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.

Über die Herkunft des starken Kabeljau-Jahrgangs 1996 in der Nordsee

Cod in the North Sea is expected to reach „Safe biological limit“ due to a strong 1996 year-class. The cod fry was seen first as 5 cm fingerlings in the catches during a hydroacoustic survey in the southeastern North Sea. Back-calculations of the water drift show with high probability that the respective spawning ground was situated in the southwestern North Sea.

Zur Bedeutung des Größenunterschieds weiblicher und männlicher Nordseegarnelen für die kommerzielle Garnelenfischerei

Aiming at a better knowledge on the distribution and fecundity of hibernating Crangon crangon (L.), the R.V. "Solea" in January is sampling shrimps in the German Bight since 1991. A total of 3.000 shrimps (1.608 females and 1.392 males) have been investigated with regard to total length, to the width of the carapace and to spawning activity.

Hinweise auf eine Überfischung grönländischer Grundfischbestände

At present, the severe decline of the fishery off Greenland is being discussed controversially. In contrast to overfishing, climate changes and emigration are itemized causal. Available German data on commercial catches and research cruises are presented for clarification. A few years after the beginning of heavy exploitation during the early sixties, the stocks of cod, golden and beaked redfish reflected a significant rejuvenescence based on catch analysis. Regular scientific surveys• for stock assessment purposes commenced in 1982 when the productivity of the stocks was already adversely affected due to low spawning stocks and extremely irregular recruitment. From this point of view, the results of the latest survey in 1995 showing stagnant fish biomass at record low level since 1991 are not surprising. The status of the cod stock is still considered severely depleted. Taking the high abundance of juvenile redfish into account, recovery of the groundfish stocks is unlikely in short term and depends on the non-predictable recruitment only.

Protecting a threatened coastal fish species through regional collaboration

Rainbow smelt (Osmerus mordax) are small anadromous fish that live in nearshore coastal waters during much of the year and migrate to tidal rivers to spawn during the spring. They are a key prey species in marine food webs, as they are consumed by larger organisms such as striped bass, bluefish, and seabirds. In addition, smelt are valued culturally and economically, as they support important recreational and commercial fisheries. The Atlantic Coast range of rainbow smelt has been contracting in recent decades. Historically, populations extended from the Delaware River to eastern Labrador and the Gulf of St. Lawrence (Buckley 1989). More recent observations indicate that rainbow smelt spawning populations have been extirpated south of Long Island Sound, and evidence of spawning activity is extremely limited between Long Island and Cape Cod, MA. In the Gulf of Maine region, spawning runs are still observed, but monitoring surveys as well as commercial and recreational catches indicate that these populations have also declined (e.g., Chase and Childs 2001). Many diverse factors could drive the recently noted declines in rainbow smelt populations, including spawning habitat conditions, fish health, marine environmental conditions, and fishing pressure. Few studies have assessed any of these potential threats or their joint implications. In 2004, the National Marine Fisheries Service (NMFS) listed rainbow smelt as a species of concern. Subsequently, the states of Maine, New Hampshire, and Massachusetts were awarded a grant through NMFS’s Proactive Conservation Program to gather new information on the status of rainbow smelt, identify factors that affect spawning populations, and develop a multi-state conservation program. This paper provides an overview of this collaborative project, highlighting key biological monitoring and threats assessment research that is being conducted throughout the Gulf of Maine. (PDF contains 4 pages)

The effects of brood stock size on the economy of catfish (Clarias anguillaris) fry production using the hormone induced natural breeding technique

89 ripe female brooders of the catfish, Clarias anguillaris (Body wt. Range 150g-1, 200g) were induced to spawn by hormone (Ovaprim) induced natural spawning technique over a period of 10 weeks. Matching ripe males were used for pairing the females at the ratio of two males to a female. Six ranges of brood stock body weights were considered as follows; <200g; 200g-399g; 400g-599g; 600-799g; 800g-999g; > 1000g and the number of fry produced by each female brooder was scored/recorded against the corresponding body weight range. The number of fry per unit quantity of hormone and the cost of production a fry based on the current price of Ovaprim (hormon) were determined so as to ascertain most economic size range. The best and most economic size range was between 400g-599g body weight with about 20,000 fry per ml of hormone and N0.028 per fry, while the females above 1000g gave the poorest results of 9,519 fry per ml of hormone and N0.059 per fry. For optimum production of Clarias anguillaris fry and maximum return on investment female brooders of body weights ranging between 400g-599g are recommended for hormone induced natural breeding exercises

The effects of brood stock size on the economy of catfish (Clarias anguillaris) fry production using the hormone induced natural breeding technique

89 ripe female brooders of the catfish, Clarias anguillaris (Body wt. Range 150g-1, 200g) were induced to spawn by hormone (Ovaprim) induced natural spawning technique over a period of 10 weeks. Matching ripe males were used for pairing the females at the ratio of two males to a female. Six ranges of brood stock body weights were considered as follows; <200g; 200g-399g; 400g-599g; 600-799g; 800g-999g; > 1000g and the number of fry produced by each female brooder was scored/recorded against the corresponding body weight range. The number of fry per unit quantity of hormone and the cost of production a fry based on the current price of Ovaprim (hormon) were determined so as to ascertain most economic size range. The best and most economic size range was between 400g-599g body weight with about 20,000 fry per ml of hormone and N0.028 per fry, while the females above 1000g gave the poorest results of 9,519 fry per ml of hormone and N0.059 per fry. For optimum production of Clarias anguillaris fry and maximum return on investment female brooders of body weights ranging between 400g-599g are recommended for hormone induced natural breeding exercises

Effects of some environmental factors on the fecundity of Tilapia species (Family Cichlidae) in Kigera Reservoir, New Bussa

The effects of some environmental factors on the fecundity of Tilapia species (Family Cichilidae) was carried out at the Kigera dam. Four Tilapia species caught were Tilapia zilli, Hemichromis fasciatus, Sarotherodon galilaeus and Oreochromis niloticus while the environmental factors considered were water temperature, Dissolved Oxygen, pH value, level of rainfall and rate of sunshine and range of time. 43 fish comprising of 25 male with (58.1%) and 18 females having (41.9%) were studied with 74.42% been sexually matured. Both high levels of rainfall and dissolved oxygen favoured fecundity. The spawning peak occurred in (July), environmental factors monitored indicated that dissolved oxygen ranges from 3.7 to 4.45mg/lit rainfall ranges from (34.90mm to 237.80mm) sunshine ranges from (5hrs-8hrs) and pH ranges from (7.35-7.45). The spawning of these species in their natural or hatchery condition is therefore best achieved during the peak of raining season

Studies on the condition factor of the Sierra Leone mangrove oyster (Crassostrea tulipa)

Sierra Leone is a tropical country where water temperatures are high throughout the year. Consequently the local oysters tend to spawn the year round, with one or two spawning peaks. The condition of such tropical oysters may not be as high as those oyesters in temperate countries since the stored glycogen is regularly utilized to form gonads. A high condition factor value indicates that the oysters have accumulated glycogen and or gonads, whereas a low condition factor value indicates that the oysters have spawned and are in the process of accumulating glycogen, which may later be utilized for gonad development. In oyster culture, condition factor studies may be supported by plankton and oyster spat settlement studies in the culture area. These studies give an indication of when oyster larvae and spat settlement are at their peak values. In Sierra Leone studies of the plankton and spat settlement are undertaken every week throughout the year. Conditions factor is obtained from the ratio weight of dry (oyster) meat x 1000/internal volume. Detailed condition factor values are shown in relation to salinity at two stations. Condition factor declines with reducing salinity, which principally occurs during the rainy season. The best times to collect spat are May to June and September to October

Deutscher Beitrag zum internationalen Makrelen(Scomber scombrus) und Stöcker- (Trachurus trachurus) Eier-Survey

Based on the results from egg and larvae surveys, mackerel and horse mackerel are thought to form three more or less distinct stocks each in the North Sea and in the waters west of the British Isles. These are firstly the southern stocks in the southern part of the English Channel, Celtic Sea and Bay of Biscay, secondly the North Sea and finally the western stocks of both species, loeated between the Shetlands and southern Norway. It is argued here that in view of the high mobility and the extended seasonal migrations of both species a c1ear separation of the stocks can hardly be maintained. In this context the results of the 1995 mackerel and horse mackerel egg survey to the southern spawning location is presented.

Biologische Verbindungen zwischen den Rotbarschbeständen Westgrönlands und der Irmingersee

Two redfish species are expected to live off western Greenland in a broad distribution area. Except for a small population of adults in the Godthab Fjord, only juvenile and adolescent specimens have been met there, tending to increase in age from the north to the south. As taxonomic identification of single specimens is difficult the distribution of species stocks cannot be clearly identified. This paper deals with spawning areas, migration and drifting routes around Greenland respectively in relation to distributional pattern of juvenile redfish off western Greenland.

Zum Auftreten von Geruchs- und Geschmacksabweichungen ("Tainting") bei Frühjahrsheringen (Clupea harengus) aus der Ostsee

An account of the occurrenee of tainting in fish and seafood with special consideration of spring spawning herring from the Baltic Sea (estuary of the river Oder) is given. About 26 % of the herring samples examined by sensory methods showed tainting. In general the intensity of taint was weak or moderate and weaker as observed years ago. Also in fishery products (pickled herring, deep fried herring in marinade) processed from tainted herrings the same or a similar sensory intensity of taint as in the raw material was observed. The source of taint is not dear. A pollution with halogenphenols from the sea water could be possible. In further investigations we will monitor the further development and try to identify the tainting compounds.

A decade of studies at Loch Fleet, Galloway (Scotland): A catchment liming project and restoration of a brown trout fishery

Loch Fleet is a small upland lake in the hills of Galloway in southwest Scotland. In the 1970s the waters of the loch became more acidic and a brown trout fishery failed. This account summarises an experimental project, the "Loch Fleet Project" initiated in 1984, designed to reverse acidification of the loch by liming parts of the catchment. Liming about 40% of the catchment in 1986 and 1987 raised the pH and calcium levels, and reduced toxic aluminium concentrations. The improved conditions had been maintained up to 1994, but water in the loch, and its principal inflow stream, is now falling close to the desired threshold of quality. After liming, restocking with local strains of trout in 1987 was successful, and a self-recruiting population became established within 2 years. Recruitment is highly variable, however, and was attributed to severe spring conditions and the limited spawning capacity of the nursery stream, rather than to water quality.

The smelt Osmerus eperlanus in Scotland

Smelt populations have been recorded since the 18th Century from at least 15 rivers in Scotland, but over the last Century the species has suffered a severe decline and has disappeared from all its former sites except the rivers Cree, Forth and Tay. These populations must now be regarded as having high conservation importance. There are probably several different reasons for this decline. In some rivers, such as the Clyde and the Stinchar, pollution in the lower reaches has prevented successful migration and reproduction. In other rivers, high weirs and barriers have completely cut off access to spawning grounds. In some estuaries and rivers, such as the Solway Firth, overfishing is believed to have been responsible for eliminating local stocks. A Species Action Plan for the smelt has been prepared and it is hoped that this will be the basis of a future conservation strategy for this species in Scotland.

A fisheries management plan for the River Tweed in the Scottish Borders

The River Tweed is, in rod-catch terms, the second most important river in Britain for Atlantic salmon, with an annual rod catch of ca.10,000 fish. This article gives an outline of the second edition of the Tweed Fisheries Management Plan, which is defined as "The co-ordination of data collection and analyses with fundamental research into relevant topics to devise management actions that will beneficially affect the future state of fish stocks". Much of the work set down for the present is concerned with setting up recording and measuring systems for fish catches and exploitation rates, and for the operation of monitoring sites for juvenile densities and adult trout and salmon spawning runs. While surveys show the present state of affairs, the collection of records and regular monitoring of sites will mean that in the future, the past will be better known through a longer series of records. Two case histories are described. The first is concerned with setting aims for managing the brown trout of the Tweed and defining the present state of the fishery. The second is an investigation into the spring salmon of the Tweed.