Sunday, April 14, 2019


It addressed the recent benchmark stock assessment’s finding that 48% of all striped bass fishing mortality is the result of fish that died after being released by recreational fishermen, briefly discussed the origins of such figure, and then went into the factors that cause such release mortality.

It was an interesting piece, and I recommend that anyone with a concern for such things click on the above link and read it.

We ought to be thinking a lot about release mortality, because there is no question that the 48% number is going to play a big part in the upcoming striped bass debate.  Should a higher minimum size for bass be proposed—and it’s hard to imagine being able to rebuild the stock if that isn’t done—one of the arguments we’re sure to hear is that a bigger minimum size will lead to more release mortality, and thus that the limit should be left where it is.

Such argument sounds good on its face, but initial impressions are often deceiving.

Maybe, before taking a stand, we should be asking “Is increasing release mortality always a bad thing?”

Yes, I know, that sounds like heresy.  But it might be best to think about some basic biology here.  The health of a fish population—of any animal population—isn’t dependent upon what happens to creatures after they die.

What matters is keeping the numbers that die—from all causes, and for any reason—within sustainable bounds.

So yes, as responsible and ethical anglers, we should be doing our best to minimize release mortality by using tackle and techniques that prevent harming and exhausting the fish, by releasing fish quickly and, preferably, without taking them out of the water, and by otherwise avoiding any preventable injury to released fish.  When we do keep a bass, we ought to make sure that fish isn’t wasted.

But all of those things, while hallmarks of responsible angling, are only means to an end, and that end is reducing overall striped bass mortality.

Because it’s overall striped bass mortality—what the scientific folks refer to as “Z”--that matters, because if the recruitment of new fish into the population isn’t sufficient to make up for the fish lost to mortality of every kind, the striped bass population, and the quality of striped bass angling, can only decline.

Such overall mortality is a combination of natural mortality (“M”), which is pretty much out of our control, and fishing mortality (“F”), which can be managed.  So in the real world, where Z always equals M + F, and fishing mortality is the only thing that managers can regulate, overall mortality is kept within sustainable limits by limiting fishermen’s kill.

You’ll note that I wrote “fishermen’s kill” rather than “fishermen’s landings”, because a dead fish is a dead fish, and has the same impact on the population, whether or not it makes it back to the dock.  And that’s why we might want to start reconsidering our attitude toward release mortality.

Because, yes, nearly 38,000,000 striped bass were released in 2017, and of those fish 9%--around 3,400,000—probably died shortly thereafter.

But that means that 91% of them—about 34,000,000 lived.

And when you’re trying to rebuild the stock, it’s the live fish that matter.

So here on the coast, where a 28-inch minimum size is currently the rule (I’m leaving Chesapeake Bay—which for the most part means Maryland—out of the discussion right now, just to keep the numbers constant, although Maryland was the single largest contributor to recreational striped bass mortality), any striped bass that meets that minimum may be legally tossed into a cooler, where mortality is an even 100%, and the survival rate is, correspondingly, zero.

When you look at it that way, the increase in release mortality that would, in theory, result from increasing the minimum size doesn’t look all that bad—9 percent instead of 100.

Just how many fish an upped limit might save, and how many more released fish would die is hard to estimate, because it’s impossible to guess what any new size limit might be.  Right now, we’re hearing a lot of suggestions, with a slot limit of some sort, or a return to the old 36-inch minimum, probably leading the pack, but until the Atlantic States Marine Fisheries Commission’s Atlantic Striped Bass Technical Committee comes up with a recommendation, all of those suggestions are just shots in the dark.  No one has any idea what the size limit needed to rebuild the stock ought to be.

But just for the sake of argument, let’s say that the minimum size was raised from 28 to 36 inches, and apply that change to bass landings here in New York (again, using New York to avoid the Chesapeake Bay-related issues that we’d have to deal with if calculations were made on a coastwide basis). 

Such a 200,000 fish savings would amount to a 42% reduction in landings, which is significant, despite the price paid in additional release mortality.

Again, those numbers are only an approximation.  Some people argue that, if the size limit were raised, anglers would fish longer, and end up releasing more fish, in order to land their one “keeper.”  If they did so, the argument goes, release mortality would spike, and minimize the benefits of a higher size limit.

While there may be a small kernel of truth in such argument--some people would fish longer and so release more bass than they would if the size limit were lower--it's extremely doubtful that the number of such anglers would be high enough to cause significant harm, since most striped bass anglers don’t fish primarily for meat; a very substantial majority of the striped bass caught are already returned to the ocean rather than killed.

Clearly, all of those releases weren’t optional—quite a few of the released bass would have been undersized.  But the percentage of fish released has remained fairly consistent, and without any clear trend, from year to year, even though the proportion of undersized to legal fish would have changed annually as various year classes moved through the population. 

Thus, in 2014, anglers kept more than 22% of their catch—the high for the time series—but one year after, in 2015, retained fewer than 10% of all bass landed.  A year later, New York's striped bass anglers landed more than 15% of their catch.  Such seemingly random fluctuations are best accounted for by the level of error inherent in the data, rather than significant changes in actual retention rates—the 15% average is probably a good approximation of the proportion of striped bass killed.

In such a catch-and-release fishery, it’s not likely that too many anglers stop fishing after they keep their one-bass daily limit, although a few may do so.  On the other hand, there are certainly unscrupulous anglers who “highgrade,” keeping the first legal fish that they catch, and then dumping it over the side, at best badly stressed and more probably dead, when they land a larger one.  (It should be noted that in some fisheries, such as the king salmon fishery on Alaska’s Kenai River, anglers may catch and release fish as long as they like, but as soon as they decide to keep one, they must take their line out of the water and not fish for the rest of the day, in part to prevent just that sort of behavior).  A higher minimum size would help to limit such misconduct, and thus partially offset whatever additional release mortality such higher minimum might cause.

So when we look at the numbers, we need to remember that it’s not the release mortality, standing alone, that matters—although, for the sake of the fish and ourselves, we should always do our best to keep that number down.  

What matters is the  fishing mortality rate, and its contribution to the rate of mortality from both fishing and natural causes.

Given that truth, an incremental increase in discard mortality might be a small price to pay for a far bigger decrease in the overall number of striped bass that die.

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