Alaska Fishery Research Bulletin Issues, Vol.7 - Summer 2000
Rebuilding Probabilities Under Alternative Management Strategies for Eastern Bering Sea Tanner Crabs
Jie Zheng and Gordon H. Kruse - Vol. 7:1-10. 2000.
Because of its depressed status the eastern Bering Sea Tanner crab Chionoecetes bairdi stock was deemed overfished in March 1999. This determination necessitated the development of a rebuilding plan. We estimated rebuilding times and rebuilding probabilities using a length-based model and computer simulations under 3 alternative rebuilding strategies for this stock: (1) a complete closure of the directed Tanner crab fishery and a maximum constraint on other fisheries, (2) no directed fishing mortality other than unavoidable bycatch mortality, and (3) a new harvest strategy for the directed Tanner crab fishery with the same bycatch constraints for other fisheries as strategy 2. Rebuilding times were estimated as 7 years for greater than or equal to 50% probability and 20 years for greater than or equal to 90% probability for strategy 1, 8 and 27 years for strategy 2, and 10 and 30 years for strategy 3. Distributions of total mature biomass were skewed; the mean biomass was much larger than the median value. The recruitment dynamic affected rebuilding time periods, probabilities of fishery closure, and mean annual yields. Estimated rebuilding times with a greater than or equal to 50% probability ranged from 4 to >35 years depending on different assumptions on recruitment. Because the history of stock assessments is short (25 years) relative to the periodicity of recruitment cycles (13-14 years), additional years of data are needed to resolve alternative recruitment models and to determine whether statistical relationships with oceanographic conditions can predict future Tanner crab recruitment success.Full Article (PDF 168 kB)
A Comparison of Fish Assemblages in Eelgrass and Adjacent Subtidal Habitats Near Craig, Alaska
Michael L. Murphy, Scott W. Johnson, and David J. Csepp - Vol. 7:11-21. 2000.
Fish assemblages were compared between sites with eelgrass Zostera marina and sites with either kelp (e.g., Laminaria saccharina) or only filamentous algae (e.g., Cladophora and Pilayella). Four pairs of sites near Craig, Alaska, were seined monthly from April to June and in September 1998. Eelgrass in June averaged 1,001 shoots/m2 (SE = 57), dry biomass was 145 g/m2 (SE = 37), and blade length averaged 49 cm (SE = 5). Overall, more species were caught at sites with either eelgrass or kelp than at sites with only filamentous algae: 41 species in eelgrass, 38 in kelp, and 26 in filamentous algae. Total catch was greater at eelgrass than at non-eelgrass sites, principally because of large catches of bay pipefish Syngnathus leptorhynchus, crescent gunnels Pholis laeta, and shiner perch Cymatogaster aggregata. Juvenile rockfish (age greater than or equal to 1) were caught frequently (94% of sites) in May to September in both eelgrass and kelp, but not at sites with only filamentous algae. Age-0 rockfish were caught only in September, nearly all (97%) in eelgrass. Catch of pink salmon Oncorhynchus gorbuscha fry, chum salmon O. keta fry, and coho salmon O. kisutch smolts was similar at eelgrass and non-eelgrass sites, except for chum salmon in June when catch was significantly lower at eelgrass sites. Gadids (96% Microgadus proximus) were uncommon; only 25 were caught, but most (72%) were in eelgrass. Catch of forage fish (Pacific herring Clupea pallasi and Pacific sand lance Ammodytes hexapterus) was similar at eelgrass and non-eelgrass sites. Eelgrass and kelp vegetation supported high biodiversity and provided important habitat for juvenile rockfish and other species. Because biological communities vary geographically, additional data from other areas are needed to obtain a full perspective of the role of eelgrass and kelp as fish habitat in coastal Alaska.Full Article (PDF 227 kB)
Depth and Habitat Distribution of Parastichopus californicus Near Sitka, Alaska
Doug Woodby, Scott Smiley, and Robert Larson - Vol. 7:22-31. 2000.
The depth distribution of sea cucumbers Parastichopus californicus was investigated in the vicinity of Sitka Sound, Alaska, to evaluate the proportion of the emergent population available to commercial dive harvesters. A submersible was used to census 20 transects to 118 m. Observations above 10-m depth were made by scuba on 10 transects. Sea cucumber densities were greatest in shallow waters, with approximately 60% of the sea cucumbers observed above 15 m and 70% above 20 m. Average densities were 0.03·m-2 on the submersible transects and 0.30·m-2 on the scuba transects. The deepest sea cucumber observed was at 87 m. Sea cucumber densities were highest on shell debris and gravel (pebbles), and lowest on mud and silt bottoms. Tests for substrate distribution generally indicated a nonrandom affinity for harder substrates, except bedrock and boulders. The mostly shallow distribution of P. californicus near Sitka exposes approximately two-thirds of the surveyed population to exploitation by commercial divers, who commonly descend to 15- or 20-m depth. The large fraction of the population in deeper water is not included in estimating the harvestable surplus, and because this leads to an underestimate of the population size, this approach provides a conservative safeguard against overexploitation.Full Article (PDF 387 kB)
Species Composition and Abundance of Juvenile Groundfishes Around Steller Sea Lion Eumetopias jubatus Rookeries in the Gulf of Alaska>
Franz J. Mueter and Brenda L. Norcross - Vol. 7:32-43. 2000.
We conducted bottom trawl surveys to determine species composition and abundance of juvenile groundfish communities around 6 Steller sea lion rookeries in the western Gulf of Alaska from 1994 to 1996. Overall, the most abundant species in our collections were rock sole Pleuronectes bilineatus, walleye pollock Theragra chalcogramma, Pacific halibut Hippoglossus stenolepis, northern sculpin Icelinus borealis, Triglops spp., Gymnocanthus spp., Pacific cod Gadus macrocephalus, slim sculpin Radulinus asprellus, and arrowtooth flounder Atheresthes stomias. Our results showed significant differences in species composition among rookeries within each of 3 depth strata and a greater abundance of juvenile groundfishes in the western part of the study area. Gadid and flatfish species were more abundant and had a higher probability of occurrence in the vicinity of sea lion rookeries on Akun, Ugamak, Atkins, and Chowiet Islands, compared to rookeries on Marmot and Sugarloaf Islands. The observed differences in species composition coincided with differences in topography, substrate composition, temperature, and salinity. A potential relationship between the abundance of juvenile groundfishes and sea lion survival is discussed.Full Article (PDF 574 kB)
Genetic Variation of Fecundity and Egg Size in Anadromous Pink Salmon Oncorhynchus gorbuscha Walbaum
William W. Smoker, A. J. Gharrett, Michael S. Stekoll, and S. G. Taylor - Vol. 7:44-50. 2000.
We studied genetic variation of fitness traits in a population of salmon that is not captive but spawns naturally and grows to maturity in nature. Additive genetic variation contributed significantly to variation of fecundity, a trait closely related to fitness, but not to variation of egg size (another trait closely related to fitness) in families drawn from an anadromous population of salmon and measured after growing to maturity in the wild. Greater fecundity-at-length in families drawn from the early-spawning component of the population suggests that variation of fecundity is itself adaptive. The families were generated by hierarchical mating of 60 male pink salmon to 120 females randomly chosen from the odd-year population at Auke Creek, Juneau, Alaska, 2 females to each male. Half were from the early (August-spawning) component and half from the late (September-spawning) component. The families were incubated separately, tagged with coded microwires, released during emigration of naturally-spawned fry (~1,000 unfed fry per family), and recovered at maturity when they returned to Auke Creek after 16 months at liberty (119 of the 120 families had surviving female members). Body size (length), egg number, and egg size (weight) were measured in 2 females sampled at random from those members having intact ovaries (i.e., before ovulation and retaining all eggs) in each returning full-sib family. Heritability (estimated from the paternal component of variation) of number of eggs was 0.8 (standard error, SE = 0.3). The estimate of genetic correlation of body length and egg number was imprecise (0.4, SE = 0.5). Mean egg number (adjusted for body size) was greater in families from the early component of the population than in families from the late component (1,501 vs. 1,351, P < 0.01). Egg size did not differ between components. Maternal effects contributed significantly to variation of egg size, suggesting the importance of special maternal environments (e.g., yolk accumulation) or nonadditive genetic effects. Our observations suggest that variations of fitness-related traits can be maintained from generation to generation in fluctuating environments by genetic variation and are important to the adaptability and persistence of salmon populations.Full Article (PDF 171 kB)
Longevity of Captive Pinto Abalones Haliotis kamtschatkana
A. J. Paul and J. M. Paul - Vol. 7:51-53. 2000.
Ten pinto abalones Haliotis kamtschatkana were captured in Sitka Sound in 1979 and held in captivity at the Seward Marine Center Laboratory. The first of them died in 1985, and 3 were still alive in 2000 when this note was written. Their shell lengths at capture ranged from 48 to 53 mm. At death 7 individuals had shell lengths ranging from 91 to 102 mm. The 3 live individuals had shell lengths of 81, 96, and 98 mm. These observations indicate pinto abalones have the capacity to live for periods exceeding 20 years in captivity.Full Article (PDF 244 kB)