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Making it Count on the 2024 Coastal Shark Bottom Longline Survey

July 08, 2024

Perseverance yields success despite uncooperative weather.

 A shark at the water’s surface, still attached to the longline. A cylindrical tag is attached to its dorsal fin A juvenile dusky shark implanted with a satellite tag and released during the 2024 survey. This tag was deployed as part of a NOAA SEFSC study to determine post-release mortality rates. Credit: NOAA Fisheries/ Michelle Passerotti

As the 12-foot waves lashed the hull of the F/V Eagle Eye II and threatened to throw me from my bunk, I briefly questioned my life choices. It was day 40 of the 2024 Coastal Shark Bottom Longline Survey and we still had a week to go. Mother Nature was proving yet again that she controls our workplace.

My job as a chief scientist is to manage a suite of factors such as weather, budgets, timelines, and personnel. This ensures we execute our survey precisely and, ultimately, maintain the integrity of the data time series. Nevertheless, in that moment as I braced myself in my bunk, my biggest lesson as a first-time chief became strikingly clear: There is no managing the weather, only navigating the gauntlet around it. Such is life on the water, and it makes for a fitting analogy to navigating the trials and tribulations of leading a fisheries survey.

 Seven of the survey crew pose for a picture on the deck of the ship.
The crew of the F/V Eagle Eye II, along with scientists Michelle Passerotti (back row, far right) and Lisa Natanson (back row, near right), prepare to embark on the 2024 survey. Credit: John Caldwell

Weather Complicates Things

We caught 1,949 sharks during this year’s survey, a slight decrease relative to the last few survey years. This was due mostly to the weather: We lost 15 of our 47 allotted sea days to weather, a 32 percent loss of productivity and an all-time high in our survey’s 28-year history.

Nevertheless, we completed 45 of 85 stations ranging from southern Florida to the Outer Banks of North Carolina. It is increasingly important to sample at those last 40 stations, between the Outer Banks of North Carolina and Delaware. It’s the northern extent of habitat ranges for the sharks we study. As climate change brings about temperature shifts, it is altering the habitat use and migration patterns of some species. Our survey captures these changes as they happen. We can’t change the weather, but ultimately strategic planning can mitigate the impacts of climate change on our surveys.

Shark Catch Report

A white shark on its side at the water’s surface at the side of a boat, a tagging pole is left, held by a person on the boat’s deck.
A juvenile white shark caught on the longline before being tagged and released: Credit: NOAA Fisheries/Michelle Passerotti

Despite the reduced number of stations, we collected a range of sharks. We tagged them and released them after documenting their size and species. Sandbar sharks accounted for about 70 percent of catch, followed by:

  • Dusky sharks (8.7 percent)
  • Tiger shark (7.5 percent)
  • Blacktip shark (4.7 percent),
  • Scalloped hammerhead sharks (4.1 percent)
  • Atlantic sharpnose, spinner, silky, white, bull, great hammerhead, and sand tiger sharks (5 percent)

Notably, we caught four juvenile white sharks on this year’s survey, the most ever caught in a single year in our time series (1996–2024). To truly determine differences in abundance year-over-year, raw catch numbers need more context—examining environmental parameters, for example. However, increasing encounters with white sharks are a good sign that the population is beginning to recover.

Shark Tagging and Recaptures

Of the 1,949 sharks caught, we tagged 1,710 with a combination of:

A woman in long pants and long-sleeved shirt wearing a sun protection hat on a boat’s deck leans over the side with a tag on a long pole, aiming for the dorsal fin of a shark tethered to on a longline at the water’s surface alongside the boat.
Michelle Passerotti prepares to tag a sandbar shark during the 2024 Coastal Shark Bottom Longline survey. Credit: Lisa Natanson.

SUNY Stonybrook provided acoustic tags to study sandbar shark movement and the Atlantic Shark Institute to study blacktip shark movement. NOAA’s Southeast Fisheries Science Center provided the satellite tags to study dusky shark post-release mortality. Tagging data helps us to learn more about life history, long-term movement patterns, habitat use, growth rates, and longevity. This survey also allows us to tag larger individuals of these species than are usually caught by scientists elsewhere, filling a critical knowledge gap for shark research.

We also recaptured nine sharks previously tagged with Cooperative Shark Tagging Program tags (seven sandbar and two dusky sharks). One shark had been tagged nearly 24 years earlier! Another notable event was recapturing a sandbar shark in the same location, 12 years to the day after her initial tagging on our 2012 survey! The other recaptures ranged from 1 to 9 years at liberty.

Collecting Biological Samples

Three sharks on the deck of a ship, their bellies open as scientists look for indications of reproductive status.
Michelle Passerotti (left) and Lisa Natanson (right) dissect sandbar sharks incidentally killed during the 2024 survey. These sharks provide valuable data on reproduction and other traits critical for shark research. Credit: Brittney Scannel

Although our goal is to tag and release the sharks we catch, a small percentage don’t survive capture. We take hard-to-get samples from these animals to help us understand more about their biology and life history.

One haul yielded fascinating data on reproduction in sandbar sharks. We dissected five females of approximately the same size, and found three completely different reproductive phases among them:

  • Two were immature and probably not ready to mate for another 1 to 2 years
  • Two were pregnant with near-term pups
  • One pupped last year but was in a resting state with no developing eggs, so would not be ready to mate until next year

This is a great illustration of the growth plasticity in sharks and the challenges to size-based management strategies. All of these sharks occupied the same habitat at the same time and were of about the same size, but in far different stages of life. Despite decades of research into these species, every data point provides another perspective to better inform our science.

Looking back on my first stint as a chief scientist, I am proud of our team’s perseverance and ability to navigate the rough patches. Every survey completed is another trove of data to improve our understanding of populations and inform our management strategies. Seeing the science play out in real time is humbling and awe-inspiring, and makes it easier to forget about those big waves throwing me out of my bunk!

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Last updated by Northeast Fisheries Science Center on July 17, 2024