ICES Journal of Marine Science

The upwelling off the NW coast of Africa in the vicinity of Cape Blanc was studied in February - March 1974 from aircraft and in September 1973 from Skylab. The aircraft study was designed to determine the effectiveness of a differential radiometer in quantifying surface chlorophyll concentrations. Photographic images of the S190A Multispectral Camera and the S190B Earth Terrain Camera from Skylab were used to study distributional patterns of suspended material and to locate ocean color boundaries. The thermal channel of the S192 Multispectral Scanner was used to map sea-surface temperature distributions offshore of Cape Blanc. Correlating ocean color changes with temperature gradients is an effective method of qualitatively estimating biological productivity in the upwelling region off Africa.

Zooplankton sampling in 1997 identified the frontal zone of the Norwegian Coastal Current as a reproduction habitat for Calanus finmarchicus in June–August. This area is subject to considerable ultraviolet radiation (UVR), as calculated from satellite observations of ozone and cloudiness. While in situ experiments indicated UVR-induced mortality in reproducing C. finmarchicus, monthly UVR doses during the actual reproduction period did not appear to affect the abundance of the resulting generation of adolescent copepodites (CIV-V) that accumulated in a fjord habitat during October 1983–2000. Local UVR in the spawning grounds of Arcto-Norwegian cod at the Lofoten Islands in March–May was positively correlated with the stock's 0-group index, which resulted in the rejection of the hypothesis that local UVR leads to high mortality of cod eggs or reduces the abundance of prey for cod larvae. Rather, the result suggests an indirect positive effect of UVR on the survival of cod eggs and larvae, possibly by controlling harmful microbes.

Eggert, H. and Tveterås, R. 2007. Potential rent and overcapacity in the Swedish Baltic Sea trawl fishery for cod (Gadus morhua). – ICES Journal of Marine Science, 64: 439–445. Many European Union (EU) fisheries have problems with depleted stocks and fleet overcapacity following the regulation of open-access regimes. Some EU countries have introduced individual vessel quotas (IVQs), which can stop “the race to catch” and provide fishers with incentives to minimize costs for a given catch. We model an IVQ fishery using a cost function approach and apply the methodology to the Swedish cod fishery in the Baltic Sea. Estimating a translog cost function for a data set of Swedish trawlers in 2001, we assess the potential gains from structural adjustment of the fleet. Results suggest a desired fleet reduction of 50–60% and a potential resource rent amounting to 25–30% of the landing value.

The case of fisheries management illustrates how the inherent structural instability of ecosystems can have deep-running policy implications. We contrast eleven types of management plans to achieve maximum sustainable yields (MSY) from multiple stocks and compare their effectiveness based on management strategy evaluations (MSE) using complex food webs in their operating models. Plans that primarily target specific stock sizes (B_MSY) consistently led to higher yields than plans to target fishing pressures (F_MSY). A new type of self-optimising control rule, introduced here to conquer uncertainty due to structural instability, led to intermediate yields. Plans to "maximise the yield from each stock separately" in the sense of a Nash equilibrium produced total yields comparable to plans to maximise total harvested biomass, but tended to be more robust to structural instability. Most types of plans outperformed single-species management plans that defined pressure targets without explicitly considering ecological interactions. Our analyses highlight trade-offs between yields, amiability to fair negotiations, and continuity with current approaches in the European context. Based on these results, we recommend directions for future developments of EU fisheries policy.

Two different ways of obtaining surface temperature structures with data from an orbiting platform are: (1) Analysis of radiometric recordings during one overpass over apparently cloud-free regions has provided the surface structures of an area. This method can be used to analyze a synoptic recording and has the further advantage of noting rapid changes in the sea surface temperatures over typical scales of a few days. (2) Mapping the sea surface temperature through use of a multispectral method which detects cloud-free conditions and uses the radiation for the determination of the sea surface temperature. This method includes data recorded from orbiting platforms over a period of 2 to 4 weeks; therefore, short-time fluctuations are smoothed out. The method is applicable to map ocean surfaces on a global scale. Both methods were used to study areas in oceans where upwelling exists.

Three abundance estimates - larval abundance estimate (June surveys), a 0-group index (August surveys) and an acoustic estimate of 1-group (September surveys) - were compared for the year classes 1981-1994 of Barents Sea capelin (Mallotus villosus Muller). There was a significant linear correlation (p=0.0001) between the 0-group index and the 1-group estimate, allowing for predictions to be made about year-class strength at the 1-group stage based on the 0-group indices. No correlation was found between the larval abundance estimate and the 0-group index, or between the abundance estimates at the larval and the 1-group stage.Copyright 1998 International Council for the Exploration of the Sea

The abundance of salmon lice was examined in two stocks of sympatric anadromous Arctic char and sea trout in sub-Arctic regions in northern Norway in June, July, and August 1992 and 1993. One stock feeds in a coastal area exposed to moderate salmon farming activity (exposed area), while the other feed in a region without salmon farms (unexposed area). The salmon lice infestation on both species differed significantly between the exposed and unexposed area as well as between years and also between weeks within the same year. We did not detect, however, any clear significant differences in salmon lice abundance between sympatric populations of Arctic char and sea trout, or between different size groups of the species. The 1992 and 1993 infestation pattern in the exposed area showed an epidemic tendency in both Arctic char and sea trout, characterised by a sudden increase in both prevalence and abundance of lice larvae in July 1992 (23.6±25.7 lice/fish) and August 1993 (19.9±20.8 lice/fish). We therefore suggest that salmon lice epidemics, previously only observed on sea trout, may also occur in populations of Arctic char, and that fish farming contributes to the elevated lice level in wild fish. The fish in the unexposed area were also infested, although at significantly lower levels than fish from the exposed area. The infestation peaked in August 1992 at 13.0±18.1 lice/fish and August 1993 at 3.9±4.5 lice/fish, suggested that lice originating on ascending wild Atlantic salmon, or lice larvae drifting from farming areas, may infest Arctic char and sea trout also in unexposed localities in Subarctic areas. Copyright 2001 International Council for the Exploration of the Sea

During a cruise in tropical waters of the Pacific Ocean, oblique plankton hauls with a special gear, designed with two nets on the same frame, were made on the RV “Coriolis” of the Centre ORSTOM of NOUMEA (New Caledonia). One of the nets was fitted with nylon gauze N° 000 (mesh aperture 0.91 mm) and the other with a fine mesh of N° 2 grade (0.34 mm). A comparative study deals with Amphipods and Copepods of the two catches. Selection lengths for the gauze N° 000 are determined. A considerable escapement through this filtering material takes place and the samples lose a great part of their representative and non-selective properties. Examination of the N° 2 mesh shows a sufficient retention of the Amphipods and an acceptable sampling of the calanoid Copepods. Nevertheless, a smaller mesh size (0.28 mm) is suggested for the Copepods as a whole.

Gurshin, C. W. D., Jech, J. M., Howell, W. H., Weber, T. C., and Mayer, L. A. 2009. Measurements of acoustic backscatter and density of captive Atlantic cod with synchronized 300-kHz multibeam and 120-kHz split-beam echosounders. – ICES Journal of Marine Science, 66: 1303–1309.Effective management strategies for Atlantic cod (Gadus morhua) in the Gulf of Maine require stock assessments based on accurate estimates of its abundance and distribution. If multibeam echosounders are to provide data for such estimates, the relationship between acoustic backscatter and fish biology must be better understood. Working towards this goal, a series of acoustic measurements was made using a 120 kHz, split-beam echosounder (Simrad EK60) and a 300 kHz, multibeam echosounder (Kongsberg EM3002). The transducers from both systems were fixed to a platform over a submerged 98 m3 cage made of 5 cm stretched-nylon mesh. After standard-sphere calibrations, the cage was stocked with live, mature Atlantic cod, with a mean total length of 80.7 cm (range: 51.5–105.0 cm). The echosounders synchronously collected acoustic data, while the cod were monitored with two underwater video cameras. Cod were incrementally removed from the cage to provide a time-series of acoustic backscatter at four densities (n = 128, 116, 66, and 23). Backscatter measurements of cod are compared between echosounders and over time, and the factors affecting the acoustically derived density estimates are discussed. The benefits and limitations of the EM3002 are highlighted.

Spares, A.D., Reader, J.M., Stokesbury, M.J.W., McDermott, T., Zikovsky, L., Avery, T.S., and Dadswell, M.J. 2007. Inferring marine distribution of Canadian and Irish Atlantic salmon (Salmo salar L.) in the North Atlantic from tissue concentrations of bio-accumulated caesium 137. – ICES Journal of Marine Science, 64: 394–404. Atlantic salmon returning from marine migrations to eastern Canada and western Ireland during 2002 and 2003 were analysed for tissue concentrations of bio-accumulated caesium 137 (¹³⁷Cs). Salmon from Canadian and Irish waters demonstrated concentrations (0.20 ± 0.14 Bq kg⁻¹ and 0.19 ± 0.09 Bq kg⁻¹, mean ± s.d., respectively) suggesting similar oceanic feeding distributions during migration. Canadian aquaculture escapees had a similar mean tissue concentration (0.28 ± 0.22 Bq kg⁻¹), suggesting migration with wild salmon. However, significantly higher concentrations in 1-sea-winter (1SW) escapees (0.43 ± 0.25 Bq kg⁻¹) may alternatively suggest feeding within local estuaries. High concentrations in some Canadian 1SW salmon indicated trans-Atlantic migration. Low concentrations of Canadian multi-sea-winter (MSW) salmon suggested a feeding distribution in the Labrador and Irminger Seas before homeward migration, because those regions have the lowest surface water ¹³⁷Cs levels. Estimates of wild Canadian and Irish salmon feeding east of the Faroes (∼8°W) were 14.2% and 10.0% (1SW, 24.7% and 11.5%; MSW, 2.9% and 0.0%), respectively. We propose that most anadromous North Atlantic salmon utilize the North Atlantic Gyre for marine migration and should be classified as a single trans-Atlantic straddling stock.

Ganzedo, U., Zorita, E., Solari, A. P., Chust, G., Santana del Pino, A., Polanco, J., and Castro, J. J. 2009. What drove tuna catches between 1525 and 1756 in southern Europe? – ICES Journal of Marine Science, 66: 1595–1604. From 1525 to 1756, catches of tuna in almadrabas (trapnets) fluctuated greatly, but the overall trend was a downwards one. The aim of this study is to assess the potential influence of climatic factors on tuna fishing. We performed time-series analysis of the climate over the years 1525–1756 and determined whether such events can be related to historical data on bluefin tuna catches in the almadrabas of Medina Sidonia. We used a generalized linear model to relate the tuna catches to climatic parameters. We carried out variance partitioning analysis of tuna catches to assess the relative contribution of climate from temporal autocorrelation. The temporal autocorrelation in tuna catches was used as a surrogate for the contribution of the population dynamics to variation in the catch series. The results indicated that climate accounted for up to 12.3% of the total variance, the temporal effects (autocorrelation) accounted for up to 38.8% of the total variance, and up to 35.7% of the catch was accounted for by the joint effect of the two components. The significant variance accounted for by climate suggests that low temperatures during the Maunder minimum (the so-called “The Little Ice Age”, years 1640–1715) may have reduced both recruitment and abundance of tuna in the North Atlantic and the Mediterranean. Our findings suggest that both environmental and population dynamic components played an important role in regulating the almadraba catches in Medina Sidonia.

Guerra, Á., Roura, Á., González, Á. F., Pascual, S., Cherel, Y., and Pérez-Losada, M. 2010. Morphological and genetic evidence that Octopus vulgaris Cuvier, 1797 inhabits Amsterdam and Saint Paul Islands (southern Indian Ocean). – ICES Journal of Marine Science, 67: 1401–1407. The coastal octopus at Saint Paul and Amsterdam Islands is Octopus vulgaris Cuvier 1797. Meristic and morphological characters, along with phylogenetic analysis of COI and COIII DNA sequences, were used to identify 11 animals collected in 2000 or 2001. The range of the species is therefore expanded to include the oceanic islands of the central southern Indian Ocean. The trees also depicted the genus Octopus as polyphyletic and O. vulgaris sense Cuvier or sensu stricto as monophyletic.

Urquhart, K., Pert, C. C., Kilburn, R., Fryer, R. J., and Bricknell, I. R. 2008. Prevalence, abundance, and distribution of Lepeoptheirus salmonis (Krøyer, 1837) and Caligus elongatus (Nordmann, 1832) on wild sea trout Salmo trutta L. – ICES Journal of Marine Science, 65: 171–173.Lepeophtheirus salmonis (Krøyer, 1837) and Caligus elongatus (Nordmann, 1832) were found on 100% and 90%, respectively, of 30 wild sea trout from the east coast of Scotland. Mean abundances of the same two sea lice were 7.8 and 7.7, respectively. The distribution of the two species of sea louse differed, however, with a greater proportion of L. salmonis in the posterior and anterior dorsal regions, and a greater proportion of C. elongatus in the caudal and posterior ventral regions.

Robinson, M. 2008. Minimum landing size for Northeast Atlantic stocks of deep-water red crab, Chaceon affinis (Milne Edwards and Bouvier, 1894). – ICES Journal of Marine Science, 65: 148–154.Annual landings of the deep-water red crab (Chaceon affinis) in the NE Atlantic have fluctuated around 1000 t for much of the past decade, but they dropped significantly in 2006. No EU or National Member State legislation governs the harvest of the species, and because of the on-board processing, it is difficult to set a single minimum landing size (MLS) based on carapace width (CW) alone. As the claws are detached during processing and represent the most valuable component of the catch, a supplementary MLS based on claw length (CL) for onshore inspection and enforcement would seem appropriate. Physiological size-at-maturity and morphometric claw data were used to derive primary (CW) and secondary (CL) MLS. All males and females are mature at 110 and 125 mm CW, respectively, and 50% of females are mature at 109 mm CW. Because of a lack of information relating to the biology, distribution, and fishing mortality of the species, and a doubt as to real landing statistics, a conservative MLS of 120 mm CW and 72 mm CL is suggested, representing the first use of commercial fisheries data to suggest MLS for this otherwise unregulated fishery.

Valle, S. R., and Herzka, S. Z. 2008. Natural variability in δ¹⁸O values of otoliths of young Pacific sardine captured in Mexican waters indicates subpopulation mixing within the first year of life. – ICES Journal of Marine Science, 65: 174–190. Oxygen stable isotopes were measured in whole sagittae of young Pacific sardine (δ¹⁸Ooto) collected throughout their range in the Mexican Pacific to quantify natural variability, to reconstruct temperature histories, and to infer whether fish mix at a population or subpopulation level. Isotopic values and derived temperature estimates (Toto) of sardine captured simultaneously showed high variability (up to 2.0‰ and 10°C at a given location). Given limited variations in salinity, this implies differences in thermal history and the prevalence of subpopulation-level mixing processes. We tested the null hypothesis of local residence by comparing δ¹⁸Ooto values with predicted isotopic values on a location-specific basis, and age- and location-specific average sea surface temperatures (SSTs) with derived Toto. Some fish exhibited values outside the local range of predicted oxygen isotope values and SSTs, suggesting that they were not permanent residents. Using an otolith growth model, we show that otolith growth and age differences cannot fully account for the variability in δ¹⁸Ooto values. The absence of significant differences in δ¹⁸Ooto values between the Pacific and Gulf indicates that oxygen isotope ratios cannot be used to examine population structure or migration among these regions. However, they can be used to infer mixing within and among subpopulations.

Hufnagl, M., Temming, A., Siegel, V., Tulp, I., and Bolle, L. 2010. Estimating total mortality and asymptotic length of Crangon crangon between 1955 and 2006. – ICES Journal of Marine Science, 67: 875–884.Total mortality (Z, year−1) of southern North Sea brown shrimp (Crangon crangon) was determined as Z = θK, based on the von Bertalanffy length–growth constant (K, year−1) and θ derived from length-based methods. Mortality estimates were based on length frequency distributions obtained from four long-term dataseries (1955–2006): German Demersal Young Fish Survey, Dutch Demersal Fish Survey, and two German Bycatch series (Büsum and East Frisia). Four methods to estimate θ and L∞ were evaluated. Highest total mortality (Z = 8 year−1) was estimated for the early 1990s, and the lowest (Z = 4 year−1) for the 1960s. Accounting for these differences, a median Z rather than mean values was calculated for the whole series, and the value ranged from 5.74 (Ssentongo and Larkin method), through 5.65 (Beverton and Holt method) and 5.64 (Jones and Zalinge method), to 5.35 (length-converted catch curves). Over the whole period, an increase in θ and a decrease in the proportion of shrimps >60 mm in the catch was observed, whereas asymptotic length L∞ remained constant (at 79.3 mm total length).

Crawford, R. J. M., Dundee, B. L., Dyer, B. M., Klages, N. T., Meÿer, M. A., and Upfold, L. 2007. Trends in numbers of Cape gannets (Morus capensis), 1956/57–2005/06, with a consideration of the influence of food and other factors – ICES Journal of Marine Science, 64, 169–177. Cape gannets (Morus capensis) breed at six colonies in Namibia and South Africa. Population size averaged about 250 000 pairs over the period 1956/1957–1968/1969 and about 150 000 pairs from 1978/1979 to 2005/2006. Over the whole 50-y period, numbers at the three Namibian colonies fell by 85–98%, with greater proportional decreases in the south. There were increases at two South African colonies between 1956/1957 and 2005/2006. The colony at Lambert's Bay increased between 1956/1957 and 2003/2004, but attacks by Cape fur seals (Arctocephalus pusillus) on birds at nests caused abandonment of the entire colony in 2005/2006. Long-term changes at colonies are thought to be largely attributable to an altered abundance and distribution of prey, especially sardine (Sardinops sagax) and anchovy (Engraulis encrasicolus). In both Namibia and South Africa, the numbers of Cape gannets breeding were significantly related to the biomass of epipelagic fish prey. Over the 50-y period, there was also a marked similarity in the proportions of gannets and epipelagic fish in the Benguela system, which were present in Namibia and South Africa. In the 2000s, there was an eastward shift in the distribution of sardine off South Africa and a large increase in the number of gannets breeding at South Africa's easternmost colony. When sardine were scarce off South Africa, gannets fed on anchovy, but off Namibia anchovy only temporarily and partially replaced sardine. Ecosystem management measures that might improve the conservation status of Cape gannets are considered.

Bacon, P. J., Palmer, S. C. F., MacLean, J. C., Smith, G. W., Whyte, B. D. M., Gurney, W. S. C., and Youngson, A. F. 2009. Empirical analyses of the length, weight, and condition of adult Atlantic salmon on return to the Scottish coast between 1963 and 2006. – ICES Journal of Marine Science, 66: 844–859. Sea age, size, and condition of adult Atlantic salmon (Salmo salar) are prime determinants of individual, and hence population, productivity. To elucidate potential mechanisms, 151 000 records of salmon returning to six Scottish coastal sites over 44 years were analysed for length, weight, and condition, by site, sex, sea age, and river age. After correcting for capture effort biases, all sites showed seasonal increases in length and weight for both 1 sea winter (1SW) and 2SW fish. However, whereas condition increased slightly with season for 2SW, it decreased notably for 1SW. Sites showed common decadal trends in length, weight, and condition. Within years, length and weight residuals from trends were coherent across sites, but residuals from condition trends were not. Rates of seasonal condition change also showed decadal trends, dramatically different between sea ages, but common across sites within sea-age groups. Longer salmon were disproportionately heavy in all seasons. 1SW condition was markedly lower in 2006. Detrended correlations with oceanic environmental variables were generally not significant, and always weak. A published correlation between the condition of 1SW salmon caught at a single site and sea surface temperatures in the Northeast Atlantic could not be substantiated for any of the six fisheries over the wider time-scales examined.

Brander, K. M. 2007. The role of growth changes in the decline and recovery of North Atlantic cod stocks since 1970. – ICES Journal of Marine Science, 64: 211–217.

Overholtz, W. J. and Link, J. S. 2007. Consumption impacts by marine mammals, fish, and seabirds on the Gulf of Maine–Georges Bank Atlantic herring (Clupea harengus) complex during the years 1977–2002. ICES Journal of Marine Science, 64: 83–96. A comprehensive study of the impact of predation during the years 1977–2002 on the Gulf of Maine–Georges Bank herring complex is presented. An uncertainty approach was used to model input variables such as predator stock size, daily ration, and diet composition. Statistical distributions were constructed on the basis of available data, producing informative and uninformative inputs for estimating herring consumption within an uncertainty framework. Consumption of herring by predators tracked herring abundance closely during the study period, as this important prey species recovered following an almost complete collapse during the late 1960s and 1970s. Annual consumption of Atlantic herring by four groups of predators, demersal fish, marine mammals, large pelagic fish, and seabirds, averaged just 58 000 t in the late 1970s, increased to 123 000 t between 1986 and 1989, 290 000 t between 1990 and 1994, and 310 000 t during the years 1998–2002. Demersal fish consumed the largest proportion of this total, followed by marine mammals, large pelagic fish, and seabirds. Sensitivity analyses suggest that future emphasis should be placed on collecting time-series of diet composition data for marine mammals, large pelagic fish, and seabirds, with additional monitoring focused on the abundance of seabirds and daily rations of all groups.

ICES J. Mar. Sci., nr. 54, 753-773 This paper focuses on the variability in physical, chemical and biological parameters during SKAGEX-90. A pronounced feature in the Skagerrak during the study was the counter-clockwise circulation of the Norwegian Coastal Current at times of strong north-westerly winds. During such conditions this surface water reached south of 57 º N and upwelling along Norwegian coast was found. The nutrient-rich Jutland Coastal Water was never found in the inner Skagerrak, it was blocked or diluted by other water masses. A large "ridge" of Atlantic water was found in the central Skagerrak. Within this area, high subsurface chlorophyll concentrations were always found and, and due to the persistence of the supply of nutrients, it is concluded that this phenomenon could be one of the main reasons for the high productivity of the Skagerrak.

Pedersen, S. A., Fock, H., Krause, J., Pusch, C., Sell, A. L., Böttcher, U., Rogers, S. I., Sköld, M., Skov, H., Podolska, M., Piet, G. J., and Rice, J. C. 2009. Natura 2000 sites and fisheries in German offshore waters.–ICES Journal of Marine Science, 66: 155–169. The principal objective of sites selected as part of Natura 2000 is to achieve or maintain a favourable conservation status of habitats and species named in the EU Birds and Habitats directives. In the German exclusive economic zone, the habitat types protected by this legislation are sandbanks and reefs; protected species include marine mammals, seabirds, and specific migratory fish species. The ICES project Environmentally Sound Fishery Management in Protected Areas (EMPAS) aims to answer two questions: (i) To what extent do specific fishing activities significantly threaten attainment of the conservation objectives of the Natura 2000 sites? (ii) What management measures would reduce these conflicts and how effective would they be at helping to ensure the favourable condition of these sites? Assessments of fishing impacts on Natura 2000 sites require basic data on the conservation status of individual habitats and species, as well as data for fine-scale distributions of ongoing fishing activities. This paper describes and discusses the process used by the EMPAS project in developing fishery-management plans for each Natura 2000 site in German offshore waters.

Bekkby, T., and Isæus, M. 2008. Mapping large, shallow inlets and bays: modelling a Natura 2000 habitat with digital terrain and wave-exposure models. – ICES Journal of Marine Science, 65: 238–241.EU member countries are obliged to protect a certain share of Natura 2000 habitats. Hence, these habitats must be mapped. This paper is an attempt to provide a tool for modelling one of the Natura 2000 habitat, the “large shallow inlets and bays” (Natura 2000 habitat 1160), using a Norwegian archipelagic area as a case study. The Natura 2000 definition of the habitat is interpreted into criteria used for modelling, and a spatial prediction is presented on a map. The effect of scale, regarding both spatial resolution of data and methodology, is also tested. This is the first publicly accessible attempt to model the Natura 2000 habitat. It shows that the result of the modelling depends on the spatial resolution of the data and the methods used in the modelling process. Using data at a 10-m and a 25-m resolution provides good results, and even the model based on the 50-m data provided an acceptable overall picture.

Maguire, J-J., Pereda, P., Duarte R., Dobby, H., and Azevedo, M. 2008. Monkfish/anglerfish across the world; common problems and common solutions: An introduction to papers presented at the ICES Theme Session in September 2007. – ICES Journal of Marine Science, 65: 1270–1271.

Demer, D. A., Kloser, R. J., MacLennan, D. N., and Ona, E. 2009. An introduction to the proceedings and a synthesis of the 2008 ICES Symposium on the Ecosystem Approach with Fisheries Acoustics and Complementary Technologies (SEAFACTS). – ICES Journal of Marine Science, 66: 961–965.

Sellanes, J., Quiroga, E., and Neira, C. 2008. Megafauna community structure and trophic relationships at the recently discovered Concepción Methane Seep Area, Chile, ∼36°S. – ICES Journal of Marine Science, 65: 1102–1111. The fauna, community composition, and trophic support of the newly discovered Concepción Methane Seep Area (CMSA) are compared with those at a nearby non-seep control. The assemblage of chemosymbiotic bivalves is defined by eight species, including the families Lucinidae, Thyasiridae, Solemyidae, and Vesicomyidae. Seep polychaetes are represented by Lamellibrachia sp. and two commensal species of the vesicomyid Calyptogena gallardoi. Although taxonomic analysis is still under way, most of the chemosymbiotic species seem to be endemics. The CMSA is a hotspot for non-seep benthic megafauna too; 101 taxa were present, but most of them are colonists or vagrants (i.e. not endemics of methane seeps). Isotope analysis supported the belief that non-symbiont-bearing species utilize photosynthetically fixed carbon, because they were isotopically distinct from the chemosymbiotic bivalve species present. It is our opinion that, at this site, which underlies one of the most productive coastal upwelling regions of the world, spatial heterogeneity and the availability of hard substratum, generated by the presence of authigenic carbonate crusts, are more important factors in attracting non-seep fauna than the availability of locally produced chemosynthetic food.

Mayfield, S., McGarvey, R., Carlson, I. J., and Dixon, C. 2008. Integrating commercial and research surveys to estimate the harvestable biomass, and establish a quota, for an “unexploited” abalone population. – ICES Journal of Marine Science, 65: 1122–1130. A key challenge facing many fisheries managers is the absence of information on the level of harvestable biomass. We describe an integrated, two-stage survey approach that was used to measure the spatial distribution and harvestable biomass of a largely unexploited metapopulation of greenlip abalone (Haliotis laevigata) over a large area of northwestern Spencer Gulf, South Australia. In stage 1, commercial fishers conducted systematic surveys to identify subareas with abalone at harvestable densities. Cpue measures from these surveys were used to map and stratify a bounded survey subregion, within which leaded-line, research-diver surveys measured absolute density and harvestable biomass (stage 2). Decision tables, showing minimum biomass at various probabilities vs. harvest fraction, were developed to provide a risk-assessment framework for quota setting. Within two years, our approach allowed, first, the mapping of the broad-scale, spatial distribution and abundance of greenlip abalone in an area of 1143 km², second, the estimation of harvestable biomass in a smaller (16.9 km²) area, and finally, the allocation by State fishery managers of an additional quota inside a newly defined management subzone. The collaborative approach we describe for providing estimates of absolute biomass over large spatial scales affords multiple advantages for the assessment and management of invertebrate dive fisheries.

For many components of marine ecosystems, the derivation of biologically significant, operational "pressure" indicators will rely on modelling fishing mortality from indicators of anthropogenic "activity". This essentially expands the well established Pressure-State-Response framework to one of Activity-Pressure-State-Response. Within the Common Fisheries Policy, the reporting of fishing effort data, the basic indicator of activity, is not mandatory. A modelling approach is therefore developed that utilizes the data that fishers are obliged to report (days absence from port, landings from each rectangle fished, and the gear used) to provide modelled estimates of fishing effort. The model is parameterized for the Scottish demersal fishing fleet using data collected through the Scottish discards observer scheme, and fishing effort over the period 1997-2004 is modelled. Reported effort data for the period 1960-1998 allowed validation of the model through direct comparison of modelled with reported data in 1997 and 1998. Combining the modelled and reported datasets revealed that Scottish fishing activity levels, remarkably constant over four decades, had declined markedly since 2000. Temporal trends in UK quotas for the main targeted demersal species are considered to assess the effectiveness of catch limitation management as a means of regulating fishing activity. Spatial patterns in effort by the four main gear types used by the Scottish demersal fleet are described, and in general terms, these have changed little over the period 1960-2004. However, distinct spatial patterns emerged in the temporal trends in each ICES rectangle, associated with the recent overall decline in Scottish demersal fishing activity. These patterns were not intuitive, and the implications of this for an ecosystem approach to management are discussed.

Rhodes, C. J. 2008. Excess acoustic absorption attributable to the biological modification of seawater viscosity. – ICES Journal of Marine Science, 65: 1747–1750. There is increasing evidence that a ubiquitous species of oceanic phytoplankton (Phaeocystis globosa) can significantly modify the rheological properties of seawater. The effect is seasonal and, during spring when the species multiplies rapidly, one can observe large increases in the viscosity of the seawater they inhabit. One of the principal determinants of acoustic absorption in a fluid is viscosity, so in addition to the well-understood modulations attributable to temperature- and salinity-dependent molecular relaxation, there may be an additional absorption component resulting from the presence of phytoplankton. Using data from recent measurements of biologically induced excess viscosity during blooms of P. globosa, the additional acoustic absorption attributable to the presence of this organism is estimated. This suggests that a novel, biologically induced acoustic-absorption mechanism may be observable in seawater for frequencies >100 kHz. The implications for a variety of at-sea acoustic-measurement activities are noted.

Reid, D. G., Allen, V. J., Bova, D. J., Jones, E. G., Kynoch, R. J., Peach, K. J., Fernandes, P. G., and Turrell, W. R. 2007. Anglerfish catchability for swept-area abundance estimates in a new survey trawl. – ICES Journal of Marine Science, 64: 1503–1511.In 2005, a new trawl survey was launched in Scotland to estimate anglerfish (Lophius spp.) abundance using swept-area estimates. This required an understanding of the herding of the fish by the gear, particularly in the zone between the doors and wing ends. TV observations at the wing ends and along the sweeps were used to quantify the behavioural reactions of anglerfish. These observations were analysed to develop a gear efficiency estimate. This paper details the construction of the net and the procedures for data collection on the survey. In all, 54 reliable observations of anglerfish were recorded at the groundgear, the wing ends, and along the sweep/bridle combination. Detailed analysis of the recordings showed that all fish in the path of the net were captured, whereas more than half of the fish between the wings and the doors were not. The fish did not appear to herd and many of the encounters with the wires were passive. An individual-based particle-tracking model was constructed to use the behavioural observations to simulate the capture process and generate an efficiency factor. The calculated efficiency factor, based on the behavioural observations, was 1.04, indicating that almost all fish encountering the sweeps and bridles were lost. The implications and suggestions for development of this work are discussed.

Kasatkina, S. M. 2009. The influence of uncertainty in target strength on abundance indices based on acoustic surveys: examples of the Baltic Sea herring and sprat. – ICES Journal of Marine Science, 66: 1404–1409. In situ, target-strength (TS) measurements at 38 kHz and an analysis of biometric fish characteristics are presented for the Baltic Sea herring (Clupea harengus membras) and sprat (Sprattus sprattus). It is demonstrated that the application of two TS–length functions for the Baltic Sea clupeids, the first for young herring and sprat and the second for adult herring, is reasonable, and the two functions can therefore replace the well-known equation used since 1983. Parameters of the proposed relationships, accompanied by their statistical characteristics, are included in a model to obtain uncertainty in acoustically derived abundance indices. Major components of survey uncertainty, such as spatial variability, species composition, and size structure, are also included in the simulation. The proposed TS functions should permit estimates of more realistic abundance dynamics of Baltic Sea clupeids, by years and age groups, thereby providing important information for stock assessment models.

Harbitz, A., Ona, E., and Pennington, M. 2009. The use of an adaptive acoustic-survey design to estimate the abundance of highly skewed fish populations. – ICES Journal of Marine Science, 66: 1349–1354. The uncertainty (relative root-mean-square error) of abundance estimates based on a simple and easily implemented adaptive design for an acoustic survey is examined. The study is limited to surveys with parallel transects and independent observations with extremely skewed distributions. The adaptive approach defines a stratum for each conventional observation and how to take additional observations in that stratum when the acoustic density exceeds a predetermined threshold. The cost (sailing distance) of each added observation is about three times that of a conventional observation. This method was demonstrated using high-resolution transect data from a herring (Clupea harengus) acoustic survey conducted in 2006 off the north coast of Norway. The primary sampling unit for this winter survey was 5 nautical miles, and the usual distance between transects was 20 nautical miles. The results indicate that an adaptive survey design would substantially reduce the root-mean-square error of the abundance estimates compared with that of the conventional survey design.

A simulation study, combining grid- and individual-based approaches, was conducted to analyse the shape of the relationship between catch per unit effort (cpue) and abundance in a tuna purse-seine fishery. To understand the effect of fleet dynamics on the interpretation of cpue, the decision-making process used by fishers while searching for the resource is modelled with artificial neural networks. The cpue of fishers operating independently (i.e. individuals) vs. fishers sharing information (i.e. a code-group) is compared, accounting for different environmental scenarios. The results show that a power curve non-proportional relationship between cpue and abundance performs better than a linear relationship. As the shape parameter of the power curve for the code-group fishers was lower in every scenario than that of individual fishers, we conclude that hyperstability, a phenomenon commonly observed in schooling fisheries, is mainly attributable to information exchange among vessels. Setting the individual-level state variables of the virtual system at a specific spatial and temporal scale may affect the results of the simulations.

Nishimori, Y., Iida, K., Furusawa, M., Tang, Y., Tokuyama, K., Nagai, S., and Nishiyama, Y. 2009. The development and evaluation of a three-dimensional, echo-integration method for estimating fish-school abundance. – ICES Journal of Marine Science, 66: 1037–1042.A three-dimensional, echo-integration method (3DEI) which uses scanning-sonar observations of a fish school to estimate its backscattering cross section (σbss = Nσbs) was developed. Coupled with a modelled estimate of the average backscattering cross section of individual fish (σbs), the 3DEI theoretically allows estimation of the number of fish in a school (N). To test the practicality of the method, measurements were made of a metal sphere simulating fish, and several spheres simulating a fish school. The 3DEI correctly measured the σbss of each target. Next, the 3DEI was applied to echo data from a herring school in the Norwegian Sea, to estimate its σbss. Several values of σbs were estimated with a prolate-spheroid model, each assuming different distributions of fish orientations relative to the sonar beam. Dividing the 3DEI-estimated σbss by these modelled σbs shows that the resulting estimates of N were closer to the skipper's estimate than those estimated using the apparent school volume. The 3DEI measurements of σbss, modelled σbs, and resulting accuracy of N depend largely on the assumed orientations of the fish relative to the acoustic beam.

Peltonen, H., Luoto, M., Pääkkönen, J.-P., Karjalainen, M., Tuomaala, A., Pönni, J., and Viitasalo, M. 2007. Pelagic fish abundance in relation to regional environmental variation in the Gulf of Finland, northern Baltic Sea. – ICES Journal of Marine Science, 64: 487–495. This study applies variation partitioning to analyse spatial patterns in hydroacoustic estimates of fish abundance in relation to regional variation in the hydrography, food resources, and geography of the Gulf of Finland, northern Baltic Sea. Using variation partitioning based on generalized additive models, daily fluctuations in hydroacoustic abundance estimates were first eliminated, and the remaining variation in fish abundance was decomposed into independent and joint effects of hydrography, food resources, and geography. The independent effect of geographic variables (spatial location and water depth) captured the largest fraction of the variation (9.3%) in the fish-abundance patterns, whereas the independent effects of hydrography (5.8%) and food resources (5.6%) captured slightly less. However, a considerable portion of the variation in fish-abundance patterns was accounted for by the joint effects of explanatory variables and may therefore be causally related to two or all three groups of variables. The model applied efficiently eliminated the spatial autocorrelation in the fish abundance between sampling units, especially at distances >2000 m. At smaller scales, the residual autocorrelation may have been due to fish behavioural patterns independent of the explanatory variables in this analysis.

Cordue, P. L. 2007. A note on non-random error structure in trawl survey abundance indices. – ICES Journal of Marine Science, 64: 1333–1337. Trawl survey time-series are routinely used in stock assessments to provide indices of relative abundance. There is the general assumption, for each year y, that the expected value of the trawl survey index (Xy) is related to the biomass (By) by a single proportionality constant q: E(Xy) = qBy. In reality, the constant q varies due to many factors. An important factor, which is almost always ignored, is the role that non-trawlable ground can play in the variation of q. A general formula is derived for the q of a stratified random trawl survey. When the survey area contains non-trawlable ground, strata-specific data on the proportion of non-trawlable ground and on the preference of the species for trawlable/non-trawlable ground is required to weight stratum estimates correctly. In the absence of the correct stratum weights, a shift in the spatial distribution of the stock can combine with differing proportions of non-trawlable ground to introduce non-random error and possibly spurious trends into biomass indices. Each survey and species/stock should be considered on a case-by-case basis. A stratum-specific assessment of the proportion of non-trawlable ground is a pre-requisite for the production of trawl survey biomass indices.

Traditionally, trawl surveys were designed to collect fishery-independent data for assessing the population dynamics of commercially exploited species. However, trawl survey data are increasingly used to describe the abundance, distribution and ecology of a wide range of species in studies of climate change and fishing effects. These new uses of survey data suggest that improved understanding of the value and limitations of existing survey designs is required. We compared the power of different survey designs (where stations are fixed, fixed stratified, random, or random stratified) to detect known trends in the abundance of depleted populations. Modelled populations were characterized by different temperature preference, density-dependent habitat selection, and patterns of small-scale aggregation (patchiness). Temperature preferences and local patchiness had an influence on the power of different surveys to detect increases in abundance, and in some scenarios, survey-area indices would consistently underestimate or overestimate trends in overall abundance. As the distributions of many fish populations have shifted in response to climate change, exhibit distribution-abundance relationships, and have been depleted by fishing, we conclude that survey indices may provide partial or unreliable information on changes in the true abundance of the wider range of species now of interest. To disentangle the effects of fishing, climate, and biology on the abundance of fish populations, and to monitor the depletion and recovery of species threatened by fishing, there should be greater emphasis on coordinating the timing, areas of coverage, and methods of sampling of surveys of the Northeast Atlantic continental shelf. Crown Copyright © 2007. Published by Oxford Journals on behalf of the International Council for the Exploration of the Sea. All rights reserved.

Aarts, G., and Poos, J. J. 2009. Comprehensive discard reconstruction and abundance estimation using flexible selectivity functions. – ICES Journal of Marine Science, 66: 763–771.The additional mortality caused by discarding may hamper the sustainable use of marine resources, especially if it is not accounted for in stock assessment and fisheries management. Generally, long and precise time‐series on age-structured landings exist, but historical discard estimates are often lacking or imprecise. The flatfish fishery in the North Sea is a mixed fishery targeting mainly sole and plaice. Owing to the gear characteristics and a minimum landing size for these species, considerable discarding occurs, especially for juvenile plaice. Discard samples collected by on-board observers are available since 1999 from a limited number of commercial fishing trips. Here, we develop a statistical catch-at-age model with flexible selectivity functions to reconstruct historical discards and estimate stock abundance. We do not rely on simple predefined selectivity ogives, but use spline smoothers to capture the unknown non-linear selectivity and discard patterns, and allow these to vary in time. The model is fitted to the age-structured landings, discards, and survey data, the most appropriate model is selected, and estimates of uncertainty are obtained.

Woillez, M., Rivoirard, J., and Fernandes, P. G. 2009. Evaluating the uncertainty of abundance estimates from acoustic surveys using geostatistical simulations. – ICES Journal of Marine Science, 66: 1377–1383. Geostatistical simulations, which can reproduce the spatial variability of a variable, are particularly helpful in estimating the uncertainty associated with the combination of different sources of variability. Acoustic surveys offer an example of such complex situations, where different data (e.g. acoustic backscatter, fish length, and fish age) must be combined to estimate abundance and its associated uncertainty. In this paper, the uncertainty of Scottish herring acoustic-survey estimates is investigated using these techniques. A specific multivariate, geostatistical model is used to describe the structural relationships, which includes highly skewed distributions of the acoustic-backscatter data and incorporates relationships between depth, mean length, and proportions-at-age. Conditional simulations, i.e. geostatistical simulations that honour the data values known at the data points, are used to generate multiple realizations of acoustic backscatter, mean length, and proportions-at-age. These are combined to produce multiple realizations of herring density over the sampled domain. Multiple realizations of total abundance and abundance-at-age are then provided. The uncertainty is assessed using basic statistics to track the significant variations of these values over the period 1989–2005. Higher coefficients of variation (CVs) are found on average for extreme ages (ages 1, 2i, 8, and 9+); otherwise, CVs are mostly around 12% for abundance-at-age and around 10% for total abundance.

Walter, J. F. III, Hoenig, J. M., and Gedamke, T. 2007. Correcting for effective area fished in fishery-dependent depletion estimates of abundance and capture efficiency. – ICES Journal of Marine Science 64: 000–000. Depletion methods are widely used to estimate capture efficiency and abundance. However, they are highly dependent on the depletion area assumed. In open-ocean depletion studies, it is difficult to determine the true area of depletion. Satellite vessel monitoring systems (VMS) offer the potential to determine the area effectively fished. Observer-collected catch-and-effort data from the 1999 Atlantic sea scallop fishery in Georges Bank Closed Area II were used to obtain spatially-explicit DeLury depletion estimates of dredge efficiency and abundance, with corrections for fished area made using VMS data. Non-area-corrected efficiency estimates often had theoretically impossible values, indicating that the naïvely assumed fished area was likely too big. Fine-scale spatial analyses on individual depletion cells confirmed this result. Corrected-area efficiency estimates exhibited reduced variability and more plausible efficiencies, with 70% of 289 individual depletion estimates falling between 20% and 55%, with a mean of 46%. Abundance estimates from individual depletion studies matched maps of abundance from a preseason survey. Results indicated a total abundance of ∼17 million pounds of scallop meat weight in the fished area, of which 6 million pounds were landed, providing an overall exploitation rate of 35%.

We propose a random effects model for disentangling population abundance and capture efficiency effects on bottom-trawl catches. The spatial distribution of individual fish is assumed random leading to a Poisson distribution for the number of individuals in the trawl path (no schooling). Capture efficiency, i.e. the proportion of individuals in the trawl path being retained by the gear, is modelled as a random variable. We propose model extensions that include the effects of body size on haul efficiency. We applied the models to several species from the Celtic Sea groundfish community based on small-scale repetitive hauls. The resulting abundance estimates allowed us to study population abundance ratios; the estimated capture efficiencies were comparable between species and showed that generally gear efficiency increases for larger species with the exception of haddock (Melanogrammus aeglefinus), which had low estimated gear efficiency despite its large body size. Model identifiability was studied using simulations and an independent trawl data set from the same area.

Simmonds, E. J., Portilla, E., Skagen, D., Beare, D., and Reid, D. G. 2010. Investigating agreement between different data sources using Bayesian state-space models: an application to estimating NE Atlantic mackerel catch and stock abundance. – ICES Journal of Marine Science, 67: 1138–1153. Bayesian Markov chain Monte Carlo methods are ideally suited to analyses of situations where there are a variety of data sources, particularly where the uncertainties differ markedly among the data and the estimated parameters can be correlated. The example of Northeast Atlantic (NEA) mackerel is used to evaluate the agreement between available data from egg surveys, tagging, and catch-at-age using multiple models within the Bayesian framework WINBUGS. The errors in each source of information are dealt with independently, and there is extensive exploration of potential sources of uncertainty in both the data and the model. Model options include variation by age and over time of both selectivity in the fishery and natural mortality, varying the precision and calculation method for spawning-stock biomass derived from an egg survey, and the extent of missing catches varying over time. The models are compared through deviance information criterion and Bayesian posterior predictive p-values. To reconcile mortality estimated from the different datasets the landings and discards reported would have to have been between 1.7 and 3.6 times higher than the recorded catches.

Certain, G., Ridoux, V., van Canneyt, O., and Bretagnolle, V. 2008. Delphinid spatial distribution and abundance estimates over the shelf of the Bay of Biscay. – ICES Journal of Marine Science, 65: 656–666. The small delphinid community (bottlenose Tursiops truncatus, common Delphinus delphis, and striped Stenella coeruleoalba dolphins) of the Bay of Biscay (100 000 km² of continental shelf along the French Atlantic coast) has been studied here by combining strip-transect aerial surveys conducted between 2001 and 2004 and ship-based surveys conducted between 2003 and 2006. Distribution was modelled spatially in relation to several large-scale descriptors of the environment. Highest densities of small delphinids were associated with the shelf break, in particular in two hotspots located in the north and the south of the bay. Using ship-based data, we found strong spatial segregation between common and bottlenose dolphins in spring, with common dolphins associated with coastal areas (and especially river plumes) and bottlenose dolphins on the outer shelf and the shelf break. Assuming a detection probability of 1, a strip-transect abundance estimate for the small delphinid community was obtained in August 2002 with 56 500 (95% CI 29 100–90 400), but relative abundance varied across months.

Løland, A., Aldrin, M., Ona, E., Hjellvik, V., and Holst, J. C. 2007. Estimating and decomposing total uncertainty for survey‐based abundance estimates of Norwegian spring‐spawning herring. – ICES Journal of Marine Science, 64: –. A method is developed to quantify the uncertainty of abundance and age-specific abundance estimates of Norwegian spring-spawning herring, accounting for the combined effect of several error sources. We present an abundance estimate adjusted for vessel avoidance, acoustic shadowing, and depth-dependent target strength, and highlight the potentially dramatic combined effect of these adjustments. Uncertainty in this estimate is affected by the precision of the adjustment formulae as well as by the sampling errors in acoustic and trawl measurements. This total uncertainty is decomposed into contributions from each source. Here, the method is applied to data from surveys on the overwintering stock in the Vestfjord system and off Vesteraalen in northern Norway in November/December of the years 2001–2004.

Zooplankton production : proceedings of a symposium held in Plymouth, England, 15-19 August 1994 / R. Harris (ed.), ICES marine science symposia ; 200 (ICES journal of marine science, ISSN 1054-3139. Vol. 52, nr. 2-3), 369-376 Motility patterns and egg production were investigated in two populations of Acartia tonsa, field animals from the Öresund and laboratory animals from a 12-year-old (ca 120 generations) culture. When observed in aquaria with a layer of Thalassiosira weissflogii in the middle, laboratory animals displayed weak aggregation behaviour, while field animals did not aggregate at all. Both populations made longer and more frequent feeding bouts inside the patch. Egg production measurements were in accordance with the behaviour of the laboratory population if no diel feeding rhythm was assumed. The field population produced fewer eggs than predicted from activity measurements, probably due to a diel feeding rhythm. It is concluded that laboratory reared A. tonsa can be used for experiments involving behaviour, but that the possible loss of diel rhythms should be a concern. Zooplankton production (1994 : Plymouth)

McLaughlin, E., Portig, A., and Johnson, M. P. 2007. Can traditional harvesting methods for cockles be accommodated in a Special Area of Conservation? – ICES Journal of Marine Science, 64: 309–317. The European Natura 2000 project attempts to balance conservation and exploitation by permitting activities that do not affect the conservation status of designated sites. Given the scale of Natura 2000, guidelines are needed to facilitate the drafting of simple site management plans. This need is particularly acute for traditional harvesting methods for which there is usually strong local opposition to the imposition of controls. These issues were examined in Strangford Lough, a special area of conservation where cockles have traditionally been harvested by hand-raking. Raking was found not to affect the ability of cockles to rebury. There were significant reductions in Zostera biomass when raking was carried out within eelgrass beds (a 90% reduction in biomass available to winter migrant birds from summer raking). Traditional harvesting methods could therefore be accepted in Strangford as long as Zostera beds are avoided. A relatively low intensity of harvesting activity in Strangford Lough probably reflects low cockle densities (average 91.8 m⁻²), with the most economically valuable individuals at some distance from points of access to the shore. An economically feasible management plan could sanction traditional harvesting and result in the implementation of more resource-intensive management only if increases in cockle stocks and market prices stimulate large increases in harvesting activity.

Fraser, H. M., Greenstreet, S. P. R., and Piet, G. J. 2009. Selecting MPAs to conserve groundfish biodiversity: the consequences of failing to account for catchability in survey trawls. – ICES Journal of Marine Science, 66: 82–89. Fishing has affected North Sea groundfish species diversity. Defining Marine Protected Areas (MPAs) to address this will rely on groundfish surveys. Species-specific catch efficiencies vary between trawl gears, and apparent species diversity distributions are influenced by the type of gear used in each survey. It may be that no single survey depicts actual diversity distributions. Two MPA scenarios designed to protect groundfish species diversity are described, the first based on unadjusted International Bottom Trawl Survey data and the second based on the same data adjusted to take account of catchability. Spatial overlap between these scenarios is low. Assuming that the adjusted data best describe the actual species diversity distribution, the level of diversity safeguarded by MPAs, based on unadjusted data, is determined. A fishing effort redistribution model is used to estimate the increase in fishing activity that is likely to occur in MPAs that take catchability into account, if closed areas based solely on the unadjusted groundfish data were implemented. Our results highlight the need to take survey-gear catchability into account when designating MPAs to address fish-species diversity issues.