Sure.
Cod are extremely aggregated into dense shoals during the winter period. Some of this is related to pre-spawning and some actually to spawning. While in the past cod spawning behaviour was often assumed to be this behaviourally vacuous process of just random mating within large groups, we now know that it actually involves a lot of complex behaviour. There are aggressive interactions among males, which allow the most dominant ones to establish territories from which they court females using a combination of exaggerated fin displays and short grunting sounds.
Basically, the thought is that by fishing on these aggregations you can disrupt these types of behaviours, with potentially negative impacts on spawning success. On that basis, there's a lot of merit to trying to avoid fishing cod during the spawning season. The management plan, it sounds like, does include some provision for a spawning closure, but unfortunately we have really inadequate information about precisely where and when cod spawn to know for sure whether or not that's going to be adequate.