HOOK, LINE & SCIENCE
Research, News, and More for Anglers
the award-winning series curated by Scott Baker and Sara Mirabilio, fisheries specialists with North Carolina Sea Grant
HOW CAN YOU TELL HOW OLD A FISH IS?
By looking into its eyes.
Scientists need accurate and reproducible measurements of the ages of fish to understand their population status, structure, and health. Similar to how trees deposit rings for each year of life, most fish deposit rings or growth bands in their bodies’ hard parts — like scales, spines, and vertebrae.
And in their “otoliths.” Also called “ear stones,” these calcium carbonate structures sit inside a fish’s head, behind the brain.
Otoliths, in general, tend to be the most-accepted structure for fish aging. Fish that are well studied and with otolith-based ages that are independently validated provide scientists a great opportunity to experiment with new aging techniques.
Capable of reaching ages beyond 50 years, red snapper is arguably one of the most studied and most recreationally important species in the world. In addition to otoliths, is there another part of the red snapper that scientists might use to estimate its age?
What did they study?
Scientists have previously used eye lenses from terrestrial animals and marine mammals to determine age. This involves measuring how amino acids change over time under different temperatures. Since eye lenses begin to form before a fish is even hatched, this process might provide a perfect record of an individual fish’s age.
Fluctuations in water temperature can affect the rate of amino acid change. To better understand the impact of water temperature on the aging technique, Derek W. Chamberlin from the University of Florida led a research team that collected otoliths and eyeballs from 29 red snapper in the northern Gulf of Mexico and 24 yellowtail snapper from the warmer Caribbean.
Using standard techniques, the team thin-sectioned whole otoliths and viewed them by microscope. When analyzing the ages of the eyeballs for comparison to the otoliths’ ages, researchers looked at only the first layers of the eye lens, which were deposited during the first year of the fish’s life.
What did they find?
Otolith-based ages ranged from 1 to 27 years for red snapper and 2 to 17 years for yellowtail snapper. At the individual fish level, eye-lens based ages were different by an average of only 1.6 to 1.7 years.
The high levels of agreement between eye-lens and otolith-based ages suggest that the eye lens technique could serve as an effective tool for estimating ages.
So what?
While the eye-ageing technique was successful for these two species, the research team identified challenges, including developing a general model to better understand how changing temperature impacts the amino acids in the eye lens over time.
By Scott Baker
full study: dx.doi.org/10.1139/cjfas-2022-0161
A research team looked into the knowledge, patterns, and motivations of recreational boaters. Credit: NC State Photos.
ARE YOU WEARING A LIFE JACKET?
In the U.S. last year, 85% of drowning victims were not.
Every year, the U.S. Coast Guard releases its annual report for boating related fatalities. It’s a somber report that tends to be published in the Spring — when people start to boat more often as the weather warms.
For the year 2022, in cases in which the cause of death was known, 75% of fatal boating incident victims drowned. Of those, when the report could determine whether drowning victims had worn a life jacket, it found 85% of the victims had not.
We, as boaters, know that we “should” wear our life jackets, but often we don’t really think about the benefits as we are about to leave the dock, only these perceived inconveniences.
But what if we could use the power and reach of social media to heighten awareness about using life jackets?
What did they study?
Researchers partnered with The Community Against Preventable Injuries to deploy a public awareness campaign on Facebook for recreational boating safety in British Columbia, Canada, targeting boaters between the ages of 25 and 55. The campaign consisted of 10 multimedia posts spread across the 2018 to 2019 recreational boating season.
Messages were related to drowning prevention, life-jacket use, alcohol use, and safety equipment. To create relatable messages, prior to content and message creation the team did extensive background research to better understand the knowledge, patterns, and motivations of recreational boaters.
After the campaign, the team analyzed Facebook engagement data and reviewed all comments.
What did they find?
The campaign was considered successful, because it was generally well-received by the intended audience.
The 10 multimedia Facebook posts were liked over 7,000 times and received over 900 shares. Of the 219 comments on the posts, almost half were positive. Fifty comments were off-topic, 45 were neutral, and only 18 were negative.
Positive commenters valued safety as one part of having a pleasant experience on the water, as opposed to being a barrier. Negative comments implied that boating safety would lead to reduced fun.
The campaign post that reached the most people, according to Facebook data, was from August 2, 2019: “Drowning doesn’t just ‘happen’ — it’s almost always #preventable. Learn what you can do to protect you and your family from boating-related fatalities. Stay safe while enjoying the water this summer!”
So what?
Creating an engaging message for a campaign is not easy. Prior to developing the campaign, the team interviewed many Canadian boaters and learned that most people knew what to do to keep themselves safe, but they often minimized safety procedures due to complacency and perceived inconveniences.
Knowing that most boaters already know what to do — and don’t like to be shamed into changing their behavior — the results show that a campaign broadly designed to challenge boaters to reflect and act on their existing knowledge may lead to heightened boating safety awareness.
By Scott Baker
full study: doi.org/10.3390/ijerph18126504
CAN FISH ESCAPE WATERS THAT ARE HARMFULLY LOW ON OXYGEN?
Sea Grant-funded research shows that spot flee quickly when oxygen levels are unsafe.
The dog days of summer brought high heat and humidity. High air temperatures also warm the water, leading to harmful living conditions for many fishes and marine organisms.
“Hypoxia” refers to water conditions where the concentration of oxygen is so low that it is harmful to organisms. Hypoxia occurs when aquatic plants — which have been intensely growing in the peak of summer — die, sink to the bottom, and are decomposed by bacteria. This decomposition uses available oxygen.
In addition, differences in salinity and temperature between surface and bottom waters limit mixing, and without mixing, the oxygen level of the bottom water is lower, creating a condition that can lead to a “dead” zone and can cause mass fish kills.
But some species can escape this fate — and J. Kevin Craig at the Beaufort Laboratory of the National Marine Fisheries Service’s Southeast Fisheries Science Center led a research team who wanted to know more about how.
What did they study?
Spot are among the most abundant transient marine species in estuaries along the U.S. Atlantic and Gulf coasts. Previous studies have shown that spot are able to avoid low-oxygen conditions in laboratory trials, but what about their movements in response to changing oxygen levels in the wild?
The research team tagged 25 juvenile spot — one-year old or younger — from the Neuse River. The river experiences agricultural and stormwater runoff that fuels recurrent, summertime hypoxia.
The small, sound-emitting tags allowed the team to track the fish. During eight windows lasting 7 to 14 days, they released and tracked 1 to 5 of the tagged fish and also monitored environmental conditions.
What did they find?
All told, the team detected spot at 859 locations.
The spot’s average swimming speed increased nearly ninefold under hypoxia, as fish traversed waters with low bottom oxygen. This increased movement spanned long distances (over 6 miles) and long periods (up to 35 hours), as they moved from the deeper main river channel to shallow, nearshore, oxygenated habitats.
The scientists grouped observed movements into three modes: (1) slow swimming in deep water when oxygen was high throughout the river; (2) rapid and highly directed swimming that traversed deep waters with low bottom oxygen; and (3) slow swimming in shallow, oxygenated waters while deeper waters remained hypoxic.
Anything else?
The scientists determined that the level of oxygen on the water bottom, water depth, and the fish’s prior swimming speed had effects on patterns of fish movement. Several other environmental variables —such as temperature, salinity, and time of day — had little effect.
So what?
This research confirmed the importance of oxygen as a driver of the short-term movements of juvenile spot, suggesting that hypoxia could affect how estuarine habitats function as nurseries and how populations of various marine species change over time.
By Sara Mirabilio
full study: doi.org/10.1007/s12237-022-01167-6
ARE FISHING TOURNAMENTS HELPFUL TO SCIENCE?
New research looks at whether historical records from fishing competitions can be useful sources of information about long-term trends in fisheries.
It can be challenging for a recreational fishing manager to obtain valid long-term data for use in monitoring the status and trends of a fishery.
Several tools are available for monitoring a fishery, beginning with structured fisheries surveys conducted by management agencies. In some fisheries, stakeholder logbook programs and fishing tournament data have been used to supplement survey data.
Recreational fishing tournaments have increased dramatically in the Southeast. Records from these tournaments could be especially valuable because the competitions have been occurring for decades.
The bonefish fishery is vital to the history and economy of the Florida Keys, and bonefish are a focus of numerous fishing tournaments, due to their year-round availability and abundance. Researchers wondered if bonefish tournament records could support or add to existing data about the health of the bonefish fishery.
What did they study?
Ross E. Boucek from Florida International University led a research team that collected bonefish tournament records from participants and organizers, as well as from press releases and media. They excluded tournaments that did not have at least 10 years of records prior to 2010 (the year of an extreme cold spell that impacted bonefish) and tournaments that did not have at least 5 years of records after 2010.
Ultimately, only a single tournament met their selection criteria: Islamorada All Tackle Bonefish Invitational Bonefish and Permit Championship, from 1968 to 2021.
Analyzing this tournament’s 53-year record in detail, the team used the average number of bonefish caught per boat per day as an index of the catch, the largest fish caught in the tournament as an index of size, and the number of tournament anglers as a measure of participation.
What did they find?
Researchers found three statistical “changepoints” — noteworthy shifts — in catch rate: an increase in 1981, a decrease in 1998, and then an increase starting in 2015.
They also found three changepoints in largest fish caught: an increase in 1982, a decrease in 2006, and a further decrease in 2016.
The researchers found four statistical changepoints in angler participation: a decrease in 1983, an increase in 1997, a decrease in 2006, and a further decrease in 2010.
These statistical “changepoints” from the tournament data were often consistent with trends in the bonefish fishery found through other methods. This suggests that tournament records can provide scientists and fisheries managers with useful information on the status of the fishery, especially in combination with other available tools.
Researchers found that tournament records did not consistently match research from other sources. This may be due to several factors, including the fact that the anglers in the tournaments were highly skilled, as well as that tournaments are not created for data collection, which leads organizers to sometimes change the rules over time to increase participation or fairness.
What’s next?
Researchers were able to successfully use tournament data to duplicate previous data about the bonefish fishery that had been collected in other ways. Maximizing the value of tournament data in the future for both scientists and resource managers would require more standardized tournament practices, improved record keeping, and continued improvement in using other assessment tools to validate the observed trends.
By Christine Ryan
full study: doi.org/10.1007/s10641-022-01299-5
For more news and science for anglers, visit HookLineScience.com.
lead photo: When it comes to a fish’s age, the eyes have it. credit: Jeff Miller/CC-BY-2.0.