Endangered Species Reintroductions - The Need for Good ScienceBy Jay DeLong
reprinted from American Currents, Spring 1998
I'm writing this from within the Olympic rain forest on Washington's Olympic Peninsula, an area which last year received over 14 feet of rainfall. Winter is the rainy season here and today was a typical January day: It rained all day, at times a light mist, at other times a torrential downpour that froze my body right through my rain gear.
I am a fisheries biologist for the Northwest Indian Fisheries Commission, and I'm spending this week in the Quinault Indian Nation, working at their Salmon River Hatchery, helping them coded-wire tag juvenile coho salmon. Coded-wire tags are tiny, uniquely-coded pieces of stainless steel wire placed in the snouts of juvenile fish. These fish retain their tags until they are removed upon capture as an adult. As a result, we gain valuable information about their survival, migration and population numbers.
It's pouring rain now, but I'm warm and dry in my motel room in the town of Amanda Park, thinking about how the management of Pacific salmon can teach us lessons about the aquarium rearing of endangered species for reintroduction into the wild. I'd like to share my thoughts with you.
A Brief Introduction to Salmon Management
Since the 1890s, Pacific salmon hatcheries have released 5.5 billion fish, mainly to produce more fish for harvest. It was thought that the ocean had an unlimited food supply, and that the limiting factor to salmon abundance was freshwater production capability. Hatcheries have been used to offset habitat destruction caused by logging, urbanization, dams, and other factors. Over time, salmon habitat became further degraded. Fewer fish became available for an ever-increasing number of fishers. The fish that were available were smaller. Concerns over the effects of hatchery fish on wild fish became a source of ongoing debate.
Despite such concerns, it is generally accepted that it is deleterious to cross the genetic traits of a wild fish with one which has been hatchery-spawned for several generations. Hatchery fish are not subjected to the same environmental pressures as wild fish, and once released survive poorly compared to fish in the wild. In other words, they just aren't trained for life in the wild. For example, hatchery fish donšt avoid predators well; a hungry heron's shadow over the water may be seen as the shadow of a hatchery worker who fed the fish three times a day for a year. To compensate for the poor survival of hatchery fish, more fish are released, which compete for food and space with their wild brethern.
Protecting a single stock is difficult and contentious because salmon stocks intermingle in salt water (a stock being defined as a genetically distinct group of fish unique to a particular stream or region). Fishing is sometimes banned in areas where depressed stocks migrate, which frustrates anglers who want to fish for other abundant stocks in these areas (called "mixed-stock fisheries"). Now that the federal government is considering listing more salmon stocks under the Endangered Species Act, the effects of protecting stocks will continue to be felt at all levels of salmon management.
Recent Improvements in Salmon Hatchery Culture
Hatchery planners are becoming wiser and more informed. A recent workshop in my state on alternative hatchery rearing methods was encouraging. People are recommending changing the standard concrete/asphalt hatchery environment to one with natural rearing channels, complete with submerged cover, areas of uneven flow, and natural substrate. There's even talk of introducing natural predators to hatchery ponds. However, hatchery work is physically demanding, and many agencies will not want the extra work associated with more complex hatchery setups. Also, remodeling hatcheries and retraining people would be a slow process, and will probably never become a reality in some areas.
Some improvements have been adopted at some facilities. New spawning protocols are in place which avoid selective breeding. And fish and eggs are not being moved between drainage basins as they had been in the past. Historically, a single hatchery's fish were often used to compensate for production shortfalls in other areas, or as founding broodstock for new hatcheries. The present approach to broodstock management is either to develop and maintain a local stock in a stream, or to maintain distinct differences between hatchery broodstock and fish that spawn in the wild.
Wild broodstocks are now regularly used in many hatcheries. Adults to be spawned are captured from among wild fish returning to the river, and their progeny are reared in the hatchery. The main benefit of wild broodstocking is that the genetic variability of the stock is not greatly diminished as often occurs with hatchery stocks (wherein particular characteristics are intentionally or accidentally selected over successive generations).
Another improvement is supplementation, or the release of salmon fry into streams away from the hatchery. These fish return as adults to spawn naturally in the stream. Supplementation is often done where the spawning potential of a stream is not being met.
This brings me to where I am as I write this. The Quinault Tribe's coho tagging program combines wild broodstocking and supplementation. Each fall the tribe captures wild coho adults from individual tributaries of the Queets River, spawns them, and rears each tributary's offspring separately. The fish (some 150,000 of them) are raised in the Salmon River Hatchery, then released just prior to smoltification back into the exact stream from which their parents were captured. Since the fish imprint on that stream's water instead of the hatchery where they were reared, more coho return to each of the Queets' tributaries.
How About Endangered Nongame Species?
So what does Pacific salmon management have to do with protecting pupfishes in California or darters in Missouri? Everything. Salmon management drives fisheries research in our country, and there is a lot of information available as a result. We need to draw on the work already done, not pluck our own plans from the air because they seem like a good thing to do for the fish. We've got to do our research. We've got to call on the experts.
First, I'd like to state the obvious: Endangered species reintroductions won't be successful unless we first address the causes of their decline. Habitat destruction and exotic species interactions are probably the two most serious problems facing America's fishes today. If you return fish into waters where poor habitat or exotics had decimated them, and those problems haven't been corrected, the fish won't survive.
Second, without scientific study, reintroductions may be detrimental to the fish. The idea that a rare fish in an aquarium could be used to restore the population in the wild is intriguing, but thinking it's as simple as rearing the fish and turning it loose in a stream is naive in light of experience and current knowledge.
The Need for Scientific Study
The Fall 1997 American Currents (p. 31) reported that several subspecies of the orangethroat darter have been elevated to species status. I'm sure darter expert Lawrence Page had known that new species like the strawberry darter were not orangethroats. What if a well-meaning aquarist had tried to boost the Strawberry Creek population of the "orangethroat darter" by releasing tank-bred orangethroat darters, or specimens transferred from another drainage? This would not have been good for the strawberry darter. Darters can hybridize. I have crossed fantail, banded and rainbow darters, and I've crossed rainbow darters and logperch (Etheostoma x Percina). I did these by hand and all crosses produced fertilized eggs. I didn't hatch them. Would the offspring be fertile? I don't know. If fertile, would they spawn in the wild? Again, I don't know. But hybridization has occurred among some rare pupfishes and among Gambusia species due solely to unwise releases. And what if the two darter species had similar habitat requirements? The aquarist would have succeeded in introducing a competitor as well. The effects of such a well-meaning reintroduction could never be undone.
My point: Know your species and the science behind them. An aquarist cannot know about the biology, distribution and status of fishes just by reading popular aquarium magazines or field guides. Contact people like Dr. Page and ask if he's aware of pertinent research. Contact your local university's zoology department and library. Contact your state's fishery agency and get as much information from them as you can. Discuss your ideas with them.
Also, know your subspecies and don't cross them, either in the stream or the aquarium (if your intent is to produce fish for release). This isn't just because a subspecies may one day be elevated to full species status; it's also because they differ genetically. If you cross two subspecies and release the progeny among one or both of their populations, you will decrease the total amount of genetic information present. Often the hybrids perform more poorly than the parents. This undesirable outcome is called outbreeding depression. If you see that individuals of the same species behave or appear differently in different streams or habitats (e.g., pools vs. riffles), don't cross them and dilute their populations. These differences may be genetic and may need to be preserved.
Learn About Ecological Relationships and Genetics
Study ecology and genetics. Why ecology? Because complex interrelationships occur in aquatic ecosystems. Learn about competitive interactions for resources, and what happens when a species is removed or added from an ecosystem. Why? Because you've got to develop an ecosystem mentality and get away from single-species thinking. If you are rearing a rare species which is now missing from its original stream, you need to consider what has happened in that stream since the species disappeared. Oftentimes, other species fill in vacant niches. Previously insignificant competitors may now be present in significant numbers.
Aquarium science has traditionally been about admiring and rearing fish, and not about improving their ability to survive in the wild. Aquarists do not breed fish for release. (No one who buys Amazon River fish thinks about one day returning the fish to the Amazon.) Instead, aquarists have created artificial strains of fish specifically for coloration, size, fecundity, and other characteristics. Some of these characteristics would make the fish a poor candidate for survival in the wild. This is called artificial selection, or domestication. Aquarists also often keep and breed generations of the same parental lineage. This is called inbreeding, which leads to the increased frequency of normally rare traits in the populations. Often these traits are detrimental to a fish's survival in the wild.
Why learn about genetics? Because it's the best management tool we have for insuring the permanent survival of species. If you have a basic understanding of genetics and natural selection, then you understand why it's important to have an adequate degree of variation in traits, or genetic variability, in the entire population. Natural selection acts on different traits of individuals and manifests itself through differences in survival and reproduction. For example, I read about a study in which a predator (a sunfish) was introduced into a tank of threespine sticklebacks. Sticklebacks with fewer vertebrae survived the longest, for they were able to outswim the sunfish easier than ones with more vertebrae. Under constant pressure from the sunfish predator, the fewer-vertebrae sticklebacks would reproduce and pass on their traits.
Our native fishes are the products of millions of years of selective environmental and biological pressures. If you destroy all but a few individuals of a species, you decrease the variability of traits from the population to what is present in the survivors. No individual normally contains all the variability present within its species, so the ability of the species to adapt and survive is dependent on the variability contained in the genes of the remaining individuals.
Think of the term "variability" as "flexibility" or "insurance". Investors usually don't put their money in a single account; instead, they prefer investing in a combination of stocks, mutual funds, bonds, etc. They are protecting their money in case one investment fails. By sustaining as much genetic information as possible within a species' population, we are insuring the survival of that species should a natural or artificial disaster befall it.
The most important factor in sustaining a high level of genetic variation is the size of its genetically effective population, which geneticists call "Ne". There are several factors which reduce Ne. Sex ratios of breeding individuals other than 1:1 reduce Ne by giving the least abundant sex a greater chance to pass on its genes. Individuals that are more fecund reduce Ne by contributing a disproportionate amount of genetic material to the next generation. And when a population declines, the only genetic information available is that contained in the surviving individuals. In this case, genetic information is permanently lost.
What Happens With Small Population Sizes?
Losing some of their genetic variability makes small population sizes more vulnerable to environmental changes. In addition, they are susceptible to three closely related effects: genetic drift, bottlenecks and inbreeding.
Genetic drift is the random loss of genetic information present in the gametes (eggs and sperm). This loss occurs at a rate that is inversely proportional to the population size. If genetic information is distributed randomly among the gametes, and the population size is too small for an adequate number of gametes to result in fertilized eggs containing all genetic information for the population, some genetic information will be lost.
A bottleneck is a dramatic decline in population size, and, hence, a permanent loss of rare genetic information. The South African cheetah experienced a severe bottleneck during its evolution and presently has seriously limited genetic variation. This is a major cause of its fight for survival today.
Inbreeding depression is caused by breeding related fish, and is possibly the most serious consequence of small population sizes. Expression of a trait is determined at the gene level by information contributed by each parent, and predictable percentages of offspring display these traits. If one parent's gene is recessive, then the trait it codes for will be expressed by a predictably small number of the offspring. Others will possess the gene, but won't express it. The population is said to be heterozygous.
The problem with breeding related individuals is that over time you remove the heterozygosity from the population and create a population homozygous at all genes (i.e., both genes code for the same trait expression). This can increase the occurrence of traits which are detrimental to a species' fecundity, disease resistance, fertility, and growth. The cheetah, for example, has difficulty breeding, has a high juvenile mortality rate, and is susceptible to a particular virus. Inbreeding depression is well-documented in fishes, too. There are cases of reproductive failure, growth reduction, bodily deformities, and behavioral changes in convict cichlids, carp, zebra fish, brook trout, and rainbow trout.
People who maintain aquarium populations of extinct-in-the-wild fishes are performing a truly noble act. By keeping a species from becoming extinct they are preserving something unique while helping to maintain biodiversity. However, even though the goodeids, pupfishes and other rare fishes now living only in aquaria or refugia are the same species which once swam in the wild, they aren't the same fish anymore. Fish need to be defined by populations, not by museum specimens or survivors in aquaria. The longer these fish are inbred the less able they are to survive in the wild. A single environmental disaster, even a minor one, and the animal is gone forever. Relying on aquarium-bred populations of endangered fish as the sole method of restoring a wild population is not the best solution to the problem of endangered species management.
So what do we do? A crucial step is to identify the goals of endangered fish management. Is a goal to prevent the immediate extinction of a species? To insure the survival of the species into the future? To insure that the species has the ability to adapt to changing environments? Of course, first and foremost we've got to do what we can to avoid extinction, and aquarium rearing can accomplish this. But our ultimate goal must be to insure healthy, genetically safe populations which can survive in the wild forever. This is why we can't wait until populations are reduced to a few individuals.
Earlier, I described lessons we learned with Pacific salmon management. I also described how we developed scientifically based hatchery techniques and spawning protocols. Such techniques are also used in Atlantic salmon management. Nongame endangered species management should be no different. The Dexter National Fish Hatchery and Technology Center in New Mexico (described in the Fall 1997 American Currents) is an effective program.
Let us not repeat the unwise and uninformed mistakes of the past. It is short-sighted and unethical to tamper with nature through poorly designed releases of fishes. We need to behave responsibly and use good science. We've got to fight for fish rights and quit complaining about our rights. Wild fish will stay wild only if they are allowed to retain that which makes them wild. The real culprit is the high value our society places on land and water use.
Used with permission. Article copyright retained by author.