Re-test harvest age constraints

[ChloeRN]

Models so far assumed harvest mortality is completely age-dependent. We should re-visit what happens if we only allow for different harvest mortality of juveniles (=first-year) and older individuals.

(If I remember correctly, this led to convergence failure in earlier versions of the model).

[ChloeRN]

Constraining mH to be the same for all adult age classes results in:

• Substantially higher average pregnancy rates
• Slightly lower denning survival
• Relatively higher mH for age class 2 and lower mH for age class 5
• Slightly lower harvest and higher natural mortality of juveniles

[ChloeRN]

• Higher among-year variation in pregnancy rates

[ChloeRN]

• Fewer immigrants in some years (but without helping with boundary estimates)

[ChloeRN]

• Somewhat more uncertain estimates of population size

[ChloeRN]

• Larger breeding population size (and more recruits, consequently)

[ChloeRN]

Equivalent comparisons with models using a Hoening prior on natural mortality showed similar tendencies, but the additional constraint did not seem to help with poor mixing / lack of convergence for these models.

[ChloeRN]

In conclusion: It is possible to constrain harvest mortality of all adults to be the same (and get models to converge). However, this leads to a shift in pregnancy rates towards values that are substantially higher than what the data indicates (= than what is estimated in independent models). At the same time, adding the constraint does not lead to substantial improvements in precision of estimates. It may therefore not be worth making this constraint.