"otherfood" in food dependent growth

[vbartolino]

Food availability and consumption are highly relevant for cod growth in the Baltic.
To account for this feedback in my cod-sprat-herring model I'm using the 'WeightJones" growth for cod.

In the manual under consumption I can read that "The summation over preys is over all preys that the predator consumes, including non-modelled prey, given as otherfood”

Questions:

• In 'otherfood' I've benthic preys and all the rest for which I know very little. Does it mean that for having an effect on cod growth the 'otherfood' has to be set to "realistic" levels as well? which is rather difficult
• Any other strategy to approach the issue so that cod growth could respond to sprat and herring fluctuations in abundance?
• Would 'Multspec' growth have the same problem/difficulty?

[bthe]

I think WeigthJones, and other consumption dependent growth functions, should be usable for your case. Similarly otherfood consumption can be estimated as a realistic time-series but I don't think that is not necessary, you can work with fixed proportions and/or specific consumption intervals. This "should" all be estimable, given that you have some data that indicates starvation such as mean weight at age.

[vbartolino]

I'm still struggling with the implementation of the weightJones growth model for the cod model. Weight-at-age data and ALK haven't helped much so far...

Is there any chance I can compare the consumption and growth related parameters that I'm using (some from literature, other estimated from evacuation rate models) with ie the cod parameters used in the cod-shrimp model? Or do you have any other suggestion? I've included my parameters at the bottom.

I think that the main problem are the growth parameters, but because I'm limitedly confident on the consumption part, I do not know where the problem is...

prey preference (eq. 4.21)
pref = 1 (for all preys)

max consumption (eq. 4.22) calculated using Baltic cod data and Jones (1978)
m0 = 0.661 ; m1 = 0 ; m2 = 0 ; m3 = 2.6549

half-feeding parameter (eq. 4.23)
H = 0

growth in weight (eq. 4.7) derived by adjusting estimates from Jones 1978 converting into KJoules and for dt=90 days
q0 = 14.976 ; q1 = 0.15 ; q2 = 56.843 ; q3 = 0.65 ; q4 = 0.081 ; q5 = 0

(eq. 4.8-9) params selected to fix f(r) = 1
p0 = 0 ; p1 = 0 ; p2 = 0 ; p3 = 0.5 ; p4 = 0.5 ; p5 = 1

length implementation (eq. 4.10)
p6 = 7 * 1e-6 ; p7 = 3

[bthe]

Your guess is as good as mine, the Icelandic cod-shrimp model doesn't use the Jones growth function so your are flipping a switch in Gadget that hasn't been used for aaaages (this inspires confidence I'm sure ;) ). But when I think about it there is a crucial likelihood component missing in Gadget and that is a length-based catchstatistic (instead of age).

[vbartolino]

It would be still helpful having some "good" cod consumption parameters to compare with.
ie. those used in the cod-shrimp model (or any other solid cod-multispecies model).
Trenkel et al. (2004) assumed m0 = 6.93e-05for cod in the Celtic Sea which is on a completely different scale compared to what I've estimated (see plot below). Am I missing something?