Warmer Choptank Water Spurs Rockfish Spawning


April 12, 1991|By Capt. Bob Spore

The 1991 rockfish season has started. No, not the rockfish catching season, the rockfish spawning season.

Water temperature in the Choptank hit the mid-60s earlier this week, and the mama rockfish started spewing out eggs.

The stripers enter the Chesapeake in March and move toward the spawning reaches of their home river systems. Most biologists believe that if a rockfish was spawned in the Choptank River, it will spawn inthe Choptank when it reaches maturity. Some believe that the rockfish from one river system are genetically a little different than rockfish from other areas.

The Department of Natural Resources considers there are four major spawning areas in the Maryland portion of the Chesapeake Bay: the Nanticoke River, the Choptank River, the Potomac River and the head of the bay, the area above Worton Point including the Sassafras River, the Bohemia River, the C & D Canal and the Elk River.

The most important of the four areas is the head of the bay,because of its size.

Spawning is dependent upon water temperature and photo period. The photo period is the number of minutes of daylight each day. Most rockfish wear fin-watches and know approximately when they should spawn.

If the water temperature reaches approximately 60 degrees during the time when the rockfish think they should be spawning, they start spawning.

As I mentioned earlier, water temperatures in the Choptank River jumped to the mid-60s earlier this week and the spawning began. Biologists said by midweek they would consider the activity in the Choptank a major spawning activity.

I presume spawning also has started in the Nanticoke River and possibly the Potomac. Upper Bay spawning is often as much as one or two weeks behind the Choptank action because of colder water temperatures.

TheDNR has assigned biologists to the Choptank and the head of the bay to gather data on the spawning stock, water conditions and as much information as possible on the condition of the spawning activity.

The striped bass are very fragile when they come out of the egg.

Normal infant striped bass mortality is greater than 99 percent. If we ever had a year where half of the eggs survived to a harvestable-sized fish, we would have rockfish coming out of the light sockets.

Atthis stage, the infant rockfish are susceptible to changes in water temperature, a pH shock caused by a heavy acid rain or the mobilization of tiny aluminum particles also caused by acid rain. Any of these events could wipe out millions of baby rockfish.

In addition to all of the pitfalls which could harm the newborn stripers, other conditions must prevail or else the new babes will starve.

When the striper comes out of the egg, it has a small amount of nourishment in a little lunch box. When that is gone, it must be able to open its mouthand find food. If there are no little critters close by for the babystripers to feed upon, they will starve.

Getting all the conditions suitable for the spawning activity to take place is against the odds. That is why the biologists prefer a protracted spawn, where spawning does not come in one big slug of eggs, but at a series of spawning events over a long period -- well into May.

This improves the probability of finding a period when the conditions are favorable and alarger percentage of the hatch survives to become juveniles, or babyrockfish that look like rockfish. At this point, the year class is fairly well-established.

The biologists return to the spawning areas in July, August and September to count the number of striped bass that survive. This young-of-year survey will give information to the fishery managers regarding the strength of the year class and the sizeof the harvest available to the fishermen when these fish reach catchable size.

Now is the time to cross your fingers and hope for fair weather for the next few weeks. Good weather might bring us a big crop of rockfish.

Then again, it might not. Biologists still don't understand everything about rockfish.

* Bob Spore is a Coast Guard-licensed charter boat captain from Pasadena. His Outdoors column appears every Friday and Sunday in the Anne Arundel County Sun.

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