Atlantic cod Gadus morhua in US waters are currently managed as 2 stocks: (1) a Gulf of Maine stock and (2) a Georges Bank and south stock. This designation is decades old and warrants re-evaluation in light of concerns that fisheries management units may not reflect biologically meaningful population units. In this study, we used 10 microsatellite loci, the PanI locus, and 5 single nucleotide polymorphism markers to characterize the population genetic structure of cod in US waters. We found significant differentiation among temporally and spatially divergent populations of cod (global F ST = 0.0044), primarily stemming from 2 potentially non-neutral loci, and evidence for a population structure that strongly contradicts the current 2-stock management model. This genetic structure was stable over a 5 yr period. Our results indicate that cod in US waters are broadly structured into 3 groups: (1) a northern spring-spawning coastal complex in the Gulf of Maine (GOM), (2) a southern complex consisting of winter-spawning inshore GOM, offshore GOM and sites south of Cape Cod, Massachusetts, and (3) a Georges Bank population. The strongest differentiation occurs between populations in the northern and southern complex (mean F ST = 0.0085), some of which spawn in the same bays in different seasons. By means of mixture analysis, young-of-the-year fish sampled on juvenile nurseries were assigned to the spawning complex of their origin. Our findings contribute to a growing body of knowledge that Atlantic cod and other marine fish populations are structured on a finer scale than previously thought and that this structure supports biocomplexity and locally adapted populations. As such, it may be warranted to re-evaluate current management units and tailor management plans toward this finer scale.KEY WORDS: Atlantic cod · Microsatellite DNA · Single nucleotide polymorphism · Population genetic structure · Stock identification · Gadus morhua Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 410: [177][178][179][180][181][182][183][184][185][186][187][188][189][190][191][192][193][194][195] 2010 the importance of processes that limit dispersal and promote self-replenishment of local populations, such as sedentary adult life history strategies (Robichaud & Rose 2004, Howell et al. 2008, spawning site fidelity (Taggart 1997), natal homing (Thorrold et al. 2001, Svedäng et al. 2007), egg and larval retention (Jones et al. 1999, 2005, Bradbury et al. 2008) and local adaptation (McIntyre & Hutchings 2003, Conover et al. 2006, Hutchings et al. 2007). The implications of such fine-scale population structure are important for effective management (Palumbi 2003, Bradbury et al. 2008, Reiss et al. 2009).One marine fish species known to exhibit fine-scale population structure in parts of its distribution is Atlantic cod Gadus morhua L. (see reviews in Waldman 2005 andCarvalho 2008). Atlantic cod is one of the most commercially important marine fishes in the world and comprises a p...

Juvenile Atlantic cod Gadus morhua (initial weight = 24.1 ± 1.4 g [mean ± SE) were fed diets in which fish meal (FM) was replaced with soy protein concentrate (SPC) and soybean meal (SBM) in isonitrogenous, isocaloric diets for 84 d. A standard marine finfish diet (3 mm, 54% protein, 14% fat) was modified to produce four experimental diets in which 50% of FM was replaced with soy at 0:1, 1:1, or 1:2 ratios of SPC:SBM and 100% FM replacement with a 1:1 ratio of SPC:SBM. No differences in mortality or feed intake were detected among treatments, and fish fed the 50% FM replacement diets, in any combination, grew as well or better than the control for all variables investigated. Cod fed the 100% FM replacement diet exhibited the lowest growth and differed from the control with respect to final body weight, growth, specific growth rate, and thermal‐unit growth coefficient. No enteritis was observed in histological sections. These results indicate that 100% fish meal replacement is not recommended, but 50% replacement can be used without significant reductions in growth or condition indices.

Follicular maturational competence and ovulatory competence in teleost fish refer to the ability of the ovarian follicle to undergo final oocyte maturation and ovulation, respectively, in response to gonadotropin stimulation and other external cues. Some gene products related to competence acquisition are likely synthesized during vitellogenic growth, as these follicles gain in vivo responsiveness to exogenous gonadotropin stimulation and can be induced to undergo maturation and ovulation. In Atlantic cod (Gadus morhua), gonadotropin responsiveness has been shown to be oocyte size-dependent, and only ovaries containing late-stage vitellogenic follicles can be induced to ovulate. The purpose of the present study was to compare gene expression patterns between mid (unresponsive) and late (responsive) vitellogenic ovaries to identify genes involved in gonadotropin responsiveness and the acquisition of maturational and ovulatory competencies. Representational difference analysis was conducted in two reciprocal comparisons using intact ovarian fragments and follicle wall-enriched tissues, and genes of interest were used in real time quantitative PCR to confirm differential expression. Few differences were detected in intact ovarian fragments, but type IV ice-structuring protein and gephyrin were upregulated later in development and may be involved in lipid and sulfur metabolism, respectively. Candidate gene assays for luteinizing hormone receptor and aromatase also exhibited significant upregulation during vitellogenesis. Many genes were differentially expressed in follicle wall-enriched tissues, including endocrine maturational regulators and smooth muscle genes. Overall, maturational and ovulatory competencies during vitellogenesis in Atlantic cod are associated with up- and downregulation of many genes involved in lipid metabolism, endocrine regulation, and ovulatory preparation.

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There is an interest to develop sugar kelp (Saccharina latissima) cultivation in the rural, eastern Maine region of the USA. Future farming efforts would benefit from an understanding of the genetic diversity and population structure of kelp, to inform management and conservation, and to identify genetic resources. The purpose of the present study was to characterize the fine-scale population genetic structure of kelp in eastern Maine, using twelve microsatellite loci. A total of 188 samples were genotyped from five sampling locations. Overall, kelp exhibited relatively low genetic diversity and small but significant differentiation among populations (FST = 0.0157). The greatest genetic difference was detected between two geographically close populations in Penobscot and Frenchman Bays, which is likely due to patterns in the Eastern Maine Coastal Current that may limit meiospore recruitment. The population structure could not be fully explained by an isolation-by-distance model. Fine-scale structuring was also detected among populations along the more continuous, eastern Maine coastline. These differences highlight that sugar kelp populations are finely structured across small spatial scales, and that future management and farming efforts should aim to maintain genetic diversity and assess the culture potential of local populations.