ICES Journal of Marine Science: Journal du Conseil

Beall, E.; Dumas, J.; Claireaux, D.; Barrière, L.; Marty, C.

doi: 10.1006/jmsc.1994.1001pmid: N/A

The spatial and temporal patterns of dispersal and the survival of Atlantic salmon (Salmo salar L.) fry and parr were analysed over 1 year in a small stream of the Basque Country (south-west France). Dispersal just after emergence was studied with eight drift nets placed 10 to 800 m downstream from an artificial redd stocked with 15 000 eyed eggs. Subsequent distribution of parr was determined by electrofishing in June, October, and February in representative sections of the stream including habitats 750 m upstream and 2400 m downstream from the redd. Early dispersal following emergence lasted 12 days for the majority (95%) of the fry population. Most fry (71%) settled within the first 200 m downstream from the redd, and 91% within the first 400 m. In June, parr were found 2400 m downstream and 750 m upstream, with 68% of the population established within 900 m downstream, and only 4% upstream. In October, there was a slight downstream shift of densities. In February, 56% of the parr were found within 900 m downstream and 11% upstream. Survival from egg planting to first dispersal in March was 51.9% and 11.3% over 1 year.

McClatchie, Sam; Greene, Charles H.; Macaulay, Michael C.; Sturley, Darrell R.M.

doi: 10.1006/jmsc.1994.1002pmid: N/A

Acoustic estimates of Antarctic krill biomass measured in four surveys around Elephant Island during the American Antarctic Marine Living Resources 1990 (AMLR90) cruises were analyzed to examine spatial and temporal variability in absolute biomass. Each survey took 5-6 days to complete, and survey mid-points were separated by 15-17 days. The depth-integrated biomass data were highly positively skewed. The biomass frequency distributions diverged progressively over time from that measured in the first survey, with greatest change occurring between survey 2 and 3. The coefficients of variation over each survey for 30 s length records (order 100m) ranged from 85 to 247%, indicating intense patchiness. Analysis of the fractal dimension of krill biomass revealed patterns that were consistent between surveys and indicated that a horizontal integration interval smaller than 100 m would be necessary to resolve much of the structure in krill spatial variability. In addition to spatial patchiness we found strong temporal variability between surveys at scales on the order of 2 weeks. Our findings indicate that the krill distributions around Elephant Island are highly variable. We suggest that data assimilation models, incorporating repeated fine-scale sampling of physical variables and acoustic back-scattering, be employed to quantify changes in krill distribution and abundance through time in regions characterized by such high variability. We conclude: (1) that sampling with resolutions finer than 100 m is necessary to determine the characteristic scales of spatial patchiness in krill distributions: and (2) the application of biophysical data assimilation models would facilitate more accurate stock assessment of krill. We suggest that traditional survey methods could be improved by introducing long-range moored sonar arrays or towed bodies to operate conjunction with ship surveys. We present estimates of the feasibility of detecting krill aggregations at up to 1-2 km range using a side-looking sonar operating at 20-40 kHz.

Punt, Andre E.; Hilborn, Ray

doi: 10.1006/jmsc.1994.1003pmid: N/A

An age-aggregated model that explicitly includes cannibalism of older fish on younger fish is developed. This model is used as the basis for determining the importance of including cannibalism in stock assessment and fishery regulation for the Cape hake stocks off southern Africa, stocks where cannibalism has been shown to be substantial. The cannibalism model is compared to a traditional Schaefer-type model in three ways. First, the two models are fitted to the catch-effort history for the Cape hake resource off northern Namibia. It is shown that the cannibalism parameters cannot be estimated from the catch-and-effort history alone, and must be obtained from other studies. Once the cannibalism parameters are specified, the two approaches provide similar fits and estimates of stock size and potential yield, although the non-cannibalistic approach is generally more optimistic. The second form of comparison involves fitting a cannibalistic model-estimation procedure and a non-cannibalistic model-estimation procedure to simulated data that contains differing levels of cannibalism. In general, both model-estimation procedures similar results, although the non-cannibalistic model-estimation procedure is more likely to result in outlying estimates of MSY when the data are uninformative. Finally, the performance of the two model-estimation procedures when combined with the fMSY harvesting strategy is evaluated. The performance of the two approaches is similar as long as the data are relatively informative. It is thus argued that management agencies should not assume a priori that including cannibalism or multispecies interactions in assessment and management procedures will necessarily provide for better fisheries regulation. It is recommended that simulation studies similar to those described in this paper be performed prior to the introduction of the extensive data collection schemes required for assessments that include cannibalism or multispecies interactions.

Albert, Ole Thomas

doi: 10.1006/jmsc.1994.1004pmid: N/A

The distribution, population structure, and diet of haddock (Melanogrammus aeglefinus L.) in the Norwegian Deep are related to seasonal and ontogenetic variations. There was a seasonal migration between relatively shallow areas in summer and deeper parts in winter. The distribution became gradually more shallow with increasing age: mature specimens were probably migrating out of the area in winter. Polychaetes, crustaceans, and ophiuroids dominated the diet, but teleosts were of less importance. The seasonal variation of diet composition dominated over ontogenetic variation. Polychaetes and bivalves were important in winter, whereas euphausiids, decapods, ophiuroids, and teleosts dominated in summer.

Albert, Ole Thomas

doi: 10.1006/jmsc.1994.1005pmid: N/A

Between 1985 and 1987 Norway pout was widely distributed at moderate depths in the Norwegian Deep, generally 5-10 m above the sea bed, but somewhat closer by day. The bathymetric distribution was progressively deeper with increasing age; within an age-group, larger individuals were distributed deeper than smaller ones. There were relatively small geographical and seasonal differences in abundance, except that the abundance tended to increase from south-east to north-west, especially for the mature part of the population in the spawning season. Close to 100% matured for the first time as II-group. The diet was highly dominated by euphausiids and the feeding was more intense at night than during the day.

Dommasnes, Are; Rey, Francisco; Røttingen, Ingolf

doi: 10.1006/jmsc.1994.1006pmid: N/A

Since 1987 the major part of the adult Norwegian spring-spawning herring stock has been wintering in the Ofotfjord and the Tysfjord, two tributaries to the Vestfjord in northern Norway. The herring enter the fjords in August-September, and leave again in January to start their spawning migration.Since 1975 the Institute of Marine Research has made regular surveys in the area in November of each year, in which the herring population has been measured acoustically. Since 1976 environmental parameters have also been recorded, including temperature, salinity, and oxygen and nitrate concentrations.This time series shows a gradual decrease in oxygen concentration in the Ofotfjord since 1987, when the herring started wintering in the fjord. High concentrations of herring are found in areas with oxygen concentrations as low as 1-2 ml l-1.The paper presents and discusses the available data. A simple oxygen budget demonstrates that the reduction content may have been caused by the wintering herring.

Brander, K. M.

doi: 10.1006/jmsc.1994.1007pmid: N/A

Data on the distribution and timing of occurrence of cod (Gadus morhua) eggs and larvae around the British Isles is presented from ichthyoplankton surveys carried out from 1953-1990 in the Irish Sea, Bristol Channel, English Channel, and North Sea. The mean date of cod spawning ranged from the end of January in the eastern English Channel to late March in the Bristol Channel. Model simulations of seasonal cycles of chlorophyll in the surveyed areas are compared with data from the Continuous Plankton Recorder and used to test the hypothesis that the timing of spawning is closely coupled to the onset of primary production. The available evidence supports the hypothesis, but is not conclusive. An alternative hypothesis, that timing is a function of water temperature, is rejected. The location and timing of spawning may be adapted to ensure that larvae encounter adequate feeding conditions.

Houde, E. D.

doi: 10.1006/jmsc.1994.1008pmid: N/A

Differences in the dynamics (growth and mortality) and energetics properties of marine and freshwater fish larvae have important implications for determining the life stages at which year-class size is established. After correcting for temperature effects, marine fish larvae, which typically weigh less at hatch, can be shown to experience mortality rates, have higher metabolic requirements, and have longer larval stage durations than do freshwater fish larvae. Growth rates and growth efficiencies are similar for the two categories of larvae. The difference in body size between typically small marine and typically large freshwater fish larvae is an important factor affecting their dynamics and energetics. Predicted mean survivorship to metamorphosis of a cohort of freshwater fish larvae is 5.30%, while that of marine larvae is only 0.12%. The probability of significant density-dependent regulation during the larval stage could be relatively high for marine species, based upon their life-history properties. The probability that episodic mortalities of larvae will have significant impacts on recruitment may be higher for freshwater fish than for marine fish. Starvation mortality is more probable for marine larvae, primarily because of their small body size, associated high metabolic demands, and possibly higher ingestion requirements. Because expected mean survivorship of freshwater larvae is 44 times higher than that of marine larvae, juvenile-stage dynamics will be relatively important in controlling/regulating recruitment levels of freshwater fishes. In contrast, properties of marine species indicate that larval-stage dynamics will have a greater influence on recruitment success.

Witbaard, R.; Klein, R.

doi: 10.1006/jmsc.1994.1009pmid: N/A

Arctica islandica has been used as an indicator organism for the intensity of bottom trawling in the southern North Sea. That this species in affected by beamtrawl fisheries is illustrated by the high of damage found on shells from heavily fished areas.Between 80 and 90% of the damage was found at the posterior ventral side of the shell. This can be explained by the orientation of the living animal in the upper sediment layer and the horizontal movement of the tickler chains on the bottom.Scars on the external shell surface were dated by internal growth lines, revealing that the sampling site had been disturbed at least once a year since 1974.The observed trends in the occurrence of scars per year show a striking coincidence with the increase in capacity of the Dutch fishing fleet over the period 1972-199).

Shackell, N. L.; Carscadden, J. E.; Miller, D. S.

doi: 10.1006/jmsc.1994.1010pmid: N/A

Associations between average temperature (°C) from 0-75 m and the size distribution of capelin (Mallotus villosus) on the northern Grand Bank (≈46°N 52°45′W-49°10′N-49°30′W) were explored, using information from research vessel surveys conducted during May from 1985 to 1992. Immature capelin were generally distributed in the northern part of the survey area while mature capelin were distributed in the south. Mature capelin are believed to migrate to the southern area in the spring, prior to onshore migration. Distribution of mature capelin was not associated with temperature on relatively small spatial (≈2000 km2) and temporal (within years) scales, but was on larger spatial (≈90 000 km2) and temporal (among years) scales. Assuming a link between maturation rate and migration, we propose that temperature is not used as a proximate cue during capelin migration, but that seasonal temperatures moderate offshore capelin migration patterns through regulating growth, maturation, and food abundance and distribution. Capelin are growing and migrating on a biological cycle but research surveys are conducted on a chronological cycle. Consequently, biomass acoustic estimates may be underestimated in cold years if spring migration into the survey area is delayed.