Use of satellite data for modelling food availability and survival of marine fish larvae

A modelling scheme is described which uses satellite retrieved sea-surface temperature and chlorophyll-a to derive monthly zooplankton biomass estimates in the eastern North Atlantic; this forms part of a bio-physical model of inter-annual variations in the growth and survival of larvae and post-larvae of mackerel (Scomber scombrus). The temperature and chlorophyll data are incorporated first to model copepod (Calanus) egg production rates. Egg production is then converted to available food using distribution data from the Continuous Plankton Recorder (CPR) Survey, observed population biomass per unit daily egg production and the proportion of the larval mackerel diet comprising Calanus. Results are validated in comparison with field observations of zooplankton biomass. The principal benefit of the modelling scheme is the ability to use the combination of broad scale coverage and fine scale temporal and spatial variability of satellite data as driving forces in the model; weaknesses are the simplicity of the egg production model and the broad-scale generalizations assumed in the raising factors to convert egg production to biomass.

An individual-based model of the early life history of mackerel (Scomber scombrus) in the eastern North Atlantic, simulating transport, growth and mortality

The main purpose of this paper is to provide the core description of the modelling exercise within the Shelf Edge Advection Mortality And Recruitment (SEAMAR) programme. An individual-based model (IBM) was developed for the prediction of year-to-year survival of the early life-history stages of mackerel (Scomber scombrus) in the eastern North Atlantic. The IBM is one of two components of the model system. The first component is a circulation model to provide physical input data for the IBM. The circulation model is a geographical variant of the HAMburg Shelf Ocean Model (HAMSOM). The second component is the IBM, which is an i-space configuration model in which large numbers of individuals are followed as discrete entities to simulate the transport, growth and mortality of mackerel eggs, larvae and post-larvae. Larval and post-larval growth is modelled as a function of length, temperature and food distribution; mortality is modelled as a function of length and absolute growth rate. Each particle is considered as a super-individual representing 10 super(6) eggs at the outset of the simulation, and then declining according to the mortality function. Simulations were carried out for the years 1998-2000. Results showed concentrations of particles at Porcupine Bank and the adjacent Irish shelf, along the Celtic Sea shelf-edge, and in the southern Bay of Biscay. High survival was observed only at Porcupine and the adjacent shelf areas, and, more patchily, around the coastal margin of Biscay. The low survival along the shelf-edge of the Celtic Sea was due to the consistently low estimates of food availability in that area.

Polychlorinated Biphenyl DDT And Dieldrin Residues In Grey Seal (Halichoerus-Grypus) Males Females And Mother-Foetus Pairs Sampled At The Farne Islands England During The Breeding-Season

PCB, DDT, DDE, dieldrin and total non-polar organohalogen residues have been determined in the blubber-lipid of grey seals (Halichoerus grypus) sampled during the 1972 breeding season (November) at the Farne Islands off the north eastern coast of England. PCBs were analysed by gas-liquid chromatography linked to a chlorine- and carbon-selective microwave plasma detector and total organohalogen residues were determined by microcoulometry. Total organohalogen residues were negatively correlated with blubber thickness and positively correlated with age in males (aged 1 to 24 y) and females (aged 5 to 38 y). However, the correlation of blubber-lipid residue with age in males depended upon the inclusion of immature (aged < 6 y) animals, and in females reflected only a small residue increment. The mean blubber organohalogen concentration of the males was significantly greater than that of the females. PCB and DDT group residue concentrations were significantly correlated. PCB, DDT, DDE and dieldrin were detected in the liver of mother/foetus pairs demonstrating transplacental movement of these residues. The possibility of the condition of the seals at breeding time influencing residue levels and of these residues influencing the health of the population is discussed.

Changes in development timing and cohort width of Neocalanus plumchrus degree ' flemingeri copepods in the eastern North Pacific

Neocalanus plumchrus/flemingeri copepods make up a large proportion of spring mesozooplankton biomass and are a valuable nutritional source for many higher trophic levels. Copepodites through to sub-adult stage are present in surface waters for a relatively short period of time each spring, and the date of maximum biomass has been calculated as the date when 50% of the population were at the sub-adult, CV stage. This index allows quite a precise date to be calculated from relatively infrequent sampling and interannual comparisons between 1957 and 2004 have demonstrated that the timing of peak abundance is significantly advanced in warmer years. However, recent data from the Continuous Plankton Recorder survey, which samples the surface NE Pacific more frequently during spring, has found that maximum numbers of CV copepodites occur after the 50% point is reached so that maximum biomass occurs some weeks later than predicted by this index (although comparisons between years show that the magnitude of the timing shift is similar). Comparisons with depth-stratified profiles from the BIONESS show that this is not just due to single-depth near-surface sampling by the CPR. We speculate on the cause of this change which could be related to the width of the cohort (which appears to now be narrower, at least in warm years) or the length of time that the CV stage needs to spend in the surface accumulating lipid before beginning diapause. A narrower cohort has implications for predators who will have less time to take advantage of this food source.

Transregional linkages in the North-Eastern Atlantic - An ‘end-to-end ’ analysis of pelagic ecosystems

This review examines interregional linkages and gives an overview perspective on marine ecosystem functioning in the north-eastern Atlantic. It is based on three of the 'systems' considered by the European Network of Excellence for Ocean Ecosystems Analysis (EUR-OC EANS was established in 2004 under the European Framework VI funding programme to promote integration of marine ecological research within Europe), the Arctic and Nordic Seas, North Atlantic shelf seas and North Atlantic. The three systems share common open boundaries and the transport of water, heat, nutrients and particulates across these boundaries modifies local processes. Consistent with the EUR-OC EANS concept of 'end-to-end' analyses of marine food webs, the review takes an integrated approach linking ocean physics, lower trophic levels and working up the food web to top predators such as marine mammals. We begin with an overview of the regions focusing on the major physical patterns and their implications for the microbial community, phytoplankton, zooplankton, fish and top predators. Human-induced links between the regional systems are then considered and finally possible changes in the regional linkages over the next century are discussed. Because of the scale of potential impacts of climate change, this issue is considered in a separate section. The review demonstrates that the functioning of the ecosystems in each of the regions cannot be considered in isolation and the role of the atmosphere and ocean currents in linking the North Atlantic Ocean, North Atlantic shelf seas and the Arctic and Nordic Seas must be taken into account. Studying the North Atlantic and associated shelf seas as an integrated 'basin-scale' system will be a key challenge for the early twenty-first century. This requires a multinational approach that should lead to improved ecosystem-based approaches to conservation of natural resources, the maintenance of biodiversity, and a better understanding of the key role of the north-eastern Atlantic in the global carbon cycle.

Large bio-geographical shifts in the north-eastern Atlantic Ocean: From the subpolar gyre, via plankton, to blue whiting and pilot whales

Pronounced changes in fauna, extending from the English Channel in the south to the Barents Sea in the north-east and off Greenland in the north-west, have occurred in the late 1920s, the late 1960s and again in the late 1990s. We attribute these events to exchanges of subarctic and subtropical water masses in the north-eastern North Atlantic Ocean, associated with changes in the strength and extent of the subpolar gyre. These exchanges lead to variations in the influence exerted by the subarctic or Lusitanian biomes on the intermediate faunistic zone in the north-eastern Atlantic. This strong and persistent bottom-up bio-physical link is demonstrated using a numerical ocean general circulation model and data on four trophically connected levels in the food chain – phytoplankton, zooplankton, blue whiting, and pilot whales. The plankton data give a unique basin-scale depiction of these changes, and a long pilot whale record from the Faroe Islands offers an exceptional temporal perspective over three centuries. Recent advances in simulating the dynamics of the subpolar gyre suggests a potential for predicting the distribution of the main faunistic zones in the north-eastern Atlantic a few years into the future, which might facilitate a more rational management of the commercially important fisheries in this region.