Bret S. Danilowicz

The Diversity of Bacterial Communities Associated with Atlantic Cod Gadus morhua

The spatial and temporal changes in the bacterial communities associated with the Atlantic cod Gadus morhua were investigated using terminal restriction fragment length polymorphism (T-RFLP) analysis of 16S recombinant DNA (rDNA). Epidermal mucous was sampled from 366 cod caught in three harvest locations (Baltic, Icelandic, and North Seas) over three seasons (spring 2002, autumn 2002, and spring 2003), and an automated method for the high-throughput processing of environmental samples was developed using a Qiagen BioRobot. The analysis revealed that a diverse consortium of bacteria were found on fish; γ-proteobacteria and Cytophaga–Flavobacter–Bacteroides (CFB) species were dominant. T-RFLP peak profiles suggested that operational taxonomic units (OTUs) related to Photobacterium sp., Psychrobacter sp., and Bacteroides sp. were common to all sites in all three seasons, but there were intersite variations in community composition. Cod caught from different seas had distinct reproducible bacterial assemblages. Whereas communities from fish caught in the Baltic and Icelandic Seas were relatively stable over the three seasons, those from fish from the North Sea changed significantly over time.

The influence of pre-recruitment growth on subsequent growth and age at first spawning in Atlantic herring (Clupea harengus L.)

Calculation of the spawning stock biomass for fisheries management requires information on the numbers or proportions of fish in each age- or length-group that are mature each year. This study was conducted to determine the relationship between growth and age of first reproduction in herring stocks around Ireland. Measurements of otolith size at the onset of the first annulus (O1) were used to compare growth during the first year of life between 1-, 2-, and 3-group spawning herring collected from spawning grounds in the Celtic Sea over a period of 3 years. The 1-group spawning fish had significantly greater mean O1 measurements, and hence showed faster growth on average during the first year of life than 2- or 3-group spawning fish. Fish that exhibited slow growth during the first year were absent from the adult spawning population at age 1, but occurred at similar levels in the samples of 2- and 3-group spawning fish. Regression of O1 radius on fish length at capture showed that growth during the first year of life had a small but significant effect on subsequent growth up to age 3. The relationship between pre-recruitment growth and subsequent growth and age at first spawning has implications for recruitment patterns of juveniles from different nursery areas and for the lifetime fecundity of population components with differential growth.

Modelling settlement in open populations of reef fishes

Processes that act on individual larvae or on whole larval cohorts can affect settlement patterns in open marine populations. The interaction of these processes is explored using an individual-based simulation model in which the temporal pattern of settlement is the culmination of spawning, larval mortality, and larval duration. The model yielded a wide range of settlement patterns derived from a single spawning pattern. Sensitivity analyses indicate temporal settlement distributions are robust to the mortality rate but are sensitive to the variance associated with larval duration. We applied real data on coral reef fishes (larval production and settlement) to our model to generate hypotheses concerning the influence of cohort-wide and individual processes on their larval lives. Settlement of four out of six species was well matched by our model. Results of species matched by our model showed an approximately equal balance of cohort-wide and individual processes on larval mortality. Results for two species suggest individual-based factors predominantly influence larval duration, while results for another suggest cohort-wide processes predominate. That the settlement of two species was not adequately described using this model suggests additional factors, such as larval behaviour, should be considered by future modelling efforts.