The diversity of the pelagic fish fauna is relatively low, especially considering the volume of water habitat available. The major advances in knowledge of these fishes have come from large scale fishing activities, plus the use of correlative satellite oceanography to determine fish associations with specific water characteristics. Because of their size, speed and ability to move great distances, there are many gaps in information about these fishes. One must remember that these fishes range throughout an enormous habitat and therefore are hard to track. Undoubtedly, there is considerable trophic interaction among these larger epipelagic fishes and their meso- and bathypelagic counterparts during diel vertical migration.
Seasonal changes do occur in the pelagic fish fauna of the Bay.
Other, long-term changes also occur. Certainly, one example of this would be the sardines, whose populations continue to increase following their crash in 1940s. There are vertical links between the epipelagic fauna and the fauna of deeper waters. The main human impacts on the epipelagic zone include shipping and fishing. Many large cargo vessels and tankers venture upon this habitat annually and a large number of chartered vessels take passengers out to view the local fauna, including birds, mammals and epipelagic fishes.