II. Fish ICES mar. Sei. Symp., 194: 31-55. 1992 Pacific salmon in Atlantic waters Yves Harache Harache, Y. 1992. Pacific salmon in Atlantic waters. - ICES mar. Sei. Symp., 194:31-55. A century of Pacific salmon introductions to Atlantic waters is summarized. Move­ ments of fish were initiated in the last century, and in many countries large quantities of eggs have been introduced into rivers on both sides of the North Atlantic Ocean. The motivations for such programmes, the techniques used, and the results arc analysed for most of the documented attempts to introduce these species in the Atlantic area, with special attention being given to recent introductions (since 1950). Programmes for the introduction of Pink salmon (Oncorhynchus gorbuscha) in Newfoundland (Canada) and the Kola Peninsula (USSR) are reviewed in detail, and the use of coho salmon (Oncorhynchus kisutch) for ranching (New Hampshire, USA) and farming (Europe) is described. Pacific salmon released in Atlantic oceanic areas have shown in most cases an aptitude for survival, growth, homing, and spawning, even in areas where environmental characteristics are substantially different from their home waters. Survival rates are generally lower than in the original range and straying relatively important. However, in spite of significant returns, all attempts to establish reproducing sea-going populations have failed in the northern hemisphere. Although not developing rapidly, the use of coho salmon for aquaculture in Europe has an interesting potential. The possible causes of success or failure of the different attempts are discussed; they include an analysis of the adaptive mechanisms of populations which exist in their original habitat, and the influence of the ecological characteristics of the receiving country on the biology of the species. With the exception of the limited initial transplants of the last century, one may note that most introductions were made in areas which did not satisfy the optimum environmental requirements of the species, and where temperature regimes were probably the main limiting factors. They were also made in insufficient numbers or during a period too limited to allow sufficient time for genetic adaptation to the new environment. The consequences of these introduc­ tions on native populations of Atlantic species are also discussed. It is concluded that ecological influence on native stocks has been limited in the cases described, and the existing experimental knowledge of the interactions between species is discussed. The risk of disseminating diseases, although no severe problems appear to have been created, must be considered carefully, as do all cases of live fish transfers in or out of the natural range of the species. In conclusion, the influence of the development of aquaculture practiccs on wild stocks is drafted. Les introductions de saumons du Pacifique dans les eaux de l’Atlantiquc nord depuis un siècle sont décrites. Les transferts d’oeufs d’Oncorhynchus ont été initiés à la fin du siècle dernier, et des quantités importantes d’oeufs ont été introduites dans les rivières européennes ou américaines dans la plupart des pays riverains. Les motivations des différents programmes, les techniques utilisées et les résultats observés sont rappelés pour la plupart des cas, cités dans la littérature, avec une attention particulière pour les introductions récentes (depuis 1950). Les introductions de saumon pink (Oncorhyn­ chus gorbuscha) à Terre-Neuve (Canada) et dans la péninsule de Kola (URSS) sont décrites de façon détaillée, ainsi que l'utilisation du saumon coho (Oncorhynchus kisutch) pour des programmes de pacage marin (New Hampshire, USA) ou d’aquacul­ ture (Europe). Les saumons du pacifique libérés dans les eaux de l’Atlantique ont montré dans la plupart des cas leur aptitude à vivre, grandir, retourner au point de lâcher et se reproduire, y compris dans des zones où les conditions hydrologiques étaient très différentes de celles de leur aire de répartition originale. Les taux de survie y sont cependant généralement inférieurs et le taux d’errance supérieur aux valeurs observées dans le Pacifique. En dépit de ces retours parfois abondants, aucune introduction n’a donné lieu, dans l’hémisphére nord, à l’établissement durable de populations se reproduisant naturellement. L’utilisation du saumon coho pour l’aqua­ culture en Europe, bien que n’ayant pas donné de développement important à ce jour 31 à démontre un potentiel intéressant pour lclevage en captivité, cependant l’activité n'a pas connu de réel développement industriel. Les causes de succès et d'échec des différentes tentatives sont analysées, incluant une discussion sur les mécanismes adaptatifs réglant le cycle biologique des diverses espèces et l'influence du milieu «récepteur» sur leur biologie. Si l’on excepte certaines des premières tentatives, la plupart des introductions ont été réalisées dans des zones ne correspondant pas aux caractéristiques optimales d'environnement pour les espèces concernées et où des températures inappropriées sont probablement les principaux facteurs limitants. Les tentatives ont également concerné des nombres trop restreints d'animaux, et pendant une période trop brève pour permettre les adaptations génétiques à un nouvel environnement. Les conséquences de ces tentatives d'acclimatation sur les popu­ lations résidentes sont discutées, concluant à une incidence écologique limitée sur les stocks indigènes, dans les cas décrits. Les connaissances concernant les interactions entre espèces, acquises expérimentalement sont analysées. Le risque de favoriser la dissémination de maladies reste le principal argument d'opposition aux tentatives d’introduction de saumons du Pacifique en Europe (comme dans tout transfert de poissons vivants), même si aucune problème grave n'a été décrit dans les diverses tentatives. La conclusion fournit quelques éléments de réflexion sur l’influence du développement des techniques d’aquaculture sur les stocks de saumons sauvages. Y. Harache: IFREM ER, Centre de Brest, BP 70, 29280 Plouzane. France. Introduction the possible ecological consequences, and in all cases they have generated much controversy. Transplanting plants or animals to allow local access to a The aim of the present paper is to summarize more resource was probably a very early preoccupation of than a century of Pacific salmon (Oncorhynchus sp.) Homo sapiens, and many domesticated species are not introductions into Atlantic waters, and to review the native to the countries in which they are cultured. possible consequences and factors important to their Among aquatic organisms, early attempts to displace success or failure. or transplant have occurred for invertebrates such as oysters, which are reasonably easy to manipulate in the adult stage. The biological characteristics of fish, whose 1. The objectives of Pacific salmon adults and juveniles are relatively difficult to transport, introductions have made the process more difficult to realize. The history of fish displacements is associated with an The main reasons proposed by the initiators of introduc­ increased knowledge of reproductive mechanisms, and tions have always been economic ones: creating a new has been stimulated by the discovery of new species in resource or a new sport or commercial fishery. Historic­ recently colonized lands. ally, human interventions have been made at various Several reproductive characteristics of salmonids - stages of the life history of salmon. concentration of the spawning stocks on limited spawn­ ing grounds and the large size and capability of the ova to Transplanting a species to create a new wild withstand mechanical manipulation - encouraged early population attempts to introduce most salmonid species beyond their natural ranges. These attempts were initiated dur­ Species which can freely reproduce ing the last century, with periods of active transfers with The most numerous and earliest cases of introductions varied objectives. An acceleration of movements associ­ followed the simplest scheme of importing eggs of the ated with economic activities has been observed during species during a limited initial period and planting them the past 20 years. Many species once confined to temper­ in rivers in order to create new wild populations which ate areas of the northern hemisphere are today rep­ could establish and colonize a vacant ecological niche or resented on all the continents in either their wild or displace less valuable native species. These populations cultivated form. might be exploited by an adequate commercial fishery in In salmonids, several cases of introductions of non- the coastal area, or a sports fishery in marine or river migratory species can be considered to have been suc­ waters. Such motivations have probably been generated cessful. but only a few examples of anadromous popu­ by the magnitude of salmon stocks from the North lation transplants have succeeded in establishing dur­ Pacific, and the apparent ease with which fisheries cnuld able self-sustaining populations. In many cases such be developed when stocks concentrated in the coastal or experiments were conducted without great concern for estuarine environment prior to reproductive migration. 32 Observations of massive returns of pink (O . gorbus- being paid particularly to introductions for which little cha) and chum (O . keta) salmon in Alaskan rivers and information is available in the international literature. the associated net fisheries; the large sockeye (O . nerka) Bristol