ICES Journal of Marine Science: Journal du Conseil

doi: 10.1006/jmsc.1993.1037pmid: N/A

Everts, J. W.; Eys, Y.; Ruys, M.; Pijnenburg, J.; Visser, H.; Luttik, R.

doi: 10.1006/jmsc.1993.1038pmid: N/A

The method recently introduced in The Netherlands for setting acceptable levels (“quality criteria”) for toxic compounds in the environment is based on the extrapolation of laboratory toxicity data on effects of chronic exposure. With this method a safe concentration for the majority of the species (95%) can be derived (maximum permissible concentration or MPC). Although the method is an important improvement of the existing procedures developed by EPA, there are shortcomings. One in particular is the fact that biomagnification (accumulation of toxins from food) is not taken into account. This paper presents a correction factor for the risk of biomagnification in marine predatory birds.

Hommen, U.; Poethke, H.-J.; Dülmer, U.; Ratte, H. T.

doi: 10.1006/jmsc.1993.1039pmid: N/A

The application of ecological models for prognosis of pollutant effects on freshwater plankton communities is demonstrated by three examples: (1) an individual-based model to predict population interactions under pollutant stress in laboratory systems: (2) a compartment model for analysis of outdoor microcosm experiments and hazard assessment of test substances; and (3) a more detailed compartment model which is developed to predict direct and indirect effects of toxins in lakes of different trophic states. Possible approaches of estimating ecological risk using the described stochastic models are presented and problems are discussed.

Schobben, H. P. M.; Scholten, M. C. Th.

doi: 10.1006/jmsc.1993.1040pmid: N/A

This paper reviews the development of two probabilistic methods for marine ecotoxicological risk assessment (HAZARD and REFEREE) in The Netherlands. Both methods are based on a comparison of no-effect threshold concentrations (NEC) for marine biota with potential environmental concentrations (PEC) and differ with respect to NEC characterization. HAZARD uses a general NEC for an ecosystem based on interspecies variation in sensitivity. In REFEREE the NEC is characterized by an exposure-effect response for single key species, and the model further deals with the ecological consequences of toxic effects. The use of ecotoxicological and marine biological data is discussed in the light of handling variation and uncertainties.

Ross, A. H.; Gurney, W. S. C.; Heath, M. R.

doi: 10.1006/jmsc.1993.1041pmid: N/A

A previously published model is used to assess the effects of potential disturbances on a sea-loch ecosystem. Nutrient enrichment on its own has little or no effect, and the only major consequence of enhanced or depressed light conditions is a phase shift in the spring bloom. For the fjordic systems modelled, the most important type of disturbance is a reduction in grazing, which can result in high levels of phytoplankton biomass for much of the year. In the absence of grazing control, primary production in these systems becomes nutrient-limited, and it is concluded that the most serious threat would be posed by a reduction in grazing rate combined with an increase in nutrient loading.

Foote, K. G.; Stefánsson, G.

doi: 10.1006/jmsc.1993.1042pmid: N/A

The problem of acoustic abundance estimation is briefly reviewed. Under proper conditions, fish density can be measured with high precision along line transects. Observed variations in fish density consequently reflect biological variations, or inhomogeneity, in spatial distribution. The particular problem of estimating fish abundance over an area from line-transect measurements of fish density is defined. Related problems of estimating the variance of the abundance estimate and of mapping the spatial distribution are also defined. A partial list of candidate methods for solving the several problems is given. Among these, the so-called spatial statistical techniques appear to be most promising because of their exploitation of the observed spatial structure.

Junquera, S.; Perez-Gándaras, G.

doi: 10.1006/jmsc.1993.1043pmid: N/A

The population structure of the anchovy stock exploited in the Bay of Biscay (ICES Division VIIIb and c) and the north-west Iberian peninsula (northern Division IXa) is analysed using 30 morphometric and eight meristic characters. Discriminant function analysis applied to morphometric (shape) characters from commercial catch samples showed that anchovies found in the northern IXa Division are detectably different from those found in the South-east Bay of Biscay (Division VIIIb, east to 4°W). Individuals sampled west to 4°W are morphologically more similar to those of Division IXa. All Bay of Biscay anchovies are clearly separable from those of Mediterranean origin, which were included in the analysis to test the suitability of the method as a discriminant tool. Meristic characters do not allow efficient discrimination between individuals from those areas.The aim of this study only to determine recognizable phenotypic patterns, matching the diversity of environmental conditions existing in the Bay of Biscay, which can contribute to an understanding of the important long-term variability of the stock, both in biomass and geographic distribution. The underlying genetic basis, taxonomic status, or degree of reproductive isolation of the groups identified are not addressed.

Laptikhovsky, Vladimir V.; Nigmatullin, Chingis M.

doi: 10.1006/jmsc.1993.1044pmid: N/A

Ripe egg dimensions in the squid genus Illex are close to the minimum for cephalopods. The average diameter varies significantly depending on species (0.77–0.82 mm in I. coindeti, 0.75–0.88 mm in I. illecebrosus, and 0.96–1.04 mm in I. argentinus), on geographical distribution intraspecifically, e.g. I. argentinus (0.96–0.97 mm in the shelf groups and 1.04 mm in the slope oceanic group), and between pre-spawning and spawning females of the summer-spawning shelf group of I. argentinus (0.97 and 0.92 mm, respectively). The potential fecundity (PF), defined as total oocyte stock both in the ovary and oviducts, depends on mantle length (ML in each species. It varies from 90 000 (ML = 150–160 mm) to 800 000 (ML = 230–250 mm) in I. coindeti, from 200 000 to 630 000 (ML = 220–280 mm) in I. illecebrosus, and from 75 000 (ML = 150–170 mm) to 1 200 000 (ML = 360–380 mm) in I. argentinus. It is possible to estimate the actual value of PF shortly before vitellogenesis begins and up to a start of spawning, when the diameter of the smallest oocytes exceeds 0.05 mm. The summer-spawning shelf females of I. argentinus release about of 70% of PF. Their spawning is intermittent and ripe egg production decreases over time with only a 50% replacement of the initial stock of vitelline oocytes and a decreasing volume of eggs at each release. Feeding activity decreases and the mantle wall and internal organs shrink once spawning commences. In spent animals, a degeneration of both vitelline and protoplasmic oocytes occurs. The squids genus Illex is one of typical r-strategists among the cephalopods.

Hoggarth, Daniel D.

doi: 10.1006/jmsc.1993.1045pmid: N/A

The life history of the lithodid crab, Paralomis granulosa, is investigated from a 16-month time series of commercial catches and scientific samples from the Falkland Islands in the South Atlantic.The mean size at morphological maturity of male crabs is estimated from chelae allometry to be 52 mm carapace length (CL) and size at 50% functional maturity of females is found to be 46 mm CL. Adult P. granulosa live in sheltered inshore waters mostly between 10 and 40 m deep, juvenile crabs inhabit the dense kelp beds in the shallowest part of this range.The percentages of the total stock in each combination of moult stage and reproductive condition are estimated for each month. The moult seasons are thus shown to be cued by the warming of the inshore waters in the austral spring with adult males moulting about a month before the females. After moulting, female crabs release new clutches of uneyed eggs, which become eyed during the austral autumn and hatch in winter. A proportion of the female crabs, increasing in the largest sizes, moult without ovulating.At all times of year, large numbers of females also exist in intermoult condition, still with uneyed eggs, suggesting that the reproductive cycle takes longer than 1 year to complete. Juvenile crabs moult at least annually, along with the smaller adult males. A biennial moult cycle is proposed for most adults of both sexes.The spatial organization of the life cycle is examined by using cluster analysis to define a few relatively homogenous communities of crabs, in terms of the sex ratio, the proportions moulting in each sex, and the reproductive condition of the females. Three main communities occur in each of the moulting and non-moulting seasons. The most central community, in the deepest water, on a soft, muddy substratum, forms the main mating aggregation of the Choiseul Sound stock, containing moulting females and the largest non-moulting males. Incubating females, mid-way through their 2-year cycle, migrate off the spawning ground to more peripheral areas. The majority of adult males in moulting condition (along with a few large, apparently non-mating, females) occur on the shallowest coastal grounds. It is proposed that adult males alternate between moulting and feeding on warmer shallow grounds in some years, and attending the central mating aggregation, without moulting, in others.

Cook, R. M.; Reeves, S. A.

doi: 10.1006/jmsc.1993.1046pmid: N/A

The assessment of the stocks of North Sea Norway pout and sandeel has been inhibited by the absence of catch-at-age data in recent years. A statistical model for the analysis of seasonal catch-at-age, effort, and research vessel abundance data is developed in which all the model parameters can be estimated even when some data are missing. The model is used to estimate the age compositions for the year when data are missing and recent stock trends. The results compare very closely with the last conventional assessment of these stocks.