Erste Ergebnisse zum Verlauf der Laichsaison von Dorschen in der westlichen Ostsee 1997

Investigations concerning the intensity and duration of spawning seasons of cod stocks are parts of the work of the reproductions ecology of commercial fish stocks in the Baltic Sea. The Institute of Baltic Fisheries Rostock has sampled and analysed data for this goal since 1992. The first data analyses for the spawning season 1997, sampled in the areas Kiel Bay, Mecklenburg Bay and Arkona Sea showed that the process of the spawning season is different compared to the years before. The spawning process starts earlier than the other years in Kiel Bay and Mecklenburg Bay. The results show that a high proportion of the spawning stock was part of the spawning process in this area. The Arkona Sea cod are regarded by ICES definition as belonging to the western cod stock. In this ICES sub-division only a low number of spawned cod was observed in March, the main spawning time of the western cod stock. Opposite to the theory of the stock units intensive spawning activities were observed in June as in the years before in the Arkona Sea.

Report of the PRA carried out at Ihale Beach, Tanzania, April 11-14, 2000

Ihale is a large landing site lying approximately 65 km. from Mwanza along the main Mwanza-Musoma highway. Ihale Beach was selected as a potential candidate for the 3-beaches study because of its proximity to Mwanza, and hence suitability for frequent monitoring; and because it is served by a road accessible during the rainy seasons. As with the first training Participatory Rural Appraisal (PRA) on Kiumba Beach on Kenya's Rusinga Island, the objectives with this PRA were as follows: (a) To identify and understand Ihale's community-based organizations and institutions which have a role in the lake's fishery. (b) To consider the key issues which arise from this study for the involvement of communities and community-based organizations and/or institutions such as those at Ihale Beach, in the co-management of Lake Victoria's fishery.

Estimating Sighting Proportions of American Alligator Nests during Helicopter Survey

Proportions of American alligator (Alligator mississippiensis) nests sighted during aerial survey in Florida were estimated based upon multiple surveys by different observers. We compared sighting proportions across habitats, nesting seasons, and observer experience levels. The mean sighting proportion across all habitats and years was 0.736 (SE=0.024). Survey counts corrected by the mean sighting proportion reliably predicted total nest counts (R2=0.933). Sighting proportions did not differ by habitat type (P=0.668) or year P=0.328). Experienced observers detected a greater proportion of nests (P

Physical measures to inhibit planktonic cyanobacteriae

In a small lake, intermittent destratification was installed after several other physico-chemical and physical in-lake therapy measures (phosphorus immobilization, permanent destratification) had been tested without great success. If an aerobic sediment-water interface can be maintained, intermittent destratification removes cyanobacteria and prevents optimal development of other members of the photoautotrophic plankton. During growing seasons, increasing abundances of small-bodied herbivores (Bosmina) and Daphnia may have accounted for relatively low phytoplankton biomass as well. Intermittent destratification is a very fast-working in-lake measure and seems to be applicable even in relatively shallow lakes (< 15 m), in which permanent destratification seems to be risky.

The production of freshwater fish for food

It has been estimated that in England and Wales fresh water covers some 340 square miles of which about one quarter is inhabited mainly by salmon and trout; in Scotland the lakes cover an area of 340 square miles. The principal object of this publication is to make available in handy form some of the methods, especially those involving the use of manures, by which crops of fish from water can be increased. The cultivation of water which this implies may be compared directly to the cultivation of farm land: the conditions for growth are made as favourable as possible, the seed is sown in the form of young fish, and after one or perhaps two growing seasons the crop is harvested. There are however many waters about the country where marketable fish are already available and can be removed without prejudice to, and indeed to the advantage of, sporting fisheries. In such cases it is necessary only to remove the fish and to rely on the natural processes of reproduction of those which are left to repopulate the water. Farming waters in the true sense is the concern of the greater part of this publication; the removal of crops of otherwise unwanted fish is considered in the last two sections on perch trapping and eel fisheries.

Vegetation Effects on Fish Distribution in Impounded Salt Marshes

We compared the density and biomass of resident fish in vegetated and unvegetated flooded habitats of impounded salt marshes in the northern Indian River Lagoon (IRL) Estuary of east-central Florida. A 1-m2 throw trap was used to sample fish in randomly located, paired sample plots (n = 198 pairs) over 5 seasons in 7 impoundments. We collected a total of 15 fish taxa, and 88% of the fishes we identified from the samples belonged to three species: Cyprinodon variegatus (Sheepshead Minnow), Gambusia holbrooki (Eastern Mosquitofish), and Poecilia latipinna (Sailfin Molly). Vegetated habitat usually had higher density and biomass of fish. Mean fish density (and 95% confidence interval) for vegetated and unvegetated sites were 8.2 (6.7–9.9) and 2.0 (1.6–2.4) individuals m-2, respectively; mean biomass (and 95% confidence interval) for vegetated and unvegetated sites were 3.0 (2.5–3.7) and 1.1 (0.9–1.4) g m-2, respectively. We confirmed previous findings that impounded salt marshes of the northern IRL Estuary produce a high standing stock of resident fishes. Seasonal patterns of abundance were consistent with fish moving between vegetated and unvegetated habitat as water levels changed in the estuary. Differences in density, mean size, and species composition of resident fishes between vegetated and unvegetated habitats have important implications for movement of biomass and nutrients out of salt marsh by piscivores (e.g., wading birds and fishes) via a trophic relay.

Das Problem „Siebkrabben“ in der Garnelenfischerei

Along with consumption shrimp, brown shrimp fisheries also land some shrimp too small for human consumption which are sieved out on land and have to be degenerated (“crushed shrimp”). This share is recorded in German official statistics besides a third fraction called “industrial shrimp”. In view of the MSC certification processes, sustainable fishing and the fishermen’s voluntary obligation to - in future - limit the shares of “crushed shrimp”, landings data from 2010 have been analysed. Depending on seasons the goal of less than 20% of “crushed shrimp” in German landings was not met in several months in 2010, especially in August, when more than 40% of the landings contained more than the proposed amount. The processing procedures aboard the vessels are shortly discussed and the proposal is made to rather increase net selectivity than use wider sieves for the cooked fraction before landing. Cooking and processing small and later rejected shrimp is an uneconomic action. Reducing the share of “crushed shrimp” serves the idea of sustainable use of shrimp stocks as well as of sound economics.

Bilan des recherches sur la crevette rose Penaeus duorarum notialis de Côte d'Ivoire et conséquences en matière d'aménagement

A summary of results obtained from 1969 to 1977 is given. It concerns the biology of the species (ecology and distribution of the adults, behaviour and diel variation of catch rates, reproduction and larval migration, juveniles migration and recruitment at sea, sexual maturity, growth and mortality by marking experiments) and the history of the fishery (catches, efforts, seasonal variations of catch rates). The combined use of a dynamic pool model of Ricker and a production model of Fox leads to the evaluation of the potential of the stock. The simulation of different and combined fishery strategies on adults at sea and juveniles in lagoons, allows the evaluation of the consequences (in yield, value, biomass and potential fecundity) of the different proposed management procedures (reductions in fishing effort, closed seasons on both fisheries).

Les saisons marines devant Abidjan

From March 1966 to March 1970 some hydrographic observations were collected twice a week at a coastal station, off Abidjan. These data show the alternation of well defined water masses over the Ivorian Continental shelf. Grouping all observations on a T-S diagram, it is possible to differentiate four marine seasons, which are typical of an austral type of climate such as is observed off Pointe Noire.

Contribution à l'écologie de quelques taxons du zooplancton de Côte d'Ivoire. 2 - Dolioles, Salpes, Appendiculaires

The seasonal variations of vertical distribution and abundance over the shelf are investigated for Doliolids, Salps and Larvacea. The 3 groups present many similar ecological features. Two maxima of abundance occur during the little and main cool seasons. The second maximum is usually the most important, except for Salps. The 3 taxons inhabit more superficial layers in cool than in warm seasons. This allows them to follow the phytoplankton maximum which drifts near the thermocline during the warm season. Pelagic Tunicates come back to the phytoplankton enrichment areas by the deeper Ivorian under-current. A relationship between the vertical distribution pattern and the life cycle (sexual or asexual generation) is suggested.

Contribution à l'écologie de quelques taxons du zooplancton de Côte d'Ivoire. 4 - Euphausiaces

Euphausiids vertical distribution on the Côte d'Ivoire continental shelf during different seasons, average zonal distrubution, mean distance to the shore, and seasonal variations in abundance computed for five years, suggest that the appearance, and the shifting of euphausiids across and along the shelf are related with the variations of the distance from the shore of the ivorian under-current. The author reports that Nyctiphanes capensis has not been found in the region.

Notes sur l'écologie de quelques taxons du zooplancton de Côte d'Ivoire. 1 - Ostracodes, Cladocères et Cirripèdes

Seasonal variations of abundance and vertical distribution over the shelf are investigated for Ostracoda, Cladocera and Cirripede larvae. The main characteristics of the environment are the periodical enrichments mainly caused by upwellings, secondly by the river floods. Ostracoda abundance variations approximately follow phytoplankton outburst. Breeding occurs all over the year. Their vertical distribution is correlated with a discontinuity layer. Diurnal migration, when it occurs in warm season consists in an upward movement during the night towards surface layers. The Ostracoda inhabit bottom layers during the day and migrate at night in intermediate and surface layers. For the main two species of Cladocera, Penilia avirostris and Evadne tergestina, abundance periods follow upwellings, especially during the main cool season. However, Cladocera can grow in low salinity but rich waters. On average Penilia inhabits more superficial waters in cold than in warm seasons. Cirripede nauplii and cypris are more abundant off rocky coasts. Their maxima are in the upwelling periods.

L'oxygène dissous en Lagune Ebrié: Influences de l'hydroclimat et des pollutions

The hydrology of the Ebrie coastal lagoon in Abidjan area is summarized. The authors describe the oxygenation in that area during the two extreme seasons of the hydrological cycle: the low-water season (March-April) and the high-water season (Sept-Oct). The influences of the continental and oceanic waters, photosynthesis, exchanges with the atmosphere and pollution are considered. The oxigen consumption of primary organic pollution represents from 9 to 12% of the content of the waters that circulates in the area. It is geographically very heterogeneous. The central basin, swept by strong marine and fresh water currents, shows a rather high level of water oxygenation. In the peripheric bays, water circulation and mixing are less important and pollution accelerates the natural eutrophic processes. During the low-water season, a vertical stratification is responsible for a bottom anoxic layer and the deposit of reduced organic silts. On the contrary, supersaturations, up to 200%, are recorded on the surface layer. During the high-water season the break of the vertical stratification sets the loose reduced silts into suspension and partly reoxygenates the bottom waters. A classification of the different areas, based on the oxygen vertical profiles is proposed.

Quelques observations sur la présence des Cumacés dans le zooplancton des eaux néritiques de Côte d'Ivoire

Cumacea were only observed in night plankton of the Côte d'Ivoire continental shelf. However they are not always observed and their occurrence seems to depend on the marine seasons. In September, December and April, the catches were very poor indeed, whereas May and June showed interesting results. Most of the species are rarely seen in the upper layer. Several activity rhythms could be shown for the most common species present in the hauls.

Biologie de Penaeus duorarum notialis en Côte d'Ivoire. 4 - Rélations entre la répartition et les conditions du milieu. Étude des variations du sex-ratio

The analysis of the geographic and bathymetric distribution of Penaeus duorarum and, particularly P. d. notialis off Côte d'Ivoire and in its whole distribution area leads to the definition of the adult ecological requirements (temperature, salinity, grain size and sediment composition, organic matter) and the importance of the thermocline in the bathmetric distribution. The population structure study shows: (1) variations of size with depth, (2) variations of sex ratio, with size, depth and seasons.