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
"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
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
"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.