why does the hatchign stop after some time? - netlogo

Question

Morning everybody
After editing my model, by adding a random spawn rate:
to migrate
if random-float 100 < random-spawn-rate
[create-turtles 2 [rt random-float 360 fd 1]]
end
i get the problem that after one kind of turtles (the boats) die out, even their random hatching seems to die out?
i tried other ways, but nothing really works
Please help me
thank you
Full code:
breed [fish a-fish]
breed [boats boat]
boats-own [profit]
to setup
clear-all
ask patches [set pcolor blue]
set-default-shape fish "fish"
create-fish initial-number-fish
[
set color grey
set size 1.0
setxy random-xcor random-ycor
]
set-default-shape boats "boat"
create-boats initial-number-boats
[
set color black
set size 1.5
set profit random (1 * profit-per-fish)
setxy random-xcor random-ycor
]
reset-ticks
end
to go
if not any? turtles [stop]
ask fish
[
move
fish-reproduce
]
ask boats
[
move-boats
catch-fish
death
reproduce-boats
migrate
]
tick
end
to move
rt random 50
lt random 50
fd 1
end
to fish-reproduce
if random-float 100 < fish-growth
[hatch 1 [rt random-float 360 fd 1]]
end
to move-boats
rt random 50
lt random 50
fd 1
set profit profit - 0.1
end
to catch-fish
let prey one-of fish-here
if prey != nobody
[ask prey [die]
set profit profit + profit-per-fish]
end
to death
if profit < 0 [die]
end
to reproduce-boats
if profit > 1
[
set profit (profit / 2)
hatch 1 [rt random-float 360 fd 1]]
end
to migrate
if random-float 100 < random-spawn-rate
[create-turtles 2 [rt random-float 360 fd 1]]
end

Answer 1

If there are no boats to hatch new boats, then no more boats will be created. Your hatch is dependent on how many boats there are.
Essentially, for a boat:
if profit > 1
[
set profit (profit / 2)
hatch-boat 1 ...
]
You cut the profit in half for every boat spawned. Unless your profit grows or remains the same, your boats will eventually die out since no more will be hatching.