Electronic Tagging of Juvenile Sablefish in Southeast Alaska
From 29 September to 4 October 2003, ABL scientists on the NOAA ship John
N. Cobb captured juvenile sablefish in St. John Baptist Bay, a rearing
location in coastal Southeast Alaska near Sitka. Thirteen of the fish were
surgically implanted with electronic, acoustically transmitting tags that
were programmed to transmit a record of temperature and depth experienced
by the fish. Mobile acoustic receivers located onboard the Cobb were used
to monitor juvenile sablefish behavior and habitat utilization in this
rearing location during the cruise. Fixed acoustic receivers located at
the head of the bay leading from the rearing location to the open ocean
are also being used to monitor the timing of juvenile sablefish emigration
from their nearshore rearing habitat to the more open waters of the Gulf
of Alaska. Short-term objectives are to use the electronic acoustic tags
to provide information on juvenile sablefish behavior and habitat use in
nearshore rearing areas and on the timing and duration of the emigration
from nearshore rearing habitat.
During the same cruise, 736 juvenile, age 0+ sablefish were tagged with
spaghetti tags, and 76 additional juvenile sablefish were also tagged with
electronic archival tags that were surgically implanted into the fish. Long-term
objectives are to utilize the electronic archival tags in addition to the
electronic acoustically transmitting tags to provide information on juvenile
sablefish behavior and habitat during their transition from nearshore rearing
areas to the age at which they are intercepted by the fishery. The electronic
archival tags monitor the temperature and depth experienced by juvenile
sablefish from the time they leave nearshore rearing areas at age 1+ or greater
until the time they recruit to the fishery at age 2+ or greater. The electronic
archival tags record temperature and depth and are designed for recovery in the
commercial fishery at age 2+ or greater.
By Tom Rutecki.
Analysis of Pacific Sleeper Shark Relative Abundance Trends in the Gulf
of Alaska and Bering Sea
Pacific sleeper sharks (Somniosus pacificus) are deepwater sharks of the
North Pacific Ocean that have been suggested as a source of Steller sea
lion mortality. Some information also suggests that abundance of the sharks
is increasing. For this study, Pacific sleeper shark data from fishery-independent
longline surveys in the Gulf of Alaska and the Bering Sea was analyzed
to determine abundance trends and whether any changes were statistically
significant. Relative population numbers (RPNs) of Pacific sleeper sharks
captured in the NMFS domestic sablefish longline surveys ranged from a
low of 79 in 1988 to a high of 2,980 in 2001. The most substantial increase
in RPNs occurred between 1992 and 1993, and RPNs remained high from 1994
to 2003. Not all the 95% bootstrap confidence intervals calculated for
annual Pacific sleeper shark RPNs in the longline surveys from 1989 to
2003 overlapped, indicating a significant increase (at the 95% confidence
level) in relative abundance occurred during this period. The increase
in RPNs was driven largely by Pacific sleeper shark catches in Shelikof
Trough, a deepwater Gulf of Alaska gully on the continental shelf between
Kodiak Island and the Alaska Peninsula. The sharks appeared to be relatively
abundant in this area. Pacific sleeper sharks may be relatively abundant
in other areas, such as on the continental shelf of the Gulf of Alaska
and Bering Sea at depths less than 200 m, but these areas are not routinely
sampled by the sablefish longline survey.
By Dean Courtney.
2003 Pacific Sleeper Shark Electronic Archival Tagging in Upper Chatham
Strait, Southeast Alaska
For this study, 49 Pacific sleeper sharks were tagged and released in upper
Chatham Strait in Southeast Alaska for recovery as bycatch from commercial
longline fisheries. Little is known about the life history or ecological
role of Pacific sleeper sharks in the North Pacific Ocean, where the sharks
could potentially interact with marine mammals such as Steller sea lions
(Eumetopias jubatus) or harbor seals (Phoca vitulina). The recovery of
electronic archival tags from the sharks will aid in identifying Pacific
sleeper shark habitat utilization and distribution in Southeast Alaska
and the potential for interactions between Pacific sleeper sharks and marine mammals.
The study area was adjacent to Point Howard in upper Chatham Strait/lower
Lynn Canal at approximately lat. 58.34°N, long. 135.04°W. ABL scientists
aboard the chartered fishing vessel Williwaw conducted 5 days of longline
operations on 3-5 June and 4-5 September 2003. Sleeper sharks were caught
using standard halibut longline gear provided by the vessel. The sharks
were tagged with electronic archival temperature and depth recording tags
mounted externally on the first dorsal fin. The archival tags record temperature
and depth for 2-5 years and store the recorded data for 5-10 years. The
ABL is offering a $200 reward for the return of the electronic archival
temperature and depth recording tags and has initiated communications with
ADF&G and with Southeast Alaska commercial longline fishing organizations
regarding the reward program.
By Dean Courtney.
|
 |
quarterly Oct-Dec 2003 sidebar
AFSC Quarterly
Research Reports
Oct-Nov-Dec 2003
Contents
Feature
Auke Bay Lab
National Marine Mammal Lab
RACE Division
REFM Division
Quarterly Index
Quarterly Home
|