Limits...
Recruitment variability in North Atlantic cod and match-mismatch dynamics.

Kristiansen T, Drinkwater KF, Lough RG, Sundby S - PLoS ONE (2011)

Bottom Line: However, the cumulative effect of higher growth rates and survival through the entire spawning season in warm years was substantial with 308%, 385%, 154%, and 175% increases in survival for Georges Bank, Iceland, North Sea, and Lofoten cod stocks, respectively.We also found that the importance of match-mismatch dynamics generally increased with latitude.This prolonged season enhances cumulative growth and survival, leading to a greater number of large individuals with enhanced potential for survival to recruitment.

View Article: PubMed Central - PubMed

Affiliation: Institute of Marine Research and Bjerknes Centre for Climate Research, Bergen, Norway. tk@trondkristiansen.com

ABSTRACT

Background: Fisheries exploitation, habitat destruction, and climate are important drivers of variability in recruitment success. Understanding variability in recruitment can reveal mechanisms behind widespread decline in the abundance of key species in marine and terrestrial ecosystems. For fish populations, the match-mismatch theory hypothesizes that successful recruitment is a function of the timing and duration of larval fish abundance and prey availability. However, the underlying mechanisms of match-mismatch dynamics and the factors driving spatial differences between high and low recruitment remain poorly understood.

Methodology/principal findings: We used empirical observations of larval fish abundance, a mechanistic individual-based model, and a reanalysis of ocean temperature data from 1960 to 2002 to estimate the survival of larval cod (Gadus morhua). From the model, we quantified how survival rates changed during the warmest and coldest years at four important cod spawning sites in the North Atlantic. The modeled difference in survival probability was not large for any given month between cold or warm years. However, the cumulative effect of higher growth rates and survival through the entire spawning season in warm years was substantial with 308%, 385%, 154%, and 175% increases in survival for Georges Bank, Iceland, North Sea, and Lofoten cod stocks, respectively. We also found that the importance of match-mismatch dynamics generally increased with latitude.

Conclusions/significance: Our analyses indicate that a key factor for enhancing survival is the duration of the overlap between larval and prey abundance and not the actual timing of the peak abundance. During warm years, the duration of the overlap between larval fish and their prey is prolonged due to an early onset of the spring bloom. This prolonged season enhances cumulative growth and survival, leading to a greater number of large individuals with enhanced potential for survival to recruitment.

Show MeSH

Related in: MedlinePlus

Frequency distribution of modeled prey sizes and observed monthly concentrations of chlorophyll-a.The relationship between prey length and prey size groups used in the model as suggested in [34] are shown in a). No size interval contains more than 12% of the total abundance (circles). The squares show the relationship between width and length [33] of the prey items, which is essential for estimating prey image size, and visibility to the larval cod. b) Climatological chlorophyll-a (mg•m−3) values from January to December for the North Sea, Iceland, Lofoten, and Georges Bank stations (also see Fig. 1). Chlorophyll-a values are used together with the temperature anomaly data to calculate the monthly prey (mesozooplankton) concentration.
© Copyright Policy
Related In: Results  -  Collection


getmorefigures.php?uid=PMC3049760&req=5

pone-0017456-g003: Frequency distribution of modeled prey sizes and observed monthly concentrations of chlorophyll-a.The relationship between prey length and prey size groups used in the model as suggested in [34] are shown in a). No size interval contains more than 12% of the total abundance (circles). The squares show the relationship between width and length [33] of the prey items, which is essential for estimating prey image size, and visibility to the larval cod. b) Climatological chlorophyll-a (mg•m−3) values from January to December for the North Sea, Iceland, Lofoten, and Georges Bank stations (also see Fig. 1). Chlorophyll-a values are used together with the temperature anomaly data to calculate the monthly prey (mesozooplankton) concentration.

Mentions: A global atlas of monthly (January to December) average (1998–2008) chlorophyll-a values were obtained from the SeaWiFS project website (http://seadas.gsfc.nasa.gov/). Chlorophyll values from the nearest four grid points surrounding the spawning locations were interpolated in space and time and used to create time-series of chlorophyll-a values. Light was modeled as a function of day of the year, latitude, and depth [29], while the attenuation coefficient was modeled as a function of monthly climatologically chlorophyll-a values (Text S1). The climatology of chlorophyll-a was used to estimate the climatology of the seasonal variation of zooplankton abundance. A lack of data prevented using actual time-series of zooplankton for all of the study locations, thus the use of the chlorophyll-a values as a proxy for the seasonal variation in zooplankton as suggested in the literature (e.g. [30]). Annual and inter-annual variability in zooplankton abundance was included through temperature, as the productivity in the ocean changes with temperature [31]. Warmer years tend to result in higher production while colder years result in lower production [8], [32]. Consequently, we used the monthly temperature anomaly to estimate monthly anomaly in zooplankton concentration. These were then interpolated to daily values, which were then added to the climatological zooplankton concentration for those days. The scaling was determined from literature reviews and comparison between the zooplankton production in warm and cold years (e.g. [33]), which suggest the maximum zooplankton production anomaly is approximately 50% of the mean seasonal zooplankton variability. For each site the mean maximum zooplankton concentration for the year was set to 80 prey items per liter, therefore the minimum and maximum zooplankton concentrations between the coldest and warmest years ranged between 0–120 prey items per liter. The prey was divided into size intervals of 100 µm ranging from 100 to 1600 µm according to the algorithm described in [34] (Fig. 3a). This range includes the typical size range (length and width) of Pseudocalanus and Calanus finmarchicus, the main prey species for cod larvae found in the four locations. In both cold and warm years the larvae usually have a relatively high number of prey items available to feed on, and the estimated numbers of prey have been compared to observations on Georges Bank and are within the observed ranges (see Text S1 for details).


Recruitment variability in North Atlantic cod and match-mismatch dynamics.

Kristiansen T, Drinkwater KF, Lough RG, Sundby S - PLoS ONE (2011)

Frequency distribution of modeled prey sizes and observed monthly concentrations of chlorophyll-a.The relationship between prey length and prey size groups used in the model as suggested in [34] are shown in a). No size interval contains more than 12% of the total abundance (circles). The squares show the relationship between width and length [33] of the prey items, which is essential for estimating prey image size, and visibility to the larval cod. b) Climatological chlorophyll-a (mg•m−3) values from January to December for the North Sea, Iceland, Lofoten, and Georges Bank stations (also see Fig. 1). Chlorophyll-a values are used together with the temperature anomaly data to calculate the monthly prey (mesozooplankton) concentration.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3049760&req=5

pone-0017456-g003: Frequency distribution of modeled prey sizes and observed monthly concentrations of chlorophyll-a.The relationship between prey length and prey size groups used in the model as suggested in [34] are shown in a). No size interval contains more than 12% of the total abundance (circles). The squares show the relationship between width and length [33] of the prey items, which is essential for estimating prey image size, and visibility to the larval cod. b) Climatological chlorophyll-a (mg•m−3) values from January to December for the North Sea, Iceland, Lofoten, and Georges Bank stations (also see Fig. 1). Chlorophyll-a values are used together with the temperature anomaly data to calculate the monthly prey (mesozooplankton) concentration.
Mentions: A global atlas of monthly (January to December) average (1998–2008) chlorophyll-a values were obtained from the SeaWiFS project website (http://seadas.gsfc.nasa.gov/). Chlorophyll values from the nearest four grid points surrounding the spawning locations were interpolated in space and time and used to create time-series of chlorophyll-a values. Light was modeled as a function of day of the year, latitude, and depth [29], while the attenuation coefficient was modeled as a function of monthly climatologically chlorophyll-a values (Text S1). The climatology of chlorophyll-a was used to estimate the climatology of the seasonal variation of zooplankton abundance. A lack of data prevented using actual time-series of zooplankton for all of the study locations, thus the use of the chlorophyll-a values as a proxy for the seasonal variation in zooplankton as suggested in the literature (e.g. [30]). Annual and inter-annual variability in zooplankton abundance was included through temperature, as the productivity in the ocean changes with temperature [31]. Warmer years tend to result in higher production while colder years result in lower production [8], [32]. Consequently, we used the monthly temperature anomaly to estimate monthly anomaly in zooplankton concentration. These were then interpolated to daily values, which were then added to the climatological zooplankton concentration for those days. The scaling was determined from literature reviews and comparison between the zooplankton production in warm and cold years (e.g. [33]), which suggest the maximum zooplankton production anomaly is approximately 50% of the mean seasonal zooplankton variability. For each site the mean maximum zooplankton concentration for the year was set to 80 prey items per liter, therefore the minimum and maximum zooplankton concentrations between the coldest and warmest years ranged between 0–120 prey items per liter. The prey was divided into size intervals of 100 µm ranging from 100 to 1600 µm according to the algorithm described in [34] (Fig. 3a). This range includes the typical size range (length and width) of Pseudocalanus and Calanus finmarchicus, the main prey species for cod larvae found in the four locations. In both cold and warm years the larvae usually have a relatively high number of prey items available to feed on, and the estimated numbers of prey have been compared to observations on Georges Bank and are within the observed ranges (see Text S1 for details).

Bottom Line: However, the cumulative effect of higher growth rates and survival through the entire spawning season in warm years was substantial with 308%, 385%, 154%, and 175% increases in survival for Georges Bank, Iceland, North Sea, and Lofoten cod stocks, respectively.We also found that the importance of match-mismatch dynamics generally increased with latitude.This prolonged season enhances cumulative growth and survival, leading to a greater number of large individuals with enhanced potential for survival to recruitment.

View Article: PubMed Central - PubMed

Affiliation: Institute of Marine Research and Bjerknes Centre for Climate Research, Bergen, Norway. tk@trondkristiansen.com

ABSTRACT

Background: Fisheries exploitation, habitat destruction, and climate are important drivers of variability in recruitment success. Understanding variability in recruitment can reveal mechanisms behind widespread decline in the abundance of key species in marine and terrestrial ecosystems. For fish populations, the match-mismatch theory hypothesizes that successful recruitment is a function of the timing and duration of larval fish abundance and prey availability. However, the underlying mechanisms of match-mismatch dynamics and the factors driving spatial differences between high and low recruitment remain poorly understood.

Methodology/principal findings: We used empirical observations of larval fish abundance, a mechanistic individual-based model, and a reanalysis of ocean temperature data from 1960 to 2002 to estimate the survival of larval cod (Gadus morhua). From the model, we quantified how survival rates changed during the warmest and coldest years at four important cod spawning sites in the North Atlantic. The modeled difference in survival probability was not large for any given month between cold or warm years. However, the cumulative effect of higher growth rates and survival through the entire spawning season in warm years was substantial with 308%, 385%, 154%, and 175% increases in survival for Georges Bank, Iceland, North Sea, and Lofoten cod stocks, respectively. We also found that the importance of match-mismatch dynamics generally increased with latitude.

Conclusions/significance: Our analyses indicate that a key factor for enhancing survival is the duration of the overlap between larval and prey abundance and not the actual timing of the peak abundance. During warm years, the duration of the overlap between larval fish and their prey is prolonged due to an early onset of the spring bloom. This prolonged season enhances cumulative growth and survival, leading to a greater number of large individuals with enhanced potential for survival to recruitment.

Show MeSH
Related in: MedlinePlus