Let’s talk about salmon development…
Every November, salmon are spawned at the Craig Brook National Fish Hatchery’s broodstock facility. The broodstock at Craig Brook NFH represent salmon from several of Maine’s wild salmon rivers and from the Penobscot River. The eggs are disinfected and placed in plastic incubation trays, like the one above, and housed in the Incubation Room at Green Lake NFH, where they will spend the winter. The eggs are kept in flat trays that are continuously flushed with water and kept at natural temperatures. During the later part of winter (January), eggs begin to develop a black spot inside the egg. This is the fishes eye (see the eyed eggs in photo below.)
At this “eyed stage” the salmon eggs are agitated by pouring them from one bucket of water to another. This procedure, called "shocking”, will cause any unfertilized eggs to turn white so they can be picked out, leaving only live eggs in the tray.
The eggs at Green Lake NFH are incubated on heated water. The incubation water at Green Lake is gradually heated from 36○F to 50○F in early February. This is done so eggs hatch and young fry are ready to feed by the beginning of April. This advancement in egg development will allow the hatchery to grow a smolt in 17 months.
Genetic samples (blood or fin clips) are taken from fish that are spawned so their offspring can be tracked throughout their lives. The trays of eggs are coded with colored tapes to assure these genetic samples are accurately tracked. Eggs supplied to Green Lake NFH will grow to smolts that will be stocked into many of the very same rivers that spawned them. As the eggs hatch, develop into fry, parr, and smolts, the individual fish can be tracked using these genetic markers, which will move with them as they move from trays to tanks.
In addition to the eggs received from Craig Brook NFH, Green Lake NFH also rears smolts to broodstock size. These “domestic broodstock” are spawned at Green Lake NFH to provide 1.3 million eggs annually to private partnership salmon hatcheries. These eggs are also used for the Maine Fish Friends program. This program is a watershed curriculum program taught in over 140 Maine schools and developed by the Maine Council of the Atlantic Salmon Federation. The photo (below) shows Green Lake NFH’s “pit” - several raceways housing three and four-year old broodstock. Craig Brook NFH has a much larger broodstock facility, representing each of the six rivers of the Gulf of Maine Distinct Population Segment (DPS) with large pools instead of raceways.
Shortly after the eggs hatch at Green Lake NFH (late March), they are transferred to the Fry Nursery Tanks just outside the Incubation Room. The controlled environment at the hatchery optimizes survival and maximizes the number of fish that will smolt in 17 months.
These fry tanks are setup to hold up to 20,000 fry per tank. The total number of salmon fry at this time is just over 1 million fish. The fry will remain in the nursery for about 2½ months, given constant care and feeding daily until the time that they have outgrown the tanks and will be moved to the outdoor facility to become parr. At this time in their development, they are about 1 to 2 inches long and are being fed about every half hour. These fish can eat up to 5% of their body weight per day. Salmon eat a specially formulated high protein diet (about 50% protein, compared to about 26% for your family pet) from the time they hatch until they are released in the spring and receive seven day a week care 365 day a year.
The salmon fry that are moved outside will quickly grow to 3½” parr and by early July the number of fish in each pool will have to be reduced. The fish are split into several empty pools to prevent overcrowding. In early September, the parr now 5½” will begin to outgrow their space again and staff will begin the process of grading.
One million fish are “crowded” into small sections of the circular tanks and the smaller parr are forced through openings in the screens, leaving the larger parr in between the screen sections (see the photo above). These larger fish (approximately 650,000) are moved to empty tanks where they will complete their growth cycle to become 7-8” smolts by the next spring. By the completion of grading all 102 tanks on station will be in use. The smaller parr (approximately 350,000) will be stocked out to their natal rivers in September and October to continue their development in the wild.
In February, when the fish reach about 6½ inches in length fish tagging begins. Hatchery staff, along with staff from the National Marine Fisheries Service (NMFS), mark approximately 231,000 pre-smolts annually. Although there are different methods of tagging fish, last year’s team used visible colored elastomer tags injected at the corner of the fish’s eye. Varying colors allow for several combinations to be achieved. These tags will be visible on the fish even as an adult returning 2 years later. Marking fish allows biologists to evaluate fish movement through a river system and identify problem areas within the river. It also allows researchers to determine the overall survival of the fish from smolt to adult.
The tagged fish are passed through a piping system from the tagging area directly into tanks outside staff reposition the pipe to fill each tank. The outdoor facility (dubbed the “Big Top” by staff) contains 102 concrete fish tanks (thirty-four 20-foot tanks and sixty-eight 30-foot tanks). At the time the tagged fish are piped into tanks outside, they are considered parr.
In early April staff recognize the beginning of the smolt phase not only by the increase in size, but also by the way the fish behave. Smolts begin to travel in the direction of the water flow instinctively drifting with the flow as if they were drifting down a river. As they enter the smolt phase, their scales become silvery like the sea, a change from the brown and gray camouflage they adopted as parr to hide in the safety of the pebbly riverbeds. The smolts being to undergo a physiological change as well. Their internal metabolism is changing so they will be able to adapt from a freshwater environment to a marine environment. These smolts, now about 7 inches in length, are ready to be moved to the rivers to begin their long, hazardous journey to the sea.
Distribution of Smolts
In April and May, hatchery staff hand-load specially equipped trucks filled with oxygenated water and deliver these smolts to the rivers. Green Lake NFH staff travel approximately 20,000 miles in a six-week period stocking all 650,000 smolts during this period. The reach of the stocking fleet extends from Massachusetts to northern Maine. Currently, fish are released into the Penobscot River basin (ME), St. Croix River basin (ME), Merrimack River basin (MA-NH), Saco River basin (ME-NH), and the Dennys River basin (ME).
Atlantic salmon, like shad, alewives and striped bass, are anadromous fish migratory fish that spend their first few years in fresh water, swim to saltwater to mature, then return to fresh water to spawn. This is important because Atlantic salmon travel down Maine’s rivers and go out to sea to mature. A few years later, they will migrate from the sea to their natal rivers, completing the cycle and ensuring a continuing growth in numbers of Atlantic salmon. Over the next two to three years, these fish travel to Greenland and return to spawn in the same rivers where they were released.
Due to the passage of the Endangered Species Act and Congressional mandates, the Green Lake National Fish Hatchery is able to fulfill the commitment to protect the endangered Atlantic salmon, help it to thrive in our rivers and continue to increase it’s numbers. By raising the salmon at the Hatchery, Green Lake National Fish Hatchery is giving the salmon a hand-up in recovery. The goal is to restore these depleted populations and preserve the genetic legacy of the Atlantic salmon. The Atlantic salmon is truly a national treasure.