Combining population genomics with demographic analyses highlights habitat patchiness and larval dispersal as determinants of connectivity in coastal fish species.

Gene flow shapes spatial genetic structure and the potential for local adaptation. Among marine animals with nonmigratory adults, the presence or absence of a pelagic larval stage is thought to be a key determinant in shaping gene flow and the genetic structure of populations. In addition, the spatial distribution of suitable habitats is expected to influence the distribution of biological populations and their connectivity patterns. We used whole genome sequencing to study demographic history and reduced representation (double-digest restriction associated DNA) sequencing data to analyse spatial genetic structure in broadnosed pipefish (Syngnathus typhle). Its main habitat is eelgrass beds, which are patchily distributed along the study area in southern Norway. Demographic connectivity among populations was inferred from long-term (~30-year) population counts that uncovered a rapid decline in spatial correlations in abundance with distance as short as ~2 km. These findings were contrasted with data for two other fish species that have a pelagic larval stage (corkwing wrasse, Symphodus melops; black goby, Gobius niger). For these latter species, we found wider spatial scales of connectivity and weaker genetic isolation-by-distance patterns, except where both species experienced a strong barrier to gene flow, seemingly due to lack of suitable habitat. Our findings verify expectations that a fragmented habitat and absence of a pelagic larval stage promote genetic structure, while presence of a pelagic larvae stage increases demographic connectivity and gene flow, except perhaps over extensive habitat gaps.

Evaluating the effects of controlled flows on historical spawning site access, reproduction and recruitment of lake sturgeon Acipenser fulvescens.

Lake sturgeon Acipenser fulvescens spawn at the base of Kakabeka Falls, a 39 m waterfall on the Kaministiquia River, a tributary to Lake Superior. Access to this historical spawning site can be restricted or delayed due to hydroelectric flow fluctuations that coincide with the A. fulvescens spawning season. The objectives of this study were to determine (a) the necessary flow conditions that facilitate spawning site access; (b) quantity and duration of flow required for successful spawning and dispersal of larvae; and (c) evaluate recruitment of juvenile A. fulvescens in relation to flow. A. fulvescens spawning migrations were tracked using a stationary telemetry receiver that logged the movements of 166 A. fulvescens fitted with radio-transmitters. Unrestricted access to the spawning site was facilitated when spawning flow was controlled at 23 m3  s-1 in 2004 and 17 m3  s-1 in 2006. Fluctuating (0.5-8.5 m3  s-1 ) and delayed spawning flows resulted in restricted and delayed access to the spawning site. Flow duration for successful egg incubation, hatch and larval dispersal was determined by sampling larvae using drift nets and quantified using cumulative temperature units (CTU). Over 10 years, 10,083 larvae were captured between 31 May and 20 July with 97% of the drift occurring prior to 30 June. From the date of first spawning to the end of larval dispersal took an average of 38.6 days, and the mean CTU value was 398.6. In general, a minimum flow of approximately 14.5 m3  s-1 from the date of initial spawning to the accumulation of c. 400 CTU ensured successful hatch and larval dispersal. During the timeframe of this study, recruitment was variable. This study described the complex and variable reproductive life history of A. fulvescens and defined spawning flow requirements ecologically, which can be used to develop operational provisions at hydropower facilities to ensure successful reproduction.

How low can they go when going with the flow? Tolerance of egg and larval fishes to rapid decompression.

Egg and larval fish that drift downstream are likely to encounter river infrastructure and consequently rapid decompression, which may result in significant injury. Pressure-related injury (or barotrauma) has been shown in juvenile fishes when pressure falls sufficiently below that at which the fish has acclimated. There is a presumption that eggs and larvae may be at least as, if not more, susceptible to barotrauma injury because they are far less-developed and more fragile than juveniles, but studies to date report inconsistent results and none have considered the relationship between pressure change and barotrauma over a sufficiently broad range of pressure changes to enable tolerances to be properly determined. To address this, we exposed eggs and larvae of three physoclistic species to rapid decompression in a barometric chamber over a broad range of discrete pressure changes. Eggs, but not larvae, were unaffected by all levels of decompression tested. At exposure pressures below ∼40 kPa, or ∼40% of surface pressure, swim bladder deflation occurred in all species and internal haemorrhage was observed in one species. None of these injuries killed the fish within 24 h, but subsequent mortality cannot be excluded. Consequently, if larval drift is expected where river infrastructure is present, adopting design or operational features which maintain exposure pressures at 40% or more of the pressure to which drifting larvae are acclimated may afford greater protection for resident fishes.

Causes of larval drift of the fire salamander, Salamandra salamandra terrestris, and its effects on population dynamics.

The larval drift of the fire salamander was investigated over a period of three years in a mountain brook (Niederbergisches Land, F.R. Germany), as well in a laboratory water channel. The rate of larval drift fluctuated between 19% and 41% of the total population of larvae in a defined section of the brook during these three years. Most (83%) of the drifting larvae were hatchlings or very young stages. The drift was dependent on the strength of the current, the number of spawning females, the presence of suitable hiding places, sufficient space and adequate food. Hungry larvae drifted more often than satiated animals. The drift behaviour of hatchlings differed distinctly from that of older larvae. The significance of ecological factors on larval drift is discussed. It is evidently a more important factor in selection than has hitherto been recognized.

Could ocean currents be responsible for the west to east spread of aquatic invasive species in Maritime Canadian waters?

The circulation in the shelf seas of Maritime Canada is predominantly in the northeast-southwest direction. Despite the mean northeast-southwest flow, a number of AIS invasions have been observed to proceed in the opposite direction - from the Gulf of Maine, around Nova Scotia, and into the southern Gulf of St. Lawrence. Flow fields from a numerical circulation model are used to investigate whether these invasions could be due to drift in ocean currents. Particle tracking experiments are performed and probability density functions (PDFs) derived that describe the probability of drifting a given upstream distance in a given drift time. Analysis of these PDFs revealed that for invasions that took 20-40 y to occur, propagule drift in ocean currents could be responsible for the upstream spread, while this was not the case for short timescale invasions (<10 y). Rafting could be responsible for both short and long timescale invasions.

Fish larvae from the upper Paraná River: do abiotic factors affect larval density?

The purpose of this study was to evaluate the role of abiotic factors on fish larvae occurrence. Samplings were carried out monthly at 12 stations (grouped in four areas) in the Amambaí, Ivaí and Paraná rivers and in the Itaipu Reservoir (upper Paraná River basin), from October 1994 to January 1995 (spawning season). Simultaneously, we obtained water temperature, pH, electrical conductivity, dissolved oxygen, water level, water velocity, and rainfall. Principal Component Analyses (PCA) and Detrended Correspondence Analyses (DCA) were applied to summarize abiotic and larvae density data, respectively. Amambaí River differed significantly from the other areas in relation to abiotic factors. Itaipu Reservoir differed significantly from the other areas considering species composition, and the Ivaí River also differed from the Paraná River. The relationship among PCA and DCA axes were significant, indicating that abiotic factors do influence larva. For example: Leporinus elongatus prefered the Amambaí River, Hypophthalmus edentatus, Plagioscion squamosissimus, and Hoplias aff. malabaricus the Itaipu Reservoir, and Pimelodus maculatus, Auchenipterus osteomystax and Iheringichthys labrosus the Ivaí River. We suggest that species selected some abiotic factors characteristic to a given environment as spawning grounds.

O objetivo deste trabalho foi avaliar o papel de fatores abióticos na ocorrência de larvas de peixes. As amostragens foram realizadas mensalmente em 12 estações (agrupadas em 4 áreas) nos rios Amambaí, Ivaí e Paraná e no reservatório de Itaipu, de outubro de 1994 a janeiro de 1995 (época de desova). Simultaneamente, foram obtidos dados de temperatura, pH, condutividade elétrica, oxigênio dissolvido, nível da água, velocidade da água e precipitação. Análises de Componentes Principais (PCA) e de Correspondência com Remoção do Efeito de Arco (DCA) foram aplicadas para sumarizar os dados abióticos e as densidades de larvas, respectivamente. O rio Amambaí diferiu significativamente das outras áreas em relação aos fatores abióticos. O reservatório de Itaipu diferiu significativamente das outras áreas quanto à composição de espécies, tendo o rio Ivaí também diferido do rio Paraná neste aspecto. A relação entre os eixos da PCA e DCA foi significativa, indicando que os fatores abióticos influenciam as larvas. Por exemplo, Leporinus elongatus preferiu o rio Amambaí, Hypophthalmus edentatus, Plagioscion squamosissimus e Hoplias aff. malabaricus o reservatório de Itaipu e Pimelodus maculatus, Auchenipterus osteomystax e Iheringichthys labrosus o rio Ivaí. Assim, sugerimos que cada espécie seleciona um conjunto de características abióticas em um dado ambiente utilizado como local de desova.