ICES Journal of Marine Science: Journal du Conseil

Polacheck, Tom; Vølstad, Jon Helge

doi: 10.1006/jmsc.1993.1001pmid: N/A

A regression model with spatially autocorrelated errors is used to explore the nature of the spatial structure of haddock on George Bank from 1963–1987. The model is fitted by a maximum likelihood (ML) estimation procedure, and the significance of the parameters is evaluated by the likelihood ratio method. The results suggest that for many of the years analyzed, information of depth and location of sampling stations can explain part of the variability of trawl catches-per-low. Information on the spatial distribution of haddock, as measured by the autocorrelation function, may be taken into account in model-based methods for estimating abundance, and may also be of use for designing future surveys. The potential use of a spatial prediction method for geographic mapping of density is discussed.

Pollock, David E.

doi: 10.1006/jmsc.1993.1002pmid: N/A

In many spiny lobsters, lifetime egg production per recruit, population egg production, and average larval settlement are all linked to mean size at maturity of females. Size at maturity is labile in these crustaceans, and like juvenile growth and survival rates, is greatly influenced by density-dependent factors. Changes in size at maturity of females (and hence in lifetime egg production per recruit) enables increases or decreases in population egg production to take place, regulating average long-term larval settlement intensity, and increasing or decreasing the degree of density-dependence of juvenile growth and survival rates. The latter determines the annual rate of recruitment to the adult stock, and together with maturity size, determines the annual egg production from the population.A feed-back process is operative, such that if egg and larval production declines to a large extent (as a result of sustained environmental changes or overfishing), growth and survival rates of juveniles increase, as does mean size at maturity of females. Increased fecundity per recruit then helps to offset the reduced egg production. This process may help explain the remarkable degree of resilience which some lobster populations display in response to high exploitation rates, but also suggests that recruitment overfishing may be currently taking place in several heavily fished lobster stocks.

Winters, G. H.; Wheeler, J. P.; Stansbury, D.

doi: 10.1006/jmsc.1993.1003pmid: N/A

Data from five spring-spawning herring stocks in the north-west Atlantic were analysed to test the effects of winter sea temperature and stock biomass on total reproductive output (i.e. ovary weight) and its constituent parts, egg size and fecundity. Annual variations in fecundity and ovary weight were best accounted for by overwintering temperatures 2–3 months prior to spawning and a density-dependent response to biomass changes. Further, annual variation in total reproductive output was much less than its constituent parts and was expressed as a non-linear trade-off between fecundity and egg size. Information available from the published literature suggests that this conservatism in reproductive output is a universal trait of herring stocks and acts to maximize efficiently larval survival under a wide range of environmental conditions.

Ugland, K. I.; Jødestøl, K. A.; Aspholm, P. E.; Krøyer, A. B.; Jakobsen, T.

doi: 10.1006/jmsc.1993.1004pmid: N/A

A large number of harp seals invaded the Norwegian coast in 1987 and 1988, when approximately 80 000 animals were drowned in the gillnet fisheries. The diet had the same composition and geographical variation as described for the previous invasion in 1902 and 1903, i.e. a dominance of cod and capelin in Finnmark, saithe in the Norwegian Sea, and herring in the Lofoten fjords. A physiological model is developed to study the sensitivity to variation in those parameters which are poorly known. An average seal is estimated to have consumed 4 ± 1 kg day−1 on the meagre diet (4.5% fat) during the invasion. In 1987 the harp seals consumed 215 000 ± 50 000 tonnes off Norway. Our estimate of the impact on the 1985 year-class of cod and the 1985 and 1986 year-classes of saithe is 110 000 000 ± 25 000 000 individuals eaten. This order of predation agrees well with the observed sudden decline of these three year-classes.

Godø, Olav Rune; Wespestad, Vidar G.

doi: 10.1006/jmsc.1993.1005pmid: N/A

The use of scientific survey data for assessing abundance of commercially important fish stocks has become a managerial necessity in many regions. Errors and bias in estimates from such surveys may thus have great economic impact. In the north-east Atlantic, abundance of cod has been estimated from bottom trawl surveys and acoustic surveys since 1981. In the Svalbard area, abundance indices derived from acoustic and bottom trawl surveys have differed considerably with discrepancies varying from year to year. At low stock abundance and particularly when the population is comprised of young fish, cod are distributed close to bottom and are thus optimally located for a bottom trawl survey, but are poorly recorded by the acoustic technique. In contrast, when abundant year-classes attain an age of 2–3 years and older, they are more pelagically distributed and clearly available for acoustic observation. Dependency on only one of the survey techniques could lead to severely biased stock estimates. A combination of estimates from the two methods is at present hindered by the lack of an absolute estimate of abundance, and by uncertainty in the actual volume sampled due to movement of fish during survey sampling. The vertical profile of the acoustic recordings and size composition and density of the population are factors which will affect fish availability to the two survey techniques differently. Such variation in availability seems to affect gadoid surveys in general. With a limited amount of additional effort changes in availability and selectivity can be monitored during the survey, and observed changes can be incorporated into analyses to compensate for potential bias due to variation in these parameters.

Richardson, Linda R.; Gold, John R.

doi: 10.1006/jmsc.1993.1006pmid: N/A

The purpose of this study were to: (i) develop mitochondrial (mt)DNA probes for two species-groups of reef fishes, and (ii) assay mtDNA restriction fragment length polymorphism (RFLP) variation in two reef fish species from the Gulf of Mexico. MtDNA probes for groupers of the genera Epinephelus and Mycteroperca and for jacks of the family Carangidae were generated and mtDNA fragment patterns of 34 enzymes were assayed from samples of red grouper (Epinephelus morio) and greater amberjack (Seriola dumerilli). Ten polymorphic restriction enzymes (yielding 12 distinct mtDNA haplotypes) were identified in the red grouper, while 19 polymorphic enzymes (yielding 23 distinct mtDNA haplotypes) were identified in greater amberjack. Estimates of percentage nucleotide-sequence divergence among haplotypes ranged from 0.09–0.59 (mean ± S.E. = 0.29 ± 0.02) in red grouper and from 0.09–1.32 (mean ± S.E. = 0.49 ± 0.02) in greater amberjack. Estimated mtDNA nucleon diversity values were 0.418 and 0.900 for red grouper and greater amberjack, respectively. Estimated intrapopulational percentage nucleotide diversities were 0.078 ± 0.003 (mean ± S.E.) for red grouper and 0.336 ± 0.006 (mean ± S.E.) for greater amberjack. Estimates of the evolutionary effective female population size (Nflel) were generated for both species and compared to Nflel values for eight other marine fish species or subspecies. The Nflel value for greater amberjack was more or less intermediate, whereas the Nflel value for red grouper was low. The latter may indicate that red grouper warrant immediate management attention. Heterologous hybridizations to mtDNAs of two other species of Epinephelus (E. adscensionis and E. fulvus) and to Myeteroperca phenax (using the red grouper probe), and to mtDNA of the horse-eye jack, Curanx lutus (using the greater amberjack probe), were successful. MtDNA data generated from red grouper and greater amberjack, as well as the potential to obtain mtDNA data from other grouper and carangid species, should prove useful in future studies of genetic variation and population differentiation in these important reef fishes.

Pihl, Leif; Ulmestrand, Mats

doi: 10.1006/jmsc.1993.1007pmid: N/A

A tagging experiment was carried out on the Swedish west coast (Skagerrak-Kattegat area, 55–59°N, 11–12°E) to study migration of juvenile cod (Gadus morhua). 437 and 4255 tagged (I-group) cod were released in early summer and autumn 1986, respectively, at five shallow (5 to 10 m) stations. Three years after release, 300(6.4%) tagged cod had been recaptured. During the summer and autumn of 1986 fish released both during the early summer and autumn 1986 were located close to the tagging sites, indicating limited movement during this time. At an age of 2 years and a standard length of 30 to 50 cm, a general offshore migration to deeper water was observed during winter of 1987. The main direction was to the south and west suggesting a migration to spawning areas in the eastern North Sea or in the southern Kattegat. The major offshore migration of 2-year-old cod suggests that local coastal spawning and coastal stocks are of minor importance on the Swedish west coast.

Basford, D. J.; Eleftheriou, A.; Davies, I. M.; Irion, G.; Soltwedel, T.

doi: 10.1006/jmsc.1993.1008pmid: N/A

A large-scale co-operative project involving a number of countries bordering the North Sea was initiated in order to provide information on the status of the benthic communities and the sedimentary environment and to assess the possible impact of anthropogenic influences on the health of the sea. In this paper the data obtained on the environmental parameters—grain size, organic carbon, chlorophyllous pigment content, and the distribution of the trace metals—are discussed together with the benthic biomass and species richness. From this information it can be seen that while the southern North Sea exhibits signs of pollution having had an impact upon the environment, the northern part has remained in a relatively unimpacted state.

Hamerlynck, Olivier; Hostens, Kris

doi: 10.1006/jmsc.1993.1009pmid: N/A

In 1988 juvenile bib (Trisopterus luscus) and whiting (Merlangius merlangus) were studied in a shallow coastal area by monthly sampling with fine-meshed nets. 0-group fish of both species are first caught in May. By the end of the first growth season bib reached about 150 mm SL (standard length), whiting about 170 mm SL. Maximal densities were recorded in June and by the end of the year most fish had left the area. The instantaneous mortality is estimated at 0.008 day−1 (0.77% day−1 for bib and 0.76% day−1 for whiting) for both species. In May both species depended almost exclusively on calanoid copepods. In June and July mysids and amphipods were the most important invertebrate prey, but small fishes such as gobies provided a substantial proportion of the energy requirements, especially in whiting. From August onwards shrimp and fish dominated the diet in both species. Using Jones' (1974) model, food consumption as per cent body weight day−1 varied between 4 and 6% during summer the declined to 2 to 3% in autumn. Total consumption per unit area of subtidal seafloor, by the 0-group fish of both species taken together, was estimated at 0.47 g ash-free dry weight (ADW) m−2 year−1 using Jones' (1974) model and at 0.57 g ADW m−2 year-1 using a conversion efficiency (P:C ratio) of 0.34.

Andreasen, Thomas Vennø; Gulliksen, Bjørn; Haug, Tore; Nilsen, Einar M.; Ringø, Einar

doi: 10.1006/jmsc.1993.1010pmid: N/A

Samples of four tissue-types from immature Atlantic halibut (Hippoglossus hippoglossus L.), captured in the autumn, were analysed for total protein content and for free and protein-bound amino acids. The analyses revealed a relatively high total protein content in the muscle tissues, whereas the liver and fin base “notch” had a lower protein content. The main amino acid residue of the protein was glutamate, with lysine, aspartate, leucine, and arginine also present in considerable amounts. The fraction of free amino acids and ninhydrin-positive substances was dominated by taurine.The results from the chemical analyses were treated statistically in order to determine possible sexual and/or tissue discrimination. This treatment revealed extensive heterogeneity between tissues, while indications of heterogeneity between sexes were doubtful.The data presented in this paper suggest a possible test diet for young Atlantic halibut and will serve as a good basis for comparison with captive halibut reared on man-made diets.