Hatcheries: Role in Restoration and Enhancement of Salmon Populations

Transcription

1 Hatcheries: Role in Restoration and Enhancement of Salmon Populations Hatcheries play a large role in the management, ecology, and evolution of Pacific salmon. Why were/are they built? What are the assumptions behind their operation, and what are the concerns?

2 Hatcheries I. Extent of hatchery production II. Why build a hatchery? i. High survival rates at early life history stages improve net productivity over a wild population. Nature is inefficient we can do better. II. III. IV. Objectives, and underlying assumptions Reasons to question the assumptions Concerns: i. Short-term: fishery management: how to handle success ii. Intermediate-term: behavioral and ecological interactions iii. Long-term: genetic consequences

3 Millions of Fish Hatchery production Pacific Northwest British Columbia Alaska coho salmon Mahnken et al. NPAFC Bull Release Year 1990

4 Hatchery production Millions of fish released Pacific Northwest British Columbia Alaska chinook salmon Mahnken et al. NPAFC Bull Release Year

5 Columbia Basin Salmon and Steelhead Hatcheries

6 Estimated % of adult wild steelhead Percent Wild Light 1987 AK B.C WA Col. R. OR CA

7 Columbia River salmon: approximate abundance, early 2000s Species Total % wild Spring chinook 200, Summer chinook 65, Fall chinook 800, Coho 700, Steelhead 300, Sockeye 125, chum ~ 2.2 million

8 Hatcheries: solution or problem? Why build a hatchery? 1. Compensate for overfishing 2. Mitigate for lost habitat (Columbia River) 3. Create or enhance a fishery (SE Alaska) 4. Supplement a weak or unstable run 5. Preserve and restore endangered run Issaquah Salmon Hatchery, King County, Washington ca. 1935; UW library archives

9 Hatcheries: solution or problem? Key assumptions: 1. The hatchery by-passes the limiting life-history stage; other habitats are under-utilized or are not limiting 2. There are no other biological interaction between hatcheryproduced and wild fish (e.g. diseases, genetic interaction, predation, etc.) 3. The survival rate of hatchery-produced fish is similar to wild fish. 4. The hatchery does not affect habitat needed by wild fish. 5. The fisheries can accommodate the more productive hatchery population without over fishing the wild one. 6. The hatchery s productivity will be stable over time.

10 Why do hatcheries work so well? They short-circuit the limiting life history stage For most fishes, the embryonic and early larval stages are characterized by very high mortality. Many species are difficult to breed in captivity or their young are difficult to feed. However, salmon are easy to breed, the large, robust embryos are easy to incubate, and the juveniles feed readily. Most wild salmon die between fertilization and emergence from the gravel (often 80-90%). It is easy to improve on the survival rates of wild salmon. Nature is inefficient we can do better. Number of years Chilko River sockeye salmon: Average = 8.3% % survival to emergence

11 Hypothetical coho salmon life tables Wild Hatchery Stage Abundance Mortality Abundance Mortality Egg % % Fry % % Parr 50 50% % Smolt 25 80% % Adult 5 72

12 Hypothetical coho salmon life tables Wild Hatchery Stage Abundance Mortality Abundance Mortality Egg % % Fry % % Parr 50 50% % Smolt 25 80% % Adult 5 72

13 Hypothetical coho salmon life tables Wild Hatchery Stage Abundance Mortality Abundance Mortality Egg % % Fry % % Parr 50 50% % Smolt 25 80% % Adult 5 72

14 Hypothetical coho salmon life tables Wild Hatchery Stage Abundance Mortality Abundance Mortality Egg % % Fry % % Parr 50 50% % Smolt 25 80% % Adult 5 72

15 Hypothetical coho salmon life tables Wild Hatchery Stage Abundance Mortality Abundance Mortality Egg % % Fry % % Parr 50 50% % Smolt 25 80% % Adult 5 72

16 Hypothetical coho salmon life tables Wild Hatchery Stage Abundance Mortality Abundance Mortality Egg % % Fry % % Parr 50 50% % Smolt 25 80% % Adult 5 80% 72 80% Spawner 1 14 If we impose an 80% fishing rate on both groups

17 If hatcheries are so efficient, how do we catch their surplus without overfishing healthy but less productive wild populations?

18 Hatcheries: solution or problem? Simulated effects of stocking and fishing on lake trout Stocking of non-native lake trout at moderate to high exploitation rates caused loss of the recipient population. Even when the stocked fish reproduce, their progeny mask the loss of the wild stock. At exploitation and stocking rates typical of lake trout populations in Ontario, the wild stock was replaced by the hatchery stock in a few generations. Native stocks having weak recruitment are least resistant to displacement by hatchery stocks and are also the most likely to be subjected to stocking. Evans and Willox Can. J. Fish. Aquat. Sci. 48 (Suppl. 1):

19 Behavioral and ecological interactions between wild and hatchery produced salmon Implicit assumptions in most hatchery programs: 1. The hatchery by-passes the limiting life history stage or habitat, and so increased production of juveniles leads to increased production of adults 2. There are no important biological interactions between wild and hatchery fish that would limit overall production (i.e., hatchery fish are simply added to the wild ones)

20 Behavioral and ecological interactions between wild and hatchery produced salmon can be complex Competition: Hatchery fish are usually larger and may be more aggressive, giving them advantages over wild fish But, wild fish may already have territories when hatchery fish are released, giving them an advantage Large size may give hatchery fish a survival advantage but life in the hatchery might make them more vulnerable to predation Atsushi Sakurai If the stream is at carrying capacity, more smolts will not be produced and the wild population may be reduced. J. Rhodes

21 Behavioral and ecological interactions between wild and hatchery-produced salmon can be complex Predation: Smolts may prey on wild salmon of other species, or smaller conspecifics. Hatchery produced fish might help swamp predators or might concentrate them. Thus, overall responses of predators, and population consequences may be difficult to predict. Belted Kingfisher

22 Smolt to adult survival of Snake River chinook % smolt to adult return hatchery wild Raymond (1988) NAJFM

23 The survival of hatchery-released fish is usually lower than that of wild fish, even though the hatchery fish are larger. Why? Predator avoidance (learned) Feeding behavior (learned) Genetics (reduced selection for adaptive behavior) Physiology (photoperiod, temperature, growth rate) Diet (essential micronutrients, fat content) Release date Inherently unfit individuals remain in the hatchery population but are culled from the wild population already????

24 The numbers of smolt released may not determine the number of adults returning (ocean effects can be strong) smolts (millions) Smolts Adults returns (millions) Year of smolt migration Numbers of coho salmon smolts entering the Oregon coastal environment and adult returns for the same year class (Brodeur 1990)

25 Hatcheries: Genetic effects Domestication Selection: Genetic divergence of wild and hatchery populations Lower fitness of hatcheryproduced fish in the wild Do we seek to isolate wild and hatchery populations or combine them? Hybridization with other species (trout)

26 Natural and sexual selection Wild females must select, prepare and defend nest sites and choose mates; males must choose and compete for access to females.

27 The hatchery staff cannot know which salmon would have chosen the best nest sites or otherwise been successful in reproducing, so there is a relaxation of selection on these traits. There may also be deliberate or inadvertent selection on other traits such as date of maturation, size, etc. In addition to these processes affecting adults, there is also selection for juveniles that adapt to confined conditions. Together, these processes are referred to as domestication selection.

28 Hatcheries: reproductive success Reproductive success of native, wild and non-native, hatchery produced steelhead in the Kalama River, WA Life history stage Survival hatch v. wild Egg to fry 85-87% Sub-yearling 76-79% Smolt 58-64% Adult 42% Leider et al. 1990

29 Hatcheries: reproductive success These effects are cumulative, and the authors concluded that the naturally spawning wild summer steelhead we examined produced from 7.8 to 9.3 times more adult offspring than did their naturally spawning hatchery counterparts. However, more than 40%...of the naturally produced adult summer steelhead were the direct offspring of hatchery spawners due to the preponderance in the spawning escapement. Leider et al Aquaculture 88:

30 Hatchery and wild salmon: two options 1. Integrated hatchery: make wild and hatchery fish as similar as possible, by breeding some wild fish in the hatchery and having some hatchery fish spawn in the river in each generation, and manage them as a single population. 2. Segregated hatchery: make the hatchery fish as different from the wild fish as possible (e.g., breeding date), limit interbreeding as much as possible, and have different fishing rates on the two components.

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