Alaska Fishery Research Bulletin Issues, Vol.8 No. 1 - Summer 2001
Estimation of Tag-Reporting Rates for Sablefish in the Northeastern Pacific Ocean
Jonathan Heifetz and Nancy E. Maloney - Vol. 8(1):1-11. 2001.
An essential component of any mark and recapture study that seeks to estimate fish population abundance, exploitation rates, or migration rates from tagging data is the tag-reporting rate. We obtained tag-reporting rates for the sablefish Anoplopoma fimbria fishery during 1980-1998 by comparing tag returns in the fishery to tag returns from a scientific survey where all tag recoveries were assumed to be reported. Analytical formulae were derived for the measurement error associated with the estimates. When pooled over geographic areas or years, estimates of reporting rates were reasonably precise with coefficients of variation (CVs) usually less than 25%. Reporting rates were highest in the central (0.385) and eastern (0.315) Gulf of Alaska, intermediate in the western Gulf of Alaska (0.269), and lowest in the Aleutians (0.174) and Bering Sea (0.169). Rates pooled over all areas increased from lows of 0.102-0.248 in 1980-1982 to a peak of 0.465 in 1985 before declining to 0.199 in 1986 and 0.157 in 1987. The reporting rate increased gradually and fluctuated between 0.376 and 0.450 since 1995. The increase in reporting in 1995 was coincidental with the implementation of the Individual Fishing Quota (IFQ) system. The linear increase in reporting rates during 1986-1998 was significant. Factors that may have influenced the reporting rate were the number of tags available for recovery, the length of the commercial fishing season, the presence of scientific observers on commercial vessels, and the tag reward program. Pooled over all years and areas the tag-reporting rate has been 0.276 with a CV of 4.2%.Full Article (PDF 201 kB)
Maximum Ages of Groundfishes in Waters off Alaska and British Columbia and Considerations of Age Determination
Kristen M. Munk - Vol. 8(1):12-21. 2001.
The longevity in some groundfish species in the eastern North Pacific Ocean and Bering Sea is remarkable. Maximum ages of some species are relatively young: walleye pollock and lingcod are 28 and 25 years, respectively. Some Sebastes species are frequently aged to be over 100 years old, with some areas producing more than a few specimens aged 120-160 years old. The oldest fish recorded from Alaska, and possibly for all of the North Pacific, is a rougheye rockfish Sebastes aleutianus captured May 2000 in southeastern Alaska, visually aged from a sagittal otolith transverse section to be 205 years old. This paper consolidates and updates the maximum ages achieved by many groundfishes collected primarily during commercial and research harvest operations north of approximately 48°N latitude in the eastern North Pacific Ocean (Aleutians, Gulf of Alaska, nearshore and inshore waters of Alaska and British Columbia) and Bering Sea, and describes typical age-determination process and error which produced these age estimates.Full Article (PDF 117 kB)
Fishing Practices Under Maximum Retainable Bycatch Rates in Alaska's Groundfish Fisheries
David R. Ackley and Jonathan Heifetz - Vol. 8(1):22-44. 2001.
Most groundfish species managed by the North Pacific Fishery Management Council are closed to directed fishing for a portion of the fishing year for various reasons, the most common being the attainment of the total allowable catch (TAC) or the seasonal allowance of the TAC. Bycatch of non-targeted groundfish species for which directed fishing is closed may be retained in other fisheries up to a maximum retainable bycatch (MRB) level established by regulation as a percentage of the directed catch retained during a fishing trip. For some species, MRB percentages are generously set at levels that exceed "natural" bycatch rates to maximize the opportunity to retain these non-targeted species while reducing overall harvest rates. When the bycatch species is more economically valuable than the target species an incentive exists to "top off" by targeting the bycatch species until the MRB level is attained. We contrast 2 fisheries in which topping-off behavior was previously anecdotally reported. Because of differing species spatial distributions, some rockfish fisheries, Sebastes and Sebastolobus, in the Gulf of Alaska usually have an observed sablefish Anoplopoma fimbria bycatch rate below the prescribed MRB. These natural bycatch rates were estimated based on National Marine Fisheries Service survey and observer program fishery data. The estimated bycatch rates were reasonably precise with most coefficients of variation less than 50% for species of interest. By examining the observed catch from individual trawl hauls in a geographical information system, we were able to demonstrate topping-off behavior with more valuable sablefish in the rockfish fishery. The temporal and spatial targeting patterns of individual vessels were tracked, and distinctive hauls with sablefish as the dominant catch were identified. Similarly, shortraker Sebastes borealis and rougheye S. aleutianus rockfish are more valuable than Pacific ocean perch S. alutus in the Aleutian Islands, and there were anecdotal reports of topping-off with the shortraker-rougheye management complex of rockfish. However, our analysis did not reveal strong evidence of this practice.
Juvenile Groundfish Habitat in Kachemak Bay, Alaska, During Late Summer
Alisa A. Abookire, John F. Piatt, and Brenda L. Norcross - Vol. 8(1):45-56. 2001.
We investigated the habitat of juvenile groundfishes in relation to depth, water temperature, and salinity in Kachemak Bay, Alaska. Stations ranging in depth from 10 to 70 m and with sand or mud-sand substrates were sampled with a small-meshed beam trawl in August-September of 1994 to 1999. A total of 8,201 fishes were captured, comprising at least 52 species. Most fishes (91%) had a total length < 150 mm and were in their juvenile stage. Overall, the most abundant fishes were the rock soles Lepidopsetta spp. and Pacific cod Gadus macrocephalus. Other common species (>5% of the total catch) were flathead sole Hippoglossoides elassodon, slim sculpin Radulinus asprellus, Pacific halibut Hippoglossus stenolepis, and arrowtooth flounder Atheresthes stomias. Depth accounted for most of the spatial variability in juvenile groundfish abundance, and neither temperature nor salinity was correlated with fish abundance. Juvenile groundfishes concentrated in either shallow (less than or equal to 20 m) or deep (50-70 m) water, with co-occurrence of some species between 30-40 m. Shallow fishes were the rock soles, Pacific halibut, and great sculpin Myoxocephalus polyacanthocephalus. Deep species were flathead sole, slim sculpin, spinycheek starsnout Bathyagonus infraspinatus, rex sole Glyptocephalus zachirus, tadpole sculpin Psychrolutes paradoxus, and whitebarred prickleback Poroclinus rothrocki. This 6-year study provides baseline data on relative abundance and distribution of juvenile groundfishes in Kachemak Bay and may provide a useful tool for predicting the presence of species in similar habitats in other areas of Alaska.Full Article (PDF 914 kB)
Young of the Year Sablefish Abundance, Growth, and Diet in the Gulf of Alaska
M. F. Sigler, T. L. Rutecki, D. L. Courtney, J. F. Karinen, and M.-S.Yang - Vol. 8(1):57-70. 2001.
Abundance is dependent on year class success, which is highly variable from year to year. We studied young of the year sablefish Anoplopoma fimbria to collect basic life history information on their abundance, growth, and diet and to determine whether forecasting year class abundance based on young of the year surveys was practical. Surface gillnet surveys were conducted annually from 1995 to 1999 along the seaward edge of the continental shelf of Alaska. Sablefish made up about one-third of the catch and were caught mostly in the central and eastern Gulf of Alaska. Growth averaged 1.2 mm·d-1. The mean date the first otolith increment formed, April 30, implied an average spawning date of March 30. Diet was mainly euphausiids. Growth rate tended to be higher in years when gillnet catches were higher, but no relationship was apparent between diet and gillnet catches.Full Article (PDF 260 kB)
Rockfish Assessed Acoustically and Compared to Bottom-Trawl Catch Rates
Kenneth Krieger, Jonathan Heifetz, and Daniel Ito - Vol. 8(1):71-77. 2001.
Rockfish Sebastes spp. abundances were assessed acoustically using echo integration and compared to rockfish catch rates using a bottom trawl. Twenty-three sites were assessed acoustically and trawled simultaneously at depths of 177-294 m in the eastern Gulf of Alaska. The acoustics sampled depths from 0.5 to 25.5 m above the seafloor, whereas the bottom trawl sampled depths from the seafloor to 10 m above the seafloor. Rockfish were the primary species caught in the trawls, and 93% of the rockfish consisted of 4 species: Pacific ocean perch S. alutus (53%), redstripe rockfish S. proriger (18%), silvergray rockfish S. brevispinis (12%), and sharpchin rockfish S. zacentrus (10%). Rockfish catch rates were 1,524-17,493 kg/h at 6 sites with rockfish schools and were 10-1,153 kg/h at 17 sites with solitary rockfish and no schools. A significant relationship between rockfish catch rates C and acoustic indices A was best explained by the multiplicative model C = 4.32 A0.83 (r2 = 0.69, P < 0.001), indicating that acoustics can be used to assess rockfish abundance.Full Article (PDF 235 kB)
Focus Issue on Groundfish Research
Susan M. Shirley - Vol. 8(1):78. 2001.
(No Abstract) Full Editorial:
This issue of the Alaska Fishery Research Bulletin exclusively features research papers on groundfishes and groundfish fisheries in Alaska. The groundfishes are a speciose group, with vastly differing life histories, habitats, and ranges. Together they make up one of the most abundant and valuable fisheries resources in Alaska and the northeastern Pacific Ocean. The patchy distribution, extensive migrations, complex habitats, and very long life spans for some groundfish species require a different approach to managing sustainable fisheries, conserving the health of the resource, assessing population abundance, predicting year class strength and recruitment, and evaluating the effects of oceanic conditions and climatic change on groundfishes. In this issue the authors present new information on early life history, juvenile growth and diet, maximum groundfish ages, improved or alternate techniques for assessing abundance and identifying year class strength, and identification of fishing patterns that maximize bycatch limits of valuable groundfish species. The research in most of these, and many other, papers was presented at the 11th Western Groundfish Conference held in April 2000 in Sitka, Alaska. The AFRB is pleased to serve as a forum for publication of groundfish research as well as other fisheries research in Alaska.Full Article (PDF 48 kB)