2010 Chautauqua Hatchery Muskellunge Mortality
In late May and June 2010, muskellunge fingerlings being reared at Chautauqua Hatchery experienced unusually high mortality as they transitioned from live brine shrimp feeding to dry feed. Diet transition for species such as muskellunge can be difficult. In recent years, the muskies at Chautauqua Hatchery typically made the transition without excessive mortality. What was different this year? This was the first year in which dry feed from a new contract vendor was used for early rearing at Chautauqua Hatchery. By the time it became apparent that this feed was not being accepted by many of the fingerlings and an alternate feed was obtained, the fish had already "split" into those that were going to survive and grow and those that became weak and died or were cannibalized.
DEC Fish Food Contract
DEC's current fish food contract was established in summer 2009. The contract specifications included minimum levels of protein and fat, and specified that manufacturers must use an existing production feed ("off the shelf") that would produce satisfactory growth and survival of fish receiving it. The nutritional requirements were established by DEC's fish culture staff under the guidance of personnel from the Tunison Laboratory of Aquatic Science in Cortland, New York. The 2009 contract did not specify exact ingredients and percentages of each ingredient whereas previous contracts (so called open formula diets) did. This specific change from open-formula diets to off-the-shelf feed was made to encourage feed companies to bid on our contract. For years, only one company had bid on DEC's feed contract, and in recent years the quality of their products and service to DEC had diminished. The first shipments of feed from the new contract vendor occurred in August 2009; additional shipments were delivered every three months after that. In April 2010, Central Office Fish Culture Program Managers and Hatchery Managers/Assistant Managers met to review the performance of the contract feed at different facilities and with different species of fish. Based on that internal review, there was no reason to anticipate a catastrophic loss of muskellunge due to non-acceptance of the new feed.
The numbers of eggs that were taken and that hatched were adequate to meet current muskellunge production and stocking needs. By the third week of May, the young muskies began to receive dry feed and brine shrimp in combination, which is standard practice. During the next week, brine shrimp feeding was reduced, and dry diet only was offered beginning May 28. There were indications that feed acceptance was low (dry feed not seen in rounded bellies), but this was not judged to be alarming. Limited acceptance of the feed continued for a few more days and staff believe that the fish had begun to separate into survivors and non-survivors (pinheads) by June 1. Dry feed was supplemented with brine shrimp in an effort to save some of the pinheads from starvation and mortality. Alternate very high quality dry feed was ordered on June 3 with overnight delivery. This very high quality dry feed, mixed with contract feed and supplemented with brine shrimp, was fed over the next week or so. During this time, mortality was judged to be very high. Pinheads starved and/or were eaten by surviving fish. Surviving fish were then fed a mixture of contract feed and high quality feed for about two weeks and mortality gradually decreased as the fish adapted to the dry diet. Fish received only contract feed starting on June 18 &19, and accepted it well and have grown satisfactorily since that time. Fish were inventoried on June 28 & 29, and as of those dates there were approximately 9,000 fingerlings. Under normal circumstances there would be 50,000 or more at that time.
What will happen for the remainder of this year's muskie rearing program?
Fish will continue to be reared indoors until they are placed into the outdoor ponds at Chautauqua Hatchery in August. Efforts to determine if surplus muskellunge may be available from agency hatcheries in other states were successful. The Pennsylvania Fish and Boat Commission will provide approximately 24,000 surplus fingerlings, which are scheduled to arrive at Chautauqua Hatchery on July 30, 2010. With good luck during the remainder of the rearing cycle, the number of fish available to be stocked this fall will be close to the recommended number.
What will we do differently next year?
It is apparent that muskellunge did not convert well to the new contract feed. In 2011 we will use alternate high quality feed alone or in combination with contract feed as fish are weaned off brine shrimp. This should allow diet transition to occur with much lower mortality than was experienced in 2010.
If there is a shortage how will this affect sport fisheries for muskellunge?
DEC's fisheries biologists point out muskellunge are long lived, so a reduced stocking should have minimal impacts to the sport fishery for them in stocked waters. Potential impacts can be further reduced if anglers release muskellunge that are caught. This practice, which is common among many muskie anglers, could be beneficial under the current circumstances.