FROM REPRODUCTION TO RECRUITMENT IN NORTH-EAST ARCTIC COD
by
R.D.M. Nash*, C.T. Marshall** & N.A. Yaragina***
*Institute of Marine Research, PB 1870, 5817 Bergen, Norway
**University of Aberdeen, Department of Zoology, Tillydrone Avenue, Aberdeen, AB24
*** Polar Research Institute of Marine Fisheries and Oceanography, 6 Knipovich St., Murmansk, 1837763, Russia
Introduction
Most current fisheries management models do not include biological detail for processes occuring between spawning and recruitment. This means that temporal trends present in biological or environmental factors can and have been ignored.
The temporal and spatial trends in stock reproductive potential (SRP) have been largely ignored, however, variation in SRP can have a fundemental influence on recruitment.
However, there are many processes occurring between spawning and recruitment that are not influenced by the parental stock.
Materials and methods
North-east Arctic cod biomass/abundunce estimates, obtained by analytical methods (VPA, XSA) and trawl-acoustic surveys, were used (ICES CM 2003/ACFM:22). Portion of mature fish were taken from the Arctic Fisheries Working Group report, whereas sex composition from Norwegian database. Individual fecundity was calculated using C.T. Marshall and co- authors method (submitted). Potential fecundity was calculated for each year, taking into account length-age composition and mean length/weight.
Spawning and feeding grounds
0° 5° 10° 15° 20° 25° 30° 35° 40° 45° 50° 55°
62°
64°
66°
68°
70°
72°
74°
76°
78°
80°
Russia Norway
Lofoten
Spitsbergen
Novaya Zemlya F
F
S
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Stock Reproductive Potential (SRP)
The transition from potential to realized egg abundance is a critical stage in the evolution of year-class strength of NA cod (connected with atresia, influenced by condition of spawners).
Furthermore, the signal in year-class strength undergoes substantial modification between the egg and larval stages. Thus, the signal in year-class strength of NA cod is determined in the earliest life history stages (Sundby et al., 1989; Mukhina, Marshall & Yaragina, 2003) before young fish settlement.
Stock Reproductive Potential (SRP)
From: Trippel 1999
Spawning Stock Biomass (SSB)
· number of mature fish at age
· mean weight of mature fish at age Stock Reproductive Potential (SRP)
Maternal reproductive experience –Condition factor –Length
Female
· proportion mature at age
· non-annual maturation of adults
· egg production (fecundity at length, age)
· viable eggs (fertilization, hatching success)
· sex ratio
· body size at age
· other factors – spawning duration – egg size, larval size
– egg nutrient and lipid content – time to starvation
– larval activity – first feeding success – compensatory growth
Paternal reproductive experience –Condition factor –Length
Male
· proportion mature at age
· non-annual maturation of adults
· testes weight
· sperm motility
· effect of male on larval fitness and early life survival
· sperm density
· fertilization rates, paired matings, in vivo sperm competition
Other factors Stock-specific values
Water temperature interaction/effects Maternal-paternal interactions
8
Males
1940 1950 1960 1970 1980 1990 2000 2010 Year
0.4 0.5 0.6 0.7 0.8 0.9 1
Proportion of the mature population that is male
1940 1950 1960 1970 1980 1990 2000 2010 Year
-13 0 13 26 39
Percent difference in mean size between spawning males and females
Should be worry about the male part of the population?
Figures to the left show fairly substantial changes in the sex ratio of the mature part of the population and illustrate fairly major changes in the relationship between mean size of mature males and females. Could this have an influence on reproductive success? Do we know enough about fertilisation success and maternal and paternal effects on survivorship in early life history stages?
0 20 40 60 80 100 120 140
-60 -40 -20 0 20 40 60
0 20 40 60 80 100 120 140
-30 -25 -20 -15 -10 -5 0 5
Abundance (millions)
Females Males
0 20 40 60 80 100 120 140
-10 -8 -6 -4 -2 0 2 4 6 8 10
1948
1970
2000
The figure above illustrates the changes in length frequency that have occurred in this stock.
At present mature males and females are more similar in length
10
Females
1950 1960 1970 1980 1990 2000
0.0 0.2 0.4 0.6 0.8 1.0
P roport io n m a tu re
1950 1960 1970 1980 1990 2000
0 5000 10000 15000 20000 25000
We ig ht ( g )
Year
Interannual variation in maturity ogive and mean weights at length: verical line separates pre and post 1980.
1940 1950 1960 1970 1980 1990 2000 2010 Year
60 70 80 90 100
Mean length of spawning females (cm)
North-east Arctic cod
1940 1950 1960 1970 1980 1990 2000 2010 Year
0.8 1 1.2 1.4
Mean relative condition of spawning females (Kn) North-east Arctic cod
In general there has been a decline in mean length of mature females over time, however there has been a corresponding increase in mean condition . The consequence is an apparent
‘compensatory’ response in the egg production per unit SSB (see bottom right panel below).
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SSB
Potential Egg production
78 79
80 81
82 8483
85
86
87 8988
90
91
92
93 94 95 9697
80 8281 83
84 85
86 898887 90
91 92
93 94 95
96
97
78 79 80
81
82 84 83 85 86 87
8988 90
91
92 93 94 95
96 97 98 0099
01 80 81 82 83
84 85 87 888689 90
91 92 93 94 95
96
97
98 99 00
01
02
03
Age 1 (bot trawl) (10 mo)
O-grp (5 mo)
Life-history model or Paulik diagram for North-east Arctic cod. The SSB data are from the VPA, egg production data calculated from relationships determined by Marshall et al.
(submitted) and O and 1 group abundances from surveys.
Some variability is generated in the transition from adult population to eggs, however, very large variability is generated through subsequent life-history stages which ultimately results in the classical stock and recruitment relationship by three years old.
These diagrams/models rely on being able to estimate the abundance of individuals at the transition boundaries e.g. metamorphosis, settlement, I year old etc.
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The challenge for stock to recruitment studies
No. Adults
Sex ratio Size structure Age structure Skippers
Potential Fecundity/
Sperm production
Realised Fecundity
+
Viable Sperm production
Viable Egg Production
Viable Hatch/
Nos at Hatch Prey fields
Habitat carrying capacity
Condition
Lipid reserves
Migration Spawning
Species specific characteristics
Climate change
Fishing pressure
Stock Reproductive Potential
References
ICES 2003. Report of the Arctic Fisheries Working Group. ICES CM 2003/ACFM:22.
Mukhina N.V., Marshall C.T., Yaragina N.A., 2003. Tracking the signal in year-class strength of Northeast Arctic cod through multiple survey estimates of egg, larval and juvenile abundance. Journal Sea Research, 50: P.57-75.
Sundby S., Bjørke H., Soldal A.V., Olsen S., 1989. Mortality rates during the early life stages and year-class strength of Northeast Arctic cod (Gadus morhua L.). Rapport Permanent verbeaux Reunion Conseil International pour l’Exploration de la Mer, 191: P.351-358.
Trippel E.A., 1999. Estimation of Stock Reproductive Potential: history and challenges for Canadian Atlantic gadoid stock assessments. Journal of Northwest Atlantic Fishery Science, 25: P.61-81.
