.50 x 80=40). Here is Bob’s population estimate for River A in 2018

100 x 40 = 667

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Therefore, according to Bob’s data, the population of River A was 667 in 2018. However, what Bob is unaware of is that he also caught 3 Steelhead in 2019 that were tagged in 2018 but had lost their tags. Because the Steelhead were not marked with anything other than a tag, Bob has no way of knowing that these 3 fish should be included as recaptures. Therefore, Bob’s original population estimate is much higher than the population really is as he actually recaptured 9 Steelhead in 2019 while he thought he only recaptured 6. The formula for Bob’s population estimate should have been the following:

100 x 40 = 444

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This example shows that by not accurately identifying marked fish in subsequent years, the population was over-estimated by 66%. This not only shows why tagging is likely not as accurate of a mark-recapture method as clipping, but it also highlights the importance of samplers in properly identifying marks in subsequent years.

What are the alternatives to marking fish but still gathering similar information?

There are no feasible alternatives to collect a similar data set to what we currently collect without scale sampling and marking Steelhead when factoring in costs, preserving habitat, health of other species and species at risk, Steelhead health, volunteer time and legislation.

Why don’t you stop sampling Steelhead?

If the NSSA were to discontinue sampling Steelhead, there would be virtually no information relating to the status of Steelhead populations in the Canadian waters of Lake Superior. This would leave fisheries managers with almost no information when trying to make sound management decisions. Not having any information poses a huge barrier when something needs to be changed, such as implementing a new regulation. By continually monitoring as many Steelhead populations as possible, we can help to provide fisheries managers with the critical information needed to manage our Steelhead populations.

There are lots of Steelhead, perhaps stop sampling now and start again if things get worse?

Some people may feel as though continuing to sample and mark Steelhead while the populations are high, at least in Thunder Bay tributaries, is not needed and that we should only continue sampling after the populations have decreased. However, the purpose of sampling and marking Steelhead is to monitor the population health, therefore if we were to cease the program, we would not have a clear indication of whether the population is in fact in decline. Angling alone is not an accurate indicator of a healthy Steelhead population. Under some environmental conditions, Steelhead may have an easier or harder time navigating upstream. Similarly, anglers may find it easier or harder to catch fish some years depending on the flow of the river. Together, these factors likely influence Steelhead susceptibility to being caught. Therefore, drawing any conclusions based from angling success alone is largely speculative.

For example: in 2017, 370 Steelhead were marked in the McIntyre River and the population estimate was 3035 individuals. In 2018, 206 Steelhead were marked in the McIntyre River and the population estimate was 4900 individuals.

Even though there were 44% fewer Steelhead marked in the McIntyre River in 2018 relative to 2017, the population was 38% larger in 2018. This clearly shows that angling success does not necessarily give an accurate representation of population size as more Steelhead were caught during the year with a smaller population estimate relative to the year with a larger population estimate. Conversely, on some other tributaries where anglers are targeting staging Steelhead early in the spring, many Steelhead are caught repeatedly. This has been shown through the high number of tag returns that we receive each year. Without having a unique identifier, such as a tag, many anglers cannot accurately say whether the fish they are catching are all unique. Anglers that are unknowingly catching the same Steelhead repeatedly can give the illusion of a large population, when in fact the Steelhead simply may not be migrating much at that time. This is often seen during cold water periods.

When will you have enough information?

The purpose of biologically sampling Steelhead is to collect annual information which can be used by fisheries managers to help monitor Steelhead populations and to support fishery management decisions when needed. For fishery managers to make the most informed decisions, it is important to have as much up-to-date information as possible. The longer the populations are monitored the better understanding we will get about how the populations respond to changing conditions (both environmental and man-made), which can lead to better management practices.