In a new study, fisheries researchers from North Carolina State University found that black sea bass (Centropristis striata) can usually survive the physical trauma that results from being hauled up from deep water then released at the surface. The finding is part of a larger study of the fish’s mortality rate, which will inform stock assessments designed to help ensure that the black sea bass fishery is sustainable.
Black sea bass are bottom-dwelling fish, and are often caught at depths of greater than 60 feet. When the fish are brought to the surface, the rapid change in pressure causes the fish’s swim bladder to expand. This forces other organs out of the way and can result in visible “barotrauma” – such as the fish’s stomach being forced partially out of its mouth.
Black sea bass with barotrauma (note stomach protruding from mouth). Click to enlarge. Photo: Jeff Buckel
Conventional wisdom long held that this sort of visible barotrauma meant that a fish would die when thrown back into the water. But that’s not true, according to the NC State study.
The research team was attempting to develop accurate estimates of “discard mortality” rates for black sea bass, meaning that they wanted to know what percentage of the fish would die if they were caught and thrown back. Discard mortality rates are used to make informed stock assessments for fish species, because it helps fisheries officials understand how many fish that are caught and released can be expected to survive. Black sea bass are a valuable species for commercial fishing and are also popular with recreational anglers. Millions of black sea bass are caught and released by recreational anglers off the south Atlantic coast of the U.S. each year.
The researchers came up with a novel method for determining the discard mortality rate for black sea bass. First, the researchers worked with a team of scuba divers to tag black sea bass in their natural habitat on the ocean floor. Then the researchers caught, tagged and released the same number of black sea bass in the same area on the same day. The fish tagged on the bottom served as a control group, since they were not subject to changes in atmospheric pressure or other injuries that could be incurred when caught and brought to the surface.
Over the next year, tagged black sea bass were caught by the researchers, or by recreational anglers or commercial fishing operations who returned the tags to the researchers. Researchers could then compare the number of tags returned from the experimental group (those tagged on the surface) to those returned from the control group (those tagged on the bottom). This allowed them to determine discard mortality rates.
The researchers had put the fish in the experimental group into one of four categories: those without visible injury; those with visible barotrauma; those with hook trauma (meaning the hook had caused significant internal injury); and “floaters” – those that couldn’t swim down into the water at all.
To their surprise, the researchers found that approximately 90 percent of the fish in the experimental group with visible barotrauma (but that weren’t floaters) survived. This was about the same survival rate as for fish that exhibited no visible injury at all. Fish with hook trauma had a survival rate of 36 percent, while floaters had a 16 percent survival rate.
“In previous work, estimates of discard mortality were limited to time periods soon after release,” says Paul Rudershausen, a research associate at NC State’s Center for Marine Sciences and Technology and lead author of a paper describing the research. “By tagging a control group, we were able to estimate the long-term effects of injuries associated with fishing.”
In addition to lending key insight into the black sea bass fishery, Rudershausen notes that the study “may give us insight into mortality for other important species with similar characteristics, such as red grouper and gag grouper.”
The paper, “Estimating reef fish discard mortality using surface and bottom tagging: effects of hook injury and barotrauma,” is forthcoming from the Canadian Journal of Fisheries and Aquatic Sciences. The paper was co-authored by Dr. Jeff Buckel and Dr. Joe Hightower, professors of applied ecology at NC State. The researchers worked closely with fisherman Tom Burgess on the project. The work was done under North Carolina Sea Grant Fishery Resource Grant projects 07-FEG-01 and 11-FEG-04.
Note to Editors: The study abstract follows.
“Estimating reef fish discard mortality using surface and bottom tagging: effects of hook injury and barotrauma”
Authors: P. J. Rudershausen, J. A. Buckel, and J.E. Hightower, North Carolina State University
Published: forthcoming, Canadian Journal of Fisheries and Aquatic Sciences
Abstract: We estimated survival rates of discarded black sea bass (Centropristis striata) in various release conditions using tag–recapture data. Fish were captured with traps and hook and line from waters 29–34m deep off coastal North Carolina, USA, marked with internal anchor tags, and observed for release condition. Fish tagged on the bottom using SCUBA served as a control group. Relative return rates for trap-caught fish released at the surface versus bottom provided an estimated survival rate of 0.87 (95% credible interval 0.67–1.18) for surface-released fish. Adjusted for results from the underwater tagging experiment, fish with evidence of external barotrauma had a median survival rate of 0.91 (0.69–1.26) compared with 0.36 (0.17–0.67) for fish with hook trauma and 0.16 (0.08–0.30) for floating or presumably dead fish. Applying these condition-specific estimates of survival to non-tagging fishery data, we estimated a discard survival rate of 0.81 (0.62–1.11) for 11 hook and line data sets from waters 20–35m deep and 0.86 (0.67–1.17) for 10 trap data sets from waters 11–29 m deep. The tag-return approach using a control group with no fishery-associated trauma represents a method to accurately estimate absolute discard survival of physoclistous reef species.
Matt Shipman | EurekAlert!
Litter is present throughout the world’s oceans: 1,220 species affected
27.03.2017 | Alfred-Wegener-Institut, Helmholtz-Zentrum für Polar- und Meeresforschung
International network connects experimental research in European waters
21.03.2017 | Leibniz-Institut für Gewässerökologie und Binnenfischerei (IGB)
The Institute of Semiconductor Technology and the Institute of Physical and Theoretical Chemistry, both members of the Laboratory for Emerging Nanometrology (LENA), at Technische Universität Braunschweig are partners in a new European research project entitled ChipScope, which aims to develop a completely new and extremely small optical microscope capable of observing the interior of living cells in real time. A consortium of 7 partners from 5 countries will tackle this issue with very ambitious objectives during a four-year research program.
To demonstrate the usefulness of this new scientific tool, at the end of the project the developed chip-sized microscope will be used to observe in real-time...
Astronomers from Bonn and Tautenburg in Thuringia (Germany) used the 100-m radio telescope at Effelsberg to observe several galaxy clusters. At the edges of these large accumulations of dark matter, stellar systems (galaxies), hot gas, and charged particles, they found magnetic fields that are exceptionally ordered over distances of many million light years. This makes them the most extended magnetic fields in the universe known so far.
The results will be published on March 22 in the journal „Astronomy & Astrophysics“.
Galaxy clusters are the largest gravitationally bound structures in the universe. With a typical extent of about 10 million light years, i.e. 100 times the...
Researchers at the Goethe University Frankfurt, together with partners from the University of Tübingen in Germany and Queen Mary University as well as Francis Crick Institute from London (UK) have developed a novel technology to decipher the secret ubiquitin code.
Ubiquitin is a small protein that can be linked to other cellular proteins, thereby controlling and modulating their functions. The attachment occurs in many...
In the eternal search for next generation high-efficiency solar cells and LEDs, scientists at Los Alamos National Laboratory and their partners are creating...
Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are less stable. Now researchers at the Technical University of Munich (TUM) have, for the first time ever, produced a composite material combining silicon nanosheets and a polymer that is both UV-resistant and easy to process. This brings the scientists a significant step closer to industrial applications like flexible displays and photosensors.
Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are...
20.03.2017 | Event News
14.03.2017 | Event News
07.03.2017 | Event News
28.03.2017 | Life Sciences
28.03.2017 | Information Technology
28.03.2017 | Physics and Astronomy