Striped Bass YOY Index

Photo by Capt. John McMurray

Photo by Capt. John McMurray

The topic of striped bass is always hot this time of year. If you hang around the waterfront – or the chat rooms or blogs – the questions are flying.

“Where are the fish? They haven’t arrived here yet.”

“Is the population crashing?”

“The stock assessment must be wrong. If not we’d be covered up in small fish by now!”

“The problem is the calculation of the striped bass young of the year (YOY) index has changed and you can’t trust the numbers.”

“There aren’t any big fish.”

“There aren’t any small fish!”

“There aren’t any freaking fish!”

It seems that most of what you see in the chat rooms is negative feedback. I’m sure if you searched a little harder than I normally do or want to do, you could find some positive postings. Somehow negative input has a lot more traction. That is also true in the general news media. Because striped bass is such a popular species, right near the top of the list for numbers of angler trips targeting a single species, it gets a lot more attention. Then when some piece of misinformation is put out in these forums, it tends to get a life of its own. Perception becomes reality.

In recent conversations with folks who have a very good understanding of striped bass management, I realized that a lot of people needed to get the real story and then, at least, they can make an informed decision or simply choose to ignore it altogether.

The one issue that popped up in several different places was a distrust of the Maryland striped bass young of the year survey. What I heard was, “They’ve changed the way they record the YOY statistics. No one knows any longer what’s correct and what isn’t! In the past, they used a simple method, with a simple graph, and it was pretty accurate for many years. Now we’ve got F factors, Y factors, plus this, minus that, times this, divided by F minus AP, squared.” Or, “I’m now more suspicious than ever if the YOY numbers from the 90s and 2000s are really comparable to the 60s and 70s.”

IMO, there are two different issues. The first is whether the science that has been conducted for the last 50-plus years is as untainted by the politics of fisheries management as people believe it was at some point in the past. The second issue is the level of distrust that has developed over the Atlantic States Marine Fisheries Commission management decision process, which, as far as striped bass is concerned, has some real warts. While some think that these are inextricably entwined, I do not believe they are. Nor is this a commentary on the ASMFC decision process. My fellow blogger, Capt. John McMurray, has covered that subject many times.

My understanding is that the YOY survey has changed very little over the years. That goes for the methodology, including the location and number of hauls of the seine as well as the timing of those hauls. Alexi Sharov, one of the lead scientists for the Maryland Department of Natural Resources, says, “Please assure the recreational community that there was no change in methodology. Both arithmetic and geometric means are calculated by MD personnel each year. However, the stock assessment committee has determined a while ago that the geometric mean is more appropriate description of recruitment variability in general (all species, not just striped bass). Geometric mean has been used for more than a decade in striped bass stock assessment. The geometric mean is usually lower than the arithmetic mean. That does not mean that the recruitment is lower; rather, it is a different way of calculating the index using the same data.”

That stability is one of the reasons that the survey is a useful tool. Like many index surveys, the actual number may have less meaning than the trend, whether it is high or low, relative changes year to year, and above or below the long-term average. Indexes, by their very nature, do not give exact numeric stock biomasses. That number would have to come from the stock assessment.

As indicated above, the index was originally calculated by an arithmetic mean and still is, but the ASMFC uses the geometric mean as its preferred index. What is the difference? Well, not a lot. Once you have converted the past arithmetic means to geometric, you have an index that shows the same trends and relative relationships, but the geometric number will be lower. I flunked higher math, so don’t ask me why they are lower, but they are. Nor from a science perspective can I tell you why geometric is better other than some smoothing of the index variability. It seems to me that the most important part is the repeatability of the long-time series. The output is available in both arithmetic and geometric numbers for the time series 1967 forward. So, pick your poison. The relative importance will be almost identical. What the ASMFC does with that output – well, that’s a different story.


"Rip" Cunningham, who owned, published and edited Salt Water Sportsman for 32 years, is also an accomplished writer and photographer. Cunningham has received several awards from the Outdoor Writers Association of America. His work has appeared in such magazines as Field and Stream, Rod and Reel, Gray's Sporting Journal, Australian Boating and the Boston Globe Magazine. Among his many accomplishments, Rip was recognized as the Conservationist of the Year from both the International Game Fish Association, the Coastal Conservation Association of Massachusetts, The Billfish Foundation and Federation of Fly Fishers. "I've earned a living from fishing, and I believe strongly that people with an interest in a given area should give something back,” he says. “It's rewarding every single day." Cunningham received his MBA from Babson College in Wellesley, MA and his BA from Rollins College in Winter Park, FL. He has two grown children and four grand children and lives with his wife and hunting dogs in Dover, MA and Yarmouth, ME. When he's not fishing or working through the items on his wife's "honey-do" list, Cunningham does some hunting and skiing.

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