Captures of northern pike on the spawning grounds and measures of egg deposition showed that from 1975 to 1978 spawning occurred in April, after the onset of spring high waters and the warming of the water above 5–6 °C. Maximal egg deposition occurs on abandoned meadows, pastures, and shrub–grass areas, in water 60 cm or less. In the Bleury Stream area, these substrates lie mostly between elevations 30 and 30,5 m. Water temperature influences the length of the spawning and incubation periods. Spawning, egg incubation, and growth of the young to a mean length of 20 mm require approximately 40 days. From 1970 to 1977, two strong year classes (1973 and 1976) were produced; they were both followed by a weak year class. Air temperatures in June, summer water levels (June–September), and also the strength of the preceding year class, had a determining effect on year class strength.

Some aspects of the reproductive biology of the polychaete Gorgoniapolynoe caeciliae have been described for the first time. Gorgoniapolynoe caeciliae is a deep-sea commensal species associated with Candidella imbricata, an octocoral that populates the New England Seamount chain. Gorgoniapolynoe caeciliae is a dioecious species with an equal sex ratio and fertile segments throughout most of the adult body. The gonads of both sexes are associated with genital blood vessels emerging from the posterior surface of most intersegmental septa. In the female, oogenesis is intraovarian with oocytes being retained within the ovary until vitellogenesis is completed. The largest female examined contained over 3000 eggs with a maximum diameter of 80–90 μm. In the male, the testes are repeated in numerous segments and consist of small clusters of spermatogonia, spermatocytes, and early spermatids associated with the walls of the genital blood vessels. Early spermatids are shed into the coelom where they complete differentiation into mature ect-aquasperm with a spherical head (4 μm), a small cap-like acrosome, and a short mid-piece with four mitochondria. Indirect evidence suggests that this species is an annual breeder that releases its gametes into seawater and produces a planktotrophic larva following fertilization. The reproductive biology of G. caeciliae is consistent with that of most other polynoids including many shallow water species suggesting that phylogenetic history strongly shapes its biology.

No abstract

With multiple invasions, the potential arises for interactions between invasives inhibiting or promoting spread. Our goal was to investigate the interaction between two invasives, Eurasian watermilfoil (Myriophyllum spicatum) and rusty crayfish (Orconectes rusticus), which co-occur in several lakes in western Quebec, Canada, and to determine their overlap with littoral fish communities. Crayfish potentially aid milfoil dispersal by fragmentation or, alternatively, inhibit its proliferation through destruction and direct consumption. With a mesocosm experiment, we quantified milfoil fragment production versus biomass reduction by crayfish. More fragments were produced at medium to high crayfish densities, with a significant reduction of milfoil only at the highest densities, demonstrating the potential for both positive and negative interactions. Second, we determined the habitat preferences of each species by conducting a survey in the same lake. There was little overlap in the species' distributions, with each preferring different habitat features, indicating either a low probability of interaction or that interaction occurred historically, resulting in a contemporary exclusion pattern. While our experiment showed a potential for significant interaction, the low natural co-occurrence of these species suggests that they do not currently influence each other or that they previously excluded each other.Résumé : L'interaction entre de multiples espèces envahissantes peut inhiber ou favoriser leur dispersion. L'objectif de notre étude était de déterminer l'interaction entre deux espèces envahissantes, le myriophylle à épis (Myriophyllum spicatum) et l'écrevisse à taches rouges (Orconectes rusticus), introduites dans plusieurs lacs de l'ouest du Québec, Canada, et de déterminer leur chevauchement avec les poissons littoraux. Les écrevisses peuvent favoriser la dispersion du myriophylle par fragmentation, mais aussi diminuer sa prolifération par leur consommation et leur destruction. Une expérience en mésocosmes fut réalisée pour quantifier la production de fragments et la réduction de la biomasse des myriophylles par les écrevisses. Plus de fragments furent produits à des densités d'écrevisses moyennes et élevées alors que seules des densités élevées réduisirent significativement la biomasse, démontrant un potentiel d'interactions positives comme négatives. Ensuite, leurs habitats préférentiels furent déterminés par un échantillonnage dans le même lac. Il y avait peu de chevauchement dans leurs répartitions, chacune préférant différentes caractéristiques de l'habitat, ce qui indique une faible probabilité d'interaction ou alors une interaction historique ayant mené à l'exclusion actuelle. Alors que les expériences indiquent la possibilité d'une interaction significative entre ces deux espèces envahissantes, le faible chevauchement et les densités dans le milieu naturel suggèrent qu'elles ne s'influencent pas pour l'instant ou qu'elles se sont exclues l'une l'autre dans le passé.