Incidence of lamprey marks on Lake Sturgeon (Acipenser fulvescens Rafinesque, 1817) in the St. Clair – Detroit River System: Implications for Sea Lamprey (Petromyzon marinus Linnaeus, 1758) effects

Laurentian Great Lakes Lake Sturgeon (Acipenser fulvescens) are hosts to lamprey species, including native Silver Lamprey (Ichthyomyzon unicuspis) and invasive Sea Lamprey (Petromyzon marinus). Silver Lamprey coevolved with Lake Sturgeon and cause negligible mortality, but Sea Lamprey can negatively affect Lake Sturgeon populations. Sea Lamprey abundance in Lake Erie has been above targets set by resource managers, with the St. Clair – Detroit River System (SCDRS) suspected as a source of Sea Lamprey production into Lake Erie. This study summarizes lamprey marking on Lake Sturgeon captured during agency assessment surveys in the SCDRS since 1996 and provides insight on the potential for Sea Lamprey to negatively affect Lake Sturgeon in the SCDRS. Lamprey marks (any lamprey species) were noted on 48.2% of Lake Sturgeon (2.5 marks/fish) and 3.3% of Lake Sturgeon assumed to be susceptible to mortality by Sea Lamprey (<760 mm TL; 0.06 marks/fish). Silver Lamprey were the only lamprey species found attached to Lake Sturgeon and there was no difference between oral disc diameters of Silver Lamprey and marks measured on Lake Sturgeon in Lake St. Clair and the lower St. Clair River (p = .45). Based on logistic regression, probability of at least one lamprey mark increased with Lake Sturgeon total length and was highest in Lake St. Clair. The probability of observing at least one lamprey mark on a 760 mm Lake Sturgeon was 8.1% or less for each sampling location in the SCDRS aside from Lake St. Clair (28.1%). Results suggest that parasitism of Lake Sturgeon by Sea Lamprey in the SCDRS is rare, particularly for Lake Sturgeon <760 mm TL. Low incidence of lamprey marks on Lake Sturgeon assumed to be susceptible to mortality from Sea Lamprey parasitism and zero occurrence of Sea Lamprey being observed attached to a Lake Sturgeon suggest Sea Lamprey at their current abundance likely have little effect on the Lake Sturgeon population in the SCDRS. Caution should be taken when using mark size to assign marks to lamprey species as there is substantial overlap among species oral disc diameters, potentially inflating the perceived impact of Sea Lamprey on Lake Sturgeon in areas with native lampreys.     

Variations of life history strategy of the arctic lamprey <Emphasis Type="Italic">Lethenteron camtschaticum</Emphasis> from the Utkholok River (Western Kamchatka)

Morphobiological traits of the lamprey from the Utkholok River (Western Kamchatka) are investigated for the first time. All present forms of lamprey (typically anadromous, anadromous early maturing forma praecox, resident) do not differ by diagnostic characters and belong to one species Lethenteron camtschaticum. Males prevail among mature specimens of various forms, smolts, and ammocoetes at later developmental stages. The forma praecox is represented by males by 92%. A hypothesis is suggested explaining the relationships of the forms and the mechanism of realization of different types of life history strategy in relation to energy resources of water bodies and the kind of feeding of different groups of ammocoetes (organic detritus or Pacific salmon carcasses decomposed after spawning).     

Population structure of arctic lamprey <Emphasis Type="Italic">Lethenteron camtschaticum</Emphasis> from the Kol River (Western Kamchatka)

Phenetic diversity is investigated and the taxonomic status of lampreys (Petromyzontidae) from the Kol basin (Western Kamchatka) is verified. Typically anadromous lamprey, anadromous lamprey forma praecox, resident lamprey, smolts, and larvae of lamprey are discovered and described. Their comparative analysis is made by standard morphometric characters. Differences between the forms by plastic characters depend on size and weight. No significant differences are found by major taxonomic characters between the forms of anadromous and resident lampreys which would indicate their taxonomic separation. Phenetic types of spawners are representatives of the population of one complexly structured species represented by life forms realizing different life history strategies (anadromous and resident), and belong to the species Arctic lamprey Lethenteron camtschaticum (Tilesius, 1811).     

Alternative migration and host parasitism strategies and their long-term stability in river lampreys from the River Endrick, Scotland

The stability of a discrete body size dimorphism of sexually mature river lamprey Lampetra fluviatilis from the River Endrick, Scotland, was examined over a 21 year period. Stable isotope analysis was used to test the hypothesis that the two size forms comprise individuals with differing migration and parasitic foraging strategies. Maturing river lamprey and the brook lamprey Lampetra planeri were trapped over 3 months each year in the periods 1983–1984 and 2004–2005. Brook lamprey catches and catches of both species combined showed no significant trend in catch rate with time. The catch rate of small body size river lamprey declined between 1983–1984 and 2004–2005 (although the difference did not reach statistical significance; P = 0·055). In contrast, there was a significant increase in the catch rate of the large body size river lamprey and as a consequence, a significant change in the relative proportion of each of the two river lamprey morphs over the study period. Analysis of the stable isotopes of C and N in muscle tissue showed that brook lamprey tissue derived its carbon from a freshwater source and had a δ¹³C more consistent with that of the River Endrick than with Loch Lomond. δ¹⁵N values for this species showed it to be feeding at the base of the food chain, consistent with filter feeding as an ammocoete. The large body size and the small body size river lamprey adults differed substantially in their δ¹³C values, with the small body size δ¹³C signature indicative of a freshwater carbon source and the large body size morph of a marine source. The small body size morph had a δ¹³C signature that was consistent with that of Loch Lomond powan Coregonus lavaretus suggesting that they share a common carbon source. The large body size morph was clearly feeding at a higher trophic level than the small body size morph. A single small body size river lamprey individual with typical morphology for that group, however, had C and N signatures that clustered with those of the large body size morphs. This individual had either migrated to sea to forage, as is typical for the species, or had been feeding on an anadromous fish with a strong marine C signature in fresh water. It is concluded that the body size dimorphism is indicative of a differential migration and foraging strategy in the parasitic phase of the life cycle of river lamprey at this site.     

Characteristics of the spawning stock of chinook salmon <Emphasis Type="Italic">Oncorhynchus tshawytscha</Emphasis> from the Apuka River (northeastern Kamchatka)

Biological features of chinook salmon Oncorhynchus tshawytscha from the Apuka River, the largest river of the northeastern Kamchatka inflowing Olyutorskii Bay of the Bering Sea, are studied. Chinook salmon from the Apuka River spend mainly a year in the river before downstream migration to the sea. The fish live in the sea for 1–4 years. The spawning migration of chinook salmon into the Apuka River begins in late May just after ice melting, and it continues until early August. The main part of the spawners enters the river during June. A hypothesis on the occurrence of two seasonal races in the Apuka River is proposed.     

Feeding habits of the blue shark, Prionace glauca, and salmon shark, Lamna ditropis, in the transition region of the Western North Pacific

We describe the feeding habits of 70 blue sharks (Prionace glauca) and 39 salmon sharks (Lamna ditropis) caught at 0–7 m depth at night by research drift gillnets in the transition region of the western North Pacific during April–May of 1999 and 2000. Blue sharks of 50–175 cm total length fed on a large variety of prey species, consisting of 24 species of cephalopods and 16 species of fishes. Salmon sharks of 69–157 cm total length fed on a few prey species, consisting of 10 species of cephalopods and one species of fish. Important prey for the blue sharks were large, non-active, gelatinous, meso- to bathypelagic cephalopods (e.g., Chiroteuthis calyx, Haliphron atlanticus, Histioteuthis dofleini and Belonella borealis) and small myctophid fishes. Important prey for the salmon sharks were mid-sized, active, muscular, epi- to mesopelagic squids (e.g. Gonatopsis borealis, Onychoteuthis borealijaponica and Berryteuthis anonychus). Our results suggest that blue sharks feed on cephalopods mainly during the daytime when they descend to deep water. Salmon sharks may feed opportunistically with no apparent diurnal feeding period. Blue sharks and salmon sharks have sympatric distribution in the transition region in spring; they have different feeding habits and strategies that reduce competition for food resources.     

Genetic Diversity in a Small Population of Sockeye Salmon Oncorhynchus nerkaWalbaum from the Ola River (the Northern Coast of the Okhotsk Sea)

The genetic structure of a small sockeye salmon population from the Ola River (Tauyskaya Inlet, the Okhotsk Sea) was shown to exhibit high heterogeneity. Significant differences of LDH-B2*and ALAT-2*gene frequencies were detected not only among samples within the spawner and juvenile groups but also between spawners and juveniles as a whole. The average heterozygosity of sockeye salmon from the Ola River was considerably lower than the corresponding values for other Asian populations. The Ola sockeye salmon is genetically similar to the population from the Pakhach River of the northwestern Kamchatka Peninsula but different from other Kamchatka populations and the Okhota River population. A hypothesis explaining the genetic differentiation of Asian sockeye populations is advanced.     

Interannual Variations of the Body Length in Sockeye Salmon Oncorhynchus nerka Smolts of Lake Kuril'skoe in Relation to External Factors

A nonlinear regression model of body length dynamics was constructed for age smolts greater than two years old of the sockeye salmon Oncorhynchus nerka of Lake Kuril'skoe (Kamchatka). The analysis of variance showed that about 93% of the variation of body length is accounted for by the fish population density and water temperature. The reasons for the increase in the body length of smolts after volcanic ashfall are discussed.     

Maximum tag to body size ratios for an endangered coho salmon (<Emphasis Type="Italic">O. kisutch</Emphasis>) stock based on physiology and performance

Many coho salmon stocks (Oncorhynchus kisutch) have been in decline during the past three decades. Canada’s most endangered salmon stock, the Thompson River coho salmon, is being studied extensively as managers attempt to reverse these population declines. Investigators are using acoustic telemetry to track the migratory behaviour and survival of the Thompson River (and other) coho salmon stocks. Coho salmon pre-smolts are relatively small compared with salmonid species that are typically studied using acoustic telemetry; therefore the identification of the appropriate sizes of fish and tags to use is critical. This study tested the effects of surgically implanting the three smallest sizes of acoustic tags currently available on the growth, survival, tag retention, swimming performance and physical condition of coho salmon pre-smolts for 300 days post-surgery. Maximum tag size to body size ratios ranged from 15–17% by fork length and 7–8% by mass for the three tag sizes (11 cm fork length for a 6 × 19 mm tag, 12.5 cm for a 7 × 19 mm tag, and 14 cm for a 9 × 21 mm tag). Based on our results, it is unlikely that coho salmon pre-smolts implanted with acoustic transmitters following these size guidelines would have poor survival in studies of freshwater migratory behaviour as a result of the surgery or the tag.     

Stellate cells storing retinol in the liver of adult lamprey,Lampetra japonica

Summary Distribution, localization and fine structure of the stellate cells in the liver of lamprey, Lampetra japonica, were studied during the spawning migration by use of Kupffer's gold-chloride method, fluorescence microscopy for vitamin A (retinol) and electron microscopy. The stellate cells in the lamprey liver differ in some of their properties from those in mammalian livers. Stellate cells which store abundant retinol in lipid droplets, occur not only in the hepatic parenchyma, but also in the dense perivascular and capsular connective tissue of the liver and in the interstitium of pancreatic tissue. In the hepatic parenchyma these cells are located perisinusoidally or along thick bundles of collagen fibrils. The stellate cells display a number of large retinol-containing lipid droplets, granular endoplasmic reticulum, tubular structures, dense bodies, Golgi complex, microtubules, and microfilaments. In the space of Disse, the stellate cells and extracellular fibrilar components such as collagen fibrils and microfibrils (11–12 nm in diameter) are intervened between the two layers of basal laminae. Differentiation and possible functions of the stellate cells in the lamprey liver are discussed.     

MOLECULAR GENETIC EVIDENCE FOR PARALLEL LIFE-HISTORY EVOLUTION WITHIN A PACIFIC SALMON (SOCKEYE SALMON AND KOKANEE,ONCORHYNCHUS NERKA)

The Pacific salmon Oncorhynchus nerka typically occurs as a sea-run form (sockeye salmon) or may reside permanently in lakes (kokanee) thoughout its native North Pacific. We tested whether such geographically extensive ecotypic variation resulted from parallel evolutionary divergence thoughout the North Pacific or whether the two forms are monophyletic groups by examining allelic variation between sockeye salmon and kokanee at two minisatellite DNA repeat loci and in mitochondrial DNA (mtDNA) Bgl II restriction sites. Our examination of over 750 fish from 24 populations, ranging from Kamchatka to the Columbia River, identified two major genetic groups of North Pacific O. nerka: a “northwestern” group consisting of fish from Kamchatka, western Alaska, and northwestern British Columbia, and a “southern” group consisting of sockeye salmon and kokanee populations from the Fraser and Columbia River systems. Maximum-likelihood analysis accompanied by bootstrapping provided strong support for these two genetic groups of O. nerka; the populations did not cluster by migratory form, but genetic affinities were organized more strongly by geographic proximity. The two major genetic groups resolved in our study probably stem from historical isolation and dispersal of O. nerka from two major Wisconsinan glacial refugia in the North Pacific. There were significant minisatellite DNA allele frequency differences between sockeye salmon and kokanee populations from different parts of the same watershed, between populations spawning in different tributaries of the same lake, and also between sympatric populations spawning in the same stream at the same time. MtDNA Bgl II restriction site variation was significant between sockeye salmon and kokanee spawning in different parts of the same major watershed but not between forms spawning in closer degrees of reproductive sympatry. Patterns of genetic affinity and allele sharing suggested that kokanee have arisen from sea-run sockeye salmon several times independently in the North Pacific. We conclude that sockeye salmon and kokanee are para- and polyphyletic, respectively, and that the present geographic distribution of the ecotypes results from parallel evolutionary origins of kokanee from sockeye (divergences between them) thoughout the North Pacific.     

Microhabitat use by the larvae of cryptic lamprey species in <Emphasis Type="Italic">Lethenteron reissneri</Emphasis> in a sympatric area

Microhabitat use by the larvae of two cryptic lamprey species in Lethenteron reissneri, Lethenteron sp. N (northern form) and Lethenteron sp. S (southern form) larvae, as well as intraspecific variations on a size-related basis, were examined in a study area (500 × 5 m) located on a stream where they showed sympatric distribution. The total number of individuals collected from each of 31 quadrats (60 × 60 cm) ranged from 0 (0 n/m²) to 13 (36.1 n/m²). The distinct difference in habitat use was not observed between the two species in the present study area. Lamprey density was not significantly independent among the size groups (small and large) for each of Lethenteron sp. N and Lethenteron sp. S. The density of each size group of the two species was significantly correlated with some habitat variables, and stepwise multiple regression analysis revealed a positive association for a substrate with a smaller particle size and deeper depth for large individuals of Lethenteron sp. N and Lethenteron sp. S, respectively, suggesting that these conditions would be suitable for burrowing. On the other hand, small individuals of both species tended to occur in areas where there was a high content of medium sand and a faster current velocity, probably reflecting a preference for respiratory efficiency. Various condition of habitat should be maintained to conserve the cryptic lampreys.     

Growth,survival, and tag retention of steelhead trout (<Emphasis Type="Italic">O. mykiss</Emphasis>) surgically implanted with dummy acoustic tags

Recent advances in micro-electronics make the study of the migration of even small marine animals (>12 cm) over many 1000s of kilometres a serious possibility. Important assumptions in long-term studies are that rates of tag loss caused by mortality or tag shedding are low, and that the tagging procedure does not have an unacceptable negative effect on the animal. This paper reports results from a study to examine the retention of relatively large (24 × 8 mm) surgically-implanted dummy acoustic tags over a 7-month period in steelhead pre-smolts (O. mykiss), and the effects of implantation on growth and survival. Although there was some influence on growth to week 12, survival was high for animals > 13 cm FL. In the following 16-week period, growth of surgically implanted pre-smolts was the same as the control population and there was little tag loss from mortality or shedding. Currently available acoustic tags can be implanted in salmonid fish ≥12 cm FL, although combined losses from mortality and tag shedding were 33–40% for animals in the 12 and 13 cm FL size classes. By 14 cm FL, combined rates of tag loss (mortality plus tag shedding) for surgically implanted tags dropped to <15% and growth following surgery was close to that of the controls. Our results suggest that studies of ocean migration and survival over periods of many months are now feasible even for animals as small as salmon smolts. Surgically implanted salmon smolts are therefore good candidates for freshwater and coastal ocean-tracking studies on relatively long time scales (months). On such time scales, even relatively small salmon smolts may move thousands of kilometers in the ocean.     

Social rank and body size as determinants of positional behavior inPan troglodytes

A yearlong study of the positional behavior ofPan troglodytes at the Mahale Mountains National Park yielded 571 hr of observation.Cant (1987) articulated four predictions concerning the relationship between body weight/branch diameter and positional behavior based on the classic suspensory-ape paradigm. He noted that only two were supported by orangutan data. Three of these four hypothesis were not supported by chimpanzee data, as follows: there was no significant difference between the three largest males and the four smallest males in (1) branch diameters (5.8 cm vs 5.2 cm) nor (2) in the percentage of arm-hanging (13.6% vs 12.1%); and (3) large males did not arm-hang significantly more often than small males in any of three support diameter categories. The fourth hypothesis, that arm-hanging should be more common among smaller branches, was supported: arm-hanging as a percentage of all posture rose from 2.5% to 8.3% to 24% as stratum size decreased from >10 cm to <3 cm. The possibility that the first three hypotheses failed because of confounding effects of a correlation between body size and social rank was examined. Multiple regressions were done on 6600 2-min instantaneous observations on focal individuals. With social rank effects factored out, larger individuals preferentially utilized smaller, rather than larger supports. When positional mode frequencies were compared between large and small males matched for social rank, large males exhibited a lower frequency of arm-hanging than small males. An unexpected result was that social rank more consistently predicted branch diameter choice than body size. The most profound trend was for high ranking males to use larger supports, even though they spent more time in the terminal branches. These results suggest that (1) suspensory behavior is functionally related to small branch diameters; (2) chimpanzees do not prefer smaller branches, rather they are forced into them by food choice limitations; and (3) social rank more profoundly affects chimpanzee behavior than body weight.     

Two morphological types in the reproductive stock of three-spined stickleback,Gasterosteus aculeatus,in Lake Harutori,Hokkaido Island

Synopsis Two morphological types of the trachurus form (completely plated morph) of three-spined stickleback, Gasterosteus aculeatus, are found in Lake Harutori, Kushiro, east district of Hokkaido Island. For convenience, the two forms are referred to as ‘large type’ and ‘small type’ on the basis of body length (discrimination at 70 mm in length). The two types were examined for morphometric, meristic and reproductive characteristics. They differ in body length, the number of lateral plates, means of the 2nd dorsal spine length/body length and of the pelvic spine length/body length, the relationship between body length and head length, between body length and gonad weight, between body weight and gonad weight, and between body length and ovarian egg number; significant differences were present for each sex. These two types were compared with the anadromous stickleback migrating into the freshwater area near Lake Harutori to breed. The anadromous fish was morphologically much more similar to the large type than the small type. It is suggested that the large type is also an anadromous form and the small type is the permanent freshwater resident.     

A size-dependent migration strategy in Atlantic salmon smolts: Small smolts favour nocturnal migration

Migration theory states that migration behavioural strategies should be optimised to maximise fitness. Many studies have shown that in downstream migrating Atlantic salmon Salmo salar L. smolts, mortality from predation is high and negatively size dependent. The most common predators are birds and piscivorous fish that are mainly daylight feeders. Given the high mortality during this stage we should expect to observe smolts to follow predator avoidance strategies that may be affected by body size. We tested the hypothesis that small smolts have a higher tendency to exhibit predator avoidance strategies (i.e. nocturnal versus diurnal migration) than larger smolts. The number and size of out-migrating/downstream-migrating wild Atlantic salmon smolts was recorded as they passed through a glass-sided channel during April-May, 1996–1999. In all years, the mean size of nocturnal migrating smolts was significantly lower than the mean size of diurnal migrating smolts. Analysis of the size of smolts, during early and late stages of the migration period showed size-dependent nocturnal migration behaviour up to the end of April. After this, no such size dependent migration pattern was observed. However, small smolts (<100 mm) were absent during this period. We suggest that nocturnal migration is an adaptive behaviour that small Atlantic salmon smolts have to avoid predation by large daylight feeding visual piscivorous predators (e.g. pike Esox Lucius L. and fish eating birds).     

Ontogenetic changes in habitat use by whitefish,Coregonus lavaretus

Synopsis The whitefish, Coregonus lavaretus, in the lake Mj?sa exhibited two niche changes during their life cycle. Juveniles (< 25 cm body length) were confined to the shallow (0–30 m) epibenthic zone. Medium sized whitefish (25–35 cm body length) expanded their habitat use to include the deep (30–90 m) epibenthic zone as well as the pelagic zone. From a body length of 35 cm, habitat use was restricted to the deep epibenthic zone. Small fish in the shallow epibenthic zone ate small and medium-sized prey (zooplankton, insect larvae and surface insects). Medium-sized fish in this zone were in addition feeding on the larger amphipod, Pallasea quadrispinosa. In the pelagic zone, the diet of medium-sized whitefish was dominated by zooplankton, although some larger prey like surface insects and age-0 smelt, Osmerus eperlanus, were also eaten. In the deep epibenthic zone, the diet of both medium-sized and large (< 35 cm) whitefish consisted mainly of the large prey P. quadrispinosa.     

Annual and seasonal changes in diets of martens: evidence from stable isotope analysis

Theory predicts that generalist predators will switch to alternative prey when preferred foods are not readily available. Studies on the feeding ecology of the American marten (Martes americana) throughout North America suggest that this mustelid is a generalist predator feeding largely on voles (Microtus sp.; Clethrionomys sp.). We investigated seasonal and annual changes in diets of martens in response to the changing abundance of small rodents (Peromyscus keeni, and Microtus longicaudus) on Chichagof Island, Southeast Alaska, using stable isotope analysis. We hypothesized that martens would feed primarily on small rodents during years with high abundance of these prey species, whereas during years of low abundance of prey, martens would switch to feed primarily on the seasonally available carcasses of salmon. We also hypothesized that home-range location on the landscape (i.e., access to salmon streams) would determine the type of food consumed by martens, and martens feeding on preferred prey would exhibit better body condition than those feeding on other foods. We live-captured 75 martens repeatedly, from mid-February to mid-December 1992–1994. We also obtained marten carcasses from trappers during late autumn 1991 and 1992, from which we randomly sub-sampled 165 individuals. Using stable isotope ratios and a multiple-source mixing model, we inferred that salmon carcasses composed a large portion of the diet of martens in autumn during years of low abundance of rodents (1991 and 1992). When small rodents were available in high numbers (1993 and 1994), they composed the bulk of the diet of martens in autumn, despite salmon carcasses being equally available in all years. Selection for small rodents occurred only in seasons in which abundance of small rodents was low. Logistic regression revealed that individuals with access to salmon streams were more likely to incorporate salmon carcasses in their diet during years of low abundance of small rodents. Using stable isotope analysis on repeated samples from the same individuals, we explored some of the factors underlying feeding habits of individuals under variable ecological conditions. We were unable to demonstrate that body weights of live-captured male and female martens differed significantly between individuals feeding on marine-derived or terrestrial diets. Therefore, martens, as true generalist predators, switched to alternative prey when their principal food was not readily available on a seasonal or annual basis. Although salmon carcasses were not a preferred food for martens, they provided a suitable alternative to maintain body condition during years when small rodents were not readily available. Received: 1 May 1996 / Accepted: 24 February 1997     

The Atlantic salmon in fresh water: spawning,rearing and production

Summary Fluvial salmonids have evolved to use the diversity of habitats in natural streams for different life history stages and at different seasons. Required freshwater habitat of Atlantic salmon can be classified generally as that suitable (i) for spawning, (ii) for feeding during the major growing period, and (iii) for overwintering.Spawning habitat of salmon is usually in rapid water at the tail of pools on the upstream edge of a gravel bar, ideally with depths about 25 cm, in mean water velocities of about 30–45 cm s^-1, with maximum velocities about 2 body lengths s^-1, and with a substrate of irregularly shaped stones of cobble, pebble, and gravel.Underyearling salmon (<7 cm TL) are most common in shallow (<15 cm) pebbly riffles, whereas older and larger parr (>7 cm TL) are usually in riffles deeper than 20 cm with a coarse substrate. Depth preference increases with size. Multiple linear regression models quantifying parr habitat have identified substrate as an important variable, with a positive relationship to an index of coarseness. Negative relationships were found with mean stream width, range of discharge, and overhanging cover. Water chemistry, especially alkalinity, nitrates, and phosphates, are important regulators of production. Although similar variables had importance, coefficients among rivers differed. Interactions occur among variables. Further studies are required to quantify productive capacity of habitat for parr. Results suggest that useful models can be derived and if a river system is mapped, and stratified by habitat, then smolt yield could be predicted and the required egg deposition could be estimated.In winter, young salmon shelter among coarse substrate or move to pools, but continue feeding, with larger parr being more active.Feeding is in general opportunistic. Food consists mainly of insects, taken primarily in the water column, but also from the surface and at the bottom. Young salmon in flowing water are highly territorial but are less so in slow or still waters. In fast water, parr use their large pectoral fins to apply themselves to the substrate, allowing them to occupy this type of habitat with little expenditure of energy. Height above the substrate decreases with water velocity, but increases with temperature and social status. Although riffles are preferred habitat, and are relatively more productive, lentic waters can be occupied where there are few predators or severe competitors and may provide significant smolt yield in some systems. Selective segregation minimizes competition between salmon and brook charr or brown trout, but brook charr and brown trout may have negative effects on underyearling salmon, and on parr in pools, whereas salmon have negative effects on small brook charr and brown trout in riffles and flats. Competition by both interference and exploitation results in interactive segregation when the resource, mainly food, becomes limiting.Limited downstream movement of underyearling salmon may occur during the summer. Older juveniles may make upstream movements, but generally migrate downstream, with most movements in the spring, and a lesser peak of activity in the autumn. Dispersal tends to be mainly downstream, indicating that for full distribution, spawning areas are best located upstream. High densities of yearling parr may have negative effects on growth and survival of underyearlings in some river systems, but apparently not in others, so that future research is required in this regard. Density-dependent growth is evident where food is limiting, and can provide an indicator of densities of cohorts so that if a quantitative relationship has been derived, mean size from a sample can give an estimate of the density at that station, with minimum size occurring at carrying capacity. Such regressions vary between habitats with differing productive capabilities, so that future research could provide useful models for assessing productive capacity of a habitat, and optimum densities. Life history strategies can change with changes in density-dependent growth rates. Present stock-recruitment functions do not take environmental variables into consideration, and have limited applicability. Further research is required to determine optimum spawning requirements for salmon in different types of river systems in different geographical areas.     

Data on the adult marine and migratory phases in the life cycle of the southern hemisphere lamprey,Geotria australis Gray

Synopsis Large numbers of the Southern Hemisphere lamprey, Geotria australis, have been found in the regurgitated food of albatrosses breeding on South Georgia. This finding suggests that this lamprey is found in large groups at sea, presumably associated with its host, and can travel very large distances from its natal streams. The length and morphology of the individuals from South Georgia, which almost certainly represent a South American stock, were compared with those of representatives of the immediately pre- and post-marine trophic stages of G. australis caught in Western Australia. No significant differences could be detected either in the number of trunk myomeres or in the number and arrangement of the teeth. The mean length of the animals (± 95% confidence limits) from South Georgia was 45.9 ± 0.90 cm compared with 10.0 ± 0.23 cm and 62.5 ± 0.85 cm in G. australis collected from Western Australia just before they had entered and returned from the sea respectively.