Atlantic capelin (Mallotus villosus) tetranucleotide microsatellites

Twelve microsatellite loci developed for Atlantic capelin (Mallotus villosus) using magnetic bead hybridization enrichment for tetranucleotide microsatellites revealed five loci composed of single repeat elements and six composed of complex repeats. Forty‐four beach‐spawning females from three different northwestern Atlantic Newfoundland beach‐spawning populations were screened at each locus. Loci were polymorphic (two to 59 alleles per locus) and all but two exhibited high heterozygosity (0.86–1). The loci are considered suitable for addressing questions related to fine‐scale population structure, spawning fidelity and survivorship/kinship issues.     

The timing of spawning in capelin (Mallotus villosus Müller) at a coastal location in eastern Newfoundland

We tested three hypotheses concerning the timing of spawning for a circumpolar species, capelin (Mallotus villosus), for which timing of larval emergence is known to be synchronized by physical conditions. The first hypothesis, developed from previous studies, was that spawning would be synchronized by upwelling events. Initial results from Middle Cove Beach in eastern Newfoundland indicated that spawning was not synchronized with upwelling. We next hypothesized that spawning was a function of several environmental variables. Results from logistic regression indicated that neither single-factor nor multi-factor models could explain the timing of spawning. Single variables could predict spawning in some years but no variable could reliably predict the time of spawning year after year. Finally, we hypothesized that the probability of spawning increased as a set of significant variables approached preferred levels. For capelin at Middle Cove, the set of variables that influence capelin spawning were identified as wave height, sea surface roughness and capelin abundance in the water. Thus only a combination of variables explained the timing of spawning for capelin. Preferred conditions for capelin spawning were wave heights less than 20 cm at the beach, a sea surface with a slight ripple, and an intermediate rank abundance of capelin in the water corresponding to hundreds to thousands of individuals. Capelin abundance alone was not a useful predictor. During the course of the study we observed a shift in the dates that capelin arrived and spawned at the beach. During 1987–1990 capelin spawned at Middle Cove Beach during June, but in more recent years (1991–1993) capelin did not arrive or spawn until July.     

Facultative semelparity in capelin Mallotus villosus (Osmeridae)-an experimental test of a life history phenomenon in a sub-arctic fish

Two alternative reproductive modes are present in fishes and reflect the age-specific mortality encountered through ontogenesis. Life-history hypotheses suggest that semelparity (i.e. death after a single reproductive event) evolves when the ratio of juvenile to adult survival is relatively high. Conversely, a relatively low ratio of juvenile to adult survival will favour iteroparity (i.e. death after two or more reproductive events). Fisheries management associates capelin (Mallotus villosus) spawning with mass mortality and semelparity even though life history models developed for this species suggest that females may follow an iteroparous trajectory. Capelin may spawn either inter-tidally on the beach or offshore in deeper, ocean waters but post-spawning survival and potential iteroparity has been notoriously difficult to assess in natural populations. Through a series of aquarium experiments we tested post-spawning survivability in a beach spawning and an ocean spawning population. The findings demonstrate that capelin which spawn offshore are absolute semelparous (death of both genders) while beach spawning capelin are iteroparous irrespective of sex. Beach spawning capelin regenerated ripe gonads from one spawning season to the next and provides the first conclusive evidence that capelin is physiologically capable of an iteroparous reproductive mode. The potential physical and biological processes which generate certain reproductive patterns in capelin are summarized and discussed in relation to life history hypotheses. We suggest that capelin is a facultative semelparous species in which dynamic changes within the semelparity-iteroparity continuum may occur as a result of subtle interactions between the spawning habitat, physical forcing, and predatory pressure.     

Trans-Arctic dispersals and the evolution of a circumpolar marine fish species complex, the capelin (Mallotus villosus)

Trans-Arctic dispersals and population and range expansions during the Pleistocene enhanced opportunities for evolutionary diversification and contributed to the process of speciation within the capelin, a northern marine-fish complex exhibiting a circumpolar distribution. Capelin is composed of four highly divergent and geographically discrete mitochondrial DNA (mtDNA) clades (609 bp; cytochrome b). Two clades occur in the North Atlantic, one associated with Canadian Atlantic waters, including Hudson Bay, and the second distributed from West Greenland to the Barents Sea. Two additional clades occur in the Arctic and northeast Pacific Oceans, representing the most recent divergence within the capelin phylogenetic tree. Judged from mtDNA diversity, capelin populations comprising all clades experienced at least one demographic and spatial reduction-expansion episode during recent Pleistocene glaciations that imprinted their molecular architecture. The large contemporary populations in the northeast Pacific and Arctic Oceans exhibited significant genetic structure whereas no such structure was detected in the equally extensive North Atlantic clades. All clades are characterized by one or two prevalent mtDNA haplotypes distributed over the entire range of the clade. Assuming a Pacific ancestor for capelin, we infer that capelin dispersed on two separate occasions to the North Atlantic. A more recent event resulted in the isolation of eastern Pacific and Arctic clades, with the Arctic clade positioned for a potential third Atlantic invasion, as revealed by the presence of this clade in the Labrador Sea. The Labrador Sea is a potential contact zone for three of the four capelin clades.     

Thermohaline tolerance and embryonic development in capelin eggs (Mallotus villosus) from the Northeast Atlantic Ocean

Capelin (Mallotus villosus) displays alternative reproductive modes throughout its circumpolar distribution. This predicts divergent thermohaline tolerance of eggs because they are incubated in either a steady offshore or variable intertidal environment. We investigate herein thermohaline tolerance of eggs from the offshore spawning Barents Sea capelin. Subsequently, we compare our data with those previously published on other offshore and intertidal spawning capelin populations across the Northeast Atlantic Ocean, with the aim of determining possible patterns in the thermohaline tolerance of eggs from the alternative reproductive modes. In a 2?×?4 factorial design various combinations of salinities and temperatures had only negligible effect on the survival of eggs until first hatch. The embryonic development rate from fertilisation until first hatch across populations and between the two reproductive modes suggested non-local thermohaline tolerance towards the physical factors during development. Finally, no differences were observed in salinity tolerance from fertilisation to first hatch between populations representing different reproductive modes. The present findings demonstrate wide thermohaline tolerance of capelin eggs regardless of population origin and reproductive mode.     

Panmictic population structure in the hooded seal (Cystophora cristata)

Two putative populations of hooded seals (Cystophora cristata) occur in the North Atlantic. The Greenland Sea population pup and breed on the pack ice near Jan Mayen ('West Ice') while the Northwest Atlantic population is thought to pup in the Davis Strait, in the Gulf of St. Lawrence (the 'Gulf'), and off southern Labrador or northeast Newfoundland (the 'Front'). We used microsatellite profiling of 300 individuals at 13 loci and mitochondrial DNA sequencing of the control region of 123 individuals to test for genetic differentiation between these four breeding herds. We found no significant genetic differences between breeding areas, nor evidence for cryptic nor higher level genetic structure in this species. The Greenland Sea breeding herd was genetically most distant from the Northwest Atlantic breeding areas; however, the differences were statistically nonsignificant. Our data therefore suggest that the world's hooded seals comprise a single panmictic genetic population.     

Polychaete assemblages of a sub-arctic Newfoundland fjord: habitat, distribution, and identification

This study explores the association of 24 polychaete species with sandy and muddy habitats located in a sub-arctic fjord, and across Atlantic Canada including Labrador, Newfoundland, and the Gulf of St. Lawrence. Key characters used to facilitate species identification are also summarized. Within Bonne Bay, distinctive polychaete assemblages were associated with specific sediment types and polychaete species richness and density were significant both predictors of corresponding total (infaunal) density and species richness. Polychaetes were denser and more diverse in sandy sediments, partly because sandy locales were associated with the outer portion of the bay, and therefore were closer to the more productive and diverse Gulf of St. Lawrence. In general, species that occupied both sediment types were more widely distributed within Bonne Bay and across the region. The biogeography of most species also suggests that the Bonne Bay fauna is transitional between Labrador and Acadian biogeographic provinces.     

Previously spawned Atlantic salmon ascend a large subarctic river earlier than their maiden counterparts

Spawning migration timing of maiden Atlantic salmon Salmo salar and previous spawners was analysed in the catches in 1989–2004 in the large subarctic River Teno in the northernmost parts of Finland and Norway. The hypothesis was that the migration timing of previous spawners and their maiden counterparts is similar, with the migration timing similar between sexes. In most cases, however, previous spawners were observed to migrate into the River Teno and its tributaries earlier than their maiden counterparts. The difference in run timing was especially evident between maiden one-sea-winter (1SW) Atlantic salmon and the corresponding group of previous spawners [1S1, 1 year at sea (1) followed by first spawning (S) and reconditioning period of 1 year (1) at sea and second spawning run] for both sexes in the River Teno and in its two tributaries. The same was also evident between 2SW maiden and 2S1 previous spawning female Atlantic salmon in the River Teno. Females showed earlier spawning migration than males both in previous spawners and maiden Atlantic salmon. Different maiden sea-age classes also showed differences in run timing as multi-sea-winter fish (2–4SW) ascended earlier than 1SW fish but the timing of 1S1 and 2S1 previous spawning females coincided. The results suggest that run timing of Atlantic salmon may not be strictly genetically fixed as previous spawners ascend earlier than they did on their first spawning migration as maiden fish, and indicated that the closeness of the reconditioning area of postspawners to the river of origin resulted in an early ascent. Run timing of different sea-age groups has major management implications if the populations are heavily exploited with numerous fishing methods in different periods of the fishing season, as in the River Teno system.     

Run timing of pelagic fishes in Gulf of St Lawrence: area and species effects

Run timings of four ubiquitous pelagic fishes in the Gulf of St Lawrence were compared for area and year effects. Run timing of alewife, Alosa pseudoharengus (Wilson), smelt, Osmerus mordax (Mitchill), and Atlantic salmon, Salmo salar L., was estimated at index rivers, and time of arrival of herring, Clupea harengus L., on spawning grounds was estimated from gillnet fisheries located around the Gulf, 1978–87. Time of pelagic fish migrations had strong species and area effects, but weak year effects. The species had their own unique migration times and durations, and could be divided into two groups: herring and smelt, which arrived in all areas of the Gulf at the same time; and alewife and salmon, which had significant area effects. Environmental data were not correlated with run timing. There was little annual variation in run timing among early-run species; only alewife had significant year effects. There was annual variation in the timing of late-run species, but it was not correlated with proximate environmental factors. Because run timing is an easily defined stock characteristic, observations over large areas and many years might be useful for understanding the impact of large-scale environmental changes on natural populations.     

Quaternary (Flandrian?) dinoflagellate cysts from the Grand Banks,off Newfoundland,Canada

A well-preserved assemblage of dinoflagellate cysts, probably of Flandrian age, was recovered from two piston cores on the Grand Banks, off Newfoundland, Canada. The assemblage, dominated by the dinoflagellate cyst species Operculodinium centrocarpum, is regarded as a mixed Gulf Stream/North Atlantic Drift—Labrador current association.     

Seabird species‐ and assemblage‐level isotopic niche shifts associated with changing prey availability during breeding in coastal Newfoundland

Shifting prey availability can lead to altered species interactions, indicated by variation in the dietary niche breadth and position of species within an assemblage. On the Newfoundland coast, annual inshore spawning migration of the dominant forage fish, Capelin Mallotus villosus, provides an excellent opportunity to investigate the influence of varying prey availability on dietary niche breadth and position among species. During June–August 2017, we investigated species‐ and assemblage‐level dietary responses to shifting Capelin availability of three Capelin‐eating, sympatrically breeding auk species, the Atlantic Puffin Fratercula arctica, Razorbill Alca torda and Common Murre Uria aalge. The diet of Leach's Storm Petrels Oceanodroma leucorhoa, which breed alongside the three auk species but are not known to rely on Capelin, was also examined to determine dietary shifts throughout breeding that were unrelated to Capelin availability. We quantified stable isotope ratios (δ¹⁵N, δ¹³C) in seabird blood components (plasma, cellular component) collected both before and after spawning Capelin arrived in the study area and compared isotopic niche breadth within a Bayesian framework. At the species level, auk trophic position increased and isotopic niche breadth narrowed after Capelin arrived, suggesting a more Capelin‐based diet. Simultaneously, trophic diversity of the auk assemblage, reflecting the extent of spacing among niches of species, decreased after spawning Capelin arrived inshore. Contrastingly, increased trophic position but broader isotopic niche breadth during higher relative to lower Capelin availability for Leach's Storm Petrel confirm that this species is probably not affected by the inshore arrival of Capelin, but instead that isotopic changes may be more related to a shift in breeding stage to chick‐rearing. Overall, our findings reiterate the importance of Capelin as a prey resource for breeding auks in coastal Newfoundland, but that the degree of reliance on Capelin varies among species, possibly allowing coexistence of these ecologically similar species. The findings highlight potential changing species interactions, such as increased competition, under declines in Capelin biomass.     

Regional differentiation of North American Atlantic salmon at allozyme loci

Allozyme variation was characterised by starch gel electrophoresis at 23 enzyme coding loci and one regulatory locus in Atlantic salmon from 53 rivers in Eastern Canada, encompassing the majority of the species' North American range. Variation among rivers was highly heterogeneous and eight of the 15 polymorphisms showed regionally restricted distributions. Nearest neighbour joining (NJ) analysis and multi‐dimensional scaling suggest six distinct regional groups; Labrador/Ungava, Gulf of Saint Lawrence, Newfoundland (excluding Gulf rivers), the Atlantic shore/Southern Uplands of Nova Scotia, the inner Bay of Fundy, and the outer Bay of Fundy. Approximately 25% of observed genetic variation was distributed among these regions with a weak though significant overall correlation of genetic and geographic distance (Mantel Test, r  = 0·255, P  = 0·005). Collectively, the rivers showed consistent divergence from European populations with strong bootstrap support for the two clusters across loci in the NJ analysis. Mean heterozygosity was 0·061 for both continental groups, but the European population showed more than twice the variation among populations. F _ST values were 0·076 and 0·176 for North America and Europe, respectively, with an overall F _ST of 0·330.     

Conservation versus commercial exploitation of seals with special reference to the Harp seal

For the past 15 years at least, government officials, scientists, observers and representatives of the news media have massed each year in the Gulf of St Lawrence, Canada, to witness the killing of Harp seals, Pagophilus groenlandicus , by the commercial sealing industry. This species has become possibly the most studied, the most reported and the most photographed species of wildlife in living memory.
Much of this attention has been directed towards arousing public opinion against the annual seal hunts in the Gulf and in the 'Front' areas of the Northwest Atlantic off the coasts of Labrador and Newfoundland. However, considerable scientific research has been done into the behavioural habits and population dynamics of the Harp seal.
Our present knowledge of this species and the co-operation afforded by the governments of Canada and Norway, enable the Labrador herd of the Harp seal to be used as testing ground for rational herd management based on sound conservation principles. But have we achieved our objective?     

Distributional patterns of humpback whales (Megaptera novaeangliae) along the Newfoundland East Coast reflect their main prey,capelin (Mallotus villosus)

On the Newfoundland foraging ground, humpback whales (Megaptera novaeangliae) primarily consume capelin (Mallotus villosus), which experienced a population collapse in the early 1990s, associated with altered timing of spawning and spawning migration. We examined whether humpback whale movement and distribution match these prey changes. Combining tour company whale sighting reports and photographs, citizen science reports of capelin spawning and scientific monitoring, whales were found to move northward along the east coast and whale aggregation presence within bays was associated with spawning capelin presence, being later in northerly bays. Whale aggregations arrived 8–20 days later than spawning capelin in northern bays, however, suggesting inconsistent tendencies to track high abundance spawning capelin aggregations during migration. Repeated scientific surveys during July–August 2009, 2010, 2012, 2014–2017, within a biological hotspot associated with capelin spawning sites in Notre Dame Bay, revealed that whale presence was influenced by the date of capelin spawning rather than capelin abundance metrics (i.e., biomass, number of shoals, shoal density, shoal area). A photo-identification catalog compiled during July–August, 2003–2017, revealed a 22% return rate of whales to the hotspot. Overall, findings suggest that capelin spawning sites are important foraging areas for humpback whales in coastal Newfoundland under these altered prey conditions.     

Foreword

Allozyme variation was characterised by starch gel electrophoresis at 23 enzyme coding loci and one regulatory locus in Atlantic salmon from 53 rivers in Eastern Canada, encompassing the majority of the species' North American range. Variation among rivers was highly heterogeneous and eight of the 15 polymorphisms showed regionally restricted distributions. Nearest neighbour joining (NJ) analysis and multi‐dimensional scaling suggest six distinct regional groups; Labrador/Ungava, Gulf of Saint Lawrence, Newfoundland (excluding Gulf rivers), the Atlantic shore/Southern Uplands of Nova Scotia, the inner Bay of Fundy, and the outer Bay of Fundy. Approximately 25% of observed genetic variation was distributed among these regions with a weak though significant overall correlation of genetic and geographic distance (Mantel Test, r = 0·255, P = 0·005). Collectively, the rivers showed consistent divergence from European populations with strong bootstrap support for the two clusters across loci in the NJ analysis. Mean heterozygosity was 0·061 for both continental groups, but the European population showed more than twice the variation among populations. F_ST values were 0·076 and 0·176 for North America and Europe, respectively, with an overall F_ST of 0·330.     

Population structure of flounder (Platichthys flesus) in the Baltic Sea: differences among demersal and pelagic spawners

We found significant population structure and isolation by distance among samples of flounder (Platichthys flesus) in the Baltic, Kattegat and Skagerrak seas using microsatellite genetic markers. This pattern was almost entirely due to a difference between flounder that have demersal spawning in the northern Baltic, as compared to pelagic spawners in the southern Baltic and on the west coast of Sweden. Among demersal spawners we found neither genetic differentiation nor any isolation by distance among sampling sites. We speculate that demersal flounder are descendants of a population that colonized the Baltic previous to pelagic spawners. The demersal flounder may thus have had longer time to adapt to the low salinity in the Baltic, and accordingly display egg characteristics that make it possible to reproduce at the low salinity levels in the northern Baltic. Among pelagic spawners significant isolation by distance was detected. Pelagic spawners have previously been shown to display clinal variation in egg size, which allows them to float also at the moderate salinity levels up to the region north of the island Bornholm. Management units for harvesting should ideally be based on true biological populations, and for the commercially important flounder up to 15 different management stocks in the Baltic have been suggested. We could not find a population genetic foundation for such a high number of management units, and our data suggest three management units: the northern Baltic (demersal populations), southern Baltic with the Oresund straits and the most northwestern sampling sites (Skagerrak, Kattegat and North Sea).     

The effect of growth rate,size, and season on oocyte development and maturity of Atlantic cod (Gadus morhua L.)

The effect of growth rate, body weight, age, and season on ovarian development and maturation was investigated for Atlantic cod (Gadus morhua L.) reared in the laboratory over 10 months, for each of two consecutive years, 1978–1980. Cod were also collected from the Gulf of St. Lawrence, the Scotian Shelf, Georges Bank, the Flemish Cap, and the N.E. Newfoundland Shelf.The state of maturity was recognized by oocyte size. Stage I oocytes did not vary in size with growth rate, season, age, or maturity, while the size of stage II oocytes was positively correlated with maturity and negatively correlated with maximum stage of development achieved. Ovarian wall thickness was positively correlated with age and maturity.The frequency distribution of stage I and II oocytes distinguished the state of maturation, with cod that would mature by the next spawning season having a minimum of 20% ($\text{x}\text{?}\text{= 42\%}$) of their oocytes at stage II or greater level of development.Maturing 3-yr-old cod had greater life specific growth rates than immature 3-yr-olds, but growth rates during the third year itself were not significantly different. A hypothesis of a three-part density-dependent mechanism controlling fecundity is postulated. Future reductions in partial recruitment and total fecundity are predicted for the Gulf of St. Lawrence cod stock based on calculated growth rates for Gulf cod in 1979.     

Spawning-strategy-dependent diets in two North American populations of Atlantic salmon Salmo salar

The diet of repeat-spawner Atlantic salmon Salmo salar was investigated using carbon and nitrogen stable-isotope values from the outer growth band of scales, which reflect the fish's consumption and growth during their most recent marine phase. Isotope values for S. salar displaying different spawning strategies were compared between and within the Miramichi and Nashwaak Rivers, New Brunswick, Canada and a Bayesian mixing model was used to infer dietary contributions from potential prey items. Significant differences in the stable-isotope values were found among spawning strategies and between rivers, indicating differences in diet and feeding area, consistent with hypotheses. Bayesian mixing model results inferred the main prey items consumed during marine feeding by S. salar to consist of hyperiid amphipods and capelin Mallotus villosus for repeat alternate spawners from both rivers, sandlance Ammodytes sp. for repeat consecutive spawners from the Miramichi River and amphipods for repeat consecutive spawners from the Nashwaak River. These results demonstrate the diversity of feeding tactics among S. salar spawning strategies from the same river and between populations from different rivers. Accounting for differences in prey availability and the subsequent impact on S. salar diet and spawner return rates (i.e., marine survival) will facilitate the application of ecosystem-based management practices, such as ensuring that fisheries for forage species do not indirectly adversely affect S. salar return rates.     

Mitochondrial DNA sequence variation and phylogeographic patterns in harbour porpoises (Phocoena phocoena) from the North Atlantic

The harbour porpoise (Phocoena phocoena)experiences high rates of incidental mortalityin commercial fisheries, and in some areasthese rates are sufficiently high to justifyconcern over population sustainability. Giventhe high incidental mortality, the resolutionof population structure will be important toconservation and management, but in the NorthAtlantic the relationships among many of theputative populations remain unclear. Aprevious genetic study demonstrated substantialgenetic differences between eastern and westernNorth Atlantic populations, however thelocation of this break remained unresolved. Inthe present study, we addressed this issue byincluding new samples from Iceland. Toinvestigate population structure, variation inthe mitochondrial DNA of 370 porpoises wascompared among six locations corresponding toseveral of the putative populations (Gulf ofMaine, Gulf of St. Lawrence, Newfoundland, WestGreenland, Iceland, Norway). The first 342base pairs of the control region were sequencedand genetic variation investigated by analysisof molecular variance (F _ST and _ST ) and ² withpermutation. Although some fine scalepopulation structure was detected, porpoisesfrom Iceland were found to be more similar tothe western populations (W. Greenland, Gulf ofSt. Lawrence, Newfoundland, Gulf of Maine) thanto Norway. Furthermore, porpoises from Norwaywere different from all other regions. Thesepatterns suggest the existence of adiscontinuity between Iceland and Norway,possibly the result of isolating events causedby repeated range contractions and expansionsthroughout Quaternary glaciation events withinthe North Atlantic. These results suggest thatharbour porpoise populations within the NorthAtlantic are distinguishable, but patterns mustbe interpreted in light of their historicalbiogeography.     

The ability of gadoids to take advantage of a short-term high availability of forage fish: the example of spawning aggregations in Barents Sea capelin

During 11 March to 4 April 2002, the distribution of Barents Sea capelin Mallotus villosus along the coast of Finnmark, northern Norway, was covered four times by combining acoustic survey with trawling, synoptically and simultaneously sampling capelin and its main fish predators; cod Gadus morhua, haddock Melanogrammus aeglefinus and saithe Pollachius virens. The surveys demonstrated how these gadoid predators were able to exploit such a short‐term abundance of forage fish. The predator aggregation as well as the stomach fullness and proportion of capelin in their diet followed the capelin spawning migration, increasing in areas and periods with increasing capelin abundance. Capelin clearly constituted most of the biomass in stomachs of cod (97%), haddock (87%) and saithe (96%). The stomach fullness was highest in cod and lowest in haddock, although in areas with low capelin abundance, saithe had more capelin in their stomachs. The total length (L_T) of capelin in predator stomachs increased with predator L_T, but the proportion of capelin in the diet was not influenced by predator L_T. The capelin in predator stomachs was significantly smaller than capelin in the trawl hauls, also when compared within the same sex, indicating feeding selectivity towards weaker individuals. Female capelin, being significantly smaller than the males, predominated in the diet of haddock, whereas in cod and saithe the sex ratio was more equal. Male capelin predominated in the predator diet during the pre‐spawning period, whereas the females predominated as the spawning commenced. During the overall study period, most of the female capelin in predator stomachs was in a pre‐spawning or a spawning stage, whereas the majority of the males appeared to be spent. Regardless of sex, the percentage of spent, relative to pre‐spawning or spawning capelin in the diet of the predators, followed the capelin spawning dynamics, increasing with time as the spawning progressed.