We extend a framework of comparative climatology of reproductive habitats of neritic pelagic fishes, heretofore focused on temperate eastern ocean upwelling systems, by adding a tropical western ocean example. Maritime weather reports off southeastern Brazil are summarized to yield distributions of wind stress, Ekman transport, wind mixing index, insolation, cloud cover and sea surface temperature for two-month segments of the seasonal cycle. These are used to describe seasonal aspects of the oceanography of the region. Vigorous coastal upwelling occurs in the vicinity of Cabo Frio-Cabo So Tomé through most of the year, relaxing only during austral fall. Directly downstream of this upwelling center lies the coastal bight between Cabo Frio and Cabo Santa Marta Grande, within which offshore Ekman transport and wind-induced turbulent mixing fall to coastwise minima. The near-coastal water column within the bight, while vertically homogeneous during winter, becomes stably stratified during summer. We infer a rather enclosed circulation pattern within the bight, with the main Brazil Current flow skirting across the bight opening rather than following the coastline into the bight interior. This coastal bight constitutes the primary reproductive habitat of the Brazilian sardine. Peak spawning activity during summer serves to place larvae into a stable, enriched environment, where they enjoy high likelihood of retention. In the manner of achieving these advantages, the reproductive strategy of this population appears to be a nearly exact analogue to those of sardine populations inhabiting eastern boundary current upwelling systems, in spite of its western ocean boundary location and the fact that a warmer water genus is involved. The conclusion is that this Sardinella population is solving similar dominant environmental problems to those faced by the more temperate Sardinops and Sardina stocks of eastern boundary systems, only at a warmer temperature range. These findings lend support to the idea that our various fragments of experience of environmental effects on fish populations are not unconnected anecdotes, as they are often treated, but are amenable to scientific generalization.
ASJC Scopus subject areas
- Ecology, Evolution, Behavior and Systematics
- Aquatic Science