For a very long time, fishery mangers have assumed that 9
percent of all striped bass caught by anglers won’t survive release. That figure comes from a
2011 study titled “Mortality of Striped Bass Hooked and Released in Salt Water.”
The authors of that study, Paul Diodati and Anne Richards,
found that
“Depth of hook penetration in the oral cavity, anatomical
site of hooking, gear type (single or treble hooks), and angler experience were
significantly related to mortality…The final model included depth of hook
penetration, gear type, and angler experience as predictor variables. Predicted mortality ranged from 3% under the
most favorable conditions to 26% for the worst set of conditions. Predicted as well as observed mortality for
the entire experiment was 9%...At the end of the experiment, condition factors
were significantly lower for surviving hooked fish than for fish that had not
been hooked.”
Many anglers have never been completely comfortable with the
conclusions of the Diodati study. Some,
particularly including fly fishermen and others who do most of their
fishing with single-hooked artificial lures, observe that, with a little
reviving, all of their fish eventually swim away, and argue that their release
mortality rate is well under 9 percent.
At the same time they, and others who catch their bass with
cast lures, often point to those who “snag and drop” with live menhaden, chum
their bass in with clams, or fish chunks of bait on the bottom, claiming that
such activities lead to levels of release mortality well above the 9 percent
standard. Such people often also look askance
at trolling for stripers, and claim that hooking a bass on a wire-line outfit,
and dragging the fish through the water for a few hundred yards while it is
being reeled in (because wire line boats don’t stop when a fish is hooked) also
ups mortality numbers.
It’s possible that all those claims are right, which is why
9 percent represents a blended mortality rate that considers both the best and
worst set of conditions that might confront a hooked fish.
It’s also possible that, under today’s conditions, the 9
percent number is no longer valid, and that a new estimate of release mortality
is needed.
Either way, it’s important to get the release mortality
figure right, since the last benchmark
striped bass stock assessment, completed in late 2018, found that recreational
release mortality was the greatest single source of fishing mortality across
the entire coastal migratory stock.
It was thus heartening to learn that the
Massachusetts Department of Marine Fisheries has embarked upon a new study to
determine how many recreationally caught striped bass survive the angling
experience.
Unlike the 2011 study, the new Massachusetts study will not
involve fish contained in a dammed salt pond.
Instead, the fish will be fitted with acoustic tags and returned to the
waters of Salem Sound, on the northeast Massachusetts coast. For the first half of the study, which will
take place this year, 175 striped bass will be caught on natural bait, both
dead and alive, which will be fished on both circle hooks and traditional J
hooks. Next year, the study will be
expanded to examine survival rates with artificial lures, and the difference in
survival rates between fish caught on single and treble hooks.
The goal of the study is to determine the number of fish
that survive for at least two weeks after release. The acoustic tags will record the swimming
movements of the fish; cessation of such swimming motion will lead to a conclusion
that the fish has died. Massachusetts
has set out 29 acoustic receivers, covering most of the water in Salem Sound,
to receive the tags’ signals. Should a
fish leave Salem Sound for other waters, acoustic receivers elsewhere in state
waters, and even in the waters of other states, can pick up its tag’s
transmissions.
It’s anyone’s guess as to what the new study will find.
There’s undoubtedly a widespread assumption that fish hooked
on circle hooks, which generally hook bass in the jaw and rarely result in gut-hooked
fish, will show a significantly lower mortality rate than those hooked on J
hooks, and that mortality for circle-hooked fish will be substantially below
the current 9 percent standard.
But anyone who expects the overall mortality rate to be less
than 9 percent might be jumping the gun.
The new Massachusetts study will differ from the 2011 study
in a number of ways that could impact the results. One is the size of the fish involved.
The striped bass observed in the 2011 study were small;
their length ranged between 27 and 55 centimeters (roughly between 11 and 22
inches). More fish fell into the 32-33
cm (about 13 inch) size range than any other.
Compared to the bass typically encountered by recreational fishermen in
the northeast, those are pretty tiny fish.
If the new study encounters larger bass than those
included in the 2011 study, and particularly if some of those bass are
substantially larger, the mere stress involved in capturing the bigger bass could
lead to a higher release mortality rate that offsets the mortality savings of
circle hook use to a greater or lesser degree.
The bass in the new study are also going to be released back
into Salem Sound, rather than into a closed-off salt pond.
That could impact release mortality in a
couple of ways.
First, it could prove a direct benefit to the fish, as they
could seek out water temperatures most conducive to their survival. In the salt pond used for the 2011 study,
water temperatures ranged between 15 and 28 degrees Centigrade (59 to 82
degrees Fahrenheit), with bottom temperatures rising as high as 25o
C (77o F). Temperatures at
the high end of that range could definitely have had a detrimental impact on the
released fish’s survival; if so, fish released into the presumably cooler waters of Salem Sound may not succumb to temperature-related mortality in as
high numbers.
At the same time, the dammed-off salt pond offered the
released fish some protection from marine predators. The authors of the 2011 study reported that
“The condition factors of control fish held in the net-pen
did not change significantly during the experiment, but conditions factors of
hooked fish held in the net-pen were significantly lower at the end. For striped bass recovered from the pond at
the end of the experiment, condition factors of both hooked and not-hooked fish
had decreased significantly from the start of the experiment, but condition
factors of hooked fish were significantly lower than those of fish not
hooked. [references deleted]”
It doesn’t take much imagination to believe that hooked
bass, released into an inshore ocean that supports healthy populations of
seals, dolphin, and various sharks, at a time when they are not in as good
condition as bass that have not been caught and released, will be both more
attractive and more vulnerable to such predators, and so will die at a higher
rate than fish contained within a closed-off salt pond.
Thus, it is hard to predict just how the new study will turn
out, and whether average striped bass mortality will be found to be higher or
lower than the currently accepted 9 percent.
And whatever mortality rate the study ultimately reveals,
there is no guarantee that such stjudy will reflect what goes on in the real
world. As the 2011 study points out,
“Hooking mortality estimated from an experiment cannot predict
population mortality unless experimental conditions represent those encountered
in the wild. For species with a broad
geographic range, such as anadromous Atlantic striped bass, it seems unlikely
that mortality recorded from an experiment would equal that of the population
over a time period of interest (typically a year). However, experiments can identify critical
factors influencing hooking mortality and can be used to develop models that
predict mortality, given values of those critical parameters…Our present model
would not be sufficient for estimating coastwide hooking mortality of striped
bass, as it does not include effects of such factors as fish size and
environmental variables (temperature, salinity) on mortality.”
The 2011 study—and, from what I can tell, the Massachusetts
study—also doesn’t include the effects of hanging a big bass from a Boga-Grip or
Chatillon scale, waving it around in the air while someone digs around looking
for a phone or a camera, tossing it back into the water from an elevated jetty,
rock or party boat deck, dragging it onto and over the stones and the sand, or…
Well, you get the idea.
The results of the new study won’t be perfect.
But depending on the size of the fish caught, how they are
handled and a number of other factors, the new study should provide a good idea
of whether the 9 percent mortality rate is a good reflection of reality, or
whether managers ought to use a lower—or higher—rate to better reflect the
impacts of recreational release.
Either way, better information can only lead to better striped bass management.
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