Release Mortality Revisited: New Research from Massachusetts DMF

Feature Photo Credit: Robbie Tartaglia

What’s going on? For decades, striped bass management relied on a 9% release-mortality estimate from a 1990s study that even its author warned wasn’t suitable for management. New research from the Massachusetts Division of Marine Fisheries has finally set the record straight—release mortality is roughly half that rate, and can even dip further for artificial and fly anglers. Combined with sharp drops in overall releases and better handling practices, this science proves that responsible catch-and-release anglers aren’t the problem—and no targeting closures are scientifically indefensible.

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Back in the early 1990s, Paul Diodati, then a striped bass biologist at the Massachusetts Division of Marine Fisheries (DMF), set out to answer one of the oldest questions in striped bass management—how many stripers actually die after being released?

Diodati designed an ambitious experiment. Roughly 1,000 striped bass were captured from a fish weir, transported by boat, loaded into a stocking truck, and finally delivered to Smith Pool, a gated tidal impoundment. It’s important to pause here—this level of handling and confinement far exceeds what a fish would ever experience in normal recreational fishing conditions. But we’ll come back to that.

Recreational fishing groups were invited to catch and release these stripers inside the impoundment. The average fish measured about 12 inches, and 173 were caught and released with tags recorded. When the experiment ended, the tidal pool was drained. Fifteen fish were missing, leading to the now-famous estimate of 9% release mortality. That 9% figure came from assuming every missing fish had died due to release mortality. What wasn’t accounted for were other possible explanations—small fish escaping through the tidal gate, predation by ospreys or eagles, or even harvest by nearby residents. The pool itself offered poor striped bass habitat, more of a muddy bowl than an estuary, and anglers reported that fish health visibly declined as research progressed through the summer.

To be clear, Paul Diodati was an exceptional scientist whose work laid critical groundwork for modern striped bass management. Our goal is not to criticize his research—it’s to acknowledge its limitations in context. In fact, Diodati himself cautioned that his findings should not be used for management decisions and called for additional study. And yet, for decades, that 9% number has quietly guided management policy. A lot has changed since the mid-90s. The science of telemetry tags has evolved significantly. The science community is more connected to the angling community than ever before. Our knowledge of striped bass has also increased exponentially. We are long overdue for a new approach. Thankfully, fast-forward nearly thirty years, and the Massachusetts DMF decided it was time to take Diodati’s recommendation literally—and run the most advanced study ever conducted on striped bass release mortality.

The new research, launched about five years ago, took a comprehensive approach. Massachusetts DMF went all-in. The goal was a more comprehensive and reliable mortality metric, which required a significantly larger data set. Every possible variable was considered, from fish condition upon release to hook type, fight time, and temperature. Released fish were given grades on a scale. A “Level One” fish was hooked in the mouth and displayed no damage. Fish were rated from Level 1 (healthy, mouth-hooked) to Level 4 (unable to swim away). Telemetry tags capable of recording tail beats were implanted, allowing researchers to track survival in real time. A vast network of acoustic receivers along the striped bass migration corridor was deployed, with partner institutions sharing detection data. In short, researchers knew exactly which fish lived and which didn’t.

The Mass DMF team also compared four hook types (three circle, one J-hook), tracked fight time, fish length, handling time, air and water temperature, and recorded detailed tackle data. To top it off, they built in angler surveys and citizen science participation, gathering data from over 8,300 striped bass—an unprecedented sample size for any saltwater species. One of the more compelling discoveries is that the most experienced and avid anglers are deciding to release their catch. Below is a few figures from this comprehensive effort. As you can see, fish length, fight time, handling time, and the type of tackle used all play a huge role in how many fish die upon release. Bait, multiple treble hooks, fight time, and time out of the water are all things that we as anglers can control – and we should.

The Results: Cutting the Old Estimate in Half

Here is the important takeaway: release mortality is roughly half of what we’ve been told for decades.

Instead of 9%, the new data show mortality between 4.2% and 4.6% across all methods. For fly anglers, that number can drop below 4%. The rate for single hook artificials remains the lowest of all hook configurations, reemphasizing campaigns for conservation-driven gear choices. This has serious implications for striped bass management. It is worth noting that catch-and-release anglers are not responsible for half of total striped bass mortality, as has so often been claimed. For the past half a decade, the “kill-at-all-costs” crowd blamed the release community for “playing with fish”. Everyone knew this wasn’t the case, but without supporting science, there was little to do other than look for a few sane commissioners to stand up for what’s right. We must combine this updated science with two additional facts: First, the number of striped bass released alive has dropped by 85% in 2025. Second, the Fisheries Effort Survey may be overestimating angler effort by up to 40%. Suddenly, the entire mortality equation looks very different. Our community held the line. Now, we finally have what is the most comprehensive release-mortality research ever done for a saltwater species—and it tells a very different story.

Catch-and-release anglers handle fish responsibly. They treat them better. They catch smaller fish. They take the time to learn and improve. And now, the science backs those dynamics. So, where does that leave us?

No-targeting closures are not scientifically defensible with this information.

Education remains essential. Anglers can and should reduce multiple treble hooks, shorten fight times, be weary of water temperature and minimize time out of water—especially for big fish.

A debt of gratitude to Massachusetts Division of Marine Fisheries for this multi-year comprehensive effort to better understand and effectively manage the most critical inshore fishery on the Atlantic Coast. We say this all the time, but we do so with reason: Mass DMF should be a model for all other agencies along the coast.