Protecting largest, most prolific fish may boost productivity of
fisheries
Overlooking capacity of large females may lead to overharvest

Date:
August 18, 2021
Source:
NOAA Fisheries West Coast Region
Summary:
Management of many of the largest fisheries in the world assumes
incorrectly that many small fish reproduce as well as fewer large
ones with similar total masses, a new analysis has found. That
can lead to overharvesting the largest, most prolific fish that
can contribute the most to the population.



FULL STORY ========================================================================== Management of many of the largest fisheries in the world assumes
incorrectly that many small fish reproduce as well as fewer large ones
with similar total masses, a new analysis has found. That can lead to overharvesting the largest, most prolific fish that can contribute the
most to the population.


========================================================================== Better protection of larger, mature females could improve the productivity
of major fisheries. This is crucial at a time when fisheries are
increasingly important in providing food resources around the world. The results were published in Proceedings of the National Academy of Sciences
this week.

"It is a fundamental question in fisheries management -- how much
reproduction can you count on?" said Dustin Marshall of Monash University
in Australia, lead author of the research. "When you are expecting
smaller females to produce the same number of eggs per body mass as
larger, older females, you're not going to have an accurate picture."
Building on Earlier Research The new research applies previous findings
that questioned longtime assumptions of fisheries management. Traditional thinking held that reproduction is a function of biomass. That means
that fish representing a certain mass would produce similar numbers of offspring regardless of their age or maturity.

However, syntheses of previous research by some of the same authors demonstrated that larger, older, and more mature fish produce more
offspring.

Also, previous work suggests that offspring of these older, larger
mothers may survive at higher rates.

Management measures, such as establishing Marine Protected Areas that
provide refuge for fish to grow larger, can help boost the yields of
fisheries and replenish depressed species. They can in effect provide
a reservoir of more mature fish with greater reproductive capacity.



==========================================================================
"We need to ask, 'How can we make the most of these fish that reproduce
more efficiently -- both to sustain the species and to support sustainable fisheries?" said E.J. Dick, a fisheries research biologist at NOAA
Fisheries' Southwest Fisheries Science Center and senior author of
the paper.

By contrast, when fishing removes the more prolific larger fish, the traditional assumptions tend to overestimate the production of eggs
and the population's capacity to replenish itself. That can lead to overharvesting which for many of the largest fisheries could remove
around twice as many fish as intended, the scientists found.

"In this paper, we connect the dots between early findings that large,
old Pacific rockfish produced more eggs per body mass than smaller ones
did, and Professor Marshall's more recent work showing that many other
species do, too," said Marc Mangel, professor emeritus of mathematical
biology at UC Santa Cruz and a coauthor. "Without recognizing this,
fisheries scientists and managers may overestimate the number of spawning
fish needed to produce a certain level of recruitment, and set mortality
levels from fishing too high." Recognizing Greater Capacity In their
new analysis, the scientists examined whether the largest fisheries in
the world take the findings into account. In many cases, they found,
fisheries do not.

"This systematic error could help to explain why some stocks have
collapsed despite active management," the scientists wrote. They
recommended that managers recalibrate future species stock assessments
to recognize the greater reproductive capacity of larger fish. This
could reduce overharvesting and may even boost the yields of fisheries.

"Such reductions could have negative repercussions in the short-term, for
both food security and the economy, but will yield positive benefits in
the long- term," the scientists wrote. They said that better recognizing
the capacity of larger fish could help boost the catches of Atlantic
cod fisheries in the longer term, for example.

"Our work suggests that modern management could respond to this challenge
by better leveraging the reproductive potential of larger, older fish
in exploited stocks more so than is presently the case, using relatively
simple policy innovations," they said.

The research was conducted by scientists from:
* Monash University * Queensland University of Technology * University
of California Santa Cruz * Leibniz Institute of Freshwater Ecology
and Inland Fisheries * NOAA Fisheries ========================================================================== Story Source: Materials provided by
NOAA_Fisheries_West_Coast_Region. Note: Content may be edited for style
and length.


========================================================================== Journal Reference:
1. Dustin J. Marshall, Michael Bode, Marc Mangel, Robert Arlinghaus,
E. J.

Dick. Reproductive hyperallometry and managing the world's
fisheries.

Proceedings of the National Academy of Sciences, 2021; 118 (34):
e2100695118 DOI: 10.1073/pnas.2100695118 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/08/210818135210.htm

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