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Genetic and biologic stock management

Hallerman Ch. 15Genetic impacts of fish introductions

INTRODUCTIONIntroductions and transfers of fish have a long history (carps and rainbow worldwide, Norwegian trout country-wide). Up to about 1960, transfers were regarded as desirable activities because of the possibility to enhance the output from fish farming as wells sportfishing. After a period with documentation of some very bad effects of introduction of new species into existing ecosystems, much more concern has characterised our perception of the practices.

Actually, ICES have long had a special Working Group dealing specifically with problens connected with "exotic species" transfers. The WGITMO (Working Group on the Introductions and Transfers of Marine Organisms) has published a "Code of Practice" for such activities.

A subset of the problems with species transfers, notably the genetic aspects, applies to introductions and transfers of within-species groupings. The problems ahve been particulatly accentuated in various species of Pacific salmonids.

Iteroparous organisms: Multiple reproduction cycles (successive years) Semelparous organisms: Reproduce only once in life

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Pink salmon (O. gorbuscha)

Pacific salmonids

Consensus phylogenetic treeof the Onchorhyncus genus.Based on morphological andmolecular data.

Branch lengths approximate relative divergences among taxa. (Hallerman Fig. 15-2)

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Coho O. kisutch

Chinook O. tshawytscha

Pacific salmonids

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Chinook Pink

Chum Sockeye


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DETECTION OF GENETIC CHANGES

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Traditional markers of genetic change

• Morphological traits (hybrids)• Redd identification/counting• Timing/location of spawning• Migration changes• Karyotyping / chromosome studies

Molecular markers of genetic change (since 1960- ies)• • Redd identification/counting• Timing/location of spawning• Migration changes• Karyotyping / chromosome studies

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POTENTIAL AND OBSERVED EFFECTS

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Overview of potential effects of the release of exogeneous, hatchery-reared fish on native populations (from Utter 1998).

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Effect of supportive breeding on effectice size of total population

Box 15.1

Relation between the effective sizes of the contributinggroups (wild or captivity bred) and the total population


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A typical management scenario of supportive breeding: (x-es denotes relative contributions from the various groups)

NW denotes wild fish NC denotes captive-bred fish

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Indirect effects and side-effects of supportive breeding and introductions

• Disease introduction (reducing sizes of natural populations -> drift effects)• Wastage of gametes (sterility or reduced fitness precludes reproductive success of hybrids• Fragmentation of habitats (displacements of native populations by naturalized nonnative groups

Direct genetic effects through introgressive hybridization

The effects depend on the resilience of natural populations to introgression, and this varies extensively with species and populations. All types of scenarios have been reported, from no effect at all and to a total wipe-out of native populations. In salmonids, virtually no case of introduction has been reported so far which is solely to the benefit of natural, native populations.

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Genetic and biologic stock management Hallerman Ch. 15Genetic impacts of fish introductions

Observed effects of trans-locations and hybridizationson performance and fitness.

Success stories are rare!

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PERSPECTIVE ON INTRODUCTIONS

The examples in this chapter have illustrated general areas of concern for the protection of native populations affected directly or indirectly byintroductions. The basic principles for appropriately dealing with theseconcerns are thorougly documented in the scientific literature and management Codes of Practice.

A very basic requirements is to identify existing genetic resources, i.e. thorough base-line studies must be performed in all cases.

A firm knowledge of population structures underlies all other genetic concernsconsidering interactions of introduced and native populations, including- field studies (ecology)- laboratory studies (genetics)- desktop studies (evolutionary histories, invasion routes)

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From a genetic conservation point of view, it has been stated that: "The best possible outcome of an introduction is a failure and thus a wasted effort".However, there may sometimes be good reasons for reinforcement of endangered wild populations, and hence there is a need for knowledge about all aspects of interactions and effects, in order to enable proper action when situations call for it.Such situations can be habitat destructions, reintroductions of populations that have been compromised by former, unfortunate practices.

Prof. Nils Ryman at the University of Stockholm, a world expert on brown trout, described the current situation this way:

" The globally increasing aquaculture industry will result in increasing incidental and intentional releases of huge numbers of fish, although those fish will represent a fairly low number of species and populations. Thus, the threat of hybridization from cutured fish to the genetic integrity of local populations must be considered a major concern".

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