Estimation of LifeHistory Key Facts
Parameter 
High 
Medium 
Low 
Very low 
Threshold 
0.99 
0.95 
0.85 
0.70 
r_{max} (1/year) 
> 0.5 
0.16 – 0.50 
0.05 – 0.15 
< 0.05 
K (1/year) 
> 0.3 
0.16 – 0.30 
0.05 – 0.15 
< 0.05 
Fecundity (1/year) 
> 10,000 
100 – 1000 
10 – 100 
< 10 
t_{m} (years) 
< 1 
2 – 4 
5 – 10 
> 10 
t_{max} (years) 
1 – 3 
4 – 10 
11 – 30 
> 30 
r_{m}is difficult to estimate in fishes 
Intrinsic rate of population increase: The intrinsic rate of population growth (r_{m}; 1/year) has been suggested as a useful parameter to estimate the capacity of species to withstand exploitation (see above). It also largely simplifies the parametrization of Schaefer models for estimating maximum sustainable yield through the relationship MSY = r_{m} * B_{inf} / 4, where B_{inf} is the maximum biomass of a particular species that a given ecosystem can support (Ricker 1975), often corresponding to the original size of the unfished population. Note that if L_{c} is close to the average length L_{r} at which juveniles join the parent stock, then the value of F_{MSY} (above) can be used to estimate r_{m} from the relationship r_{m} = 2 * F_{MSY} (Ricker 1975). It seems that 0.4 * L_{inf} is a first approximation of L_{r}. We are exploring this and other options to estimate r_{m}. One can calculate the time (t_{d}) in years that it would take a strongly reduced population to double in numbers if all fishing ends, from t_{d} = ln(2) / r_{m}.


Our approach to estimate generation time 
Generation time: This is the average age (t_{g}) of parents at the time their young are born. In most fishes L_{opt} (see above) is the size class with the maximum egg production (Beverton 1992). The corresponding age (t_{opt}) is a good approximation of generation time in fishes. It is calculated using the parameters of the von Bertalanffy growth function as t_{g} = t_{opt} = t_{0 } ln(1  L_{opt} / L_{inf}) / K. Note that in small fishes (< 10 cm) maturity is often reached at a size larger than L_{opt} and closer to L_{inf}. In these cases, the length class where about 100% (instead of 50%) first reach maturity will contain the highest biomass of spawning fishes, resulting usually in the highest egg production. As an approximation for that length class we assume that most fish will have reached maturity at a length that is slightly longer than L_{m}, viz.: L_{m100} = L_{m} + (L_{inf}  L_{m}) / 4, and calculate generation time as the age at L_{m100}. This is applied whenever L_{m} >= L_{opt}.
Lengthweight: This equation can be used to estimate the corresponding wet weight to any given length. The default entry is L_{inf}, thus calculating the asymptotic weight for the fish of the population in question. The parameters ‘a’ and ‘b’ are taken from data in FishBase with a median value of ‘a’ and with the same length type (TL, SL, FL) as L_{inf}. Users can click on the ‘Lengthweight’ link to see additional data. Users can change the length or the values of ‘a’ and ‘b’ and recalculate the corresponding weight.
Wholebody nitrogen and crude protein: L.J. Ramseyer (2000, in review; see also www.mi.nmfs.gov/Nfish.html) has analysed the relationship between wholefish wet weight and wholebody nitrogen content for 68 species and hybrids, based on data extracted from the literature. He found the following relationship: log N (g) = 1.03 * (log wet weight)  1.65; n=2811, r^2=0.996, p<0.001. For the conversion from nitrogen to crude protein he gives the ratio: crude protein = 6.25 * nitrogen. We have added these relationships here for your convenience.
Trophic level: The rank of a species in a food web can be described by its trophic level (troph), which can be estimated as: Troph = 1 + mean trophs of food items; where the mean troph is weighted by the contribution of the various food items (Pauly and Christensen 1998). The default value and its standard error as shown in the Key Facts sheet are derived from the first of the following options that provides an estimate of troph based on: 1) diet information in FishBase, 2) food items in FishBase, and 3) sizeadjusted troph estimates from species with relatives for which (1) or (2) are available (see Box 23 where the comparative method for estimating troph is described)].


A simple tool to estimate population food consumption 
Food consumption: The amount of food ingested (Q) by an agestructured fish population expressed as a fraction of its biomass (B) is here presented by the parameter Q/B. FishBase contains over 160 independent estimates of Q/B extracted mainly from Palomares (1991) and Palomares and Pauly (1989) and also from Pauly (1989). These estimates were obtained using Pauly’s (1986) equation, viz.: Q/B = [(dW/dt) / K_{1(t)}] / [W_{t}N_{t}d_{t}] integrated between the age at which fish recruit (t_{r}) and the maximum age of the population (t_{max}); where N_{t} is the number of fishes at age t, W_{t} their mean individual weight, and K_{1(t)} their gross food conversion efficiency (= growth increment / food ingested). These Q/B estimates are available in FishBase for only 98 species and for most of these, there is only one Q/B estimate per species. In the few species for which several Q/B values are available, the median Q/B value is taken and a ‘Food consumption’ link is provided to the user for viewing the details of these studies. For other species, Q/B is estimated from the empirical relationship proposed by Palomares and Pauly (1999), viz.: log Q/B = 7.964 – 0.204 log W_{inf} – 1.965T’ + 0.083A + 0.532h + 0.398d; where W_{inf} (or asymptotic weight) is the mean weight that a population would reach if it were to grow indefinitely, T’ is the mean environmental temperature expressed as 1000 / (C + 273.15), A is the aspect ratio of the caudal fin indicative of metabolic activity and expressed as the ratio of the square of the height of the caudal fin and its surface area, ‘h’ and ‘d’ are dummy variables indicating herbivores (h=1, d=0), detritivores (h=0, d=1) and carnivores (h=0, d=0). The default value for W_{inf} is taken either from L_{inf} and the lengthweight relationship (see above) or from W_{max} (maximum weight ever recorded for the species) when an independent estimate of W_{inf} is not available in FishBase. Values of A were assigned, for each of the different shapes of caudal fins considered here, using the median A values based on 125 records in FishBase of species with A and caudal fin shape data (from left to right: lunate, forked, emarginate, truncate, round, pointed, double emarginate and heterocercal). Note that five of these eight shapes share the same median value, that which is used as the default A value for the empirical estimation of Q/B when an independent estimate is not available. We are working on a method that will better separate categories of caudal fins. Values of the feeding type indicators ‘d’ and ‘h’ are assigned according to which feeding category the species belongs: detritivore, herbivore, omnivore (default) and carnivore. These categories are determined either from the Main food or the Trophic level (detritivores troph < 2.2; herbivores troph < 2.8; carnivores troph > 2.8). When the default category ‘Omnivore’ is highlighted, Q/B is estimated as the mean of the Q/B values obtained for herbivores and carnivores. The temperature used in the estimation of M above is applied in the empirical estimation of Q/B. The Q/B estimate is automatically recalculated when the tail fin shape and/or the feeding types are changed. The Recalculate button is provided when values of W_{inf} and A are reentered, e.g., in cases where no possible/guessed values of W_{inf} are available in FishBase.


Comments 
The Key Facts page is still very much evolving and we welcome comments and suggestions for its further improvement to any of the authors.


Acknowledgments 
We thank Eli Agbayani for programming the many changes we requested when developing the Key Facts page. We thank the FishBase Team for assembling the data that allowed us to implement this approach.


How to get there 
You get to the KEY FACTS routine by clicking on the respective button in the BIOLOGY window of the species in question.


Internet 
On the Internet, you get to the ‘Key Facts’ page by clicking the respective link in the ‘More information’ section of the ‘Species Summary’ page. Note that you can save the Key Facts page to your harddisk and that it will function offline.


References 
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Version of 17 July 2002.
