It is a common observation of fishermen that certain areas of the open sea are more productive of fishery species than others.
By experience, fishermen know the location of these areas but they may not know why fish and other marine species abound there. What matters to them is that they are able to catch the fish they need to support their families.
The case of shallow water habitats such as mangroves, seagrass beds, and coral reefs is a different matter. People, regardless of their knowledge of fish and their skills in catching them, can easily determine whether or not fish are found in these habitats by simple observation.
Because these marine habitats are usually accessible, people have been heavily exploiting them to the point that they are now not only overfished but degraded as well.
One result is that in general, the deeper parts of our seas are still in relatively better condition than the shallower coastal areas.
This explains why many species, especially fish, are rare or even absent from coastal ecosystems, and efforts have been made to build up the biodiversity of these heavily-exploited parts of the marine environment.
One of the present conservation programs of the Philippine government is the Integrated Coastal Resource Management Project initially implemented in five regions (Regions 2, 3, 5, 7, and 11).
One of the marine areas that have been shown to be rich in biodiversity and fishery resources is the Dipolog Strait, the portion of the Bohol Sea lying between southern Negros and Dipolog City, province of Zamboanga del Norte.
The presence of rich fishery and biodiversity resources is quite obvious to marine biologists; in this marine area, sardines abound, and a flourishing canned sardine industry exists in Dipolog City, providing incomes to some residents of the City.
It is not only the large populations of sardines that characterize the fishery resources of Dipolog. The fish species such as tuna, mackerel, and top carnivorous and pelagic fish groups that feed on the sardines are also abundant in the Dipolog Strait.
Since the sardines feed on plankton, we have to assume that plankton are produced in large amounts in Dipolog Strait. It is now known from satellite imagery and from oceanographic studies that indeed, plankton, as basis for marine food chains, are also produced in large amounts through the phenomenon called upwelling.
Through upwelling, nutrients needed for plankton production are carried upward from the bottom of Dipolog Strait to the upper layers of water where plankton are produced with the aid of sunlight as energy source (photosynthesis).
The recent oceanographic studies on the dynamics of the Bohol Sea and the Dipolog Strait (and other straits in the Philippines) have been published in the journal Oceanography (Vol. 24, No. 1, March 2011) which explains the oceanographic processes responsible for the high productivity of marine biodiversity in the Dipolog Strait.
Dipolog Strait is the meeting place of two waters, one coming from the Pacific Ocean through the Surigao Strait, and another coming from the South China Sea through the Sulu Sea.
These water movements, plus the bottom structure of the Dipolog Strait, account for the upwelling occurring in the Strait, which is one of the basis for its high productivity.
The case of Dipolog Strait’s high productivity illustrates the important role of studies in marine biology and oceanography in understanding how our marine environment functions in providing us with ecosystem benefits.
