The feeding conditions of capelin during summer. Field observations in 1979 and 1980

The Institute of Marine Research has, since 1979, carried out investigations on the capelin feeding conditions in the Barents Sea during the summer season. This program is aimed at obtaining data that can contribute to the understanding of the factors affecting the capelin growth in this area. The program is based on the working hypothesis that as the ice edge in the Barents Sea recedes northwards during the summer, new areas become available for biological production. If a series of observations are made from the ice edge towards the south, different phases in the production process can be found, from nutrients via phytoplankton and zooplankton to the capelin. In this program an attempt is made to follow the development of this production process in order to make the feeding conditions for the capelin and its variations. This will give background information for better predictions on the development of the capelin stock and with that, a better exploitation of the resource. The present report describes the methods used in the field work in order to verify the mentioned hypothesis. Most of the results obtained during the summer seasons of 1979 and 1980 are presented in the form of tables and figures and only with brief comments

Ecological investigations in the marginal ice zone in the Barents Sea the summers 1979 and 1980

During the summers of l979 and 1980, ecological investigations were carried out in the marginal ice zone in the Barents Sea. In the investigation an attempt is made to follow the development of the production processes, from nutrients via phytoplankton and zooplankton to capelin, in order to map the feeding conditions for the capelin and its variations. The methods used in the field work and most of the results obtained during the two summer seasons are presented by ELLERTSEN -et -al. (1981). In the present report we discuss and summarize the field results so far and compare them with the results from a model. The results show a close relationship between ice melting and recession and a phytoplankton bloom occurring at the ice edge. It seems that the decrease in salinity in the upper few meters due to ice melting produce a sharp increase in water stability. Thereby favourable conditions are created for an intense phytoplankton bloom. This bloom seems to occur somewhat earlier than the spring bloom in the areas of the Barents Sea not covered by ice, where water stability is mainly influenced by the warming of the upper layers. Zooplankton development follows very close that of the phytoplankton, with a bloom starting near the ice edge. The biomass was found to increase with the distance from the edge. This tendency is most clear in the upper layers, where the zooplankton spawning and the development of the zooplankton larvae occur. The main bulk of the zooplankton consisted of the copepod Calanus finmarchicus. The most numerous species was the small copepod Oithona similis. There was a change in age composition of -C. finmarchicus with the distance from the ice, the nauplii and the younger copepodite stages predominating in the north. The younger stages (I-III) were most abundant in the surface layer where they had hatched earlier in the year, while the older stages (IV-V and adult females) had overwintered and predominated in the deeper layer. The stomach contents of 12-18 cm capelin from several stations were investigated. The stomach filling seemed to be related to the plankton density in the sea, with highest filling in areas with much plankton. The species composition in the stomachs roughly corresponded with the plankton composition, with a tendency to a higher numeric percentage of euphausiids and chaetognaths in the stomachs than in the plankton. Near half of the contents, as weight, consisted of calanoid copepods, while the euphausiids, chaetognaths and amphipods made up 30, 10 and 6 per cent of the weight respectively. A model describing the growth of phytoplankton and zooplankton along a north-south section in the Barents Sea is also briefly described. Using ice map data obtained via satellite, several simulation runs have been performed. The dynamics of the phytoplankton growth seems to agree with what we believe it should according to the available data. However, some discrepancies indicate areas that should be further investigated in order to increase our knowledge and improve the model. The zooplankton part of the model produces results that are more questionable. Variations in zooplankton biomass are reasonably calculated whereas the stage distribution does not fit our data. Reasons for this are discussed

Spawning strategy and a mechanism for adaptive larval production in Arcto-Norwegian cod

The Arcto-Norwegian cod is spawning in the temperature stable Atlantic water, and the eggs ascend into the more temperature variable coastal water. Changes in time of peak spawning, up to 10 days within the last 60 years, are caused by changes in the cod´s age composition, peak spawning of first-time spawners being somewhat delayed. In contrast, the peak spawning in the coastal water of Calanus finmarchicus, whose nauplii are the almost exclusively food organism for the first feeding cod larvae, vary with more than 40 days due to temperature variations. It is a clear tendency for the majority of nauplii abundance peaks to be situated ahead of the peak first feeding cod larvae, especially during warm years. The temperature covariate in the spawning areas in the Norwegian coastal waters and the feeding areas of cod in the Barents Sea. High temperatures during the egg and larval stages favour the feeding condition of the larvae hatched first, since the concentration of nauplii is higher in the first part of the larval period. These larvae from the larger, high fecund cod females, are the largest and probably the most viable larvae produced during the season. During periods of decreasing temperatures in the feeding areas and the spawning sites, the production of viable larvae is more variable. High temperatures also improve and extend the feeding areas tn the Barents Sea, giving support for larger year-classes. In both temperature regimes the age compostition of the spawning population of Arcto-Norwegian cod will effect the degree of match between the production cycle of nauplii and first feeding cod larvae. The spawning strategy of Arcto-Norwegian cod in relation to Calanus finmarchicus can be named a modified match/mismatch hypothesis, ensuring a adaptive larval production to varying temperature regimes of the feeding areas of the cod

Kopepodnauplier på Møre våren 1986 - næringstilbudet til sildelarver [HELP 11]

Kopepodnauplier inngår som en viktig del av næringen til sildelarver. På den bakgrunn ble det våren 1986 foretatt en undersøkelse over forekomsten av nauplier i forhold til sildelarver på Møre. Kopepodnauplier og sildelarver hadde en felles horisontalutbredelse med de største konsentrasjonene over gytefeltene for sild. Kun en litendelav sildelarvene i området ble observert med tarminnhold, vilket antas å skyldes en kombinert effekt av at larven tømmer tarmen når den fanges og at larvene har en dybdefordeling noe forskjellig fra hovedmengden kopepodnauplier. En sammenligning er foretatt mellom effektiviteten av planktonpumpe og håv. Pumpen er mest effektiv, og resultatene tilsier at omfattende tester av håver og flowmetre bør foretas før neste sesong

Food consumption rate and gut evacuation processes of first feeding cod larvae In: The propagation of cod Gadus morhua L.: an international symposium, Arendal, 14 - 17 June 1983

Laboratory experiments with cod larvae (Gadus morhua L.) during optimum feeding conditions showed that cod larvae were sporadic feeders rather than continuous feeders. Digestion rate of copepod nauplii was less than 30 min, but varied with gut content volume. The cod larval gut evacuation rate varied with food availability and state of digestion of the gut content. Criteria for larval gut content analysis for the evaluation of the cod larval feeding conditions in the sea are given

Sampling fish larvae with large pumps; quantitative and qualitative comparisons with traditional gear. In: The propagation of cod Gadus morhua L.: an international symposium, Arendal, 14 - 17 June 1983

Different types of submersible pump systems, ranging in capacity from 3 to 60 m^3/min, have been tested during the period 1977-83 to collect fish eggs and larvae from discrete depths in the Lofoten area. Comparisons have been made with regard to the quality and quantity of eggs and larvae sampled with different plankton nets. Almost without exception the pump samples contain more cod eggs and larvae per m^3 than vertical net hauls, indicating a significantly lower filtration efficiency than the 100% used in the calculations. The quality of larvae sampled by vertically hauled nets was very good. The quality of the larvae depends upon the filtration pressure and time from capture to fixation of the larvae. Thus larvae sampled by pumps with high water velocity and the high speed sampler Gulf-III had a high percentage of damaged larvae. Due to the time lag from capture to fixation, most of the larvae collected with the MOCNESS were also in a bad condition. A large filtration system, 60 m^3/min, based on a submersible 80 cm slow-rotating propeller, is described. Comparisons with MOCNESS for quantitative reasons and to the vertical net for qualitative reasons showed good agreement

The 'critical period' concept - a century of recruitment research

Journal homepage: http://www.int-res.com/journals/meps