The FIB-model. A dynamic model for prediction of recovery of a fish population after influence from acidic water or other environmental stressors

Summary

Monitoring programmes have over the last ten years shown increasing recovery in water chemistry following reduction in sulphur emission. Improvement in water quality has also to some extent resulted in recovery of acid sensitive fauna. It has for long existed response models for ground water, evaluating water quality following different sulphur reduction scenarios over time (MAGIC model). At present a few biological models for recovery of aquatic fauna has been developed, but testing and verifications of such models is difficult since response data are in an early face. The FIB-model (?Fisk I Bedring? or ?Fish in Recovery?) is a new model that tries to visualise the expected time for a defined recovery, where the goal is to have a ?healthy fish population?. In the FIB-model, female fish has the key role. Each lake will be defined to have a typical spawning age, as well as a maximum age for females only. The mathematical principle behind the model is the ?Fibonacci-numbers?. For each lake, one will have to determine the oldest possible year class that exist or can have existed there, and then back-calculate to the youngest. In the present visualisation, we have assumed repeated spawning every year until maximum age, despite the fact that in extreme environments like in alpine and Arctic areas, several resting years between spawning do occurre. At the start of a simulation, we define a set of year classes to be represented. This can be all or a few, representing from ?a healthy? to slightly or strongly affected population. The model can simulate stocking, liming, episodic mortality (due to acid episodes, freezing of spawning areas, drought etc.), and then demonstrate the time until all year classes will be represented. The figure shows a FIB-simulation of a lake with the two oldest year classes represented (7 and 8 years) with successful reproduction from start. Age at first spawning is 4 years. After 14 years, all year classes are represented (1). Unsuccessful reproduction in year 6 and 7 results in a 16 years recovery (2), while another reproduction failure in year 10 increases the recovery period to 21 years. In alpine and Arctic areas, fish can reach ages of more than 30 years. In such cases, as well as during recovery from acidification after a lake has reach an ANClimit for reproduction, the time lag of biological recovery will be decades.