page 455 Introduction 455 Redfish spawning areas and time 458 Larvae and fry (0-group) distribution and drift patterns 459 Juvenile distribution, nursery areas, and migration pattern 463 Adult distribution 463 Genetic differentiation 471 Conclusions 474 Acknowledgements 475 References 475 AbstractSignificant controversies exist over the three types of Sebastes mentella found in the Irminger Sea and adjacent waters. Preliminary genetic studies have given evidence for the existence of three distinct groups, characterized using several molecular genetic markers. The biological or ecological significance of these between-group differences has, however, not been evaluated. In the present paper, we review the life cycle of S. mentella in this area, based on published data. Spawning of S. mentella in the Irminger Sea takes place in a single area above Reykjanes Ridge. The larvae drift towards East Greenland from where they are carried to West Greenland (NAFO Subareas 0+1). Later they return to East Greenland where the main nursery area has been identified. There is evidence for a migration of juvenile fish from the nursery area into the open Irminger Sea, where many different cohorts spawn. We also compare these ecological data with the genetic results and we conclude that the observed genetic differences can be derived from possible genetic drift, selection or mostly from temporal variation (age dependency) which has also been reported for other species with as high longevity as S. mentella. We conclude that S. mentella in the Irminger Sea and adjacent waters comprises one single population.

Age determination of redfish is difficult. In this paper, the ages of Sebastes mentella on the Flemish Cap are validated by following year classes from 1991 to 2000. The criteria used for S. mentella are consistent and coherent. The growth of different year classes is described and compared, and density-dependence is demonstrated to influence the growth rate of the strong 1990 year class, growth of that year class being the slowest of those followed. The slow rate of growth prevented that year class from maturing at the anticipated age. Growth is also compared between sexes, of S. mentella, S. marinus, and S. fasciatus, revealing that females grow faster than males. Finally, growth rate is compared among species. S. marinus grows fastest and S. mentella slowest, although the influence of density-dependent growth in S. mentella needs to be taken into consideration.

Historical hydrographic data together with data from Spanish bottom trawl surveys are used to estimate geostrophic circulation over Flemish Cap and transport and heat fluxes across the 47°N line from 1988 to 2000. The data show a recurrence of anticyclonic circulation on Flemish Cap in July. We conclude that the topography plays a major role in determining the dynamics over the Cap. A coherent cold flow originating in the Labrador Current (LC) skirts around the northeastern flank with geostrophic velocities of ~0.07 ms-1 and partly recirculates around the southern and southwestern flanks of the Cap with a mean flow of ~0.03 ms-1 , thereby isolating a central anticyclonic core. This core generally contains warmer and less saline waters than the surrounding waters. The most significant source of variability of the water masses over Flemish Cap is linked to the variability of the advective flows, principally the offshore branch of the LC and oscillations of the north wall of the North Atlantic Current (NAC). The estimated mean northward and southward geostrophic heat fluxes over the Cap across 47°N balance to within approximately 10%, although with suggestions of a long-term trend in the net heat flux from positive (northward) in the late-1980s to slightly negative (southward) in the second half of the 1990s. The latter is attributed to an increase in the offshore branch of the Labrador Current over the bank. Linkages between the geostrophic heat fluxes over Flemish Cap and the shift in the Coastal Slope Water System and the NAO are examined. Enhanced Labrador Current flow during 1995-2000 was observed to strengthen the anticyclonic gyre anchored to the topography of the Cap.

Fecundity of redfish Sebastes mentella and Sebastes norvegicus in the Irminger Sea and Icelandic waters was analyzed in relation to several maternal features and oocyte developmental stages. The mean potential fecundity in S. norvegicus was estimated to be 123,300 oocytes and relative fecundity averaged 116 oocytes g-1. Mean potential fecundity in S. mentella was 50,013 oocytes and relative fecundity was 64 oocytes g-1. Strong fecundity down-regulation (50% on average) was observed during oocyte development estimated from September to November, when oocytes reached the advanced stage of vitellogenesis. This result implies that fecundity can only be comparable between individuals presenting the same stage of oocyte development. However, the development rates differed between species and between stocks, and therefore the same stage is reached at a different time of the year. Fecundity varied significantly with female weight and length, while condition had little influence on fecundity variation.

Morgan, M. J., Garabana, D., Rideout, R. M., Román, E., Pérez-Rodriguez, A. and Saborido-Rey, F. 2013. Changes in distribution of Greenland halibut in a varying environment. – ICES Journal of Marine Science, 70: 352–361. Fish are expected to respond to changing oceanographic temperature by altering their distribution. Off the coast of Newfoundland, Canada, there have been major changes in oceanographic temperature over the last several decades, with both record cold and record warm years being observed. Greenland halibut is an important flatfish species in the area, and is distributed in deep waters over a very wide geographic range. Thus, it might be buffered from temperature change in the overall area by reduced temperature variation at depth, and the diverse temperature conditions over its wide range. We examined intrapopulation variation in temperature and depth distribution, and the biological changes in relation to changes in available temperature. On the Flemish Cap, variation in available temperature was limited, and changes in depth were related to changing age composition and the differential depth distribution with age/size. In other areas there was a larger decline in available temperature, and associated with this, Greenland halibut moved to deeper waters and occupied warmer temperatures than they had previously. Concurrently, growth declined and condition increased. This study shows that shifts in distribution may not result in maintenance of homogeneous environmental conditions, and that resulting biological changes will be difficult to predict.

Egg production methods have been used successfully in the provision of advice for fisheries management. These methods need accurate and unbiased estimates of fecundity. We explore the reproductive strategy of horse mackerel and estimation of fecundity. Fecundity and fecundity regulation in relation to condition was investigated over a number of years. Fulton's K, lipid content, and hepatosomatic index increased after the start of spawning, though decreased again at the end of spawning. The increase in the gonadosomatic index, fecundity, and body condition after the onset of spawning suggests that horse mackerel utilizes food resources during the spawning season and might be an income breeder. However, the decline in K and lipid before the spawning season suggests that the first batch of oocytes is developed on stored energy. Fecundity varied between years and within a spawning season. Over latitude, variations in fecundity were small. K and lipid content are not reliable indices as proxy for fecundity. Batch fecundity appears to be heterogeneous across the spawning season but homogeneous across latitude. The homogeneity of batch fecundity over latitude could indicate that the daily egg production method is an appropriate approach for estimating the abundance of a wide ranging species, as horse mackerel.

The present study contributes to a better understanding of the daily spawning dynamics of southern NEA mackerel (Scomber scombrus) with implications for the estimation of batch fecundity. It shows that there is a time window during the day, mainly in the afternoon, during which the advanced oocyte mode in imminent spawners separates from the remaining, smaller oocytes. This synchronicity in the separation of the spawning batch amongst imminent spawners corroborates evidence for the existence of daily spawning synchronicity in the population. This is particularly important for applications of the daily egg production method, DEPM, because such pattern facilitates both the ageing of eggs for the estimation of the daily egg production at sea and the ageing of postovulatory follicles for the estimation of spawning frequency. For NEA mackerel, batch fecundity could only be measured when a clear hiatus was established between the spawning batch and the smaller oocytes. Hydrated females that do not show such hiatus would not be valid for batch fecundity measurements suggesting that the “hydrated oocytes method” is not fully applicable for this stock. Knowing the time of day at which the batch is separated, will facilitate the sampling of valid females for the estimation of batch fecundity.

The autodiametric method is a highly streamlined method for estimating fecundity of fish with determinate oocyte development pattern. Greenland halibut presents a peculiar reproductive strategy with two simultaneously cohorts one of large vitellogenic oocytes (for the current year) and another one of small vitellogenic oocytes (for the subsequent year). Results of this study showed that autodiametric method can be applied to estimate fecundity in Greenland halibut. Additionally, spatial differences in the autodiametric calibration curve were observed in the Northwest Atlantic, but did not translate into differences in fecundity at length. This is the first time that spatial differences between ACCs of the same species have been reported, what could be the result of (i) the unusual oocyte development pattern, or (ii) spatial differences in oocyte biochemistry. More research on the relative dynamics of oocyte cohorts simultaneously present in Greenland halibut ovaries and the factors (endo- or exogenous) influencing oocyte packing density could provide a better understanding of observed geographical differences.