Beschreibung des aktuellen Verlaufes der jährlichen Reifeentwicklung und der Laichaktivitäten von Dorschen in der Arkonasee (ICES SD 24)

Abstract The spawning activities of cod were described in the Arkona Sea from 2009 to 2012 and were compared with estimates of the period 1992 – 1999. Cod spawned mainly from beginning of June till the middle of July every year. In the same period spawning was observed in the Bornholm Sea. The spawning activities in July were limited by water temperature above the critical limits. Spawning activities in spring which were observed in the 90 ties were of lower importance between 2009 and 2012. Higher proportions of spent cod were observed in the Arkona Sea in August and autumn between 2009 and 2012 compared to the earlier period, indicating immigration of cod from the Bornholm Sea after spawning. The study showed that higher proportion of cod with developing sex products were observed in the Arkona Sea between 2009 and 2012 compared to the 90 ties. Kurzfassung Die Laichaktivitäten der Dorsche in der Arkonasee werden für den Zeitraum 2009 – 2012 dargestellt und im Vergleich mit dem Zeitraum 1992 – 1999 diskutiert. Die Hauptlaichaktivitäten haben im Untersuchungszeitraum von Anfang Juni bis Mitte Juli stattgefunden und lagen damit in ihrem jahreszeitlichen Verlauf innerhalb der Zeitperiode der Laichaktivitäten in der angrenzenden Bornholmsee. In der Arkonasee wurden jeweils im Juli diese Ereignisse durch ansteigende Wassertemperaturenbegrenzt. Die, noch in den 90-er Jahren beobachteten, Laichaktivitäten im Frühjahr haben aktuell an Bedeutung verloren. Im Spätsommer und Herbst war ein, im Vergleich zu den 90-er Jahren, höherer Anteil an abgelaichten Tieren in der Arkonasee zu beobachten, der als Indiz für eine Zuwanderung von abgelaichten Dorschen aus der Bornholmsee gewertet wird. Insgesamt hat der Anteil an Tieren mit sich entwickelnden Geschlechtsprodukten (aktive Laicher) im Untersuchungszeitraum, im Vergleich zu den 90-er Jahren, zugenommen.

An uncommon period of cold and change of lapse rate in the Rocky Mountains of Colorado and Wyoming

EXTRACT (SEE PDF FOR FULL ABSTRACT): Temperature and lapse rate show extreme departures from mean values for May 1981 through October 1986 at the high-elevation station D1 on Niwot Ridge in the Front Range, Colorado. If the D1 record is accurate, this period may present an opportunity to identify factors that influence temperature at high elevations, but not necessarily at low elevations. This paper focuses on four questions: (1) Is the D1 temperature record accurate? (2) What is the geographical extent of this anomalous cold period? (3) Are there any identifiable contributing factors or physical events relating to this period? (4) Is there evidence of a similar anomalous period in the past?

A video method for quantifying size distribution, density, and three-dimensional spatial structure of reef fish spawning aggregations

There is a clear need to develop fisheries independent methods to quantify individual sizes, density, and three dimensional characteristics of reef fish spawning aggregations for use in population assessments and to provide critical baseline data on reproductive life history of exploited populations. We designed, constructed, calibrated, and applied an underwater stereo-video system to estimate individual sizes and three dimensional (3D) positions of Nassau grouper (Epinephelus striatus) at a spawning aggregation site located on a reef promontory on the western edge of Little Cayman Island, Cayman Islands, BWI, on 23 January 2003. The system consists of two free-running camcorders mounted on a meter-long bar and supported by a SCUBA diver. Paired video “stills” were captured, and nose and tail of individual fish observed in the field of view of both cameras were digitized using image analysis software. Conversion of these two dimensional screen coordinates to 3D coordinates was achieved through a matrix inversion algorithm and calibration data. Our estimate of mean total length (58.5 cm, n = 29) was in close agreement with estimated lengths from a hydroacoustic survey and from direct measures of fish size using visual census techniques. We discovered a possible bias in length measures using the video method, most likely arising from some fish orientations that were not perpendicular with respect to the optical axis of the camera system. We observed 40 individuals occupying a volume of 33.3 m3, resulting in a concentration of 1.2 individuals m–3 with a mean (SD) nearest neighbor distance of 70.0 (29.7) cm. We promote the use of roving diver stereo-videography as a method to assess the size distribution, density, and 3D spatial structure of fish spawning aggregations.

Die Reproduktion von Dorschen (Gadus morhua L. und Gadus morhua callarias L. ) in der Ostsee unter besonderer Berücksichtigung der Arkonasee. Teil I: Allgemeiner Verlauf des jährlichen Reifeprozesses und der Laichaktivitäten in den verschiedenen Gebieten

From 1993 to 2003 special surveys were conducted to analyse temporal and spatial aspects of the spawning activities of cod in the Baltic Sea. The ICES advice for cod in the Baltic Sea is based on yearly stock assessments of two separate stocks the western (SD 22 – 24) and the eastern stock (SD 25 – 32). Both stocks are characterized by different spawning seasons. The general progression of the maturity suggests that two types of development can be distinguished. In the western Baltic Sea (SD 22) the maturity development is temporal stable, with a relative short, main spawning period from March to April - spring spawner. In the Arkona Sea and Bornholm Basin the main spawning season starts in June and probably finishes in September - summer spawner. The proportion of spawners in summer is significantly higher than in spring in the Arkona Sea and Bornholm Basin. This again underlines the importance of the Arkona Sea for the reproduction success of the eastern Baltic cod stock. The analysis furthermore show, that the proportion of male spawners was significantly higher than the proportion of female spawners in all areas and the investigated months. This observation suggests that the reproductive success is only limited by the number of female cod which participates in the spawning process.

Die Fruchtbarkeit von Dorschen in der Ostsee - was verrät sie uns?

About 1500 ovaries of Baltic cod were prepared for estimating the potential absolute and relative individual fecundity. The female cod were sampled in the Belt Sea, ICES Subdivision (SD) 22, in the Arkona Sea, SD 24, and in the Bornholm Sea, SD 25. The investigations started in1992 and until 1999 cruises were carried out to catch female cod in the different sub-divisions every year. The results shows that the potential fecundity is not a stable biological parameter, and that significant changes are possible within a relative short period. It was demonstrated that the developments of the potential individual fecundity of the western (Gadus morhua morhua) and eastern Baltic cod stocks (Gadus morhua callarias) were different. In contrast to the stable individual fecundity of the western cod the absolute and relative fecundity of the eastern repeat spawners increased from 1993 to 1999, significantly. The reason of this development seems to be the dramatic decrease of the eastern cod stock and the more successful reproduction of individuals that produce oocytes with a lower dry weight in combination with a higher relative fecundity.

Deutsche und internationale Dorschfischerei in der Ostsee im Jahr 1998

In 1998 the longtime series of the standardized bottom trawl surveys conducted in the western Baltic (ICES Sub-division (SD) 22 and 24 since 1978) during spring and autumn and also in the eastern Baltic (ICES Sub-division since 1993) during spring were continued. The results of the surveys as well as those of a sampling programme carried out on board of commercial cutters (mainly financed by an EU study project) and on the market, the investigation of the survival rate of the discards, and the landing statistics are the basis of the analysis of the German and international cod fishery in 1998. The German cod fishery was concentrated on the ICES SD 22 and 24 (total landings 9722 t). The total landings from the fishing grounds east off Bornholm, the traditional German fishing ground, amounted only to about 1270 t. The German cod quota was utilized at 64 %. The fishery in the ICES SD 22 and 24 was characterized by a discard rate of undersized cod of 13 %. That corresponds to about 7.3 million specimens of 0-group, one- and two-years-old youngfish, respectively. The total international cod landings of the Baltic amounted to 101 500 t. In comparison with 1997 (total landings 129 600 t) the landing decreased by 23 %. The percentage utilization of the cod TAC (1998: 140 000 t) amounted to 74 % in 1998.

Die biologischen Voraussetzungen für einen guten Dorschnachwuchs verbesserten sich 1994 in der westlichen Ostsee

The investigations on the fecundity of cod from different areas of the Baltic Sea started in 1992. The samples were collected in ICES Sub-divisions 25 (Bornholm Sea). 24 (Arkona Sea) and 22 (Mecklenburg and Kiel Bay). This article surnmarizes the results of 435 analysed gonads from females of age groups 1 to 8 with total length of 24 - 116 cm of the years 1992 to 1995. The gonads were prepared and analysed according to the methods which were deseribed in Bleil and Oeberst (1993). The aim of the investigations is to estimate the reproduction potential of cod for different areas and years. For this reason the absolute and relative fecundity were analysed for estimating the dependence on the total length, for age groups and the weight of females. These data were estimated for the populations Gadus morhua morhua and Gadus morhua callarias. Preliminary results have shown that the absolute fecundity (fabs) is dependent on whole weight of the females. The influence of sub-divisions (SD) and years to the fecundity are very low. Additional to this data was calculated the population fecundity for the western Baltic Sea stock (SD 22 and 24). The numbers of produced ripe eggs within the western Baltic were estimated with 4055.59 x 10(9) for 1993 and 6949.85 x 10(9) for 1994.

Quantitative Larvenanalyse des Rügenschen Frühjahrsherings in den Laichsaisons 1991 und 1992

Das bereits vom ehemaligen Institut für Hochseefischerei, Rostock, routinemäßig durchgeführte Heringslarvenprogramm im Greifswalder Bodden wird als Beitrag zur Bestandsschätzung des Rügenschen Frühjahrsherings (RFH) zunehmend unter ökologischen Gesichtspunkten im Institut für Ostseefischerei (IOR) in Kooperation mit der Universität Rostock (Fachbereich Biologie) weitergeführt. Die quantitative Larvenanalyse ermöglicht über den Anteil des aus dem Greifswalder Bodden stammenden Nachwuchses eine Voraussage über den Erfolg der in einem weitaus größeren Seegebiet (ICES SD 22+24) produzierten Nachwuchsjahresklassen. Vorliegende Publikation dokumentiert erste Ergebnisse hinsichtlich der Heringslarvenverteilung im Saisonverlauf 1991 und 1992.

Niedrige Gehalte an toxischen Schwermetallen in Seefischfilet (Ergebnisse der 81. Reise des FFS "Walther Herwig")

Auf der 81. Reise des FFS "Walther Herwig" im März 1987 in die Gewässer östlich Schottlands, Irlands und Nordfrankreichs wurden auf dem Nord-Süd-Schnitt "Westbritische Gewässer-östlicher Kanalausgang nördliche Biskaya" zahlreiche Einzelfischproben für die spätere spurenanalytische Bestimmung der toxischen Schwermetalle Blei und Cadmium gezogen. Bei den Proben handelt es sich um den verzehrbaren Anteil (Muskel, Filet) von kommerziell genutzten Meeresfischen, die den Hols lebend entnommen wurden.

Report on the 1992 stock assessment of the Wyre catchment

The aim of this study was to assess the status of the juvenile salmonid and coarse fish populations of the Wyre catchment. Emphasis was placed on an examination of the distribution of spawning and nursery areas for salmonids within the study area and an assessment of the status of juvenile salmonid stocks. The species distribution and spawning areas for other fish species were also identified where possible and the status of the Wyre coarse fishery, downstream of Churchtown Weir, assessed. This report examines the results of stock assessment surveys carried out in the Wyre catchment between 2/06/92 and 11/08/92. Forty-six sites were surveyed from Tarnbrook Wyre (SD. 598577) and Marshaw Wyre (SD. 614541) downstream to St Michaels (SD. 465411). Flow, habitat and in-river obstructions have been shown to affect juvenile salmonid densities. A habitat description is provided for each site studied during the course of this study.

Swanside Beck, fisheries survey, 22nd September 1992

Swanside Beck is formed from a number of minor tributaries which rise in the Middop area to the west of Barnoldswick. The Beck is approximately 10 km long from the source of its longest tributary (SD. 850445) to the confluence with the River Ribble (SD. 769455). Swanside Beck has one major tributary, Ings Beck, which rises from a number of sources on Twiston Moor and is approximately 6km in length from the source of its longest tributary (SD. 812418) to the confluence with Swanside Beck (SD. 785453). Both Swanside and Ings Becks are important spawning and nursery areas for salmon and sea trout from the River Ribble. In recent years a perceived decline in the migratory fish population of the becks has been reported. This decline has been reported in terms of both adult returns and juvenile production and has been particularly noted in Swanside Beck. The aim of this survey was to assess the likely benefits to Fisheries and Conservation interests of the adoption of a set aside policy for agricultural land adjacent to Swanside Beck. The survey also formed part of an on-going Fisheries study of factors limiting juvenile migratory salmonid production in Swanside Beck. This section of the report deals with the Fisheries aspects of the survey.

River Ribble sheep dip incident September 1997. Electric-fishing survey report

This report summarises the findings of a series of electric-fishing surveys carried out at four sites on the River Ribble from September 1997 to September 1998. The aims of these surveys were to assess the impact on juvenile salmonids of a pollution incident involving Synthetic Pyrethrin (SP) that occurred near High Birkwith I (SD 802 767) in September 1997.One of these sites was 2.65km upstream of the pollution whilst the remaining three were at varying distances downstream. Data was collected during surveys of the River Ribble in 1992, 97 and 98. The 1997 and 1998 surveys were carried out specifically to monitor for any possible effects of the SP discharge. Data are shown as grades derived from the National Fisheries Classification scheme (NFC). Results are given for the four salmonid life stages; 0+ trout, >0+ trout, 0+ salmon, >0+ salmon and also Total Salmonids.

Distribution, growth, and mortality of sailfish (Istiophorus platypterus) larvae in the northern Gulf of Mexico

Ichthyoplankton surveys were conducted in shelf and slope waters of the northern Gulf of Mexico during the months of May–September in 2005 and 2006 to investigate the potential role of this region as spawning and nursery habitat of sailfish (Istiophorus platypterus). During the two-year study, 2426 sailfish larvae were collected, ranging in size from 2.0 to 24.3 mm standard length. Mean density for all neuston net collections (n=288) combined was 1.5 sailfish per 1000 m2, and maximum density was observed within frontal features created by hydrodynamic convergence (2.3 sailfish per 1000 m2). Sagittal otoliths were extracted from 1330 larvae, and otolith microstructure analysis indicated that the sailfish ranged in age from 4 to 24 days after hatching (mean=10.5 d, standard deviation [SD]=3.2 d). Instantaneous growth coefficients (g) among survey periods (n=5) ranged from 0.113 to 0.127, and growth peaked during July 2005 collections when density within frontal features was highest. Daily instantaneous mortality rates (Z) ranged from 0.228 to 0.381, and Z was indexed to instantaneous weight-specific growth (G) to assess stage-specific production potential of larval cohorts. Ratios of G to Z were greater than 1.0 for all but one cohort examined, indicating that cohorts were gaining biomass during the majority of months investigated. Stage-specific production potential, in combination with catch rates and densities of larvae, indicates that the Gulf of Mexico likely represents important spawning and nursery habitat for sailfish.