FOR REDUCING INADVERTANT TAKE
to tables and figures associated with this report, some
of which are .pdf files, can be found at the end of this
report. [Reading .pdf files requires Adobe Acrobat
here for information on how to download this program.])
AND BYCATCH WASTAGE OF SKATES AND SHARKS
IN ALASKAN HOOK-AND-LINE FISHERIES
FISHERIES INFORMATION SERVICES
JUNEAU, ALASKA SEPTEMBER 2000
of the Report
and sharks are the major components of the "other
species" quotas under the Fisheries Management Plans
for Groundfish in the Bering Sea and Aleutian Islands
(BSAI) and the Gulf of Alaska. In 1998 the BSAI quota
of "other species" was exceeded by 15%. In 1999
bycatch of skates by some vessels participating in Community
Development Quota (CDQ) fisheries was higher than anticipated,
threatening boat quotas. In 1998 the Alaska Board of Fisheries
took action to close the state commercial fishery for
sharks and establish permit requirements for fishing for
skates and rays in state waters. Given these concerns
and the wider international concern about shark conservation,
the North Pacific Fisheries Management Council has recently
initiated action to develop amendments to the two Plans,
affecting sharks and skates.
project is intended to expand information about the distribution
of sharks and skates in a way useful to fisheries planners,
and to hook-and-line fishermen, the group of Alaskan fishermen
who most frequently encounter these species. It also provides
recent information about utilization; given that some
level of bycatch is inevitable in hook-and-line fisheries,
there may be potential to develop markets for fish that
are currently being discarded.
fisheries off Alaska pursued by hook-and-line (H&L)
vessels include Pacific cod, Greenland turbot and sablefish.
The Bering Sea/Aleutian Islands (BSAI) H&L Pacific
cod season opens January 1 and continues until its first
trimester quota is reached, usually in late March or April.
The Gulf of Alaska Pacific cod fisheries, also starting
January 1, vary by area and may close due to cod quota
or halibut bycatch cap, but are generally all closed to
H&L gear by late winter. Fishing for Greenland turbot
in the BSAI opens May 1 and usually closes the same month.
The sablefish fishery is managed under an individual fishery
quota system and is open March 15 to October 15, with
most of the fishing taking place during the more clement
months May to September. The second season BSAI cod season
opening has been either September 15 or September 1 (there
was no second season in 1993). It lasts at least through
October, and sometimes into December, depending on quota.
In 1999 and 2000, about a dozen H&L catcher/processors
with Community Development Quota (CDQ) cod quotas fished
outside of the open-access season, including summer months
when cod fisheries have historically been closed.
provided in this report are from records taken by at-sea
observers, which have been audited, put into final format
and stored in the NORPAC database. The bulk of the Pacific
cod and Greenland turbot catch is taken by large catcher/processors,
freezer longliners which have fisheries observers on board
at least 30%, and in most cases 100% of their fishing
time. In contrast, only about 50 of the more than a thousand
sablefish boats carry observers, and rarely for more than
a week or two during the season; there are few observer
records compared to those of other H&L fisheries.
requested from the NORPAC database all H&L records
with skate or shark catches indicated. Data were delivered
as a single Excel database, including fields for trip,
date of set, location of set, number of hooks, total catch,
species, species number and weight, and estimated retention.
I imported this file into Microsoft Access, and for ease
of analysis sorted it by year and produced Excel files
with annual data. Next I sorted each annual file by species.
For sharks, I calculated Catch per unit effort (CPUE)
in number of fish per 1000 hooks deployed, as this is
the effort standard in use for analyzing bycatch of a
similarly infrequent species group, birds. For skates,
I calculated kilograms per 1000 hooks.
each set I also calculated the weight of species retained,
by multiplying the observer's estimate of retained percent
by the set weight.
I converted the latitude/longitude information to the
decimal degree format that could be used by the Geographic
Information Systems (GIS) program ARCVIEW.
of the time I spent on this project was in determining
the appropriate time/area strata, and testing options
of how to display the data in order to make it most understandable.
originally anticipated using monthly time strata. After
producing drafts of monthly maps for two sample years,
it became clear that this level of detail for was not
particularly helpful. Changes in skate bycatch distribution
in particular mainly reflected the movements of the fleet
as determined that approximate the seasons of the different
longline fisheries described above. I did the same for
sharks, except that for 1998 I developed monthly maps.
point data can be portrayed with varying symbol size (as
I did in my 1998 S-K project where I mapped halibut bycatch
in H&L Greenland turbot fishery), or color variations
(as in NOAA technical memorandum NMFS-AFSC-88). With a
very large number of points, color variations are easier
to interpret. I portrayed three classes (data ranges)
to portray, similar to the NOAA technical memorandum which
used high, medium and low CPUEs.
classified the CPUE data by the "natural breaks"
method, which is the default classification method in
ArcView. Natural Breaks finds groupings and patterns inherent
in data by finding breakpoints between classes using Jenk's
optimization method. The Jenk's method minimizes the sum
of the variance within each of the classes. Of course
each subset of data produced somewhat different natural
break points, and it was necessary to pick common cut-off
points for each map in order to achieve consistency. For
skates, I choose breaks at 75 and 250 Kg/1000 hooks. For
sharks, I choose 1 and 10 individuals/1000 hooks.
general rule that has been applied to use of NMFS-collected
data is to produce only summaries that include 4 or more
reporting entities. While this is easily done for graphs
or tables, it is difficult to apply with newer techniques
of data visualization such as GIS. It can be accomplished
by pooling data, either by time or area strata. FIS's
first (1993) S-K project pooled data by month and 1 degree
by 1/2 degree rectangles, consistent with similar efforts
at the time, and sufficient for its purpose of an overview
of halibut bycatch. However, that approach to pooling
data defeats the purpose when the intent is to map areas
of concentrations or scarcity of a species.
originally planned to map all data provided, portraying
Gulf and BSAI separately. After producing the first draft
set of maps I realized that areas to the extreme west
and east (West of 175 degrees west in the Aleutian Islands
and east of 146 degrees in the Gulf) included observations
from very few trips (boats). In some time-strata only
one or two trips were included. In consideration of confidentiality
of data from these boats, I truncated the map. This lead
to a loss of one piece of important information: relatively
large numbers of sharks are taken in the summer in the
Eastern, particularly Southeastern, Gulf of Alaska. Possibly
NMFS researchers currently involved in shark research
in this area can use this NORPAC information to aid in
their ongoing studies.
OBSERVATIONS (all table, figures, and maps can
be linked to through a table at the end of this document)
1. summarizes weights and numbers of all shark species
reported, and two skate categories (unidentified and identified),
by year. An average size is also calculated. Because the
category "unidentified sharks" is so large,
I am reluctant to make assumptions about trends in catches
of the identified shark species. Less than 0.1% of the
skates were identified by species.
2. summarizes NMFS' "best blend" estimated catch
of "other species" by hook-and-line gear for
years 1993 to 1999 (1992 is unavailable) and compares
it to total catch weight of sharks and skate in NORPAC
database for each of these years.
1-24 are maps of skate locations and CPUE category by
trimester for years 1992-1999. Pages 25-42 are similar
maps for sharks by trimester for years 1992-1997. I prepared
monthly maps for 1998; these are on pages 43-53. Maps
54, 55 and 56 are for trimesters of 1999.
are only 11 records in the entire database that indicate
any retention of sharks. These include four records from
1997 which indicated 9 spiny dogfish shark and 3 Pacific
sleeper shark were retained, four records from 1998 which
indicated 3 spiny dogfish shark and 43 Pacific sleeper
shark were retained, and 1 record from 1999 showing retention
of 5 spiny dogfish shark.
skates, I looked at the last three years in detail. During
these years, observers made estimates of the percent of
fish retained in each observed set. In 1997, 22 of 176
observer cruises included some records with some skates
retained. Comparable numbers for 1998 are 21 of 189 cruises,
and in 1999, 43 of 198 cruises. The increase in 1999 is
a result of the requirement of full retention of all groundfish
species on CDQ vessels. This also accounts for the increase
in actual amounts, shown in figures 1-3.
has been recent interest in pursuing a directed fishery
for skates when Pacific cod closes. By choosing rates
in excess of 250 kg/1000 hooks, these maps display rates
that are in the upper 10% of CPUEs (rather than upper
third of CPUEs as shown in the NOAA tech memo). It is
more likely, though clearly not guaranteed, that boats
would encounter sufficient concentrations of skates in
those areas in order to qualify for a skate target. Conversely,
fishing in areas where skate CPUEs are less than 75 kg/1000
hooks decreases the probability that skate bycatch will
exceed a CDQ boat quota, or that large quantities of skates
will be caught, discarded and wasted.
of skates (as calculated from this database) was 79% in
1997, 86% in 1998 and 84% in 1999. Although there are
monthly variations in retention, they are not consistent
among years. The higher retention rates in the fall of
1999 are at least partly the result of required retention
in CDQ fisheries that occurred during that time. Improvement
in skate retention during other target fisheries will
be driven by market conditions and the degree to which
individual boats can be flexible in their processing operations.
comprise from 2-5% of the "other species" H&L
bycatch on an annual basis. As such they do not present
much of a concern for fishermen as far as contributing
to bycatch quotas, or as an opportunity to develop new
products or markets. Thus, the chief value of the shark
distribution maps may be as a contribution to the developing
information base about sharks in North Pacific waters.
Much is still to be learned about the distribution and
habits of all the species of sharks, a group unique life
history characteristics separates them from most of the
other fish taken by H&L fishermen under current management
Guide to Catch and Bycatch in Alaskan Hook-and-Line Fisheries.
1994. Fisheries Information Services.
Study of Bycatch Avoidance by Hook-and-Line Fishermen
in Greenland turbot fisheries. 1998. Fisheries Information
L.W., A. Greig and R.F. Reuter. 1998. CPUE, length and
depth distributions of major groundfish and bycatch species
in the Bering Sea, Aleutian Islands and Gulf of Alaska
regions based on groundfish fishery observer data. U.S.
Dep. Commerce, NOAA Tech. Memo. NMFS-AFSC-88.
for Amendment 62/63 to the Fishery Management Plans for
the Groundfish Fisheries of the Bering Sea/Aleutian Islands
and Gulf of Alaska to Revise Management of Sharks and
Skates. 1999. Staff, North Pacific Fishery Management
Council and Alaska Dept. Fish and Game.
thank Dr. Dan Ito of the Observer Program and his staff
for provision of the NORPAC data. I also thank Thorn Smith,
director of North Pacific Longline Association, and owners
of freezer-longliners who provided the industry support
for this project.