ICES Journal of Marine Science: Journal du Conseil

Kingsley, Michael C. S.

doi: 10.1006/jmsc.2002.1299pmid: N/A

Beacham, Terry D.; Brattey, John; Miller, Kristina M.; Le, Khai D.; Withler, Ruth E.

doi: 10.1006/jmsc.2002.1253pmid: N/A

We examined variation at seven microsatellite loci (Gmo3, Gmo8, Gmo19, Gmo34, Gmo35, Gmo36, and Gmo37) and PanI in some 5230 Atlantic cod (Gadus morhua) from 19 inshore and offshore locations around Newfoundland and Labrador. The mean FST estimate over all loci was 0.0080. Overall, the cod populations surveyed conformed to an isolation-by-distance structure, cod from more distant locations tending to be more genetically distinct. Among offshore sites, the Flemish Cap population (NAFO Division 3M) was the most distinctive, and among inshore sites, the Gilbert Bay population in southern Labrador (2J) was the most distinctive. In NAFO Divisions 3KL, no significant genetic differentiation was observed among inshore northern cod sampled in four bays (Notre Dame, Bonavista, Trinity, and Conception) along the northeast coast of Newfoundland, and the data do not support the hypothesis of separate “bay stocks”. Annual variation within sampling sites was as large, on average, as the differentiation among sampling sites. The inshore northern cod were distinct from the population in Gilbert Bay and from most offshore northern cod populations. On average, over all populations, regional differences in allele frequencies were seven times larger than annual variation. The offshore samples were more heterogeneous, and there may be at least three distinct offshore spawning populations of northern cod. In Subdivision 3Ps, no consistent differentiation was observed among sampling sites, two in inshore bays (Placentia, Fortune), and two offshore (Burgeo Bank, Halibut Channel). The southern Grand Bank (Divisions 3NO) may have a separate spawning population from those in other offshore sites, but additional sampling is required to confirm population distinctiveness.

Morris, Corey J.; Green, John M.

doi: 10.1006/jmsc.2002.1228pmid: N/A

The growth, length at age, time of spawning, food, and movements of the genetically distinct, resident northern Atlantic cod (Gadus morhua L.) in Gilbert Bay, Labrador, were studied over four consecutive years (1998–2001). Angling and plankton nets were used to sample all stages of the life history. During the study, 2453 cod were tagged with Floy t-bar tags, but none were recaptured outside the bay. Length-at-age is smaller than those of other Atlantic cod off Newfoundland and Labrador. Males mature at 31.0–35.5 cm total length (TL) and 4–6 years of age, and females at 31.4–42.1 cm, 4–8 years of age. Spawning starts shortly after ice retreats from the bay, usually in mid-May, and lasts for ∼3 weeks, a much shorter duration than reported for other northern cod. Timing appears critical to the retention of spawning products in the bay. Stomach contents indicated a wide range of benthic prey but that food availability may be low, contributing to the slow growth rate, individual cod targeting a small number of prey types. Gilbert Bay cod could be threatened if they continue to be managed as part of the Newfoundland–Labrador northern cod stock.

Stensholt, Boonchai K.; Aglen, Asgeir; Mehl, Sigbjørn; Stensholt, Eivind

doi: 10.1006/jmsc.2002.1249pmid: N/A

Data (trawl, acoustic, CTD) from scientific surveys along the Norwegian coast, in the North Sea, in the Barents Sea, west of the British Isles, and in the Irminger Sea are used. The vertical density distributions of blue whiting, cod, haddock, redfish, saithe, capelin, and herring are described in relation to environmental conditions and physiological limitations. The first four surveys mainly cover banks and shelf areas shallower than 500 m. The last two surveys, aimed at blue whiting and redfish, mainly cover shelf edge and deep-sea areas with depths from 200 to 1300 m and from 440 to 3000 m. In regard to cod some information from data-storage tags is used.For physoclists the relative vertical profile of each acoustic sample i.e. acoustic-area backscattering coefficient (sA), is expressed in terms of the relative pressure reduction level from seabed up to surface. Thus relative vertical profiles with different bottom depths are normalized and are made compatible for a discussion in terms of the free vertical range (FVR). This restriction to rapid vertical movement is evident in the physoclist species studied. For samples in the shelf area, the profiles show that blue whiting, haddock, saithe, cod, and redfish are mainly distributed within the bottom half of the water column. Some fish adapt to pelagic living especially in areas with high acoustic density and where the bottom is deep. Here a pelagically living fish is defined as an individual fish having a current free vertical range that does not include the seabed.For demersal fish, day and night relative vertical profiles are corrected for unequal day and night losses in the bottom acoustic dead zone, which is the zone near the seabed where echoes from fish cannot be discriminated from the sea bottom echo. Day and night samples are separated by the sun's passing 5° below the horizon. In most years evidence of diurnal vertical migration is found for all investigated species. In many cases of demersal fish there is a higher relative acoustic density (sA-values) in the mid-range of the bottom half of the water column in the daytime as opposed to the night-time. At night there is a degree of separation, one group of fish descends to aggregate near the seabed and another ascends. Inter-annual variations in the diel movement from different parts of the stock are discussed in relation to the inter-annual variations in age composition of the stock.

Beare, D. J.; Reid, D. G.

doi: 10.1006/jmsc.2002.1207pmid: N/A

Long-term, seasonal and spatial patterns in spawning activity of Atlantic mackerel (Scomber scombrus) along the continental shelf west of Europe were investigated. Stage I egg densities from all eight available international, triennial surveys (1977, 1980, 1983, 1986, 1989, 1992, 1995 and 1998) were modelled using generalized additive models. The data showed that seasonal and spatial patterns of spawning activity varied inter-annually. Total annual egg production peaked in 1989 with minima in 1983 and 1998. Further examination of these trends (1977–1998) showed that the intensity of spawning activity has shifted location, declining in the south and rising in the north. There was no direct link between stage I egg densities and sea surface temperature, although the rate of temperature increase along the shelf edge was strongly related to the total annual egg production by the mackerel.

Sætre, R.; Toresen, R.; Anker-Nilssen, T.

doi: 10.1006/jmsc.2002.1180pmid: N/A

The Norwegian spring-spawning herring is characterized by large, long-term stock size variations. The main population dynamics mechanism explaining these fluctuations is variation in recruitment. The recruitment to the stock varies by nearly three orders of magnitude. This study examines recruitment variability of herring emphasizing environmental influences on the determination of year-class strength, and on environmental signals indicating recruitment strength, such as conditions for breeding seabird populations. The Atlantic puffin (Fratercula arctica) is an important top predator of 0-group herring and its colonies in northern Norway are strategically situated for that purpose. Results from a long-term population study of puffins are incorporated into the study. The year-class strength for the Norwegian spring-spawning herring is predominantly determined before most of the herring larvae have passed the puffin colonies, i.e. in July. The extremely good year-classes, such as 1983, 1991 and 1992, seem to be characterized by very low mortality north of the colonies, i.e. during July–August. Based on the mean temperature in the Barents Sea in January (prior to spawning), the number of high wind speed events off northern Norway in April and the fledging success of puffin, we can predict year-class strength of herring in July.

Høst, Gudmund; Berg, Erlend; Schweder, Tore; Tjelmeland, Sigurd

doi: 10.1006/jmsc.2001.1176pmid: N/A

An approach to estimating the statistical uncertainty in age-specific abundance of Norwegian spring-spawning herring is presented. The method is applied to data from a survey on the overwintering stock in the Vestfjord system of northern Norway in December 1996. It is based on building separate statistical models for acoustic and biological data. The acoustic data are modelled as a gamma-transformed spatial random field and fitted to echo readings from the survey. The biological data are fitted to a two-stage model using multinomial sampling from Dirichlet-distributed age proportions. Uncertainty in the abundance by age distribution is obtained by bootstrapping. Previous assessments have a priori taken the abundance by age from a skewed distribution, such as gamma or log-normal families. In contrast, this analysis results in an estimated abundance by age that seems symmetric and does not display heavy tails.

Yoneda, Michio; Yamasaki, Shunji; Yamamoto, Keisuke; Horikawa, Hiroshi; Matsuyama, Michiya

doi: 10.1006/jmsc.2002.1254pmid: N/A

The age and growth of John Dory, Zeus faber, collected in the East China Sea between April 1999 and March 2001 was determined from vertebral centra. Length frequencies of males and females differed, and all fish >400 mm total length (TL) were female. The zonation pattern on the centrum surface was distinct, and a set of translucent bands (annuli) was visible. The precision of age estimates was relatively high for all ages. Monthly changes in the frequency of appearance of a translucent band on the outer margin of the centrum, and in the marginal increments, indicate that ring marks form once annually, between December and March. John Dory grow rapidly in their first year and more slowly thereafter. Male fish had 1–13 ring marks, females 1–15. Using the observed TLs at age, the growth of male John Dory can be expressed as TLt=446.7 [1−exp{−0.128 (t+1.465)}] and that of females as TLt=580.2 [1−exp{−0.112 (t+0.772)}]. Females seemingly grow faster and live longer than males, most fish older than 10 years being female.

Lekve, Kyrre; Stenseth, Nils Chr.; Gjøsæter, Jakob; Dolédec, Sylvain

doi: 10.1006/jmsc.2002.1247pmid: N/A

Long-term temporal variation in the community structure of fish species richness over the period 1953–1994 along the Norwegian Skagerrak coast is analysed in relation to abiotic environmental factors (oxygen saturation, salinity and temperature respectively at the sea surface, 10 and 50 m depth). Data on the observed number of fish species derive from a long-term and ongoing beach-seine monitoring programme being conducted each autumn. Data on observed fish species richness are analysed using multivariate techniques especially designed for the coupling of environmental and biological tables (Co-inertia analysis). The correlation structure of the abiotic variables is investigated by applying the STATIS (“Structuration des Tableaux A Trois Indices de la Statistique”) multivariate technique. We demonstrate that environmental variables in the deeper waters are linked to the community structure of the coastal zone of the Southern Skagerrak Coast. It is suggested that this effect probably operates through the Norwegian Coastal Current (NCC) and is a proxy measure for advective processes.

Bradshaw, C. J. A.; Hindell, M. A.; Michael, K. J.; Sumner, M. D.

doi: 10.1006/jmsc.2002.1246pmid: N/A

There is increasing emphasis put on the correlation of marine predator behaviour and foraging performance with the bio-physical properties of the ocean environment. However, spatial error in the estimated position of animals and the accuracy of interpolated, physical oceanographic data require the assessment of the appropriate spatial resolution at which to assess relationships. We recorded surface temperature data from 17 archival tags attached to female southern elephant seals at Macquarie Island during the post-lactation foraging trip of 1999–2000. Archival-tag temperature data were associated with twice-daily, at-sea positions derived from light levels (i.e., “geo-location”). We compared these surface temperatures and their associated spatial error to satellite-derived Multi-Channel Sea Surface Temperature (MCSST) data to assess at what spatial scale the agreement between the two data sources was highest. We considered scales from 50×50 km through to 500×500 km grid cells, at 50×50 km increments. Averaged over all individuals and assessed in fortnightly time periods, we found a peak in agreement between the mean surface temperature recorded by the archival tags and the MCSST data at 350×350 km grid cells (122 500 km2). We used logistic regression model selection to examine the effects of spatial scale, time period, latitude, longitude, and MCSST variance per grid cell on the agreement between the data sources. The most parsimonious model included all main effects, and a significant interaction between time period and latitude. There was also a trend for reduced agreement at higher latitudes, and there was a peak in temperature agreement in the general region around 180° longitude. There were two peaks in agreement during the early and latter parts of the post-lactation foraging trip, resulting probably from the more northerly latitudes travelled during these times and the improved MCSST coverage in the summer months. The 350×350 km scale recommended by this study should be appropriate for the study of coarse-scale associations between marine predators located using geo-location and physical oceanographic data during summer. However, the approach remains valid for predators located at sea using other positioning methods.