1,721,031 research outputs found
Diet data for haddock (Melanogrammus aeglefinus) from two capelin spawning areas in Finnmark County, Norway, during 2005 and 2006
No full textDiet data for haddock (Melanogrammus aeglefinus) were collected from two capelin (Mallotus villosus) spawning areas in Finnmark, Norway, during 2005–2006. Haddock were sampled using bottom trawl, and stomach content analysis was performed to estimate the proportions (wet weight) of various prey groups. The data were obtained and analyzed as part of a PhD project investigating predation on capelin eggs and capelin. These data are presented in the PhD thesis: Mikkelsen, N. (2013). Predation on the demersal fish eggs of capelin Mallotus villosus and lumpsucker Cyclopterus lumpus in relation to recruitment. PhD thesis, Department of Arctic and Marine Biology, Faculty of Biosciences, Fisheries and Economics, University of Tromsoe. UiT The Arctic University of Norway (former University of Tromsoe) funded a Phd-scholarship for the first author (N. Mikkelsen
Diet data for Rabbitfish (Chimaera monstrosa) and Velvet belly (Etmopterus spinax) from Malangen fjord in Troms County, Norway, during 2017
No full textDiet data for the fish species Rabbitfish (Chimaera monstrosa) and Velvet belly (Etmopterus spinax) were sampled from Malangen fjord in Troms County, Norway, during 2017. C. monstrosa and E. spinax were sampled using a modified shrimp trawl (sampling otter trawl) at depth of 450 m (17.89 oE, 69.60 oN) by the research vessel Johan Ruud at UiT The Arctic University of Norway. A total of 67 stomachs from C. monstrosa were sampled on 2017-04-26 (n = 11), 2017-05-02 (n = 11), 2017-05-03 (n = 9), 2017-05-04 (n = 10), 2017-05-08 (n = 10) and 2017-10-26 (n = 15). A total of 50 stomachs of E. spinax were sampled on 2017-04-26 (n = 5), 2017-05-02 (n = 10), 2017-05-03 (n = 10), 2017-05-04 (n = 10) and 2017-10-26 (n = 15)
Diet data for Atlantic cod (Gadus morhua), saithe (Pollachius virens), capelin (Mallotus villosus), Atlantic herring (Clupea harengus), witch (Glyptocephalus cynoglossus), long rough dab (Hippoglossoides platessoides) and whiting (Merlangius merlangus) from Ullsfjord in Troms County, Norway, during 2010
No full textDiet data for Atlantic cod (Gadus morhua), saithe (Pollachius virens), capelin (Mallotus villosus), Atlantic herring (Clupea harengus) witch (Glyptocephalus cynoglossus), long rough dab (Hippoglossoides platessoides) and whiting (Merlangius merlangus) from Ullsfjord in Troms County, Norway, during 2010. Cod were sampled from shallow water (file: Diet_G_morhua_Ullsfjord_2010_shallow, average depth of 15 m) using fish rod and from deep water (file: Diet_G_morhua_Ullsfjord_2010_deep, average depth of 280 m) using a shrimp trawl. Saithe (file: Diet_P_virens_Ullsfjord_2010.txt), whiting (file: Diet_M_merlangus_Ullsfjord_2010.txt), witch (file: Diet_G_cynoglossus_Ullsfjord_2010.txt), long rough dab (file: Diet_H_hippoglossides_Ullsfjord_2010.txt), capelin (file: Diet_M_villosus_Ullsfjord_2010.txt), herring (file: Diet_C_harengus_Ullsfjord_2010.txt were also sampled at deep water using shrimp trawl. The data was collected and analysed as part of the project: Investigating coastal ecosystem structure and dynamics using Ecopath/Ecosim ecosystem models and stable isotope data. Proportions wet weight of various prey groups were estimated based on stomach analysis. The data is used in the publication: Pedersen, T., Ramsvatn, S., Nilssen, E.M., Nilsen, M., Morissette, L., Ivarjord, T., Systad, G.H., Kolsum, I., Fause, H., 2016. Species diversity affects ecosystem structure and mass flows in fjords. Regional Studies in Marine Science 3: 205-215. doi: 10.1016/j.rsma.2015.10.00
Diet data for Atlantic cod (Gadus morhua), saithe (Pollachius virens), haddock (Melanogrammus aeglefinus), Atlantic herring (Clupea harengus) and long rough dab (Hippoglossoides platessoides) from Ullsfjord and Soerfjord in Troms County, Norway, during 1992-1996
No full textDiet data for Atlantic cod (Gadus morhua), saithe (Pollachius virens), haddock (Melanogrammus aeglefinus), Atlantic herring (Clupea harengus) and long rough dab (Hippoglossoides platessoides) from Ullsfjord and Soerfjord in Troms County, Norway, during 1992-1996. The data was collected and analysed as part of a project investigating possibilities for sea ranching of released reared cod juveniles. The fish were sampled using bottom trawl. Proportions wet weight of various prey groups were estimated based on stomach analysis. The data is used in the publication: Pedersen, T., Nilsen, M., Nilssen, E.M., Berg, E., Reigstad, M. 2008. Trophic model of a lightly exploited cod-dominated ecosystem. Ecological Modelling 214: 95-111. https://doi.org/10.1016/j.ecolmodel.2007.12.01
Diet data for Atlantic cod (Gadus morhua) from the Steigen and Hamaroy area in Nordland County, Norway, during 1993-1996.
No full textThe data set gives diet composition of Atlantic cod (Gadus morhua) sampled using gill-nets at three locations at 7-50 m depth in the Steigen and Hamaroy area during 1993-1996. Proportions of prey wet weight of each prey group are given for seven predator length intervals and in total, 754 cod stomachs were analyse
Diet data for Atlantic cod (Gadus morhua), haddock (Melanogrammus aeglefinus), saithe (Pollachius virens), Atlantic halibut (Hippogloussus hippoglossus) and sea trout (Salmo trutta) from Porsangerfjord in Finnmark County, Norway, during 2009-2011
No full textDiet data for Atlantic cod (Gadus morhua), haddock (Melanogrammus aeglefinus), saithe (Pollachius virens), Atlantic halibut (Hippogloussus hippoglossus) and sea trout (Salmo trutta) from Porsangerfjord in Finnmark County, Norway, during 2009-2010. Cod were sampled from shallow water (file: Diet_G_morhua_Pors_shallow, average depth of 15 m) using fish rod and from deep water (file: Diet_G_morhua_Pors_deep, average depth of 180 m) using a shrimp trawl. Saithe(file Diet_P_virens_Pors.txt), haddock (file Diet_M_aeglefinus_Pors.txt) and Atlantic halibut (file Diet_H_hippoglossus_Pors.txt) were also sampled at deep water (average depth of 180 m) using shrimp trawl. Sea trout (file: Diet_S_trutta_Pors.txt) was sampled using gill nets at shallow water (2 m depth). The data was collected and analysed as part of the EPIGRAPH program. Proportions wet weight of various prey groups were estimated based on stomach analysis. The data is used in the publication: Pedersen, T., et al. (2018). Effects of the invasive red king crab on food web structure and ecosystem properties in an Atlantic fjord. Marine Ecology Progress Series 596: 13-31
Overview of sources for and specification of time series data for scenario simulations using the Pedersen et al. Barents Sea Ecosim model for the period 2000-2100
No full textTo run simulations using the large Pedersen et al. (2021) Barents Sea Ecosim model, time series with environmental drivers and biomass and catch data to compare with simulation output values are needed. This data set give an overview of time series that can be used to run simulations using the Ecosim model for the period 2000-2100. The Pedersen et al. (2021) Ecopath with Ecosim model have 108 functional groups and time series for biomass, relative biomass, catches, fishing mortality and environmental drivers (temperature, primary production, biomass forcing of some functional groups) are reviewed and listed in the time serie data files. These time series can be used to run future scenarios. There are three files with complete sets of time series for three alternative fishing mortality level scenarios; low fishing mortality, business as usual and high fishing mortality. There are also three alternative environmental drivers corresponding to the temperature time series for the RCP 2.6, RCP 4.5 and RCP 8.5 scenarios from Bentley et al. (2017) and these are given as variables in each of the three time serie data sets. These data were compiled as part of the Nansen Legacy project
Anglerfish Lophius piscatorius L. in Faroese waters. Life history, ecological importance and stock status
Full text linkAnglerfish Lophius piscatorius has during the last two decades become a highly exploited resource and is now one of the five most economically important demersal fish species in the Faroese fishery. Despite this, there is at present little information available on the population status of anglerfish in Faroese waters. The main aim of this study is to increase the biological knowledge of anglerfish and to perform an assessment of the stock in order to evaluate the sustainability of the anglerfish fishery and to investigate trophic interactions between anglerfish and other commercially important demersal fish species.
Anglerfish illicia, the first fin ray, were used for age reading. The age determinations were validated and concluded to be useful in an age-based assessment because the growth rates were consistent with length frequency and mark-recapture analyses. Anglerfish have a very high growth rate during their first year of life, compared with the older ages. Males mature at a lower length and younger age than females. The L50 for males and females was 58 cm and 84 cm, respectively, corresponding to an age of around four years for males and seven years for females. Observations of spawning males and females, egg-ribbons and pelagic anglerfish larvae revealed that anglerfish have a prolonged spawning season, which peaks from February to April. In addition, observations showed that there are at least two local spawning areas, one southwest of the Faroe Plateau and one in the Faroe Bank area.
Large anglerfish tagged with data storage tags and conventional tags showed a seasonal offshore-onshore migration. They migrated to shallow depths in summer to feed and to deeper waters in winter, presumably to spawn. Anglerfish performed vertical movements up into the water column, and were most active in these vertical movements during the winter time and during the nights, and light intensity seemed to trigger the migrations. Anglerfish distribution was temperature dependent, since anglerfish generally preferred temperatures warmer than 4ºC, usually between 6.5–11ºC. This may explain why anglerfish were distributed deeper west of the Faroe Bank area compared to the Faroe Plateau, which is surrounded by cold water deeper than approximately 500 m.
Anglerfish in Faroese waters preyed on a variety of food items. They were generally eating fish and the most important prey species in terms of numbers were Norway pout and blue whiting, whereas cod and haddock contributed most in weight. Annual consumption by anglerfish on commercially important demersal species, such as cod, haddock and saithe, was estimated to correspond to 33, 19 and 2% of the landings and to 75, 20 and 2% of biomass losses due to natural mortality, respectively. Even with this high cod consumption by anglerfish, cod cannibalism and fishing mortality still have greater impact on the cod stock dynamics than predation by anglerfish. The annual biomass loss of anglerfish due to cannibalism was estimated to nearly 15% of the annual loss due to natural mortality.
Anglerfish in Faroese waters may be regarded as a separate stock because all life stages are found in the area, local spawning area, seasonal offshore-onshore migration on the Faroe Plateau, together with insignificant emigration/immigration (< 5%). An age-based stock assessment of anglerfish in Faroese waters for the period 1999–2011 showed that the stock biomass ranged between 9000 and 19000 t with a peak in 2004–2005 and the fishing mortality for age 3–8 varied between 0.2 and 0.5 year-1. The yield per recruit curve indicated that the stock was slightly growth overfished. Decreasing the fishing mortality could potentially increase the yield per recruit by around 10% leading to a 50% higher equilibrium biomass of anglerfish. No clear stock-recruitment relationship was found. On the other hand, anglerfish year-class strength was correlated with environmental variables, such as sandeel abundance. Hence, the rather short time series of anglerfish year-class strength provides little or no evidence of recruitment overfishing. It is recommended that stock assessments should be performed on an annual basis, allowing managers to react timely when there are signs of overfishing or recruitment failure due to natural or fishery causes
Population dynamics of cod, Gadus morhua, in Porsangerfjord, Northern Norway - Analysis of back-calculated length at age from otoliths in 1992 and 2009
Full text linkThe thesis investigates growth of Atlantic cod (Gadus morhua) caught in 1992 and 2009, in Porsangerfjord North-Norway, with use of back-calculated length at age based on cod otoliths. The cod population in Porsangerfjord ecosystem have experienced major changes in abundance during the last decades: a dramatic decline in the costal cod population, and environmental influences.
A back-calculation method estimating length at previous age was done on cod otoliths. The otoliths were embedded in black resin and transversely cut before photographed in a stereomicroscope. Growth zones in otoliths were measured and growth was back-calculated for previous length at age.
In the outer areas (A - B) adult cod, above 5 years of age, were longer at age in the second time period (1998 - 2009) than cod from the first time period (1980 - 1992). Adult cod grew faster in outer areas than in inner areas (C - D) in 1992. In outer area cod had better growth for 1 year old, and 5 - 7 year old, than in inner area (C) in 2009.
In conclusion, increasing sea temperature seem to play maybe the most important role in increased mean length at age for adult cod, above 5 years of age, caught in 2009, compared to cod caught in 1992. In addition, a shift from abundance of cod in inner areas with cold sea temperature in 1992, towards outer warmer areas in 2009 has probably also contributed to increased length at age for older cod
Populasjonsbiologi hos fem fiskearter i Malangen, Nord-Norge. Vekst, kjønnsmodning og dødelighet hos vassild (Argentina silus), hyse (Melanogrammus aeglefinus), kolmule (Micromesistius poutassou), sølvtorsk (Gadiculus argenteus thori) og øyepål (Trisopterus esmarkii)
Full text linkEndringer i klima, miljø og beskatning har gjort at sammensetningen av fiskebestandene endrer seg. Livshistorieparametere som lengde ved alder, lengde og alder ved kjønnsmodning og naturlig og total dødelighetsrate gir viktig informasjon for å kunne forvalte fiskebestandene. Vassild (Argentina silus), hyse (Melanogrammus aeglefinus), kolmule (Micromesistius poutassou), sølvtorsk (Gadiculus argenteus thori) og øyepål (Trisopterus esmarkii) i Malangen i Troms ble undersøkt ved å gjennomføre fire innsamlingstokt i perioden januar til september 2018. Ved å undersøke tilstedeværelse, beregne vekstmønster, kjønnsmodning ved lengde og alder, samt estimere total og naturlig dødelighet er med på å kunne gi informasjon om hvordan dynamikken hos disse artene er i Malangen.
Alle de undersøkte artene var tilstede i januar, men det var liten fangst av vassild under det første toktet. Øyepål ble ikke registrert i fangsten i mai, men var tilbake i fangstene i september. Det kan virke som om gytemoden kolmule trekker ut av Malangen på våren og slutter seg til resten av kolmulebestandene ved gytefeltene. Hyse var representert i alle innsamlingene, men alderen på individene begrenset seg til 1-4 år. Det er mulig at Malangen fungerer som oppvekstområde for hyse, før gytemodne individer trekker mot gyteområder som for eksempel i Balsfjord.
Vassild, kolmule, sølvtorsk og øyepål hadde lavere lengde ved alder sammenlignet med de samme artene i Nordsjøen, ved Færøyene og vest for de Britiske øyer. For å undersøke vekstutviklingen ble von Bertalanffys vektfunksjon benyttet. Estimert L∞ var fra 15,1 cm hos sølvtorsk til L∞ på 36,5 cm hos vassild. Det ikke var mulig å bergene von Bertalanffys vekstparametere for hyse basert på datamaterialet. Vekstindeksen φʹ (Phi`) varierte fra 2,27 hos sølvtorsk til 2,71 hos kolmule. Kjønnsmodning inntrådte i hovedsak ved både større lengde og høyere alder for artene i Malangen sammenlignet med bestandene i sørligere havområder. Hyse ble også sammenlignet med Barentshavet for å se hvordan vekstmønsteret og kjønnsmodningsmønster utvikler seg i artens nordligste utbredelsesområde.
Det er lav fiskeriaktivitet i Malangen og for de fleste artene ble den totale dødelighetsraten Z satt lik M. Alle artene bortsett fra øyepål hadde høyere naturlig dødelighetsrate enn for bestandene i sammenligningsområdet. Dette er estimat som er viktig å følge tett opp, særlig ved innføring av ulike forvaltningsregimer. Forvaltningen av ulike fjordsystemer må gjøres med tett overvåkning av disse livshistorieparametere for de ulike fiskeartene
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