scholarly journals Changing recruitment capacity in global fish stocks

2015 ◽  
Vol 113 (1) ◽  
pp. 134-139 ◽  
Author(s):  
Gregory L. Britten ◽  
Michael Dowd ◽  
Boris Worm
Keyword(s):  
Environmental Changes ◽  
Meta Analysis ◽  
Chlorophyll Concentration ◽  
Fish Stock ◽  
Productive Capacity ◽  
Large Variability ◽  
Fish Stocks ◽  
Large Marine Ecosystems ◽  
The North ◽  
Spawning Stock

Marine fish and invertebrates are shifting their regional and global distributions in response to climate change, but it is unclear whether their productivity is being affected as well. Here we tested for time-varying trends in biological productivity parameters across 262 fish stocks of 127 species in 39 large marine ecosystems and high-seas areas (hereafter LMEs). This global meta-analysis revealed widespread changes in the relationship between spawning stock size and the production of juvenile offspring (recruitment), suggesting fundamental biological change in fish stock productivity at early life stages. Across regions, we estimate that average recruitment capacity has declined at a rate approximately equal to 3% of the historical maximum per decade. However, we observed large variability among stocks and regions; for example, highly negative trends in the North Atlantic contrast with more neutral patterns in the North Pacific. The extent of biological change in each LME was significantly related to observed changes in phytoplankton chlorophyll concentration and the intensity of historical overfishing in that ecosystem. We conclude that both environmental changes and chronic overfishing have already affected the productive capacity of many stocks at the recruitment stage of the life cycle. These results provide a baseline for ecosystem-based fisheries management and may help adjust expectations for future food production from the oceans.

Decadal changes in the North Sea food web between 1981 and 1991 — implications for fish stock assessment

2006 ◽  
Vol 63 (11) ◽  
pp. 2586-2602 ◽  
Author(s):  
Alexander Kempf ◽  
Jens Floeter ◽  
Axel Temming
Keyword(s):  
Food Web ◽  
North Sea ◽  
Fish Stock ◽  
Fish Diet ◽  
Data Set ◽  
The North ◽  
Stock Biomass ◽  
Spawning Stock ◽  
The North Sea ◽  
The Impact

The North Sea ecosystem of the early 1980s differed substantially from that of the early 1990s. The current North Sea multispecies fisheries assessment models are parameterized by fish diet data sets that reflect both ecosystem states, as the stomachs were sampled in 1981 and 1991. In this study, multispecies virtual population analysis (MSVPA) was parameterized with either diet data set, leading to different model food webs, each representing the predator's diet selection behavior and spatiotemporal overlap with their prey in the two respective ecosystem states. The impact of these changes in predator preferences and spatiotemporal overlap on recruitment success and on stock developments could be demonstrated by using either stomach data set to estimate historic and future spawning stock biomass and recruitment trajectories. The observed changes in the food web mainly impacted the hindcasted recruitment trajectories, whereas spawning stock biomass estimates were quite robust. In the prediction runs, the differences in the survival rate of the recruits decided whether fish stocks of commercially important species (e.g., Gadus morhua, Merlangius merlangus) would recover or collapse in the near future.

scholarly journals Systmod II: Approaching a real dynamic computer model for fish stock assessment and development of fishery strategies

2016 ◽  
Author(s):  
Kristin Hamre ◽  
Steinar Moen ◽  
Johannes Hamre
Keyword(s):  
Stock Assessment ◽  
Growth Function ◽  
Field Studies ◽  
Fish Growth ◽  
Fish Stock ◽  
Initial State ◽  
Fish Stocks ◽  
Spawning Stock ◽  
Fish Stock Assessment ◽  
In The Beginning

Simulating development of fish stocks may be as complex as calculation of the development of the atmosphere, which is treated in meteorology as an initial value problem in physics. This approach was first proposed by Abbe and Bjerknes in the beginning of the 20 th century and today huge systems of differential equations are used to predict the weather. A similar approach to fisheries biology and ecology requires a real dynamic population model, which calculates the development of fish stocks from an initial state with equations that are independent of time. Here we present Systmod II, which uses a length-based growth function with a parameter for environmental variation and length-based data structure. The model uses monthly time steps to integrate population growth by moving fish to higher length groups as they grow. Since fish growth and maturity correlate more with length than with age, this gives comprehensive and clear results. The model was validated for Norwegian Spring-Spawning herring, using observed data from ICES working groups, and correlations (R2) between simulated and observed stock (total stock, spawning stock and catchable stock, numbers and biomass) were above 0.93. At present, the model makes reliable predictions on the short term (3 year for herring). For long term forecasts, better predictions of recruitment are needed . Since length is the main variable of the growth function, the state of the fish stock, including variability in length per yearclass, can be measured in situ, using hydro-acoustic trawl surveys. Data for modelling of many of the relations are still lacking, but can be filled in from future field studies.

scholarly journals Skilful prediction of cod stocks in the North and Barents Sea a decade in advance

2021 ◽  
Author(s):  
Vimal Koul ◽  
Camilla Sguotti ◽  
Marius Årthun ◽  
Sebastian Brune ◽  
André Düsterhus ◽  
...  
Keyword(s):  
Barents Sea ◽  
Statistical Prediction ◽  
Fish Stock ◽  
Fish Stocks ◽  
Ocean Climate ◽  
The North ◽  
Stock Biomass ◽  
The North Sea ◽  
Linear Effects ◽  
Effects Of Temperature

Abstract Reliable information about the future state of the ocean and fish stocks is necessary for informed decision-making by fisheries scientists, managers and the industry. However, multiyear regional ocean climate and fish stock predictions have until now had low forecast skill. Here, we provide skillful forecasts of the biomass of cod stocks in the North and Barents Seas a decade in advance. We develop a unified dynamical-statistical prediction system wherein statistical models link future total stock biomass to dynamical predictions of sea surface temperature, while also considering different fishing mortalities. We evaluate non-linear effects of temperature and fishing on cod biomass, and provide evidence of climate-derived predictability in cod stocks. We forecast the continuation of unfavorable oceanic conditions for the North Sea cod for the coming decade which would inhibit its recovery at present fishing levels, and a decrease in Northeast Arctic cod stock compared to the recent high levels.

scholarly journals The dynamics of fish populations at low abundance and prospects for rebuilding and recovery

2014 ◽  
Vol 71 (8) ◽  
pp. 2141-2151 ◽  
Author(s):  
Ray Hilborn ◽  
Daniel J. Hively ◽  
Olaf P. Jensen ◽  
Trevor A. Branch
Keyword(s):  
Meta Analysis ◽  
Reference Points ◽  
Fishing Pressure ◽  
Fish Stocks ◽  
Stock Size ◽  
Surplus Production ◽  
Total Surplus ◽  
Spawning Stock ◽  
Low Levels ◽  
Rule Out

Abstract Previous meta-analysis of spawner–recruit relationships suggested that depensatory behaviour is uncommon, and stocks pushed to low abundance are unlikely to suffer decreases in recruitment more severe than would be expected based on the decline in spawning stock. Using an updated database that has over 100 stocks that were depleted to less than 20% of their maximum observed stock size, we tested for depensatory behaviour in both total surplus production and recruitment and we also examined the probability of stock increase as a function of stock size and fishing pressure. The number of stocks that showed a significant improvement with depensatory models was less than that expected by chance. Hierarchical meta-analysis showed that the majority of the evidence was for no depensatory behaviour but could not rule out depensation at very low stock sizes. Stocks that are depleted to low abundance are expected to rebuild when fishing pressure is reduced if the environment has not changed but there is considerable evidence that the majority of fish stocks are impacted by changes in productivity regimes. Nevertheless, if stocks are very heavily depleted and fishing pressure is not reduced to quite low levels, the expected recovery time is both uncertain and long. Very low abundance should clearly be avoided for many reasons and the range of abundance where depensation cannot be ruled out is well below commonly adopted limit reference points.

scholarly journals Is the East Asian flora ancient or not?

2017 ◽  
Vol 5 (6) ◽  
pp. 920-932 ◽  
Author(s):  
Yong-Sheng Chen ◽  
Tao Deng ◽  
Zhuo Zhou ◽  
Hang Sun
Keyword(s):  
Northern Hemisphere ◽  
Asian Monsoon ◽  
Environmental Changes ◽  
Meta Analysis ◽  
East Asian ◽  
Species Differentiation ◽  
Seed Plants ◽  
Origin And Evolution ◽  
The North ◽  
The Impact

Abstract The East Asian flora (EAF) is a key biodiversity hotspot for understanding the origin and evolution of Northern Hemisphere floras, but there is an ongoing debate on whether it is a museum or a cradle for seed plants. Within the EAF, two main floras, the Sino-Himalayan Flora (mainly the Rhododendron Flora) and the Sino-Japanese Flora (mainly the Metasequoia Flora), have been recognized. Previous studies suggested that the EAF is ancient and the Metasequoia Flora is older than the Rhododendron Flora. To test this hypothesis, we synthesized molecular as well as fossil data on seed plants, focusing on the biogeographical origins and historical evolution of the EAF. We compared the ages of its two constituent floras, and examined the impact of the Asian monsoon and other environmental changes on the development of EAF through meta-analysis. Our results suggest that the EAF might be relatively young, with most of its clades originating since the Miocene. The Rhododendron Flora and the Metasequoia Flora are probably of a similar age. The formation and development of the Asian monsoon might have been the main factors that have driven the evolution of EAF. In the Rhododendron Flora, the north-south mountain chains increased the concentration of species and reduced extinction, and the barriers between the east and west have resulted in species differentiation, which triggered it to become a diversity center. The EAF appears to have multiple biogeographical origins, having closely affiliated not only with other floras in the Northern Hemisphere, but also with Gondwanan floras.

scholarly journals Skilful prediction of cod stocks in the North and Barents Sea a decade in advance

2021 ◽  
Vol 2 (1) ◽  
Author(s):  
Vimal Koul ◽  
Camilla Sguotti ◽  
Marius Årthun ◽  
Sebastian Brune ◽  
André Düsterhus ◽  
...  
Keyword(s):  
Barents Sea ◽  
Statistical Prediction ◽  
Fish Stock ◽  
Past Performance ◽  
Fish Stocks ◽  
Ocean Climate ◽  
The North ◽  
Future State ◽  
Stock Biomass ◽  
The North Sea

AbstractReliable information about the future state of the ocean and fish stocks is necessary for informed decision-making by fisheries scientists, managers and the industry. However, decadal regional ocean climate and fish stock predictions have until now had low forecast skill. Here, we provide skilful forecasts of the biomass of cod stocks in the North and Barents Seas a decade in advance. We develop a unified dynamical-statistical prediction system wherein statistical models link future stock biomass to dynamical predictions of sea surface temperature, while also considering different fishing mortalities. Our retrospective forecasts provide estimates of past performance of our models and they suggest differences in the source of prediction skill between the two cod stocks. We forecast the continuation of unfavorable oceanic conditions for the North Sea cod in the coming decade, which would inhibit its recovery at present fishing levels, and a decrease in Northeast Arctic cod stock compared to the recent high levels.

Effect of Changes in Recruitment Levels on Multispecies Long-term Predictions

1993 ◽  
Vol 50 (11) ◽  
pp. 2315-2322 ◽  
Author(s):  
Henrik Gislason
Keyword(s):  
Gadus Morhua ◽  
Atlantic Cod ◽  
Relative Increase ◽  
Clupea Harengus ◽  
Melanogrammus Aeglefinus ◽  
Fish Stocks ◽  
The North ◽  
Predation Mortality ◽  
Spawning Stock ◽  
Relative Change

A multispecies model (MSFOR) is used to predict the relative change in equilibrium yield and spawning stock biomass (SSB) of commercially important fish stocks in the North Sea resulting from a reduction in the fishing mortality generated by the roundfish fishery. Because predation mortality is a function of the abundance of prey and predators the results will depend on recruitment. Assuming recruitment to be independent of stock sizes the effect of changes in recruitment is studied by repeating the predictions at all possible combinations of ±50% changes in predator and prey recruitment levels. All of the predictions result in a relative increase in the SSB of Atlantic cod (Gadus morhua) and saithe (Pollachius virens) and in a relative decrease in the SSB of Atlantic herring (Clupea harengus) and Norway pout (Trisopterus esmarkii). In these cases the sign of the relative change is robust to recruitment changes. However, for haddock (Melanogrammus aeglefinus), sprat (Sprattus sprattus), and sandeel (Ammodytes marinus) the relative change in SSB is found to be either positive or negative depending on the level of recruitment. The predictions for haddock are highly sensitive to changes in the level of saithe recruitment.

scholarly journals Systmod II: Approaching a real dynamic computer model for fish stock assessment and development of fishery strategies

2016 ◽  
Author(s):  
Kristin Hamre ◽  
Steinar Moen ◽  
Johannes Hamre
Keyword(s):  
Stock Assessment ◽  
Growth Function ◽  
Field Studies ◽  
Fish Growth ◽  
Fish Stock ◽  
Initial State ◽  
Fish Stocks ◽  
Spawning Stock ◽  
Fish Stock Assessment ◽  
In The Beginning

Simulating development of fish stocks may be as complex as calculation of the development of the atmosphere, which is treated in meteorology as an initial value problem in physics. This approach was first proposed by Abbe and Bjerknes in the beginning of the 20 th century and today huge systems of differential equations are used to predict the weather. A similar approach to fisheries biology and ecology requires a real dynamic population model, which calculates the development of fish stocks from an initial state with equations that are independent of time. Here we present Systmod II, which uses a length-based growth function with a parameter for environmental variation and length-based data structure. The model uses monthly time steps to integrate population growth by moving fish to higher length groups as they grow. Since fish growth and maturity correlate more with length than with age, this gives comprehensive and clear results. The model was validated for Norwegian Spring-Spawning herring, using observed data from ICES working groups, and correlations (R2) between simulated and observed stock (total stock, spawning stock and catchable stock, numbers and biomass) were above 0.93. At present, the model makes reliable predictions on the short term (3 year for herring). For long term forecasts, better predictions of recruitment are needed . Since length is the main variable of the growth function, the state of the fish stock, including variability in length per yearclass, can be measured in situ, using hydro-acoustic trawl surveys. Data for modelling of many of the relations are still lacking, but can be filled in from future field studies.

Estimating uncertainty of data limited stock assessments

2016 ◽  
Vol 74 (1) ◽  
pp. 69-77 ◽  
Author(s):  
Alexandros Kokkalis ◽  
Anne Maria Eikeset ◽  
Uffe H. Thygesen ◽  
Petur Steingrund ◽  
Ken H. Andersen
Keyword(s):  
Stock Assessment ◽  
Assessment Method ◽  
Fish Stocks ◽  
Stock Status ◽  
North East ◽  
The North ◽  
Stock Biomass ◽  
Uncertainty Estimates ◽  
Stock Assessments ◽  
Spawning Stock

Many methods exist to assess the fishing status of data-limited stocks; however, little is known about the accuracy or the uncertainty of such assessments. Here we evaluate a new size-based data-limited stock assessment method by applying it to well-assessed, data-rich fish stocks treated as data-limited. Particular emphasis is put on providing uncertainty estimates of the data-limited assessment. We assess four cod stocks in the North-East Atlantic and compare our estimates of stock status (F/Fmsy) with the official assessments. The estimated stock status of all four cod stocks followed the established stock assessments remarkably well and the official assessments fell well within the uncertainty bounds. The estimation of spawning stock biomass followed the same trends as the official assessment, but not the same levels. We conclude that the data-limited assessment method can be used for stock assessment and that the uncertainty estimates are reliable. Further work is needed to quantify the spawning biomass of the stock.

Towards a new recruitment paradigm for fish stocks

1997 ◽  
Vol 54 (4) ◽  
pp. 969-977 ◽  
Author(s):  
D J Gilbert
Keyword(s):  
Time Series ◽  
Null Hypothesis ◽  
Meta Analysis ◽  
Fish Stock ◽  
Test Statistic ◽  
Mean Values ◽  
Fish Stocks ◽  
Independent Events ◽  
Alternative Hypotheses ◽  
Stock Recruitment

The stock recruitment paradigm involves the hypothesis that recruitment (R) to a fish stock is positively related to the spawning stock biomass (SSB) of the stock, at low SSB. I propose a ``recruitment states'' hypothesis wherein R is independent of SSB but has different mean values during successive periods. Meta-analysis was used to test the null hypothesis that recruitment is a series of random, independent events, against these two alternative hypotheses, for 153 marine spawning bony fish stocks and 31 salmonid stocks. A test statistic for the stock recruitment paradigm, based on estimating derivatives from the first differences of the time series, was not significant for the marine stocks. The null hypothesis was rejected for the salmonid stocks. Recruitment states models significantly fitted time series for the marine stocks. Ricker models also significantly fitted these data, conflicting with the derivatives test result. However, because SSB is dependent on R, lagged by the age at maturity, a period in a low recruitment state would tend to lead to a period of low SSB. Therefore, the significance of the fit to the Ricker model may have been spurious. The recruitment states model best explained the meta-dataset for the marine stocks.

Sign in / Sign up

Export Citation Format

Share Document