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From the April 2012 Conservationist

Hundreds of trout in the water

One fish, two fish; enough fish?

Trout Stocking in New York State

By Phil Hulbert and Fred Henson

The large truck pulls up alongside the stream and the first bulging net of squirming, splashing trout is handed down to be released. A crowd starts to gather. Some are here because they know the fish are being stocked; others just happened by and are interested in what's going on. Everyone-young children and veteran anglers alike-have expressions of delight on their faces as the fish are carried down to the water and released into the stream.

A man empties fish from a mesh bag into a bucket
Hatchery staff scooping out fish to
be stocked. (Photo: James Clayton)

A few in the crowd question if a nearby stream will also be getting some fish, and someone asks how, and if, they can have some fish stocked into their favorite stream. Both are questions that have been asked many times as trout stocking is arguably the most familiar fisheries activity the public sees. In fact, stocking is a major tool used by biologists to manage a trout stream fishery, and approximately 3,000 miles of coldwater streams in New York are actually stocked annually.

So how do DEC biologists decide which waters should receive hatchery-raised trout and which waters have enough wild trout to sustain themselves? And for streams that are to be stocked, how do biologists determine how many trout to put in there? The answer is complicated, and one that took decades of studying streams where angler creel surveys (anglers are interviewed to find out how many fish were kept) and biological sampling surveys had been conducted.

Known as Catch Rate Oriented Trout Stocking (CROTS), the process that directs New York's trout stocking was actually developed nearly 30 years ago and remains the basis for DEC's stocking program today. CROTS uses biological data (wild and stocked trout mortality rates, and estimates of a stream's ability to support a trout population) and estimates of fishing pressure, angler catch and harvest rates to determine where and how many fish to stock. For example, if the current population (or standing crop) of wild trout occupies most or all of a stream's estimated capacity to support trout, stocking is not necessary. Likewise, waters where there is limited public access, very light fishing pressure, or ecological conditions that make trout survival unlikely (such as high water temperatures or low oxygen levels), would not receive stocked fish either.

A boy with a red bucket full of young trout, pouring them into the water
Photo: James Clayton

When deciding how many fish to stock in an area, a manager's goal is to achieve a healthy balance between resident fish left in the stream and fish available for anglers. In New York State, the intent of the CROTS system is to attain an average catch rate of one fish for each two hours of fishing effort over either part or the entire fishing season. This rate was selected largely because it was the average observed in many of the historical creel surveys conducted in New York, and it was judged to be a satisfactory catch rate to most anglers.

With any management strategy, adjustments are often necessary. For example, high quality streams that can support larger numbers of trout, and streams managed with very restrictive creel limits (number of fish an angler can take) and high minimum length limits (smallest size fish an angler can keep), are typically managed to allow anglers to catch more and possibly larger fish than might be available if the statewide limit (currently five trout per day, no minimum length limit) was in effect. This provides anglers with additional fishing opportunities, but still maintains healthy trout populations in those waters.

Many changes have occurred since CROTS was first developed, and so DEC is taking a hard look to see if more permanent adjustments should be made. Together with the Cornell University Cooperative Fish and Wildlife Research Unit, DEC biologists are currently working on a statewide study to determine if the underlying assumptions in the system are still valid, and ultimately figure out what, if anything, needs to be adjusted. For example, when the system originated, most anglers kept the trout they caught. Today, however, many anglers release most, if not all, of their catch, even if the fish can be legally harvested. Therefore, a greater number of trout survive than was factored into the original CROTS model. Conversely, increased predator numbers such as mergansers, and an increase in extreme weather events associated with climate change could lead to more rapid depletion of stocked trout in some waters, which translates into lower catch rates.

The statewide study is being conducted on nine streams. Fieldwork began in 2011 and will continue for several more years. For each stream, biologists are: stocking known numbers of specially-marked fish which allows biologists to determine when they were stocked; conducting fish population estimates after stocking to assess the persistence of stocked trout (how long they remain/live in a stream section); and counting and interviewing anglers who are fishing the stream (a creel survey).

Fish are marked at the hatchery prior to stocking by clipping one or more fins in a pattern unique to that batch. Since multiple batches of fish are often stocked in the same stream during the course of the season, this helps biologists identify the rate at which fish from each batch are removed. DEC personnel look carefully for these clips during both the population assessments and the creel survey.

Biologists wearing waders and carrying nets walk down the center of a stream
Biologists use electrofishing to help
determine how many stocked trout
survive in a stream (Photo: Jim Zanett)

During a creel survey, a creel clerk is assigned to each stream to perform counts of anglers and to interview them about their catch. The hours that the clerk is present on the stream are based on a randomized schedule designed to capture representative angler use on weekdays, weekends and holidays. In addition to looking for fin clips and measuring harvested trout, clerks ask how long the angler has been fishing that day, how many fish they catch/release, and their zip code. Knowing anglers' zip codes enables biologists to determine how far anglers travel to fish a particular stream. Clerks also ask anglers whether they drive alone to the stream, or share a ride with another angler. This information helps biologists estimate the number of anglers based on a count of parked cars, very useful for streams where it is difficult to see all of the anglers from the road.

In addition to creel surveys, biologists are estimating trout populations to determine how many stocked trout survive in the streams. Biologists use nets to isolate a designated section of stream. A crew outfitted with equipment that generates an electrical field strong enough to immobilize the fish then makes three passes through the section. After each pass, the stunned fish are scooped into a holding tank and then weighed, measured, and examined for clipped fins (indicating whether they are wild or stocked fish) before being released downstream of the isolated section. Some fish elude capture during each pass, and the total number of fish captured on each pass should decrease.

Ideally, the field work for estimating the trout population is done twice a season: once within two weeks of stocking to assess early season mortality; then again toward the end of the season. Once all the data is collected, biologists can apply a mathematical equation that uses the number of fish captured on each pass to estimate the total number of fish present. Thus the number of trout stocked can be compared with the number of trout that are still present at two dates during the fishing season.

Last year, biologists and creel clerks had the opportunity to speak with numerous anglers who enjoyed hearing about the work being done. Hopefully, the next few years will provide many more opportunities like this, and shed light on jobs that need to be done before that first net-full of stocked trout hits the water.

DEC and Cornell are excited about re-examining the CROTS model to see how applicable it is to today's fishery. They know that New York licensed anglers have a significant investment in hatchery-reared trout, and are committed to make sure we use stocking to enhance recreational fishing in a way that makes scientific, social and economic sense.

Phil Hulbert is the chief of DEC's Bureau of Fisheries. Fred Henson is an aquatic biologist responsible for the coldwater fisheries unit.


Editor's Note: To read more about fish stocking in New York, see "Labor of Love" in the April 2011 issue of Conservationist.

Photo: DEC