As challenging as that can be, it's nowhere near as tough as the job Ontario fisheries managers face in keeping track of fish communities in the province's 250,000 lakes. It just isn't possible to collect detailed information on each lake in the province -- and that's the challenge that led to the Fisheries Assessment Units (FAUs).
Of the 12 units in the assessment network, eight focus on inland lakes (Lake Nipigon, Lake of the Woods, Quetico-Mille Lacs, Algonquin, Muskoka Lakes, Haliburton-Hastings, Kawartha Lakes, and Lake Simcoe). These inland fisheries assessment units conduct long-term monitoring studies on a set of representative fish communities and lakes across the province.
Assessment work is also performed by the four Great Lakes Management Units (Ontario, Erie, Huron and Superior). Long-term monitoring by the Great Lakes Management Units supports fisheries management on the Great Lakes and contributes fisheries data upon which provincial policy recommendations are based.
Monitoring of inland lakes is based on the principle that lakes with similar fish communities can be treated as a "type" because they respond to stress factors in a similar and predictable manner. Identifying representative lakes by fish community type is based on the presence or absence of six major species: brook trout, lake trout, lake whitefish, northern pike, smallmouth bass and walleye. Knowledge gained from the study of these representative lakes is applied to the management of similar type lakes.
Assessment Units collect long-term data on fish populations, fish habitat and associated stresses. This data is analyzed to give MNR biologists a better understanding of how fish communities respond to different pressures and how this may affect the number or type of fish that a lake can produce. With this information, MNR can adjust its fisheries management strategies in areas such as fishing regulations and fish stocking.
Monitoring the Stress on Fish Communities
Stresses regularly monitored by MNR's Fisheries Assessment Units include:
- Eutrophication - or the accelerated aging of a lake, results when the supply of nutrients (phosphorus and nitrogen) to the lake increases. Nutrient supply is usually related to the amount of development (cottages, urban, agricultural) within the watershed. FAUs measure phosphorus and nitrogen concentrations in the water and monitor other signs of lake aging such as water clarity and deep water oxygen concentrations.
- Exploitation - means the harvest of fish through recreational or commercial fishing. Lakes can naturally support a certain level of harvest. However, if this level is exceeded (that is, if more fish are removed than can be replaced naturally), then fish populations can crash and may take decades to recover. FAUs regularly monitor angling effort and the harvest of sport and commercial species as well as other indicators of exploitation such as fish abundance, growth and survival.
- Introductions - Introduction of non-native species can have an impact on the native fish populations and their habitat. Examples of introduced species which have had significant negative impacts are zebra mussels, sea lamprey, and Eurasian water-milfoil.
- Physical alterations - Often when shorelines of lakes were developed for cottages, resorts or industry, significant and undesirable changes occurred to the nearshore fish habitat. Wetlands were dredged or filled. Bottom substrate and logs were cleared for swimming and boating. These changes had serious effects on fish spawning, nursery and feeding areas. FAUs attempt to document and describe the extent of these impacts.
- Water level fluctuations - Water levels in many lakes in Ontario are controlled for a variety of reasons including navigation, water power development, flood control and, historically, for logging. Although many lakes undergo natural fluctuations in water levels, artificial manipulations can have significant negative effects on fish populations by disrupting spawning and incubation. FAUs monitor water level fluctuations and spawning of important fish species.
- Acidification - Lakes may acidify as a result of acid rain and snow within the watershed. Acid precipitation results from the burning of fossil fuels such as coal and oil. FAUs measure the pH level of the water as well as the potential of the water to buffer further acid inputs (the alkalinity).
Field Studies
FAUs conduct a variety of field studies to collect important information on fish populations and the stresses affecting them. Examples of the more common and visible (to lake residents and anglers) field programs include:
- Trapnetting -- Trapnets operate on the same principle as minnow traps. Fish are captured when they are funneled into the net, and once inside are unable to find the narrow opening to get back out.
A piece of net called a "lead" is tied to shore and runs out to the tunnel entrance of the trap. When fishing cruising along the shoreline encounter the lead, they work their way along it out to the trap. Only fish large enough to be retained by the mesh making up the net are caught. Once caught, the fish are free to swim around inside the net. Minnows and the younger age groups of larger species can go right through the mesh of these nets and are, therefore, not sampled.
Fisheries technicians check the nets and remove the live fish. Some specimens are weighed, measured, have a scale sample removed (used to determine the age of the fish), and then are released. All the other fish are counted, then released. Tags are applied if fisheries managers need an estimate of angling mortality, or to determine fish movements.
From trapnetting data fisheries managers can determine growth rates, the size and age structure of fish populations, and the relative abundance of the various fish species. This information helps determine the status of the fish community. By knowing the current situation and trends from the past, fisheries can be managed to ensure a healthy future.
Trapnets are not effective for sampling all fish species. Because they are set in shallow water they tend to be good for catching warmwater species such as bass and sunfish, but not so effective for sampling coldwater species such as brook trout and lake trout.
- Gillnetting -- Gillnets are another type of sampling gear used by biologists to capture fish. Generally these nets are set on the bottom of the lake and can be placed in either deep or shallow water.
As the name implies, fish swimming into the net become entrapped by their gill cover plates. Gillnets come in a variety of mesh sizes. Generally, the size of fish caught is related to the size of the mesh. Large mesh sizes capture large fish but allow small fish to swim through freely.
Gillnets can be used in a couple of different ways. In some cases they are set overnight. Fish that are trapped in the gillnet for a long period of time, such as overnight, often die. However, these fish are sampled and provide valuable information for biologists. Small bones, called otoliths, that are found in the head of the fish, are removed and used to age the fish. Otoliths provide much more reliable age information than scales but they cannot be removed without sacrificing the fish.
Gillnets may also be set for short periods of time to ensure that fish remain healthy and can be released alive. Generally, in this situation, small mesh gillnets are used to entangle large fish by their teeth. This technique has been used successfully to sample brook trout and lake trout populations.
In both of the above cases, the nets are set at randomly selected sites in the lake. By keeping track of the number of fish of each species caught in each net, the biologist can determine the relative abundance of that species of fish in the lake. When the same sampling technique is used on several lakes, the results can be compared between lakes to assess the health of an individual lake relative to the average of the other lakes.
When using gillnets, the field crew collects the same basic data as described above for trapnets. Similarly, gillnetting provides biologists with the same basic information for managing the fishery and ensuring that fish populations remain healthy over time.
- Creel Survey -- The purpose of a creel survey is to estimate the total number of fish harvested by anglers, the effort by each angler to catch the fish, and the total fishing effort. Biological information such as size, weight, and age of the catch is also collected.
The creel survey is designed in much the same fashion as a public opinion survey. Samples are collected at random from morning and afternoon/evening periods, weekdays and weekend days, and from both shoreline anglers and boat anglers.
On each sample day a crew will cover the lake. If the lake is large, it will be divided into sectors and then one or more sectors will be covered. The number of anglers fishing on the lake or in the sector are counted, usually at two or more different times during the day. This allows an average fishing activity to be calculated for the day, since anglers are continuously coming and going.
In addition to these counts, the survey crew usually approaches some anglers to conduct an interview. Anglers are asked several questions, including where they live, what time they started fishing, how many fish of each species they have caught and kept. Often the survey crew will also ask to sample the angler's catch to measure length and weight and to collect scales to determine the age of the fish. All information collected is taken back to the office for analysis.
Creel surveys provide valuable information to fishery managers on fishing effort and harvest and the condition of the fish populations and how the situation might be changing over the years.
- Angler Diaries -- It is often not practical to conduct a creel survey on lakes with very low angler numbers, on lakes that are difficult to access or on very large lakes that are difficult to cover. In these cases, voluntary angler diary programs are a useful to collect information on angler use patterns and success rates.
Volunteer anglers are provided with a diary to record the details of their fishing trips. For each trip they are asked to record:
- fishing location
- date
- total time fished
- number of lines used
- numbers of fish kept and released
Although additional information, such as type of bait and fish length, weight and scales, is extremely valuable to the biologist it is usually left to the discretion of the angler to collect. Individual fishing diaries are treated as confidential; the information in the diary is available only to the person who submitted the diary. This ensures that the angler's secret fishing locations or techniques are protected.
At the end of the season, anglers turn in their diaries and the data are analyzed.
Angler diary programs are considered to be a cost-effective means of monitoring trends in fisheries and confirming information from other sources. They are also an opportunity for anglers to support management of the fishery.
- Shoreline Habitat Mapping -- Mapping of shoreline areas is used to identify critical fish habitat such as spawning sites, nursery areas and fish feeding areas. Mapping can be repeated on a regular basis, every few years, to look for changes in the extent and quality of habitat. Generally, this type of survey is carried out during the summer months when aquatic vegetation is well established.
The field crew slowly cruises the shoreline, noting on a map:
- the type of bottom substrate
- the type and extent of beds of aquatic vegetation
- any shoreline structures such as docks and boat houses
- the shoreline slope and vegetation
- location of shore dwellings and other structures
The crew may also take photographs or videos of the shoreline to serve as a historical record, and to help pinpoint important features such as spawning sites.
- Limnology surveys -- Limnology surveys provide Information on the chemical and physical characteristics of a lake. Such information helps MNR biologists evaluate the health and suitability of a lake for various fish species.
At different times of the year a limnology crew may visit the lake to collect water samples and make a series of measurements. The most common measurements include:
- an oxygen and temperature profile
- secchi depth (which measures water clarity and is related to lake productivity)
- pH and conductivity (which are also related to lake productivity)
The water samples are taken back to the lab where they are tested for chlorophyll a, alkalinity, phosphorus and nitrogen. Measurements and water samples are usually collected at the deepest point of the lake or basin. These results are used to characterize general conditions in the broader waterbody.
On some lakes, cottage associations or interested individuals may be involved in the collection of total phosphorous and secchi depth data. The program, called the "Lake Partner Program", is sponsored by the Ontario Ministry of the Environment.
- Radio Tracking -- Radio tracking is used to answer specific questions about a fish species. Radio tracking can provide information on such things as home range, seasonal movements, spawning locations, as well as temperature and habitat preference.
The radio transmitter the fish wears is custom built for size, weight, radio frequency, battery life, antenna type and its method of attachment to the fish. A common type is the transmitter that is surgically implanted in the fish. The fish is captured, anesthetized and then has the transmitter surgically implanted in the body cavity. The whole process takes about twenty minutes per fish. When the fish has recovered, it is released. It can then have its movements followed using a radio signal receiver.
The use of radio tracking allows biologists to answer questions that could not be addressed using normal fisheries assessment methods
