[env-trinity] CBB: How Timing Of Fishing Seasons Impacts Spawning, Life History Patterns

[Sari Sommarstrom]

The Columbia Basin Bulletin: Weekly Fish and Wildlife News

www.cbbulletin.com

December 1, 2017             Issue No. 853

 

Study Brings Attention To How Timing Of Fishing Seasons Impacts Spawning,
Life History Patterns

 

A new University of Washington study points to an often overlooked factor
that is hampering the ability of fish to reproduce: the timing of fishing
seasons. 

 

The paper, http://onlinelibrary.wiley.com/doi/10.1111/faf.12248/full,
appearing online last month in the journal Fish and Fisheries, is one of
only a handful of studies that considers how the timing of fishing efforts
might disproportionately target certain fish and change the life history
patterns of entire populations.

 

"The more you think about it, the more pervasive you realize it is," said
senior author Tom Quinn, a UW professor of aquatic and fishery sciences.
"The real purpose of this essay is to raise the profile of this neglected
issue."

 

The authors build the case for more attention on timing by outlining
examples of how fishing seasons have altered a population's makeup --
specifically, its diversity and productivity. 

 

Fishing regulations, the patterns and habits of people who fish, and even
weather can increase fishing efforts at certain times, putting more pressure
on fish during a short period. For salmon in particular, migration and
spawning are timed so that both parents and offspring have the highest
chance for survival. Fishing that targets only early or late-arriving fish
can, over many generations, reduce the numbers moving and spawning at the
time that is most favorable for them biologically, the researchers explain. 

 

This may also affect the ability of fish to adapt to climate change. If
colder stream water necessary for spawning turns up later each autumn due to
climate change, fish must "choose" between being fished or being fried --
when they otherwise would adapt to changes and swim upstream whenever water
temperatures proved adequate.

 

"We are reducing the ability of fish to find good environmental conditions,"
said lead author Michael Tillotson, a UW doctoral student in aquatic and
fishery sciences. "We're perhaps also reducing the ability of fish to adapt
to climate change."

 

Salmon return from the ocean to the streams in which they were born to spawn
at predictable times throughout the year. The migration and spawning timing
vary over the years for each salmonid species, but factors such as daylight
hours and water temperature are natural markers that drive when salmon will
start their journey home.

 

Commercial and tribal fishing seasons are built around salmon's reproductive
timing; regulations vary, but in general, fishing can occur in the ocean and
rivers starting on a specific day as salmon migrate home to spawn. The
season ends on a predetermined date, or when a certain number of fish are
caught.

 

For example, if a fishery opens on Aug. 1, salmon that return to their natal
streams before that date are home free. In contrast, fish migrating on the
first of the month or after can face an incredible amount of fishing
pressure, especially if the weather is favorable and the conditions good for
harvesting. 

 

When this pattern repeats year after year, a population can evolve to
migrate earlier or later because parents that migrate early tend to have
kids that migrate early, too. But those changes also affect their ability to
survive; migrating earlier in the summer means spawning in warmer water,
which isn't favorable for egg survival. Returning too late also decreases
chances for survival.

 

"By disrupting this long-evolved distribution of timing, you can reduce the
reproductive output of adults or the survival of their offspring," Tillotson
said. "This paper is serving as a call to attention for researchers."

 

While salmonid species were the focus of this study, the findings could be
applied to other fish that have equally complex migration and breeding
behaviors. Fishing seasons often are set around periods when breeding adults
congregate in a specific location, which also puts undue pressure on fish
during an important period of their lives.

 

Fishing season dates should reflect the biology of fish, recognize the
importance of timing and be responsive to changes, the authors say. The goal
of management, in addition to making sure enough fish spawn, should be
ensuring those that do reflect the diversity of the total population. This,
the researchers said, is key for giving salmon and other fish the best
chance to adapt in a changing world.

 

They hope other scientists and fisheries managers will apply these findings
to their own data and respective fish populations, and ultimately devise
fishing regulations that will be viable for the future.

 

"We would like to think creatively about how to integrate climate-driven
processes with fishing to be more protective of the populations, and more
sustainable in fishing practices in the long run," Quinn said.

 

 

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