Rockfish Index Contains Good News And Bad News


Fewer Young Fish Survived Spawning Process

September 23, 1990|By Capt.Bob Spore

Rockfish enthusiasts got some good news and bad news Thursday when the Department of Natural Resources released the 1990 Striped Bass Young-of-Year Index.

The report indicates how well this year's striped bass survived the spawning process. Biologists say the index is an indicator of relative abundance and is the best tool we have to determine the strength of the year-class. The biologists also say that by the time the year-class develops into the juvenile stage -- where they look like fish -- the year-class is established.

Testing during July, August and September determines the index. DNR biologists visit 22 sites in the major spawning areas during the three months and fish a haul seine twice at each site. They divide the number of striped bass caught by the number of times they fish the net. The result is the index.

The bottom line is that the 1990 year-class doesn't look so good. The annual index is only 2.1 -- eight is considered average. By contrast, the 1989 index was 25.2.

There was some good news this year. You could tell because this page of the press package was typed in extra large print. For example: "The resident stock has increased in overall relative abundance since 1985. Biologists can see there are more age classes represented in the stocks in recent years.

"The spawning stock has increased in overall relative abundance since 1985. A higher proportion of female striped bass have been noted on the spawning grounds. And more age classes of females are included in the spawning stock."

Those statements indicate that the stock is well on its way to recovery. The spawning stock is numerous and composed of many different year-classes, exactly what the biologists say is required.

This year's YOY survey contained one other interesting note: A large number of last year's fish were caught in the biologists' nets. There is one theory that last year's year-class may have eaten this year's fish while they were in the larva stage, which would explain why a good spawning year is often followed by a year of poor reproduction.

To be honest, I was surprised at the low index. I knew that there were a large number of spawning fish on the spawning grounds in April and some biologists thought that there might have been even more eggs this year than last. My early prediction, before any testing, was an index of 13.6; one of the senior biologists predicted 13.2.

What can go wrong? Many things. The striped bass in the larvae stage is very delicate. Water temperature can go down -- a drop of three or four degrees can cause almost total mortality. A strong (acid) rain storm can cause a pH spike that has killed striped bass in the laboratory. And quite possibly last year's rockfish may have eaten this year's crop. No one will ever really know for sure.

The 1990 YOY index will not begin to have a impact on the rockfish harvest regulations until the 1993 harvest allocation is computed; until then the fish will be too small.

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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