Research on Bycatch
Quick links to:
1. Accounting
for bycatch in management of the Pacific halibut fishery
2. The
Bycatch Compensation Model
3. Compilation
of historical bycatch mortality and size distributions.
For the first two years that I was at the IPHC, I was involved
with research on halibut bycatch. Bycatch is the term by which halibut
caught outside the directed fishery are referred. The most important
of the non-directed fisheries in which bycatch occurs are the groundfish
fisheries in the U.S. and Canada. These include trawl, longline and
pot fisheries that are targetting on such species as walleye pollock (Theragra
chalcogramma), Pacific cod (Gadus macrocephalus), yellowfin
sole (Limanda aspera) and rockfish (Sebastes spp.).
The terms bycatch and bycatch mortality are often used interchangeably
though, properly speaking, they shouldn't. All bycaught halibut must
be returned to the sea as quickly, and with as little additional damage,
as possible. A percentage, highly variable by fishery, of the bycaught
halibut die and those fish constitute the bycatch mortality.
I concentrated on two areas of research. First, and
foremost, I looked at the issue of "bycatch compensation." Since
the 1980s, the IPHC has "compensated" the halibut stock for the effect
of bycatch. This compensation has taken the form of reducing the
total allowable catch. Initially, the directed catch was reduced
by approximately 1.41 x the bycatch mortality. This value was used
as it represented the estimated yield loss to the directed fishery.
Later, the compensation was reduced to 1.00 x bycatch mortality.
This change was made since it was reasoned that the compensation should
be based on lost reproductive potential. Calculations showed that
a pound of catch forfeited from the setline catch replaced the lost egg
production from a pound of bycatch. There were at least two problems
with this method however. First, much of the bycatch was adult halibut
and their removal was being treated differently than adults taken in the
setline fishery. Secondly, the compensation was being done in proportion
to the recruited biomass by area. Because a significant fraction
of the bycatch mortality are juvenile fish still migrating to their recruitment
area, the effects of the bycatch are usually felt in areas other than where
the bycatch takes place. If you want to read about the model I codeveloped
with Bill
Clark to address these deficiencies, then proceed to
Since Bill and I developed this model, a new
method of compensating for the bycatch of juveniles has been developed.
To read about it, visit Bill's
home page or follow this direct
link.
My other area of research concerning bycatch
was to develop an historical record of bycatch mortality back to 1974.
In addition to the mortality estimates, I also compiled estimates of the
size distribution of the bycatch. These data were required for the
annual stock assessment. Up until 1996, the bycatch data never entered
the stock assessment since the data quality was so poor. This work
involved dredging thorough stacks of old data reports and contacting various
people involved with managing those other fisheries that impacted halibut.
An excruciatingly detailed account of the work as well the final bycatch
mortlaity totals for 1974-1995, and the associated length frequency distributions,
can be read about in
Compilation
of historical bycatch mortality and size distributions.
In the course
of completing the two above mentioned tasks, I also completed a few other
duties which were summarized for the sake of historical completeness in
the annual IPHC Report of Assessment and Research Activities (the "RARA").
SQL
Bycatch Database, Domestic Groundfish Fishery, 1990-1994
Sampling
Halibut Bycatch in the Domestic Groundfish Fisheries
This page last updated on February 19, 1997.
Copyright © Steven R. Hare